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Published by Ksenija Topolovec-Miklozic Andreas Pauschitz Arshia Fatemi 23rd International Colloquium Tribology Industrial and Automotive Lubrication Conference Proceedings 2022 23rd International Colloquium Tribology Industrial and Automotive Lubrication 25th to 27th January 2022 Technische Akademie Esslingen Published by Ksenija Topolovec-Miklozic Andreas Pauschitz Arshia Fatemi 23rd International Colloquium Tribology - Industrial and Automotive Lubrication Conference proceedings 2022 Bibliografische Information der Deutschen Nationalbibliothek Die Deutsche Nationalbibliothek verzeichnet diese Publikation in der Deutschen Nationalbibliografie; detaillierte bibliografische Daten sind im Internet über http: / / dnb. dnb.de abrufbar. The German National Library lists this publication in the German National Bibliography. Detailed bibliographic data are available in the Internet at http: / / dnb.dnb.de. The work including all its parts is protected by copyright. Any use outside the narrow limits of copyright law without the consent of the publisher is inadmissible and punishable. This applies in particular to reproductions, translations, microfilming and storage and processing in electronic systems. The present work was created with great care. However, errors cannot be completely ruled out. Neither the publisher nor the authors or publishers therefore accept any liability for the correctness, topicality and completeness of the work and its electronic components. Das Werk einschließlich aller seiner Teile ist urheberrechtlich geschützt. Jede Verwertung außerhalb der engen Grenzen des Urheberrechtsgesetzes ist ohne Zustimmung des Verlages unzulässig und strafbar. Das gilt insbesondere für Vervielfältigungen, Übersetzungen, Mikroverfilmungen und die Einspeicherung und Verarbeitung in elektronischen Systemen. Das vorliegende Werk wurde mit großer Sorgfalt erstellt. Fehler können dennoch nicht völlig ausgeschlossen werden. Weder Verlag noch Autoren oder Herausgeber übernehmen deshalb eine Haftung für die Fehlerfreiheit, Aktualität und Vollständigkeit des Werkes und seiner elektronischen Bestandteile. © 2022. Alle Rechte vorbehalten. expert verlag GmbH Dischingerweg 5 · D-72070 Tübingen E-Mail: info@verlag.expert Internet: www.expertverlag.de Printed in Germany ISBN 978-3-8169-3547-6 (Print) ISBN 978-3-8169-8547-1 (ePDF) Technische Akademie Esslingen e. V. An der Akademie 5 · D-73760 Ostfildern E-Mail: maschinenbau@tae.de Internet: www.tae.de 23rd International Colloquium Tribology - January 2022 Preface Two challenging years have passed since the last Tribology Colloquium in 2020. We have had to learn quickly to work predominantly mobile and to exchange ideas in video conferences. This demands much more from our bodies and constantly increases the need to meet and exchange in face-to-face meetings again. However, the challenge lies not only in organizing events with a higher number of on-site participants, but also in the changes in the industrial market environment. Climate protection measures and CO2 reduction requirements are becoming more and more concrete, and e-mobility has also been given a clear roadmap and timeline. This is leading to a shift in emphasis in tribology and, above all, is significantly influencing cooperation between knowledge providers and industry. The further development of tools in data science and the application of these tools in tribology is also steadily increasing. Also, we as tribologists are forced to evaluate tribological data from analyses, experiments, laboratory or field tests with modern tools of statistical mathematics, which are summarized under the term Data Science. The end of the era when, for example, kilohertz data from a friction and wear experiment lasting several hours was summarized in a diagram with a horizontal axis of about 15 cm for discussion with the customer is near or already over. In the future, the evaluation of the data must be much more detailed with the help of software tools and made available to the customers and other possible users in databases worldwide. The 23rd International Colloquium Tribology covers a broad spectrum of current tribological topics in its various disciplines: It focuses on new trends in lubricants and additives, test methods and measurement technologies, coating surfaces and underlying mechanisms with the key topics of sustainability (including e-mobility) and digitalization in tribology. Special sessions are dedicated to sustainable lubricants and the i-Tribomat initiative. Hopefully, most of us will be able to attend on-site and meet colleagues in person; however, some of us will also participate virtually and support emission reduction measures and show that we live the goals of tribology as well. Prof. Dipl.-Ing. Dr. Andreas Pauschitz AC2T Research GmbH, Austria Member of the Steering Committee 23rd International Colloquium Tribology - January 2022 7 Table of contents P Plenary Lectures P.1 E-Mobility, Sustainability, Markets, Raw Materials 23 Dr. Lutz Lindemann P.2 Different Dimensions of Sustainability 25 Inga Herrmann, Sebastian Dörr P.3 Tribological Optimisation for Sustainable Lubrication Design 27 Prof. Roland Larsson, Marcus Björling, Yijun Shi, Anders Pettersson P.4 From Emerging Trends to Current Lubrication Challenges: STLE’s View 31 Dr. Ken Hope P.5 Novel Nanocomposite with Ionic Liquid and Graphene for Electroconductive Radial Plain Bearings 33 Susanne Beyer-Faiss, Dr. Yasmin Korth, Dr. Tobias Amann, Dr. Thomas Schubert, Dr. Sebastian Plebst P.6 Tribology in the Age of Digitalization and Green Deal - Building Digital Services! 37 Franz Pirker P.7 Base Oil Benchmarking for Gear Oils in Electric Vehicle Drivetrains 41 Dr. Steffen Glänzer P.8 Vacuum Tribology of Superhard ta-C Coatings 43 Dr. Volker Weihnacht, Lars Lorenz, Fabian Härtwig, Stefan Makowski, Frank Kaulfuß P.9 An Innovative Multi-Scale Approach to Reduce Friction of Automotive Lubricants from Hydrodynamics to Boundary Lubrication 45 Prof. Denis Mazuyer, Juliette Cayer-Barrioz 1 Trends Lubricants and Additives 1.1 Novel Lubricant/ Lubrication Concepts 1.1.1 Liquid Amides - Novel, High Performance Base Oils 51 Dr. Claire Ward 1.1.2 Comparisons of Boundary Lubricant Additive Screening Strategies, Including DOE Methods, Utilizing Twist Compression Tests (TCT), Early in the Lubricant Formulation Process 53 Ted G. McClure, Alexes Morgan, Robert Stubbs 1.1.3 Scientific Evaluation of Investigations on the Load Carrying Capacity of Carbide Cylindrical Gears Lubricated with Water 57 Karl Jakob Winkler, Thomas Tobie, Klaus Michaelis, Karsten Stahl 1.1.4 Tribology of Ionic Liquids and Graphene - a Synergistic Combination 61 Dr. Thomas Schubert, Dr. Sebastian Plebst 8 23rd International Colloquium Tribology - January 2022 1.1.5 Biomimetic Water-Based Lubricant Development: Nanoencapsulation with Liposomes 63 Manoj Murali, Philippa Cann, Marc A. Masen 1.1.6 Reversible Viscosity Tuning Using UV-Light 65 Dr. Dominic Linsler, Chris Gäbert, Stefan Reinicke, Theodora Rangova, Florian Schlüter, Martin Dienwiebel 1.1.7 Electrostatic Sensing for White Etching Cracks (WECs) in Rolling Contacts * Ling Wang 1.1.8 Formation of White Etching Crack Under Sliding, Boundary Lubrication and Additional Current Passage Using Modern Lubricant Compositions 67 Daniel Cornel, Florian Steinweg, Francisco Gutiérrez Guzmán, Georg Jacobs, Adrian Mikitisin 1.1.9 Alternative Lubricants in Wind Turbines to Avoid WEC Formation 71 Dominik Kürten, Stefan Grundei, Jörg Franke, Sebastian Plebst, Andreas Kailer 1.1.10 Novel Transmission Lubricants for New Generation Vehicles 73 Ratnadeep Joshi, Lakshmi Katta, Sarita Seth, Pankaj Bhatnagar, Deepak Saxena, SSV Ramakumar 1.1.11 Improvement of Tribological Performances of MoDTC induced by Methylenebis(dithiocarbamates) in Engine Lubricants: Enhanced Durability of MoDTC and their Friction Reducing Capability under Engine Operating Conditions 77 Yu Min Kiw, Pierre Adam, Philippe Schaeffer, Benoît Thiébaut, Chantal Boyer 1.1.12 Theoretical and Computational Estimation of the Value of the Coefficient of Friction of the Synovial Fluid of Human Joints 81 Sergey Vasiliy Fedorov 1.2 Metalworking 1.2.1 Development and Characterization of Ultra-Low Foaming Metalworking Products 87 Bellini Marco, Pota Simone 1.2.2 Naphthenic Base Oils - Tailoring Emulsion Stability 89 Thomas Norrby, Jinxia Li, Linda Malm 1.2.3 Do Biofilms in Metakworking Fluid System Matter? 91 Frederick J. Passman 1.2.4 Improving Microbial Control Without Excess Reserve Alkalinity in MWF Formulations 93 Harish Potnis, Clayton Cooper 1.3 Lifetime Behaviour 1.3.1 Oil Nitration in a Large-Scale Device for Artificial Alteration 97 Adam Agocs, Charlotte Besser, Marcella Frauscher, Nicole Dörr 1.3.2 An Experimental Study of the Effect of Thermal Aging on the Lubrication Performance of EALs 101 Mar Combarros, Ariadna Emeric, Gerard Cañellas, Ángel Navarro, Marc Alumà, Taro Ehara 23rd International Colloquium Tribology - January 2022 9 1.3.3 Enhanced Engine Lifetime by Use of Premium Fuel 105 Marcella Frauscher, Adam Agocs, Thomas Wopelka, Andjelka Ristic, Florian Holub, Wolfgang Payer 1.3.4 Influence of Mechanical, Thermal, Oxidative and Catalytic Processes on the Thickener Structure 109 Markus Grebe, Michael Ruland 1.3.5 The Unexpected Behaviour of Synthetic Esters as Cobase Stocks on Resistance to Oxidation 113 Siegfried Lucazeau 1.3.6 Next Generation Anti-Wear Development 115 Christelle Chretien 1.4 Greases 1.4.1 Polyglycols as High Performant Base Oil Component in Modern Greases 121 Cristina Schitco 1.4.2 Less could Be More - Formulating High-Performance Greases 125 Mehdi Fath-Najafi, George Diloyan, Jinxia Li 1.4.3 Novel Basestock Technology for EV Bearing Grease Applications * Sven Meinhardt 1.4.4 Calcium Sulfonate Greases - Improving Biodegradable Solution Thanks to 1-Step Process 127 Guillaume Notheaux, Laura Hue 1.5 Friction Modification/ Efficiency 1.5.1 Longer Lifetime of Wind Turbine Bearings and Gears Using Phyllosilicate-Additives 133 Stefan Bill 1.5.2 Low friction with Polymer Friction Modifier in Steel/ Steel Contact: a Combined Tribology and Physico-Chemical Approach 137 Nasrya F. Kossoko, Clotilde Minfray, Michel Belin, Benoît Thiébaut, Frederic Dubreuil 1.5.3 New generation of Nanolubricants Fuel Economy 141 Marta Hernaiz, Iker Elexpe, Estibaliz Aranzabe, Tomas Pérez Gutierrez, Beatriz Dominguez 1.5.4 Axle Lubricant Composition Impact on Efficiency and Work Loss Using Light Duty Truck Erive Axle 145 Arjun Goyal, Donna Mosher 1.5.5 Development of a new fuel efficient, shear stable axle lubricant to meet new U.S. Green House Gas requirements 149 Arjun Goyal, Donna Mosher 1.5.6 Understanding the Friction and Wear Behavior of In-service Lubricants 153 Angela Tortora, Deepak H. Veeregowda, Simon Regauer, Christoph Rohbogner 1.6 Lubricants in Electric Vehicles 1.6.1 Novel Defoamers for Use in Low Viscosity Electric Vehicle Fluids 157 Noriko Ayame, Akira Takagi, Go Tatsumi 10 23rd International Colloquium Tribology - January 2022 1.6.2 Test Method to Determine Improvements of E-Drive Efficiency 159 Michael Schulz 1.6.3 A Novel Class of Biobased Organic Friction Modifiers Revealing the Superlubricity Effect: Tribology and Application Experience in Motor Oil and e-Fluid Formulations 161 Arthur Coen, Karima Zitouni, Ward Huybrechts, Philippe Blach, Anne-Elise Lescoffit, Boris Zhmud 1.6.4 Improving Gear and Thermal Efficiency of Electric Vehicle Fluids Using Group V Base Stocks 165 Gareth Moody, Bethan Warren, Nicholas Weldon 1.6.5 Polymers as Important Additives in E-Drive Fluids 169 Dmitriy Shakhvorostov, Stephan Wieber, Roland Wilkens, Andreas Hees 1.6.6 Enhanced Gear Lubricity for Lubricant Oils Applied to Transaxles in HEVs and EVs 173 Keiichi Narita 1.6.7 Improved Energy Efficiency and Thermal Management in EVs Using Novel Synthetic Base Stocks 177 Babak Lotfi 2 Automotive and Transport Industry 2.1 Lubricant 2.1.1 Impact of Lubricant Formulation on Surface Damage in Electric Vehicle Transmissions 183 Alexander MacLaren, Amir Kadiric 2.1.2 Optimizing the Mo Concentration in Low Viscosity Fully Formulated Engine Oils 187 Aaron Thornley, Yuechang Wang, Chun Wang, Jiaqi Chen, Haipeng Huang, Hong Liu, Anne Neville, Ardian Morina 2.1.3 Rheological Properties of Lubricants and their Correlation with Fuel Economy Performance 191 Maryam Sepehr, Sara Zhang, David Morgan, Ramoun Mourhatch, Peter Kleijwegt, Claire Chommeloux 2.2 Engine 2.2.1 In-Bore Engine Component Tribology 197 M. Priest, M. F. Fox 2.2.2 Radioactive Tracer Engine Wear Test Development 199 Peter M. Lee, Gregory A.T. Hanson 2.2.3 Squeeze Film Investigations in a Simulating Piston-Ring Cylinder Liner Experimental Set-up 203 Polychronis Dellis 2.2.4 The Effect of Friction Modifier and Viscosity on Piston Rings/ Cylinder Liner Friction in Floating Liner Single-Cylinder Engine Tests 207 Abdullah Alenezi, Benoît Thiébaut, Cayetano Espejo, Ardian Morina 2.2.5 Thermal Expansion Influence on the Scuffing Initiation in a Piston Ring Cylinder Liner Contact 209 Simona Dahdah, Nans Biboulet, Antonius Lubrecht, Pierre Charles 23rd International Colloquium Tribology - January 2022 11 2.2.6 A fast Piston-Ring/ Cylinder-Liner Friction Prediction Based on a Semi-Analytical Hydrodynamic Model and Real Measured Surface Topography 213 Thomas Lubrecht, Nans Biboulet, Antonius Adrianus Lubrecht, Johnny Dufils 2.3 Electric Impact 2.3.1 The Impact of Bearing Currents on the Failure Modes of Motor Bearings in Electric Vehicles * Duncan Nicoll 2.3.2 Mounting Positions of Electrical Connectors and the Wear of Coatings under Vibration Loads 219 Kevin Krüger, Dirk Hilmert, Jian Song 2.4 Friction 2.4.1 Design, Reliability and Service Life Predictions of Tribological Contacts in Drive Systems 225 Michael Gless, Anette Schwarz 2.4.2 Influence of the Rotation Direction of the Cam on the Friction Losses of a Cam/ Finger Follower Contact 229 Johnny Dufils, Christophe Héau, Etienne Macron, Philippe Maurin-Perrier 2.4.3 Wet Friction Material and Fluid Screening on Benchtop Rig 233 Carlos J. Sanchez, Peter M. Lee 3 Industrial Machine Elements and Wind Turbine Industry 3.1 Gears 3.1.1 How Friction Modifier Influences the Dynamic Friction behavior in Wet-Running Clutch Systems and its Potential for Extended Use in Hybrid Drive Trains 239 Arne Bischofberger, Katharina Bause, Sascha Ott, Albert Albers 3.1.2 Wear analysis of Spur Gears in Consideration of the Temperature 243 Chan IL Park 3.1.3 Design for Reliability of Gear Systems Concerning Wear 247 Arshia Fatemi, Poorna Satish Chowdary Maddukuri 3.2 Bearing 3.2.1 Effect of Water Absorption in Bearing Greases on Wear and Corrosion 251 Ivan Delic, Adler Michael, Karl Adam, Franc Bardin 3.2.2 Tribo-Dynamics for a 3D-printed Multilattice Structure-based Air-foil Bearing 255 Ali Usman, Marcus Liwicki, Andreas Almqvist 3.2.3 Static Performance Analysis of Porous CMC Journal Bearings for Cryogenic Applications 259 Artur Schimpf, Helge Seiler, Markus Ortelt, Dennis Gudi, Martin Böhle 3.2.4 Study of the Early Stages of Subsurface Cracks and Microstructural Alterations in 100Cr6 under Hydrogen and RCF Influence 263 Fernando José López-Uruñuela, Beatriz Fernandez-Diaz, Bihotz Pinedo, Josu Aguirrebeitia 12 23rd International Colloquium Tribology - January 2022 4 Coatings, Surfaces and Underlying Mechanisms 4.1 Lubricant-Surface Interaction 4.1.1 Physical and Numerical Investigation of the Friction Behavior of Graphite Lubricated Axial Ball Bearings 271 Arn Joerger, Markus Spadinger, Katharina Bause, Sascha Ott, Albert Albers 4.1.2 Influence of Humidity on Graphite Lubrication: the Road to Turbostratic Carbon 275 Carina Morstein, Andreas Klemenz, Martin Dienwiebel, Michael Moseler 4.1.3 Effect of Lubricants on Hydrogen Permeation under Rolling Contact of Steel 277 Yoji Sunagawa, Hiroyoshi Tanaka, Joichi Sugimura 4.2 Tribologiy Behaviour 4.2.1 Tribological and Microstructural Analysis of PVD Coatings: Deposited on High Chromium Steel Substrates for Cold Rolling Applications 281 A. Carabillò, A. Lanzutti, F. Sordetti, M. Magnan, M. Querini, O. Azzolini, L. Fedrizzi 4.2.2 Nanoscale Wear Behavior of CVD Grown Monolayer WS 2 285 Himanshu Rai, Deepa Thakur, Deepak Kumar, Zhijiang Ye, Viswanath Balakrishnan, Nitya Nand Gosvami 4.2.3 Tribological Behaviour of W-S-C Coated Ceramics in a Vacuum Environment 289 K. Simonovic, T. Vitu, A. Cammarata, A. Cavaleiro, T. Polcar 4.3 Surfaces Reactions 4.3.1 Investigation of Friction Surfaces During a Preconditioning Process Concerning the Behavior of Surface Parameters and Friction Coefficient Stability 295 Rüdiger Fehrenbacher, Arn Joerger, Katharina Bause, Sascha Ott, Albert Albers 4.3.2 Improving the Tribological and NHV Behavior of Gears by Mechanochemical Surface Finishing 299 Linus Everlid, Martin Bengtsson, Morteza Najjari, Florian Reinle, Andreas Storz, Boris Zhmud 4.3.3 Influence of Black Oxide Coating on Micropitting and ZDDP Tribofilm Formation 303 Mao Ueda, Hugh Spikes, Amir Kadiric 4.4 Oxidation & Wear 4.4.1 Mechanisms of Tribo-Oxidation in High-Purity Copper 309 Julia S. Rau, Shanoob Balachandran, Reinhard Schneider, Peter Gumbsch, Baptiste Gault, Christian Greiner 4.4.2 Wear of Electrical Contacts of Equal Motion Amplitude and Equal Force in Different Directions 313 Dirk Hilmert, Kevin Krüger, Haomiao Yuan, Jian Song 4.4.3 Improving Abrasive Wear Performance of Polymers 317 Helena Ronkainen, Jani Pelto, Vuokko Heino, Mikko Karttunen 23rd International Colloquium Tribology - January 2022 13 5 Test Methodologies and Measurement Technologies 5.1 Seals & Polymer Testing 5.1.1 Development and Verification of a Test Method for Determining the Compatibility of Elastomers with Cooling Lubricants 325 Dr. Stephan Baumgärtel 5.1.2 Accelerated Compatibility Test of Sealing Material and Lubricant in a Dynamic Stress Collective 327 Ameneh Schneider, Josef Brenner, Felix Zak 5.1.3 Fluorescence Investigation of Wetting in Soft Rough Contacts: Role of Micro-Asperities * Dr. Michele Scaraggi 5.1.4 Influences of Roughness, Moisture Content and Lubrication on Friction of Polymers Against 100Cr6 331 Joel Voyer, Heinz Haider, Claudia Mayrhofer, Igor Velkavrh, Tom Wright 5.1.5 A Novel Measurement Procedure to Analyse the Friction of Rod Seals in Relation to Pre-Defined Shear Rates and Starved Lubrication Conditions 335 Oliver Feuchtmüller, Lothar Hörl, Frank Bauer 5.1.6 A new Approach for the Friction and Wear Characterization of Polymer Fibers under Dry, Mixed and Hydrodynamic Sliding 339 Justus Rüthing, Regine Schmitz, Frank Haupert, Michael Sigrüner, Nicole Strübbe 5.2 Lubricant Stability 5.2.1 Novel Electrical Current Feed Apparatus for Aging Simulation of Lubricants 345 Yasmin Korth, Susanne Beyer-Faiss 5.2.2 Thermo-Oxidation Activation Energies of grease Antioxidants by RapidOxy Method mDIN 51830-2 * Markus Matzke 5.2.3 Laboratory-Based Reproduction of Shear-Degraded Greases by Use of a Grease Worker 347 Christoph Schneidhofer, Michael Schandl, Nicole Dörr, Thomas Macheiner, Lukas Fritzer 5.2.4 Application of the Non-linear Behaviour of Longitudinal Ultrasonic Waves in Lubrication Monitoring 351 S. Taghizadeh, R.S. Dwyer-Joyce 5.3 Rheology 5.3.1 Observation of Grease Flow by Particle Imaging Velocimetry 355 Haruka Iki, Kazumi Sakai, Reo Miwa, Ryosuke Sato, Norifumi Miyanaga 5.3.2 Visualization of Grease Distribution in a Ball Bearing Using Neutron Imaging Technology * Kazumi Sakai 5.3.3 High Pressure, High Shear Viscometry - Lubricant Characterization for Highly Loaded Contacts 357 Lukas Mebus, Georg Jacobs, Clément Larriere, Arnaud Riss, Jonathan Raisin, Florian König 5.4 Tribometry 14 23rd International Colloquium Tribology - January 2022 5.4.1 How to Reduce Time and Cost in Tribology Testing? * Dr. Dirk Drees 5.4.2 Investigation of Rolling and Lateral Slip on the MopeD Qs2STg 500 363 K.-O. Karlson, H. Buse, J. Molter 5.4.3 The Use of the MTM rig for Wear Testing 367 Matthew Smeeth, Clive Hamer 5.4.4 Tribological Assessment of Marine Distillate Fuels under a variant HFRR Method 371 Theodora Tyrovola, Fanourios Zannikos 5.4.5 Innovative Design of Electrical Lubricants TestRig for E-grease and E-fluids * Deepak H. Veeregowda 5.4.6 Conductive Layer Deposits and the Development of Bench Test Technology for Electric Vehicle Drivetrains 375 Greg Miiller, John Bucci, Gunther Mueller, Rico Pelz, Timothy Newcomb 5.4.7 Tribological Simulation of Friction Torque Test using SRV and EHD Tribometer - A new Approach for Performance Evaluation of Energy Efficient Engine Lubricant 377 Rameshwar Chaudhary, Inder Singh, Punit Kumar Singh, S. Bhadhavath, Dr. S. Seth, R. Mahapatra, M. Sithananthan, A.K. Harinarain, Dr. P. Bhatnagar, Dr. D. Saxena, Dr. SSV Ramakumar 5.4.8 Investigation into the effect of lubricant viscosity in engine bearing film thickness using embedded ultrasonic transducers. 381 Henry Brunskill, Andy Hunter, Am Ho Sung, Junsik Park, Rob Dwyer-Joyce 5.4.9 Investigations of the Ball Motion Behaviour in Spindle Bearings under Dynamic Loads 385 Hans-Martin Eckel, Christian Brecher, Stephan Neus 5.5 Lubricant Analysis 5.5.1 Improved Oil Condition Monitoring of Industrial Gear Oils 391 Dipl.-Ing. Rüdiger Krethe, Dr. Thomas Fischer 5.5.2 Study of the Capacity of Spectroscopy UV-Vis and NIR to Quantify Fuel Dilution on Used Engine Oil 393 Bernardo Tormos, Vicente Macián, Benjamín Pla, Adbeel Balaguer 5.5.3 On the role of Microorganisms for Lubricants - Sometimes Good, Sometimes Bad 397 Peter Lohmann, Gerhard Gaule 5.5.4 Studying the Action of Surface Active Lubricant Additives by Surface Analytical Methods 399 T. Rühle, J. Eickworth, M. Dienwiebel 5.6 Metrology in Tribology (Wear) 5.6.1 Continuous Wear Measurements of Diamond-like Carbon (DLC) Based on Radioactive Isotopes 403 Manuel Zellhofer, Martin Jech, Ewald Badisch, Ferenc Ditrói, Andreas Kuebler, Paul Heinz Mayrhofer 5.6.2 Quantifying Wet Brake Chatter Using an Accelerometer 407 Michael Botkin, Caroline Mueller 23rd International Colloquium Tribology - January 2022 15 5.6.3 The Identification of an Adequate Stressing Level to Find the Proper Running-In Conditions of a Lubricated DLC-Metal-System 409 Joachim Faller, Matthias Scherge 6 Digitisation in Tribology 6.1 Rolling Contact 6.1.1 Contact and Lubrication Aspects on Predicting the Contact Area in Lubricated Hot Rolling 415 André Rudnytskyj, Martin Jech, Josef Leimhofer, Stefan Krenn, Georg Vorlaufer, Markus Varga, Carsten Gachot 6.1.2 Wear Modeling of Non-conformal Rolling Contacts Subjected to Boundary and Mixed Lubrication 417 Andreas Winkler, Marcel Bartz, Sandro Wartzack 6.2 Digitisation 6.2.1 Artificial Intelligence in Tribology: Design of New Dispersants Using Artificial Intelligence Tools. 423 Nuria E. Campillo, Pablo Talavante, Ignacio Ponzoni, Axel J. Soto, María J. Martínez, Roí Naveiro, Ramón Gómez-Arrayas, Mario Franco, Shin-Ho Kim Lee, Pablo Mauleón, Guillermo Revilla-Lopez, Marco Bernabei 6.2.2 Preparation of Measured Engineering Surfaces for Digital Twins in Tribology 425 Yuechang Wang, Abdullah Azam, Mark C.T Wilson 6.2.3 Tribological Experiments in the Age of Big Data 429 Nikolay T. Garabedian, Paul J. Schreiber, Christian Greiner 6.2.4 Digitalization and Lubricant Analyses - an Efficient Partnership 433 Stefan Mitterer, Michael Linnerer 6.3 Simulation 6.3.1 Molecular Dynamics Simulation on the Behavior of Viscosity Modifying Polymers in Oil 437 Shuhei Yamamoto, Kazunori Kamio, Yoshiki Ishii, Deboprasad Talukdar, Kosar Khajeh, Gentaro Sawai, Kyosuke Kawakita, Eiji Tomiyama, Hitoshi Washizu 6.3.2 Molecular Dynamics Study of the Adsorption of Organic Friction Modifiers on Iron Oxide Surfaces 441 Pablo Navarro Acero, Stephan Mohr, Marco Bernabei, Carlos Fernández, Beatriz Dominguez, James Ewen 6.3.3 Diversification of Evaluation Options for Tribological Measuring Results Using Origin and Phyton 445 Thomas Witt 6.4 Modelling 6.4.1 Designing a REACH Conform Small Conrod Bearing of a Plunger Pump with the Help of EHD Simulation 449 Vincent Hoffmann, Felix Hartmann, Christian Stelzer 16 23rd International Colloquium Tribology - January 2022 6.4.2 Predicting Electric Vehicle Transmission Efficiency Using a Thermally Coupled Lubrication Model 453 Joseph F. Shore, Athanasios I. Christodoulias, Anant S. Kolekar, Frances E. Lockwood, Amir Kadiric 6.4.3 Polymer-Coated Plain Bearings During Start-Stop Operation - an Experimental and Numerical Assessment 457 Florian König, Georg Jacobs 6.5 Sliding Contact 6.5.1 An Experimental Study and Numerical Modelling of Nanocomposite Coating Wear in Sliding Contact 463 Professor Zulfiqar A Khan 6.5.2 Effect of Thermal Conductivity of Bearing on the Thermal Wedge in Parallel Slider Bearing 465 Tae-Jo Park, Jeong-Guk Kang 6.5.3 Slender EHL Contacts under high Sliding Conditions 467 Marko Tošić, Thomas Lohner, Roland Larsson 6.5.4 Opportunities and Applications for Artificial Intelligence in Sealing Technology 471 Matthias Baumann, Lukas Merkle, Frank Bauer 6.6 Soft Contacts 6.6.1 Improved Design Process of Dry-Running Radial Plastic Plain Bearings by Coupling Laboratory Tests and Component Simulation 477 Marc Fickert, Andreas Gebhard 6.6.2 The lubrication of Soft Rough Interactions Unraveled by Lattice Boltzmann Simulation * Dr. Michele Scaraggi 6.6.3 Tribological Behavior Study of Elastomer - Hard Substrate Contact in Marine Environment 479 Claire Robin, Ahmad Al Khatib, Jean-Marie Malhaire, Jean-François Coulon 7 Sustainable Lubrication 7.1 Sustainability by Design Using Tribological and Lifecycle Assessment Tools 485 Amaya Igartua, Raquel Bayon, Gemma Mendoza, B. Zabala, Mathias Woydt 7.2 Innovations in Sustainable Base Oils: Separating Fact from Fiction * Matthew Kriech 7.3 Addressing Sustainability Needs of the Lubricants Industry: Innovative Base Stocks with Significant Greenhouse Gas Emissions Reduction Potential 489 Sabrina Stark, Edith Tuzyna, Christian Prokop, Cristina Vilabrille Paz 7.4 Novel, Bio-based Group V Basestocks for EV Applications: Customizable Performance with Reduced CO 2 Footprint 493 Arthur Coen, Ben Deweert, Anne-Elise Lescoffit, Marion Kerbrat 7.5 Sustainable Grease Production: Optimizing Energy Efficiency and Carbon Intensity * Dr. Georg S. Dodos 23rd International Colloquium Tribology - January 2022 17 7.6 The Importance of Sustainability and Carbon Negative Footprint in the Lubricants Industry * Matthew Kriech 7.7 CO 2 ZERO - How Lubricants Contribute to Climate Neutrality 497 Apurva Gosalia 7.8 Innovations and Regulations for Biobased and Sustainable Lubricants and Additives * Mark Miller 7.9 Assessment of Biobased Lubricants Compatibility with Metals * Dr. Georg S. Dodos 8 Digital Tribological Services: i-Tribomat 8.1 Digitalization of Tribological Systems for Decision-Making * Dr. Donna Dykeman 8.2 From Service Request to Standardized Tribological Data Sets 501 Alvaro Garcia 8.3 Trusted Tribological Materials Characterisation Services 503 Mirco Kröll, Reinhard Grundtner, Katharina Newrkla, Dirk Spaltmann, Francesco Pagano, Bihotz Pinedo, Erik Nyberg, Markus Söderfjäll, Vuokko Heino, Helena Ronkainen 8.4 Upscaling Materials Performance 507 Ulrike Cihak-Bayr, Marin Herr, Franz Pirker 8.5 Friction Control by Surface Texturing in Internal Combustion Engines 511 Konstantinos Gkagkas, Franz Pirker, András Vernes 8.6 Novel Journal Bearing Materials for Wind Turbine Gearboxes 515 Taneli Rantala, Kaisu Soivio Appendix Scientific-Technical Board 519 Index of Authors 521 * not available at the time of publication MASCHINENBAU, PRODUKTION UND FAHRZEUGTECHNIK Besuchen Sie unsere Seminare, Lehrgänge und Fachtagungen. 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Maschinenbau und Feinwerktechnik Fahrzeugtechnik Elemente, Maschinen und Anlagen Entwicklung und Konstruktion Werkstoffe und Betriebsstoffe Qualität, Mess- und Prüftechnik Verfahrens- und Oberflächentechnik, Korrosion Fertigungs- und Produktionstechnik Instandhaltung Betriebliche Organisation Arbeitssicherheit, Umwelt- und Strahlenschutz SEMINARE, LEHRGÄNGE, FACHTAGUNGEN Infos und Anmeldung: www.tae.de/ go/ maschbau Plenary Lectures 23rd International Colloquium Tribology - January 2022 23 E-Mobility, Sustainability, Markets, Raw Materials Dr. Lutz Lindemann FUCHS PETROLUB SE Mannheim, Germany Corresponding author: lutz.lindemann@fuchs.com 1. Introduction The industry faces numerous massive disruptive changes which haven’t been seen before in modern history at the same time. We are facing four disruptions at more or less the same time, which will change the industrial environment significantly. The society and industry have to find solutions regarding political/ geopolitical changes, drastic change in the industrial environment through the change in drive train technologies and mobility behaviour (i.e. e-mobility), sustainability requirements, digitalization and heavy disturbance in the raw material value chains. What does it mean to our industry in Europe, Americas and China? What can be done? A trial. 1.1 The Disruptions 1.1.1 Geopolitical Changes The geopolitical changes will lead to a reduction in globalization and transform the world’s economy back into a regionalized world. We have to deal with technology regions in 3 (4) different world regions with different speeds in technological development and regulatory frames in China, EU and USA. We can see already an independent development of Chinese technology with own specifications and trends. China’s target is clearly to become independent. [1] This implies a significant increase in costs to operate different technology backbones and infrastructures. USA moves in the same direction. Europe sits in between all chairs. EU will be disrupted through their own regulatory and political situation (i.e. raw materials, value chains). 1.1.2 Mobility E-Mobility and change in mobility behaviour will change the lubricant market faster than expected.[2] We will probably see a stable market environment worldwide but a significant drop in the EU market demand by 10-20% in 10-15 years [4]. New products will come up but will not substitute the losses in the “old drive trains”. One can say around 2030 we will see the end of the ICE for passenger cars and probably and trend to FC and/ or ICE with e-fuels and H2 fired engines. The overall market (OEM and Aftermarket) will commoditize. 1.1.3 Sustainability Sustainability requirements are most relevant for the European market and hits the market and the industrial world most. This effects the raw material side directly and indirectly, the energy supply, the mobility behaviour, the economical system per se and the overregulation. The industry has to deal with - Green Deal - 2050 Net Zero (for whom? ) [4] - Chemical Strategy for Sustainability [5] - Circular economy [6] - Change of the refinery landscape - availability from primary raw materials in Europe will become limited This regulatory setup will change the petrochemical industry, especially in view of the requirements regarding circular economy. Base oil availability, petrochemical feed stocks etc. will become a headache in Europe. 1.1.4 Raw Material availability The raw material availability will be distorted by geopolitical risks as experienced in the cases of magnesia, phosphorus, silicon and shortages in the value chain, especially computer parts. The regulatory of the EU will ban raw materials which are essential for the lubricant industry like Li, certain amines, phosphorus containing compounds, boron compounds etc. Due to the reduced demand in fuels in the coming years refineries need to adapt to the different slates in the industry. Whether this is possible is a question mark. Around 35% of refining capacity is on risk. The lubricant industry needs to adapt to recycling requirements coming up in 2023 or later. That means that a substitution of up to 70% of the base oils [6] should be substituted by recyclates. This requires more discussions within the community and the associations how to handle these requirements. Since the technology is not there to provide the qualities the lubricant industry needs. 24 23rd International Colloquium Tribology - January 2022 E-Mobility, Sustainability, Markets, Raw Materials 2. Conclusion The lubricant industry will have to cope with additional requirements in the different regions. US hasn’t found its way and stabilize in the coming years on the today’s way. China will move towards independency. That means deep localisation in China for all markets incl. R&D and raw materials. Europe will see the biggest changes. Therefore, the industry in Europe has to join forces (like the sustainability task force of UEIL), with all stakeholders to avoid that the above shaped scenario hits our industry in an overregulated and uncoordinated way, since the interdependences between all factors described is difficult to predict. We need to come to a regulatory environment which supports the targets but does not destroy the opportunities. References [1] 13th National People’s Congress on March 2021 14th Five-Year Plan (2021-2025) for National Economic and Social Development of the People’s Republic of China (PRC) [2] Diverse Announcements Daimler, VW, BMW, Stellantis [3] FUCHS Market Research - April 2021 [4] The European Green Deal, EU-Commission, COM/ 2019/ 640, Brussels, December 2019 [5] Chemicals Strategy for Sustainability, COM/ 2020/ 667, EU-Commission, Brussels, 14.10.2020 [6] A new Circular Economy Action Plan, COM/ 2020/ 98, EU-Commission, Brussels, 11.3.2020 23rd International Colloquium Tribology - January 2022 25 Different Dimensions of Sustainability Inga Herrmann VSI German Lubricant Manufacturers association, Hamburg, Germany Corresponding author: inga.herrmann@vsi-schmierstoffe.de Sebastian Dörr VSI German Lubricant Manufacturers association, Hamburg, Germany 3. Introduction Climate change and sustainability are key terms in our daily lives - and more and more companies are claiming to act in a climate neutral way: whether to seriously demonstrate there responsibility for a livable planet or simply to promote climate neutral products for marketing purposes. But is this the right approach to sustainable business? “Green marketing” is the task, “green washing” too often the result! 3.1 Subheading (2 columns) One of the best-known standards is the Greenhouse Gas Protocol which divides the carbon footprint into Scope 1 - 3: Scope 1 includes direct emissions - that is relatively simple. Scope 2 already takes into account energy supply and is more demanding. Scope 3 is extremely complex, as all aspects of the value chain, services, in-use phase and end-of-life as well as the side effects - utilities, waste treatment, employee commuting, business travel etc. have to be included. Sustainability has more dimensions than just the carbon footprint of an individual or a company. It also requires the consideration of environmental impact, resource constraints and social aspects (as the German “Supply Chain Act”). This is indeed a dramatic change for society and economy! Sustainable business is a key issue for the whole society and hits the lubricants industry at its core: What do lubricant manufacturers need to do to improve their own sustainability measures? What changes can we expect in our upstream chain - availability of raw materials, responsibility for selections? What do our key customers expect and demand? How can a reliable and comparable carbon footprint be calculated in a competitive environment? How do society and legislation affect our business models? What impact does the financial sector have on our activities? What will our market look like in 20 years? How do we deal with offsetting of emissions? Sustainable business models are already demanded by our key customers such as OEMs; investments are evaluated according to sustainable key figures; raw materials have to meet much stricter criteria than before. Most resources are limited and we need to use them appropriately. Climate change and reducing the carbon footprint of our activities are challenges and in some cases already mandatory. 26 23rd International Colloquium Tribology - January 2022 Different Dimensions of Sustainability The European Green Deal and other legal and societal requirements will have a strong impact on the European lubricants industry, forcing it to integrate sustainability into its economic activities. Annual sustainability reporting has been mandatory for larger companies in Europe since 2018. The development of specific measures that are reliable, transparent and accepted is of great importance for lubricant manufacturers, their suppliers and distributors as well as customers in order to create a level playing field. 4. Conclusion The German VSI (German Lubricant Manufacturers association) is working closely with OEMs, institutions and other associations to create such a sustainability concept in order to calculate the carbon footprint of lubricants, assess the supply chain and develop business models for the circular economy. References [1] Ghg Protocol - The Ofy [2] VSI - German Lubricant Manufacturers association 23rd International Colloquium Tribology - January 2022 27 Tribological optimisation for sustainable lubrication design Prof. Roland Larsson Division of Machine Elements, Luleå University of Technology, Sweden Corresponding author: roland.larsson@ltu.se Marcus Björling Division of Machine Elements, Luleå University of Technology, Sweden Yijun Shi Division of Machine Elements, Luleå University of Technology, Sweden Anders Pettersson Division of Machine Elements, Luleå University of Technology, Sweden 1. Introduction As with most other product development processes, the lubrication design has followed an optimisation procedure with two main goals, the best possible performance, and the lowest possible cost. In some cases, additional constraints have been added such as adequate safety and high efficiency. Over the past decades, sustainability has become increasingly important, but not a constraint on the optimisation. It has only been a profitable addition when it has been possible to claim that the product is made of renewable materials or produced in a sustainable way. Without sacrificing performance. But what happens if sustainability or circularity become constraints that must be considered? What happens if the product must be made from fossil-free, renewable materials and/ or if it must be possible to re-manufacture or re-use it? Then it may not be possible to get as good performance as before. 2. Circular economy Circular economy is a way to keep materials in the use-loop as long as possible. Ideally, the materials should be in use forever and no virgin material should be needed to be added [1]. In lubrication this is not possible since there is always a certain loss due to spill and evaporation. Two ways to obtain sustainability are possible, to re-condition and re-use the lubricants over and over again, or to use lubricants made from renewable, fossil-free, raw materials. In the latter case, it may not be possible to achieve as good performance as with petroleum-based oils without re-optimising the entire tribo-system. Today’s lubricants and tribo-systems have been optimised for more than a hundred years. When we start using completely new base fluids, we must redo the tribo-optimisation to get as high performance as today. In this presentation we will discuss how this can be done. We will compare petroleum-based oils, natural oils, and water-based fluids from a cost and sustainability perspective. 3. Base fluid candidates A vast majority of today’s lubricants are made from petroleum, i.e., mineral oils. The reason is the very good availability of hydrocarbon fractions of suitable viscosity when fuels are produced from the crude oil lower viscosity fractions. The raw material cost for mineral oils, consequently, also become very low due to the large volumes of crude oil. Most other fluids with similar viscosity would work as lubricants when it comes to machine components such as plain bearings. When the contact forces increase, however, oils have the good advantage of being strongly pressure sensitive. The viscosity increases dramatically, and the oil becomes solid-like in lubricated contacts such as those found in ball bearings or in between gear teeth. The pressure-sensitivity is normally described by the pressure-viscosity coefficient, defined as: where is dynamic viscosity and is pressure. Many fossil-free alternatives to mineral oils have pressure-viscosity coefficients on a similar level as mineral oils. That is in the range 15-20 GPa -1 . Some examples of alternative, fossil-free oil candidates are synthetic esters and other synthetic hydrocarbons made from renewable sources [2][3][4][5]. The cost for fluids like this is very much higher than for mineral oils. Another problem is that they are often made from natural oil plants such as rapeseed or sunflower. Such oils are also used as food and there will thus be a competition with the supply of food to an increasing world population. 28 23rd International Colloquium Tribology - January 2022 Tribological optimisation for sustainable lubrication design Another category of base fluid candidates are water-based compounds. Or more correctly, water-soluble compounds. The advantage with such water-based lubricants (WBL) would be that it is possible to make them non-toxic, fire-resistive, and easy to clean surfaces contaminated by the lubricants. Typical fluids are poly-alkylene glycols (PAG) and glycerol [6]. In this presentation we are focussing on the latter type. Glycerol is produced in relatively large volumes but far from the volumes of mineral oils. The problem is that all mentioned fossil-free candidates are not produced in sufficient amount, and they all make use of natural oils. Glycerol is, for example, a waste product from biodiesel (RME) production using natural oils as raw material. Still, glycerol is a low-cost product. Glycerol has a disadvantage in having a low pressure-viscosity coefficient. It is around 5 GPa -1 [7]. Other water-soluble base fluids have the same problem. The difference in may sound little but implies that viscosity at 1 GPa may be some 3 orders of magnitude lower than for mineral oils and, as explained below, this will make the lubricating film thinner. One advantage with low is, however, that friction in full film, elastohydrodynamic lubrication (EHL) is extremely low, up to 4-5 times lower than for mineral oils [7]. If we can design for full-film lubrication then WBLs should have excellent friction behaviour in, for example, gears. 4. Re-design for WBL As mentioned, tribo-systems with oils are optimised over more than hundred years. Just to replace them without changing anything else in the tribo-system can hardly be done and most comparisons between the performance of mineral oils and WBL will show that the oil will perform better, at least in terms of wear performance. To make it possible to obtain as good lubricating performance in EHL, for the WBL, as for the oil we need to compensate for the low . The Hamrock-Dowson equation [8] can be used for this purpose. Film thickness is proportional to pressure-viscosity coefficient and viscosity in the following way: If the is assumed to be 18 for the oil and 5 for the WBL then viscosity must increase by (18/ 5)0.49/ 0.68 ≈ 2.5 times to maintain the same film thickness. Another alternative is to keep the film parameter [9] constant, then surface roughness must be reduced to approximately half the value compared to the oil lubricated contact. But the film parameter is criticised as a measure of lubrication quality [10] and the film parameter presented by Hansen et al. shows better accuracy [11]: where is the surface roughness reduced peak height, is the central film thickness, and is a number smaller than 1 and a function of asperity summit radius. The larger summit radius, the larger . Transition to full film lubrication takes place when >1. Consequently, by optimising roughness with large asperity summit radii it would then be possible to obtain the same as for an oil lubricated case. 5. Mixed and boundary lubrication The base oil is providing the hydrodynamic functionality of the lubricant but its high performance under severe conditions is controlled by additives. The chemistry of WBL is completely different than for oils so a new family of tribo-improvers must be developed. There are some few (public) attempts made, for example using myoinositol [6]. Zapata et al. [12] made a study on micro-pitting under mixed lubrication conditions. They showed that the WBL gave rise to less micro-pitting since the wear was much more pronounced than for the oil. The fractured top-layer was, therefore, continuously worn off and kept fatigue effects to a minimum Furthermore, it might be necessary to apply coatings since film formation is less efficient with low lubricants. 6. Conclusions and remarks There is no single fossil-free alternative to mineral oils as lubricant base fluids. Instead, we may see a big variety of base fluids, both oily ones and water-soluble ones. Water-based or water-soluble base fluids (WBL) have an advantage in being non-toxic, fire-resistive, and water washable. Potentially they also have significantly better friction performance. But they have poorer film forming properties than oils. This can be compensated by using higher viscosity, smoother surfaces, optimised topography, and/ or coated surfaces. In future lubricated systems we will need to design with sustainability as a demand and this will make it necessary to re-design for the use of WBL. An important question to raise (even if it is not the scope of this presentation) is if we need to design the system at the edge of its performance? Is downsizing always the right thing to do? The life-cycle cost (economically and sustainably) may be lower if we oversize the system and reduce the risk of wear to a minimum. 23rd International Colloquium Tribology - January 2022 29 Tribological optimisation for sustainable lubrication design References [1] Walter R. Stahel, W. R., ”The circular economy“, Nature, 531, 435-438 (2016). [2] Rubin, B., Glass, E.M., ”The air force looks at synthetic lubricants“, 1950, SAE Technical Papers [3] Pettersson, A., ”High-performance base fluids for environmentally adapted lubricants“, 2007, Tribology International, 40(4), pp. 638-645. [4] www.novvi.com [5] www.biosynthetic.com [6] Matta C., Joly-Pottuz L., De Barros Bouchet, M.I., Martin J.M., Kano, M., Zhang Q., Goddard W.A., ”Superlubricity and tribochemistry of polyhydric alcohols”, Physical Review B - Condensed Matter and Materials Physics, 78 (828), 2008. [7] Shi, Y., Minami, I., Grahn, M., Björling, M., Larsson, R., ”Boundary and elastohydrodynamiclubrication studies of glycerol aqueous solutions as green lubricants“, Tribology International, 69 (2014) 39-45. [8] Hamrock, B. J.and Dowson, D., ”Isothermal elastohydro-dynamic lubrication of point contacts, part I, theoreticalformulation“, ASME J. Lubr. Tech., 1976, 98, 223-229. [9] Tallian, T.E.: ”On competing failure modes in rolling contact“, ASLE Trans., 10, 418-439 (1967). [10] Cann, P., Ioannides, E., Jacobson, B., Lubrecht, A.A.: ”The lambda ratio - a critical re-examination“, Wear, 175, 177-188 (1994). [11] Hansen, J., Björling, M., Larsson, R., ”A New Film Parameter for Rough Surface EHL Contacts with Anisotropic and Isotropic Structures”, Tribology Letters (2021) 69: 37. [12] Zapata, J.G., Björling, M., Shi, Y., Prakash, B., Larsson, R., “ Micropitting performance of Glycerol-based lubricants under rolling-sliding contact conditions“, accepted for publication in Tribology International. 23rd International Colloquium Tribology - January 2022 31 From Emerging Trends to Current Lubrication Challenges: STLE’s View Dr. Ken Hope This presentation will cover the issues that are described in the current STLE Emerging Trends Report and look at what has evolved in the areas of Tribology and Lubrication Engineering. Even though the title says “Lubrication Challenges” it is important to recognize that it includes challenges related to tribology, materials, and sustainability issues. The report is published every three years and is created through a research methodology that engages with STLE members, thought leaders and industry organizations to compile a view on the overall direction of lubrication trends. A forecast is never perfect, but this process pulls together for foreseeable future direction and challenges from the perspectives of over 600 experts in this field, which is roughly a 60: 40 split between US: International. Input came from individuals working in R&D, Sales, and Marketing. It highlighted needs and issues in application sectors of transportation, medical & health, energy, and manufacturing. The specific discipline fields were a) workforce issues, b) research funding, c) materials cost and availability, d) government regulations and e) Safety, Environment, basic human needs. This report has helped to identify and predict the impact of important technologies and areas of concern as they relate to the field, industry and even society and the world economy. It also explores the possible consequences of those trends, both positive and negative. STLE and others have used the report to facilitate a conversation on a global scale, through press releases and media, conferences, and various other media, relative to the needs of industry and society. There are key conclusions for each of the application sectors mentioned above. Specifically in the transportation section, the report identified that the field is undergoing significant advancement in fuel efficient vehicles in response to regulatory pressures. The chief development is the electric and hybrid vehicles as well designs for internal combustion engines (ICE) and autonomous vehicle (AV) technologies. Respondents identified an expectation of a “great deal of advancement” in EV, autonomous driving, EV transmissions, growth in hybrid vehicles, light-weighting materials, and conductive vs. non-conductive fluids. As we can see now from 2022 the views from a few years ago were very accurate. Barriers and market resistance to moving toward EVs from ICEs were also highlighted. This included several issues regarding the infrastructure required for EVs, cost, range anxiety, government subsidies and battery pricing. Autonomous vehicles were highlighting the advantages of fuel efficiency and travel time, vehicle ownership patterns, vehicle networking and a cyber security issue. Participants stressed that while it is advancing quickly, the technology is not yet mature enough to take hold on a wide scale. In the Medical sector the report identified issues in the medical prosthetics field related to the titanium alloys that are being replaced with ceramic or metal polymers due to nano-scale corrosion and the potential of metals entering the bloodstream. In addition, additive manufacturing opportunities would allow tailor made prosthetic devices and implants. The need to post process 3D printed devices to improve surface roughness was also pointed out as well as the need to research the performance of 3D printed parts. The specific discipline fields segment covered Energy, Manufacturing, Workforce issues, and Research funding. Energy-related issues ranked to be of greatest relative importance and increased significance are improved energy storage, batteries to substitute for liquid fuel, lower emission requirements, CO2 and methane capture, sustainability, availability of Lithium and rare earth elements and wind energy. In the Manufacturing field interest levels are increasing for ways to enhance productivity and efficiency, use of environmental acceptable lubricants, lighter and stronger materials, digitalization of industrial processes, more durable greases and lubricants, 3D printing and the impact of recycling. The Workforce field identified the primary issues as the aging workforce in tribology and lubrication engineering and the training for current employees or new hires. This issue continues today and will likely remain a future concern. Furthermore, in the Research funding field for all the areas that have been mentioned it was noted that this funding is determined by government and industry priorities. Participants felt most strongly (85%) that there would be a significant increase in battery technology research, which includes energy storage, and alternative energy sources. STLE is now beginning the planning stages for the next trends report. There continue to be new developments and a tremendous amount of interest in lubrication and tribology related to electric and hybrid vehicles and in many other tribology and lubrication issues that impact the future for people around the globe. We invite conference participants to share their input as STLE plans the 2023 Emerging Trends Report. Note: a free copy of the 2020 report, as well as the two earlier reports, are available on the STLE website (www.stle.org). 23rd International Colloquium Tribology - January 2022 33 Novel Nanocomposite with Ionic Liquid and Graphene for Electroconductive Radial Plain Bearings Susanne Beyer-Faiss Dr. Tillwich GmbH Werner Stehr, Horb-Ahldorf, Germany Corresponding author: susanne.beyer.faiss@tillwich-stehr.com Dr. Yasmin Korth Dr. Tillwich GmbH Werner Stehr, Horb-Ahldorf, Germany Dr. Tobias Amann Fraunhofer-Institut für Werkstoffmechanik IWM, Freiburg, Germany Dr. Thomas Schubert IOLITEC Ionic Liquids Technologies GmbH, Heilbronn, Germany Dr. Sebastian Plebst IOLITEC Ionic Liquids Technologies GmbH, Heilbronn, Germany 1. Introduction Precision engineering has to meet the challenge to continuously improve performance and efficiency of precision sliding elements, although they are becoming smaller and smaller. The miniaturization of parts raises the demands on the lubricants to generate low friction and wear values even at higher specific pressures. This is a particular challenge, when systems are constructed with plastic materials, which are widely used in this field. Applications in practice show, that actual solutions come to their limits, when components have to deal with new surrounding conditions, for example with electrostatic charge going along with disruptive discharge, which harms materials as well as lubricants extremely up to damage. Plastic plain bearing material as well as the lubricant are insulators, and electrostatic charge is favoured. The idea is to create a plain bearing system, which allows to consistently deviate electric charge in any operating condition of the bearing even under hydrodynamic lubrication, so all parts of the plain bearing including the lubricant have to be equipped with a certain defined electric conductivity. In a joint research project an innovative concept for a sliding bearing system is being developed, consisting of a steel shaft combined with an optimized polymeric nanocomposite bearing material and an adapted electrically conductive lubricant, using ionic liquids (IL) and graphene (Project acronym: EPiG). 2. Approach 2.1 IL-Graphene-Compounds The compounds were developed in a multi-stage process. The selection criteria for the base polymer were favorable mechanical and tribological properties. The ILs were rated for their electrical conductivity, their corrosion resistance, and their long-term resistance towards the base polymers. Purity, price and compounding properties were used as evaluation criteria for the various types of graphene. The decision was made in favor of the base polymer PA66 in combination with IL P 666(14) BTA with a high electrical conductivity (114.8 µS / cm) and a reduced graphene oxide (rGO), which is produced in a wet chemical process using the Hummer method with an adjacent reduction. In addition, compounds with carbon nanotubes CNT were also produced in order to achieve higher electrical conductivity. 34 23rd International Colloquium Tribology - January 2022 Novel Nanocomposite with Ionic Liquid and Graphene for Electroconductive Radial Plain Bearings The content of P 666(14) BTA has been set on an identical level for all compounds, whereas the contents of graphene rGO and CNT has been varied: PA66 compounds Content IL Content rGO Content CNT Specific volume resistivity [ohm.cm] PA66 base polymer - - - 1.63E+15 4% rGO - 4 - 1.09E+15 IL+2% rGO fix 2 - 1.20E+15 IL+4% rGO fix 4 - 3.38E+14 IL+4,25% rGO fix 4.25 - 2.07E+12 IL+4,75% rGO fix 4.75 - 1.21E+11 IL+8% rGO fix 8 - 1.23E+09 IL+3% CNT fix - 3 1.79E+05 IL+4% CNT fix - 4 1.27E+05 IL+3% CNT+1% rGO fix 1 3 2.01E+05 Table 1: Composition of IL-graphene-compounds with specific volume resistivity according to IEC 60093. The percolation threshold of the PA66-IL-graphene compounds is higher than 4% graphene content. The electrical conductivity is very low overall. Compounds with CNT achieve an electrical conductivity, which is higher by ten orders of magnitude. 2.2 IL-Graphene-Lubricants Selection criteria for the lubricants were resistance to aging and oxidation, use at low temperatures down to -40 ° C, compatibility with the plastic material and the possibility of varying the viscosity. Solubility in the base oil, electrical conductivity, no corrosion with steel and stability under current flow were required for the IL [1]. The choice fell on PAO in combination with IL N 8881 BTA and the reduced graphene oxide, which is also used in the compounds. The major challenge was to prepare stable graphene- IL dispersions, which are at the same time electrically conductive. IL-graphene-dispersion D1311-90, which has been used for the tribological evaluation of the IL-graphene-compounds, has an electric conductivity of 1.96 µS/ cm and a viscosity of 64.2 mPas . s at 20°C. The stability of the dispersion lasts about 3 weeks. 3. Experimental and Results To characterize the friction and wear behavior of the modified polymeric bearing materials in contact with the adapted lubricant, tests are performed in tribological model systems under rotating motion. 3.1 Tests in Model System Sphere-on-Prism Friction and wear tests have been performed using the sphere-on-prism (ISO 7148-2) model system under unidirectional rotating motion using ½” spheres out of steel 1.3505 and the compounds listed in Table 1. Friction coefficients were monitored dependent on sliding speed (0-210 mm/ s) and load (1-3-6 N) at 25 °C (short term tests). Wear tests were done with v=28,2 mm/ s and 30N load at ambient temperature (100 hours long term tests). All IL-graphene compounds show a very good response to lubrication with the base oil PAO. Static COF are below 0.15 and sliding COF range around 0.05 and below. Some compounds even show static COF below 0.1. The wear reduction is very good. Lubrication with the PAO-IL-graphene-dispersion D1311-90 give in any case tested a higher static COF, in between 20 to 50 % for the graphene containing compounds and up to 100 % for the CNT containing compounds, followed by a steeper decline of COF when raising the sliding speed. This difference cannot be explained by the viscosity, since the difference in viscosity of both fluids is only 4 mPa . s. One effect could be the adhesion of the graphene, which is part of the PA66-compound as well as the IL-graphene-dispersion. D1311-90 also show a good response in terms of wear reduction, only in some cases wear is little higher compared to lubrication with the base oil. 3.2 Tests in Model System Plain Bearing on Shaft Based on the results from 2.1 two materials were injection moulded into plain bearings: PA66-IL-4.25% rGO compound, who shows favorable tribological behavior and a good response to lubrication combined with a certain conductivity. The other PA66-compound material combines IL- CNT and rGO. This compound exhibits a higher conductivity by seven orders of magnitude. Tests are performed in model system bearing-on-shaft (ISO 7148-2, alternating rotating motion). The lubricated, electrically conductive plain bearing systems are checked in long-term tests under application-related conditions in start-stop operation. For this purpose, a slide bearing test stand was converted for galvanic coupling [2] and for testing under current flow [3]. Tests are performed in sliding combination with a steel 1.3505 shaft (diameter 5 mm) and a bearing load of 50 N under an intermittently rotating movement with 1000 cycles, each with an increasing and decreasing profile of the 23rd International Colloquium Tribology - January 2022 35 Novel Nanocomposite with Ionic Liquid and Graphene for Electroconductive Radial Plain Bearings rotation speed from zero to max. 1600 rpm (continuously accelerated within 120s) and reverse (continuously reduced within 10s). In between the cycles a standstill period of 5s is established, symbolizing 1000 start-stop conditions. In addition, the linear wear of the bearing is monitored. Figure 1: Evaluation of friction behavior of novel electrically conductive nanocomposite bearing system, lubricated with an EC lubricant. 4. Conclusion The combination of ionic liquid with graphene has a potential for making a plain bearing system consisting of a modified PA66-compound and an adapted lubricant dispersion electrically conductive to such an extent, that electrostatic energy can be continuously dissipated during operation. The tribological behavior of the base polymer (friction and wear) is not negatively influenced and corresponds to that of established plastic plain bearing materials. The development of adapted lubricants with IL-graphenes with a defined low conductivity turns towards the right direction. However, the long-term stability of the IL-graphene dispersions has to be further improved, since it is important for maintaining the tribological function. References [1] Korth, Y.; Beyer-Faiß, S.: Untersuchungen von Ionischen Flüssigkeiten unter Stromfluss. GfT Jahrestagung 2021, 27.-29. September 2021, Online Konferenz. [2] Amann, T.; Gatti, F.; Oberle, N.; Kailer, A.; Rühe, J.: Galvanically induced potentials to enable minimal tribochemical wear of stainless steel lubricated with sodium chloride and ionic liquid aqueous solution, Friction 6 (2), 7, 2018. [3] Gatti, F.; Amann, T.; Kailer, A.; Baltes, N.; Rühe, J.; Gumbsch, P.: Towards programmable friction: control of lubrication with ionic liquid mixtures by automated electrical regulation, Scientific Reports 10 (1), 1-10, 2020. Acknowledgements The project, on which this report is based, is funded by the German Federal Ministry of Education and Research (BMBF) under the code 03XP0220 (term 01.05.2019 to 30.04.2022). The authors are responsible for the content of this publication. 23rd International Colloquium Tribology - January 2022 37 Tribology in the Age of Digitalization and Green Deal - Building Digital Services! Franz Pirker AC2T research GmbH, Wiener Neustadt, Austria Corresponding author: franz.pirker@ac2t.at 1. Introduction The potential for saving energy and reducing costs was the key reason to define tribology as its own scientific discipline. 55 years after the birth of tribology, digitalisation and the Green Deal are the drivers and challenges at the forefront of industrial development and take first place on the agenda of the European Commission. How can tribology position itself in the age of digitalisation? Which new digital tools and possibilities should be taken advantage of? What examples from other fields are there? In mobility, MaaS („Mobility as a Service“) is a good example of employing digital technology to develop a service that satisfies the needs of the population as well as the demands of resource efficiency and CO2 reduction. Additional requirements for the success of such services are a digital business model and the cooperation of different stakeholders. In the area of simulation and software, new business models and services are already well established - SaaS („Software as a Service“) being a prime example. The trend goes away from one-time purchases towards needs-oriented usage and the appropriate payment systems. With the European research project i-TRIBOMAT („Intelligent Open Test Bed for Tribological Materials Characterisation“), the path towards TaaS - Tribology as a Service - is presented. 2. Tribology’s impact on Green Deal The European Green Deal is a set of initiatives from policy side by the European Commission with the central aim to make Europe climate neutral in 2050.[1][2] An impact assessed plan will also be implemented to increase the EU’s greenhouse gas emission reductions for 2030 to at least 50% and towards 55% compared with 1990 levels. Lowering the friction and wear by developing new material solutions for tribological applications has substantial environmental effects and directs towards low carbon future. The study carried out on the influence of tribology on global energy consumption, costs and emissions, by Holmberg and Erdemir [3], concluded that in total, about 23% (119 EJ) of the world’s total energy consumption and 8120 Mt/ year of CO2 emissions originates from tribological contacts. By using new technologies for friction reduction, energy losses due to friction and wear could potentially be reduced by 40% in the long term (15 years) and by 18% in the short term (8 years). On a global scale, these savings are 1.4% of the Gross Domestic Product (GDP) annually and 8.7% of the total energy consumption in the long term and reduction in CO2-emission globally by 1460 MtCO2 can be achieved! Figure 1: Overview of the European Green Deal 3. Digitalization - a misunderstood word Digitization is usually understood to mean only individual new technologies like Digital Twin, AI Artificial Intelligence, Blockchain or similar. Therefore, digitization is often misinterpreted and misunderstood. A very accurate definition of digitalization has been published by Gartner, Inc. [4] “Digitalization is the use of digital technologies to change a business model and provide new revenue and value-producing opportunities; it is the process of moving to a digital business.” Very illustrative examples of the implementation of digital business models are Google, Apple, Facebook Amazon, so called GAFAs. What they all have in common is a platform where the customer can use and buy services easily, quickly on a transparent cost basis. In the technological field, there are the first attempts at digital business models such as SaaS (Software as a Service). The ad- 38 23rd International Colloquium Tribology - January 2022 Tribology in the Age of Digitalization and Green Deal - Building Digital Services! vantage of SaaS is that the client does not need to install any software or have a computer with sufficient computing power to run simulations. The licensing models are also very customer-friendly; for example, you are only charged according to the number of simulations carried out. 4. From research project to service provider The funded European H2020 project i-TRIBOMAT develops new digital services which, already in the development stage, facilitate the rapid and cost-efficient selection of materials, as well as the prediction of the tribological performance of products regarding efficiency and lifetime. The project connects the entire tribological characterisation infrastructure of five European research centres and links it to an IT-platform using IoT technology. This allows the client to choose between over 100 different characterisation tools. The data is centrally stored and further processed in a newly developed cloud-based material database. The clients can access their data any time and can easily request an advanced analysis or create their own reports. Without needing a particular expertise, clients can carry out simulations in virtual workrooms, allowing them to use their material data to rapidly and cost-efficiently predict operational characteristics without constructing a prototype. All digital services can be customised and booked by the client on the web-based platform. The connection of infrastructures and the new digital services result in the emergence of Europe’s largest tribology centre (a joint venture of the five research centres), which offers and markets all services on a webbased platform. 5. Tribology as a Service - TaaS - The Platform i-TRIBOMAT - The European Tribology Centres core is a platform on which various services can be booked - from standardised tribometer tests and additional characterisation services (service 1) to data driven services (service 2) and simulations in virtual workrooms based on a SaaS concept (service 3) see Figure 2. Figure 2: Overview services and integrated workflow All 3 services combined are representing the integrated workflow to up-scale materials performance in a tribological component. If a customer wants to know how a new material performs in his component under operation, the material will be tribological tests, the test results and test data is stored in a secure manner and can seamless integrated into simulation models. These models are up-scaling the performance of the component with the input of real test data. These leads to an accelerated component development process saving time and costs for the customer. 6. Digital Business models - complete - not compete Thereby, i-TRIBOMAT wants to create the basis for the European Tribology Centre. Additionally, digital business models which enable the sustainable operation of the platform as an independent business have been developed. The B2B relation are shown in Figure 3, where i-TRIBOMAT will be the Single Entry Point for industrial customers. The partners are acting as service providers, depending on the kind of service. Figure 3: B2B Modell i-TRIBOMAT 7. Conclusion Digitisation is the opportunity and challenge that European industry must take on and utilise. You can’t think in terms of isolated methods and hypes like digital twins or simulation, but you have to build digital business models in order to be able to offer added value to your customers. Integrated platforms such as i-TRIBOMAT show the possibility of how even competing companies can reposition themselves together and thereby create a unique market place. References [1] COM(2019) 640 final; COMMUNICATION FROM THE COMMISSION TO THE EUROPE- AN PARLIAMENT, THE EUROPEAN COUN- CIL, THE COUNCIL, THE EUROPEAN ECO- NOMIC AND SOCIAL COMMITTEE AND THE 23rd International Colloquium Tribology - January 2022 39 Tribology in the Age of Digitalization and Green Deal - Building Digital Services! COMMITTEE OF THE REGIONS; The European Green Deal, European Commission [2] ANNEX to the COM(2019) 640; COMMUNI- CATION FROM THE COMMISSION TO THE EUROPEAN PARLIAMENT, THE EUROPEAN COUNCIL, THE COUNCIL, THE EUROPEAN ECONOMIC AND SOCIAL COMMITTEE AND THE COMMITTEE OF THE REGION; The European Green Deal, European Commission [3] K. Holmberg, A. Erdemir, Friction 5(3) 263 (2017) [4] https: / / www.gartner.com/ en/ information-technology/ glossary/ digitalization, downloaded 25.10.2021 Acknowledgement This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No. 814494, project i-TRIBO- MAT. More details: https: / / www.i-tribomat.eu/ . 23rd International Colloquium Tribology - January 2022 41 Base Oil Benchmarking for Gear Oils in Electric Vehicle Drivetrains Dr. Steffen Glänzer Clariant Produkte Deutschland GmbH, Clariant Innovation Center, August-Laubenheimer-Strasse 1, 65926 Frankfurt 1. Summary The market penetration of electric vehicles is a major global trend resulting from regulations intended to reduce greenhouse gas emissions. OEMs, suppliers and researchers are looking for base oils that meet new e-fluid needs which happen to be different than for lubricants used in internal combustion engine vehicles. So far, few systematic studies benchmark crucial properties of e-fluid base oils. This paper will compare base oil properties of polyalphaolefins and various new polyalkylene glycole solutions covering the following topics: 1) energy efficiency, 2) cooling performance, 3) electrical properties, and 4) sustainability. One major finding is that polyalkylene glycols offer the possibility to optimize and finetune these properties over a wide range. In summary, friction can be reduced down to the level of superlubricity (coefficient of friction below 0.01) and heat transfer efficiency can be increased up to 30%. In addition, Clariant Polyglykols offer the possibility to formulate hazard label-free and readily biodegradable fluids. 2. Introduction Improving energy efficiency is one of the main goals in today’s electric vehicle powertrain development. The gear lubricant can contribute to achieve higher energy efficiency, which results in a longer range of the electric vehicle. Secondly, increasing energy density of the electric motor requires more efficient cooling concepts. Direct cooling of the electric motor using a gear lubricant with excellent heat transfer properties can be an excellent solution.[1] In addition, the lubricant for electric vehicle reduction gears should have suitable electric properties. It should be thermo-oxidatively stable, and it should be label free and readily biodegradable. As only limited data is available in comparing different base oil solutions for electric vehicle drivetrains, Clariant conducted a benchmarking study launching four new base oils. The following base oils were selected, all having the same viscosity at 100°C of 3-4 mm2/ s: Polyglykol E01 P Polyglykol E02 A Polyglykol E03 A Polyglykol E04 E PAO 3.6 Viscosity at 40 °C (mm 2 s -1 ) 13 12 13 22 15 Viscosity at 100 °C (mm 2 s -1 ) 3.2 3.6 3.4 4.1 3.6 3. Results Values on energy efficiency were determined using an elastohydrodynamic (EHD) ball-on-disc tribometer. As parameters, different pressures (800 N mm-2 and 1200 N mm-2), temperatures (40°C and 80°C), and a sum speed of 1.6 m/ s were selected. The slide-to-roll ratio of the ball and disc were varied between 0.0 (pure rolling) and 1.0 (high amount of sliding). Selected results are shown in Graph 1. Surprisingly, the coefficient of friction varies dramatically depending on the selection of the base oil. POLYGLYKOL E04 E showed a outstandingly low coefficients of friction. E.g. at 800 N mm-2, 40°C, sum speed of 1.6m/ s and a SRR of 0.6 the coefficient of friction is less than half compared to PAO (0.021 vs. 0.047). Notably, the coefficient of friction of POLYGLYKOL E04 E is significantly lower, even though the viscosity of POL- YGLYKOL E04 E is higher compared to PAO at 40°C. POLYGLYKOL E02 A and POLYGLYKOL E03 A show coefficients of friction lower than PAO 3.6, whereas the coefficient of friction of POLYGLYKOL E01 P is higher compared to PAO 3.6 Conditions: Pressure: 800 N mm -2 Temperature: 40°C sum speed: 1.6 m/ s Graph 1: Coefficient of friction of different base oils 42 23rd International Colloquium Tribology - January 2022 Base Oil Benchmarking for Gear Oils in Electric Vehicle Drivetrains As a second important property heat transfer of the different base oils was evaluated. For forced turbulent flow conditions, the Mouromtseff Number Mo applies [2]. The higher Mo the more effective the heat transfer. Mo is influenced by the density of the oil, the thermal conductivity, the heat capacity and the dynamic viscosity. All parameters were evaluated and Mo was determined at 40°C and 100°C for all fluids. Remarkably, the heat transfer Mo of POLYGLYKOL E03 A and POLYGLYKOL E04 E are between 10% and 30% higher compared to PAO 3.6 (Graph 2). At 40°C the best heat transfer properties are observed for the base oils POLYGLYKOL E02 A, POLYGLYKOL E03 A and POLYGLYKOL E04 E. At 100°C the highest heat transfer is observed for POLYGLYKOL E04 E. PAO 3.6 showed the lowest Mo at 40°C and the second lowest Mo at 100°C. Graph 2: Relative heat transfer Morel of different base oils. Furthermore, the electric conductivity of the different base oils was investigated. For the application the electric conductivity should be high enough to avoid electro-erosion in bearings because of high voltage build up and subsequent electrical discharge. On the other hand, the electric conductivity should be low enough to avoid short circuits. Minimum and maximum values for the required conductivity are still under discussion. In the benchmarking study PAO 3.6 revealed the lowest conductivity of <1pS/ m and Polyglykol E04 E showed the highest conductivity of approx. 20mS/ m. As the last aspect, sustainability properties were compared. PAO 3.6 is not readily biodegradable, whereas POLYGLYKOL E01 P, POLYGLYKOL E03 A and POL- YGLYKOL E04 E are readily biodegradable. Moreover, POLYGLYKOL E01 P, POLYGLYKOL E02 A, POLY- GLYKOL E03 A and POLYGLYKOL E04 E are hazard label-free according to GHS. Literature [1] McGuire, N. (2021), The brave new world of electric vehicle fluids, Tribology Lubrication Technology [2] Simons, Robert E. (2006), Comparing Heat Transfer Rates of Liquid Coolants Using the Mouromtseff Number, Electronics cooling. 23rd International Colloquium Tribology - January 2022 43 Vacuum tribology of superhard ta-C coatings Dr. Volker Weihnacht Fraunhofer IWS, Dresden, Germany Corresponding author: volker.weihnacht@iws.fraunhofer.de Lars Lorenz TU Dresden, Institute of Manufacturing Science and Engineering, Dresden, Germany Fabian Härtwig TU Dresden, Institute of Manufacturing Science and Engineering, Dresden, Germany Stefan Makowski Fraunhofer IWS, Dresden, Germany Frank Kaulfuß Fraunhofer IWS, Dresden, Germany 1. Introduction Diamond-like amorphous carbon (DLC) coatings attract a great deal of interest due to their exceptional mechanical and tribological properties. Especially the superhard ta-C coatings show superior behaviour with extraordinary low wear rates combined with low friction under lubricated and even under unlubricated conditions in ambient air. In the absence of humidity, especially in a vacuum, ta-C coatings tend to exhibit unfavourable friction behaviour. In this contribution, a systematic vacuum-tribological study on ta-C coatings with variation of air pressure, counter body material and doping of ta-C with other elements is carried out. The aim was, to see why ta-C coatings lose their superior tribological performance in the lack of atmosphere and if there are possibilities to improve the behaviour while retaining the general advantages of ta-C. 2. Experiments The ta-C coatings were produced using the Laser-Arc process [1]. An approximately 0.1 µm thick Cr layer was used as an intermediate adhesion layer. The thickness of the ta-C coating was about 3 µm. In order to eliminate the deposition-related defects from the coating, a mechanical polishing was subsequently carried out. In addition to the pure ta-C coatings, softer a-C coatings and doped (t)a-C: X coatings (X = B, Cu, Fe, Mo and Si) were also produced. The doping was about 5 at% and was achieved via laser arc evaporation of graphite composite targets. The coatings were applied to 18 mm x 13 mm x 3 mm flat specimens of 100Cr6. As counter bodies in tribological experiments balls with Ø 10 mm were used. Beside experimental series with uncoated 100Cr6 steel balls, also balls made from Brass, Bronze, Copper, Al2O3, SiC and ta-C coated steel were used. A TETRA BASALT-C UHVT-14 ultra-high vacuum tribometer was used for tribological investigations both in oscillation and rotation mode. The parameters for oscillation mode were 5 N normal load, 3 mm stroke, 0.5 Hz frequency. For rotation experiments, 5 N normal load and 3 mm/ s sliding speed were applied. 3. Results 3.1 Variation of humidity The influence of humidity on friction and wear of ta-C vs. steel was measured using oscillation-mode tribometry. 44 23rd International Colloquium Tribology - January 2022 Vacuum tribology of superhard ta-C coatings Fig. 1: Wear track on ta-C (left) and abrasion on the 100Cr6 steel ball counter body (right) after 2000 cycles in oscillation tribometer at different atmospheres. The wear results (Fig. 1) show that both the wear track on the ta-C coating and the abrasion from the steel ball increase with each reduction in air pressure. In normal air (1000 mbar), neither a wear mark on the ta-C coating nor abrasion on the steel ball can be detected. Already at a reduction of the air pressure to 1/ 100, there are significant amounts of wear and also an obvious tribochemical change on the tribocontact of the steel ball. Fig. 2: Friction coefficient of ta-C vs. 100 Cr6 as a function of air pressure in an oscillation-mode vacuum tribometer. Fig. 2 shows the mean friction coefficients as a function of air pressure. As already found in wear results, also for friction a systematic deterioration with decreasing pressure can be observed. 3.2 Variation of counter body material In another series, the influence of counter body material on friction and wear behavior of ta-C coatings was tested. These tests were carried out in rotation mode in the vacuum tribometer at a pressure of about 3x10-7 mbar. Fig. 3: Friction coefficient of ta-C vs. different counter-body materials (balls) in an rotation-mode vacuum tribometer at about 3x10-7 mbar. From the results in Fig. 3 it can be seen, that the friction force can be significantly reduced by using counterparts different from steel. The highest friction is observed for a ta-C coated steel ball, i.e. a ta-C/ ta-C pairing, followed by a ta-C/ steel contact. A significant reduction is observed for Alumina, Bronze, and particularly for Brass. 4. Summary The results show that the tribological behaviour of ta-C in vacuum has to be considered in a very differentiated way and is not an intrinsic property of ta-C. It depends strongly from atmospheric pressure and from counter body material. Friction results are achieved that differ by up to an order of magnitude and wear rates over several orders of magnitude. For example, while the contact of ta-C/ steel in high vacuum is associated with a coefficient of friction of about 1, the coefficient of friction decreases to even ultra-low friction values for ta-C in contact to Brass. This is only a small selection of a large number of results with different variations of atmosphere, counter body and doping of ta-C coatings in this study. The presentation goes into detail about the various dependencies. In addition to the friction and wear results, individual analytical results on the friction contacts are also presented. References [1] F. Kaulfuss et al., “Effect of Energy and Temperature on Tetrahedral Amorphous Carbon Coatings Deposited by Filtered Laser-Arc,” MDPI Materials (Basel, Switzerland), vol. 14, no. 9, 2021. 23rd International Colloquium Tribology - January 2022 45 An innovative multi-scale approach to reduce friction of automotive lubricants from hydrodynamics to boundary lubrication Prof. Denis Mazuyer École Centrale de Lyon, Laboratoire de Tribologie et Dynamique des Surfaces, CNRS UMR5513, Écully, France Corresponding author: denis.mazuyer@ec-lyon.fr Juliette Cayer-Barrioz École Centrale de Lyon, Laboratoire de Tribologie et Dynamique des Surfaces, CNRS UMR5513, Écully, France 1. Introduction The tribological mechanisms, associated in particular with the formation, the maintenance of a lubricating film with fluids of low viscosity and its capacity to circumscribe the dissipation by friction to a value as low as possible were investigated over all the lubrication regimes. The authors tackled the problem by treating separately the compliant contacts operating at low pressure (crankshaft bearing) and the non-compliant contacts subjected to high pressures (timing, piston ring/ liner). An experimental methodology was implemented covering 11 decades of sliding velocities and contact pressure, from 10-10 to 10 m/ s and up to few GPa, thanks to the development of IMOTEP research platform. As part of this study, the in situ multi-scale tribological analysis allowed us, among other things: • to study the effects of a progressive confinement of the contact and to evaluate the resistance to interfacial shear of the formed films; • to identify the mechanisms at the origin of the generation of lubricating films for different tribological conditions, representative of the operating conditions of the upper engine contacts; • to establish generalized Stribeck curves and friction / pressure / velocity maps. Figure 1: Multi-scale analysis of the lubrication regimes 2. Experimental strategy All the lubrication regimes were analyzed for various lubricants and surfaces using three dedicated tribometers (see figure 1) developed at the Ecole Centrale de Lyon: The boundary regime (BL) was simulated using a molecular tribometer (ATLAS [1]) making it possible to measure the tribological behavior of adsorbed molecular layers, under moderate contact pressure (from 1 MPa to 50 MPa), as a function of the sliding speed (from 0.1 nm / s to 100 nm / s); The mixed regime (ML), the elastohydrodynamic regime (EHL) and the transitions between these lubrication regimes were investigated thanks to the IRIS tribometer [2] that allows independent and simultaneous control of the sliding and entrainment speeds to achieve Stribeck and traction curves. Positioned under an infrared spectrometer, the chemical species passing through the contact can also be analyzed; The hydrodynamic regime (HL) was studied on a fully-instrumented journal bearing bench (shaft diameter = 5 mm, radial clearance = 5 µm) in which the position of the shaft, the friction torque, the oil temperature and the lubricating film rupture zone are measured as a function of time over a speed range of up to 10,000 rpm [3]. The confinement ratio of the lubricant film has an order of magnitude of 1 to 1000, in these three test rigs. To illustrate this strategy, this talk was focused on the tribological behaviour of a Group III+ base oil (BO) and its mixture with a PMA Viscosity Index Improver (BO + PMA). 3. Main results 3.1 Lubricant film thickness For a PMA solution concentrated at 3%w/ w, boundary film thickness was measured at about 10 nm on metallic surface, using both the ATLAS molecular tribometer and IRIS tribometer (see Figure 2). This boundary film was mechanically characterized: it is highly elastic, its shear 46 23rd International Colloquium Tribology - January 2022 An innovative multi-scale approach to reduce friction of automotive lubricants from hydrodynamics to boundary lubrication elastic modulus G is equal to 90 MPa under a 50 MPa contact pressure, and this film is purely repulsive. An additional image analysis of the interferograms grabbed with IRIS tribometer showed that patches of PMA covered all the Hertzian contact in BL. This boundary film thickness was detected at low entrainment velocity (less than 20 mm/ s). At higher velocity, in EHL regime, the film thickness followed the classical elastohydrodynamic prediction as shown in figure 2. In order to better understand the in situ and in real-time lubricating film nature, and to identify the different chemical species entrained in and around the contact, an infra-red spectroscopy analysis was performed: the analysis of the response of the C=O bond allows us to quantify the local concentration in polymer. In hydrodynamic regime, the 5mm hydrodynamic film was established, showing the major influence of the fluid rheology. Figure 2: Evolution of the lubricant film thickness for BO and the mixture BO + PMA versus the entrainment product. 3.2 Friction dissipation The friction of this PMA solution was analyzed at low velocity, when the two boundary films were in contact: high friction values were measured, associated to a viscoelastic contribution. However, the existence of these PMA boundary films induced a reduction in friction compared to the base oil. At higher velocity and higher pressure, a Stribeck curve was measured. We were able to show that the existence of the PMA boundary film shifted the mixed/ EHL regime transition towards lower velocities compared to that measured with the base oil. The shear was also localized in the hydrodynamic film. In hydrodynamic regime, for few mm thin films, two regimes were identified: a non-thermal regime of fluid shear, for acceleration and deceleration, and a thermal regime during which the temperature increases due to shearing. Apart from changing the viscosity-temperature relation, the presence of PMA due to adsorption also modified the cavitation zone extension. The non-Newtonian properties of the fluid under high shear were also investigated. Figure 3: Evolution of the viscous shear stress versus the entrainment product at the contact temperature for BO and the mixture BO + PMA. 4. Conclusion This innovative multi-scale approach allows one to identify lubrication mechanisms, in terms of film thickness and friction, over 11 decades of sliding velocities and contact pressure, thanks to the development of IMO- TEP research platform. In addition, an in situ analysis is developed based on a coupled optical measurement, infra-red and mechanical spectroscopy. On an illustrative example, we showed here that the interactions between the metallic surface and a viscosity-improver additive induced the formation of a boundary film that protected the surfaces, shifted the lubrication regime transitions to lower velocities and reduced the friction mechanisms in all regimes, via different mechanisms including shear localization, cavitation extension, etc. References [1] Crespo, A., Mazuyer, D., Morgado, N., Tonck, A., Georges, J.-M., and Cayer-Barrioz, J., “Methodology to Characterize Rheology, Surface Forces and Friction of Confined Liquids at the Molecular Scale Using the ATLAS Apparatus”, Trib Lett. 65, 4, 2017, Article number 138. [2] Bonaventure, J., Cayer-Barrioz, J., and Mazuyer, D., “Transition Between Mixed Lubrication and Elastohydrodynamic Lubrication with Randomly Rough Surfaces”, Trib Lett. 64, 3, 2016, Article number 44. [3] Barazzutti, J., Cayer-Barrioz, J., and Mazuyer, D., “A new in-situ methodology for understanding hydrodynamics journal bearing”, 8th International Tribology Conference, September 17 - 21, 2019, Sendai. Trends Lubricants and Additives Novel Lubricant/ Lubrication Concepts 23rd International Colloquium Tribology - January 2022 51 Liquid Amides - Novel, High Performance Base Oils Dr. Claire Ward Croda Europe Ltd., Goole, UK Corresponding author: claire.ward@croda.com 1. Introduction Synthetic esters are widely used within the lubricants industry. Their chemistries can easily be tuned to achieve a broad range of properties, making them beneficial in numerous industrial and automotive applications. However, in systems where there is the possibility of water contamination combined with elevated temperatures, certain esters can be prone to hydrolysis which compromises the performance and lifetime of the ester base fluid. Amides can be an attractive alternative for such appli-cation areas and Croda has developed a new synthetic base stock to fulfil this unmet need. Unlike primary and secondary amides, tertiary amides can be designed to remain liquid at low temperatures so they can be used as (co-)base fluids. This research exploits the benefits of tertiary liquid amides and shows that through carefully controlling the chemistry of the amide building blocks, a wealth of beneficial properties can be achieved. This paper discusses the properties and performance of one novel liquid amide derivative. 2. Outline This research showcases the benefits of the amide within fully formulated oils for a number of industrial and automotive applications, especially those where water ingress can be detrimental to performance. The amide is investigated as a neat base oil or a co-base oil at 2.5-10 % dose and the performance is compared to other Group V base oils, including commercially available esters base fluids. 3. Stability benefits of amides Base oil is the major constituent of lubricant formulations, so inherent hydrolytic and oxidative stability of this component can play an important role (alongside the additives) in improving the service life of the formulation in an application. To showcase these stability features, a steam turbine formulation was investigated as this application is exposed to the challenging conditions of a high temperature environment with water contamination and high-speed mixing from the rotating machinery. An ISO VG 46 formulation was made with several different base oils and a standard turbine & compressor oil add pack (0.6 % recommended dose) for polyalphaolefin (PAO) and mineral oil systems. The hydrolytic stability was tested using the beverage bottle method (ASTM D2619, Cu, H 2 O, 93 ºC) and an extended 240 hour experiment was completed as well as the standard 48 hour test [1]. Even over the extended time-period, the liquid amide only experienced a baseline change in acid value, comparable to the PAO system, while the di-ester base oil showed significant change in acid value due to hydrolysis (Figure 1). This is in line with the trends seen by the hydrolytic stability of the neat, untreated base oils in the SS 155181: 2012 test [2]. Figure 1: Steam turbine formulation hydrolytic stability Figure 2: Steam turbine formulation oxidative stability The oxidative stability of the steam turbine formulations was tested using the turbine oil oxidation stability test (TOST) method (ASTM D943, Cu & steel coils, H 2 O, O 2 , 95 ºC) [3]. Figure 2 shows the liquid amide system 52 23rd International Colloquium Tribology - January 2022 Liquid Amides - Novel, High Performance Base Oils had significantly better oxidative stability than the di-ester formulation, and gave comparable performance to the Group III mineral oil system, which reached the maximum 2.0 mg KOH/ g total acid number (TAN) around 10 000 h. The PAO formulation was the only system to exceed the 10 000 hours maximum test time with a low TAN (0.4 mg KOH/ g), but it is worth noting that the anti-oxidant package was specifically designed for PAO and mineral oils. 4. Amides as solvency boosters One of the main uses of the liquid amide is as a co-base oil due to enhanced polarity vs. comparable esters, giving it excellent solubility properties for polar additive packages in formulations. The liquid amide is compatible with a wide range of fuels and base oils from Group I, II, III, IV and V, but it is not water-soluble. This is important for a co-base oil as it facilitates the blending of stable formulations to meet the desired application physical properties as well as the target costs. Co-base oils are especially useful in severely hydrotreated base oils such as PAO and gas-to-liquid (GTL) because they only contain fully saturated, non-polar hydrocarbon species, which dramatically decreases the solvent power [4]. Figure 3 shows the room temperature (RT) stability of two PAO-based industrial formulations over 3 months. With no co-base oil, both additives are incompatible with the PAO fluid, showing separation or sedimentation. A typical polyol-ester can help to give a clear, stable formulation. However, the liquid amide co-base oil solubilises the additive packages more consistently and at a lower dose rate of 5 % to give clear, bright formulations [5]. Figure 3: PAO solvency booster 3 month study at RT Figure 4 shows a similar stability experiment looking at the solubility of a polymeric friction modifier in a GTL system. Without a co-base oil, the friction modifier is insoluble in GTL. This can be remedied with a co-base oil such as a polyol ester at 5 %, but the liquid amide shows superior solubility booster powers by achieving the same stabilising effect at a lower dose of 2.5 %. Figure 4: GTL solvency booster 3 month study at RT 5. Conclusion This paper examines a tertiary liquid amide which has been structurally designed for use as a novel, high performance base oil in industrial and automotive applications. The hydrolytic and oxidative stability benefits of the new liquid amide base oil could offer enhanced product performance and lifetime over some conventional esters in challenging high temperature environments with the potential for water ingress. The intrinsic differences in amide and ester polarity also expand the solubility properties of this new base oil, helping to create stable formulations with some challenging components. References [1] ASTM D2619-21, Standard Test Method for Hydrolytic Stability of Hydraulic Fluids (Beverage Bottle Method), ASTM International, West Conshohocken, PA, 2021, www.astm.org [2] SS 155181: 2012, Petroleum and related products - Determination of the hydrolysis characteristics of oils and fluids - Hydrolytic stability test method, Swedish Institute for Standards, Stockholm, Sweden, 2021, www.sis.se [3] ASTM D943-20, Standard Test Method for Oxidation Characteristics of Inhibited Mineral Oils, ASTM International, West Conshohocken, PA, 2020, www.astm.org [4] Zhmud, B., Roegiers, M., “New base oils pose a challenge for solubility and lubricity”, 2009, 89, 21-24. [5] Chen, X., Kurchan, A., Shen, Z., 2015, “LUBRI- CATING OILS”, WO 2015/ 175778. 23rd International Colloquium Tribology - January 2022 53 Comparisons of Boundary Lubricant Additive Screening Strategies, Including DOE Methods, Utilizing Twist Compression Tests (TCT), Early in the Lubricant Formulation Process Ted G. McClure Sea-Land Chemical Co./ SLC Testing Services, Westlake, Ohio, USA Alexes Morgan Sea-Land Chemical Co./ SLC Testing Services, Westlake, Ohio, USA Robert Stubbs Sea-Land Chemical, Europe, Ltd., Manchester, United Kingdom 1. Introduction Lightweighting is requiring changes in manufacturing methods and materials. Lubricant additive availability is being altered. Lubricant formulations must be developed quickly in this dynamic environment. Rapid and flexible friction test methods, including twist compression tests (TCT), are being used by formulators, along with statistical mixture design of experiments (DOE) techniques. Mixture DOE methods are used to quantify the relative contributions of ingredients to a response in mixtures, predict the response for untested mixtures of the ingredients, and optimize combinations for the response(s) [1]. However, when beginning a project, formulators have numerous additives available, many, with little or no comparative friction test data available with the surface materials of interest. The purpose of this work is to compare boundary lubricant additive screening strategies using TCT tests, while providing useful test data for an austenitic stainless steel 304, (ISO X5CrNi18-9). 1.1 Additive Screening Strategies Formulators have several options for screening additives. Any of these strategies may be used to select additives for further work. One factor at a time (OFAT) is the most basic. It involves testing one variable at a time. Pairs of additives tested individually and together to identify binary synergies is another common screening approach. Mixture DOE screening methods are used to estimate the relative contributions of ingredients to a response, in mixtures, and predict the response for untested mixtures of the ingredients, using linear models. [1] 1.2 Twist Compression Test (TCT) The TCT is a bench test used to rank lubricant performance under boundary and E.P. conditions. TCT creates lubricant starvation conditions, under high pressure, and sliding contact: a condition common to operations in areas where lubricant film failure is likely to occur [2]. In this test COF vs. time graphs are generated. TCT has been used to compare E.P. additive responses in different base stocks, and wear tracks have been used for to study lubrication mechanisms [3]. Figure 1: Twist Compression Test Schematic 1.3 Experimental A D-optimal non-simplex mixture screening DOE was developed, using Design Expert 12 software, to evaluate a series of nine lubricating additives. This resulted in a 23-test matrix. Fig. 1: Screened additives and design space constraints 54 23rd International Colloquium Tribology - January 2022 Comparisons of Boundary Lubricant Additive Screening Strategies, Including DOE Methods, Utilizing Twist Compression Tests (TCT) TCT was used to evaluate this 23 sample DOE at 13.8MPa interface pressure and 10rpm, 1.2cm/ s velocity. Test materials were 304 stainless steel (ISO X5CrNi18-9) flat sheet and D2 tool steel annular specimens, hardened to approximately 62Rc. Specimens were cleaned with odourless mineral spirits, followed by n-heptane. An excess of lubricant was applied with disposable pipettes immediately before testing. All tests included four repeats. Data was collected at 50Hz. The TCT response used in this analysis was the time until lubricant film breakdown (TBD). The TBD was set at the time when the coefficient of friction (COF) first reached 0.18. This COF threshold was determined by observing annular specimens after testing for adhesion. TBD is used to compare lubricants in their ability to survive the test conditions and prevent adhesive wear. 2. Results and Conclusions A reference blend, containing all nine additives is included in the DOE. The resulting linear model equation in real % units is shown below, with terms in order of decreasing effect on TBD. Screening DOE is limited to linear models, giving little to no information on interactions. The model does provide information useful for specifying the design space to investigate in further work with additives selected. TBD = 0.49*SO(A) + 0.46*SE(E) + 0.33*PEL(B) + 0.32*FA(H) + 0.09*ND(J) + 0.08*Poly(G) + 0.008*VO(C) + 0.02*EHS(D) - 0.01*PEH(F) This is represented visually below in Figure 2. Fig. 2: Trace plot of effect on TBD of increasing or decreasing additive levels relative to reference blend. Based on this analysis, the best candidates for further study and optimization are the sulfurized olefin (SO), Sulfurized ester/ olefin (SE), C-18 ethoxylated phosphate ester, and the polymerized fatty acid (FA). One factor at a time (OFAT) is the most basic and involves testing one variable at a time to identify promising candidates for further work. The factor varied can be different additives, various concentrations of a specific additive, or additives in various base stocks. A variation on this is when one is modifying an existing product. Individual additives may be added to a finished product of interest and tested. Figure 3 is an example of an OFAT screening with 304 SS for TBD. This previous work ranks TBD for, SO and PEL in the same order as the screening DOE. The OFAT approach does not give information on percentage ranges for additives in further work. Fig. 3: OFAT TCT TBD Ranking with 304 SS [4] Screening pairs of additives is another screening strategy used to identify synergies. The additives are tested individually and in combination. This includes the data that is obtained with the OFAT approach, along with information on a single interaction. Figure 4 below is an example of synergy on 304 SS between SO and a 400 TBN calcium sulfonate. Vertical lines show TBD. Fig. 4: TCT COF vs time graphs: TBD synergy [4] Each of these screening strategies have advantages and disadvantages, and may be selected based on what is known about the project status, application and additives 23rd International Colloquium Tribology - January 2022 55 Comparisons of Boundary Lubricant Additive Screening Strategies, Including DOE Methods, Utilizing Twist Compression Tests (TCT) along with the budget, and time limits. Figure 5 summarizes typical effort involved for each strategy. Fig. 5: Testing required summary References [1] Cornell, J.: Experiments with Mixtures, 3 rd Ed. Ch. 1-2, 5. (2002) [2] Schey, J.: Trib. in Metalworking, (1983) 211-212 [3] J. Baltrus, T. McClure, G Bikulčius, S. Asadauskas: Formation of Carbonaceous Nano-Layers under High Interfacial Pressures during Lubrication with Mineral and Bio-Based Oils, Chemija, vol 25 (2014), 3 161-170 [4] T. McClure, Presented STLE Annual Mtg (2017) 23rd International Colloquium Tribology - January 2022 57 Scientific Evaluation of Investigations on the Load Carrying Capacity of Carbide Cylindrical Gears Lubricated with Water Karl Jakob Winkler Gear Research Center (FZG), Technical University of Munich, Garching, Germany Corresponding author: karljakob.winkler@tum.de Thomas Tobie Gear Research Center (FZG), Technical University of Munich, Garching, Germany Klaus Michaelis Gear Research Center (FZG), Technical University of Munich, Garching, Germany Karsten Stahl Gear Research Center (FZG), Technical University of Munich, Garching, Germany 1. Introduction The preservation of the planet earth as our habitat is of great importance. One contribution to the preservation of our planet is the use of environment-friendly lubricants. The idea is to lubricate gears with water instead of conventional mineral or synthetic oil. The cylindrical test gears are made of carbide composite to achieve the necessary resistance against water corrosion and gear failures. The innovative combination of carbide composite gears and water lubrication is a step to sustainable gear sets and has been patented [4]. The investigations were conducted on a Pulsator rig (bending strength) and a FZG back-to-back gear test rig using established and standardized test methods. The results of the gear investigations were made available to the gear research center FZG by the Reintrieb GmbH (Vienna) for further scientific evaluation. 2. Experimental Investigations The following experimental investigations are conducted according to the corresponding test procedures: • Tests based on a unified test procedure [2] regarding the tooth root bending strength. • Tests based on the standardized test procedure DIN ISO 146351 [3] regarding the scuffing load carrying capacity. • Tests based on a unified test procedure [5] regarding the pitting and high-speed wear (wheel rotational speed of n 2 = 1500 min -1 ) load carrying capacity. • Tests based on a unified test procedure [1] regarding the low-speed wear (wheel rotational speed of n 2 < 500 min -1 ) load carrying capacity. Table 1 shows the corresponding material and lubrication used for the conducted tests. The material underly a non-disclosure agreement by the Reintrieb GmbH. All gears are made out of carbide composite material with different compositions of tungsten carbide and further alloying elements. Table 1: Material and lubrication for the tests Test Material Water tooth root bending trength A, B, C, D no lubrication needed scuffing A salt water pitting and high-speed wear at n 2 = 1500 min -1 C, D distilled water low-speed wear at n 2 < 500 min -1 C, D tap water (without salt) Table 2 lists the main geometry data of the applied test gear set Type C. The pulsator tests were performed on the pinion of this gear type. Table 2: Main geometry data of the test gear Type C Description Symbol Value center distance a 91,5 mm normal module m n 4,5 mm number of teeth z 16 / 24 width b 14 mm pressure angle α 20° helix angle β 0° 58 23rd International Colloquium Tribology - January 2022 Scientific Evaluation of Investigations on the Load Carrying Capacity of Carbide Cylindrical Gears Lubricated with Water Figure 1 shows an exemplary photographic documentation of the test gear set Type C. Figure 1: Exemplary photographic documentation of the test gear set Type C Figure 2 shows the FZG back-to-back test rig used for the scuffing, pitting and high-speed as well as low speed wear tests. Figure 2: FZG back-to-back tests rig 3. Results The tests regarding the tooth root bending strength were conducted as an initial screening for the different composite materials. Figure 3 shows the results of the tests regarding the tooth root bending strength of the different carbide composite materials (blue) and a commonly used case carburized steel 18CrNiMo7-6 as comparative reference (green). It must be noted that the values are based on a limited number of tests and are not statistically validated. Figure 3: Results of screening tests regarding the tooth root bending strength (long life) For the carbide composite materials A and B the measured endurable nominal tooth root stress is 30 % lower compared to the reference case carburized steel. The carbide composite materials C and D show endurable nominal tooth root stresses above the reference case carburized steel. It is thus decided to use the materials C and D for further investigations regarding the pitting and high-speed wear as well as the low-speed wear. Parallel to the tests regarding the tooth root bending strength, a screening test regarding the scuffing load carrying capacity was conducted for the material A. The load stage 9 was completed without scuffing, while in load stage 10 the gear set failed due to tooth root breakages at the pinion and the wheel. The nominal tooth root stress at load stage 10 correlates with the endurable nominal tooth root stress from Figure 3. Further tests specifically aimed at the scuffing load carrying capacity were not conducted. However, for all following tests with critical scuffing conditions, especially the pitting and highspeed wear tests, scuffing was not observed. Figure 4 shows an exemplary result of a pitting and highspeed wear test. For all tests, pittings were not observed. The linear wear coefficient clT is an important parameter to measure wear. The results show, that the linear wear coefficient does not clearly correlate with the load. Figure 4: Exemplary results of a pitting and high-speed wear test (material D) 23rd International Colloquium Tribology - January 2022 59 Scientific Evaluation of Investigations on the Load Carrying Capacity of Carbide Cylindrical Gears Lubricated with Water Figure 5 shows exemplary results of a low-speed wear test. The results show, that the linear wear coefficient is significantly higher compared to the values of the pitting and high-speed wear test from Figure 4. The results furthermore show, that the linear wear coefficient decreases with higher rotational speeds, indicating certain film formation properties of water. Figure 5: Results of a low-speed wear test (material D) For high-speed and low-speed wear tests, the linear wear coefficients were increased compared to experience-based values for conventional steel gears with oil lubrication. The material D showed a corrosive behaviour and thus higher wear compared to the material C. 4. Conclusions The investigations showed the following results: • Lubrication of carbide gears with water is technically possible. • The test results regarding tooth root bending, scuffing and pitting are comparable to conventionally manufactured and oil lubricated steel gears. • The main factor limiting the gear life time is wear. The amount of wear can vary with the operating conditions such as load and rotational speed. • Further investigations are required for the optimization of the material-lubricant system. The benefits of these research results are: • High potential of sustainable lubrication with water instead of mineral or synthetic oil was proven. • Environmentally friendly lubrication of gears with water is possible in nature reserves both on land and at sea. Acknowledgement: This work was funded by Reintrieb GmbH as well as the project COMET InTribology1, FFG-No. 872176 (project coordinator: AC2T research GmbH, Austria). References [1] Bayerdörfer, I., et al., Method to Assess the Wear Characteristics of Lubricants FZG Test Method C/ 0,05/ 90: 120/ 12, Hamburg, Anmeldung: 1997. [2] Bergmann, C., et al., FVA-Merkblatt Nr. 0/ 5 - Empfehlung zur Vereinheitlichung von Pulsatorversuchen zur Zahnfußtragfähigkeit von vergüteten und gehärteten Zylinderrädern, Frankfurt, Anmeldung: 1999. [3] Deutsches Institut für Normung e.V. (DIN), Zahnräder - FZG-Prüfverfahren - Teil 1: FZG-Prüfverfahren A/ 8,3/ 90 zur Bestimmung der relativen Fresstragfähigkeit von Schmierölen (ISO 14635- 1: 2000), DIN ISO 14635-1: 2006, Berlin, Anmeldung: 2006. [4] Lais, S., Getriebe. Inhaber: Reintrieb GmbH, Ed., Patentschrift EP2614000, Anmeldung: 2011, Publikation: 2018 [5] Schedl, U., et al., Einfluss des Schmierstoffes auf die Grübchenlebensdauer einsatzgehärteter Zahnräder im Einstufen- und im Lastkollektivversuch, Frankfurt/ Main, Anmeldung: 1997. 23rd International Colloquium Tribology - January 2022 61 Tribology of Ionic Liquids and graphene - a synergistic combination Dr. Thomas Schubert IoLiTec GmbH, Heilbronn, Germany Dr. Sebastian Plebst IoLiTec GmbH, Heilbronn, Germany Corresponding author: plebst@iolitec.de 1. Introduction Ionic liquids (ILs) are a comparatively new class of substances with interesting profiles of properties, such as high thermal stability, low vapour pressure, incombustibility, and a high surface tension. Due to the huge variety of possible ion combinations, many properties can be adjusted to fit to a specific application. In the early 2ks it became evident that ionic liquids can also reduce significantly friction and wear whether used as additive or pure lubricant. In this context, recent publications have shown a beneficial and sometimes even synergistic behaviour between ILs and graphene: To explore this interesting field of technology, the project EPiG was funded by the German Federal Ministry of Education and Research to further investigate the interaction between ionic liquids and graphene as lubrication additives. Besides these encouraging results of IL- -graphene-dispersions, first investigations have shown that their addition to a Polyamide 6.6 matrix improves its tribological behavior significantly. In our conference contribution we will present our latest results from this EPIG-project and we will further discuss the potential impact of Ilgraphene-mixtures if applied by design to alternative polymer matrices together with a general outlook on this dynamic field of research. 2. Results and discussion (2 columns) The EPiG - (Entwicklung elektrisch leitfähiger Schmierstoffe und angepasster Polymer-Nanokomposite für Gleitlager durch Verwendung ionischer Flüssigkeiten und Graphen) Project is divided in two parts 1. Part one focusses the lubricant system, in generating a conductive, long-term stable mixture of suitable base oil compositions, ionic liquids and graphene. 2. Part two aims to produce electric conductive PA 6.6 - polymers with a combination of suitable ionic liquids and graphene or carbo-nanotubes. Furthermore, the lubricant and the polymer will be tested in exemplary conditions. Figure 1: Four point measurement of IL/ Carbon improved PA6.6-Polymers. The contribution will focus mainly on part two showing the influences of graphene, ionic liquids and carbo nanotubes on the mechanical and electrical properties of PA6.6. It will furthermore show two different approaches in compounding PA6.6 polymers (kneading and screw extruder). 62 23rd International Colloquium Tribology - January 2022 Tribology of Ionic Liquids and graphene - a synergistic combination Figure 2: Chemical structure of conductivity promoter in PA-6.6 P666(14) BTA. 3. Conclusion It could be shown, that ionic liquids in combination with graphene or carbonano-tubes can provide a critical role to reduce the electrical resisitivity of polyamid 6.6 and pao based lubricants. In terms of long term stability further optimization is needed. References & Acknowledgments The project, on which this report is based, is funded by the German Federal Ministry of Education and Research under the code 03XP0220 (term 01.05.2019 to 31.10.2021). The authors are responsible for the content of this publication. We are grateful for the funding of the research work, and we would like to thank the funding provider Projektträger Julich PtJ for the good cooperation. 23rd International Colloquium Tribology - January 2022 63 Biomimetic water-based lubricant development: Nanoencapsulation with liposomes Manoj Murali Tribology Group, Imperial College London, United Kingdom Corresponding author: mm8415@ic.ac.uk Philippa Cann Tribology Group, Imperial College London, United Kingdom Marc A. Masen Tribology Group, Imperial College London, United Kingdom 1. Introduction The replacement of traditional mineral oil lubricants with water-based bio-compatible fluids has long been a desirable, if unrealised, ambition in many applications. This is particularly relevant in marine-based energy generation systems, where oil-based lubricants create a high risk of environmental pollution. The use of bio-lubricants has been explored in several previous studies [1], however no significant technological advances have been achieved. Most of the work has focused on traditional lubrication mechanisms, with bio-molecules being employed to form an adsorbed surface film which reduces friction. However, due to their inherent biological, thermal and/ or oxidative instability, bio-molecules are unsuited to long-term industrial applications. The alternative approach is to use stable, bio-friendly molecules, designed to exploit the lubrication mechanisms found in nature. These mechanisms have evolved to be far more diverse than those found in traditional “mineral oil” tribology and are, as yet, poorly understood [2,3]. Our investigation focuses on the lubrication mechanism of DSPC liposomes with additive payloads encapsulated within their core. The utilisation of liposomes was inspired by synovial fluid which is an excellent lubricating medium in human joints [4]. Synovial fluid contains liposome forming surface active phospholipids which have been theorised to be a significant contributor to its excellent lubricating performance [5,6]. The additional inclusion of payload delivery was then built upon through the observation of hagfish (myxinidae), a slime-producing marine fish that releases mucin filled vesicles as a defence mechanism to increase the surrounding local viscosity of seawater, a very effective defence mechanism against predators [7]. This biomimetic foundation led to the development of aqueous DSPC liposomal solutions (ALS) separately encapsulated with mucins, sugars and wear additives. Tribology tests were carried out on a reciprocating device, HFRR, (High Frequency Reciprocating Rig, PCS Instruments, London, UK) with ALS and hexadecane as a low-viscosity oil reference. Wear and friction were significantly reduced for the ALS compared to water alone. The test demonstrated that nanocapsules enter the contact and are ruptured by high shear stresses, allowing for the encapsulants within to be released to lubricate the contact. The research forms a foundation to explore synthetic nanocapsules such as polymersomes which provide additional benefits in chemical stability, adaptability and longevity. 2. Methods 2.1 Preparation and characterisation of ALS ALS were prepared by the thin film hydration method [8]. Briefly, DSPC was dissolved in a mixture of chloroform-ethanol ( 99: 1, v/ v) and stirred for 3 min to ensure complete dissolution. A rotary evaporator was used under vacuum at 60 °C to remove the solvent from the resulting homogeneous samples and obtain a thin lipid film. Next, the thin lipid film was hydrated with a chosen payload solution and thermostated for 1h at a temperature above the DSPC phase transition temperature of 55 °C to form multilamellar liposomes. Following this, the multilamellar liposomes were downsized to form small unilamellar liposomes by extruding using an extruder (Avanti, USA) through polycarbonate membranes (Whatman, Inc.) with a defined pore size of 100 nm (21 cycles). The temperature was maintained at 60 °C during the entire extrusion process. The DPSC: payload molar ratio was kept constant for all payload variants. The DSPC-payload liposomes prepared were dialysed in deionised water for 6 h via a dialysis tube (molecular weight cutoff: 300kDa) to remove any free payload from the solution. Hydrodynamic diameters and zeta potentials of the obtained ALS were measured with a dynamic light scattering instrument (Zetasizer Pro, Malvern Instruments, Malvern, UK) at 25 °C. Their morphologies were imaged by using a cryogenic field-emission scanning electron microscope (Tescan Myra SEM, Brno, Czechia). 64 23rd International Colloquium Tribology - January 2022 Biomimetic water-based lubricant development: Nanoencapsulation with liposomes 2.2 Friction and wear measurements Friction experiments were performed to assess the benefits of nanoencapsulation for lubrication performance by comparing the friction and wear results obtained on deionised water, hexadecane and empty DSPC liposomes with ALS, in which payloads were encapsulated within the vesicular core structure. This lubrication performance was investigated using a HFRR. Tests were performed on a 440C stainless steel sliding pair at 25 ºC, at a load of 0.5N, a frequency of 50Hz and a stroke length of 1mm. Some results are shown in Figure 1, showing the average coefficient of friction for hexadecane, DSPC liposome solution and deionised water. Wear performance was investigated using a white light interferometer (ContourGT Optical Profiler, Bruker, Massachusetts, USA). Wear scar cross sectional area at the wear track midpoint was measured and compared for the lubricants tested. The adsorption of the encapsulated additives was assessed by Raman Spectroscopy (alpha300R Raman Imaging Microscope, WITec, Ulm, Germany) of the resulting wear marks. 3. Results and discussion Figure 1: Comparison of average coefficient of friction of deionised water, hexadecane and empty DSPC liposomes A strong reduction in coefficient of friction is seen with liposomal solutions compared to deionised water and hexadecane. This has, for example, led to a reduction in friction coefficient from 0.3 in deionised water to 0.1 in the DSPC liposomal solution (Figure 1). Table 1: Comparison of average wear scar midpoint cross-sectional area Lubricant Average wear scar midpoint cross-sectional area (µm 2 ) Deionised Water 72.232 Hexadecane 1.943 DSPC Liposome 7.683 Wear performance is also improved (Table 1) through the addition of liposomes, however a low-viscosity oil such as hexadecane remains a better performer. The addition of payloads into the liposome is set to further improve the wear performance of ALS lubricants, which remains the limiting factor between water based lubricants and oil-based lubricants. The mechanisms behind the performance differences are explained through observational studies and Raman in which adsorption of additives through liposomal payload delivery at the contact can be investigated. 4. Conclusion ALS successfully demonstrates a reduction in both friction and wear compared to deionised water alone, moreover when combined with a wear reducing payloads the wear performance of a low-viscosity oil such as hexadecane can be approached through utilising such a system. This research demonstrates that the primary failings of past water-based lubricants have the potential to be overcome through the application of encapsulated liposomes. The lubrication mechanism achievable through this approach is both active and novel in its workings, and presents the viability of sustainable lubricants for industrial applications. References [1] Ahlroos T, Hakala TJ, Helle A, Linder MB, Holmberg K, Mahlberg R, et al. Biomimetic approach to water lubrication with biomolecular additives. Proc Inst Mech Eng Part J J Eng Tribol. 2011; 225(10): 1013-22. [2] Fan J, Myant CW, Underwood R, Cann PM, Hart A. Inlet protein aggregation: a new mechanism for lubricating film formation with model synovial fluids. Proc Inst Mech Eng H. 2011 Jul 4; 225(7): 696-709. [3] Porte E, Cann P, Masen M. Fluid load support does not explain tribological performance of PVA hydrogels. J Mech Behav Biomed Mater. 2019; 90: 284-94. [4] McCutchen CW. The frictional properties of animal joints. Wear. 1962 Jan 1; 5(1): 1-17. [5] Klein J. Molecular mechanisms of synovial joint lubrication. Proc Inst Mech Eng Part J J Eng Tribol. 2006; 220(8): 691-710. [6] Pawlak Z, Oloyede A. Conceptualisation of articular cartilage as a giant reverse micelle: A hypothetical mechanism for joint biocushioning and lubrication. BioSystems. 2008; 94(3): 193-201. [7] Böni L, Fischer P, Böcker L, Kuster S, Rühs PA. Hagfish slime and mucin flow properties and their implications for defense. Sci Rep. 2016; 6(February): 1-8. [8] D L, Y B. Liposomes: preparation, characterization, and preservation. Methods Biochem Anal. 1988 Oct 31 23rd International Colloquium Tribology - January 2022 65 Reversible Viscosity Tuning using UV-Light Dr. Dominic Linsler Fraunhofer IWM, Mikrotribologie Centrum µTC, Karlsruhe, Germany Fraunhofer Cluster Programmable Materials CPM Corresponding author: dominic.linsler@iwm.fraunhofer.de Chris Gäbert Fraunhofer IAP, Potsdam, Germany Fraunhofer Cluster Programmable Materials CPM Stefan Reinicke Fraunhofer IAP, Potsdam, Germany Fraunhofer Cluster Programmable Materials CPM Theodora Rangova Fraunhofer IWM, Mikrotribologie Centrum µTC, Karlsruhe, Germany Fraunhofer Cluster Programmable Materials CPM Florian Schlüter Fraunhofer IWM, Mikrotribologie Centrum µTC, Karlsruhe, Germany Fraunhofer Cluster Programmable Materials CPM Martin Dienwiebel Fraunhofer IWM, Mikrotribologie Centrum µTC, Karlsruhe, Germany Karlsruhe Institute of Technology KIT, IAM, Karlsruhe, Germany Fraunhofer Cluster Programmable Materials CPM 1. Introduction Viscosity is an intrinsic property of a lubricant that can be changed by various measures. But in a final product, it follows a given temperature dependency. In many cases, the choice of a lubricant or the scope of application is limited by the viscosity. Conversely, a reversibly tunable viscosity allows the expansion of the parameter field of technical applications. Various systems with switchable viscosity are known, besides “smart liquids” with polarizable particles, microgels and responsive micelles, dissolved responsive polymers are described to enable bond formation controlled by an external trigger, thus facilitating programmability. Here, we use anthracene esters as photoresponsive group that allow a reversible chain extension and thus viscosity increase by UV irradiation. Among the stimuli for responsive materials, UV light sources have many advantages: They are non-invasive and commercially available at relatively low cost. Furthermore, parameters like intensity, wavelength, duration and area of exposure allow precise spatiotemporal control over the programming of a material. 2. Materials and Methods We present results of functionalized polydimethylsiloxane (PDMS) and polyalkyleneglycole (PAG) and mixtures of a. PDMS with a non-functionalized silicone oil and b. PAG with water. The polymer chains of both lubricants were functionalized with anthracene moieties at their termini that show an equilibrium reaction between the cross-linked and separated state. The chemical equilibrium can be shifted by the irradiation of UV-light with wavelength of 365 and 254 nm, respectively, see figure 1. Viscosity measurements were performed in a rheometer with a parallel plate setup using a custom made fused silica top plate for UV transparency, see figure 2. 66 23rd International Colloquium Tribology - January 2022 Reversible Viscosity Tuning using UV-Light Figure 1: reversible anthracene photodimerization [1]. Figure 2: setup in the rheometer with the transparant plate and functionalized lubricant under UV irradiation. 3. Results and discussion The parameters for characterization of the tunable viscosity are the absolute range of modulus that changes under light irradiation and the speed of the chain growth. The dilution of functionalized polymers with a liquid of lower molecular weight yields to a faster viscosity change due to a higher mobility of the functionalized chains accompanied by a decrease of the range of possible modulus variation, due to the change of the chain length distribution. This is exemplary shown for PAG diluted with water in different ratios from 2: 3 to 1: 4, see figure 3. All mixtures show an exponential increase of viscosity until the chemical reaction levels off after 14 and approx. 40 minutes, respectively, in the case of higher dilutions. The change in viscosity by light irradiation also significantly modifies the stribeck curve. During several experiments with duration of 5000s in mixed lubrication, no degradation of the lubricant due to the shear in a tribological contact was found, indicating adequate shear stability of the anthracene dimer. Figure 3: Loss modulus over time for various mixtures of PAG with water. Irradiation time with 365nm UV-light of 90 minutes is indicated by the dashed lines. Note the logarithmic scale. 4. Conclusion The analysis of the response of two anthracene-functionalized lubricants to UV-irradiation shows significant viscosity changes by more than two decades considering the loss modulus. The dilution of the functionalized oils yields the expected decrease of the absolute range of viscosity variation and increases the speed of the polymer chain growth. Sufficient shear stability makes the functionalized lubricants interesting for future applications of adaptive viscosity. This work has been funded by the Fraunhofer-Gesellschaft through the Cluster of Excellence “Programmable Materials CPM” References [1] van Damme, Jonas und Du Prez, Filip. Anthracene-containing polymers toward high-end applications. Progress in Polymer Science, 82: 92-119, 2018. 23rd International Colloquium Tribology - January 2022 67 Formation of White Etching Crack under sliding, boundary lubrication and additional current passage using modern lubricant compositions Daniel Cornel RWTH Aachen University, Institute for Machine Elements and Sytems Engineering, Schinkelstrasse 10, 52062 Corresponding author: daniel.cornel@imse.rwth-aachen.de Florian Steinweg RWTH Aachen University, Institute for Materials Applications in Mechanical Engineering, Augustinerbach 4, 52062 Francisco Gutiérrez Guzmán RWTH Aachen University, Institute for Machine Elements and Sytems Engineering, Schinkelstrasse 10, 52062 Georg Jacobs RWTH Aachen University, Institute for Machine Elements and Sytems Engineering, Schinkelstrasse 10, 52062 Adrian Mikitisin RWTH Aachen University, Central Facility for Electron Microscopy, Mies-van-der-Rohe Straße 39, 52074 Aachen, Germany Summary This contribution investigates the influence of modern lubricant formulations on the formation of White Etching Areas/ White Etching Cracks (WEA/ WEC). The main variation parameters are surface acting additives, especially extreme pressure-/ anti wear additives and corrosion inhibitors. Experiments using a thrust bearing and a radial bearing test rig indicate that modern lubricant formulations minimize WEA/ WEC formation risk under proven WEA/ WEC conditions such as high-sliding under boundary lubrication. In contrast, full fluid lubrication with additional current passage impressed on the aforementioned formulations can lead to WEA/ WEC. 1. Introduction Increasing power densities of drivetrains and drivetrains components also result in increasing demands on the associated lubricants and machine elements. Therefore, a wide range of testing methods is used to evaluate the performance of tribological systems. The wear and fatigue performance of a lubricant in rolling contacts can be, for example, evaluated using standarizered tests, such as the FZG Pitting test or the FAG FE8 Wear test. Among others, lubricants can also be evaluated regarding elastomer compatibility or foaming behaviour. The development of standardized tests for further damage patterns, such as white etching areas/ white etching cracks (WEA/ WEC), still requires a further understanding of the relying tribological mechanisms. In this context, the test guideline according to FVA 707 V forms the basis for the assessment of the tribological system “thrust bearings” regarding the risk of WEA/ WEC formation [1]. However, understanding the additive’s contribution to this type of damage and the influence of further parameters, such as current passage, needs to be further investigated. Lubricants consist of base oil and additives, with additional solubilizers being used depending on the base oil. The corresponding percentages, especially of the additives, vary depending on the aimed application, e.g. gearbox and engine oils in automotive applications have a much higher additive content or different additives than gearbox oils for wind applications. The influence of the oil formulation on the formation of WEA/ WEC has been discussed in a large number of studies [2, 3, 4, 5]. The majority of published research focuses on fully formulated oils or model oils, using WEA/ WEC-promoting additives. Especially the well-known Zinc-dialkyl-dithiophosphate (ZnDDP) and over based calcium sulphonate (Ob CaS) have been investigated regarding their influence on the formation of WEA/ WEC. However, these are additives that are no longer used in modern wind oil formulations. 68 23rd International Colloquium Tribology - January 2022 Formation of White Etching Crack under sliding, boundary lubrication and additional current passage using modern lubricant compositions Therefore, this contribution focuses on the influence of modern, i.e. without metal-containing additives, formulated lubricant formulations on the formation of WEA/ WEC. The main variation parameters are surface acting additives, especially extreme pressure-/ anti wear additives and corrosion inhibitors. Furthermore, each formulation also contains the same set of fixed additives, such as antioxidants, metal deactivators and defoamers. The investigations are carried out on component level using boundary lubrication and high sliding on the one hand and on the other hand full fluid lubrication with additional electrical loads. 2. Techniques and experimental methods In contrast to previous studies, no known WEA/ WEC critical oils are used here. All experiments have in common the usage of Polyalphaolefin (PAO) with Trimethylol propane tricaprylate (TMTC) as a solubilizer and a set of fixed additives. The base oil was blended with a viscosity grade of ISO VG 100 (ν 40°C ≈ 100 mm²/ s) and antioxidants, metal deactivators (Tolutriazol) and defoamers (Silicone) as fixed additives. Additives of the group’s extreme pressure/ anti-wear (EP/ AW) and corrosion inhibitors (CI) react significantly with the bearing surface and therefore influence the reaction layer formation and thus affect multiple tribological properties such as friction and permeability, e.g. to hydrogen. In the context of the presented investigations, sulphurised olefin (EP/ AW) and alkyl succinic acid half ester (CI) are used. The base oil formulation together with the fixed additives is later referred to as blend “0”. Adding the EP/ AW and CI additives mentioned before is referred to as blend “1”. Within the research project (c.f. Chapter 5), 14 further lubricant formulations were tested using for example dithiophosphate, aminphosphate and triphenyl phosphate as EP/ AW Additves and imidazoline, amid and neutral calcium sulphonate as CI. The rolling contact tests were performed using a thrust bearing and radial bearing test rig. The thrust bearing test rig (FE8) uses cylindrical thrust bearings of type 81212, and the radial bearing test rig (RBT) uses angular ball bearings of type 7206. Testing is carried out until either 500 h are passed or a vibration level, usually caused by spalling, surpasses a set threshold. Regarding the operating conditions, both test rigs have shown a lubricant sensitivity in the past and are operated under known WEA/ WEC critical conditions. While the investigations on the FE8 focus on boundary lubrication conditions [1], the RBT test are conducted in full fluid lubrication under additional current passage. Test bearings on both test rigs are operated at a bearing temperature of 100 °C and Hertzian pressure of ≈ 2.1 GPa. All further operating conditions are shown below (Table 1). Table 1: Test conditions Test Test rig Oil blend J s [A/ mm²] SRR [%] λ [-] 1 FE8 0 0 0 ± 12 0.5 2 FE8 1 0 ± 12 0.5 3 RBT 0 0.3 ≈ 0 ± 13* 2.3 4 RBT 1 ≈ 0 ± 13* 2.3 J s : Apparent bearing current density; SRR: Slide roll ratio; λ: Specific film thickness * Calculated for similar operating conditions in Arnaud Ruellan 2014 3. Results The test results, focussing on blend 0 and 1, are presented in Table 2. While Test 1 reached undamaged 500 hours, test 2 resulted in a premature failure after 109 h. Test 3 and 4 have reached 500 hours but with significant damage, due to an incorrect threshold setting. Regarding the 14 additional FE8 tests mentioned in chapter 2, no WEA/ WEC could be confirmed throught the conducted metallographic investigations. Table 2: Test results Test Test rig Runtime [h] Metallographic results 1 FE8 500 No damage 2 FE8 109 Pitting (Shaft washer) 3 RBT 500 Spalling & WEC (Outer ring) 4 RBT 500 Melted surface (Outer ring) To observe microstructural alterations and crack networks, metallographic investigations were conducted on all tests. After preparation, samples were etched in 3 % nital solution. The cross-sections of tests 1 and 2 (FE8) did not exhibit any WEA/ WEC. In contrast, test 3 (RBT) displayed WEAWEC under the outer ring’s raceway (OR, c.f. Figure 1). The inner ring (IR) & OR from test 4 exhibited a frosted surface attributed to the electrical discharges. The OR’s axial cross-section revealed melted layers on the OR’ surface, which appear white in light optical microscope (LOM, c.f. Figure 2). 23rd International Colloquium Tribology - January 2022 69 Formation of White Etching Crack under sliding, boundary lubrication and additional current passage using modern lubricant compositions Figure 1: Micrograph of test 3’s outer ring (OR). WEA/ WEC appeared in the axial cross-section. Figure 2: Micrograph of test 4’s outer ring (OR). The raceway surface showed melted layers in the axial cross-section. 4. Conclusion Initial results on the thrust bearing test rig, under proven WEA/ WEC inducing loads (see also FVA 707 V and VI), indicate that modern formulations minimize the risk of WEA/ WEC formation under boundary lubrication conditions with high-sliding. As so far, no WEA/ WEC-related failures could be generated in FE8 tests with the used formulations. In contrast those modern formulations lead to WEC or melted surfaces in tests on the RBT under full fluid lubrication and additional current passage. Further investigations are needed to determine if the results are solely related to the formulation and therefore to single additives. 5. Acknowledgments The research project FVA 707 VI (IGF-Nr. 20881) is supported by the Federal Ministry of Economic Affairs and Energy (BMWi). The authors would like to thank the FVA as well as the participating member companies for the support and the helpful advice. References [1] M. Linzmayer et al.: Interlaboratory comparison: Round robin test for the damage reproduction of white etching crack in cylindrical roller thrust bearings, Wear 480-481 (2021) 203925. https: / / doi. org/ 10.1016/ j.wear.2021.203925 [2] Gould, B. et al.: The Effect of Lubricant Composition on White Etching Crack Failures, Tribology Letters 67 (2019). https: / / doi.org/ 10.1007/ s11249- 018-1106-y [3] Richardson, A.D. et al.: The effect of over-based calcium sulfonate deter-gent additives on white etching crack (WEC) formation, Tribology International 133 (2019) 246-262. https: / / doi.org/ 10.1016/ j.triboint.2019.01.005. [4] Franke, J. et al.: Influence of Oil Formulation on White Etching Crack Formation Depending on WEC Main Mechanism, International Colloquium Tribology 2020, Technische Akademie Esslingen. [5] Manieri, F. et al.: The origins of white etching cracks and their significance to rolling bearing failures, International Journal of Fatigue 120 (2019) 107-133. https: / / doi.org/ 10.1016/ j.ijfatigue.2018.10.023. 23rd International Colloquium Tribology - January 2022 71 Alternative lubricants in wind turbines to avoid WEC formation Dominik Kürten Fraunhofer Institute for Mechanics of Materials IWM, Germany Corresponding author: dominik.kuerten@IWM.fraunhofer.de Stefan Grundei Klüber Lubrication München SE & Co. KG, Germany Jörg Franke Schaeffler Technologies AG & Co. KG, Germany Sebastian Plebst IoLiTec Ionic Liquids Technologies GmbH, Germany Andreas Kailer Fraunhofer Institute for Mechanics of Materials IWM, Germany 1. Introduction Bearings in wind turbines must be protected against premature failures in order to increase their reliability and availability. Most of the bearings suffer from hydrogen embrittlement due to tribological loading, lubricant degradation, contamination and electrical interference. White etching cracks (WEC) are one of the most reported damages in rolling element bearings and still an open area of research. Alternative lubricants are urgently required to counteract this problem. Lubricants with significant improved conductivity were identified as a possible measure to prevent harmful chemical and electrical influences. 2. Results and Discussion Adding ionic liquids (IL) to non-polar lubricants is challenging because their solubility is limited. Moreover, impurities in the ILs can strongly affect the tribological behavior. Therefore, structural motifs of ILs were selected, for which sufficient solubility in lubricants can be expected to achieve sufficient electrical conductivity of the lubricant. Rolling contact fatigue (RCF) tests with thrust roller bearings offer the opportunity to characterize different lubricants concerning their affinity to hydrogen embrittlement in bearings. Various test series with different oils and IL and additive contents have so far shown that a significant improvement in running behavior is achieved by adding ILs. 2.1 Improvement of bearing life Figure 1: Comparison of the running time for different model lubricants. Figure 1 shows a comparison of the results of an RCF test for a gearbox oil with different IL contents. 3 tests were conducted for each lubricant sample. The pure gearbox oil leads to a bearing damage after a test duration of 80 - 95 hours in all cases. Adding a low content of IL to the gearbox oil improves the bearing performance. Maximum test durations of 150 hours were reached in 2 of 3 tests. With higher IL content no damage occurred within the test duration of 150 h. An XPS analysis of washers from bearing tests with pure gear box oil and with high IL content show the formation of a phosphate layer on the bearing surface due to additive reactions. Possibly formed by an anti-wear or friction modifier additive. In the case with a high IL content the formation of an additional, nitrogen and fluorine layer was detected on the surface as residues of the IL. 72 23rd International Colloquium Tribology - January 2022 Alternative lubricants in wind turbines to avoid WEC formation 2.2 Applying a Potential to the bearing A special test set-up was designed for carrying out rolling tests with superposed electrical potentials. The working electrode is positioned in the lubricant and the counter electrode is directly in contact with the stationary lower ring of the rolling bearing. Different electric voltages can be applied between the two electrodes, if the lubricant is electrically conductive. -1V +1V Figure 2: Photographs of rollers and cross-sectional optical micrographs of bearings test under different potentials To investigate electrochemical influences on friction, wear and hydrogen generation, tests can be carried out at anodic (oxidation) and cathodic (reduction) potential. RCF test with the gearbox oil + high IL content and different potentials show the ability to trigger the formation of WEC due to the applied potential. A cross-sectional analysis of the tested bearings is presented in Figure 2. Hydrogen was formed under an anodic potential during RCF testing. 2.3 Wear behaviour of ionic liquids The wear behavior of a base oil and additivated variants with IL additives in different concentrations was investigated in oscillating sliding test with an Optimol SRV tribometer. The COF was slightly influenced by these additives. In contrast, the wear behavior was strongly modified by the IL: The lubricant with a high IL content shows significantly lower wear compared to the pure base oil (Figure 3). Figure 3: SRV tests with a base oil and different IL contents, indicating a reduction of the wear volume with increasing IL content. 3. Conclusion On the basis of these results it is concluded that ILs as additives for fully formulated lubricants can help to increase lubricity and reduce their electrical resistance. Improving the conductivity of the lubricant helps to avoid bearing damage such as WEC and additionally improves the tribological properties of the lubricants. The wear resistance of tribological systems in particular is positively influenced. 4. Acknowledgement The Authors thank the Federal Ministry for Economic Affairs and Energy for funding of the project “WindPower-Life” grant number 0324208A-D. 23rd International Colloquium Tribology - January 2022 73 Novel Transmission Lubricants for New Generation Vehicles Ratnadeep Joshi Research & Development Centre, Indian Oil Corporation Ltd, Sector-13, Faridabad, India-121007 Corresponding author: Email: joshir2@indianoil.in Lakshmi Katta, Sarita Seth, Pankaj Bhatnagar, Deepak Saxena, SSV Ramakumar Research & Development Centre, Indian Oil Corporation Ltd, Sector-13, Faridabad, India-121007 1. Introduction Electrification or e-mobility is witnessed as one of the prominent routes towards meeting the ever-tightening emission targets being implemented worldwide. The current and future developments of EV lubricants have a common goal to minimize friction loss, enhance durability, boost efficiency, and strengthen other performance aspects. Satisfying these salient goals for EVs would pave the way towards a greener future [1, 2]. Transmission lubricants will play an important role in e-mobility. However, development of transmission lubricants for EVs is dependent on various aspects set by OEMs due to their own unique transmission technology and type of e-motor system (wet or dry), utilizing lots of copper windings and new materials(elastomers, plastic and other materials). Hence, customised EV lubricants are required for smooth & trouble free operations meeting various OEM needs suiting to their hardware. Technical requirements for EV transmission lubricants are additional and specific compared to conventional transmission oils as indicated in Figure 1. Figure 1: Comparative Performance of EV Tranmission Oil w.r.t Conventional tranmission oils In view of the specific require, development of a high performance Electrical vehicle transmission oils, there are many parameters to be carefully selected and measured. Selection of base oils, viscosity modifier and suitable additive components play an important role in development of EV transmission lubricants. The critical parameters are conventional transmission oil properties likeantirust, anti corrosion, anti wear/ EP and special properties for electric vehicle applications are seal compatibility / plastic material/ other materials compatibility and electrical properties. In this paper, author’s have aimed for development of a robust transmission oil with extended drain potential which can be used in wet and dry both type of e-motor applications interval. Three candidate oils (A, B & C) were developed in the author’s laboratory. Performance assessment methodology included series of lab-screening tests. Detailed comparative evaluation of the candidate oils was done w.r.t. different performance parameters including low temperature fluidity (Table 1), tribological tests like Extreme Pressure(EP)/ Antiwear(AW) characterisitcs, shear stability test, film forming properties & FZG scuffing load test. Candidate oils were also evaluated for electrical properties like electrical conductivity and brake down voltage (BDV) measured at ambient condition (Figure 2). Copper resistivity test was done to assess the electrical resistivity (also known as specific electrical resistance) and to check electric current effect on copper wire. This test is important for the fluids, which are in direct contact with new components of the electric motor (wet type e-motor) transmissions. Test was conducted at 120 °C with 1mA current source and by using specific copper wire. The copper wire degradation was measured by plotting resistance (Ω) vs time duration in Figure 3. Further, vehicle level Noise, vibration, and harshness (NVH) testing was carried out by mounting the test vehicle on a chassis dynamometer and measuring the noise & vibration with the help of a digital signal processing Fast Fourier Transform (FFT) analyzer in Figure 4. 74 23rd International Colloquium Tribology - January 2022 Novel Transmission Lubricants for New Generation Vehicles Table 1: Physicochemical & performance data of Candidate oils Oil Category Test Methods OIL A OIL B OIL C Base oil Category Mineral Synthetic Synthetic Viscosity Grade SAE J 306 SAE 80W90 SAE 75W90 SAE 75W90 Kinematic Viscosity @ 100 ºC, cSt D-445 15.72 15.22 16.18 Aniline point , ºC D-611 113 119.2 121 Viscosity Index D-2270 143 178 181 BF viscosity @-40 ºC, cP D-2983 >150000 34394 40091 Sulphur, % D-2622 2.11 1.82 0.12 Weld Load, kgf IP 239 400 400 200 Load Wear Index, kgf D-2783 55.89 55.89 29.93 KRL shear stability @20hrs CEC- L-45-A-99 7.0 8.40 8.80 FZG gear test rig, scuffing load stage A10/ 16.6R/ 90 ºC 14 14 10 Figure 2: Conductivity and BDV results of candidate oils Figure 3: Copper resistivity test on candidate oils Figure 4: FFT Analysis of Candidate oils in electrical vehicles 23rd International Colloquium Tribology - January 2022 75 Novel Transmission Lubricants for New Generation Vehicles 2. Results and discussion: It can be seen from the comparative Physico-chemical & performance data (Table 1) that Oil B & C are superior in low temperature performance properties w.r.t. Oil A as measured by Brookfield viscosity test (ASTM D 2983). Oil A & Oil B found to be superior in tribological performance, i.e., EP/ AW tests, KRL Shear stability test and in FZG Scuffing load stage test (IP239, D2783, CE- CL-45-A-99 FZG and A10/ 16.6R/ 90 °C), are w.r.t Oil C. Interestingly, Oil C has shown superior performance w.r.t Oil A & Oil B (Figure 5 & 6) in extended copper corrosion test and vapour phase copper corrosion test. Similarly, in copper resistivity test, Oil C has performed better w.r.t Oil A & Oil B. All the three candidate oils were also tested for vehicle level NVH testing to assess vehicle level transmission noise and fluid’s dampening effect for reduction of cabin noise. Fast Fourier Transform Analysis shows that at low and at high-speed conditions Oil B & C are superior w.r.t. Oil A. Figure 5: Vapor phase copper corrosion-120 deg c 72 h Figure 6: Copper corrosion by ASTM D 130- 120 degc, 100 h 3. Conclusion Electrical vehicles require customised transmission oils and the requirements vary from OEM to OEM. These oils should be compatible with all the materials in contact with the oil in an electric vehicle transmission system. The present study shows, that a candidate oil with excellent properties for EV transmission lubricants has been developed; however, there is still a need to generate more data and explore new test methods for evaluation of EV transmission lubricants in line with OEM specific needs. References [1] Khurana A. Ravi Kumar V. V. and Sidhpuria M. A Study on the Adoption of Electric Vehicles in India: The Mediating Role of Attitude Vision, 24(1) 23-34, 2020 [2] https: / / www.electrichybridvehicletechnology.com/ features/ the-new-age-of-lubricants-for-electric-vehicles.html 23rd International Colloquium Tribology - January 2022 77 Improvement of tribological performances of MoDTC induced by methylene-bis(dithiocarbamates) in engine lubricants: Enhanced durability of MoDTC and their friction reducing capability under engine operating conditions Yu Min Kiw University of Strasbourg, CNRS, Institut de chimie de Strasbourg UMR 7177, F-67000 Strasbourg, France TotalEnergies Solaize Research Center, BP22-69360 Cedex, France Pierre Adam University of Strasbourg, CNRS, Institut de chimie de Strasbourg UMR 7177, F-67000 Strasbourg, France Philippe Schaeffer University of Strasbourg, CNRS, Institut de chimie de Strasbourg UMR 7177, F-67000 Strasbourg, France Corresponding author: p.schaef@unistra.fr Benoît Thiébaut University of Strasbourg, CNRS, Institut de chimie de Strasbourg UMR 7177, F-67000 Strasbourg, France Chantal Boyer University of Strasbourg, CNRS, Institut de chimie de Strasbourg UMR 7177, F-67000 Strasbourg, France 1. Introduction Energy saving, worldwide concerns over CO 2 emission and the introduction of new engine oil specifications are among the major driving forces to increase fuel economy in internal combustion engines [1-3]. One of the most general trends to improve the fuel efficiency is the use of molybdenum dithiocarbamates (MoDTC) (Figure 1a) as effective friction modifiers in lubricants since they lower significantly the friction coefficient at the tribological contacts under boundary lubrication conditions [4-7]. Despite their excellent efficiency in reducing friction coefficient to relatively low values, the tribological performances of MoDTC in engine oils still highly depends on the nature and chemistry of the other additives present in the formulated oils. The occurrence of synergistic or antagonistic interactions between MoDTC and other lubricant additives plays an important role in minimizing the friction in automobile engines. In this context, our work is dedicated to investigating the impact of methylene-bis(dithiocarbamates) (MBDTC) (Figure 1b) as a lubricant additive on the service lifetime of MoDTC in formulated lubricants. For this purpose, comparative engine tests were performed using the same formulated engine oils containing MoDTC without and with the addition of MBDTC (referred to as oil A and oil A MBDTC , respectively). Oil performances were compared in terms of tribological properties, duration of friction reducing capacity of the lubricants, evolution of fuel consumption of the engines and evolution of the concentrations of MoDTC as a function of time. In addition, laboratory oil ageing experiments were carried out under thermal (non-oxidizing) and thermo-oxidative conditions to study in more details the interactions between MoDTC and MBDTC at the molecular level. The evolution of MoDTC and of their transformation products was followed by HPLC-MS, NMR and Probe-MS analyses. Focus has been put on the evaluation of the effect of zinc dithiophosphates (ZnDTP) (Figure 1c) and oxidative conditions on the interactions between MoDTC and MBDTC. A comprehensive understanding of the underlying chemical transformation of MoDTC and the effects on the tribological performances of lubricants is expected to offer new strategies for molybdenum tribochemistry optimization in real engine systems. Figure 1: Chemical structures of (a) molybdenum dithiocarbamate (MoDTC); (b) methylene-bis(dithiocarbamates) (MBDTC); (c) Zinc dithiophosphate (ZnDTP) R: alkyl chains 78 23rd International Colloquium Tribology - January 2022 Improvement of tribological performances of MoDTC induced by methylene-bis(dithiocarbamates) in engine lubricants 2. Results and Discussion Based on engine tests performed using a formulated engine oil containing MoDTC and MBDTC and, for comparison, the same formulated engine oil devoid of MBDTC, our study has shown that the combined use of MoDTC and MBDTC results in an enhanced preservation of fuel efficiency with ageing time. This was most likely related to the interactions between MoDTC and MBDTC which has a beneficial effect on the functional lifetime of MoDTC in lubricants, allowing the friction coefficient of engine lubricants to be maintained at lower level for longer periods of time and, as a consequence, fuel consumption to be reduced. Indeed, MoDTC could be detected, using a specifically developed HPLC-MS method, in the formulated lubricant containing MBDTC over a longer period of engine test. Since the remaining MoDTC after prolonged engine functioning were shown to exclusively bear ligands corresponding to DTC moieties from MBDTC, it can be assumed that the prolonged existence of MoDTC was due to the progressive replacement of the degraded DTC ligands from MoDTC educts by DTC ligands released from MBDTC during engine functioning (Figure 2). These newly formed MoDTC complexes were progressively consumed (as was the case for the genuine MoDTC species), but they were shown to be concomitantly regenerated and remained in the formulated engine oil at concentrations high enough to ensure the reduction of the friction coefficient to lower levels for an extended duration, as indicated by the tribological measurements. For the MoD- TC educts progressively degraded upon engine functioning, MBDTC thus represents a “stock” of DTC ligands which can be released during engine functioning to regenerate new MoDTC species, leading to better tribological performance of the engine oil. Figure 2: Ligand transfer reactions between MoDTC and MBDTC; R1, R2: alkyl chains We completed these studies by investigating in detail, the interactions between MoDTC and MBDTC at the molecular level in the presence of other additives using laboratory oil ageing experiments under thermal (non-oxidizing) and thermo-oxidative conditions (NO 2 in air). It could be shown that the reactions between MoDTC and MBDTC appeared to be catalyzed by ZnDTP and oxidative conditions (NO 2 in air). The Lewis acid properties of Zn(II) complexes as well as the capacity of Zn(II) to activate dithioacetals have been previously reported in other contexts [8,9]. Therefore, in this study, Zn(II) ions are likely to act as Lewis acids to activate the cleavage of C-S bonds from MBDTC, thereby facilitating the release of dithiocarbamate ligands from MBDTC and thus favouring ligand transfer from MBDTC to MoDTC. Besides, oxidative condition (NO 2 in air) was also shown to induce the release of dithiocarbamate ligands from MB- DTC, even in the absence of ZnDTP or Zn(II) ions. 3. Conclusion The extension of friction reducing properties of engine oils for longer periods of time plays an important role in energy saving and in coping with global environmental problems. The control of thermo-oxidative degradation of Mo-based friction modifiers upon engine functioning remains a key challenge to achieve this objective. In this context, we showed that the interactions between MoDTC and MBDTC has a beneficial effect on the functional lifetime of MoDTC in engine lubricants and on the persistence of their tribological properties resulting in an enhanced preservation of fuel efficiency. This effect has been shown to be associated with DTC ligand transfer reactions between MBDTC and MoDTC and it was assumed that the DTC ligands from MBDTC were progressively transferred to the metal core of MoDTC after oxidative degradation of their ligands. As a result, the concentrations of MoDTC could be preserved at a useful level over extended ageing periods, thus maintaining their friction reducing properties in engine oil. MBDTC thus represents potentially a “stock” of DTC ligands which can be progressively released during engine functioning and can replace the degraded ligands from MoDTC educts under thermo-oxidative conditions following Zn(II) catalyzed and/ or oxidative processes. The results obtained provide insight for future additive design by considering similar delayed ligand transfer mechanisms demonstrated by MB- DTC aimed at extending the functional lifetime of MoDTC. References [1] Tseregounis, S.I., McMillan, M.L. and Olree, R.M., “Engine oil effects on fuel economy in GM vehicles separation of viscosity and friction modifier effects”, SAE Technical Paper No. 982502, 1998. [2] Hoshino, K., Kawai, H. and Akiyama, K., “Fuel efficiency of SAE 5W-20 friction modified gasoline engine oil”, SAE Technical Paper No. 982506, 1998. [3] Johnson, M.D., Jensen, R.K., Clausing, E.M., Schriewer, K. and Korcek, S., “Effects of aging on frictional properties of fuel efficient engine oils”, SAE Technical Paper No. 952532, 1995. [4] Graham, J., Spikes, H. and Korcek, S., “The friction reducing properties of molybdenum dialkyldithiocarbamate additives: Part I factors influencing friction reduction”, Tribol. Trans., 44, 2001, 626-636. [5] Graham, J., Spikes, H. and Jensen, R., “The friction reducing properties of molybdenum dialkyldithiocar- 23rd International Colloquium Tribology - January 2022 79 Improvement of tribological performances of MoDTC induced by methylene-bis(dithiocarbamates) in engine lubricants bamate additives: Part II durability of friction reducing capability”, Tribol. Trans., 44, 2001, 637-647. [6] Spengler, G. and Webber, A., “On the lubricating performance of organic molybdenum compounds”, Chem. Ber., 92, 1939, 2163-2171. [7] Grossiord, C., Varlot, K., Martin, J.M., Le Mogne, Th., Esnouf, C. and Inoue, K., “MoS 2 single sheet lubrication by molybdenum dithiocarbamate”, Tribol. Int., 31, 1998, 737-743. [8] Salter, M.H., Reibenspies, J.H., Jones, S.B. and Hancock, R.D., “Lewis acid properties of zinc(II) in its cyclen complex. The structure of [Zn(Cyclen) (SC(NH 2 ) 2 ](ClO 4 ) 2 and the bonding of thiourea to metal ions. Some implications for zinc metalloenzymes”, Inorg. Chem., 44, 2005, 2791-2797. [9] Sutton, L.R., Donaubauer, W.A., Hampel, F. and Hirsch, A., “Tris(thioacetals) from benzene hexathiol: towards covalent self-assembly”, Chem. Commun., 10, 2004, 1758-1759. 23rd International Colloquium Tribology - January 2022 81 Theoretical And Computational Estimation Of The Value Of The Coefficient Of Friction Of The Synovial Fluid Of Human Joints Sergey Vasiliy Fedorov Kaliningrad State Technical University, Kaliningrad, Russia, fedorov@klgtu.ru 1. Introduction The principle of natural (living) and constructed machines and tribosystems is discussed. Machine tribosystems as machine subsystems possess basic functional meaning of objects transformation movement (energy) inside machine. So machine is taken as supertribosystem. Energy scheme of tribopair (Figure 1) has 1, 2 tribosurfaces and 3 third (compatible) body. Figure 1: Schematic view of friction’s contact (elementary tribosystem) in energy interpretation [1]. Friction process is analyzed as a global phenomenon of energy transformation and dissipation from the triboergodynamics [1-3] point of view. Regularities of structural-energy evolution of friction contact (tribosystem) demonstrate (Figure 2) that the friction process itself in the area of compatibility of rubbing surfaces (machine friction) is characterized by two friction coefficients - adaptive (Amontons) µ adapt and dissipative µ dis : . (1) Here ; ; V f is the deformable (friction) volume; V adapt -adaptive and V dis dissipative friction volumes; µ-friction coefficient; N normal load; h i , l f linear sizes of elementary contact. The latent (potential), accumulated energy density ∆u e of defects of structure is an integral parameter of tribostate and damageability (failure ( )). The dynamic dissipated energy density is an integral parameter of tribostate too and capacity for work. Here . Figure 2: Structural-energy diagram for evolution of rubbing surfaces [1-3]. Entropy interpretation of friction coefficients These friction coefficients have entropy interpreting: . (2) Here S U configuration entropy of friction (contact) volume; - inertia entropy of compatible friction volume (entropy of dissipative structures); S * critical entropy of elementary tribosystem (friction volume). Both these friction coefficients are probability parameters of tribosystem state. Adaptive friction coefficient - is parameter of resistance to movement and damage of volume contact probability: . (3) Dissipative friction coefficient - is a parameter of facilitating to movement and capacity for work of contact volume (elementary tribosystem) probability: . (4) 82 23rd International Colloquium Tribology - January 2022 Theoretical And Computational Estimation Of The Value Of The Coefficient Of Friction Of The Synovial Fluid Of Human Joints 2. The rule of natural machine (mechanism) Additive entropy principle of supertribosystem as an entropy sum of its subsystems - tribosystems is discussed. The rule of natural machine as a total sum of adaptive friction coefficients of its tribosystems which is equaled to unit is formulated. . (5) The generalized friction coefficients of natural machine as a natural supertribosystem are suggested. The most characteristic equation of natural machine as natural supertribosystem has the form: (6) (7) (8) , (9) Here ; ; the generalized friction coefficients of natural machine as a natural supertribosystem; n MACH number of machines or the degree of complexity. Quantitative row (Table 1) of possible natural tribosystems (adaptive and dissipative friction coefficients) forming natural machine, i.e. natural supertribosystem is constructed. Table 1: Quantitative row of possible tribosystems (adaptive and dissipative friction coefficients) forming natural machine (mechanism). 0,5 0,5 2 0,25 0,75 4 0,2 0,8 5 0,1 0,9 10 0,05 0,95 20 0,04 0,96 25 0,025 0,975 40 0,02 0,980 50 0,01 0,990 100 0,005 0,995 200 0,004 0,996 250 0,0025 0.9975 400 0,002 0,998 500 0,001 0,999 1000 0,0005 0,9995 2000 0,0004 0,9996 2500 0,00025 0,99975 4000 0,0002… 0,9998… 5000… 3. Synovia friction coefficient of natural machines To check the calculated set of living machines (Table 1) it is necessary to study living machines, e.g. structural, kinematic schemes of man and horse. These structural kinematic schemes are skeletons of man and horse. The basis of these skeletons for kinematic couples: links - bones and tribopairs - joint hinges. According to information [4,5] human skeleton is composed of 270 bones in the early age and of 220 bones in mature age. The horse skeleton is composed of 252 bones. As it is seen this number of links (n mach ) in these living machines correspond to a calculated set of natural machines with the machine number n mach =250. This result allows to assess the value of friction coefficient of synovial liquid of joint hinges of living organisms (machines). From Table 1 we have for n mach =250 the value of adaptive friction coefficient equal to µ adapt =0,004. This value should be taken for synovia friction coefficient. Modern tribology treats this level of friction coefficient as the level of superlubrication [6]. 23rd International Colloquium Tribology - January 2022 83 Theoretical And Computational Estimation Of The Value Of The Coefficient Of Friction Of The Synovial Fluid Of Human Joints Thus, the friction in live machines has the most optimal, i.e. the ideal level. The physical model of the behavior of synovial lubrication [7] can be represented by the essence of self-organizing processes during friction [8]. References [1] Fedorov, S.V., “Energy Balance of Friction and Friction Coefficient in Energetical Interpretation”, Tribology in Industry, 37, 3, 2015, 380-389. [2] Fedorov, S.V., “Nano-Structural Standard of Friction and Wear”, Tribology in Industry, 40, 2, 2018, 225-238. [3] Fedorov, S.V., “Friction Energy Balance Regularities And Tribology’s Nano-Structural Standard”, COMADEM, 23, 1, 2020, 13-30. [4] “Skeleton. Great Soviet Encyclopaedia” [in Russian], Vol. 23, Soviet Encyclopaedia, Moscow, 1976. [5] “Horse Skeleton”, available at: http: / / www.horseof-ream.vsau.ru/ inter/ bone.html [6] Erdemir A, Martin J.-M., Luo J., “Superlubricity”, Elsevier, 2020, Paperback ISBN: 9780444643131 [7] Chikama, H., “The Role of the Protein and the Hualuronic Acid in the Synovial Fluid in Animal Joint Lubrication”, J. Jpn. Orthop. Ass. - 1985 (59) №5, 559-572. [8] Fedorov, S., “Selforganized Nano-quantum Solid Lubricant”, Tribologue + Schmierungstechnik, 63, 3 2016, 5-13. Metalworking 23rd International Colloquium Tribology - January 2022 87 Development and characterization of Ultra-Low Foaming Metalworking products Bellini Marco Bellini SpA, Zanica (BG), Italy Corresponding author: mbellini@bellini-lubrificanti.it Pota Simone Bellini SpA, Zanica (BG), Italy 1. Introduction The development of low foaming metalworking fluids arises from several reasons. In the last years, there is a tendency to migrate on semi-synthetic MWFs, with a lower oil/ surfactants ratio, and ester-based MWFs that require higher HLB surfactants. These necessities, paired to continuous improvement of additive package and elongation of time of life of emulsions lead sometimes to foaming issues on semi-synthetic MWFs. In addition to this, many filters could gradually remove antifoams from emulsions. If this happen, the effect of antifoam breaks down, causing foaming problems. The idea is to develop products that could counteract this problem by buffering antifoam loss on their own. 2. Results and discussion A deep study on MWFs formulation and components is performed, resulting in long-lasting ultra-low foaming products. Foaming properties are measured with an automatic foam analyser. MWFs optimization goes through two different ways: first optimize the formulation without antifoam and then find the best antifoam. An internal method to check antifoam compatibility is developed while a strong MWFs formulation revision is done. The initial part of this work is dedicated to collecting data and elaborate ad hoc method to reproduce on-the-field feedback of working emulsions. Aging of concentrates, temperature and stress tests are just few of the studied parameters. 2.1 Formulation optimization MWFs have many components used as stabilizers or additives, such as surfactants or phosphate compounds. During this work, each component is analysed in synthesized water (fixed hardness and fixed temperature) to find the most suitable one in terms of foaming properties and surface tension. Figure 1: Foamability of different surfactants Using Design Of Experiment (DOE) technique a new formulative approach is investigated. A fixed starting ‘base product’ is used to develop a new ultra-low foaming MWF. A narrow range of n selected surfactants is used to stabilize MWF concentrate starting from ‘base product’. The first aim is to find more combinations of these n surfactants that can guarantee concentrate stability. After that, a safe area is studied deeper, testing foam performances. The best formulation is a trade-off obtained maximizing concentrate stability response and minimizing foaming. Experimental effort has been reduced by using D-optimal design. 88 23rd International Colloquium Tribology - January 2022 Development and characterization of Ultra-Low Foaming Metalworking products Figure 2: DOE contour plots Generally, MWFs have a strong increase in foam volume after a certain period. This behaviour is enhanced if MWF concentrate is stressed at high temperature. A study on foamability and foam stability before and after concentrates aging is performed. 2.2 Study of antifoams As broadly known one of the most effective class of antifoams is silicon-based products. This class of antifoams often is not compatible with high alkalinity semi-synthetic MWFs. Even if antifoam is highly effective at t=0, incompatibility occurs as flocculation and loss of effectiveness. The more the time passes the higher is the loss in terms of performances. This causes several negative feedbacks on the field that generally intensify during summer period when temperature rises up. Find the best antifoam for a selected formulation means find a trade-off between performances and compatibility. We have studied and developed an internal method to assess compatibility in 7 days using spectroscopy paired to visual check of concentrates. Performances loss is studied collecting several foam data after fixed periods and related to spectroscopic data. Spectroscopic data are collected and the difference between samples with and without antifoam is studied. Collected and elaborated data allow predicting if a selected antifoam will be suitable in a defined MWF formulation. 3. Conclusion This new formulation approach guarantees a strong improvement in foaming properties because of many reasons: selection of low-foaming raw materials, knowledge of components interactions, check of formulation aging, compatibility of selected antifoams, etc. Several comparisons are shown comparing new formulations and old ones. A strong improvement on selected MWFs is achieved. 23rd International Colloquium Tribology - January 2022 89 Naphthenic Base Oils - Tailoring Emulsion Stability Thomas Norrby Nynas AB, Naphthenics TechDMS, Nynäshamn, Sweden Corresponding author: thomas.norrby@nynas.com Jinxia Li Nynas AB, Naphthenics TechDMS, Nynäshamn, Sweden Linda Malm Nynas AB, Naphthenics TechDMS, Nynäshamn, Sweden 1. Introduction In this study, several MWF Soluble oil and Semi-synthetic emulsions based on two different naphthenic base oils were created. The purpose was to elucidate any and all influence on the properties of these emulsions arising from difference in the fundamental properties of the base oils employed. The naphthenic base oils utilized were two 22 cSt oils, one straight cut (narrow cut) and one blended oil (a wider cut). Two Soluble oil non-ionic emulsifier systems, and four different semi-synthetic (anionic and non-ionic blends) formulations were investigated in soft and hard water, with respect to emulsion droplet size and stability over time. The emulsion particle size, and the emulsion stability as a function of time, was determined by static light scattering utilizing a Malvern MasterSizer equipment, and a TurbiScan unit. The results show that the two base oils yield emulsions with very similar properties under a wide variety of chemistries and conditions. 1.1 Base oils • Base Oil B has a slightly higher colour ASTM <1.0 (vs. <0.5) • Base Oil A and B have similar Aniline Point 77 °C (vs. 77 °C) • Very similar Carbon Type Content by ASTM D 2140 in both base oils • Base Oil A has about 10 °C higher Flash Point by ASTM D 93 Penske-Martin; (A) 173 °C vs. (B) 162 °C • An average of six brands in a previous Nynas study was found to be 159 °C • NB! Blended base oils are rather common in the market Distillation curves by ASTM D 86 and ASTM D 2887 also display different cure shape, and the blended Base oil B displays more lighter ends (lower IBP) and more high boiling components (Higher FBP) 1.2 Emulsions Stability Experiments 90 23rd International Colloquium Tribology - January 2022 Naphthenic Base Oils - Tailoring Emulsion Stability Soluble oil experiments were done across HLB values ranging from 9 to 13, as published previously [2]. The main correlation was found to be Aniline Point and viscosity, and no major differences between Base oil A and B can be seen in the Soluble oil non-ionic model formulations. 1.3 MWF concentrates We have previously published a study of Semi-synthetic Metalworking fluids [1]. We could see that small changes in the complex formulations (15 + components) in the case of Semi-synthetics did display different emulsion stability and droplet size distribution, depending on base oil viscosity and water hardness. In the present study, either the straight cut Base oil A or the Base oil blend B was tested versus a number of different MWF concentrates. As seen in the graph below, Base oil A prefers concentrate MWL 3, and Base oil B performs better with MWL 2 2. Conclusion The careful selection of components in the case of the Semi-synthetic formulations thus can be made so that either the straight cut Base oil A, or the blended Base oil B displays smaller droplet size and higher emulsion stability. Additive concentrates thus can and should be tailored to match also the finer details of the differences between even closely related base oils. References [1] T. Norrby, J. Li., L. Visuri, ”Model MWFs based on Naphthenic base oilsstraight cut or blend? ”, STLE Annual Meeting 2021. [2] T. Norrby, L. Malm, P. Wedin, G. Ponti, “Emulsion Stability in Semi-Synthetic MWF formulations”, Proceedings of the 21 st International Colloquium Tribology, January 2018, Technische Akademie Esslingen, Germany 23rd International Colloquium Tribology - January 2022 91 Do Biofilms in Metalworking Fluid Systems Matter? Frederick J. Passman Biodeterioration Control Associates, Inc., Princeton, New Jersey, United States Corresponding author: fredp@biodeterioration-control.com 1. Introduction Historically, condition monitoring for microbial contamination has focused on measuring bioburdens in bulk fluid samples. However, biofilm communities create several significant metalworking fluid (MWF) management challenges. First, they are non-uniform. Samples must be collected from diagnostic, rather than representative locations. Second, biofilms are resistant to microbicide treatments. Third, biofilms readily reinfect recirculating MWF once the microbicide concentration has decreased to less than its critical concentration. Although the use of bioresistant MWF has decreased the need for microbicide tankside additions to control planktonic populations, it has not necessarily reduced the risk of bioaerosol generation. This paper will address the importance of biofilm bioburden monitoring and control, and the implications of effective control on bioaerosol exposures. 2. Biofilm Composition In ASTM Practice E2169 [1] a biofilm is defined as a film or layer composed of microorganisms, biopolymers, water, and entrained organic and inorganic debris that forms as a result of microbial growth, proliferation, and excretion of polymeric substances at phase interfaces (liquid-liquid, liquid-solid, liquid-gas, and so forth). Diverse species of bacteria and fungi can be detected in biofilm communities or consortia. Importantly, depending on its location within a biofilm matrix, a given type of microbe (genetic type - operational taxonomic unit, OTU) can have substantially different morphologies (just as human cell morphologies vary) and physiological properties. Moreover, microbes within biofilms use molecular signal molecules to communicate [2] and are quite promiscuous - regularly exchanging genetic material among measures [3]. The material that forms biofilm matrixes is called extracellular polymeric substance - EPS. EPS is a complex mixture of polymeric molecules including, carbohydrates, deoxyribonucleic acid (DNA), lipids, lipopolysaccharides, and proteins. Once though to be a uniform mass, like a gelatinous coating, the EPS matrix is now known to be structurally complex. As illustrated in figure 1, the EPS matrix has channels trough which fluid can pass, zones that are nearly cell-free (thought to be used for nutrient storage), and zones in which microbial cells are densely packed. Biofilms release cells into the environment passively when outer layers are eroded away by fluid flow and actively when EPS bursts open to eject microbes (figure 2). Thus, biofilm communities are reservoirs for MWF recontamination, and - by extension - bioaerosols. Figure 1: Biofilm structure schematic. Figure 2: Biofilm consortium - active and passive planktonic cell release. 3. Biofilm Distribution in MWF Systems Although biofilms can grow on any wetted surfaces, they tend to be thickest at the MWF-sump wall-air interface and on surfaces on which MWF mist accumulates (i.e., splash zones) as shown in figures 3a and b. 92 23rd International Colloquium Tribology - January 2022 Do Biofilms in Metalworking Fluid Systems Matter? 4. Antimicrobial Pesticide Resistance Because the heaviest accumulations are not on surfaces that are in continuous contact with recirculating MWF, they are difficult to treat. Moreover, even when microbicides can be reliably brought into contact with biofilms, effective treatment typically requires 10x to 1000x the dose that is effective against planktonic (free-floating) cells [4]. Successful biofilm disinfection routinely requires repeated treatment as illustrated in figure 4. Figure 3: Biofilms on MWF system surfaces - a) sump wall at MWF-wall-air interface; b) on underside of a deck plate (sluice cover). Figure 4: Effect of repeated microbicide treatment on biofilm growth - a) Intact biofilm on MWF system surface; b) Initial dose kills exposed cells near EPS surface; c) 2nd dose further degrades EPS and kills additional cells; d) 3rd dose kills remaining cells and disinfects surface. 5. Conclusion Biofilms are complex EPS structures that provide a micro-environment in which microbial consortia can carry out activities that no single consortium member could. As units, they function like primordial, multi-cellular organisms. Because of their unique structural and functional properties, biofilms serve as reservoirs for both bioaerosols and recontamination of recirculating fluids. References [1] ASTM E2169-17, Standard Practice for Selecting Antimicrobial Pesticides for Use in Water-Miscible Metalworking Fluids, ASTM International, West Conshohocken, PA, 2017, www.astm.org, https: / / doi.org/ 10.1520/ E2169-17 [2] Lim, J., Lee, K-M, Park, C.Y., Kim, H.V., Kim, Y., and Park, S., “Quorum Sensing is Crucial to Escherichia coli O157: H7 Biofilm Formation under Static or Very Slow Laminar Flow Conditions”, BioChip J., 2016, 241-249, https: / / doi.org/ 10.1007/ s13206-016-0310-9 [3] Maunders, E., and Welch, M., “Matrix exopolysaccharides; the sticky side of biofilm formation”, FEMS Microbiol Let., 364, 13, 2017, 34 pp, https: / / doi.org/ 10.1093/ femsle/ fnx120 [4] Passman, F.J., and Küenzi, P., “Microbiology in Water-Miscible Metalworking Fluids”, Tribol. Trans., 63, 6, 2020, 1147-1171, https: / / doi.org/ 10. 1080/ 10402004.2020.1764684 23rd International Colloquium Tribology - January 2022 93 Improving Microbial Control Without Excess Reserve Alkalinity in Metalworking Fluid Formulations Harish Potnis ANGUS Chemical Company, Buffalo Grove, USA Clayton Cooper ANGUS Chemical Company, Buffalo Grove, USA 1. Introduction Over the course of the history of metalworking fluids formulations, amines have played a vital role in providing key performance attributes and helping drive a variety of innovations in a fluid design. However, selecting the right combination of „basic“and „complimentary amines“ remains one of the more complex challenges for today’s formulators. Today, by using the right combination of basic and specialty / complimentary amines, formulators can reserve the alkalinity of a metalworking fluid formulation and maintain expected performance without excess buffering. Most high-quality amines can eliminate the requirement of reserve alkalinity and help improve a formulation’s resistance to microbial growth (due to their branched structure), as well as provide improved corrosion control in iron / steel in multi-metal fluids and enhanced pH. Below is the guideline formulation and an overview of the amines evaluated by ANGUS Chemical Company. 2. Alkalinity vs. Microbial Studies This lab study investigates the relation of fluid life to reserve alkalinity throughout different amine combinations. Base amines (without TEA) include AB / AEPD, 4A, MIPA, DGA, MEA and their impact on fluid life. AB / AEPD shows exceptional fluid life of over 13 weeks (using ANGUS-modified ASTM E2275) at relatively low alkalinity levels. (refer to picture 1) 94 23rd International Colloquium Tribology - January 2022 Improving Microbial Control Without Excess Reserve Alkalinity in Metalworking Fluid Formulations (Picture 1) When the base amine formulas were combined with TEA (which raises the alkalinity), the results show that fluid life is independent of reserve alkalinity. This is contrary to the conceptthat adding TEA to increase reserve alkalinity will result in increased fluid life. When all base amines are combined with BAE (butylaminoethanol), we still see better results with AB / AEPD at relatively low reserve alkalinity levels. Furthermore, we combined all base amines with the unique amine chemistry of 3A4O (3-amino-4-octanol), and observed excellent results when combined with AB / AEPD. This improvement was not exclusive to AB / AEPD, however, as all base amines were improved significantly with the addition of 3A4O. As a result, we observe again that the proper selection of amine combination will bring a positive impact in overall fluid performance. Our corrosion resistance studies were conducted using the IP-287 method with cast iron chips. We focused on all of the base amine formulations as well as those in combination with TEA at a dilution of 2.5% in tap water. (refer to picture 2) (Picture 2) It can be clearly observed that among the base amine formulations without TEA, AB / AEPD performed the best while all other amines showed corrosion. Combing these formulations with 10% TEA was sufficient in protecting against all corrosion at 2.5%, however, this performance was achieved when using AB / AEPD alone. 3. Conclusion Through the results of our analysis, we can conclude that alkalinity does not always help to improve fluid longevity and formulations can be made without excessive alkalinity. Formulators can achieve better corrosion control properties with TEA, but must compromise on other properties such as Al staining, Co and Cu leaching. AB / AEPD can be an excellent choice to achieve synergistic effects of both base amine and complementary amines, and adding 3A4O (3-amino-4-octanol) into existing metalworking fluid formulations can boost overall performance. Lifetime Behaviour 23rd International Colloquium Tribology - January 2022 97 Oil nitration in a large-scale device for artificial alteration Adam Agocs AC²T research GmbH, Wiener Neustadt, Austria Corresponding author: adam.agocs@ac2t.at Charlotte Besser AC²T research GmbH, Wiener Neustadt, Austria Marcella Frauscher AC²T research GmbH, Wiener Neustadt, Austria Nicole Dörr AC²T research GmbH, Wiener Neustadt, Austria 1. Introduction Lubricant condition and tribological performance in an internal combustion engine are strongly interrelated. Trends in engine development are predominantly focusing on lower emissions, which are often achieved by higher compression ratios and turbocharged engines. This, combined with larger mileage oil change intervals, requires increasing stability of engine oils. Several artificial alteration methods are available to simulate lubricant degradation [1], however, nitration of the engine oils is often overlooked in standardized tests. Nitration is of great interest, as petrol and diesel passenger vehicles show significant differences in this regard [2-3], which might be tied to emission values. Diesel engine oils generally exhibit lower nitration [2-3], possibly due to the higher combustion temperature in compression ignition (Diesel) engines, as nitration products show a rapid decomposition above 160 °C [2]. Furthermore, large quantities of test oils with defined and reproducible degrees of degradation are necessary to make reliable predictions on performance and lifetime of engine components. Hence, the provision of test oils by artificial simulation including nitration is required [1]. The study at hand presents a novel alteration method, where up to 200 liters of ‘used’ oil can be produced for the purpose of engine bench testing or component testing in the development phase. This method is capable of close-to-reality simulation of nitration, oxidation, and additive degradation of engine oils. Comparability regarding relevant chemical degradation parameters of the altered oils with used oils from a modern turbocharged petrol vehicle is presented. 2. Materials and methods 2.1 Engine oil A commercially available 5W-30 engine oil suitable for both diesel and petrol engines with approvals for ACEA C3, API SN, BMW longlife-04, MB 229.51, MB 229.52, VW 502.00/ 505.00/ 505.01, and GM dexos2™ was selected. The engine oil formulation is relatively conservative, it contains calcium carbonate as base reserve, both phenolic and aminic antioxidants (AOs) and zinc dialkyldithiophosphate (ZDDP) as an antiwear additive (AW), but no boron-based AW or molybdenum-based friction modifiers, such as molybdenum dithiocarbamate (MoD- TC) can be detected. 2.2 Field test A field test using a conventional passenger car was conducted, where the corresponding results are described in detail in [4]. The selected vehicle was equipped with a modern, turbocharged petrol engine with 1.4 L displacement and 88 kW maximal power output. The car was operated under real driving conditions, predominantly at high-speed (freeway) utilization, which resulted in approx. 20,000 km total mileage in 8 months, accordingly, comparable to a typical oil change interval. 2.3 Artificial alteration The artificial alteration was conducted similarly to the methodology presented in [1]. In doing so, 180 L fresh oil was inserted in a jacketed steel reactor. The oil sample was kept under constant stirring, tempered between 110 °C and 140 °C and subjected to a metered air flow containing 0 ppm to 3000 ppm NO 2 . The experimental parameters were continuously adjusted to achieve the 98 23rd International Colloquium Tribology - January 2022 Oil nitration in a large-scale device for artificial alteration desired ratio of oxidation and nitration in the alteration system. Samples were taken at regular intervals for subsequent oil analysis, where the results were continuously used to modify the experiment parameters (feedback). The goal of the study was to reproduce the condition of the final used oil sample from the field test, corresponding to approx. 20,000 km mileage in a timely and cost-efficient manner. 2.4 Oil condition monitoring The following oil parameters were determined for both the field test as well as the artificially altered samples: • Oxidation and nitration via Fourier-transformed infrared spectroscopy (FT-IR) according to the methods described in [2-4] • Residual amounts of phenolic and aminic AOs as well as ZDDP compared to the fresh oil, based on the FT-IR spectra, using the methods described in detail in [2-4] • Neutralization number (NN) according to DIN ISO 6618 [5] and total base number (TBN) according to DIN ISO 3771 [6] 3. Results and discussion Figure 1 displays the oxidation and nitration of the final used oil sample (field test) as well as the final artificially altered product. Both parameters are showing a very close agreement, with differences in the range of 0.1 - 0.2 A/ cm only. Figure 1: Oxidation and nitration of the final used and artificially altered oil samples The residual additive content of the final field test sample and the artificially altered sample are presented in figure 2. ZDDP and both phenolic and aminic AOs show severe degradation during the lifetime of the lubricant. Comparable to oxidation and nitration, the used and artificially altered samples are showing very similar final values, which supports the analogous oil condition in both samples. Figure 2: Residual ZDDP as well as phenolic and aminic AO content compared to the fresh oil in the final used and artificially altered samples. Figure 3 shows the NN and TBN of the fresh oil, as well as of the final used and altered oil samples. The NN increases during both the field test and the artificial alteration, generally due to the production of organic acids due to oxidation reactions [2; 4]. Subsequently, the TBN decreases as the base reserve partially neutralizes said organic acids. [2; 4]. The field test and the artificial alteration are showing good comparability, once again highlighting the similarity of the artificial alteration with the real field samples. Figure 3: NN and TBN of the fresh as well as the final used and artificially altered oil samples Furthermore, it has to be highlighted that the artificial alteration only required approx. 10 days to simulate the degradation occurring during 20,000 km utilization. 4. Conclusion The obtained final artificially altered oil sample showed very good comparability to the used oil sample selected as reference in regard of oxidation, nitration, ZDDP and AO depletion, NN accumulation and TBN reduction which suggests a very good overall chemical comparability. Accordingly, it was proven that the presented artificial alteration method is highly suitable for the rapid production of test oils in large quantities. 23rd International Colloquium Tribology - January 2022 99 Oil nitration in a large-scale device for artificial alteration References [1] Besser C. et al.: Generation of engine oils with defined degree of degradation by means of a large scale artificial alteration method. Tribol Int 2019; 132: 39-49. https: / / doi.org/ 10.1016/ j.triboint. 2018.12.003. [2] Agocs A. et al.: Comparing oil condition in diesel and gasoline engines. Ind Lubr Tribol 2020; 72: 1033-9. https: / / doi.org/ 10.1108/ ILT-10- 2019-0457. [3] Agocs A. et al.: Comprehensive assessment of oil degradation patterns in petrol and diesel engines observed in a field test with passenger cars - Conventional oil analysis and fuel dilution, Tribol Int 2021; 161. https: / / doi.org/ 10.1016/ j.triboint. 2021.107079. [4] Dörr N. et al.: Engine oils in the field: a comprehensive chemical assessment of engine oil degradation in a passenger car. Tribol Lett 2019; 67: 68. https: / / doi.org/ 10.1007/ s11249-019-1182-7. [5] DIN ISO 6618: 2015-07. Petroleum products and lubricants - Determination of acid or base number - Colour-indicator titration method. Berlin: Deutsches Institut für Normung; 2015. [6] DIN ISO 3771: 1985-04. Petroleum products; total base number; perchloric acid potentiometric titration method. Berlin: Deutsches Institut für Normung; 1985. [7] Agocs A. et al.: Production of used engine oils with defined degree of degradation in a large-scale device. Acta Tech Jaurinensis 2020; 13(2): 131-50. https: / / doi.org/ 10.14513/ actatechjaur.v13.n2.546. 23rd International Colloquium Tribology - January 2022 101 An experimental study of the effect of thermal aging on the lubrication performance of Environmental Acceptable Lubricants (EALs) Mar Combarros IQL, Castellgalí, Spain Corresponding author: m.combarros@iql-nog.com Ariadna Emeric IQL, Castellgalí, Spain Gerard Cañellas IQL, Castellgalí, Spain Ángel Navarro IQL, Castellgalí, Spain Marc Alumà IQL, Castellgalí, Spain Taro Ehara IQL, Castellgalí, Spain 1. Introduction Synthetic esters are currently used in many applications, including automotive and marine engine oils, gear oils, compressor oils, hydraulic fluids or greases since they can offer outstanding properties. These properties such as biodegradability, low temperature flow or thermal oxidative stability can be tailor-made by molecular design [1]. In this paper thermal-oxidative behaviour was investigated and its influence on tribological performance assessed. An ester degrades by two main mechanisms at high temperatures: physically, evaporation of the volatiles, and chemically, due to oxidation / polymerization but also to an evolution of gases CO, CO 2 , especially at higher temperatures [2]. These phenomena cause an increase in viscosity and formation of deposits which may limit the lubricant applications specially nowadays were an extended service life is usually required. 2. Methods 2.1 Materials The aging behavior of four different products was investigated. The influence of sterical hindrance in the propagation of the polymerization was studied using two different structures: Product A and B. The influence of antioxidant additives on polymerization was investigated adding a mixture of aminic/ phenolic antioxidant additives. Product C, product with no additives was compared to product D which has a 0.5 % of additive. Table 1: Main properties for the products used A B C D KV 40 °C (cSt) 67.1 68.7 100 100 KV 100 °C (cSt) 10.8 11.7 14.0 14.0 Viscosity index 152 165 141 137 AN (mgKOH/ g) 0.09 0.06 0.15 0.36 RSSOT (min) 144 159 247 1082 Volatility-TGA (%) 61 45 24 17 Thermo-oxidative properties were studied by means of RSSOT for the oxidation and TGA for its volatility. TGA measurements were measured in a large furnace after a 1h isothermal step at 250 o C. The main properties are shown in Table 1. 102 23rd International Colloquium Tribology - January 2022 An experimental study of the effect of thermal aging on the lubrication performance of Environmental Acceptable Lubricants (EALs) 2.2 Thermal aging: Thermal degradation was evaluated using 600 g of product in a round bottom flask, heated with an electrical heater at 180 o C for 168 h. As a catalyst 0.6 g of powder Fe was used. The product was maintained at a constant speed of 60 rpm with a magnetic stirrer and at open air. After the test, the product was vacuum filtered. 2.3 Analytical evaluation of aging The evolution of the aging process was monitored evaluating the change on total acid number, viscosity, weight, FT-IR, and GPC/ SEC. The presence of oxidized compounds was assessed using FT-IR [3]. The polymerization degree was evaluated using Permeation chromatography / size exclusion chromatography (GPC/ SEC) with a refractive index (RI) detector. GPC has been used by several researchers to study degradation of oils [4,5,6]. 2.4 Tribological performance analysis Stribeck curves were generated using a PCS Instruments MiniTraction Machine at 150 °C with an applied load of 36 N. An ANSI 52100 steel disk and a ¾” ball were used. A slide-to-roll ratio of 150 % was maintained during the measurements. 3. Results 3.1 Chemistry The mechanism by which the products are degraded is a radicalary mechanism. Initial steps of oxidation originate hydroperoxides, oxoand hydroxy-compounds and it is initiated by high temperatures. In later stages high molecular weight products are formed [2,7]. The main properties of the thermal aged products are depicted in Table 2. As we can see, viscosity increases in all four cases specially if the sterically hindrance degree is lower (Product A). During the aging process, volatiles have formed due to two main effects: physical effect of evaporation of the initial products and formation of low molecular compounds. Apart from that, the acid number also increases significantly in all cases. Thanks to the addition of an antioxidant, the initiation of polymerization can be delayed as we can see if we compare viscosity of product D with that of product C. From the FT-IR analysis (Figure 1) we can conclude that the polymerization is in a later stage since the presence of aldehydes is limited. This phenomenon can also be extracted from the GPC/ SEC analysis. Higher molecular weight products are present which relates to the viscosity increase. Table 2: Products properties after aging A B C D KV 40 °C (cSt) 1194 422 586 146 KV 100 °C (cSt) 83.1 41.8 45.6 17.6 Viscosity index 146 151 128 133 AN (mgKOH/ g) 26.9 16.5 10.5 5.5 RSSOT (min) 135 103 135 317 Weight loss (%) 22 17 8.6 2.9 Figure 1: FT-IR of product B 3.2 Tribology Figure 2: Stribeck curve for product A, before and after aging Lubricity studies of the compounds before and after aging show that the friction coefficient in the hydrodynamic regime increases because of the viscosity increase as we can see in the Stribeck curve, Figure 2. The higher viscosity of the products also diminishes the coefficient in boundary and mixed regime as a thicker film is formed. 23rd International Colloquium Tribology - January 2022 103 An experimental study of the effect of thermal aging on the lubrication performance of Environmental Acceptable Lubricants (EALs) 4. Conclusion As a result of the aging process, the main and most obvious change of the product is a viscosity increase due to polymerization and to a lesser extent, evaporation, and formation of gases. There are no relevant functionality changes after the aging process as we have seen per FT- IR analysis. Sterical hindrance of the product delays the propagation of the polymerization. Moreover, the presence of an antioxidant delays the oxidative initiation, extending the service life. The increase of viscosity due to polymerization increases coefficient of friction in hydrodynamic and it leads to a higher film formation in boundary. Using the presented methodology, degradation can be predicted; thus, we can design new organic structures extending service life while maintaining a superior performance. References [1] Boyde, S. (2020). Esters. In L. Rudnick, Synthetics, Mineral Oils, and Bio-Based Lubricants (S. Chapter 3). Boca Raton: : CRC Press. [2] Bakunin, V., & Parenago, O. (1992). A Mechanism of Thermo-oxidative Degradation of Polyol Ester Lubricants . Journal of Synthetic Lubrication. [3] Duong, S., Lamharess-Chlaft, N., Sicard, M., Raepsaet, B., Galvez, M., & Da Costa, P. (2018). New Approach for Understanding the Oxidation Stability of Neopolyol Ester Lubricants Using a Small-Scale Oxidation Test Method. ACS Omega, 3, 10449-10459. [4] Ali, A., Lockwood, F., Klaus, E. E., & Duda, J. L. (1979). The Chemical Degradation of Ester Lubricants. ASLE Trans., 267-276. [5] Mousavi, P., Wang, D., Grant, C., Oxenham, W., & Hauser, P. (2005). Measuring Thermal Degradation of a Polyol Ester Lubricant in Liquid Phase. Ind. Eng. Chem. Res., 44, 5455-5464. [6] Wu, Y., Li, W., Zhang, M., & Wang , X. (2013). Oxidative degradation of synthetic ester and its influence on tribological behaviour. Tribology International, 16-23. [7] Yu, Z., & Yang, Z. (2011). Fatigue failure analysis of a grease-lubricated roller bearing from an electric motor. J. Fail. Anal. Prev., 11, 158-166. 23rd International Colloquium Tribology - January 2022 105 Enhanced engine lifetime by use of premium fuel Marcella Frauscher AC 2 T research GmbH, Wiener Neustadt, Austria Adam Agocs AC 2 T research GmbH, Wiener Neustadt, Austria Thomas Wopelka AC 2 T research GmbH, Wiener Neustadt, Austria Andjelka Ristic AC 2 T research GmbH, Wiener Neustadt, Austria Florian Holub OMV Downstream GmbH, Vienna, Austria Wolfgang Payer OMV Downstream GmbH, Vienna, Austria Summary In order to evaluate the impact of premium fuels containing elevated levels of friction modifier (FM) additives regarding wear, engine test bench investigations were performed with a conventional fuel and with a premium fuel containing FM. All tests utilised an artificially aged engine oil that simulated the condition of a reference used oil after 25,000 km of operation. Thus, a large-scale artificial ageing of 180 L engine oil was carried out with oil condition monitoring by means of conventional parameters and high-resolution mass spectrometry. Oil analysis confirmed a comparable condition of the artificially aged oil with the reference used oil. Additionally, SRV ® tribometer experiments with the artificially aged oil proved a significantly higher coefficient of friction compared to the fresh oil but similar tribological performance compared to the reference used oil. During the engine bench tests, wear was monitored via wear particle concentration in the oil by means of optical emission spectroscopy as well as by radio isotope concentration method with activated piston rings. Both analytical methods found a significantly lower wear in the engine bench test operated with premium fuel with FM compared to tests with conventional fuel. Moreover, subsequent used oil analysis from bench test oil samples by mass spectrometry showed a transfer of the FM from the fuel into the engine oil. In particular, an increase in FM with proceeding engine operation time was observed. Hence, the usage of premium fuels may lead to enhanced engine lifetime. 1. Introduction In times of high claims towards sustainability the possibility to enhance lifetime of combustion engines by boosting aged engine oil via high-quality fuels with elevated levels of additives such as FM is a topic of high interest in the automotive and fuel sector. Within this study, a comprehensive approach was chosen comprising the artificial generation of an engine oil commercially available but in a well-defined condition comparable to an oil towards its end of lifetime, engine test rig runs with basic and premium fuels, and high-resolution wear measurement as well as mass spectrometry. The results revealed a significant impact of the fuel quality on the engine oil as well as on the occurring wear in the engine. 2. Materials and methods A reference used oil after 25,000 km of operation was characterised by conventional parameters such as oxidation or viscosity, and high-resolution MS to identify the residual FM content. According to this condition a largescale artificially oil alteration similar as described in [1] using elevated temperature, synthetic air and shear stress was conducted. This resulted in 180 L aged oil with the same characteristics as the reference used oil, and almost fully degraded FM. 106 23rd International Colloquium Tribology - January 2022 Enhanced engine lifetime by use of premium fuel The similarity was not only shown by analytical results, but also with SRV ® tribometer experiments. Experiments were carried out with following parameters: 100Cr6 polished plate 100Cr6 standard ball, 50 N, 1 mm and 30 Hz. Aliquots of the fresh, the artificially aged and the reference used oil were tested. As top compression rings in the engine test rig, standard X90CrMoV18 rings were used for the engine bench test. For the wear measurement with the radio-isotope concentration (RIC) method the piston rings were activated in a cyclotron facility, which means that a known amount of radioactive tracer isotopes was produced within a surface layer of the piston rings with a few micrometres thickness. As tracer isotope Co57 was used. The RIC method mainly consists of a gamma radiation detector, which detects the emitted gamma activity of the tracer isotopes. The amount of wear can be derived with two methods: 1) by measuring the activities of each piston ring before and after the bench test. The difference of the measured activities can be converted to a wear volume or wear height, and 2) by measuring the activity of the lubricant which transports the wear particles containing the tracer isotopes to the radiation detector in a closed lubricant circuit [2]. The latter method can be used as continuous wear measurement during a test run, which was not done in this study. Engine test rig experiments with artificially aged oil without noteworthy residual FM content were performed with commercially available basic and premium fuel, whereas the premium fuel contained an additive package including a higher dose of FM. At the beginning, during the experiment and at the end of the test rig runs (120 h in total) oil sample aliquots were taken to monitor the FM content via MS. Additionally, the activated piston rings were measured by RIC and wear was determined after the test runs. For the determination of the piston ring wear the piston ring activities were measured before and after the engine bench test in a well-defined position. These measurements were repeated thirty times for statistical reasons to reduce the uncertainties. The wear volume or average wear height were calculated from the differences of the activities before and after the engine bench test. 3. Results 3.1 Artificial oil ageing in large scale In accordance to the reference used oil (25,000 km) the artificially aged oil was produced with an oxidation of 18 A/ cm, fully consumed anti-wear additive and partially consumed antioxidants within 55 hours in a large-scale alteration device (see figure 1). Figure 1: An increasing oxidation while partially to fully depletion of additives was detected during large scale artificial ageing. A viscosity index decrease, which indicates the decomposition of the oil by the applied shear stress during the entire time, and an oxidation increase was monitored during the entire ageing process. The FM depletion was determined in the end sample by MS. It was confirmed that in the desired end condition of the aged oil, the antiwear additive as well as the FM were fully depleted (see figure 1). To show the similarity in performance with the reference used oil from the field SRV ® tribometer experiments were performed. Both, the artificially aged oil as well as the reference used oil showed similar results regarding coefficient of friction and friction curve, while the fresh oil was performing significantly better. 3.2 Piston ring wear with RIC Table 1 shows the results of the RIC wear measurements of the piston rings for test runs carried out with basic fuel without FM and premium fuel containing FM. The wear volume is the total wear volume worn off throughout the whole test and the wear height is meant to be the average wear height over the whole running surface calculated by dividing the wear volume by this surface area. The results are given as relative values comparing the premium with the basic fuel. Table 1: piston ring wear volume and average wear height for engine bench tests without (basic fuel) and with (premium fuel) friction modifier (FM) relative to each other Test specification Piston ring wear volume Piston ring wear height Basic fuel 100 % 100 % Premium fuel 23,69 % 23,77 % The results show a significant reduction in wear volume for the premium fuel compared to the basic fuel by more than a factor of 4. 23rd International Colloquium Tribology - January 2022 107 Enhanced engine lifetime by use of premium fuel 3.3 Characterisation of used engine oil with MS During both engine test rig experiments, with basic and premium fuel, engine oil aliquots were taken, and elemental analysis and MS measurement were conducted. The elemental analysis revealed a faster and slightly higher increase of iron in the oil with increasing running time for the test with basic fuel not containing any friction modifier. The MS explains this observation by revealing significant differences in the engine oil samples. While for both engine oil series only a slight decrease of antiwear additives and phenolic antioxidants was found there was a significant change regarding the FM content and the aminic antioxidants. The samples from the experiment with basic fuel did not only show no FM increase, but also a higher degree of aminic antioxidant depletion, further increasing with longer operation time. For the engine test rig performed with premium fuel a considerable amount of FM was detected in the oil samples. This content was increasing over the operation time, and at the same time degradation products were built up. Compared with the content in the premium fuel itself, a remarkably higher amount of FM was found in the engine oil after 120 h of operation time than in the pure premium fuel. This indicates a transfer from the fuel to the engine oil, and an accumulation of the FM over time as depicted in figure 2. Figure 2: Mass spectra of the premium fuel containing FM, engine oil samples after large-scale ageing with fully depleted FM, and samples after an operation time from 15 - 120 h. 4. Summary and conclusion By using the large-scale ageing device with selected and pre-defined conditions, the generation of a test oil similar to a reference used oil regarding the desired oil parameters was enabled. The degradation of the FM was detected by high-resolution MS in both oils, the reference used oil as well as the artificially aged oil and their similar performance was confirmed by SRV ® tests. Engine test rig experiments with activated piston rings were performed using a basic fuel without FM and a premium fuel including a FM additive package. RIC measurements of the piston rings revealed a considerably higher wear when using the basic fuel compared to test runs with premium fuel. MS measurements of engine oil samples were able to explain this effect, as an accumulation of FM additive in the oil when using premium fuels was observed. A transfer from fuels containing FM additives in certain amount takes place, and an improvement in wear behaviour is achieved. This effect was additionally observed with piston rings already showing wear from previous test runs. Hence, an enhanced lifetime by wear reduction when a premium fuel is used regularly can be concluded. 5. Acknowledgements The work presented was funded by the Austrian COMET program (Project InTribology, Nr. 872176) and carried out at the “Excellence Centre of Tribology” (AC 2 T research GmbH). References [1] Besser C., Agocs A., Ronai B., Ristic A., Repka M., Jankes E., McAleese C., Dörr N.: Generation of engine oils with defined degree of degradation by means of a large scale artificial alteration method, Tribol. Int., Vol 132, p 39-49, Elsevier B.V., ISSN 0301-679X, DOI 10.1016/ j.triboint.2018.12.003, 2018 [2] Jech, M. (2012): Wear Measurement at Nanoscopic Scale by means of Radioactive Isotopes. Vienna University of Technology. 23rd International Colloquium Tribology - January 2022 109 Influence of mechanical, thermal, oxidative and catalytic processes on the thickener structure and thus on the service life of rolling bearings Markus Grebe Competence Center for Tribology, Mannheim University of Applied Sciences Corresponding author: m.grebe@hs-mannheim.de Michael Ruland Competence Center for Tribology, Mannheim University of Applied Scien 1. Introduction Constant further developments in application technology with the aim of higher economic efficiency and power density place ever greater demands on mechanical components and construction elements and thus also on the lubricating greases used. This is particularly true in the area of roller bearings, in which lubricating greases are often used with high mechanical stress and in wide temperature ranges. A current example is the rolling bearings in the assemblies of hybrid vehicles, which are subjected to extreme thermal and mechanical loads due to engine downsizing, high speeds and the radiant heat from the combustion engine. Investigations at the Competence Center for Tribology Mannheim (KTM) show that the grease service life for roller bearing lubrication, even at high temperatures, does not only depend on classic oil aging [Greb18]. In numerous roller bearing tests and by means of rheological measurements it could be shown that the loss of the lubricating effect is often a consequence of the change in the thickener structure [Greb19]. Mechanical, thermal, oxidative and catalytic processes play a decisive role here. As part of the lecture, the current status of a DGMK project will be presented, in which the significance of these individual influencing factors on the change in the thickener structure and thus on the bearing life is determined through targeted individual investigations and detailed tests. The calculation of the service life of grease-lubricated rolling bearings is based on the fatigue strength of the bearings in accordance with ISO 281. However, under critical operating conditions, such as high temperatures, failure due to a lack of lubrication occurs even before this fatigue limit is reached. Since many roller bearing systems are lubricated for life in practice, the service life of the bearing depends on the service life of the grease and not on the fatigue life of the bearing. The service life of the grease, however, is not a clearly determinable characteristic value that can easily be determined by a standard test. For this reason, various laboratory aging processes (RapidOxy, TGA, DSC), laboratory tests (Shell roller) and endurance runs in roller bearing test rigs (e.g. FE8-test, FE9-test, R0F-test) are usually used in development in order to obtain information about the expected service life of a component. These tests are very time-consuming and costly, so that the industry is constantly looking for new, innovative and meaningful screening tools [Greb2021]. In the DGMK project 788 “Screening test method for lubricating greases” it was shown that the loss of the lubricating effect of a grease is strongly influenced by the thickener degradation. Recent publications by other scientists confirm this hypothesis and reinforce the need for research [e.g. Dorn16, Kuhn17, Yuxi18, Zhou18]. In the case of soap thickened greases, this effect has been shown to occur well before the actual base oil aging and is accordingly limiting service life. The catalytic effect of the cage material apparently has a different and previously unknown effect on this effect than on classic oil aging. The current running research project aims to clarify which influencing factors ultimately play the decisive role and how the effect can be positively influenced. In technical applications, a wide variety of causes can lead to irreversible damage to the lubricants. A thermo-oxidative degradation depends strongly on the ambient conditions. In non-encapsulated systems, the oxidation of the lubricant leads to the formation of acids, polymers, condensates and deposits. This process depends on the temperature, the presence of catalysts such as metal surfaces or wear debris, the oxygen supply and the aging products produced. Furthermore, coking effects can occur due to the aging of the lubricating grease and thus the degradation and polymerization of the lubricating grease, but 110 23rd International Colloquium Tribology - January 2022 Influence of mechanical, thermal, oxidative and catalytic processes on the thickener structure and thus on the service life of rolling bearings also due to insufficient lubrication, especially at elevated temperatures and high speeds [Klein98; Brau15]. In addition to thermo-oxidative aging, a lubricating grease is also subject to high mechanical-dynamic stress in use. The importance of the individual influencing factors was clearly shown in the recent DGMK project 788. The focus of this follow-up project will be on changing the thickener structure as a result of mechanical, thermal, oxidative and catalytic stress. The chemical and structural changes are detected and examined using the most modern analytics and microscopy: • Mechanical stress: FE9, Walk apparatus according to Klein (Figure 1) • Structure of the thickener system: scanning electron microscopy, partly “cryo-SEM” • Rheology: Yield stress, flow curves, elastic and plastic modulus • Aging: RapidOxy, TGA, DSC, oven aging [Dorn19] • Analytics: FTIR, HPLC-MS, GC-MS, PDSC, ICP. Figure 1: Shear tester acc. Klein This project is based on an empirical approach. That means, numerous laboratory tests on aging depending on temperature, ambient medium and catalytic elements will be carried out and evaluated. The focus is on the so-called RapidOxy test, as this is becoming increasingly important in industry (ASTM D8206, DIN 51808) [Matz2021]. The main part of the tribological tests will be application-oriented roller bearing tests on the multi-station roller bearing test bench MPWP based on the FE9 test. Different parameters and bearing types are tested. These tests are supplemented by high-speed tests in order to meet the special requirements of e-mobility. The aim is to gain knowledge for the first time as to how the thickener structure changes during aging and mechanical stress, how this can be proven and what influence this has on the lubrication and thus on the performance and service life of the rolling bearing. 2. First test results Figure 2 shows the different run times in the FE9-test for all 8 model tests. Figure 2: Run times of the different model greases in the FE9 test (blue mineral oil based, red: PAO) With the help of the apparatus acc. Klein, greases can be sheared under defined conditions. The grease is pumped in a circle, which works like a gear pump. The change in the rheological parameters (yield point & loss modulus) is then determined using a rheometer measurement. Figure 3 shows the derease of the shear stress of the modell greases after 24h and 72 h. Figure 3: Decrease in shear stress at 3 1 / s after 24h or 72h in the shear test acc. Klein 3. Conclusion As part of the project, the influence of individual effects on the change of the thickener structure of a lubricating grease is examined. The procedure and the first detailed results were presented here. Further test results will be shown during the lecture. 23rd International Colloquium Tribology - January 2022 111 Influence of mechanical, thermal, oxidative and catalytic processes on the thickener structure and thus on the service life of rolling bearings References [Klei98] Kleinlein, E.: Einsatz von Wälzlagern bei extremen Betriebs- und Umgebungsbedingungen, expert Verlag, Renningen, ISBN 3-8169-1608-2, 1998. [Brau15] www.braun-waelzlager.de. [Dorn16] Dornhöfer, G.; Ermittlung der Schmierfettgebrauchsdauer mit zeitraffender Prüfmethode und Übertragbarkeit; Tagungsband GfT-Jahrestagung; 2016. [Kuhn17] E. Kuhn: Modellierung zum Schmierfettverschleiß im stationären Reibungsprozess; Tagungsband GfT-Jahrestagung; 2017. [Yuxi18] Yuxin Zhou, Rob Bosman & Piet M. Lugt (2018) A Model for Shear: Degradation of Lithium Soap Grease at Ambient Temperature, Tribology Transactions, 61: 1, 61-70. [Zhou18] Yuxin Zhou, Rob Bosman, Piet M. Lugt (2018) A Model for Shear Degradation of Lithium Soap Grease, Trib. Trans. 61: 1, 61-70, DOI: 10.1080/ 10402004.2016. 1272730. [DGMK788] Abschlussbericht des Forschungsvorhabens 788; IGF-Vorhaben Nr. 18615 N: 12/ 2018. [Greb18] M. Grebe; C. Müller; J. Molter; S. Hiesinger: Einflussfaktoren auf die Schmierfettgebrauchsdauer im Wälzlager, 59.Tribologie-Fachtagung 2018, Gesellschaft für Tribologie e. V. (GfT), ISBN 978-3- 9817451-3-9. [Greb19] M. Grebe, J. Molter; T. Isik: Einflussfaktoren auf die Schmierfettgebrauchsdauer; 60. Tribologie-Fachtagung, Gesellschaft für Tribologie e. V. (GfT), Tagungsband 2019; S. 418 - 427; ISBN 978-3-9817451- 4-6. [Matz21] Matzke M., Beyer-Faiss S., Grebe M., Höger O.: Thermo-oxidative grease service life evaluation - laboratory study with the catalytically-accelerated method using the RapidOxy; Digitaler Tagungsband 62. Tribologie-Fachtagung, Gesellschaft für Tribologie e. V. (GfT), 2021. [Greb2021] Grebe, M: Tribometrie - Anwendungsnahe tribologische Prüftechnik als Mittel zur erfolgreichen Produktentwicklung; Expert- Verlag, ISBN 978-3-8169-3521-6 (print), 2021. 23rd International Colloquium Tribology - January 2022 113 The unexpected active behaviour of synthetic esters as cobase stocks on resistance to oxidation Siegfried Lucazeau NYCO, Paris, France 1. Introduction Synthetic esters are group V, performance base fluids recognised as being highly resistant to thermo-oxidation. In particular, neopolyol esters demonstrate outstanding performance in high temperature environments. As a result, neopolyol esters are used in high temperature applications such as jet engine oils, turbine oils, high pressure compressor oils, or high temperature chain oils, where they provide extended lifetimes, excellent stability in operation and added cleanliness for the equipment. Beside full ester formulations, esters may also be used as components or cobase fluids. Whilst they have long been used as components of PAO based formulations to ensure the solubility of additives and as seal swell agents, they may also prove to be useful as boosters of thermo-oxidative performance. 2. Esters as boosters The neopentyl structure found in neopolyol esters combines inherent resistance to thermal degradation, as well as steric hindrance protecting, to various extents depending on structure, hydrogen atoms from oxygen attack. Such a structure not only delivers resistance to thermo-oxidation but also favours degradation pathways resulting in reduced sludge and deposit formation. When introduced in ISO VG 32 and ISO VG 100, gr II and PAO based compressor oils formulations, neopolyol esters did improve resistance to oxidation and cleanliness, as illustrated by ASTM D4636 oxidation test, GFC- Lu-27-A-13 Micro-Coking Test and thermogravimetric analyses. Whilst it is somewhat expected that introducing an oxidatively stable base fluid in a formulation proportionally reduces the effects of oxidation, things may not be that intuitive. • Performance in oxidation test does not follow the treat rate of ester, lower treat rates seem to generate better results in some cases • Thermogravimetric curves do not always show different kinetics with various ester treat rates The above findings rule out any proportionality mechanism or dilution effect of esters. In addition, the detergency effect brought by esters may explain cleaner metal plates in the MCT test but does not shed light on the oxidation or thermogravimetric test results. It looks as if esters could stabilize the whole formulation against oxidation, just like an antioxidant would. The question therefore lies in the antioxidant/ ester system in the formulation: is there an interaction between antioxidants and esters that would extend the action of the antioxidant? Figure 1: Micro-Coking Test and ASTM D4636 test results 3. Interactions between esters and antioxidants Further thermogravimetric testing shows that in the absence of antioxidant, the ester does not improve much the ability of the formulation to resist oxidation. Furthermore, these curves do show an Oxidation Induction Time that seems to be dependent upon the treat rate - a behaviour that is observed on formulations using various treat rates of antioxidant (the higher the treat rate, the longer the OIT). 114 23rd International Colloquium Tribology - January 2022 The unexpected active behaviour of synthetic esters as cobase stocks on resistance to oxidation This goes to show that the ester/ antioxidant system behaves like a longer lasting antioxidant, just as though the antioxidant was protected by the ester. Figure 2: Thermogravimetric analysis - 175°C, oxygen ISO VG 32 formulations 4. Going further Since metals from additives (Zinc, Molybdenum, Calcium, Magnesium…) may act as anti or pro-oxidants, it would be interesting to extend that study to determine if some metals are able to further synergize with the antioxidant/ ester system or if the presence of some metals are detrimental to this mechanism. 5. Conclusion Esters may be used in high performance lubricants, as full base fluids. They may also be introduced as cobase fluids to improve stability at high temperature. They are able to act as antioxidation and cleanliness boosters for mineral oils or PAO based formulations, using cost effective treat rates as low as 5%. One hypothesis is that esters combine with antioxidants to make them deplete more slowly and be more stable. But this is only one of the benefits that may be expected from introducing synthetic neopolyol esters in mineral oil or PAO based formulations. 23rd International Colloquium Tribology - January 2022 115 Next-generation anti-wear development Christelle Chretien SOLVAY, Bristol, PA - USA christelle.chretien@solvay.com 1. Introduction To protect our health and our environment, cleaner transportation is urgently needed, with an ultimate goal of zero emissions and carbon neutral. To achieve it, the following solutions have to be developed: • Solutions for electric vehicles (EV): more robust anti-wears (AW)/ EP for E-driveline lubricants • Solutions decreasing friction for both Internal Combustion Engines (ICE) and E-drivelines to save fuel and electricity • Solutions free of Metal and Sulfur for cleaner gas emission and better compatibility with E-drivelines. The objective of this paper is to present: • Introduce the technology of next-generation anti-wear • Describe its main benefits 2. Purpose of this project The objective of this project is to develop a next generation of anti-wear additive presenting the following features: • Ashless, Sulfur-free, and low phosphorus content • Providing equivalent or better wear prevention and improving energy efficiency 3. Technology description As the toolbox of chemicals is more and more limited, the idea is to look out-of-the-box and develop a technology of anti-wear not existing today in the industry. The technology we propose as a next-generation anti-wear is very unique as: • The Phosphorous so the anchoring group is outside of the backbone of the polymer bringing a freer access to the surface • It is based on a co-polymer. Different monomers are used to achieve the right balance between surface adhesion and oil solubility. This technology can be depicted as the following: Figure 1: Polymeric Anti-Wear (Polymeric AW) 4. Prior art analysis This analysis of the prior art shows the uniqueness of this Polymeric AW technology as: • It directly coats the surface as a polymer when ZDDP reacts first with the surface to form a polymeric tribofilm on the surface. • It’s anchoring group is easily reachable as it is outside of the backbone. 4.1 Standard anti-wear technology Zinc dialkyldithiophosphate (ZDDP) is the standard anti-wear additive technology in the lubricant industry in a wide majority of applications. To form a tribofilm, ZDDP decomposes into long polyphosphate films which are polymers, under high loads and high temperatures [1]. ZDDP provides very good anti-wear performance at an optimized cost. It is multifunctional as it also provides 116 23rd International Colloquium Tribology - January 2022 Next-generation anti-wear development extreme pressure, anti-oxidation and corrosion inhibition [2]. Its drawback is that it contains Zinc and Sulfur producing harmful vehicle emissions, impacting some types of wear and yellow metallic surfaces. In addition, its performance on fuel economy is quite limited. New regulations, hardware and specifications require today to develop alternatives. 4.2 Polymeric Anti-wear To understand the patent landscape on anti-wear, a patent search was conducted focusing on anti-wears in lubricants. 475 patents appeared from this search. By focusing specifically on polymeric anti-wears, only 5% of the patents claim the use of polymeric antiwears with polyphosphorus and fluorinated polymers. For exemple, the patent application US 2012/ 0309656 claims the use of a polyphosphate in combination with an anti-oxidant to have a better wear prevention in automotive application. Figure 2: Polyphosphate 5. An Innovative solution under development Among the different candidates developed at a lab scale, one candidate has shown leading performances with 11 benefits identified: • Metal-free, Sulfur-free and very low Phosphorus content • Good anti-wear performance • Friction level similar to ZDDP • Tremendous thermo-oxidative stability • Very low sludging tendency • Harmless on viscometrics, foam, and corrosion • Excellent solubility in standard base oils • Very low acidity level Major highlights are: 5.1 Physico and Chemical properties This transparent liquid solution has both a very low phosphorus content at 0.32wt% with a low TAN at 7 mg KOH/ g. 5.2 Anti-wear performances Based on the Falex Pin and Vee wear test, a 45% decrease in wear was observed compared to ZDDP when both used at 1wt% in a Group II base oil. Figure 3: Falex Pin and Vee wear evaluation 5.3 Viscometrics Slight to no increase was observed on the kinematic viscosity after the addition of 1wt% of Polymeric AW. Shear stability and cold flow properties are not impacted when using 1wt% of Polymeric AW in a group II base oil showing a viscosity loss of only 0.3% after a 20 hour KRL. 5.4 Oxidation and thermal stability No impact on a fully formulated oil top treated with 1wt% Polymeric AW after 192 hours at 160C of oxidation: equivalent kinematic viscosity, acid number and deposit formation: Figure 4: After oxidation for 196 hrs at 160C Thermal stability is outstanding as it is above 300C and leaving no residue. 23rd International Colloquium Tribology - January 2022 117 Next-generation anti-wear development 6. Conclusion The Polymeric AW technology shows strong potential as a next-generation anti-wear thanks to the different benefits it provides, on top of anti-wear prevention. Further evaluations are ongoing in fully formulated formulation and specifically in the EV segment to assess its potential. References [1] “Overview of automotive engine friction and reduction trends-Effects of surface, material, and lubricant-additive technologies”: DOI 10.1007/ s40544- 016-0107-9 [2] “ZDDP’s uncertain future” in the TLT Tribology & Lubrication Technology - September 2019 Greases 23rd International Colloquium Tribology - January 2022 121 Polyglycols as High Performant Base Oil Component in Modern Greases Cristina Schitco Clariant Produkte GmbH, Frankfurt am Main, Germany Corresponding author: cristina.schitco@clariant.com 1. Introduction The industrial growth, rise in automation, and the electromobility trend increase the need of high-performance greases [1]. Simultaneously, there is an increase focus on environmentally friendly greases to meet the worldwide sustainability efforts [2]. The base oil is a major component in greases and influences several important properties of the final product [3]. This work describes the relevant properties of polyglycols and how these synthetic base oils can meet the modern requirements of the grease formulators. 2. Chemical Structure and Properties Polyalkylene glycols (PAGs) are synthetic polymers with highly adjustable properties. By varying such factors like starting alcohol, amounts of ethylene and propylene oxide as shown in Figure 1, PAGs can be tailored to a manyfold of properties and application requirements. Some of the adjustable properties include viscosity, viscosity index, polarity, miscibility in various oils, pour points, thermal properties, lubrication, etc. PAGs can be theoretically available in any ISO VG class, e.g., starting with ISO VG 15 up to ISO VG 1000 and beyond. Figure 1: Chemical structure of a PAG. R stands for the starting alcohol 2.1 High Temperature Behavior PAGs posses typical flash points well above 200 °C. The flash points depend on the molecular weight and polarity, i.e., the amount of ethylene oxide contained in the molecule. Higher the molecular weight and the polarity of the molecule, higher flash points up to 270 °C can be observed. The thermal-oxidative resistance rises with the ethylene oxide and molecular weight as well. PAGs have a clear burn-off which facilitates the cleaning processes. 2.2 Material Compatibility and Oil/ Oil Miscibility Material compatibility is an important parameter when choosing the base oil for a certain grease application. Incompatibilities may promote premature failure of the material or the entire system. PAGs are notoriously not compatible with simple paints. Our tests show that PAGs exhibit compatibility with EPDM RM 69, elastomer NBR 28/ SX, and two component epoxy-based primers Primer M 20 and P 22. Table 1 shows the results of EPDM compatibility test. Table 1: EPDM compatibility test in analogy to ISO 4925, average of two measurements, EPDM RM 69, 100 °C, 7 days ISO VG 46, hydrophilic * requirements ISO 4925 Relative change in volume +0,9% min. 0% max. 10% Change in hardness IRHD -3 min. -15 max. 0% * contains antioxidant package The miscibility of PAGs depends strongly on its molecular weight and hydrophobicity. Low molecular weight hydrophobic PAGs are typically miscible in low viscous naphtenic, parrafinic, vegetable, or some type of esters, e.g., polyol esters, trimelliate esters. In limited concentrations, the low molecular weight hydrophobic PAGs are miscible in low viscous polyalphaolephines (PAOs). 2.3 Low Temperature Behavior The pour points of the base oils are an important characteristic for the low temperature applications. The pour points of the PAGs are typically low, decreasing with the increase of propylene oxide content and the decrease of molecular weight. Hydrophobic PAGs reach pour points well below -50 °C as shown in Table 2. Tailored version can reach values even below -70 °C. 122 23rd International Colloquium Tribology - January 2022 Polyglycols as High Performant Base Oil Component in Modern Greases Table 2: Pour points of selected PAGs according to DIN ISO 3016 type of PAGs pour point (°C) ISO VG 15, hydrophobic -66 ISO VG 100 - 1000, hydropho-bic -40-36 ISO VG 46 - 1000, hydrophilic -50-35 ISO VG 15, hydrophilic, modified -72 * * according to ASTM D 7346-14 2.4 Lubrication Properties High Viscosity Index (VI) allows applications over a wide range of temperatures. Polyglycols have typically very high VI, e.g., around 200 - 290, allowing high load carrying capacities. One of the strongest benefits of PAGs lies in its lubrication properties. Figure 2 shows a SRV curve of an ISO VG 1000, hydrophilic PAG, non-additivated. Figure 2: SRV curve of an ISO VG 1000, hydrophilic PAG according to DIN 51834-2-2010 at 50 °C The friction coefficient remains stable over the entire run of the test, with a value of around 0,1. The wear scar shows a low average value for a non-additivated oil of only 0,560 mm. 2.5 Heat Transfer Properties Figure 3: Thermal conductivity of several PAGs measured by TPS technique: 0°C (first column), 50 °C (second column), 100 °C (third column) Hydrophilic PAGs possess high thermal conductivity in the range of 0,19 W/ m/ K suitable for applications which require high heat transfer properties. On the other hand, hydrophobic PAGs display lower thermal conductivities in the range of 0,16 W/ m/ K. 2.6 Sustainability and Regulatoric Considerations PAGs have an excellent sustainability profile. Nearly all hydrophilic PAGs up to ISO VG 1000 and the hydrophobic PAGs up to VG 100 are readily biodegradable. With very few exceptions, nearly all PAGs are label free. 2.7 Grease Formulation To show case the use of a PAG in grease application, a Li/ Ca mixed grease of NLGI 2 has been manufactured based on an ISO VG 15, hydrophilic PAG with a very low pour point of -72 °C. The properties of the grease are compared with a similar grease based on PAO in Table 3. To highlight is the high VI of the PAG oil and superior mechanical stability of the PAG based grease. Table 3: Comparative properties of a PAG and PAO from ISO VG 15 properties PAG grease PAO grease Oil Viscosity index 1 210 127 Pour point 2 (°C) -73 -75 Grease Consistency 3 275 281 Work stability 3 291 322 Drop point 4 (°C) 186 190 Oil separation 5 -2,3 -6,7 Wear scar 6 (mm) 0,54 0,73 1 ASTM D 2270, 2 ASTM D 7346-14, 3 ASTM D 217, 4 ASTM D 566, 5 ASTM D 1742, 6 ASTM 2266 3. Conclusion The polyglycol class of synthetic fluids offer a lot of development opportunities for the grease formulators. The PAGs are especially suitable for those grease applications requiring excellent lubricity properties, low pour points, and superior sustainability profile. References [1] Andrew, J. M., “The future of lubricating greases in the electric vehicle era”, Tribology and Lubrication Technology, 75, 5, 2019, 38-44. [2] Commission Decision 05/ 360/ EC of 26 April 2005 establishing ecological criteria and the related as- 23rd International Colloquium Tribology - January 2022 123 Polyglycols as High Performant Base Oil Component in Modern Greases sessment and verification requirements for the award of the community eco-label to lubricants, Off. J. E.C., 2005, p. L118. [3] Fischer, D., Jacobs, G., Stratmann, A. and Burghardt, G., “Effect of base oil type in grease composition on the lubricating film formation in EHD contacts”, Lubricants, 32, 6, 2018. 23rd International Colloquium Tribology - January 2022 125 Less Could Be More - Formulating High-Performance Greases Mehdi Fath-Najafi Nynas AB, SE-418 78 Gothenburg/ Sweden Corresponding author: Mehdi Fathi-Najafi - mefa@nynas.com George Diloyan Corresponding author: Mehdi Fathi-Najafi - mefa@nynas.com Nanotech Industrial Solutions Inc., Avenel 07001, NJ, USA Jinxia Li Nynas AB, SE-149 82 Nynäshamn/ Sweden 1. Abstract Proper lubrication is one of the core parts for equipment protection and life. To meet industry demands, grease manufacturers continuously improve the performance of the lubricating greases. The vital parameters such as extreme pressure, shock, wear, friction, shear, temperature, and presence of water are affecting the performance of the grease and subsequently the life of the tools and the productivity. Thus, formulators of the lubricating greases have to consider all the above parameters when designing a high-performance grease. Obviously use of various additives are “must” in most of the high-performance greases, but then both higher cost and some difficulties to predicate the behaviors of the product in a “real life” condition. For example, it is well known that some of the additives may interfere with each other or/ and result to chemical interaction with the metal surface which in some cases are undesirable. The aim of this work was to investigate the possibilities of developing a high-performance grease with two main features; 1) chemically neutral character such as solid lubricants and 2) as few components as possible which may also result to a reasonable cost for the formulators. 2. Introduction Industries widely use solid particles to enhance its tribological properties such as extreme pressure (EP), wear and friction. Micron size and platelet/ lamellar structure particles of WS 2 , MoS 2 , PTFE and Graphite have been known as a lubricious solid and widely used in various industrial applications. Tribological properties such as antifriction, Anti-Wear (AW) and extreme Pressure (EP) properties in greases play a very important role in industrial applications such as mining, automotive, steel production etc. The aim of this work was to demonstrate the possibility of formulating a high-performance grease with fewer components by using different solid lubricants instead for traditional anti-wear and extreme-pressure additives. 3. The Solid Lubricants IF-WS2 nanoparticles are spherical particles that were invented in 1992 by Reshef Tenne in the Weizmann Institute of Science. In this paper a paste dispersion of IF-WS 2 nanoparticles has been tested in various type of greases. Then, wear, friction, and extreme-pressure characteristic along with other physical properties have been evaluated and benchmarked against MoS 2 . Previous studies have demonstrated that IF-WS 2 nanoparticles provide excellent shock absorbing properties along with anti-wear, anti-spalling and pitting, friction reducing, and extreme pressure properties due its morphology and size, [2]. 4. Experimental work & Results The thickener type that was selected for this study was lithium complex and the base fluids were naphtenics, and the blends of naphthenics with paraffinic Gr I, II and polyalfaolefine respectively. More details of the selected naphthenic oils could be found on the website of Nynas, [3]. In total six different greases were prepared with different base oils. Table 1 shows properties of the base oils used in this study. The thickener consisted of lithium hydroxide, 12-hydroxy stearic acid and azelaic acid. Notable that the manufacturing conditions were kept constant for all six greases. IF-WS 2 and 2H-MoS 2 were mixed in the LiX base greases using FlakTec Speed Mixer IF-WS 2 and MoS 2 solids were tested at 0.25% and 1.00% respectively in each grease sample. 126 23rd International Colloquium Tribology - January 2022 Less Could Be More - Formulating High-Performance Greases Table 1: Typical characteristics of the base oils used in the preparation of the greases. Remarks Base Oil Visc. @40 °C, (mm 2 / s) Visc @100 °C, (mm 2 / s) Pour Point, (°C) Oil 1 Napht A 700 29.0 -15 Oil 2 Napht B 600 21.8 -12 Oil 3 Napht B + Paraf (Gr II) 194 14.9 -30 Oil 4 Napht B + PAO 198 14.8 -30 Oil 5 Napht B + Paraf (Gr I) 200 14.3 -27 Oil 6 Napht C + PAO 75 8.7 -42 In total six grease formulations were evaluated in this study in which the base oils described in Table 1 were used. Results in Figure 1 below demonstrates that the Lithium complex grease with IF-WS 2 particles even at low percentages increase the performance in extreme pressure and wear. Figure 1: EP properties comparison of tested samples according to ASTM D2596 MoS 2 particles showed some friction reducing properties however no improvements in EP properties and in some cases increased wear. It is worth to note that Grease #2, that contained naphthenic oil, showed significantly high EP properties and overall excellent tribological properties. 5. Summary The aim of this work was to investigate possible platforms to produce high performance grease with minimized components. Both to have high tribological and physico-chemical properties yet at lower cost. Within the frame of this study, six lithium complex greases were produced based on various naphthenic base oils as well as blends of naphthenic oils and paraffinic group I, II and polyalfaolefine respectively. Although, the use of naphthenic base oil has reduced the thickener content, but a direct correlation between the viscosity of these naphthenic base oils and the thickener content, the degree of oil separation and the mobility of the greases at -20 °C were also been found. The work benched marked two solids - MoS 2 and IF- WS 2 . The outcome demonstrated if one percent of IF- WS 2 is used in Lithium complex grease significantly higher load carrying capability (620kgf weld point) and up to fifty percent reduction in wear will be obtained. The unique spherical shape of IF-WS 2 and sub-micron size, could be responsible for the significantly better performance to the final lubricant formulation when compared with MoS 2 . Reference [1] H. Zhang, S. B. Lu, J. Zheng, J. Du, S. C. Wen, D.Y. Tang, and K.P. Loh, Optics Express, 22 (6), (2014), 7249 [2] P.U. Aldana, F. Dassenoy, B. Vachera, T. Le Mognea, B. Thiebautb, A. Bouffet, Tribology Transactions, 59 (1), (2016), 178 [3] www.nynas.com/ en/ product-areas/ base-oils 23rd International Colloquium Tribology - January 2022 127 Calcium Sulfonate Greases - Improving Biodegradable solution thanks to 1-step process Guillaume Notheaux SEQENS (ex PCAS), Porcheville, France Corresponding author: guillaume.notheaux@seqens.com Laura Hue SEQENS (ex PCAS), Porcheville, France 1. Introduction Over Based Calcium Sulfonate (OBCaS) greases are well known in the industry [10-11,13], confirmed by the growing market demand [1]. During the 22nd ICT in 2019 [2], the possibilities of the “1-step process” have been put forward, especially the advantage to choose 100 % of the carrier of the final grease. The first biodegradable OBCaS grease has been disclosed as example with some excellent results known on OBCaS grease. Thanks to users and market feedback, and to fit the new HPM grease specifications, 3 main items have been selected, and will be studied in this 2 nd step : - Improvement of corrosion preventive properties under dynamic wet conditions according to the ASTM D6138 (Emcor) - Offer a new grade with the same behavior in cold environment / flow pressure according to DIN51805 (Kesternich method) - Improvement of oxidation stability according to ASTM D8206-18 (RSSOT) These 3 refinements may seem independent but are closely related and can be solved with the one step process. 2. Improvement of the corrosion properties under dynamic wet conditions and new grades 2.1 Opportunities High thermal stability, intrinsic anticorrosion properties [3], mechanical stability, water resistance [12] and lubricating properties are driven by the 3D micellar core/ shell structure [4]. Pumpability at low temperature is mainly related to the base oil viscosity but could also be affected by the soap amount and the consistency [5][6]. First proposal in the 22nd ICT 2019 was based on a compromise ISO 46 carrier/ NLGI grade 2. But the market demand pushed 2 other combinations: - ISO150 carrier / NLGI grade 2 (good opportunity to increase performances but not for low temperature behavior) - ISO46 carrier / NLGI Grade 0 (good for low temperature behavior but not for performances) On the two grades requested, expectations were also to increase the Emcor test results, but this could unfortunately also affect all other properties and especially biodegradability. Meanwhile, the initial grade (ISO46/ NLGI grade 2) will also be improved. 2.2 Study follow-up Switching from a carrier to another, or adjusting the consistency are simple to manage with the 1-step process. Working on these 2 new products, the first idea to improve the Emcor test results was to use common additives. Different chemistries were tested to boost the rust inhibitor properties and water resistance (like phosphite/ phate derivatives, imidazoline, amine phosphate, ANsulfonate, or tack. polymer...). However, effects on biodegradability, on consistency/ rheology, on AW performance, or simply no better Emcor results were found. The second idea was to introduce different co-acids during the process in order to reinforce the top layer of the micellar structure, according to the carpeting theory, to improve water resistance. 128 23rd International Colloquium Tribology - January 2022 Calcium Sulfonate Greases - Improving Biodegradable solution thanks to 1-step process There are a lot of examples in the literature for acid and co-acid use in the conventional OBCaS grease 2-step process, such as 12HSA [7], but also acetic acid, boric acid, phosphoric acid... [8] mainly to help the amorphous to calcite conversion or to decrease the amount of soap. In our specific 1-step process, co-acids must be integrated to the top layer of the micelle to strengthen it. The main difficulties were to define how to achieve it, without changing rheological behavior, since the micellar structure is directly impacted. The key is not only the selection of co-acids but also a very well-balanced ratio of each co-acid, and the order of addition. Positive results are shown below. 2.3 Results 3. Improvement of the oxidation stability 3.1 Opportunities These new grades are based on complex esters to ensure biodegradability. Obviously, the impact on oxidation stability is a key topic, especially for OBCaS greases famous for their high temperature stability. 3.2 Study follow-up The first selection of antioxidants was made according to the Lusc-list [9]. Phenolic (ph) and aminic (am) antioxidants (AO) are the common chemistries used, but the specific molecule, quantity and ratio must be finetuned thanks to a DoE (Design of Experiment). For practical reasons, the DoE was performed in the carrier instead of the grease : 40 experiments were selected to cover the disjoined domain. Since the DoE was performed on esters, the possibility of extrapolation on greases need to be checked and validated. The point in time of AO introduction during the process had a surprising effect. This key parameter could dramatically affect the consistency of the grease. If the AO is added at the beginning of the reaction, the final grease will not reach the desired consistency by influencing the micellar organization. Since the reaction is made under nitrogen, the addition of AO at the end is the option adopted. 23rd International Colloquium Tribology - January 2022 129 Calcium Sulfonate Greases - Improving Biodegradable solution thanks to 1-step process 3.3 Results All detailed results will be presenting during ICT. If there are slight interactions, the main effects remain largely prevalent. (Ester type, AO amount) In ISO150 the best combination is 50/ 50 L115/ L06 at 2 % with an estimated RSSOT > 600 min. In ISO46: 60/ 40 L115/ L06 at 2 %, RSSOT > 400 min. Impact on viscosity after oxidation: No statistically significant effect was found, but a natural tendency is visible; higher the amount of AO, less the viscosity increases. Extrapolation on greases: Globally, the RSSOT model is identical in grease and ester (excepted one point which needs further investigation) as shown below in ISO 150. Correlation were made at 200, 400 and 600min results: 130 23rd International Colloquium Tribology - January 2022 Calcium Sulfonate Greases - Improving Biodegradable solution thanks to 1-step process Oxidation mechanism is a free radical reaction (init./ prop./ branch./ term.), and we just studied the 1st option of free radical deactivation. Future other options deserve to be investigated as hydroperoxide decomposition or inhibiting the metal catalytic. 4. Conclusion “One-step process” has interesting advantages by selecting 100 % of the carrier in OBCaS. Biodegradable grease is the best example. Changing the carrier or consistency is quite simple and overcoming the initial carrier’s drawback is easily achievable with this process. Studies on carrier and on grease could be split for quicker experimentations. On top of that, the improvement of performances by dealing on the structure, could be done without using classical additives. Biodegradability or other sensible performances are more easily maintained or even improved. References [1] Annual NLGI meeting (2018), NLGI grease survey [2] G.Notheaux, C.Felix at ICT 2020, Fully Customizable Calcium Sulfonate Greases for Optimum Performances, [3] D.Authier, A.Herman, L. Muntada, E. Ortega, L.Ribera, B.Saillant, ELGI 2013, Calcium sulfonate greases: A solution to water resistance [4] W.Macwood, R.Muir (1998) Calcium Sulfonate Grease … One decade later, NLGI’s 65th Annual meeting [5] D’HOLLANDER V. (2018) Les graisses lubrifiantes, IFP Train. [6] G.Fish, Calcium sulphonate greases “Performance and application overview” Lubrisense White Paper (2014) [7] Olson William D.; Muir, Ronald J.; Eliades, Theo “Sulfonate Grease Improvement”; U.S. Patent No.5,338,467, (1994) [8] J.Andrew Waynick, NLGI spokesman March/ April 2020, vol.84 [9] Lubricant Substance Classification list v24/ 06/ 2021 [10] A.Da Costa d’Ambros, ELGI 2019, Calcium sulfonate complex grease, a legendary technology adapted to future requirements [11] G.Fish, W.C.Ward, STLE 2012, Calcium Sulfonate Grease Formulation [12] Y. Zhou, R. Bosman & P. M. Lugt (2019) On the Shear Stability of Dry and Water-Contaminated Calcium Sulfonate Complex Lubricating Greases, Tribology Transactions, 62: 4, 626-634 [13] Dr. George S. Dodos, Navigating the future; lubrication grease in Marine applications, Eurogrease Oct-Nov-Dec 2020, N°4 Friction Modification/ Efficiency 23rd International Colloquium Tribology - January 2022 133 Longer Lifetime of Wind Turbine Bearings and Gears Using Phyllosilicate-Additives Stefan Bill REWITEC GmbH, Lahnau, Germany stefan.bill@croda.com Abstract REWITEC, as a part of Croda Int Plc, is a developer and manufacturer of an innovative particle-based surface treatment Phyllosilicate-technology for increasing the reliability and lifetime of wind turbine gears and bearings. The active particles are compatible to all common oils and greases and use lubricants as a carrier to build through their adsorption a protective and repairing phyllosilicate-based coating on the surface. The modified surface has a significantly lower surface roughness, which ensures a better load distribution, lower local pressure and lower tribological stress. Additionally, due to the special layered material structure the particles can be sheared in the tribological contact, which leads to a reduction in friction. All in all, when applying the products systems can run better with reduced friction, wear, surface roughness and temperature. These effects lead to great reliability and longer lifetime and reduce costs. In this presentation we would like to show our new scientific study about the lifetime calculation of a grease-lubricated wind turbine bearing (1.5 MW) with and without the technology application. The project is a cooperation between Croda and Sentient Science who performs lifetime calculations using digital clone method based on real friction coefficient and surface roughness data. The project includes data generation using MTM test bench, in a wind turbine bearing and subsequent simulation based on this data and bearing geometry. The simulation shows that with REWITEC the probability for a bearing failure significantly decreases which leads to a lifetime extension of up to 17.3 years. 1. Introduction While wind power is enjoying significant growth, it is also important to understand its limitations. Multiple studies have confirmed that wind turbines suffer from reliability issues: The EU’s RELIAWIND study aimed to examine current reliability of large wind turbines. The study found that electrical systems accounted for the highest failure rate, but gearbox failures accounted for the highest amount of downtime (14 days) [1]. Another study, by the National Renewable Energy laboratory (NREL) also found that gearbox failures contributed the greatest amount of downtime of any single wind turbine component, while the majority of wind turbine gearbox failures (76.2%) are caused by bearings. Gears were the second leading cause of failures (17.3%) [2,3,4]. A later review by [5] also suggested that reliability of gearboxes has not improved over time and that drivetrain technology has not yet fully matured. Figure 1 displays the annual failure rate and downtime per failure by component. For offshore wind turbines, reliability is even more critical, with marine operations costing significantly more than onshore. Efforts have been made to remove the gearbox from offshore wind turbine designs completely, with Siemens Gamesa announcing in 2017 that all offshore wind turbines will be direct drive in the future [6]. The market leader, Vestas, however, has committed to offshore wind turbines with gearboxes, with one source suggesting up to a 10% increase in material costs for a direct drive vs wind turbine with gearbox [7]. A review by [8] revealed that gearbox failures for offshore wind turbines happens at about three times the onshore rate. Maintenance of wind turbines is essential to prevent and mitigate failures. However, ongoing operation and maintenance (O&M) is costly, representing around 25% of the total cost of the wind turbine over its lifetime [10]. 134 23rd International Colloquium Tribology - January 2022 Longer Lifetime of Wind Turbine Bearings and Gears Using Phyllosilicate-Additives 2. Friction reduction in bearings The following MTM test shows the friction performance in a common grease with and without PHYLLOSILI- CATE-ADDITIVE at different rolling/ sliding ratios. Following test parameters were used: load 70 N, temperature 23°C, velocity 700 mm/ s, time 172 s. The diagram shows that the friction coefficient can be significantly reduced for all bearing relevant (0 to 40%) rolling/ sliding combinations by up to a maximum 38 %. Figure 2: Coefficient of friction at different rolling/ sliding ratios in grease Mobil SHC 681 without (blue) and with (green) PHYLLOSILICATE-ADDITIVE. Figure 1: Annual failure rate and downtime per failure by component, adapted from [9]. 3. Conclusion PHYLLOSILICATE-ADDITIVE technology helps to significantly reduce or even prevent the damage, whereby an application is recommended for both new and already damaged systems. The technology is an innovative lubricant additive with a protective and repairing effect, which mainly consists of phyllosilicates in the form of micro and nanoparticles. The particles use lubricant as a carrier to reach the rubbing metal surfaces and to coat damaged areas them by adsorption. The new, modified surface is optimized and protected from a tribological point of view, so that surface roughness, friction, wear, and temperature in the system are reduced. This leads to a significant improvement in efficiency and lifespan. The tests confirmed the expected improvements in friction and wear with all common experimental methods. Beside the classical friction and wear reduction, PHYLLOSIL- ICATE-ADDITIVE technology can repair partly damaged surfaces, which increases the lifetime enormously. Overall, utilizing the PHYLLOSILICATE-ADDITIVE leads to higher efficiency, higher reliability, and longer lifetime. References [1] Final Publishable Summary of Results of Project ReliaWind, ReliaWind Project Nr 212966 [2] https: / / grd.nrel.gov/ #/ stats [3] Wind Turbine Drivetrain Condition Monitoring During GRC Phase 1 and Phase 2 Testing S. Sheng, H. Link, W. LaCava, J. van Dam, B. McNiff, P. Veers, and J. Keller [4] National Renewable Energy Laboratory S. Butterfield and F. Oyague Boulder Wind Power 23rd International Colloquium Tribology - January 2022 135 Longer Lifetime of Wind Turbine Bearings and Gears Using Phyllosilicate-Additives [5] Wind turbine reliability data review and impacts on levelized cost of energy Cuong Dao | Behzad Kazemtabrizi Christopher Crabtree [6] Wind turbine reliability: A comprehensive review towards effective condition monitoring development Estefania Artigaoa, Sergio Martín-Martíneza,b, Andrés Honrubia-Escribanoa,b, Emilio Gómez-Lázaroa,b,* [7] https: / / www.siemensgamesa.com/ en-int/ newsroom/ 2017/ 11/ sgre-launches-new-wind-power-solutions-new-geared-turbine [8] https: / / www.reuters.com/ article/ us-vestas-windresults-gearbox/ vestas-bets-on-geared-turbines-topropel-it-to-margin-goal-idUSKBN1FS2X0 [9] Wind turbine reliability data review and impacts on levelized cost of energy Cuong Dao | Behzad Kazemtabrizi Christopher Crabtree [10] Chizhik et al., Wear 426-427 (2019) 835-844 23rd International Colloquium Tribology - January 2022 137 Low friction with polymer friction modifier in steel/ steel contact: a combined tribology and physico-chemical approach Nasrya F. Kossoko Université de Lyon, Ecole Centrale de Lyon, Laboratoire deTribologie et Dynamique des Systèmes LTDS, CNRS-UMR 5513, F-69134, Ecully, France Clotilde Minfray Université de Lyon, Ecole Centrale de Lyon, Laboratoire deTribologie et Dynamique des Systèmes LTDS, CNRS-UMR 5513, F-69134, Ecully, France Michel Belin Université de Lyon, Ecole Centrale de Lyon, Laboratoire deTribologie et Dynamique des Systèmes LTDS, CNRS-UMR 5513, F-69134, Ecully, France Benoît Thiébaut Total Marketing & Services, Centre de Recherche de Solaize, Chemin du Canal, BP 22, 69360, Solaize, France Frederic Dubreuil Université de Lyon, Ecole Centrale de Lyon, Laboratoire deTribologie et Dynamique des Systèmes LTDS, CNRS-UMR 5513, F-69134, Ecully, France Corresponding author: frederic.dubreuil@ec-lyon.fr 1. Introduction Polymer Friction Modifier (PFM) are interesting alternatives to classical lubricant friction modifiers but their tribological performance remains to be clearly demonstrated and understood (1). Up to now the development of PFM in automotive lubricant was mainly supported by chemical modification performed on viscosity index modifier molecules like polyacrylate derivatives (2). A breakthrough has been recently achieved by the synthesis of new diblock polymeric systems with a major chemistry change (3). This additive is a diblock polymer with PIB and PEG moieties patented by Croda (4). This work aims to study the friction behavior of this diblock PIB-PEG PFM blended to PAO 4 base oil in steel/ steel contact under severe lubrication conditions and to clarify the action mechanism of the PFM in the contact. 2. Low friction coefficient with a new PFM under boundary lubrication In a previous work (5) we have investigated the action mechanism of this PFM via the combination of multiple tribological tests (steel/ steel contact pin on disc reciprocating and MTM) and various surface characterisation techniques (ToF-SIMS and SFM). Under severe lubrication conditions (classically Pmax = 1 GPa, v = 3mm/ s) and various temperatures we have established that for both MTM and reciprocating tests, solutions containing 1% wt PFM (in PAO 4 base oil) systematically reduce the friction compared to base oil. High temperature measurements (100°C) leads to much lower friction coefficient (0.03) than room temperature ones (cf Figure 1). The performance of this PFM is even better than MoDTC a classical friction modifier. Compared to reciprocating conditions, measurements performed on a MTM at various sliding to roll ratio give the same trends with no impact of the SRR, nor the rubbing speed on the results obtained for complete experiments (including Stribeck curves as preand post-rubbing steps) Fig. 1: Friction coefficient under Pmax = 1GPa, v = 3mm/ s at 25 and 100°C. 138 23rd International Colloquium Tribology - January 2022 Low friction with polymer friction modifier in steel/ steel contact: a combined tribology and physico-chemical approach Optical analysis performed on disc trace after MTM experiment evidenced a film of additive at the steel surface. To understand the way the PFM is trapped ToF-SIMS depth profiles have been performed inside and outside friction scars. Negative ions observed at the surface indicates that the fragment coming from linker between PIB and PEG is the closest part of the molecule to the iron surface (red peak on Figure 2). Fig. 2: Depth profile of the following species C 2 H 3 O- (black) , C 3 H 3 O 2 - (yellow) , CHO 2 - (red) ,C 8 H- (green) and Fe- (blue) , Fe 2 O 3 - (purple) 3. Influence of rubbing conditions Although there is no doubt on the efficiency of this PFM to reduce friction compared to pure base oil, the behaviour of the additive is dependent on the tribological test and conditions. MTM and Reciprocating test are not always similar. Indeed reciprocating experiments show a large variability on the final friction coefficient that could be analysed in terms of two states with “low” or “high” friction coefficient (4). Furthermore, a minimum value of the travel length is mandatory to access stable low friction values. We can conclude that the adsorbed layer of PFM in the contact is fragile and difficult to build under reciprocating tests. The alternate move of the bead on the plane might be at the origin of this behaviour. On the other hand we have a high reproducibility on the MTM apparatus. Classical MTM experiments are divided into 3 parts first a Stribeck curve, then a rubbing phase and finally another Stribeck curve. During this experiment the movement of the bead in contact differs a lot from reciprocating test in terms of rolling, sliding distance and speed. 4. Step by step MTM Test analysis The influence of each steps as been studied to emphasize the difference between MTM and reciprocating test. Various experiments have been conducted to isolate and combine the steps and their contribution to the final frictions results. Interestingly it appears that the first Stribeck curve have a big influence on the tribological behaviour of the PFM: during the rubbing phase in the boundary regime (1 GPa, 3mm/ s) a transient period where the friction coefficient is gently reduced can be evidenced. This induction time is absent when a first Stribeck curve has been performed. Furthermore, without a first Stribeck curve, one can notice an impact of the SRR during the rubbing step and the final friction coefficient. For a better understanding of Stribeck curve’s impact on the surface changes, post processing imaging have been done on friction scars by in situ scanning force microscopy (cf Figure 3). Fig. 3: Topographic image (10x10 mm) of a MTM trace realized in PAO4 in tapping mode after a Stribeck curve. On figure 3, one can notice some big patches of additive in the sliding trace after a first Stribeck curve at 150% SRR, v= 3mm/ s, Pmax = 1 GPa. Those patches of PFM aggregates are not always present after rubbing test and quite mobile at the surface. They are never present with reciprocating experiments. Those aggregates shows the feeding impact of the contact during the Stribeck curve were the rubbing distance is quite long and initial condition not to severe. Preliminary results on some sub-conditions during the Stribeck curve (speed range, rubbing distance, SRR value) to get stable low friction coefficient will be presented. 5. Conclusion In this presentation we have deeply studied the action mechanism of a new polymer friction modifier. Under boundary conditions this additive is quite efficient at high temperatures. However the film adsorbed at the interface is fragile, a good supply of the contact interface in PFM is necessary to achieve low friction coefficients. 23rd International Colloquium Tribology - January 2022 139 Low friction with polymer friction modifier in steel/ steel contact: a combined tribology and physico-chemical approach References [1] Guegan J, Southby M, Spikes H. Friction Modifier Additives, Synergies and Antagonisms. Tribo Lett 2019; 67: 83 [2] Fan J, Müller M, Stöhr T, Spikes HA. Reduction of Friction by Functionalised Viscosity Index Improvers. Tribo Lett 2007; 28: 287-98 [3] Hobday I, Eastwood J. Friction Modifiers for Next Generation Engine Oils. Lube Mag 2014: 27-34 [4] Chen et al (Croda) - Patent WO2015065801A1 [5] Kossoko N.F, Dubreuil F, Thiébaut B, Belin M and Minfray C. Diblock polymeric friction modifier (PFM) in the boundary regime: Tribological conditions leading to low friction Tribo. Int. 2021; 163: 107186. 23rd International Colloquium Tribology - January 2022 141 New generation of nanolubricants fuel economy Marta Hernaiz TEKNIKER research centre, Eibar, Spain Corresponding author: marta.hernaiz@tekniker.es Iker Elexpe TEKNIKER research centre, Eibar, Spain Estibaliz Aranzabe TEKNIKER research centre, Eibar, Spain Tomas Pérez Gutierrez REPSOL Technological centre, Madrid, Spain Beatriz Dominguez REPSOL Technological centre, Madrid, Spain 1. Introduction Climate change is one of the greatest challenges of our era, however, the need to ensure access to energy to ensure quality of life and economic development is just as important. The Sustainable Development Goals (2015-2030) [1], are a United Nations-driven initiative to continue the development agenda; through Climate Action Goal, calls for urgent action to address climate change and its effects; the figures to be faced such as the 50% increase in CO 2 emissions since 1990; and the increase in emissions between 2000-2010 is higher than in the previous three decades, highlights the need to define the necessary measures to meet responsibilities and facilitate a prosperous, supportive and compatible future with climate security and the limits of the planet. The need to reduce emissions does not exclude the use of fossil fuels but requires a significant change of direction; the transition to a sustainable energy system offers the opportunity to improve energy efficiency from source to use ensuring better quality of life and economic growth, while reducing the environmental footprint of the energy sector. Fuel Economy lubricants are the alternative to meet EU requirements to reduce fuel consumption while maintaining engine protection performance. Lubricant manufacturers are facing a new challenge and need to explore new technologies. The use of nanotechnology and nanomaterials (NM), (one or more external dimensions is in the size range 1-100 nm.) [2] offers a new range of lubricants and in recent years the number of studies on the potential of nanomaterials to improve the performance of lubricants is increasing [3]. The limited information available on long-term systems and the evolution of the properties and performance achieved with the dispersion of nanomaterials shows that currently the biggest challenge for nanofluids in general, and nanolubricants in particular, is the challenge of long-term stabilisation, and this property is what limits the market penetration of this type of product. The most common stabilisation strategy for NMs in a fluid is the use of surfactants that induce steric and electrostatic stabilisation on the NM, although this route, despite its advantages such as cost and simplicity of preparation, generates nanofluids with limited stability over time, which makes it not the most appropriate strategy. In this work we present the surface functionalisation of a nanomaterial as a dispersion strategy to obtain a stable and functional system over time. The physical anchoring of a chemical compound on the surface of the NM seeks to cover several objectives, on the one hand to ensure maximum compatibility between NP/ fluid, on the other hand to maintain the properties inferred to the lubricant over time, for this it is necessary to maintain the cluster size distribution. 2. Nanoparticle surface functionalization A metal oxide nanoparticle of 50nm has been surface functionalised through an esterification reaction with a fatty acid. The fatty acid due to its polarity will increase the stability of the NM in the fluid once it is dispersed, in the esterification reaction between the carboxyl group (COO-) of the fatty acid and the surface hydroxyl group (OH-) of the NM; the polar head is oriented towards the nanoparticle and the aliphatic chain (apolar) is oriented towards the oil stabilising the NM in the lubricant. 142 23rd International Colloquium Tribology - January 2022 New generation of nanolubricants fuel economy Figure 1: NM Surface functionalization Nanoparticle surface functionalization has been optimized via two main characterization techniques; infrared spectroscopy (FTIR) to identify determinate chemical bonds that prove the existence of covalent bonding between MO surface and carboxylate group of fatty acid, and thermogravimetric (TGA) technique to determine organic content in the NP surface. Figure 2: CH 2 bond symmetric & asymmetric at 2800cm -1 and COO bond of carbonyl at 1650cm -1 As Figure 2 shows spectroscopic analysis by FTIR evidence the characteristic peaks of fatty acid onto nanoparticle surface as reported by Suhaib [4]. Organic content in NP surface determined by TGA suggest a deposition of 80% in mass of fatty acid onto MO surface (Figure 3). Figure 3: TGA test of Np and functionalised NP 3. Nanolubricant formulation and performance characterisation Obtained functionalized nanomaterials have been dispersed in a PAO based fully formulated lubricant at different loads (0.2%, 05% 1% wt). Dispersion strategy of NP has been assisted by mechanical stirring assisted by ultrasonication device for 5min. Following figure show the aspect of nanolubricants once prepared and after 30 days of storage. As the photo shows the dispersion of functionalized nanoparticles not only improve nanofluid long-term stability also the colour and visual aspect of nanolubricant have been not affected, and this is an important property in lubricants and not reported in previous studies. Figure 4: Aspect and stability of formulated nanolubricants The tribological performance has been measured using a ball-on-disk tribometer (SRV) with a contact pressure up to 1.3GPa, 10mm/ s and at 80ºC. The friction coefficient (COF) and wear scar results expressed as percentage reduction for each system are plotted graphically. As can be seen, the use of functionalised NMs reduces both parameters and although the higher the concentration of NMs the greater the reduction in terms of COF, 1%wt has been considered as the optimum concentration, as a balance between tribological performance and NP load, reaching up to a reduction of 12% in COF and more than 5% in ball wear scar. Figure 5: Experimental results of SRV tribological test of nanolubricants 4. Nanolubricant characterisation Selected nanolubricants with 1% of functionalized metal oxide as functional additive has been characterized to determine other important physic parameters, such us viscosity (@40ºC and 100ºC), viscosity index, termoxidative stability by HPDCS (OIT in min) and cooling 23rd International Colloquium Tribology - January 2022 143 New generation of nanolubricants fuel economy properties expressed as overall heat transfer coefficient (h). Following table summarised experimental results. Table 1: Summary of main physic and thermal nanolubricant properties Property Reference PAO OIL 1.0% F-MO % variation D0.5 190nm OIT (min) by HPDSC 49,33 59,09 +20 h [KW/ m 2 K]*ɸ 40ºC 78,696 80,914 +2,82 h [KW/ m 2 K]*ɸ 100ºC 207,299 215,440 +3,93 IV 194 207 +6.7 Viscosity 40ºC 0.1577 0.1350 Viscosity 100ºC 0.0211 0.0214 5. Conclusion In this study the nanolubricant formulation by dispersion of surface modified metal oxide nanoparticle has been evaluated with the main objective to obtain nanolubricants with improved tribological performance, with long term stability and without modified aspect and colour of reference fluid, important but not reported property in lubricants. Proposed esterification route evidence effective chemical anchorage of fatty acid into NP surface evaluated by FTIR spectroscopy. By TGA the fatty acid content in the NP surface has been quantified reaching up to 80% of organic load. Performance, evaluated by tribological test, and main physic-chemical parameters, have shown that proposed strategy not only improve friction coefficient and antiwear properties of lubricant, also cooling properties and viscosity index have been booster without limit thermooxidative behaviour. The NM stability resilience and the good visual aspect of the obtained nanolubricant suggest exceptional potential as a new fuel economy nanolubricant. References [1] The 2030 agenda for sustainable development. United Nations. sustainabledevelopment.un.org [2] Recommendation on the definition of a nanomaterial 2011/ 696/ EU. [3] R.Saidur, K.Y.Leong, H.A.Mohammed. “A review on applications and challenges of nanofluids”. Renewable and Sustainable Energy Reviews. Volume 15, Issue 3, April 2011, Pages 1646-1668. [4] S.U. Ilyas, M. Narahari, J.T.Y. Theng, et al., “Experimental evaluation of dispersion behavior, rheology and thermal analysis of functionalized zinc oxideparaffin oil nanofluids”, Journal of Molecular Liquids (2019). 23rd International Colloquium Tribology - January 2022 145 Axle lubricant composition impact on efficiency and work loss using light duty truck drive axle Arjun Goyal BASF Corporation, Florham Park, NJ, USA Corresponding author: arjun.goyal@basf.com Donna Mosher BASF Corporation, Florham Park, NJ, USA 1. Introduction Axle lubricant composition impact on axle efficiency and work loss was studied. The testing was performed on a light duty pick-up truck drive axle with lubricants of various compositions. The results of the study showed that the lubricant composition consisting of base oil type, additive technology, thickener (viscosity modifier) and finished fluid viscosity has significant effect on the average efficiency and work losses. The study evaluated several commercially available SAE J2360 approved lubricants as well as experimental formulations. The data show the thickener component had a significant impact to the results. These results will be used to improve further axle lubricant compositions to meet the United States Environmental Protection Agency’s (EPA) Green House Gas (GHG) regulations that improves fuel economy and reduces carbon pollution. A light-duty pickup truck axle of 235 mm rig gear diameter having axle ratio of 3.21: 1 was installed on a dynamometer at an independent lab. The tests were completed using United States Environmental Protection Agency (EPA) Green House Gas (GHG) testing protocol. The total work loss and average efficiency over the cycle was measured with various lubricants. The observations are summarized below. 1.1 Test Repeatability Efficiency and Total Work Loss using a commercial oil was re-run three times during the testing. The results did not significantly change during the study. The average efficiency and total work loss data is provided in Figure 1 below. Figure 1 Two oils were prepared using different SAE J2360 commercial additive packages having the same base oil and thickener. The data in Figure 2 below show that the additive package has minimal effect on work loss or efficiency in this axle design. 146 23rd International Colloquium Tribology - January 2022 Axle lubricant composition impact on efficiency and work loss using light duty truck drive axle Figure 2 1.2 Viscosity Effect The influence of finished fluid viscosity was studied. Oils were blended with different viscosity grades using the same additive and base oil. The viscosity was adjusted by the amount of thickener. All the oils tested are expected to meet SAE J2360 specification requirements. Work Loss and Average Efficiency, as shown in Figure 3 and 4, were significantly affected by varying fluid viscosity. Figure 3 The work loss continued to decrease with viscosity but started increasing above SAE 75W-80 viscosity grade. Similar observation (Figure 4) was seen with average efficiency. The efficiency continued to improve with decrease in viscosity but started increasing beyond SAE 75W-80 grade oil. Figure 4 From viscosity related work it, was observed that the optimal viscosity to get lowest work loss and improved efficiency is with a SAE 75W-80 viscosity grade (9.0 to 10.5 cSt @100°C). 1.3 Base Oil Effect For this study, oils were blends of similar viscosity using different base oil types. As shown in Figure 5 below, base oil type has significant effect on both work loss and efficiency. 23rd International Colloquium Tribology - January 2022 147 Axle lubricant composition impact on efficiency and work loss using light duty truck drive axle Figure 5 The results showed PAG base oil types performed best while Group II performed worst. 1.4 Thickener (Viscosity Modifier) Effect Several commercial and experimental thickener types were studied in same base oil and additive system. All the oils were SAE 75W-85 viscosity grade. The results are shown in Figure 6 below. Figure 6 It is shown that thickener (viscosity modifier) type has the most significant effect on the efficiency and work loss. This new knowledge is being used to generate highly efficient lubricants. 1.5 Conclusion The results of this study showed that base oil type, additive, thickener (viscosity modifier) and finished fluid viscosity have significant effect on the average efficiency and total work loss. Several commercial and experimental lubricants were evaluated in this study meet or are expected to meet the SAE J2360 specification requirements. The thickener type has significant influence on the efficiency. The study is being used to identify combinations of base oil and thickener types for a given viscosity grade to progress highly efficient lubricants needed to meet the US EPA GHG standards. 23rd International Colloquium Tribology - January 2022 149 Development of a new fuel efficient, shear stable axle lubricant to meet new U.S. Green House Gas requirements Arjun Goyal BASF Corporation, Florham Park, NJ, USA Corresponding author: arjun.goyal@basf.com Donna Mosher BASF Corporation, Florham Park, NJ, USA 1. Introduction The United States Environmental Protection Agency (EPA) and the National Highway Traffic Safety Administration (NHSTA) on behalf of the Department of Transportation (DOT) have enacted rules to establish the reduction of Green House Gas (GHG) emission (CO2) and fuel consumption of new on-road heavy duty vehicles. To meet these regulations, U.S. Vehicle Builders developed new axle designs with reduced weight, lowering axle ratios and improved gear technology, and lower oil level in axle sump. Current 2021 GHG regulations are met with the existing high performance axle lubricant. Meeting new 2024 GHG (and 2027 GHG) requirements will require axle oils to provide higher efficiency (fuel savings) and reduction in CO 2 reduction (Green House). Reduction in lubricant viscosity can provide fuel savings; however, reduction in viscosity can lead to metal-to-metal contact thus leading to higher component wear and reduced equipment life. Base oil, thickener, and performance package accounts for the majority of finished axle oil formulation. The performance package has minimal contribution to the fuel efficiency. Base oil and thickener provide the required efficiency. 1.1 Performance Package A new performance package to meet long oil drain performance was developed for this program. 1.2 Base Oil Selection It is well known that PAO (polyalfaolefin) base axle oil provides lower traction (efficiency gain) as measured by MTM (Mini Traction Machine) compared to other base oil such as Group III and Group II+. Figure 1 1.3 Thickener Selection BASF proprietary system which provides shear stability and long drain capabilities was used to evaluate various thickeners. The extended length KRL shear test data shows that the candidate oil maintains constant viscosity for 200-hours (predictor of oil viscosity after 500,000 miles (800,000 kms) of no drain service. Figure 2 1.4 SAE J2360 Approval The new candidate oil met the SAE J2360 specification requirements and has been approved by the SAE Lubricants Review Institute (LRI). In addition, the candidate oil met Dana SHAES 256 RevE stringent specification 150 23rd International Colloquium Tribology - January 2022 Development of a new fuel efficient, shear stable axle lubricant to meet new U.S. Green House Gas requirements requirements such as Wet L-37-1 (represents running through the water), High Temperature L-37-1 (operation at high temperature), L-37-1 (extended-length spalling test), and static and dynamic seal tests. 1.5 Cleanliness A 200 hours (four times the requirement for SAE J2360) extended length test was completed on candidate oil to show cleanliness characteristics. The extended length test shows good correlation with cleanliness observed in no-drain 500,000-mile (800,000 km) field performance. Table 1 ASTM D5704 (L-60-1) J2360 Limits (50 hrs) Candidate Oil (200 hrs) Viscosity Increase, 100°C, % 100 max 12 Pentane Insolubles, wt% 3 max 0.9 Toluene Insolubles, wt% 2 max 0.1 Carbon/ Varnish (10=clean) 7.5 min 9.4 Sludge (10=clean) 9.4 min 9.8 1.6 Low and High Temperature Characteristics The candidate oil showed excellent low and high temperature properties indicative of suitability in extreme temperature conditions. Figure 3 1.7 Fuel Efficiency The MTM data comparing traction coefficient (friction losses) are shown below. The candidate oil provided significant reduction in traction coefficient compared to a leading commercial oil. Figure 4 In laboratory dynamometer testing, using a commercial light duty pickup truck axle, efficiency was measured, fuel consumption and CO 2 generation was calculated. The U.S. EPA GEM method was used for the calculation with regional, urban, and multipurpose duty cycles tested. The candidate oil outperformed commercially available oils (80W-90 and 75W-90) by using less fuel and generating less CO 2 . Figure 5 23rd International Colloquium Tribology - January 2022 151 Development of a new fuel efficient, shear stable axle lubricant to meet new U.S. Green House Gas requirements In a controlled over-the-road truck test with a tandem axle (front and rear carriers), the candidate oil provides 0.79% fuel saving and 5.2°C temperature reduction compared to leading commercial oil. Figure 6 1.8 Field Tests The field tests are progressive satisfactorily on this oil in North America in line-haul application. Several test units have accumulated over no-drain 240,000 miles (approx. 400,000 km). The used oil iron content data from one fleet is shown below. The increase in iron content is relatively lower compared to factory-fill oil indicative of reduced component (gear) wear. Figure 7 1.9 Conclusion This paper describes the development of a new lower viscosity, shear stable, synthetic heavy-duty axle lubricant. The lubricant consists of a unique combination of synthetic base oil (PAO) and proprietary viscosity improver (thickener) which results in superior low-and-high temperature properties with excellent extended-length shear stability. The new lubricant meets the SAE J2360 and leading North American axle manufacturers rigorous extended drain specification requirements. The new axle lubricant also shows fuel savings of 0.79% and front axle temperature reduction of 5.2°C over a leading fuel-efficient SAE 75W-90 axle lubricant. Using EPA estimates, the use of new fuel-efficient lubricant is estimated to save over $300 and reduce carbon dioxide (CO 2 ) by over 200 kg per truck per year. 23rd International Colloquium Tribology - January 2022 153 Understanding the friction and wear behavior of in-service lubricants Angela Tortora Ducom Instruments Europe B.V., The Netherlands Deepak H. Veeregowda Ducom Instruments Europe B.V., The Netherlands Simon Regauer OELCHECK GmbH, Germany Christoph Rohbogner OELCHECK GmbH, Germany The lifetime of in-service lubricants is specified by the manufacturers usually on time-frame operating hours or driven distance. Only if the used oils are controlled by trend analysis, experienced tribologists will use contamination, oxidation or additive depletion for a decision, whether the oil can remain in service. It is a general understanding, that depletion of friction reducing and EP-additives over time will lead to higher wear and friction on the lubricated components. However beside changes in the additive composition measured by the ICP or IR-spectra there is no relationship what kind of laboratory test will show the depletion in the application. In this study, we have developed a rapid test method to screen the additive depletion of in-service lubricants using a four-ball tester or FBT-3 (see Figure 1). The trend-oil samples used for this study were ISO 320 wind-mill gear oils, used in an FZG drive gear, and 5W-30 engine oils out truck-engines in regular kilometer intervals. Trend analysis by ICP and other instruments of these oils showed only small changes in the concentration (ppm) of key additive elements like Zn, P and S. It lets assume that there is periodic depletion of additives with a potential effect on corrosion inhibition, friction reduction and antiwear resistance. To verify its influence on antiwear and antifriction behavior samples of these oils were tested for 60 sec at 740 MPa in FBT-3. In situ friction and ball wear scar diameter were measured for each oil. Test results showed an increase in friction coefficient or wear (see Figure 2) due to the small changes in additive concentration (ICP) for in service gear oils. However, in service engine oils showed a decrease in wear and no relationship between friction coefficient and additive concentration. This preliminary study shows that a 60 sec four ball test method can detect tribological effect of in-service additive changes. However, future work that includes tests on more in service trend oil samples is recommended. This big data will be used to determine measurement precision for this test method that can add significant value in maintenance of critical components and allows comments on the sustainability of the lubricants during its lifetime. Figure 1: Description of the Ducom Four Ball Tester (FBT-3) with Image Acquisition System (IAS). ISO 320 wind-mill gear oils 5W-30 engine oils Figure 2: Ball mean wear scar diameters obtained from FBT-3. Lubricants in Electric Vehicles 23rd International Colloquium Tribology - January 2022 157 Novel Defoamers for Use in Low Viscosity Electric Vehicle Fluids Noriko Ayame ENEOS Corporation, Lubricants R&D Dept, Yokohama, Japan Corresponding author: ayame.noriko@eneos.com Akira Takagi ENEOS Corporation, Lubricants R&D Dept, Yokohama, Japan Go Tatsumi ENEOS Corporation, Lubricants R&D Dept, Yokohama, Japan 1. Introduction Lubricant foaming can cause problems such as lowering of cooling efficiency and breaking down of oil film which triggers wear or seizure [1]. Therefore, defoamers are critical additives in lubricants especially for electric and hybrid vehicles. Conventionally, polydimethylsiloxane (PDMS) have been used as defoamers for automotive lubricants [2]. Compared with other lubricant additives, PDMS is unique in terms of not dissolving in the lubricants and working as a defoamer when keeping a finely dispersed state. However, due to its high density, PDMS is prone to sedimentation during a long-term storage. Additionally, centrifugal force and filter adsorption make PDMS distribution uneven under use in mechanical devices. As a result, the defoaming performance of PDMS gradually disappears [2]. Furthermore, lower viscosity lubricants can improve energy efficiency and cooling performances of motors [3, 4], so the demand for super low viscosity lubricants is growing, but PDMS partially dissolves into the such super low viscosity lubricants, leading to the increase of foaming. To solve these problems, the improvement of PDMS defoamers has been needed. 2. Results and discussion In this study, the effect and mechanism of a novel defoamer, a highly dispersed PDMS (HD-PDMS) were investigated. The HD-PDMS was designed to improve its dispersibility in lubricants by a micellization technology which prevents the aggregation and adsorption of PDMS. The results of particle size measurements using the dynamic light scattering method showed that the particles of the HD-PDMS kept smaller sizes within lubricants than those of the conventional PDMS. In addition, the HD-PDMS also gave much better defoaming performances after the centrifugal separation or filtration which simulates the practical uses in automobiles, as shown in Fig.1. For use in super low viscosity lubricants, fluorinated PDMS defoamers have better defoaming performances than PDMS. On the other hand, the fluorinated PDMS has the higher density, leading a poorer dispersibility than PDMS. The micellization technology was also applied to improve the dispersibility of the fluorinated PDMS. The experimental results showed that this micellization technology was also effective for improving the fluorinated PDMS, suggesting that the fluorinated HD-PDMS can maintain the defoaming performance for a long period of time even in super low viscosity lubricants. Fig.1: defoaming performance of HD-PDMS 158 23rd International Colloquium Tribology - January 2022 Novel Defoamers for Use in Low Viscosity Electric Vehicle Fluids References [1] Tonća Ćaleta Prolić, Anđelko Lepušić, 2012, “EF- FECT OF FOAMING ON THE ANTIWEAR PROPERTIES OF LUBRICATING OILS,” goriva i maziva, 51, 1, 29-46. [2] Kalman Koczo, Mark D. Leatherman, Kevin Hughes, Don Knobloch, 2017, “Foaming Chemistry and Physics,” Lubricant Additives: Chemistry and Applications, Third Edition, 337-384. [3] Kurosawa, O., Matsui, S., Komiya, K., Morita, E. et al., 2003, “Development of the Fuel Saving Low Viscosity ATF,” SAE Technical Paper 2003-01- 3257. [4] Beyer, M., 2019, “Lubricant Concepts for Electrified Vehicle Transmissions and Axles,” Tribology Online, vol.14, No.5 23rd International Colloquium Tribology - January 2022 159 Test Method to Determine Improvements of E-Drive Efficiency Dipl.-Ing. (FH) Michael Schulz ISP Salzbergen GmbH & Co. KG Contact: m.schulz@isp-institute.com Electrification of mobility is continuously increasing and the pace is even higher than expected. As a consequence, Battery Electric Vehicle (BEV) population is growing rapidly and a significant market share is expected in the future. Even though BEVs are rated as a highly efficient mobility concept, there is still room for improvement of e-drive units’ (EDU) efficiency and performance, with the increase of the driving range being a key element. Aside from design changes, mechanical and software improvements, the lubricant of the step gear and the cooling fluid which controls the temperature of the e-motor and power unit can also contribute to these improvements. So far, no standards are available to determine the influence of those e-fluids on the efficiency of the respective driveline. ISP developed a test method to demonstrate the potential for efficiency gains that are possible with dedicated low viscosity fluids. The test method describes how to set up the test stand, control the operation and gives a guideline for the most efficient way of testing. The development was done on a Volkswagen, first generation EDU, which is used in the Golf Mk. 7 and E-up vehicles. Fig. 1 shows the test matrix which has been defined for the first part of the development. Thirty four individual speed/ load steps have been measured to identify the areas of high potential for efficiency increases. Fig. 1: Running Order of the Speed / Load Matrix 160 23rd International Colloquium Tribology - January 2022 Test Method to Determine Improvements of E-Drive Efficiency The running order was selected in a way that the fluid temperature increases constantly from step to step in order to keep the stabilisation time of the temperature at a minimum. The mechanical power output was controlled to the set-point and the electrical input power measured, the difference between the two power levels has been calculated as system efficiency. A 3-D efficiency mapping was plotted (Fig. 2) based on the measurements which were taken at the end of each speed/ load step. Fig. 2: 3D Efficiency Mapping of the EDU For the determination of the efficiency gains of two different fluids, it has been assumed that the efficiency of the electric motor is constant and all differences which have been measured are linked to the transmission fluids. This assumption was based on the fact that the e-motor cooling was externally controlled and the ambient conditions kept constant over the whole measurement test development programme. As a result of this, efficiency improvements of over 3% were measured between the two different fluids. In the second phase of the test method development, Worldwide Harmonized Light Vehicles Test Cycles (WLTC) were performed. For the start of the first WLTC the fluid was conditioned to -10 °C and 23 °C, following which no further control was done on the fluid temperature and only the e-motor coolant and the ambient temperature controlled to the given set points. Fluid temperature differences of up to 5 K were measured and an efficiency improvement of 1.7 % confirmed the reduced friction of the low viscosity fluid against the conventional lubricant in the WLTC. Although the volume of the e-fluid in the system is quite low, it has been demonstrated that the efficiency with the introduction of low viscosity fluids can be improved significantly. Dedicated additive technology which also reduces friction and oil foaming can improve this benefit even further. Additional improvements are also expected from the cooling efficiency of integrated systems and EDUs where the fluid takes over the e-motor cooling in addition to the lubrication of the step gears. Further R&D on EDUs is expected in the coming years and this general test method can be adapted to current and future technologies to support the hardware and fluid development. 23rd International Colloquium Tribology - January 2022 161 A Novel Class of Biobased Organic Friction Modifiers Revealing the Superlubricity Effect: Tribology and Application Experience in Motor Oil and e-Fluid Formulations Arthur Coen OLEON s.a., Compiègne, France Karima Zitouni OLEON s.a., Compiègne, France Ward Huybrechts OLEON s.a., Compiègne, France Philippe Blach OLEON s.a., Compiègne, France Anne-Elise Lescoffit OLEON s.a., Compiègne, France Boris Zhmud BIZOL Germany GmbH, Berlin, Germany Corresponding author: zhmud@bizol.de 1. Introduction Increased lubricant performance requirements drive a steady growth in the market share for synthetic lubricants. Combined with proper additives, synthetic base oils can be used to manufacture top-tier energy saving lubricants. One type of additives deserves special attention in this connection: friction modifiers that are an indispensable tool for “smart lubricant” engineering. In this study, the tribological properties of a novel biobased friction modifier comprising polymerized fatty acid glycerol ester (PFAGE) are described. PFAGE forms gel-like adsorption layers that contribute to surface repulsion. As a result, the additive reveals very interesting tribology at low sliding speeds. In particular, it has the ability to maintain full-film lubrication in a loaded contact in the zero sliding speed limit, the behaviour ass °Ciated with the superlubricity effect. This tribological behaviour is rationalized using a dynamic adsorption model. 2. Lubricant formulation experience Friction modifiers can roughly be grouped into two major categories: (1) particulate systems (PTFE, graphite, graphene, MoS 2 , WS 2 , IF-WS 2 , nanoboric acid, copper/ copper oleate nanoparticles, etc.); and (2) adsorption layer forming systems, which in their turn, can be monomolecular (glycerol mono-oleate, sorbitan mono-oleate, esters of hydroxycarboxylic acids, phosphate esters, borate esters, fatty acids, fatty amides, fatty amines, ethoxylated fatty amines, ammonium phosphate ionic liquids, etc.) and polymeric (methacrylates, polyesters, polyethers, polyamides, polymerized vegetable oils, etc.). The main advantage of particulate systems is their relatively high chemical stability, while their chief disadvantage being the propensity for separation. Particulate systems tend to render lubricant formulation opaque in appearance, which is not always acceptable. Adsorption layer forming systems are numerous: there are hundreds of commercial products on the market. Despite the many undisputed advantages over their API Group I mineral counterparts, modern “synthetic” base oils of API Group III and IV are characterized by low solvent power and may cause elastomer compatibility and miscibility issues [1]. This necessitates deployment of solubility improvers, such as esters and alkylated naphthalenes, in lubricant formulations. Organic friction modifiers (OFMs) are expected to have borderline solubility in order to achieve adequate affinity to metal surface while maintaining a certain bulk reserve of the additive. 162 23rd International Colloquium Tribology - January 2022 A Novel Class of Biobased Organic Friction Modifiers Revealing the Superlubricity Effect: Tribology and Application Experience Table 1: Examples of solubility improvers commonly used in lubricant formulations *Not soluble means that more than 20% solubility improver is needed Another important requirement is that OFMs will not interfere with EP/ AW additive action at high loads. Reactions of EP/ AW additives such as ZDDP are activated by combination of pressure and shear forces. Since OFMs are surface active, they may form compact adsorption layers that passivate EP/ AW additives. The chief difference between monomolecular and polymeric friction modifiers is the compactness of adsorbed layers. Whereas monomolecular OFMs tend to produce dense “brush-like” molecular layers, polymeric OFMs produce “gel-like” adsorption layers. These layers cause repulsion between the surfaces, contributing to the socalled “superlubricity” effect [2]. Surface-gel-forming OFMs are less likely to engage into competitive adsorption with EP/ AW additives. This allows one to develop formulations combining favorable antiwear properties with improved fuel economy. Another important practical consideration is the effect retention. As oil is ageing, friction modifiers may lose their effect. For instance, MoDTC-doped lubricants tend to quickly lose their efficiency due to oxidation. In contrast, PFAGE-doped oil reveals much better effect retention. This tendency can be demonstrated in a simple MTM test, see Fig. 1. (a) (b) Fig. 1: MTM test data comparing MoDTC and PFAGE in API Group III base oil after (a) 2 h ageing at 100 °C, and (b) 8 h ageing at 100 °C followed by additional 8 h at 130 °C. Two current standards, Sequences VIE and VIF (ASTM D8114 and D8226), commonly used to measure fuel economy performance of passenger car motor oil mandate that fuel economy at two different aging stages is determined: FEI1 after 16 hours (fresh oil) and FEI2 after 109 hours (aged oil) [3]. It is always important to balance formulations in order to exploit potential synergisms and minimize possible antagonistic effects between different additives. For instance, PFAGE efficiency proved to be strongly affected by common detergency additives present in commercial additive packages. 23rd International Colloquium Tribology - January 2022 163 A Novel Class of Biobased Organic Friction Modifiers Revealing the Superlubricity Effect: Tribology and Application Experience Fig. 2: MTM test data comparing MoDTC and PFAGE used as top-up additives in a commercial motor oil after 2 h ageing at 100 °C. In the presence of surface-gel-forming friction modifiers, lubricant films may reveal complex non-Newtonian rheology. Fig. 3 Rheology of lubricant films in the presence of surface-gel-forming OFMs. References [1] B. Zhmud, M. Roegiers, New Base Oils Pose a Challenge for Solubility and Lubricity. Tribology and Lubrication Technology 65 (2009) 34. [2] B. Zhmud, A. Coen, K. Zitouni, Fuel Economy Engine Oils: Scientific Rationale and Controversies, SAE Tech. Paper 2021-24-0067. [3] P. Lee, B. Zhmud, Low Friction Powertrains: Current Advances in Lubricants and Coating, Lubricants 9 (2021) 74. 23rd International Colloquium Tribology - January 2022 165 Improving Gear and Thermal Efficiency of Electric Vehicle Fluids Using Group V Base Stocks Gareth Moody Corresponding author: gareth.moody@croda.com Bethan Warren Nicholas Weldon Croda Europe Ltd, Snaith, United Kingdom 1. Introduction The formulating process to produce dedicated transmission fluids for electric vehicles is ongoing, with a focus on several key parameters where standard ATF formulations fell short. New formulations deal primarily with material compatibility (copper, insulating materials and elastomers) and having a low level of electrical conductivity. There has also been a recent drive to maximise thermal properties of these fluids and lower traction to improve gear efficiency. Here, Group V base fluids will be shown to have exceptionally low levels of traction and high levels of thermal conductivity whilst being fully compatible with key materials and Group 1 - 4 base oils. These fluids can be mixed with other base oils to enhance their properties and improve vehicle efficiency when formulated into an electric vehicle gear fluid. Improving gear efficiency has the effect of increasing driving range. It is well established that range anxiety is a key reason why many people would not consider purchasing an electric vehicle. Battery costs are still high ($100-$150 per kW) and because of this, any additional range which can be gained via fluid optimisation can potentially be justified. Further extensions in range can be achieved by reducing fluid viscosity which reduces churning and drag but this must not be at the expense of wear protection and cooling ability. 2. Results The Group V base oils used in this work are esters in the viscosity range 2.5 - 5.5 cSt at 100C. Table 1: viscosity of esters used (low viscosity) Name KV 40 cSt KV 100 cSt VI Group III 3 cSt 12.0 3.2 115 Group IV PAO2 5.0 1.7 238 Fluid 1 9.6 2.9 158 Fluid 2 7.7 2.4 135 Fluid 3 11.5 3.2 149 Figure 1: Traction curves of low vis ester fluids 1-3 vs Group III and Group IV base oils at 40°C and 100°C 166 23rd International Colloquium Tribology - January 2022 Improving Gear and Thermal Efficiency of Electric Vehicle Fluids Using Group V Base Stocks Table 2: viscosity of esters used 4-6 cSt Name KV 40 cSt KV 100 cSt VI Group III 4 cSt 19.3 4.2 122 Group IV PAO4 18.6 4.1 124 Fluid 4 19.0 4.5 163 Fluid 5 20.0 4.4 140 Fluid 6 26.0 5.4 157 The traction curves in Figure 1 were created at a high speed of 2.2 m/ s and load of 16N across a SRR of 0 - 100%. The oils in Figure 1 are neat ester with no additives. Here, all esters have lower levels of traction than the Group III mineral oil and all except one are lower than the PAO. The first point here is that esters can have very low traction, but not all esters. The structure required to achieve this must be considered. Of all the esters tested Fluid 1had the lowest level of traction. Figure 2: Traction curves of low vis ester fluids 4-6 vs Group III and Group IV base oils at 40°C and 100°C Again, at 100°C, the pattern is the same with the ester fluids having lower traction than Group III base oil. From the results it can be seen that using an ester can reduce traction and therefore theoretically improve gear efficiency in a system at high, constant speeds similar to conditions on a highway. The next step was to create more representative formulations which could be used in vehicles. As Fluid 1 showed good low traction properties it was selected for further evaluation. This involved firstly combining the fluids with an additive package to see the influence of this on the traction and then secondly using 20% of Fluid 1 alongside either Group III or Group IV basestock and an additive package used at the recommended treat rate. These were then compared against the same formulation without Fluid 1. Figure 3: Fully formulated Fluid 1 vs Group III 3 cSt traction curves at 40°C and 100°C. The ester fluid has significantly lower traction than the Group III base oil and the additive package appears to have no influence on its performance. At 40°C, the reduction is around 35% and at 100°C the reduction is around 40%. The significance of the reduction is such that the performance of the ester based formulation at 40°C is similar to the performance of the Group III at 100°C despite there being around a threefold difference in viscosity (11.4 cSt for Fluid 1 and 3.4 cSt for Group III). This has important implications not only for efficiency but also potentially for longevity of parts. As a general trend, lubricants have been decreasing in viscosity to improve efficiency and reduce energy consumption but in this case, the same level of traction can be achieved with a higher viscosity fluid. Although efficiency gains have been shown at high speeds, testing drive cycles such as WLTP and indeed real-life driving will also involve much lower speed travelling along with stopping and setting off. Here, the conditions are much harsher and the lubricant is more likely to be in boundary or mixed conditions. To test this, another MTM method was used with low speeds (0.2 m/ s) and higher loads (25N). The influence of a base oil on friction is closely related to its effect on film thickness which will be discussed during the presentation. As well as gear efficiency, thermal properties of fluids are also very important. It is not uncommon for the electric motor and gear system to be incorporated into a single unit and utilise the same fluid for both gear lubrication and motor cooling. In this case, a higher thermal conductivity of a fluid would aid cooling. To assess this, the thermal conductivity of the fluids was tested with the esters in general having a higher thermal conductivity than Group III and IV at 40°C and 80°C. 23rd International Colloquium Tribology - January 2022 167 Improving Gear and Thermal Efficiency of Electric Vehicle Fluids Using Group V Base Stocks Table 3: Thermal conductivity values of fluids Name Thermal cond. 40°C W/ mK Thermal cond. 80°C W/ mK Group III 3cSt 0.124 0.119 Group IV PAO2 0.128 0.120 Fluid 1 0.139 0.130 Fluid 2 0.133 0.126 Fluid 3 0.139 0.133 Group III 3cSt 0.124 0.119 Group IV PAO2 0.128 0.120 Fluid 1 0.139 0.130 Fluid 2 0.133 0.126 Fluid 3 0.139 0.133 3. Conclusion Some esters haven been shown to have exceptionally low traction compared to Group III and Group IV fluids. In particular at high speeds, the traction reduction was up to 30-40% at both 40°C and 100°C The addition of an additive package did not have a negative effect on the performance of Fluid 1. Esters in general have a higher thermal conductivity than mineral oil or PAO. References [1] https: / / www2.deloitte.com/ uk/ en/ insights/ focus/ future-of-mobility/ electric-vehicle-trends-2030. html [2] Kurihara, Isao, and Osamu Kurosawa. “Design and Performance of Low-Viscosity ATF.” SAE Transactions, vol. 116, SAE International, 2007, pp. 805-12, [3] De Laurentis, N., Cann, P., Lugt, P.M. et al. The Influence of Base Oil Properties on the Friction Behaviour of Lithium Greases in Rolling/ Sliding Concentrated Contacts. Tribol Lett 65, 128 (2017). https: / / doi.org/ 10.1007/ s11249-017-0908-7 23rd International Colloquium Tribology - January 2022 169 Polymers as important additives in E-drive fluids Dmitriy Shakhvorostov New Mobility Manager, Oil Additives, Evonik Operations GmbH, Germany Corresponding author: dmitriy.shakhvorostov@evonik.com Stephan Wieber New Mobility Manager, Oil Additives, Evonik Operations GmbH, Germany Roland Wilkens New Mobility Manager, Oil Additives, Evonik Operations GmbH, Germany Andreas Hees New Mobility Manager, Oil Additives, Evonik Operations GmbH, Germany 1. Introduction The fully electrical or partially electrical (hybrid) power train for passenger vehicles is the currently preferred solution to achieve the GHE reduction targets (1-2). Both pure battery electrical and fuel cell electrical vehicles have very similar drive trains. Optimization of the latter is ongoing with the purpose of range extension. All components (mechanical transmission, electric motor, power electronics) need to achieve all together the maximum efficiency at given durability (1). The efficiency improvement can contribute to CO 2 reduction during use phase and also extend EV range. Alternatively, or in addition it can be used to reduce cost and CO 2 emissions during production (e.g. by means of battery size reduction). New concepts of the drive train combine all three elements - transmission, motor and power electronics in one housing. Such topology has the advantage of having no electrical interfaces and saving space and weight, as well as a better heat dissipation, since the lubricant is in direct contact with the motor Cu windings and electronic elements of the power electronics. The latter are desired to be dimensioned as small as possible and providing high specific power which requires very efficient cooling. The new lubricant has to withstand elevated tribological loads and provide more efficient heat transfer, while being compatible with all new materials in the system. In this paper we discuss how the alkyl methacrylate-based polymers can be useful for these seemingly mutually exclusive requirements. 1.1 Viscosity Since the introduction of the first CO 2 emission limits a trend to reduce the kinematic viscosity of the driveline lubricants could be seen (10 years ago was the kinematic viscosity at 100°C (KV100) 9-30 cSt, now 4-9 cSt (2) (3)). The reduction of KV100 occurs to reduce the operating viscosity during the certification cycle, which can be done alternatively/ additionally with a viscosity index improver (VII). The formulation with an VII can also provide specific rheological properties which are beneficial at high rpm or high temperature (for instance enabling sufficiently high viscosity to obtain a sufficiently stable lubricant film protecting from excessive wear, see Figure 1). Figure 1: Comparison of three formulations based on pure base stock, including conventional polyalkyl methacrylates (PAMA) and comb polymers. Viscosity index improvers are required to have sufficient shear stability and optimal thickening efficiency at low (-40…40°C, typically as low as possible) and at high (80…150°C, typically as high as possible) temperatures. For mineral oils it is also important to have good wax compatibility/ inhibition behavior. Modern comb polymers suffice these conditions quite well - they possess a polar back bone and relatively long side chains. The thickening mechanism is described by the solvation of the backbone and side chains. Both can be optimized to achieve a better combination of shear stability and thickening efficiency to formulate oils with far less temperature dependent viscosity or in other words with higher 170 23rd International Colloquium Tribology - January 2022 Polymers as important additives in E-drive fluids viscosity index (VI) as seen in Figure 1. The thickening of these polymers at low temperatures is quite insignificant and allows the use of relatively thick base stocks. The shear stability of the polymers defines the stability of the viscosity profile (optimized for the start of service) during the lifetime. Shear induces mechanical degradation of polymers and thickening becomes less, which resembles itself in the viscosity reduction of the formulation (see figure 2). The shear loss (viscosity reduction in %) is usually measured after tapered roller bearing in a 192 h test. With comb polymers it is possible to formulate oils with high VI and still pass severe requirements on shear loss, even with relatively high KV100 = 6 cSt, as seen in figure 2. The low temperature viscosity must be kept as low as possible for efficient oil pumping, efficient lubrication and cooling at starting conditions. This is realized at best with the synthetic base stocks and comb technology (see Figure 3). Figure 2: Comparison of shear stability of the formulations with different base stocks (API Gr III or polyalphaolefins-PAO) and corresponding VII technology. Comb polymers enable high VI formulations with sufficient shear stability. All formulations are defined at fresh KV100 = 6cSt and same Dispersant/ Inhibitor-additives. Figure 3: Comparison of Brookfield viscosity of the formulations (KV100 =6 cSt) with different base stocks (API Gr III or PAO) and VII technology. 1.2 Transmission Efficiency The mechanical transmission efficiency is dependent on several parameters, but specifically on the operation cycle and used lubricant. The newest requirements for the transmission efficiency are defined based on the Worldwide harmonized Light vehicles Test Procedure (WLTC). We have used an electrical highly integrated axle transmission with 150 kW power and maximum speed of 16000 rpm from a European manufacturer to study the influence of the operating viscosity or VI, VII type and the base stock composition. The formulation parameters are summarized in table 1. These represent the currently often used targets on kinematic viscosity and low temperature viscosity requirements. The transmission was operated at the characteristic torque and rpm combinations, replicating the WLTC cycle. In Figure 4 the final results on reduction of mechanical transmission losses are shown. In these results it can be seen the benefit of operating viscosity reduction/ high VI of the oil, the use of comb polymers, polymer functionalization and base oil type. Moreover, there is a benefit of using a higher viscosity grade of Gr III base stock in these formulations. Table 1. Example formulations with conventional polyalkylmethacrylates (PAMA) and comb polymers. All formulations have included same Dispersant/ Inhibitor-additives and exhibit similar KV100. Figure 4: Reduction of the mechanical losses in transmission upscaled to the WLTC operation mode with use of different formulations from table 1. Several parameters such as operating viscosity or VI, used base stock composition and polymer functionalization impact the efficiency. 23rd International Colloquium Tribology - January 2022 171 Polymers as important additives in E-drive fluids This has also an additional benefit of improved oil evaporation loss and flash point. Such a formulation strategy can only be followed if a polymer can provide very low thickening at low temperatures to suffice Brookfield requirements. Use of fully synthetic polyalphaolefin base stock compositions provide further significant losses reduction in the range of 20%. Figure 5: Electrical conductivity of the pure Gr III 4cSt base fluids treated with 10% of the different VIIs. The shown data represents the polymer contribution to the electrical conductivity of the formulation at nearly maximum treat rate. Values are shown as function of the kinematic viscosity, which varied by temperature increase from room temperature to 150°C. 1.3 Compatibility The challenge for the formulator is to provide a fluid with increased tribological performance and less aggressive behavior against materials such as elastomers, Cu and insulation materials as well as low electrical conductivity. The polyalkylmethacrylates and comb polymers are the ingredients, which can slightly increase the electrical conductivity of the base oil, especially if functionalized (Figure 5). This electrical conductivity increase is though not critical since the currently acceptable level of electrical conductivity is in the range of >10 nS/ m at 100°C. For these requirements the formulator has no limitation in the choice of the polymer for the desired functional properties in the formulation.The polymers have no negative impact on the Cu corrosion either as seen in table 2. Functionalized polymers can even provide a protective function as seen in the pure base stock API Gr III + 10% polymer blends. Table 2: Cu-corrosion rating after the ASTM D130, 180°C, 3h. Results show that polymers do not harm Cu, or even provide protective function if functionalized. 1.4 Wear and Durability The well-known property of E-motors is the availability of significant torque (>40 Nm) already at relatively low rpm (<800 rpm) compared to internal combustion engines. Figure 6: Results of the four-ball test ASTM D 4172 with API Gr III base stock and blends with 10% polymer. Two effects can be seen, the effect of operating viscosity and the effect of functionalization with F-PA- MA2 polymer. The latter delivers wear scar diameter comparable with formulations having full set of AW/ EP additives. This property is great for the efficient acceleration of the vehicle but brings additional care for the durability of the transmission due to reduced lubricating film thicknesses at above-described conditions. Functionalized PAMAs can help maintaining the sufficient lubricating film thickness at the desired lubricating conditions (which can be seen in Figure 6). In four ball test experiment it is recognizable that blends of 10% polymer in API Gr III oils can provide wear scars (0.6 mm) comparable with fully formulated fluids containing full set of AW/ EP additives. In addition to the wear in the four-ball apparatus one can see that pitting damage in both gear and bearing elements can be reduced and double the lifetime (see Figure 7). Figure 7: FZG PT C/ 9/ 90 FVA2/ IV and FE 8 pitting tests with 3 repetitions each show doubling of the lifetime with a formulation containing 6% of the functionalized F-PAMA2. Both formulations have KV100=6 cSt and full set of AW/ EP additives. 172 23rd International Colloquium Tribology - January 2022 Polymers as important additives in E-drive fluids 2. Conclusion New requirements to the compatibility of the lubricant with the electrical components force formulators to look for new ways to formulate fluids and use existing additives. Owing to the good no-harm performance of the polyalkylmethacrylates and comb polymers these polymers can be useful in several aspects: • Comb polymers enable the use of thicker base stocks in the formulation with severe requirements on shear stability and low temperature performance • Comb polymers and especially functionalized types are very suitable to improve efficiency of the electrical power train. • Functionalized PAMA and Comb can provide benefits in durability of gear and bearing elements. In addition, these can be useful for Cu protection. • Both linear PAMA and COMB structures are fully compatible with E-drive components. References [1] Bundesministerium für Umwelt, Naturschutz und nukleare Sicherheit. [Online] 01. September 2021. [Zitat vom: 02. 09 2021.] https: / / www.bmu.de/ themen/ klimaschutz-anpassung/ klimaschutz/ nationale-klimapolitik/ klimaschutzplan-2050. [2] UNECE Vehicle Regulations. [Online] https: / / unece.org/ transport/ vehicle-regulations. [3] Electric Axle Drive Module for high Speeds. Domian, Hans-Jörg, Ketteler, Karl-Hermann und Scharr, Stephan. Berlin: Springer, 2013, ATZ Worldwide, Bd. 13, S. 10-13. [4] Wincierz Christoph, Michael Mueller, Aidan Rose. Corporate experience of Evonik Oil Additives. [Befragte Person] Dmitriy Shakhvorostov. 6. 12 2011. [5] The Effect of Viscosity Index on the Efficiency of Transmission Lubricants. Vickerman, Richard J., Kevin Streck, Elizabeth Schiferl, and Ananda Gajanayake. 2010, SAE International Journal of Fuels and Lubricants, S. 20-26. 23rd International Colloquium Tribology - January 2022 173 Enhanced Gear Lubricity for Lubricant Oils Applied to Transaxles in HEVs and EVs Keiichi Narita Idemitsu Kosan Co.,Ltd./ Lubricants Research Laboratory, Ichihara-shi, Japan Corresponding author: keiichi.narita.0440@idemitsu.com 1. Introduction Numbers of hybrid electric vehicles (HEVs) and electric vehicles (EVs), which provide an excellent fuel economy and reduced carbon dioxide emission, are increasing. 1) E-Axle (transaxle for electric vehicles) is an electric drive unit that integrates a motor, an inverter and reduction gears, which is highly versatile and has high fuel efficiency. E-Axle is being developed by various manufactures. For further improvement in motor performance and dedicated utilization for EVs, these units are expected to become a downsized transaxle in future. In addition, for street use with frequent starts and stops, around half of motor power loss is caused by copper loss, which is affected by the coil temperature. 2) Heat transfer property for motors, which is called as motor cooling is an important issue for E-Axle to improve the efficiency of driving motors. Automatic transmission fluids (ATFs) are used in some cases as a lubricant for E-Axle. 2) The main performance requirements for E-Axle fluids are (1) cooling ability for motors (2) durability for gears and bearing components. In addition to (1) and (2), also required properties are oxidation stability, anti-forming and compatibility for elastomers, similar to conventional ATFs. ATFs have complex compositions designed to provide lubrication and friction control for shift devises, and are not always optimal as E-Axle fluids. Lubricant additives providing excellent lubricity may generally tend to reduce electric resistance on the condition that the motor coil is immersed in axle fluids. This lubricant aspect involves the ability of the oil limit corrosion of copper elements, mainly copper wiring and electronic sensors. 3) At present, the lubricant properties on the cooling performance have not been systematically studied. An effective oil for E-Axle may be expected provide high performance in electrical compatibility at extremely low viscosities, at higher speeds in an operating condition. In this study, we report the results aimed mainly at improving cooling ability by base oil properties and extending durability for gear components. 2. Cooling performance for E-Axle fluids Excellent cooling can be obtained for oil-cooled system because oil is highly insulating and the motor is immersed directly into it. It is reported that a three-phase squirrel-cage induction motor is operated at the maximum temperature of 150 °C. 1) Therefore, it is important to focus on the heat transfer behaviour from 100 to 150 °C. A laboratory test method for the cooling at a forced convection condition was originally designed. The test oil is supplied by the oil pump from the oil tank, and is controlled at a constant flow rate of 0.5 kg/ min. and at 70 °C temperature. Oil bulk temperature in oil pan may be around 70-80 °C in normal use. The test oils are flowed through the rectangular section, the copper plate attached the heater is set up. Heat flux at 160 W was supplied to the copper plate to reach 150 °C. The change in the copper plate temperature was monitored by thermocouples and then the cooling speed was calculated through differentiating the temperature by time. Figure 2 shows the effects of viscosity and type of base oil on the cooling speed. Test oils were prepared so that viscosities at 70 °C was from 1.3 to 16.4 mm 2 / s by using different type base oils. It is obvious that the cooling speed increase with lower viscosity oils. Comparing between hydrocracked mineral and naphthene mineral base oil with similar viscosity 8-9 mm 2 / s, hydrocracked base shows a better cooling ability. In addition, synthetic base oil results in an excellent cooling performance. The difference in cooling speed among base oil type may be caused by their molecular structure. Hydrocracked base oil includes more normal chain saturated hydrocarbon rather than naphthene base oil. Thermal vibration energy will come down to the main chain, and such energy transferred through collisions with neighbouring molecules is promptly propagated to the end of the main chain through intermolecular heat transfer, leading to a higher heat conductivity. 174 23rd International Colloquium Tribology - January 2022 Enhanced Gear Lubricity for Lubricant Oils Applied to Transaxles in HEVs and EVs Figure 1: Effects of base oil on the cooling performance 3. Gear lubricity for E-Axle fluids Applying a transmission fluid with extremely lower viscosity to E-Axle system would potentially give an advantage for a better motor cooling. It is known that low friction in gears is achieved by using lower viscosity gear oils. 3) However, it is necessary to consider a negative impact on the durability of gear components. The gear pitting fatigue life by lubricants was evaluated by using a FZG (Forshungsstelle fur Zahnrader and Getriebebau) gear test rig. Gear type C is operated at a pitch line of 8.3 m/ s speed in torque stage 302Nm at 90 °C oil temperature. The pitting life is defined as the number of load cycles when the mostly damaged gear flank exceeds about 5 mm 2 . The test oils were prepared by blending a hydrocracked mineral base stock and three kinds of additive formulation. Figure 2 shows the effects of test oil viscosity and additive formulation on the FZG pitting life. First, the viscosity of test oils was varied from 4.0 to 6.3 mm 2 / s at 90 °C with the same additive formulation A (circle plot in Figure 3). The gear fatigue life decreased with lowing viscosity in proportion to the viscosity 0.7 , which could be influenced by the difference in the oil film thickness calculated under EHD lubrication regime. Figure 3 shows the optical images of the post-test gear flank surface at the 19 million load cycles from the test oil with 4.0 mm 2 / s viscosity and additive formulation A. Macropitting was observed on the overall gear flank surface. This damaged area shows the shape of an inverted triangle, which seems to be due to a typical surface originated rolling fatigue. There are many micropitting under the pitch line, which could promote a rapid growth of macropitting. In the upper part of dedendum area, there are many micropitting. Significant adhesion wear occurred in the lower part of dedendum. The high stress and sliding action of the gear tends to result in removing material and ploughing material toward the pinion root. This adhesion wear in the case of lower viscosity oil was more significant than that of higher viscosity. Secondly, the additive formulation was found to be a great influential impact on the fatigue life. The sample with higher viscosity 8.6 mm 2 / s at 90 °C and additive formulation B (rhombus plot in Figure 3) shows a shorter fatigue life than the case of additive formulation A. Interestingly, the oil containing additive formulation C (square plot in Figure 3) demonstrates a longer fatigue life in spite of the lowest viscosity of all tested samples. Combining X-ray photoelectron microscopy (XPS) analysis with sputtering by ion irradiation enables depth-profiling investigation of interfaces with multi-layer films. The XPS results revealed that the film composed of calcium and phosphorus species was formed with 100-200nm thickness in case of longer life sample. This tribofilm could minimize adhesion in the contact regions in the pinion dedendum region, leading to prevent from generating micropitting, with a longer fatigue life. We propose that lower viscosity fluid with appropriate additive formulation would give an advantage for motor cooling and gear lubricity for E-Axle. Figure 2: Effects of oil viscosity and additive formulation on the gear pitting life Figure 3: Images of the post-test gear flank surface at FZG 19 million load cycles from the test oil with 4.0 mm 2 / s viscosity and additive formulation A 4. Conclusions We investigated the lubricant impact on the motor cooling performance and the gear lubricity. Lowering kine- 23rd International Colloquium Tribology - January 2022 175 Enhanced Gear Lubricity for Lubricant Oils Applied to Transaxles in HEVs and EVs matic viscosity of lubricants improved cooling performance in forced convection condition, and this cooling speed could be greatly influenced by base oil molecular structure. The gear fatigue life decreased with lowering viscosity of oils. Interestingly, a sort of additive formulation could extend the gear pitting life. Tribofilm derived from anti-wear agent could play a role in minimizing adhesion wear, leading to a longer fatigue life. References [1] Society of Automotive Engineers of Japan, Inc. ed. Automotive Technology Handbook-Design (EV-Handbook) Edition, 2016. [2] Onimaru, et.al., “Heat analysis of the hybrid electric vehicle (HEV) Motor cooling structure using ATF”, Denso Technical Review, 13,1,2008. [3] Leonardo Israel Farfan-Cabrera, “Tribology of electric vehicles : A review of critical components, current state and future improvement trends”, Tribology International, 138,473-486,2019. [4] Ellichello, et.al., “Point-surface-origin micropitting caused by geometric stress concentration”, GEAR TECHNOLOGY, January 2011, 54-59. 23rd International Colloquium Tribology - January 2022 177 Improved energy efficiency and thermal management in EVs using novel synthetic base stocks Babak Lotfi ExxonMobil Chemical Company 1. Abstract Advanced hardware designs aim to optimize performance of electric vehicles. To maximize energy efficiency, manufacturers are looking for lower viscosity lubricants. These challenges require stepout lubricant performance and novel base stock molecules. Integrated drive units, where the lubricant is also used to cool the e-motor and electrical components, bring new challenges around thermal management, electrical properties, and material compatibility. Base oil, the major component of the lubricant formulation, plays a critical role in delivering enhanced performance. Therefore, base stock properties are becoming more critical when developing superior lubricants. This research explores the use of novel PAOs in EV driveline fluids. Their balance of low viscosity and volatility, critical for the optimum performance of EV fluids, enables lubricant formulations below 3 cSt KV 100 to deliver maximum energy efficiency benefits. Novel PAOs, along with other synthetic base stocks, have been evaluated for their energy efficiency, thermal management, and electrical properties. Thermal management and cooling properties of synthetic base stocks have been studied compared to next best alternatives in an actual e-motor system. Testing suggests superior performance of synthetic base stocks which results in lower system operating temperatures. This enables increased input power and a more compact design of the system. Novel PAOs also demonstrate improved energy efficiency, which enables extended driving range. 2. Introduction Innovation is key in driving new technology opportunities. Fig. 1. depicts next generation synthetic PAOs in comparison to conventional PAOs and Gr II and Gr III base stocks. Next generation synthetic PAOs can provide an excellent balance of low viscosity and low volatility properties, which can provide an advantage for drive unit (gear-box and e-motor) performance in EV applications where new challenges like material compatibility and operating conditions pose new requirements in comparison to conventional driveline design. Novel synthetic PAOs bring new solutions and products to address increasingly challenging demands in EV as well as many other applications. Fig. 1: Viscosity vs. volatility. 178 23rd International Colloquium Tribology - January 2022 Improved energy efficiency and thermal management inEVs using novel synthetic base stocks 3. Thermal management As discussed, many automotive manufacturers have been adopting the integrated drive-unit design. In this approach, a single fluid is being used for cooling the electric-motor and electrical components, in addition to lubricating the gears, bearings and possibly clutches in the drive-unit. This can pose new challenges to the fluid development, while the compact design in the integrated system can provide more efficiency in vehicles. In this design, synthetic base stocks like PAO with desirable dielectric properties and enhanced thermal properties compared to Gr II/ III base stock can provide superior thermal management. This method can also provide a safer, lighter, and more efficient system. 4. Energy Efficiency Improving energy efficiency in both conventional and electric vehicles (including both hybrid and fully EVs) has been of high interest for automotive manufacturers. EV driveline fluids are essential in maximizing the energy efficiency in drive unit systems. Higher energy efficiency in mechanical systems, like reduction gears, can offer extended range, which is highly valuable for automotive manufactures and consumers. In this work, FZG energy efficiency FVA 345 has been used to evaluate the traction coefficient between a next-gen PAO blend and Gr II+/ III+ blend. Fig 2. shows the nextgen PAO blend has significantly lower traction than the Gr II+/ III+ blend at different lubrication regimes. Results suggest higher energy efficiency for the next-gen PAO blend compared to the Gr II+/ III+ blend, which can extend driving range in EVs. Fig. 2: FZG energy efficiency test (FVA 345), next-gen PAO blend vs. Gr II+/ III+ blend at similar viscosity (KV100) 5. Conclusion • EV design and performance targets continue to evolve and continue to bring new challenges for EV fluids • Low-viscosity low-volatility next-gen PAOs help bring new solutions to address challenging demands in EVs • Next-gen PAOs can enable enhanced thermal management and improved energy efficiency resulting in extended driving range for EVs Automotive and Transport Industry Lubricant 23rd International Colloquium Tribology - January 2022 183 Impact of Lubricant Formulation on Surface Damage in Electric Vehicle Transmissions Alexander MacLaren Imperial College London, London, UK Corresponding author: dam216@imperial.ac.uk Amir Kadiric Imperial College London, London, UK 1. Introduction Power losses in electric vehicle (EV) drivetrain transmissions are responsible for a much larger portion of the overall energy loss than in internal combustion engine powered vehicles [1]. The electrification of the fleet of passenger cars worldwide, as part of the global drive to reduce CO 2 emissions, requires tackling consumer range anxiety, and hence maximising driving range and battery duty cycle [2], both of which depend on mechanical transmission efficiency. Drivetrain losses can be divided into load-dependent (traction) and load-independent (churning, windage) components, which depend primarily on gearbox architecture and oil rheology [3]. Owing to the relatively high speeds in EV gearboxes, oil churning losses caused by rotating gears and bearings are a major contributor to drivetrain loss. The current trend for reducing gearbox oil viscosity has the effect of mitigating these viscous losses. However, transmission lubricants must also prevent surface damage by providing a hydrodynamic film, even under the aggressive conditions of high motor torque and low entrainment speed, for which high lubricant viscosity is required. To ensure the transmission is reliably efficient over lifetime, the gearbox design and lubricant formulation must reconcile these competing requirements to control friction, wear, and surface fatigue damage. To achieve this, efficiency and reliability must be considered together to be optimised through drivetrain design and lubricant formulation. In this study, a selection of custom made and commercial EV transmission lubricants are assessed in terms of their ability to resist surface damage modes in EV transmissions, including scuffing and micropitting. The formulations tested include a water-based lubricant, an automatic transmission fluid, a gear oil, and a common base oil. Scuffing performance is evaluated in a ball-on-disc tribometer under EV-representative conditions using a recently developed test method based on contrarotation which improves test repeatability and allows the effect of lubricant viscosity and chemical formulation to be examined independently [4]. Micropitting is studied using a proven methodology employing a triple-disc machine, enabling close control of contact conditions, and allowing the evolution of micropitting with contact cycles to be monitored [5]. Results are discussed in terms of lubricant chemistry, tribofilm evolution, asperity contact stresses and wear during the test, with a particular focus on the water-based fluid. 2. Experimental Procedure Two sets of experiments were conducted, one to investigate micropitting, and the other for scuffing, two primary damage modes of gears and bearings in EV helical reduction gearboxes. The contact conditions were chosen to replicate those experienced by the motor pinion tooth contacts during rapid acceleration, based on the gear geometry of a drive unit from a popular EV currently on the market. 2.1 Micropitting The triple-disc rolling contact fatigue machine (MPR by PCS Instruments), shown in Figure 1, was employed to examine the micropitting performance of each fluid under the conditions given in Table 1. AISI 52100 specimens and line contact conditions were used in all tests, maintaining a lambda ratio of 0.4 to enable a representative comparison in the boundary regime. Table 1: Contact conditions for MPR tests Max. Hertz Pressure p 0 1.5 GPa Entrainment Speed U e 3.902 m/ s Slide-Roll Ratio SRR -5 % Lambda Ratio Ʌ 0.4 ± 0.02 The MPR allows independent control of disc speed ωdiscs and roller speed ωroller, hence any entrainment speed Ue = (Udiscs+Uroller) and slide-roll ratio SRR = × 100 % is possible up to tangential speeds of 4 m/ s. The upper disc load P was controlled and the roller drive torque measured, allowing traction coefficient μ to be calculated. 184 23rd International Colloquium Tribology - January 2022 Impact of Lubricant Formulation on Surface Damage in Electric Vehicle Transmissions Figure 1: Configuration of discs and roller in PCS MPR test The roller and disc surfaces were inspected at intervals during the test, according to the schedule in Table 2. Inspections were conducted by optical microscopy of the roller surface, and stylus profilometry of the three discs and the roller, at 4 positions, 90° apart, on each. Table 2: Inspection Intervals for Micropitting Test Step 10 3 Cycles Cumulative Roller Inspection Disc Inspection 1 50 50k 2 50 100k 3 450 550k 4 450 1M 5 1000 2M - 6 1000 3M - 7 2000 5M - 8 2000 7M - 9 4000 11M 2.2 Scuffing Scuffing performance was evaluated using a ball-on-disc tribometer from PCS instruments, the ETM, capable of independent control of ball and disc tangential speeds up to 4 m/ s, traction force measurement, and contact pressure up to 3.5 GPa for AISI 52100 steel specimens. The Spacer Layer Imaging Method (SLIM) was used to examine the ball surface at set intervals to establish tribofilm thickness and qualitatively monitor wear on the ball surface. The test method was based on that previously developed by Peng et al [4]. An initial running-in step at low speed and SRR was employed to achieve maximally comparable contact conditions. Successive increases in SRR in contrarotation (SRR >200 %) at constant entrainment speed were then conducted, interspersed by a rest step to allow thermal equilibration, during which a SLIM image was taken. The test was stopped at the onset of scuffing, characterised by a rapid and irreversible increase in traction coefficient, accompanied by appreciable noise and vibration from the ETM. 3. Results Progression of roller material loss was evaluated via stylus profilometry, a typical example is given in Figure 2 . The evolution of the roller surface throughout the micropitting test allows the progress and nature of the damage to be monitored, as shown in Figure 3. These and other results will be presented in the talk. Figure 2: Example evolution of micropitting wear on the roller profile during test on gear oil Figure 3: Example optical microscope images of roller surface evolution throughout micropitting test on gear oil 23rd International Colloquium Tribology - January 2022 185 Impact of Lubricant Formulation on Surface Damage in Electric Vehicle Transmissions 4. Conclusion Micropitting, wear and scuffing failure were successfully generated on steel specimens across a representative range of candidate EV transmission lubricants, allowing a comparison of their performance under conditions experienced in EV transmission components. References [1] Kadiric, A., & Shore, J. (2021). Prediction of Power Losses in Electric Vehicle Transmissions. STLE Virtual Annual Meeting & Exhibition. Online. [2] Pevec, D., Babic, J., Carvalho, A., Ghiassi-Farrokhfal, Y., Ketter, W., & Podobnik, V. (2019). Electric vehicle range anxiety: An obstacle for the personal transportation (r)evolution? . 4th International Conference on Smart and Sustainable Technologies, SpliTech 2019. [3] Christodoulias, A. I., Olver, A. V., Kadiric, A., Sworski, A. E., Kolekar, A., & Lockwood, F. E. (2014). The efficiency of a simple spur gearbox - A thermally coupled lubrication model. American Gear Manufacturers Association Fall Technical Meeting 2014, AGAM FTM 2014, 81-98. [4] Peng, B., Spikes, H., & Kadiric, A. (2019). The Development and Application of a Scuffing Test Based on Contra-rotation. Tribology Letters, 67(2), 37. [5] Wainwright, B., & Kadiric, A. (2021). The Effect of Surface Roughness and the Λ Ratio on the Initiation and Progression of Micropitting Damage. STLE Virtual Annual Meeting & Exhibition. Online. 23rd International Colloquium Tribology - January 2022 187 Optimizing the Mo concentration in low viscosity fully formulated engine oils Aaron Thornley Insitute of Functional Surfaces, School of Mechanical Engineering, University of Leeds, Leeds, England Corresponding author: mnatho@leeds.ac.uk Yuechang Wang Insitute of Functional Surfaces, School of Mechanical Engineering, University of Leeds, Leeds, England Chun Wang Insitute of Functional Surfaces, School of Mechanical Engineering, University of Leeds, Leeds, England Jiaqi Chen Sinopec Lubricant Company, Beijing, China Haipeng Huang Sinopec Lubricant Company, Beijing, China Hong Liu Sinopec Lubricant Company, Beijing, China Anne Neville Insitute of Functional Surfaces, School of Mechanical Engineering, University of Leeds, Leeds, England Ardian Morina Insitute of Functional Surfaces, School of Mechanical Engineering, University of Leeds, Leeds, England 1. Introduction Original equipment manufacturers (OEMs) are constantly finding new ways to increase the fuel economy for their vehicles. Such drive for better fuel economy has been increased due to strict CO 2 emissions legislation from countries and regions such as China and Europe. Therefore, OEMs have to implement different solutions to meet these requirements set by international governments. One efficient approach to increase the fuel economy that OEMs are taking is to decrease the viscosity of the engine oil. Previous research has shown that a 2.75% fuel efficiency increase can be achieved using an SAE 5W-20 oil compared to an SAE 10W-30 oil. Lowering the viscosity further still produces positive results; a 1.5% increase can be achieved using a 0W-20 compared to a 5W-30. A new oil grade has been introduced recently as SAE 0W-8 to counteract the tighter CO 2 reductions further. Since this is a relatively new oil grade, little research has been conducted on 0W-8 engine oils. However, recent studies have shown that a fuel economy increase of 0.57% and 0.8% can be obtained using a 0W-8 engine oil compared to 0W-16 [1]. Decreasing oil viscosity generates more metal-to-metal contact between the components, especially at high temperatures where the oil is at its thinnest [2]. In addition, components that make up the piston assembly, exhaust, and inlet valve all have increased friction when lowering the oil’s viscosity, as these operate at lower lambda ratios. The increased fuel economy demands are causing countries like Japan to increase the concentration of molybdenum dithiocarbamate (MoDTC) to very high amounts of 1000+ ppm, which supposedly gives prolonged fuel economy boosts. However, when lowering the oil’s viscosity, the concentration of boundary additives has to be increased due to a decrease in lambda ratio at the tribo-contacts and additive depletion due to oxidation [3]. In addition, there is also a need to reduce the amount of sulfur, which is part of the MoDTC molecule within engine oils due to its harmful effects on the engine and its relatively high cost [4,5]. Therefore, understanding the behavior of MoDTC concentration in fresh oils and aged oils is extremely important, which will directly lead to the optimization of MoDTC in low viscosity oils. 188 23rd International Colloquium Tribology - January 2022 Optimizing the Mo concentration in low viscosity fully formulated engine oils 2. Methodology MoDTC needs to perform in the low viscosity conditions but does not need to be present in significant excess such that it is expensive/ inefficient and will increase SAPS level of the oil. It is also not necessarily the highest Mo concentration producing a ≈ 0.04 friction value in the boundary lubrication regime, which is the lowest friction obtained with this additive. A low friction value of ≈ 0.04 must be achieved over a range of lambda ratios to produce an overall performance similar to its higher concentration counterparts, including wear. In total, six different Mo concentrations ranging from 85 to 1000 ppm, including an oil with 0 ppm of Mo, were selected for this research. All friction tests were conducted using a mini traction machine (MTM) with traction and Stribeck phases. A space layer imaging (SLIM) unit attached to the MTM enabled zinc dialkyl dithiophosphate (ZDDP) tribofilm thickness measurements to be obtained at set intervals during the tests. To understand the influence Mo concentration has on tribochemistry, x-ray photoelectron spectroscopy (XPS) and Raman techniques were used. Finally, wear generated during the MTM testing was analyzed using an NPFlex, and tribofilms were removed before wear measurements using EDTA solution. 3. Key results Figure 1 displays the steady-state friction and wear coefficients obtained from MTM and NPFlex analysis for the selected Mo concentrations. Increasing the Mo concentration decreases the coefficient of friction, and there is a threshold value to which the ≈ 0.04 friction is achieved. Wear increases with the addition of MoDTC but does not significantly change when Mo concentration increases past the optimum value. The Stribeck curves taken towards the end of the test, under a varying lambda ratio, are shown in figure 2. Mo concentrations ≥ 350 ppm all produce ≈ 0.04 friction across the range of entrainment speeds/ lambda ratios. The 180 ppm displays increased friction during the Stribeck curve compared to a constant speed due to the Mo concentration influencing the MoS2 layer thickness and its formation and removal rate. Finally, figure 3 displays the total intensity counts of MoS 2 within the tribofilm matrix for each steady-state friction. From the figure, a threshold value of total intensity counts is required to produce a ≈ 0.04 friction tribofilm. As the Mo concentration increases, the total intensity counts increase to a maximum value, to which further increases would not significantly change the intensity counts. Figure 1: Steady-state friction and wear coefficients for selected Mo concentrations. Figure 2: Final Stribeck curves taken for all Mo concentrations. Figure 3: Steady-state friction vs total intensity counts of MoS2 within the tribofilm matrix for all friction-reducing tribofilms. 23rd International Colloquium Tribology - January 2022 189 Optimizing the Mo concentration in low viscosity fully formulated engine oils 4. Conclusion In this research study, the optimum Mo concentration for ultra-low engine oil is between the range of 180 to 350 ppm. The lowest Mo concentration, which produces similar friction and wear results to its higher concentration counterparts. Increasing the Mo concentration decreases the induction time to reach steady-state friction due to increased MoS 2 layer thickness in the ZDDP dominant tribofilm in the beginning stages of film formation. The optical film thickness of the ZDDP tribofilm significantly decreases with the addition of MoDTC due to its decomposition products preventing its formation. Increasing the Mo concentration past the optimum value does not significantly change the steady-state film thickness. The rate of formation and removal of MoS 2 within a ZDDP dominant tribofilm is highly dependent on Mo concentration, and the formation rate becomes more significant with higher Mo concentration. Increasing the Mo concentration increases the total intensity counts of MoS 2 within the ZDDP dominant tribofilm up to a specific concentration, 500 ppm in this study. Any further increase in Mo concentration does not result in higher total intensity counts. Adding MoDTC into a fully formulated oil increases the wear generated due to competitive surface absorption. However, increasing the Mo concentration past the optimum value does not negatively impact the wear, with negligible differences. References [1] Okuda S, Saito H, Nakano S, Koike Y. Development of JASO GLV-1 0W-8 Low Viscosity Engine Oil for Improving Fuel Efficiency considering Oil Consumption and Engine Wear Performance. 2020; 1-9. [2] Bovington C, Korcek S, Sorab J. The importance of the Stribeck curve in the minimisation of engine friction. Tribol Ser. 1999; 36: 205-14. [3] De Feo M, Minfray C, De Barros Bouchet MI, Thiebaut B, Martin JM. MoDTC friction modifier additive degradation: Correlation between tribological performance and chemical changes. RSC Adv [Internet]. 2015; 5(114): 93786-96. Available from: http: / / dx.doi.org/ 10.1039/ C5RA15250J [4] Yan L, Yue W, Wang C, Wei D, Xu B. Comparing tribological behaviors of sulfurand phosphorus-free organomolybdenum additive with ZDDP and MoDTC. Tribol Int. 2012; 53: 150-8. [5] Spikes H. Low-and zero-sulphated ash, phosphorus and sulphur anti-wear additives for engine oils. Lubr Sci. 2008; 20(2): 103-36. 23rd International Colloquium Tribology - January 2022 191 Rheological properties of Lubricants and their correlation with fuel economy performance Maryam Sepehr Chevron Oronite Company LLC, Richmond California, USA Sara Zhang Chevron Oronite Company LLC, Richmond California, USA David Morgan Chevron Oronite Company LLC, Richmond California, USA Ramoun Mourhatch Chevron Oronite Company LLC, Richmond California, USA Peter Kleijwegt Chevron Oronite Technology BV, Rotterdam, The Netherlands Claire Chommeloux Chevron Oronite Company LLC, Richmond California, USA 1. Introduction One of the least expensive pathways to achieving improvements in vehicle fuel economy is through changes to engine lubricant viscosity and composition [1]. Driven by ever more stringent emissions regulations, OEMs are therefore requiring engine oils to continue protecting engines at lower viscosities and reduced friction. Different engine operating conditions represent a range of lubrication conditions, and to better understand the full impact of engine lubrication process, one must understand how oils perform in these conditions. In general, additives in lubricants help to provide the right balance of fuel economy while maintaining durability protection. The focus of the present study is on the hydrodynamic lubrication regime, and rheological properties of oils were investigated and correlated to their fuel economy performance in different engines, Mercedes Benz OM 501 LA and Detroit Diesel DD13, and driving cycles, WHTC (World-Harmonized Transient Cycle) and modal. 2. Testing A series of fully formulated oils were tested in OM 501 LA in WHTC driving cycles, and in DD13 in modal operating conditions. A rotational rheometer MCR 302 (from Anton Paar), and high shear viscometer USV (from PCS Instruments) were used to measure the rheological properties of these oils at different shear rates from 1 to 10 7 s -1 at different temperatures, from 20 to 120°C, with an increment of 20°C. A generalized Newtonian fluid model, Carreau-Yasuda model [2], was used to fit the experimental data, and compared to fuel economy performance of the oils in different engines. 3. Results and discussion An example of rheological profiles of different fully formulated multi-grade lubricating oils is shown at 100°C in Figure 1. Viscosity is lower for lower viscosity grades, and one can also note more distinct shear thinning behaviour for heavier oils, between 10 4 - 10 7 s -1 . These oils were tested in a DD13 engine under modal operating conditions. Results of FEI (Fuel Economy Improvement) compared to a baseline SAE 10W-30 oil are summarized in Figure 2. 192 23rd International Colloquium Tribology - January 2022 Rheological properties of Lubricants and their correlation with fuel economy performance Figure 1: Viscosity profile of different fully formulated multi-grade oils at 100°C. Figure 2: Fuel Economy Improvement of oils tested in DD13 in modal operation. Higher viscosity oils result in lower FEI in the engine. One expects for different viscosity grade oils to see significant differences in their rheological profile and FE performance. A strong correlation can be observed between rheological profile and FEI of these oils in wide range of shear rates. The developed rheological method and profiles can also differentiate oils within same viscosity grade, and correctly rank and predict their FE performance. This is specifically useful in considering weighting of discrete operating points in modal engine operation test procedures. Figures 3 and 4 show the rheological profiles and FEI results of a series of SAE 0W-20 oils tested in OM 501 LA, respectively. For simplicity, the FEI results of run 1 of WHTC and rheological profile of oils at average oil sump temperature of WHTC 1 st run have been shown in these 2 figures. Figure 3: Viscosity profiles of different SAE 0W-20 oils at 82°C, the average oil sump temperature of run 1 of WHTC driving cycle. The blue box represents a proposed engine/ driving operation window of shear rate. Figure 4: Fuel Economy Improvement of SAE 0W-20 oils tested in OM 501 LA. Results correspond to the 1 st run of WHTC. The difference between the rheological profiles (Figure 3) and FEI (Figure 4) of the SAE 0W-20 oils are smaller than the difference seen for different viscosity grade oils (shown in figures 1 and 2). In addition, one can also note that, at constant temperature, the viscosity curve of these oils may cross over at different shear rates, which is caused by different shear-thinning behaviour of these oils. As an example, at a constant temperature, viscosity of Oil E is the lowest at lower shear rate, and the highest at higher shear rates. On the other hand, Oil B shows the highest viscosity at lower shear rate, and the lowest at higher shear rate. Oil B show stronger shear-thinning behaviour compared to Oil E. Depending on the engine/ driving operation window, FEI results may vary for the same oils. In the case of OM 501 LA, applied shear rates in the operation window are not higher than 10 7 s -1 . Therefore, in this engine and driving conditions, Oil E with lower viscosity at low shear rates shows the highest FEI, and Oil B shows one of the lowest 23rd International Colloquium Tribology - January 2022 193 Rheological properties of Lubricants and their correlation with fuel economy performance FEI. It can be noticed that FEI of oils has strong correlation with their rheological profile in proposed the engine/ driving operation window of shear rate. In addition to shear-thinning behaviour of oils, their response to temperature or their VI also plays a role on their response in different engine operating conditions. More examples will be discussed during the presentation, showing how the developed rheological profile can well describe and correlate to FEI of oils, particularly for engines and driving cycles with dominant hydrodynamic lubrication regimes. 4. Summary Rheological properties of lubricating oils are crucial in understanding frictional losses in different parts of an engine, in different operating conditions. In the present study, the rheological properties of a series of fully formulated multi-grade lubricating oils, tested in engines, were investigated using different types of rheometer/ viscometers over a range of temperatures and shear rates, and a generalized Newtonian model was used to fit the experimental data. The results of developed rheological methods can be used to predict relative fuel economy performance of oils in an engine under driving conditions with dominant hydrodynamic regimes. This technique is an effective tool in development of more fuel-efficient motor oils. References [1] Miller, T. “The Road to Improved Heavy Duty Fuel Economy”. Directions in Engine-Efficiency and Emissions Research (DEER) Conference, 2010. [2] Carreau, P; De Kee D; Chhabra, R; “Rheology of Polymeric Systems: Principles and Applications”, Hanser Publishers, 1997 Engine 23rd International Colloquium Tribology - January 2022 197 In-Bore Engine Component Tribology M. Priest, M. F. Fox Faculty of Engineering and Informatics, University of Bradford, UK 1 Baker, A J S, et.al, Intl.Symp.Mar.Engrs., Tokyo, paper 256, 2.5.59-70, 1973. 2 Dimitroff, E, et.al, Trans.ASME, 406, July 1969 3 Economu, P N, et.al, ‘Piston Ring Lubrication’, Pt.1, ASME, New York 1979 4 Richard, G P, Proc.8th Leeds-Lyon Symp. Tribology, Paper VII(ii), 1982; Bush, G P, et.al, Trib.Intl., p.231, 24, 1991 5 Saville, S B, et.al, SAE 881586, 6 Bagshaw, J, et.al, Trib.Int, 30, 1997. 1. Introduction Only 25% of fuel energy is delivered to light vehicles wheels, 40% for heavy duty transport. Piston and ring pack component internal friction is a major loss, at ~20% of overall efficiency. Total fuel efficiency improvements must be improved in concert with weight reduction, improved thermodynamic efficiency and reduced rolling resistance. Given light vehicle electrification, heavy duty i/ c engines will be required for the foreseeable future. Understanding i/ c engine in-bore component tribology requires knowledge of the lubricant’s role. Conventional wisdom to the 1960’s held that a thin lubricant film at the piston/ bore interface was the same as the sump but at higher temperatures; lubricant above the top ring either evaporated or burned. However, a standing ring of lubricant was demonstrated in the piston ring zone 1 ; inter-ring gas from an operating engine showed extensive degradation of simultaneous oil samples 2 . This changed appreciation of lubricant conditions in the piston led to extensive modelling and testing by Dowson et.al. 3 Figure 1: Piston Ring Lubrication Model This modelling, and the large body of further research it inspired, clearly showed that piston rings operate with a very thin film of lubricant, <1μm towards TDC and BDC, with the upper rings starved of lubricant by the action of the oil-control ring at the base of the piston. The lubricant viscous flow interactions between the rings, Figure 1, and the added effects of gas flow through the ring pack and the inertia of the reciprocating piston, demonstrated that lubricant could reside in this region for some considerable time. Analyses of lubricant samples from the bore wall at the 1 st ring TDC reversal position of diesel engines showed the ring zone lubricant to be severely degraded compared to the sump. The extent of degradation of base oils and additives meant that different lubricant grades could not be differentiated 4 . More measured, differentiated, degradation of base oils and additives was found by continuous internal sampling from the first ring groove of operating engines 5 . Insights gained led to improved lubricant formulation and performance. As one example, ZDDP’s sequentially degraded through several intermediates to the sulphide. A lubricant transport model equilibrated a large (sump) Continuous Flow Stirred Tank Reactor, CFSTR, with a similar (ring zone) reactor and calculated relative base oil and additives degradation rates 6 . Figure 2: Lubricant Transport Model Between Sump and Ring Zone as Two Continuous Flow Stirred Tank Reactors in Equilibrium 198 23rd International Colloquium Tribology - January 2022 In-Bore Engine Component Tribology ‘Residence time’ measurements of lubricant in the ring zone showed how the ring pack controlled flow for both large and small engines, and for different sampling positions. Second ring groove, intermediate land, first groove and crown land samples showed progressive base oil and additive degradation at different rates as the lubricant progressed up the piston face. Degradation of additives was shown to primarily occur in the 1 st ring zone with base oil degradation in the 1 st ring/ crown land region. Continuous measurement of gas and lubricant flow rates as functions of diesel engine speed and load showed plateaus between 40-75% of an engine range 7 , Figure 3. Figure 3: Oil Flow Rates from 1 st and 3 rd Ring Positions, CAT 3406 Engine, 700-1900rpm. 7 C J Jones, PhD Thesis, dMU(UK), 2000 8 Notay, R S, et.al,Trib.Intl, 112, 129, 2019. 9 OME Smith, PhD Thesis, Leeds(UK), 2 Different ring pack designs for the same piston showed substantial changes in oil and gas flow rates, enabling reduced emissions without increased wear. ‘Residence time’ measurements of ring zone lubricant using compatible ‘tracer’ compounds showed how the ring pack controlled flow for both large and small engines, and different sampling positions. For the CAT 3406 engine at 1400rpm, residence times ranged between 6 minutes from the 2 nd ring, 16min for the inter-ring land, 26min from the 1 st ring and 72min for the crown land. ‘Laser Induced Fluorescence’ in the bore wall of both a motored and fired engine measured lubricant film thickness as the piston ring assembly passed the observation point. The changes in oil film thickness between and above the ring pack were consistent with the previous sampling results. Significant differences in oil film thickness were observed between new and ‘end of service use’ oils 8 .‘ An ‘In-Bore Friction Loss Measurement’ system was developed to measure friction losses between an operating piston and bore. A range of organic compounds was added to a standard fuel as potential friction modifiers. Switching between standard fuel and fuels with friction modifier additives showed distinctive patterns of friction reduction. The optimum organic compounds showed friction loss reductions of 4% by introducing lubricants directly into the combustion chamber and piston ring zone as friction modifiers 9 . 23rd International Colloquium Tribology - January 2022 199 Radioactive Tracer Engine Wear Test Development Peter M. Lee, Gregory A.T. Hanson Southwest Research Institute, San Antonio, Texas, USA. 1. Introduction Engine wear has been a concern since the internal combustion engine was first developed. As internal combustion engines became main stream and vehicle manufacturers started selling them in their millions each year, an industry was established around testing lubricants for, amongst other things, wear protection. Southwest Research Institute (SwRI ® ) is part of this Industry, testing lubricants through engine Sequence tests to qualify them for lubricant standards. In parallel with this, SwRI ® has developed research capabilities to assist lubricant, additive and OEM clients in understanding wear phenomena in engines. SwRI ® developed Radioactive Tracer Technology (RATT ® ) for real time engine wear evaluations. This involves irradiating engine components using either bulk or surface layer activation using radioactive sources. The decaying activated parts release isotopes, which can be detected by radioactive detectors. Once the engine is assembled, the engine components wear during engine operation, becoming wear debris in the oil and releasing the isotopes. The level of isotopes present in the oil is then detected, and the strength of the signal for each isotope correlated with the mass of wear material in the oil. 2. Testing A 2.0L Ecoboost direct injection gasoline engine with activated valvetrain, top piston rings, liner and turbo thrust plate was used, and conditions investigated to further understand the technology and guide future RATT ® engine wear testing programs. The project team had three questions: 1. What is the correct data collection time for the RATT ® signal? 30, 120 or 300 seconds. 2. What effect does engine build mid test have on test repeatability? 3. Is there a ‘settle’ time for the engine to return to ‘normal’ wear conditions after a severe engine cycle that has created high wear events? In addition, the team had interest in measuring valvetrain wear during both hot and cold oil temperature engine cycles in preparation for future engine test development work on modern engine architectures. Also, with continued drive towards reduced viscosities, SAE 0W-16 and SAE 0W-08 oil was used to investigate the effects on wear using viscosities lower than the recommended engine lubricant viscosity of 5W-30. Table 1 shows the test lubricants used in this project. Well established operating conditions for this engine were used, as shown in Table 2. Table 1: Test Lubricants, Viscosity and Additive package Test Lubricant Viscosity Add. Pack 0W-08 0W-08 A 0W-16 0W-16 A 5W-30 Medium Wear (MW) 5W-30 A 5W-30 Low Wear (LW) 5W-30 B 5W-30 High Wear (HW) 5W-30 C 200 23rd International Colloquium Tribology - January 2022 Radioactive Tracer Engine Wear Test Development Table 2: Engine operating conditions; name and description Operation Condition Description Stop-Start, Very Cold (SS_VC) Start, immediate hard acceleration at high load to moderate speed for 10 sec, drop to low load/ moderate speed for 20 sec, stop engine, soak off 1 min, repeat for extended period of time. Very cold engine temperatures. Boundary Lubrication (Boundary) Start at moderate load and moderate engine speed. Hold throttle while slowly ramping engine speed to idle. Warm engine temperatures. Transient Speed: Low Load, Cold (TS_LL_Cold) Ramp engine speed from medium to high RPM at low engine torque and cold engine temperatures. Transient Speed: Low Load, Hot (TS_LL_Hot) Ramp engine speed from medium to high RPM at low engine torque and hot engine temperatures. Shortened Sequence IVA (IVA) Ramp engine speed from idle to 1500 RPM at constant torque. Warm engine temperatures. 3. Results During each sample time (30s, 120s and 300s) the oil is constantly flowing through the detector. As such, the wear measurements taken are an average of that time. Significant differences were observed comparing results with the standard deviation obtained over the sample times. Most reliable results are obtained when the standard deviation is the lowest and the wear rates are significantly higher than the standard deviation. 120s was the best for the camshaft, top ring face, liner and turbo thrust plate wear. For the top ring side wear, 300 seconds gave the best results. Only one sample rate can be used, therefore, 120 second sampling time was selected for all future work. Mid matrix the engine was removed from the test stand, disassembled and reassembled twice with the purpose of observing any change in wear rate due to the rebuild. It was observed that immediately following the rebuild, a spike in wear occured for the camshaft and top ring face and that it took only 4 hours of running to re-establish its pre teardown wear rates. Tests were undertaken on the High Wear oil to investiage the effects of severe high wear engine cycles on subsequent cycles. The majority of the components showed no significant change in wear when comparing the before and after severe wear test. The few that did, showed a temporary reduction in wear. A 1h run-in stabilized this. Camshafts primarily operate in the mixed to boundary lubrication regime. In these regimes, there is little lubricant and therefore, bulk viscosity has little impact on wear. In these regimes, it is the wear resistance of the additive package that is of greatest importance. In Figure 1, it is important to remember that we are seeing the effects of two things on the results: The same additive package with three different viscosity grades and the same viscosity grade with three different levels of wear protection. Figure 1: Camshaft wear for each test cycle and lubricant The effect of additive package can clearly be seen in the IVA, SS_VC and TS_LL_Hot cycles with the expected low wear oil being low, medium wear oil being in the middle and the higher wear oil being noticeably higher. This shows that it is possible to develop a camshaft wear test that will differentiate between test lubricants for modern architecture engine. The current IVA and IVB engine tests were developed as low temperature wear tests in the belief that the additives are not activated at the lower temperatures. However, it is interesting to note that in this work significantly more camshaft wear was observed during the hot engine cycle. Both the Boundary and TS_LL_Cold cycles did not show the anticipated relationship between wear and additive package. For the boundary cycle, this may have been due to the fairly low levels of wear being measured vs. the average standard errors. For the TS_LL_Cold cycle, it may have been due to the increased viscosity (caused by cold oil temperatures) of the lubricant forcing the contact more into mixed regime, where additive package will have less effect. The 0W-08 lubricant was run through the engine as the last five engine runs. This engine was designed to operate on a 5W-30 lubricant and therefore, this was not expected to go well, hence it being the final part of the text matrix. Tests were run in order of anticipated engine wear severity from the least to the most. The turbo failed during the final test. The turbo failure may have been due to the low viscosity of this lubricant or the fact that the engine had 23rd International Colloquium Tribology - January 2022 201 Radioactive Tracer Engine Wear Test Development already run the 97-hour run-in and 48 test cycles or, more likely, a combination of both. In general, comparing the 0W-08 wear results with other wear results, the higher wear values anticipated were not observed. 4. Conclusion Five distinct conclusions resulted from this work: 1. 120s was found to be the most statistically accurate sample time for RATT ® wear measurements. 2. The effect of engine tear down and rebuild on differences in preand post-test wear did not have a significant effect. Results showed a 4h post build run-in sufficient to stabilize wear rates. 3. Results showed little evidence to support concerns that severe engine cycles could have an effect on wear during the next engine test cycle. 4. Hot and cold test cycles showed camshaft wear could be produced and measured on this engine. It was observed that significantly more wear occurred during the hot engine cycle. 5. The engine operated successfully on SAE 0W-08 lubricant. Lower wear was measured than anticipated. This work has maintained confidence in the RATT ® engine wear technology and will guide future RATT ® engine wear testing programs undertaken at SwRI ® 23rd International Colloquium Tribology - January 2022 203 Squeeze Film Investigations in a Simulating Piston-Ring Cylinder Liner Experimental Set-up Polychronis Dellis School of Mechanical Engineering Educators, ASPETE, Athens, Greece Corresponding author: pasd@city.ac.uk 1. Introduction The study of overall load carrying capacity of the pistonring and liner lubricated interface leads to the tribological explanation and evaluation of the different parameters that affect the lubricated conjunction and the surface interaction. The main focus is on optimising lubrication and promote effective lubrication of the surfaces in contact. As part of this, friction reduction, cavitation initiation and development, which in turn limits the load carrying capacity and measurement of the oil film thickness, flow rate and oil film pressure has become a priority that eventually leads to emissions reduction. The saviour in lubrication terms is the squeeze film effect at low velocities where a thick enough film to sustain the load capacity is non-existent. According to Stachowiak and Bachelor [1], an extremely useful characteristic of squeeze films is that they provide increased load capacity (although temporarily) when a bearing is suddenly subjected to an abnormally high load. As regards to the motion of either side of the bearing surface, the squeeze film force is always opposite in direction to their motion. 2. Squeeze Film: Minimum oil film thickness (MOFT) - Friction force measurements - Load capacity of piston-ring Evidence of squeeze film effect can be found in the minimum oil film thickness measurements where one can notice that the measurement profile is not symmetric. As Bolander et al [2] have pointed out, the point of absolute minimum of the oil film thickness measurement is shifted a few degrees from the TDC and BDC. Friction peaks correspond to asperity interaction, contact between the piston-ring and liner surfaces where the boundary lubrication prevails. The lubricant begins to squeeze out of the contact area while the pressure generated through this squeezing motion shifts the profile towards the center line [2]. The interpretation of the minimum oil film thickness measurements is important as it identifies the lubrication rheology phenomena that in turn, affect the load capacity of a certain piston-ring configuration. 2.1 Experimental set-up In a simplified single-ring test rig, a steady piston-ring section is placed under a flat surface used as a reciprocating liner. The idealised simulation test rig benefits from simplified lubrication conditions compared to the real engine taking advantage of the simple design layout. As a result, solid and repeatable results are taken allowing the lubricant film characteristics to be examined in isolation. Sensors that measure oil film pressure, thickness (optical - LIF and electrical capacitance), friction and imaging, provide the necessary parametric data to study the effect of speed, load, temperature, piston-ring curvature and variable lubricant properties. When the liner decelerates, the interface reaches a state of mixed lubrication and asperity interaction and frictional losses continue to decrease until the liner reaches boundary lubrication close to the dead centers, as the squeeze film prevails. As the liner accelerates away from the dead centers, the lubricated film begins to develop. While being close to the dead center, asperity interaction between the surfaces remains significant with the squeeze film effect also taking place, resulting in beneficial oil support as it is supported partly by the lubricant present in the contact [3]. Increase in temperature in a lubricant model investigation had the effect of decrease in oil film thickness and advanced the initiation of cavitation and enhanced its intensity [4]. Less viscosity results in less squeezing force from the oil around the dead centers and thus greater asperity contact force is generated to support the radial ring load. Less oil squeezing force is responsible for more asperity contact around the dead centers [5]. The purpose of this study is to show the effect of squeeze film variation and extract useful parametric results that show the effect of different lubricants and setups on friction peaks / losses, correlate and verify them to other measurement techniques for the single ring set-up (such as MOFT measurements). Cavitation initiation and development is another factor that should be taken into account and assess whether cavitation development at the beginning of the stroke together with impeding or aiding factors, play a significant role in friction peaks and MOFT minima. Eventually, a clearer picture will be 204 23rd International Colloquium Tribology - January 2022 Squeeze Film Investigations in a Simulating Piston-Ring Cylinder Liner Experimental Set-up attained to the aspects of load carrying capacity of the ring and the rheological behaviour of chemical additives with a view to establishing the likely performance gains in new lubricant formulations. 2.2 Results In a set of experiments focused on high temperature testing, high friction peaks were noticed when oil viscosity changed to lower values as lubricant temperature increases and MOFT decreases significantly [6]. At higher temperatures the asperity interaction at the boundarymixed lubrication region is intense giving considerably higher friction results than the ones taken at lower temperatures. As MOFT decreases with high temperature, friction force peaks move closer to the dead center of the stroke with absolute friction values that are significantly higher. This gives evidence that the squeeze film effect does not have a strong impact at high lubricant temperatures. Figure 1: Temperature effect on friction force peaks at 300 rpm, 3371 N/ m load, top dead center [6]. In previous publications it was shown that for the MOFT measurements, high load testing is combined with squeeze film movement towards the dead centers of the stroke. High temperature testing showed that the MOFT decreases significantly from ambient temperature (33 °C) to 50 °C and that the squeezing action is getting marginal. The same action is shown in Figure 2 for the friction peaks [7]. For a set of different lubricants, the properties of which can be found in Table 1, friction force peaks have different behaviour close to the dead centers. Figure 2 shows that for similar speed and load and temperature testing conditions friction force peaks move closer to the dead centers for the lubricant that has the lowest VI, V40 and HTHS (High Temperature, High Shear) viscosity. Figure 2: Lubricant properties effect on friction force peaks at 300 rpm, 971 N/ m load. It has been verified that different forms of cavitation appear after the dead centers of the stroke that accompany the squeeze film which is measured in the capacitance and friction signals [4, 6, 7, 8]. The geometry of the piston-ring affects the friction force as well. The flatter the piston-ring, the lower the friction force peak and they also appear earlier in the stroke [6]. Table 1: Oils tested for temperature-friction investigations Blend Code 003B 006E/ 02 005A/ 02 002A/ 02 Grade 0W-30 0W-40 0W-20 10W-40 HTHS(mPas) 3.30 3.4 2.14 4.05 V 100 (cSt) 12.16 12.8 6.04 14.97 V 40 (cSt) 68.93 66.8 31 97.8 VI 182 196 146 160 3. Conclusions • The squeeze film effect between the liner surface and the piston ring, shift the friction force peaks, as it forces the lubricant flow to delay compared to the liner movement. • With an increase in load in every lubricant the flow reversal due to the squeeze film effect appears closer to the dead centers. That could be also attributed to the fact that the viscous film impedes the liner’s reciprocation. • With an increase in reciprocation speed for constant load, friction force maxima have lower absolute measurements and appear at a greater distance from the dead centers. • Large radius of curvature for the ring profile promotes effective squeeze action at the ends of the stroke, as the flatter ring enhances a stronger squeeze effect than the curved ring at the dead centers. • Different oil blends produce different appearance for the friction peaks in terms of their distance from the dead centers. • Load capacity is affected by the cavitating region. 23rd International Colloquium Tribology - January 2022 205 Squeeze Film Investigations in a Simulating Piston-Ring Cylinder Liner Experimental Set-up References [1] Stachowiak G.W. and Bachelor A.D., “Engineering Tribology”, ELSEVIER, 1993. [2] Bolander, N. W., Steenwyk, B. D., Sadeghi, F. and Gerber, G. R., “Lubrication Regime Transitions at the Piston Ring - Cylinder Liner Interface”, Proceedings of the Institution of Mechanical Engineers Part J: Journal of Engineering Tribology, Vol 219, 2005. [3] Dellis P.S., “Piston-ring performance: limitations from cavitation and friction, International Journal of Structural Integrityˮ, Vol. 10 No. 3, pp. 304-324, 2019. [4] Nouri J. M., Vasilakos I., Yan Y., “Cavitation between cylinder-liner and piston-ring in a new designed optical IC engine”, Int. J. of Engine Research, (on line first) 9 Apr 2021. [5] Tian, T., Wong, V. W., and Heywood, J. B. “A Piston-Ring Pack Film Thickness and Friction Model for Multigrade Oil and rough surfaces”, SAE paper 962032, 1996. [6] Dellis P., “Effect of Friction Force between Piston Rings and Liner: a Parametric Study of Speed, Load, Temperature, Piston-Ring Curvature and High-Temperature, High-Shear Viscosity”, Proc IMechE, Part J: J Engineering Tribology, 224(5): pp. 411-426, 2010. [7] Dellis P., “Oil Film Thickness Measurements Combined with High Temperature Friction Investigations in a Simplified Piston-Ring Lubrication Test Rig”, Tribology in Industry, 41 No. 4, 471-483, 2019. [8] Dellis P., “Cavitation initiation and patterns in engine lubricants as a result of different operating conditions and lubricant properties”, STLE Virtual Annual Meeting and Exhibition, May 17-20, 2021, New Orleans, USA. 23rd International Colloquium Tribology - January 2022 207 The Effect of Friction Modifier and Viscosity on Piston Rings/ Cylinder Liner Friction in Floating Liner Single-Cylinder Engine Tests Abdullah Alenezi Institute of Functional Surfaces (iFS), School of Mechanical Engineering, University of Leeds, Leeds,UK Corresponding author: mn06ana@leeds.ac.uk Benoît Thiébaut Centre de Recherches de Solaize, TOTAL, Solaize, France Cayetano Espejo Institute of Functional Surfaces (iFS), School of Mechanical Engineering, University of Leeds, Leeds,UK Ardian Morina Institute of Functional Surfaces (iFS), School of Mechanical Engineering, University of Leeds, Leeds,UK 1. Introduction The AVL “floating liner” friction single-cylinder engine (FRISC) was used to perform tests at fired and motored modes at different loads and speeds using fully formulated oils. This extended abstract presents an analysis of friction force raw data to investigate the effect of molybdenum dithiocarbamate (MoDTC) concentration and oil viscosity on friction reduction throughout piston strokes, particularly at boundary regimes of reversal points at Top Dead Centre (TDC) and Bottom Dead Centre (BDC). 2. Methodology 2.1 Formulated Oils In this paper, the effect of two oil properties on friction performance have been investigated: the effect of small amount increments of MoDTC additive and the effect of two viscosity grades (HTHS 2.1 & 3). The HTHS1.7 and HTHS2.1 oils were used as reference oils. Table 1 provides the details of the first and second groups of the tested oils. The oils were provided by TOTAL. Table 1: Test Oils Description 1st Group of Oils 2nd Group of Oils A1 HTHS2.1 A2 HTHS1.7 (0W8) B1 HTHS2.1+ 0.5wt% Mo B2 HTHS1.7 + 0.1wt% Mo C1 HTHS2.1+ 1.0wt% Mo C2 HTHS1.7 + 0.3wt% Mo D1 HTHS3 D2 HTHS1.7 + 0.5wt% Mo E2 HTHS1.7 + 0.7wt% Mo 2.2 AVL FRISC Engine Tests Conditions/ procedure Both oil groups were tested at 90 °C for oil/ coolant. For the first group, each oil was tested at motored mode with four speeds and fired mode with four load/ speeds. Each condition was run for three stages (Loop 1  Stabilisation run 15 hrs  Loop 2). Frictional force was measured at every 0.2º crank angle. For the second group, a new liner was fitted for each test. All tests were at 1200 rpm/ 6.5 bar except the 4 th test was at 1000 rpm/ 12 bar. The first test was performed by ramping up MoDTC oils for one hour each (i.e., starting by no Moly oil  0.1% Mo  0.3% Mo  0.5% Mo  0.7% Mo). The 2 nd , 3 rd and 4 th tests were performed by HTHS1.7 oil first and then 0.1%, 0.5%, and 0.5% Mo, respectively. 3. Results and Discussion All lubrication regimes (e.g., boundary, mixed and hydrodynamic) exist at the contact between piston rings/ liner along each stroke and they control the friction force results [1, 2]. At the reversal points (TDC and BDC), the boundary and mixed lubrication regimes dominate the contact while at the mid stroke, the hydrodynamic regime exists because of high piston speed and the surfaces are expected to be not in contact, but the friction occurs because of shear force and pressure difference between oil film layers [2, 3]. Moreover, the profile of load, speed 208 23rd International Colloquium Tribology - January 2022 The Effect of Friction Modifier and Viscosity on Piston Rings/ Cylinder Liner Friction in Floating Liner Single-Cylinder Engine Tests and temperature along the stroke travel are changeable according to operating conditions [1]. MoDTC started to reduce friction significantly from 0.3% Mo and onwards while 0.1 % Mo had slight effect, as shown in Figure 1. In addition, MoDTC concentration was seen to contribute remarkably in friction reduction at the bottom one third of piston at BDCs. This indicates that 0.3 to 0.7% Mo oils have successed to form more low friction MoS 2 tribofilm than the 0.1% Mo oil. Overall, the 0.7% Mo has the highest friction reduction at all piston positions except at TDCs. However, all MoDTC concentrations showed insignificant effect at TDCs. This can be attributed to the dominant effect of the boundary lubrication regime which exists due to high combustion gases pressures and temperatures as well as the low piston speed [4]. Furthernore, it can be seen that the upwards strokes (Compression & Exhaust) show more friction reduction at the mid strokes and BDCs than downwards strokes (Intake & Exhaust). This can be attributed to the dominant effect of the boundary lubrication regime which exists due to high combustion gases pressures and temperatures as well as the low piston speed [4]. Furthernore, it can be seen that the upwards strokes (Compression & Exhaust) show more friction reduction at the mid strokes and BDCs than downwards strokes (Intake & Exhaust). This can be attributed to low pressure at the begining of the strokes. Figure 1: Friction reduction (%) at ramping up MoDTC A similar approach has been used to test the oils with different viscosity properties. Friction results from those tests will be shown and discussed in the main paper. 4. Conclusion In conclusion, 0.3 to 0.7% Mo have strong influence on friction reduction at BDCs. All MoDTCs showed insignificant friction reduction at TDCs Viscosity showed a significant effect on friction reduction with higher HTHS at reversal points especially at TDCs. References [1] Priest, M. and Taylor, C.J.W. Automobile engine tribology—approaching the surface. 2000, 241(2), pp.193-203. [2] Nagar, P. and Miers, S. Friction between Piston and Cylinder of an IC Engine: a Review. SAE Technical Paper, 2011. [3] Profito, F.J., Tomanik, E., Lastres, L.F. and Zachariadis, D.C. Effect of lubricant viscosity and friction modifier on reciprocating tests. SAE Technical Paper, 2013. [4] Priest, M. Factors influencing boundary friction and wear of piston rings. In: Tribology series. Elsevier, 2000, pp.409-416. 23rd International Colloquium Tribology - January 2022 209 Thermal expansion influence on the scuffing initiation in a piston ring cylinder liner contact Simona Dahdah Univ Lyon, INSA-Lyon, CNRS UMR5259, LaMCoS, F-69621, France. Groupe PSA, Velizy Villacoublay, France. Corresponding author: simona.dahdah@insa-lyon.fr Nans Biboulet Univ Lyon, INSA-Lyon, CNRS UMR5259, LaMCoS, F-69621, France. Antonius Lubrecht Univ Lyon, INSA-Lyon, CNRS UMR5259, LaMCoS, F-69621, France. Pierre Charles Groupe PSA, Velizy Villacoublay, France. 1. Introduction The piston-ring/ cylinder-liner (PRCL) contact influ-ences the overall performance of internal combustion engine (ICE) as it causes half of the engine losses [1]. Hence, the importance to study the phenomena acting in this contact as well as its lubrication system. In addi-tion, the PRCL pack may be exposed to scuffing. Scuff-ing is a failure mode that can appear in a lubricated contact with sliding bodies [2]. It is accompanied by temperature and friction increase. Its occurrence in the ICE is rare but once it initiates, the damage is cata-strophic and permanent, thus the importance to predict its initiation. Several factors contribute to scuffing initiation. Oil quantity and contact temperature as well as the contact load are crucial parameters [3]. In the current study scuffing initiation is predicted through a thermal approach. The reduction of the lubricant film thickness increases the friction and the temperature leading to a thermal expansion. The latter in turn in-creases the contact load and the contact temperature [4]. This is the thermo-mechanical effect. Moreover, the temperature gradient generates a surface tension gradient and a lubricant convection can take place leading to a temporarily local lack in lubricant. These two effects accentuate the scuffing initiation risk in the PRCL contact. On the contrary, the ring passage along the liner redistributes the oil in the contact and helps to avoid starvation [5]. This effect delays the scuffing initiation. This study aims to model the contribution of the mentioned effects to scuffing occurrence. 2. Model 2.1 Marangoni effect Figure 1: Marangoni effect model Figure 1 describes the Marangoni effect, the lubricant flows from the low surface tension zone (γ low) to the high surface tension zone (γ high). The oil convection leads to the appearance of a localized lack of lubricant. The oil quantity moved due to the Marangoni effect is quantified as a surface as a function of the temperature and surface tension gradients. In addition, the lubricant redistributed due to the ring passage is also quantified as a moved surface. Both surfaces are compared is order to predict the scuffing initiation limit. 210 23rd International Colloquium Tribology - January 2022 Thermal expansion influence on the scuffing initiation in a piston ring cylinder liner contact 2.2 Thermo-mechanical effect Figure 2: Thermo-mechanical effect loop The thermo-mechanical effect is modelled via a loop shown in figure 2. Assuming that a temporarily local lack of lubricant occurs in the contact, the coefficient of friction increases and an additional heat flux is generat-ed that causes an increase in the contact temperature. The temperature gradient leads to a ring deformation, and an additional load is generated. The oil film thick-ness is then calculated and the coefficient of friction is defined via the Stribeck curve. The loop runs until the contact temperature re-stabilizes to the nominal tem-perature or it exceeds the lubricant additive desorption limit. 3. Main results Different cases are given in table 1. The red color in the table indicates the scuffing initiation risk whilst the green one refers to the safe zone where no risk of scuffing exists. When the contact temperature exceeds the limit temperature of the oil additive system desorption (Tlimit=180°C) or when the surface displaced due to the Marangoni effect is larger than the redistribution due to the ring passage, scuffing risk exists. Otherwise, scuff-ing initiation is prevented. The correct way to read the table is to compare the cells with the same color of the input parameter, which is the only parameter varied between the two cases. By comparing case 2 to case 1, the initial temperature increase varies. In case 1, the increase of 15°C did not lead to scuffing initiation, and the contact opeartes in the safe zone. Whilst, in case 2, the temperature increase is suffisient to cause scuffing and the contact no longer operates in the safe zone. Case 3 is also compared to case 1, the oil supply regime carries the difference out. When the lubricant film thickness decreases, the coefficient of friction in-creases, as well as the generated heat. A transition from the safe zone tot he risk zone occurs. To study the effect of the heated zone width, case 4 is compared to case 2. For the same temperature increase, scuffing is delayed when the width of the heated zone increases. In case 4, scuffing is prevented and the contact operates in the safe zone. A transition from the safe zone to the risk zone takes place between case 4 and case 5 when the lubricant supply regime becomes more severe. 4. Notation Table 2: Problem parameters Symbol Parameter T Temperature [°C] ΔT Temperature increase [°C] p contact Contact pressure [pa] p additional Additional pressure [pa] μ Coefficient of friction [-] u m Mean velocity [m/ s] v Lubricant velocity [m/ s] q Heat flux [w/ m2] h 0 Oil film thickness [m] h mean Mean oil thickness [m] s Heated zone width [mm] λ Oil distribution wavelength [mm] σ Surface roughness [m] γ Surface tension [N/ m] η Oil viscosity [pa.s] 5. Conclusion This study models the interaction between the tempera-ture, the oil film thickness and the contact load. The scuffing initiation limit is predicted as a function of three effects: the thermo-mechanical effect, the Marangoni effect and the ring displacement effect. The first two effects 23rd International Colloquium Tribology - January 2022 211 Thermal expansion influence on the scuffing initiation in a piston ring cylinder liner contact accentuate the scuffing initiation whilst the third one contributes to delay the scuffing risk. The three of them depend on the problem operating parameters. References [1] S.C.Tung, and M.L.McMillan, “Automotive tribology overview of current advances and challenges for the he future,” Tribology International, 37, 3, 2004, 517-536. [2] F.Saedi, S.Shevchik, and K.Wasmer, “Automatic detection of scuffing using acoustic emission,” Tribo-logy International, 94, 2016, 112-117. [3] P.Obert, T.Mlüler, H.J.Füßer, and D.Bartel, “The influence of oil supply and cylinder liner temperature on friction, wear and scuffing behavior of piston ring cylinder liner contacts-a new model test,” Tribology International, 94, 2016, 306-314. [4] C.Fang, X.Meng, X.King, B.Zhao, and H.Huang, “Transient tribo-dynamics analysis and friction loss evaluation of piston during cold-and warm-start of a SI engine,” International Journal of Mechanical Sciences, 133, 2017, 767-787. [5] M.Organisciak, G.Cavallaro, and A.Lubrecht, “Variable lubricant supply of a starved hydrodynamic line-ar contact: lubricant lateral flow for smooth and laser textured surfaces,” Proceedings of the Institution of Mechanical Engineers, Journal of Engineering Triboln ogy, 221, 3, 2007, 247-258. Table 1: Different cases Parameter Unit Case 1 Case 2 Case 3 Case 4 Case 5 s=λ mm 4.4 4.4 4.4 6.25 6.25 T 0 °C 90 90 90 90 90 ΔT °C 15 20 15 20 20 Oil supply regime mean oil supply regime mean oil supply regime mean oil supply regime mean oil supply regime mean oil supply regime h 0 =h mean m 8e -7 4.3e -8 3.4e -7 7e -7 4e -8 T °C 90 182 182 90 182 Surface Marangoni mm 2 2e -7 1.6e -6 9.5e -7 1.4e -7 7e -7 Surface ring passage mm 2 5e -9 1.2e -5 8e -6 3.4e -9 4e -6 Operating condition no risk of scuffing risk of scuffing risk of scuffing no risk of scuffing risk of scuffing 23rd International Colloquium Tribology - January 2022 213 A fast Piston-Ring/ Cylinder-Liner friction prediction based on a semi-analytical hydrodynamic model and real measured surface topography Thomas Lubrecht Univ Lyon, INSA-Lyon, CNRS UMR5259, LaMCoS, F-69621, France. IREIS, HEF GROUPE, Andrézieux-Bouthéon F42160, France. Corresponding author: thomas.lubrecht@insa-lyon.fr Nans Biboulet Univ Lyon, INSA-Lyon, CNRS UMR5259, LaMCoS, F-69621, France. Antonius Adrianus Lubrecht Univ Lyon, INSA-Lyon, CNRS UMR5259, LaMCoS, F-69621, France. Johnny Dufils IREIS, HEF GROUPE, Andrézieux-Bouthéon F42160, France. 1. Introduction It is no longer possible to ignore the impact of the human activity on the earth global warming. In 2018, transport sectors relying on Internal Combustion Engines (ICE) technologies have emitted about 6.8 Gt of CO2 (about 18% of worldwide CO2 emissions) [1-2]. For decades, tribologist have worked to reduce ICEs friction and thus improve their efficiency and reduce their polluting emissions [3]. Regarding todays context, industrials and laboratories have shown even more interest in improving the tribological performance of the piston assembly which accounts for about 50% of the total friction losses in ICEs [3]. Within the piston assembly, the Piston-Ring / Cylinder- Liner (PRCL) contact is the most susceptible to generate significant friction losses because of its tough operating conditions. Numerical simulations have the advantage of being cheap and fast compared to full engine tests. For these reasons many PRCL friction prediction models have been elaborated [4-6]. However, full engine tests give global results while numerical methods mainly focused on one physical phenomenon. For example, complex solvers have been developed trying to understand the hydrodynamic contact physics [7]. Whereas simplified stochastic methods have been used to solve the dry contact challenge [8-10]. According to the authors, in order to be attractive for industrials a simulation tool has to be easy, fast, robust while being consistent with the physics involved. Therefore, a new approach to PRCL friction prediction has been computed. 2. Method It is well known that the PRCL contact operates in the mixed and hydrodynamic lubrication regime [11]. Hence, to correctly simulate the contact a combined hydrodynamic/ dry solver model has been elaborated. 2.1 Hydrodynamic contact Based on the Iso-Viscous-Rigid transient Reynolds equation for smooth starved contacts, the ring force balance and the oil flow balance at the contact, N. Biboulet et al. [12] developed a system of four equations and four unknows. Using a non-linear solver, they managed to compute the ring flying height for a variety of operating conditions. The main benefits of this method are the direct consideration of the oil starvation, the oil transport (i.e. oil accumulation) and the squeeze effect. 2.2 Dry contact Usually, PRCL friction simulation relies on stochastic dry contact theories such as developed by Greenwood & Williamson [8] or Greenwood & Tripp [9]. These theories are easy and quick to compute but they are based on non-measurable surface parameters. In order to avoid this, a different approach is suggested. First, a surface topography is measured as shown in Figure 1. Secondly, the measured topography is used as an input in a highperformance numerical tool [13] computing the load / separation-height curve shown in Figure 2. Lastly, the previous curve is interpolated allowing a direct assessment of the load carried by the solid asperities at a given flying height. Only a few iterations are required to com- 214 23rd International Colloquium Tribology - January 2022 A fast Piston-Ring/ Cylinder-Liner friction prediction based on a semi-analytical hydrodynamic model and real measured surface topography pute the ring minimum film thickness fulfilling the ring force balance, considering hydrodynamic and solid contact physics. Figure 1: Measured liner topography Figure 2: Load-separation curve (circle: load, quares: real contact area ratio) 3. Results Figure 3 shows typical results computed using the previously described method, highlighting a continuous transition through lubrication regimes. One can observe the film squeeze effect at the bottom and top dead centre where the film thickness is not zero. At mid-stroke, oil starvation due to limited oil supply is studied and the ring flying height is steady. The friction is mainly generated by viscous forces. During the combustion stroke (at about +10° crankshaft angle) solid contact between the ring and liner occurs due to the incylinder pressure rise. The friction is dominated by solid contact. Figure 3: Compression ring friction (solid line) and minimum oil film thickness (dashed line). 4. Conclusion Based on a combined approach, a PRCL friction prediction model dedicated to industrial handling has been developed. Key model outcomes are listed below: • Simulations allow a fast and reliable prediction of • PRCL friction for various operating conditions. • Coupling between the semi-analytical hydrodynamic • model and the dry contact model relying on • measured surface topography shows a coherent • transition throughout the different lubrication regimes. • The solid contact model presented offers a fast and • physical meaning alternative to usual stochastic • contact theories. References [1] IEA, “Tracking Transport 2020”, IEA, Paris, 2020. [2] Friedlingstein et al., “Global Carbon Budget 2021”, Earth Syst. Sci. Data Discuss, [preprint], in review, 2021. [3] Holmberg, Kenneth, Peter Andersson, and Ali Erdemir, “Global Energy Consumption Due to Friction in Passenger Cars.”, Tribology International 47, 2012, 221-34. [4] T. Tian, V. W. Wong, and J. Heywood, “A piston ring-pack film thickness and friction model for multigrade oils and rough surfaces”, SAE Technical Paper, vol. 962032, 1996. [5] E. Tomanik, “Modelling the hydrodynamic support of the cylinder bore and piston rings with laser textured surfaces”, Tribology international, 59, 90-96, 2013. 23rd International Colloquium Tribology - January 2022 215 A fast Piston-Ring/ Cylinder-Liner friction prediction based on a semi-analytical hydrodynamic model and real measured surface topography [6] R. I. Taylor, “Squeeze film lubrication in piston rings and reciprocating contacts”, Proc IMechE Part J: J Engineering Tribology, 229, 8, 977-988, 2015. [7] Noutary, M.-P., N. Biboulet, and A.A. Lubrecht, “A Robust Piston Ring Lubrication Solver: Influence of Liner Groove Shape, Depth and Density.”, Tribology International 100, 2016, 35-40. [8] J. A. Greenwood, and J. P Williamson, “Contact of nominally flat surfaces.”, Proceedings of the royal society of London. Series A. Mathematical and physical sciences, 295, 1966, 300-319. [9] J. A Greenwood, and J. H. Tripp, “The Contact of Two Nominally Flat Rough Surfaces.”, Proceedings of the Institution of Mechanical Engineers 185, 1, 1970, 625-33. [10] B.N.J Persson, “Contact Mechanics for Randomly Rough Surfaces.”, Surface Science Reports 61, 2006, 201-27. [11] Heywood, John B, “Internal Combustion Engine Fundamentals.”, New York: McGraw-Hill, 1988. [12] N. Biboulet and A.A. Lubrecht, to be published, 2021. [13] Sainsot, P, and A. A. Lubrecht, “Efficient Solution of the Dry Contact of Rough Surfaces: A Comparison of Fast Fourier Transform and Multigrid Methods.”, J 225, 8, 2011. Electric Impact 23rd International Colloquium Tribology - January 2022 219 Mounting Positions of Electrical Connectors and the Wear of Coatings under Vibration Loads Kevin Krüger Precision Engineering Laboratory, Ostwestfalen-Lippe University of Applied Sciences and Arts, 32657 Lemgo, Germany Dirk Hilmert Precision Engineering Laboratory, Ostwestfalen-Lippe University of Applied Sciences and Arts, 32657 Lemgo, Germany Jian Song Precision Engineering Laboratory, Ostwestfalen-Lippe University of Applied Sciences and Arts, 32657 Lemgo, Germany Corresponding author: jian.song@th-owl.de 1. Introduction During operation electrical connectors are exposed to various kinds of environmental conditions, e.g. mechanical loads and thermal cycling. Especially in automotive applications, mechanical loads impact on devices and their connectors for example by vibrations. These vibrations induce micro-motions in the contact zone between the mating parts inside the connectors and subsequently cause wear of the protective coatings. Depending on the mounting position of the electrical connectors the vibrations affect the contacts and their protective coating in different ways. Vibration of the connector-cable assembly in the mating direction induces a relative sliding movement between the mating partners. In contrast, rocking motions are induced by vibration in the orthogonal directions. The aim of this study is to analyse the influence of the direction of vibration on the degree of wear of silver coated electrical contacts. Automotive connectors are mounted on test setups in three different orthogonal directions, to replicate the vibrations along three mutually perpendicular axes. Furthermore, the connectors are stressed in vibration tests according to the TLF 0214 [1]. After performing the vibration tests, the wear of contacts in tested connectors is investigated. 2. Theory Silver coatings are particularly used in applications where connectors need to maintain low and stable contact resistance, as in the case of safety systems. These coatings inhibit fretting corrosion and enhance the performance of the contacts [2, 3]. Nevertheless, silver coatings are subjected to fretting wear which can eventually lead to a wear through of the protective coatings resulting in a failure of the contact. Thereby fretting wear is caused by relative motions between the contact partners. Vibrations in field and likewise in test conditions generate a mixed type of movement. On one hand, this is caused by relative motions between the vehicle or the excitation device (shaker) and the connector as well as between the connector housing parts and the contacts. On the other hand, micro-motions of the contacts inside the connectors are significantly influenced by movements of the attached wirings [4-6]. This study investigates the influence of the vibration direction on the degree of wear of silver coatings. Retrieved from the TLF 0214 technical guideline for validating low voltage automotive connectors the vibration directions are shown in Fig. 1. The X-direction corresponds to the mating direction whereas the Yand Z-direction are normal to the mating direction. Fig. 1: Vibration directions according to [1] 3. Experimental Setup The chosen specimens are high performance automotive connectors which are approved for the highest vibration class V6 of the TLF. The contacts have a 3 µm silver coating with 1 µm nickel underlayer and copper as base material. For the tests the specimens are mounted on three different test setups which cover the mentioned directions. The vibration tests are conducted according to V6 which defines a swept sine test in the frequency domain of 100 to 2,000 Hz with the acceleration ampli- 220 23rd International Colloquium Tribology - January 2022 Mounting Positions of Electrical Connectors and the Wear of Coatings under Vibration Loads tude rising from 15 g up to 82 g. Additionally, the specimens are subjected to a thermal cycling test following the DIN EN 60068-2-14. During testing the contact resistance is measured continuously by using the four-terminal sensing method. After completion of tests, the specimens are analysed in regard to wear of the coating. Firstly, the contact areas are optically inspected. Further, the coating thicknesses are determined using the X-ray fluorescence spectroscopy (XRF) method and the shape of the wear area is geometrically measured via the confocal microscopy (CLSM). Accordingly, the XRF is used to analyse the coating thickness in the contact zone whereas the CLSM measures the surface topology. In case of a potential wear through the contact areas are also examined by the energy-dispersive X-ray spectroscopy (EDS). The correlation between the wear depth and the vibration direction is then determined using these results. 4. Results and Discussion In test the specimens neither show an electrical failure nor a considerable rise in contact resistance according to the TLF 0214. After conducting the tests, randomly chosen contacts are removed from the housings and analysed. The optically most worn contact areas for each vibration direction are contrasted in Fig. 2. While the X-direction does only show a slight amount of wear and scratch marks from mating and unmating, the Y-direction shows a significant amount of wear. On the left side of the contact area base material is visible which indicates a wear through of the coating. In the Z-direction a certain degree of wear is visible and on the right side of the contact area a slight wear through exists. Overall, these figures represent the general tendency. Fig. 2: Most worn contact areas of each direction In Tab. 1 the coating thickness reduction for all three directions are compared to the original condition. The X-direction shows less change in the coating thickness with the maximum reduction being 0.9 µm and the range 1.3 µm. In contrast the Z-direction shows a significant reduction as the maximum is 2.6 µm and the range is 3.5 µm. The coating thickness reduction of the Y-direction is even severe with the maximum being 2.8 µm and the range 4.1 µm. Tab. 1: XRF comparison with new parts Coating thickness reduction [µm] Mean Max Range SD σ X-direction 0.0 0.9 1.3 0.3 Y-direction 0.7 2.8 4.1 0.9 Z-direction 0.5 2.6 3.5 0.6 As the X-direction neither shows potential wear through nor a substantial thickness reduction, it is considered noncritical and no further investigation is made. Specimens of the Yand Z-directions with a significant coating thickness reduction are geometrically measured via the CLSM. The depths of the most worn out pits in the contact areas are listed in Tab. 2. The Z-direction shows a maximum depth of 10.0 µm and a range of 8.9 µm. By contrast the Y-direction shows an even higher maximum depth of 24.8 µm and a range of 22.3 µm. The difference between the XRF and the CLSM is due to the better measurement resolution of the CLSM. Tab. 2: CLSM of the wear scars Depth of most worn out pits [µm] Mean Max Range SD σ Y-direction 5.8 24.8 22.3 4.3 Z-direction 3.5 10.0 8.9 1.6 Though it might be assumed from fretting corrosion tests that the X-direction is the critical direction for wear of the coatings, this does not apply to the results of the vibration tests. In fact, the snap-in locking mechanism almost entirely inhibits relative motions between the mating partners in the mating direction. However, in the Yand Z-direction the attached wires cause significant micro-motions of the contacts. This is due to the fact, that the rotation of the tab is not sufficiently damped. In both directions the wear is well-advanced and some specimens are even worn through. Compared to each other the Y-direction shows a higher influence on the wear of the protective silver coatings for the chosen connector. Nevertheless, both excitation directions are considered critical directions in general. 5. Conclusion A very good correlation between the mounting position and the degree of wear of the coatings can be ascertained. Whereas the mating direction is noncritical in regard to the wear of protective silver coatings at vibration loads, 23rd International Colloquium Tribology - January 2022 221 Mounting Positions of Electrical Connectors and the Wear of Coatings under Vibration Loads the directions normal to the mating direction show a significant amount of wear after the vibration tests. The results provide valuable information for the design of wiring harnesses and the test design for connectors. References [1] ZVEI - Zentralverband Elektrotechnik- und Elektronikindustrie e.V.: Technischer Leitfaden - TLF 0214: Validierung von Automotive-Niedervolt-Steckverbindern, 2021. [2] Fouvry, S., Jedrzejczyk, P., Perrinet, O. et al.: Introduction of a „Modified Archard Wear Law“ to Predict the Electrical Contact Endurance of Thin Plated Silver Coatings Subjected to Fretting Wear, 2012. doi: 10.1109/ HOLM.2012.6336604. [3] Yuan, H., Song, J., Schinow, V.: A Modification of the Calculation Model for the Prediction of the Wear of Silver-Coated Electrical Contacts with Consideration of Third Bodies, 2018. doi: 10.1109/ HOLM.2018.8611633. [4] Zhang, F., Flowers, G. T., Dean, R. N. et al.: A study on axial vibration-induced fretting corrosion in electrical connector pair, 2016. doi: 10.1109/ HOLM.2016.7780023. [5] Sawada, S., Saitoh, Y., Iida, K.: Deterioration Mechanism of Connectors Used in Long Driven Vehicles, 2015. doi: 10.1109/ HOLM.2015.7355087. [6] Zhang, F., Flowers, G. T., Dean, R. N. et al.: A study on axial vibration-induced fretting corrosion in electrical connector pair, 2013.doi: 10.1109/ HOLM.2016.7780023. Friction 23rd International Colloquium Tribology - January 2022 225 Design, Reliability and Service Life Predictions of tribological Contacts in drive Systems Michael Gless, Anette Schwarz ContactEngineering.de, Stuttgart, Germany Corresponding author: Michael Gless Contact@ContactEngineering.de Abstract During design process different design solutions have to be considered and compared. In early stage fulfillment of requirements and functions, reliability and service lifetime have to be confirmed. This presentation shows a systematic way how modelling and optimization of design helps to find robust design solutions. The practical approved reliability estimation shows three steps to find robust and reliable design, to choose best design solution and to fulfill required reliability and service lifetime. Advantage of in early stage optimized design avoids many wear mechanisms and helps to focus on unavoidable mechanisms. In addition to calculation and simulation, presented method also considers accelerated testing on tribometers. Furthermore, data from products in the field and production-accompanying testings are collected and evaluated. Presented reliability estimation approach is applied to evaluate a medium-lubricated concentrated contact in high pressure pump drive. In a second example approach is applied to control and use of abrasive wear for self-sharpening effect of a blade. In a third example wear is estimated in a plastic gear drive of a toothbrush. Engineering challenges are to choose best design in an early stage. Many requirements are addressed. Design to cost, milestones and timeline targets. In addition, there are aims like do it right the first time. Therefore, it is essential to choose robust design and material selection in early state, to prevent use of non-robust designs, late changes or even failures (cost rule of 10 th ). Established are development processes for example according VDI 2222. This is a very systematic way for development of a new design. Furthermore, this process helps to make and to document decisions. On the other hand, reliability of chosen solution is not considered at all. Reliability standards are not available, or products are operated outside the standardized operating conditions e.g., mixed lubrication, medium lubricated or dry contacts. Potentials like data collection and smart services are not taken into account. This presentation addresses these aspects. A systematic Design for Reliability service life and reliability estimation for components and connections is shown. Goal is to reach system reliability target and choose appropriate design solution. Figure 1: Fault-Tree-Analyses. Breakdown of required system reliability to component and failure mechanism. In meantime familiar with automotive and aviation processes we had during last years in aviation important lessons learned. Scope is to give a practical oriented overview how best design can be chosen, how reliability can be predicted and how first tests on component level preferred under accelerated conditions can be done. In short it helps to make design decisions easier, to minimize changes in late development state. 226 23rd International Colloquium Tribology - January 2022 Design, Reliability and Service Life Predictions of tribological Contacts in drive Systems Contacts are heart pieces and Achilles’ sinew in engineering. After a general picture of used processes (design, reliability) a comparison and verification of designs of mechanical and electrical contacts is shown. 1. First step: Requirements and Functions In a first step requirements and functions are addressed and verified. These enables a simulation driven development, the evaluation of influencing factors, optimization and therefore robust designs. 2. Second Step: Identification of Failure and Wear Mechanism Relevant Failure and Wear Mechanism are visualized in wear maps. Figure 2: Wear Mechanisms of a concentrated contact visualized in a wear map. In concentrated contacts fatigue is a lifetime limiting failure mechanism and requires a closer look. All other wear mechanisms are not service time limiting. Wear limits have been found in parallel accelerated tribometer tests. Aim of first step to describe the correct reproduction of the behavior, however, not to describe all microscopic details. Furthermore, awareness of tribological complexity, however, not to get lost in details. Aim is to avoid wear mechanism where possible (robustness, optimization) and to focus on main service time limiting mechanism in operating. In medium-lubricated concentrated contacts is fatigue lifetime limiting failure mechanism and requires a closer look. 3. Evaluate resulting stress caused by loads vs. strength/ resistance Estimate Reliability and Service time. Verify and quality assurance with Data from products in production-accompanying testing and field (digital twins) Figure 3: Accelerated lifetimes on test rig compared to field test. Lifetime limiting failure mechanisms is fatigue because of mechanical load. Lifetime-model according to Ioannides, Harris [1] allows transferability between test rig and field results. 4. Application of method on different Design- Examples Presented method has been approved on a medium-lubricated concentrated contact in high pressure pump drives [3]. In addition, wear is predicted. The cutting edge. Use of abrasive wear for self-sharpening effect of a blade Figure 4: Design for self-sharpening. Left: Tribological system with different abrasive wear rates enables controlled wear. Base material has a higher wear rate compared to hard coating. Right: Field result on agriculture cutting blade. 23rd International Colloquium Tribology - January 2022 227 Design, Reliability and Service Life Predictions of tribological Contacts in drive Systems Wear is estimated in a plastic gear drive of a toothbrush, too. Wear is dominating and lifetime limiting. Within linear wear/ steady-state wear regime extrapolation of test results is possible. Furthermore, reliability of electrical Contacts and Connections is evaluated. Method enables a methodical comparison of different Design solutions, to find most robust connection. 5. Conclusion A practical driven approach enables a methodical comparison of different design solutions, evaluates design components and influences with respect to reliability. Relevant wear mechanisms are visualized in wear maps. Robust design helps to avoid wear mechanism and to focus on/ evaluate service time limiting mechanisms. Tribometer testing supports/ verifies Strength and Material behavior. In addition, production accompanying, and field data are considered. Shown approach has been successful applied in several design projects e.g. • to estimate fatigue in concentrated contact, • to control abrasive wear for self-sharpening, • to estimate sliding wear in different contacts and • to design electrical contacts and connections. References [1] Ioannides, E.; Harris, T. A.: Fatigue Life Model [2] ISO 281: Rolling bearings [3] Gless, Michael: Wälzkontaktermüdung bei Mischreibung, Diss, O.v.G. Univ. Magdeburg [4] FIDES Reliability Methodology for Electronic Sys. [5] MIL Handbook 217-F [6] IEC-61709 Electronic Components Reliability 23rd International Colloquium Tribology - January 2022 229 Influence of the rotation direction of the cam on the friction losses of a cam/ finger follower contact Johnny Dufils Institut de Recherche En Ingénierie des Surfaces (IREIS), HEF Group, Andrézieux-Bouthéon, France Corresponding author: jdufils@hef.group Christophe Héau Institut de Recherche En Ingénierie des Surfaces (IREIS), HEF Group, Andrézieux-Bouthéon, France Etienne Macron Institut de Recherche En Ingénierie des Surfaces (IREIS), HEF Group, Andrézieux-Bouthéon, France Philippe Maurin-Perrier Institut de Recherche En Ingénierie des Surfaces (IREIS), HEF Group, Andrézieux-Bouthéon, France 1. Introduction Mechanical friction losses in the cylinder head of internal combustion engines stand for 7 to 15% of the total mechanical losses in a fired engine [1]. Replacing roller finger followers in valvetrains by sliding finger followers has many advantages, among others it enables to reduce the weight of the valvetrain and the resulting dynamic forces. In addition, using DLC-coated sliding finger followers instead of roller finger followers allows to reduce friction power losses up to 50%. In the following, the influence of the rotation direction of the cam on the friction losses of a DLC-coated cam/ DLC-coated sliding finger follower contact is assessed. 2. Materials & Methods 2.1 Testbench In order to assess the influence of the rotation direction of the cam on the friction losses, a dedicated single cam test bench operating real automotive engine components was used (Figure 1). The testbench is equipped with a dynamic torque-meter connected to the camshaft and a high-sample frequency acquisition system so that the instantaneous torque applied on the camshaft is measured. Figure 1: Geometry of the tested valvetrain system and positioning of the oil spray lubricating the cam/ finger follower contact. 2.2 Testing conditions Both the cam and the sliding finger follower were DLC-coated (a-C: H). The main test parameter was the rotation direction of the cam with respect to the oil spray lubricating the cam/ finer follower contact. The other test parameters are presented in Table 1. Table 1: Testing conditions Oil viscosity grade 5W30 Oil temperature Room temp. & 80°C Camshaft speed From 350 to 2500 rpm 230 23rd International Colloquium Tribology - January 2022 Influence of the rotation direction of the cam on the friction losses of a cam/ finger follower contact 3. Results With an oil at 80°C, a reduction of the average friction torque is observed in the counterclockwise direction compared to the clockwise direction (Figure 2). This friction torque reduction leads to a reduction of friction power losses up to 30%. No difference in friction is observed when the oil is at room temperature. Figure 2: Comparison of the average friction torque as a function of the camshaft rotation speed in the clockwise and counterclockwise rotation directions. The evolution of the average friction torque for the reference roller finger follower is also plotted for comparison The instantaneous torque enables to identify how friction losses are distributed in the cam/ finger follower contact as presented in Figure 3(a). By calculating the mechanical torque needed to open and close the valve if there was no friction in the system, it is possible to calculate the contribution of friction in the measured instantaneous torque. The contribution of friction in the instantaneous torque is the friction torque that is presented in Figure 4(a). For each cam revolution, the pad of the sliding finger follower is rubbed twice as illustrated in Figure 3(b) thus there are two turnaround points on the pad. The two vertical dashed red lines on Figure 3 show that most of the friction power losses occur when the contact point on the pad moves from one turnaround point to the other. Figure 3: (a) Comparison of the instantaneous torque as a function of the cam rotation angle in the clockwise and counterclockwise directions. The dashed black line is the torque needed to open and close the valve if there was no friction in the system. (b) Evolution of the contact position on the pad of the sliding finger follower as a function of the cam rotation angle in the clockwise and counterclockwise directions Figure 4: (a) Evolution of the friction torque and oil film thickness as functions of the cam rotation angle in clockwise and counterclockwise directions at identical contact positions on the pad (b) Evolution of the contact position on the pad as a function of the cam rotation angle. Circled numbers are the number of times a given area of the pad is rubbed in the clockwise and counterclockwise directions per revolution. In Figure 4, the instantaneous friction torque is plotted as a function of the cam angle at identical contact positions on the pad. It shows that, even though oil film thickness calculations [2] give identical values, instantaneous fric- 23rd International Colloquium Tribology - January 2022 231 Influence of the rotation direction of the cam on the friction losses of a cam/ finger follower contact tion losses are dependent on the cam rotation direction and that, after the turnaround points, friction is affected by the cam having already wiped the pad surface. 4. Discussion Thermal and transient effects controlling the oil film thickness in the cam/ finger follower contact may explain some of the differences seen in the instantaneous friction torque. The differences in instantaneous friction after the turnaround point suggest an oil starvation effect due to the surface of the pad having been rubbed by the cam combined to a screening effect of the oil spray by the cam. The intensity of the starvation seems to be dependent on the cam rotation direction. Indeed, in the counterclockwise direction, the cam is oiled by the spray just before entering the contact whereas in the clockwise direction, the cam is oiled by the spray just after leaving the contact and thus can be removed from the cam by its rotation. 5. Conclusion With an oil at 80°C, a reduction up to 30% of the friction power losses is observed in the counterclockwise rotation direction compared to the clockwise rotation direction. The lifetime of the a-C: H coating is also affected by the rotation direction: wear is lower in the counterclockwise direction compared to the clockwise direction. Using DLC-coated sliding finger followers associated with an adequate positioning of the follower with respect to the rotation direction of the cam, it is possible to reduce the friction power losses of 65% compared with the roller finger follower reference. References [1] Wong, V.W. & Tung, S.C., “Overview of automotive engine friction and reduction trends-Effects of surface, material, and lubricant-additive technologies” Friction 4, 2016, 1-28. [2] Grubin, A.N., “Fundamentals of the Hydrodynamic Theory of Lubrication of Heavily Loaded Cylindrical Surfaces” Central Scientific Research Institute for Technology and Mechanical Engineering, Book n°30, 1949, 115-166. 23rd International Colloquium Tribology - January 2022 233 Wet Friction Material and Fluid Screening on Benchtop Rig Sanchez, Carlos J. Southwest Research Institute, San Antonio, Texas, USA Corresponding author: carlos.sanchez@swri.org Lee, Peter M. Southwest Research Institute, San Antonio, Texas, USA 1. Introduction This work discusses the use of a benchtop screening test for evaluating the performance of wet clutch materials and automatic transmission fluids (ATF). Tests were conducted with a Bruker TriboLab using small-scale friction discs and reaction plates to replicate the SAE #2 test. Specifically, the bench test modelled the GM 3-Day wear test; contact pressures, sliding speeds, temperatures, engagements, and a condensed test profile that runs over a few hours. Friction coefficient is calculated using a torque cell and measured throughout, and 3D wear profiles of the friction discs are measured ex situ. Tests conducted using the condensed test profile displayed correlation to the full-scale test in ranking different types of friction materials, and potential for ranking fluid formulations. Similar to the full-scale test, one of the primary indicators is the gradient of friction coefficient versus sliding speed at the start of tests compared to the end of test. Although the bench test varies in magnitude from the full-scale test, the trends show an indication of performance for clutch materials and fluids. 1.1 Background and Methods Wet friction materials are designed to operate in some form of fluid. A common example are the materials used in clutch packs and torque converters. These materials are typically made from a woven material, paper being prevalent. By design, friction materials are porous and compressible. The porosity allows for absorption of the fluid, and creates many points of contact for the counter surface to slide against more readily. In clutch packs, the friction material is bonded to one plate and engages with a smooth metal plate to transfer torque. The performance of a clutch system will depend on the material type, geometry, compressibility, surface finish, and fluids. In the automotive industry, there is great interest to improve the effectiveness of clutch engagement to increase fuel economy and overall performance. There are several test methods available for evaluating friction materials and transmission fluids (ATF) in full clutch systems. One such method is the SAE #2 test. This test uses full size clutch packs, and runs them in a similar manner as an actual engine. There are several test profiles that can be run, but the one presented herein is the General Motors (GM) 3-day wear test. This test runs at 3 pressures, 3 temperatures, and 14 speeds. There are several phases of the test that involve speed ramps both up and down, continuous slip sequences, and stepped speeds; which loop several times. As the name suggests this test takes 3 days to run. The goal of many tribological tests is to scale down to a bench setup to increase throughput and efficiency when evaluating materials. For wet friction materials, the aim is to investigate the relationship between coefficient of friction (COF) and speed. Clutches will engage at various speeds while transferring torque. This increase and decrease in speed under load will also result in stick-slip behaviour. Decreased COF with increasing speed will result in an effect called “shudder.” When designing a bench test, the contact geometry of the materials, the rotation of the instrument, the loading mechanism, and the test environment are considered. The bench test uses a 1 inch diameter disc, with a ring shaped friction material bonded to the top surface. The friction material is manufactured and bonded in the same manner as a full sized friction disc. The reaction disc was manufactured from mild steel, and given a specific surface finish. Based on the contact area of the ring shaped material, the contact pressures can be scaled in accordance with the SAE # 2 test procedure. Likewise, the rotational speeds are scaled according to the effective radius of the smaller disc. All tests were performed on a Bruker UMT TriboLab instrument. The instrument uses a rotational drive unit to rotate the reaction disc, and a six-axis load sensor to measure the forces acting on the friction material disc. The test setup also includes a heated oil bath, with a peristaltic pump that circulates the test fluid at all times. A thermocouple is placed above the reaction disc to control and measure the system temperature. The bench test consists of variable pressure engagements at different speeds and temperatures. Within the sequences are a series of stick-slip engagements, and continuous 234 23rd International Colloquium Tribology - January 2022 Wet Friction Material and Fluid Screening on Benchtop Rig slip cycles. The test is designed to replicate the GM 3-day wear test, which contains 10 phases. The first, fourth, and last phase are the measurement and inspection of the parts. The actual test sequences comprise running the materials through various speeds, contact pressures, and temperatures. There are numerous cycles, some of which repeat or loop. In this study, the 3-day wear test was reduced to run within one day. This was accomplised by running the individul sequences in a specific order that yielded comparable friction results and wear on the friction material. The data reduction produced coefficient of friction versus speed for the stick-slip, discrete speeds, and continuous slip cycles. Additianlly, coeffieicnt of friction versus time to analyze breakayway friction response. The friction materials were all inspeted in the same manner as the full scale test. A Keyence optical microscope was used to measure the profile height of the material at different phases of the test. Results of the bench test showed similar trends in performance for the friction materials tensted. The magnitudes of the friction response, and the overall wear were much lower than that seen on the full-scale test. However, the relative behavior from one material type to another was comparable. Therfore, the bench test has the potential to serve as a screening method for studying the behavior of new material pairs. The outsome of the bench test can then be used to determine suitable candidates for fullscale analysis. 2. Conclusion A benchtop screening method was developed for evaluating the performance of wet clutch materials and automatic transmission fluids. The test uses small-scale friction material discs, and reaction plates. Through careful modelling of the real system conditions, the bench results demonstrated similar friction curve behaviour to those seen in an SAE #2 test rig using the same parts and fluids. Through this method, relative comparisons can be made to rank the performance of friction materials. The bench test offers more flexibility and efficiency when investigating numerous material types. At present, the method presented herein has been shown to be most effective in screening friction material, but more work is needed to determine effectiveness for fluid comparisons. References [1] Fuji Y, Snyder T, Waldecker R, Tobler W, Davis L, Scherzer M, Zander, D, Dynamic Characterization of wet friction component under realistic transmission shift condition. SAE Technical Paper 2006- 001-0151. 2006 [2] Senatore A, D’Agostino V, Di Guida R, Petrone V. Experimental Investigation and neural network prediction of brakes and clutch friction material behaviour considering the sliding acceleration influence. Tribology International 2011; 44(10): 1199- 1207. [3] Shaffer S, Freshly T, Papanicolaou S. Benchtop screening of wet clutch materials. Tribology International 2018; 121(08): 161-166. Industrial Machine Elements and Wind Turbine Industry Gears 23rd International Colloquium Tribology - January 2022 239 How friction modifier influences the dynamic friction behavior in wet-running clutch systems and its potential for extended use in hybrid drive trains Arne Bischofberger Karlsruhe Institute of Technology (KIT), IPEK - Institute of Product Engineering, Karlsruhe, Germany Corresponding author: arne.bischofberger@kit.edu Katharina Bause, Sascha Ott, Albert Albers Karlsruhe Institute of Technology (KIT), IPEK - Institute of Product Engineering, Karlsruhe, Germany 1. Introduction The modern clutch system with its good controllability offers a multitude of possibilities for extending the basic function of the clutch with additional functions such as dynamic control and vibration reduction. Especially in view of the change in mobility and energy resource consumption, a function extension to a demand-oriented vibration reduction can provide the possibility to reduce the dimensions of conventional vibration reduction systems and thus save installation space and mass, especially in hybridized powertrains. The potential for this function extension is presented e. g. [1, 2] and could be proven in previous investigations as shown e. g. in [3]. In [3] it is shown that the tribological system has a significant influence on the vibration reduction effect. A specific design of the tribological system can favor other vibration-reducing effects besides damping. How the tribological system has to be designed for this intended usage and which properties influence the behavior is not sufficiently known and is being researched at IPEK. In this publication the friction coefficient curve is adjusted by means of a specific change in the tribological system and the extent to which this adjustment affects the dynamic friction coefficient behavior is investigated. 2. Validation Approach 2.1 Validation Environment and Research Method The investigations are conducted under use of a high dynamic test bench at IPEK. The validation environment enables the investigation of wet-running multi plate packages during controlled micro slip operation. It is developed in such a way that precise statements on the dynamic friction behavior as well as the vibration reduction effect can be made. According to the IPEK X-inthe-Loop approach [4], both input-side and output-side drive train dynamic interactions are considered. Detailed information about the validation environment is shown in Figure 1 and can be found more detailed in [5, 6]. The tests are performed in a dynamic slip operation. Therefore, a differential speed between input and output of the clutch is set. The base speed of the prime mover is superimposed with a sinusoidal excitation. The measurements are then evaluated in the stabilized dynamic continuous slip mode. Figure 1: Powertrain-in-the-Loop test bench with Inlinemodule for the investigation of wet-running multi plate packages including consideration of dynamic drive train interactions, based on [5] 2.2 Objective of Research Four different tribological systems are used as the object of research. Each tribological system is composed of a multi plate package consisting of two friction plates and three steel plates, as well as a lubricant used as cooling oil. The tribosystems differ in their oil variants. TS 1 uses a common ATF. In TS 2 to TS 4, the additives in the oil are specifically changed by adjusting the friction modifier. The differences between the variants regarding the characteristics of stationary friction behavior are listed in Table 1. 240 23rd International Colloquium Tribology - January 2022 How friction modifier influences the dynamic friction behavior in wet-running clutch systems and its potential for extended use in hybrid drive trains Table 1: Tribological system variants: variations of oil Oil Design (stationary fricition behavior) TS A Conventional ATF TS B High friction coefficient (µ) at low and high differential speed TS C Low µ at low, high µ at high diff. speed TS D Low µ at low and high diff. speed 2.3 Dynamic Friction Behavior The dynamic friction behavior is evaluated with characteristic values presented in [7]. In addition to the values absolute friction coefficient and friction coefficient gradient, which are also common in characterization of quasi-stationary friction behavior, the parameter ‘Hysteresenausdehnung’ d max is considered for a first description on the form of the friction hysteresis. Figure 2 shows the characteristic values based on an exemplary dynamic friction coefficient curve. Figure 2: Dynamic friction behavior values ‘Reibungszahl’ (friction coefficient) , ‘Hysteresenausdehnung‘ (hysteresis expansion) and ‘Reibungszahlgradient’ (friction coefficient gradient) [7] 3. Results: Dynamic Friction Behavior The differences in the dynamic friction coefficient behavior between the tribological systems are presented here using a reference test with fixed parameters for surface pressure, differential speed, drive speed, cooling oil flow as well as defined sinusoidal excitation. Each test is performed a total of three times for each tribological system. The evaluated characteristic values of the tribosystems are compared in the following boxplots. Results of further tests, e. g. at higher excitation amplitudes, are presented in the full publication. Figure 3: Dynamic friction behavior, characteristic values in reference test (each three runs) of the tribological systems TS A-TS D It can be observed that all tribosystems show differences in dynamic friction behavior. TS C shows a similar mean friction coefficient and a similar hysteresis shape as the reference system TS A, but a larger gradient. TS B shows a similar gradient to TS C, but has a reduced friction coefficient compared to TS A. TS D, on the other hand, shows the significantly lowest friction coefficient and the highest gradient of all systems. In addition, the hysteresis expansion is reduced compared to TS A - TS C. The adjustment made regarding the friction modifier (FM) also affects the dynamic friction coefficient behavior and the shape of the hysteresis. It can be seen that the adjustments of the FM in the range of the stationary friction behavior, however, lead to different characteristics in the dynamic friction behavior. Here, the adjustment of the FM to low friction values also reduces the hysteresis ex- 23rd International Colloquium Tribology - January 2022 241 How friction modifier influences the dynamic friction behavior in wet-running clutch systems and its potential for extended use in hybrid drive trains pansion at the same time, but increases the gradient in the investigated range (TS D). In general, it can be concluded that an adjustment of the FM towards an increased positive gradient over a larger range of the differential speed does not necessarily also lead to an increase of the gradient in the dynamic slip operation (see TS B and TS C). This may result from the fact that, depending on the excitation amplitude, the dynamic friction coefficient curve only changes over a small range of differential speeds. Thus, the sliding speed changes at high frequency, but also only in a small range, which ensures that the change in the FM seems to has only a limited effect here. 4. Conclusion and Outlook The investigations show that the modifications made by adapting friction modifiers do have an effect on the dynamic friction coefficient behavior during dynamic continuous slip operation. A modified friction coefficient curve adjustment was thus made possible. In future investigations, the vibration reduction effect in the wet-running clutch system will be investigated with the various friction coefficient curves of the tribological system variants. Correlation analysis is to be used to investigate the extent to which characteristics of the dynamic friction coefficient behavior affect vibration-reducing mechanisms in the friction contact. 5. Acknowledgement The investigations presented in the publication were performed as part of the IGF-Project 21378-N. The authors acknowledge the funding of the research project. The IGF-Project 21378-N of the “Forschungsvereinigung Antriebstechnik e.V. (FVA)“ is funded by the Federal Ministry for Economic Affairs and Energy through AiF within the program for Industrial Collective Research (IGF) based on a decision of the German Bundestag. References [1] Lutz, D. u. Verein Deutscher Ingenieure: Kupplungsmanagement - ein Baustein zur Drehschwingungsdämpfung. VDI Berichte 697 (1988), S. 219- 256 [2] Albers, A.: Elektronisches Kupplungsmanagement (EKM) - Die mitdenkende Kupplung. 4. Internationales Kolloquium Torsionsschwingungen im Antriebsstrang, 20. April 1990, Baden-Baden. 1990 [3] Albers, A., Bischofberger, A. u. Ott, S.: Wet clutch as an enabler of cost-efficient hybrid drive systems Decoupling as functional extension. 20. Internationales Stuttgarter Symposium. Automobil- und Motorentechnik. Wiesbaden: Springer Vieweg 2020, S. 251-265 [4] Albers, A., Behrendt, M., Klingler, S. u. Matros, K.: Verifikation und Validierung im Produktentstehungsprozess. Handbuch Produktentwicklung. In: Udo Lindemann (Hrsg.). München: Carl Hanser Verlag 2016, S. 541-569 [5] Ott, S. u. Basiewicz, M.: Innovative validation environments and methods for holistic clutch system development. Antriebstechnisches Kolloquium ATK 2017 (2017) Tagungsband 17, S. 12 [6] Bischofberger, A., Ott, S. u. Albers, A.: Die nasslaufende Kupplung als Stellglied zur Schwingungsreduzierung im Antriebsstrang - Einflüsse eines veränderten Tribosystems. Forschung im Ingenieurwesen (2020) 85, S. 1-10 [7] Bischofberger, A., Bause, K., Ott, S. u. Albers, A.: Extended Abstract: Untersuchung des anwendungsnahen, dynamischen Reibverhaltens nasslaufender Lamellenkupplungen am Beispiel zweier Tribosystemvarianten. Reibung, Schmierung und Verschleiß Forschung praktische Anwendung. 62. Tribologie Fachtagung 2021. 2021, 21/ 1 - 21/ 5 23rd International Colloquium Tribology - January 2022 243 Wear analysis of spur gears in consideration of the temperature Chan IL Park Gangneung-Wonju National University/ Dept. of Mechanical Engineering, Gangwon-do/ Wonju, South Korea Corresponding author: pci@gwnu.ac.kr 1. Introduction The gear wear is one of the important failure modes in gear systems with the tooth bending fatigue, contact fatigue, and scoring. The gear wear can also cause the change of tooth profile from its designed tooth profile. It leads to the reduction of mesh stiffness and in turns, changes the noise and vibration characteristics of the gear system significantly. Gear teeth has the rolling and sliding motion except sole rolling at the pitch. Meshing teeth are separated by a lubricant film during the rolling and sliding motion. The lubricant film is not always enough to separate the meshing teeth when the temperature rise due to friction occurs. The temperature rise can cause to change the lubrication regime. Therefore, this study analysed the wear of spur gears in consideration of the temperature. To do so, the load of spur gears with friction is obtained by solving the simultaneous equations of load-deformation equations and moment balance equation. The sliding speed and the contact pressure at the meshing position are also calculated. Gear temperature is obtained by the commercial FE code and in-house program. Finally, the wear depth of spur gears under the mixed elastohydrodynamic lubrication is calculated in consideration of temperature. 2. Wear analysis Surface wear in the gear tooth contact with combined sliding and rolling motions is one of several failure modes. The most widely used wear model is the dry-contact Archard’s wear model as follows [1]; , (1) where V is the volume of the worn out material (m 3 ); K is the dimensionless wear coefficient; W is the applied normal load (N); s is the sliding distance (m); H is hardness of the contact surface (Pa). Under the assumption that the hardness of contacting surfaces is constant during the wear process, Archard’s wear equation can be reformulated as , (2) where h is the wear depth and k is a dimensional wear coefficient (k=K/ H). To consider the mixed elastohydrodynamic lubrication and the surface temperature, the modified equation with the asperity load ratio and the fractional film defect is given by [2-4] , (3) where L a is the asperity load ratio of the two contact surfaces (percentage) and the fractional film defect ѱ can be expressed as , (4) where X is the diameter of area associated with an adsorbed lubricant molecule (m); t 0 is the fundamental time of vibration of molecule in adsorbed state (s); E a is the heat of adsorption of oil molecules on surfaces. R g is the gas constant (J/ mol K); T s is the surface temperature (K). 3. Thermal analysis Contact surface temperature of gears consists of the bulk temperature T b and the flash temperature T f as follows; T s =T b + T f , (5) The bulk temperature is the average temperature while the flash temperature is the instantaneous temperature rise. The bulk temperature is calculated by FE thermal analysis. The heat flux due to the sliding friction of spur gears is expressed as , (6) where µ is friction coefficient of gear; v s is the relative sliding velocity; is the mean contact pressure. In FE modelling of a single tooth of gears, thermal boundary condition and heat flux on model faces are imposed [5,6]. Assuming that Hertz theory on the contacting surface is valid, the flash temperature predicts by Blok’s equation as follows; 244 23rd International Colloquium Tribology - January 2022 Wear analysis of spur gears in consideration of the temperature (7) Where W n is the normal load per the face width (N/ m); k t is thermal conductivity (W/ (m∙K)); ρ is density (kg/ m 3 ); c p is specific heat capacity (J/ (kg ºC)), v 1 ,v 2 are the perpendicular velocity to the line of action (m/ s); a H is Hertz contact half-width (m). 4. Results and discussion For the wear and thermal analysis, normal force and friction force of the spur gear with data of Table 1 and true involute profile are calculated in torque 20 N∙m, using the moment balance and force-deformation equations [7]. Gear material is SM45C and oil is SAE-80W-90. The heat flux at 3,000 rpm is calculated by in-house program. Bulk temperature is analyzed by MSC Nastran FE code as shown in Figure 1. Bulk temperature is higher at the approach than at the recess of driving gear, and average bulk temperature is 28.65 ºC. Flash temperature is calculated by Blok’s equation. Using the surface temperature, wear depth under the mixed elastohydrodynamic lubrication is calculated. Figure 2 shows wear depth at every 1000 cycle to 10,000 cycles. The gear approach suffers more wear than the gear recess and pitch point do not wear due to no sliding motion. Figure 1: Bulk temperature by FEA Table 1: Gear data Tabelle Driving Driven Normal module (mm) 2 Normal pressure angle 20° Center distance (mm) 58 Whole depth (mm) 4.26 Number of teeth 30 26 Face width (mm) 16 13 Outside radius (mm) 32.9 28.86 Pitch radius (mm) 30 26 Root radius (mm) 28.64 24.6 Addendum mo. co. 0.57 0.55 5. Conclusion This study analysed the wear of spur gears in consideration of the temperature. Bulk temperature and flash temperature for tooth surface temperature are calculated. Wear depth of spur gears under the mixed elastohydrodynamic lubrication is analysed. The gear approach suffers more wear than the gear recess and pitch point do not wear due to no sliding motion. Figure 2: Wear depth of driving gear Acknowledgement This research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (NRF- 2020R1I1A3A04036891). References [1] A. Flodin, S. Andersson, Simulation of mild wear in spur gears, Wear 207 (1997) 16-23. [2] A. Beheshti, M.M. Khonsari, An engineering approach for the prediction of wear in mixed lubricated contacts, Wear 308 (2013) 121-131. [3] M. Masjedi, M.M. Khonsari, An engineering approach for rapid evaluation of traction coefficient and wear in mixed EHL, Tribol. Int. 92 (2015) 184-190. 23rd International Colloquium Tribology - January 2022 245 Wear analysis of spur gears in consideration of the temperature [4] H. Wang, C. Zhou, Y. Lei, Z. Liu, An adhesive wear model for helical gears in line-contact mixed elastohydrodynamic lubrication, Wear 426-427 (2019) 285-292. [5] Y. Shi, Y. Yao and J. Fei, Analysis of Bulk Temperature Field and Flash Temperature for Locomotive Traction Gear, Applied Thermal Engineering 99 (2016) 528-536. [6] C. M. C. G Fernandes, D. M. P Rocha, R. C Martins, L. Magalhaes, and J. H. O. Seabra, Finite Element Method Model to Predict Bulk and Flash Temperature on Polymer Gears, Tribol. Int., 120 (2018) 255-268. [7] C. I. Park, Tooth Friction Force and Transmission Error of Spur Gears due to Sliding Friction, Journal of Mechanical Science and Technology 33(3) (2019) 1311-1319. 23rd International Colloquium Tribology - January 2022 247 Design for Reliability of Gear Systems Concerning Wear Arshia Fatemi Robert Bosch Corporate Research, Renningen, Germany Corresponding author: Arshia.fatemi@de.bosch.com Poorna Satish Chowdary Maddukuri Freiberg University of Mining and Technology 1. Introduction Wear is one of the main damage mechanisms in gears operating at low speed. In the case of gears with a small module (smaller than one), wear also exists at higher rotational speeds and could be the main lifetime limiting damage mechanism [1]. In grease lubricated systems, wear might be the predominant damage mechanism due to starvation, channeling and absence of the lubricant [1]. Due to the uncertainties in wear models, it is difficult to predict the product life with confidence levels in tribological systems, while in structural mechanics (particularly fatigue), calculating lifetime distributions and failure probabilities are well established. This work shows that a lifetime distribution can be determined from tribological stresses and strength-related parame-ters considering scatterings. The reliability can then be determined as the probability of reaching the required service life. Since damage models and statistical ap-proaches are rarely used to predict reliability in wearing systems, therefore, the methodology of structural me-chanics is adopted to calculate a lifetime for wearing systems. 2. Methodology It can be shown that analogous to structural mechanics, a tribological system can also be described in terms of 1. Tribological Stress, 2. Tribological Strength 3. Damage Model and 4. Failure Criteria. Lifetime for a continuously wearing system is defined as the time, at which the wear reaches the maximum failure criteria or maximum allowable wear (Wmax) based on the extracted damage model. Figure 1 illustrates a generic form of the reliability concept in an “Archard-Like” wearing system. The Abscissa represents the stress (e.g., nor-mal force), whereas the slope of the curve can be under-stood as “strength” which amounts to various times reaching the allowable wear value (Wmax). The distribu-tion of this time is considered as lifetime distribution. Considering wear in lubricated gear systems, one of the most successful methods in literature is based on the seminal work of Plewe [2]. According to his work, the wear of the gear systems can be calculated utilizing a film thickness-dependent linear wear coefficient (CIT) acquired by a defined FZG back-to-back gear experi-ment. Figure 1: Lifetime distribution due to variability of wear curves in a linear wear system (Archard-like). For calculating wear in practical applications, a given scattering of input parameters is expected. There are mainly two sources of scatterings available in wearing systems. 1. Scattering of Stresses-related parameters (e.g., temperature, nominal contact stress, film thick-ness) 2. Scattering of Strength-related model parameters (e.g., linear wear coefficient as a result of slope and intercept of Plewe chart. Since the slope is as-sumed to be constant, the intercept will be the de-ciding value) The scattering of input variables propagating through the damage model leads to a lifetime distribution, expressed by a probability density function. This is possible if we can define the lifetime based on the damage model and failure criteria. The most common probability plots used in reliability analysis are normal, Weibull, and lognormal. Ideally, the scattering of model input parameters must be ob-tained by test programs with many repetitions. This might be a very timely procedure if the wear models are complicated and need more than one parameter. In reliability engineering, there are many ways and meth-ods to deal 248 23rd International Colloquium Tribology - January 2022 Design for Reliability of Gear Systems Concerning Wear with the scattering of input parameters. The most commonly used to derive the functional form of the lifetime distribution from the distributions of the involved parameters are Monte-Carlo Simulation and Latin Hypercube Sampling. Since there are few scatter-ing parameters in the Plewe wear model, the choice of sampling methods is not very essential. 3. Results and Discussion A Design for Reliability (DfR) methodology has been formulated for gear systems from the Plewe wear mod-el in OptiSLang. The considerably uncertain variables such as temperature and Plewe intercept to verify the influences on the lifetime of the pinion. The lifetime distributions are presented in the form of, e.g., L10 lifetime. Table 1: Statistical examples of the input parameters which scatter considerably Input Parameter Defined PDF Mean Standard deviation Temperature [°C] Norma1 115 15 Plewe Intercept [mm] Lognormal 2E-06 4.5E-07 The L10 lifetime (the time that 90 % of the gears will survive without failing by surface wear) could be achieved as the basis for calculating the gear lifetime and reliability. The statistical moments of lifetime distributions of the pinion are shown in Table 1. OptiSLang software provides a fitted distribution from the histogram of the responses. Plewe describes the damage model for Design for reliability (DfR) of gear systems is formulated. 4. Conclusion A Latin Hypercube sampling (LHS) has been adopted in order to handle several scattering model inputs in OptiS- Lang. For the reliability analysis, the input pa-rameters such as temperature and Plewe intercept are considered. It is observed that temperature significantly affects the wear life and is followed by Plewe intercept. Lifetime distributions of the pinion from the DfR implemented methodology on the gear damage mecha-nism and lifetime model in the form of L10 lifetime can be presented. References [1] A. Dobler; Risk and Avoidance of Wear in Small Gears Drives; GETLUB conference 2018 [2] H. Winter und J. Plewe, „Calculation of Slow Speed Wear of Lubricated Gears,“ AGMA Paper, Bd. November, pp. 9-18, 1982. Bearing 23rd International Colloquium Tribology - January 2022 251 Effect of water absorption in bearing greases on wear and corrosion Ivan Delic AC2T research GmbH, 2700 Wiener Neustadt, Austria Adler Michael AC2T research GmbH, 2700 Wiener Neustadt, Austria Karl Adam 2voestalpine Stahl GmbH, 4020 Linz, Austria Franc Bardin TotalEnergies SE, 69360 Solaize, France 1. Introduction Water as well as aqueous solutions and emulsions are commonly used as coolants in industrial machinery. Insufficient sealing of bearing components can result in a contamination of the lubricant with coolant. Therefore, the focus of this work is set on the effects of water on grease performance and bearing materials. To generate a better understanding of grease-water interaction, experiments with water-grease blends were performed. Properties including water absorption capacity and water retention in dependence of temperature and time and the effect on standardized grease properties such as cone penetration or oil separation were investigated. The impact on corrosion inhibition was evaluated using standardized tests as well as an in-house corrosion test developed to determine the effects on standstill corrosion. Friction and wear properties were elaborated using selected tribometrical test devices following standardized procedures for comparability of the results. As the gathered findings provide insight into the behaviour of water contaminated grease, they possibly allow a better assessment of grease lifetime and maintenance intervals of grease lubricated components. 2. Methods and material All investigations were carried out on two commercially available Calcium sulfonate complex greases (CaSX) with different base oil viscosity. The greases were chosen as CaSX greases are commonly used in water rich environment due to good performance with water ingress as reported by Bosman et al. [1]. For the evaluation of water absorption capacity, grease water mixtures with different water contents were prepared using a quarter scale grease worker. 60 double strokes were found to be sufficient for good mixing. Deionized water was used for the experiments. The maximum amount of water mixable into the grease was evaluated optically by formation of water droplets in the mixture. The optical result was confirmed using Karl Fischer titration. Subsequently, the mixtures were used for the characterization of water retention. Droplets of grease were put on glass plates and the water content was continuously evaluated using Karl Fischer titration. Investigations on the change in consistency due to water ingress were performed using similar grease water mixtures. Further, the change in oil bleed due to water ingress was assessed using a modified filter paper test where a defined volume of grease is put in a cylindrical form and put on filter paper. The corrosiveness of the grease-water mixtures was assessed using a modified copper corrosion test according to ASTM D4048. To evaluate the protective properties against standstill corrosion, cylindrical rollers made of bearing steel (DIN ISO 1.3505) were exposed to mixtures of synthetic sea water and grease. Wear protection and extreme pressure properties were investigated using a 4-ball test rig and a high frequency reciprocating rig (HFRR or SRV) according to corresponding ASTM standards (ASTM D2266 ; D2596; D5706; D5707). 252 23rd International Colloquium Tribology - January 2022 Effect of water absorption in bearing greases on wear and corrosion 3. Results and discussion Figure 1: Grease water mixtures immediately after mixing (top) and after 4 days at room temperature (bottom) After the described experiments, water absorption capacity was found to be about 55 % mass regardless of base oil viscosity. Regarding water separation, it was observed that the water content was mainly reducing in surface near areas while the water content in the centre of the droplets remained constant over the investigated time-period. As expected, the decrease was faster with increasing water content. Similar results were observed with increased temperature and during other experiments. The tests show that discoloration occurs with water ingress. The penetration depth of both greases decreased with water ingress (indicating the grease becoming more rigid) until water contents of about 40 % were reached. An increase of penetration depth and a rougher grease structure were observed at that point. For lower water concentrations a linear correlation regarding penetration depth is reported. Figure 2: Penetration depth in dependence of water content for selected calcium sulfonate complex grease Oil bleed was determined gravimetrically after the grease and paper were exposed to increased temperature. In both cases the oil bleed was decreased with water ingress. A higher decrease was observed for the grease with a higher base oil viscosity. The results were compared to standardized oil separation methods where similar trends were observed. Copper corrosion was found to be more severe for grease without water contamination. However, circular structures were observed on copper platelets for all mixtures. This indicates evaporation and contact loss between the grease and material surface. Regarding standstill corrosion, good protection was maintained for all inspected mixtures. Significant corrosive attack was only detected with oversaturated mixtures where a formation of water droplets was observed. Water ingress resulted in lower wear protection for all investigated greases. A decrease in weld load. Similar results were found for the weld load. 4. Conclusions and outlook High water absorption capacity makes CaSX greases suitable for the use in water rich environments. The capacity can mainly be ascribed to the thickener structure forming inverted micelles as described by Bosman et al. and others [1,2]. That behaviour was confirmed by comparison of different base oil viscosities. Thickening and reduction in oil bleed can also be attributed to the formation and interaction of micelles in the thickener structure. The described properties are believed to have a significant impact on tribological performance of the grease as described by Cyriac et al. [4]. Corrosive attack was mainly observed in the presence of free water as described in literature [1]. Evaporation of water during copper corrosion tests is linked to circular structures on the copper surface. Similar structures were observed in bearing investigation regarding corrosive damage. Another correlation with the corrosion behaviour described in literature is given in the behaviour of the standstill corrosion experiments. Formation of free water is also linked to worsened wear protection as described by Cyriac et al. [4] and Huddedagaddi et al. [5]. As most properties responsible for wear and corrosion protection are affected by water ingress, an implementation of a monitoring method for the water content of greases is of great importance. The optical changes of the greases could be of use in the assessment of the usability regarding water contamination. Further investigations on tribological performance are currently being carried out. The idea is to link degradation of grease performance to simple grease properties to allow for a quick check of grease during operation. Obtained limits to water contamination can be used in the implementation of an inline monitoring to prevent critical failure. 5. Acknowledgement This work was funded by the project COMET InTribology1, FFG-No. 872176 (project coordinator: AC2T research GmbH, Austria). References [1] Rob Bosman & Piet M. Lugt (2018) “The Microstructure of Calcium Sulfonate Complex Lubricat- 23rd International Colloquium Tribology - January 2022 253 Effect of water absorption in bearing greases on wear and corrosion ing Grease and Its Change in the Presence of Water”, Tribology Transactions, 61: 5, 842-849 [2] Pierre Belot, “Complex Calcium Sulfoante Grease - A unique approach to industrial grease lubrication”,7th Lubricating Grease Conference, Cochi, India, Feb. 2005 [3] Gurt, Alan & Khonsari, Michael. (2020). “An Overview of Grease Water Resistance”. Lubricants. 8. 86. 10.3390/ lubricants8090086 [4] Cyriac, F., Lugt, P.M., Bosman, R. et al. Impact of “Water on EHL Film Thickness of Lubricating Greases in Rolling Point Contacts”. Tribol Lett 61, 23 (2016) [5] Channabasappa B.Hudedagaddi, Anirudh G.Raghav, Angela M.Tortora, Deepak H.Veeregowda, “Water molecules influence the lubricity of greases and fuel”, Wear, Volumes 376-377, Part A, 15 April 2017 23rd International Colloquium Tribology - January 2022 255 Tribo-dynamics for a 3D-printed Multilattice structure-based air-foil bearing Ali Usman EISLAB Machine Learning, Luleå University of Technology, Luleå, Sweden Corresponding author: ali.usman@ltu.se Marcus Liwicki EISLAB Machine Learning, Luleå University of Technology, Luleå, Sweden Andreas Almqvist Division of Machine Element, Luleå University of Technology, Luleå, Sweden Tribology has been a significant research concern for more than a hundred years because a large amount of the input energy to a mechanical system is wasted in overcoming friction. Fossil-based products (e.g., mineral lubricant) have been used to minimise friction since the beginning of mechanical systems, thus, causing severe environmental impacts. Eco-friendly fossil-free lubrication systems are needed, and a completely new tribo-optimization must take place to reduce energy consumption with minimal environmental risks. An example of a machine element lubricated with fossil-free lubricant is the Air bearing, which lubricated with air. Foil and bump strips-based bearings is a typical type of air-bearings. Since additive manufacturing is replacing traditional manufacturing approaches, a critical understanding of AM-based airfoil bearing is needed. In this work, a 3D printed multilattice structure-based air-foil bearing is considered, and tribo-dynamics and structural response are evaluated in the present work. A fully coupled, lubrication-structure mechanics model is utilised to investigate the transient response of an airfoil bearing. Results encourage usage of Multilattice structures for outperforming stability and tribological performance of aforementioned typical airfoil bearings. 1. Introduction Research devoted to understanding and improving the tribology of machine elements lubricated with petroleum-based products has been the concern of tribologists for more than hundred years now. In the future, fossil-free products and processes must be introduced, and a completely new tribo-optimisation must occur to reduce energy consumption and CO 2 emissions. The EU has set itself a 32.5% energy savings target by 2030. Tribology plays a vital role by actively reducing friction losses in all mechanical power transmitting systems. In total, ~20% (103x10 18 Joule! ) of the world’s total energy consumption is used to overcome friction. It is thus evident that even a slight friction reduction can significantly impact achieving EU 2030 targets. Tribology plays a significant role in technology transition since all new technologies encounter tribological problems before being optimally utilised and downsized. This is because wear and friction create obstacles for the development of new sustainable technology. Lightweight and new-technology materials typically have reduced tribological performance, making new materials impossible to replace conventionally used materials (e.g. steel). However, Additive Manufacturing (AM) now enables design engineers to design and manufacture lightweight structures of traditional engineering materials grown into 3D to replace heavy/ dense machine components manufactured through traditional subtractive manufacturing. Since CO 2 emissions are still increasing globally, it is urgently vital to find ways to improve energy efficiency, use fossil-free alternatives, and introduce renewable materials. Airfoil bearings lubricated with air are used in high-speed applications, e.g., aircraft jet turbines, turbochargers, etc. Optimised tribology is essential for the reliability and efficiency of high-performance technological systems, and there is a need for continuous improvements to prolong service life and reduce power losses. New production technologies, AM, will create new types of tribological surfaces and challenges. AM surfaces must carry as much load as surfaces made with conventional methods. However, AM also opens up possibilities to make materials and surfaces with better performance and new functionality. This study exploits the capabilities of AM to investigate the utilisation of 3D multi-lattice structures to provide damping and stiffness to airfoil bearing. A mixed lubrication model that includes mass conserving and surface roughness effects is used to evaluate tribological performance. A tribo-structure coupled model is used to evaluate tribo-dynamics. The mathematical model considered in this study can be found in [1-3]. 256 23rd International Colloquium Tribology - January 2022 Tribo-dynamics for a 3D-printed Multilattice structure-based air-foil bearing 2. Results Following are key results of the study showing hydrodynamic load on the multi-lattice (Figure 1) and corresponding structural response (Figure 2). Figure 1: Dimensionless hydrodynamics load on the foil and 3D multi-lattice. Developing pattern of asperity load (Figure 3) and fluid load (Figure 4) on the foil over the time from initial start-up (0 s) to steady-state (3 s) are also shown corresponding to developing speed, eccentricity, and attitude angle (Figure 5). Stiffness evaluation of the multi-lattice structure used in this study is also shown in Figure 6. Figure 2: Internal reaction of the material (MPa) to the deformation caused by load on the foil. Figure 3: Developing pattern of asperity load (kPa) with time, top to bottom 0.1 s, 1 s, and 3 s, respectively. Figure 4: Developing pattern of fluid load (MPa) with time, top to bottom 0.1 s, 1 s, and 3 s, respectively. 23rd International Colloquium Tribology - January 2022 257 Tribo-dynamics for a 3D-printed Multilattice structure-based air-foil bearing Figure 5: Transient shaft speed, eccentricity, and attitude angle during the start-up time of the airfoil bearing extending to a fully steady state. Figure 6: Stiffness of the 3D multi-lattice structure under the influence of structural load. 3. Conclusion A tribo-dynamics of an airfoil bearing during the start-up of the rotary machinery is evaluated. A comprehensive mathematical model is used that include a cross-domain lubrication model and corresponding structural mechanics in a fully coupled manner. The stiffness coefficient of the 3D structure is found to be ~3600 kPa/ mm, and lattice is found to be supporting load successfully as Von Mises stress criteria show the yielding of the structure is within the structural integrity range. References [1] Söderfjäll M, Larsson R, Marklund P, Almqvist A. Texture-induced effects causing reduction of friction in mixed lubrication for twin land oil control rings. Proceedings of the Institution of Mechanical Engineers, Part J: Journal of Engineering Tribology. 2018; 232(2): 166-178. [2] COMSOL, Structural mechanics modules documentation, https: / / doc.comsol.com/ 5.4/ doc/ com. comsol.help.sme/ StructuralMechanicsModuleUsersGuide.pdf. [3] Almqvist, A., Burtseva, E., Ràfols, F. P., & Wall, P. (2019). New insights on lubrication theory for compressible fluids. International Journal of Engineering Science, 145. 23rd International Colloquium Tribology - January 2022 259 Static Performance Analysis of Porous CMC Journal Bearings for Cryogenic Applications Artur Schimpf Technical University of Kaiserslautern/ Chair for Fluid Mechanics and Fluid Machinery, Kaiserslautern, Germany Corresponding author: schimpf@mv.uni-kl.de Helge Seiler German Aerospace Center/ Institute of Structures and Design BT, Stuttgart, Germany Markus Ortelt German Aerospace Center/ Institute of Structures and Design BT, Stuttgart, Germany Dennis Gudi Technical University of Kaiserslautern/ Chair for Fluid Mechanics and Fluid Machinery, Kaiserslautern, Germany Martin Böhle Technical University of Kaiserslautern/ Chair for Fluid Mechanics and Fluid Machinery, Kaiserslautern, Germany Abstract Highly performant and efficient rocket propulsion is widely used with cryogenic propellants. The associated high-speed turbopumps, exposed to high mass flow and high-pressure rise, are primarily provided with ball bearings. The use of porous bearings is now intended to reduce friction, increase durability and enable an increase in running cycles. This study investigates an innovative micro-porous journal bearing design made of ceramic matrix composites (CMCs) in a specific fiber-layup, with liquid nitrogen as a representative cryogenic lubricant. A static load is applied to the bearing, and the radial clearance is examined. A porous liner made of layered carbon fiber-reinforced carbon (C/ C) was used for this investigation. 1. Introduction The turbopump (TP) is a crucial part of a reusable rocket engine. In order to increase the longevity of a turbopump, alternatives to rolling element bearings are being developed. Hydroand aerodynamic lubrication offers the advantage of less wear and higher rotational speeds to improve performance. Xu et al. [1] present a review of promising bearing technologies for the next generation of turbopumps. Bearings based on a fluid film offer the advantage that wear is minimized or even negated during the start-up or shut down phase. Childs et al. [2] carried out ramp measurements to simulate the run-cycles. The measurements were carried out with pressurized air on orifice bearings. Hannum et al. [3] experimented with a hybrid of rolling and fluid film bearing with liquid nitrogen (LN2) lubrication. This study presents the first results of the further work of [4]. Measurements with air lubrication have already been carried out on pressurized porous CMC for suitability in turbomachines. No instabilities (pneumatic hammer) occurred due to the compressibility of the gas. In this report, the first experiments with liquid nitrogen are evaluated. This measurement series is intended to simulate operation with cryogenic propellants. 260 23rd International Colloquium Tribology - January 2022 Static Performance Analysis of Porous CMC Journal Bearings for Cryogenic Applications 2. Experimental method Figure 1: Test setup for LN2 bearing experiments The porous liner (see Figure 1) has an inside diameter of 28 mm, an outside diameter of 40 mm and a length of 35 mm. At room temperature, the radial clearance between the “Zero-Expansion-CMC” liner and the shaft is 30 μm ± 5 μm. The liner is pressurized with liquid nitrogen and evaporates at the axial ends in the atmosphere. The evaporated nitrogen is pumped out as best as possible at both ends. An electric motor drives the shaft. Two aerostatic support bearings are pressurized with filtered and dried compressed air of 7.35 bar. The radial load on the test bearing is examined with a stepper motor. The load is determined with an S-shaped force sensor. The resulting eccentricities are determined with laser triangulation sensors. 3. Results Three series of experiments were tested with pressurized liquid nitrogen (9 bar). Prior to the tests, the test bearing was aligned with the shaft, while compressed air was supplied. At the beginning of each series of tests, the ball valve of the compressed air supply was closed and the LN2 line opened. The measurements were started as soon as the lubrication consisted of liquid nitrogen. The rotational speed was increased to 2000 rpm and the radial force increased gradually. The measurement was terminated as soon as the fog began hindering the optical distance sensors (see Figure 1). At the end of each series, the LN 2 line was closed and the airline opened. The compressed air prevented the shaft from icing up on the liner and made further measurements possible within 30 minutes. The vertical displacement of the shaft was determined with the sensors VS 1 and VS 2 . An increase in the radial load increased the tilting of the shaft. A rigid shaft was assumed, and the tilting at the z-level of the test bearing housing V t was calculated. Figure 2: Experimental results Figure 2 shows the radial load and the resulting eccentricity. The eccentricity was assessed using the difference between the measured vertical displacement V and the tilt Vt. 4. Discussion Prior measurements [4] with pressurized air (up to 6 bar) and rotational speeds of up to 8000 rpm showed 23rd International Colloquium Tribology - January 2022 261 Static Performance Analysis of Porous CMC Journal Bearings for Cryogenic Applications a mainly vertical eccentricity. Accordingly, the focus for this measurement was placed on a vertical determination of the eccentricity. Optical measurements instruments could be used for the determination of the eccentricity due to the suction of the evaporated nitrogen. The measurements were terminated depending on the formation of fog. The gap width during the series of measurements was not specified due to the lack of information about the temperature distribution of the shaft and the resulting thermal deformation. The series of measurements carried out the correlation between the increase in the load-carrying capacity and the vertical displacement. Exp. 2 and 3 show a tendency to reduce the standard deviations due to an increase in the radial load. A comparable trend became precise with air measurements, too (see [4]). The first test series shows higher fluctuations in the measured values, possibly due to a premature start of the measurement with a gas-liquid N2 mixture. 5. Conclusion This study determined the load-carrying capacity and the resulting eccentricity of a new type of micro-porous CMC journal bearing design. A functionally representative porous C/ C bearing was lubricated with pressurized LN 2 . The data provide preliminary evidence about the suitability of the C/ C liner for cryogenic application under the tested operating conditions targeting further stepwise verification effort in more realistic high-performance rocket TP environment. References [1] Xu, J., Li, C., Miao, X., Zhang, C., and Yuan, X., 2020, “An Overview of Bearing Candidates for the Next Generation of Reusable Liquid Rocket Turbopumps,” Chinese J. Mech. Eng.English Ed., 33(1). [2] Childs, D. W., Klooster, D., Borchard, H., Pavelek, D., and Phillips, S., 2016, “Transient Lift-off Test Results for an Experimental Hybrid Bearing in Air, Simulating a Liquid Hydrogen Turbopump Start Transient,” Proceedings of the ASME Turbo Expo. [3] Hannum, N. P., and Nielson, C. E., 1983, “The Performance and Application of High Speed Long Life Hybrid Bearings for Reusable Rocket Engine Turbomachinery,” NASA Tech. [4] Schimpf, A., Ortelt, M., Seiler, H., Gu, Y., Schwarzwälder, A., and Böhle, M., 2021, “Experimental Investigation of Aerostatic Journal Bearings Made of Carbon Fiber-Reinforced Carbon Composites,” J. Tribol. 23rd International Colloquium Tribology - January 2022 263 Study of the early stages of subsurface cracks and microstructural alterations in 100Cr6 under hydrogen and RCF influence Fernando José López-Uruñuela Tekniker, Basque Research and Technology Alliance (BRTA), C/ Iñaki Goenaga, 5, 20600 Eibar, Spain Department of Mechanical Engineering, University of the Basque Country (UPV/ EHU), Bilbao, Spain Corresponding author: fernando.lopez@tekniker.es Beatriz Fernandez-Diaz Tekniker, Basque Research and Technology Alliance (BRTA), C/ Iñaki Goenaga, 5, 20600 Eibar, Spain Bihotz Pinedo Tekniker, Basque Research and Technology Alliance (BRTA), C/ Iñaki Goenaga, 5, 20600 Eibar, Spain Josu Aguirrebeitia Department of Mechanical Engineering, University of the Basque Country (UPV/ EHU), Bilbao, Spain 1. Introduction WEC and WSF have been studied for the last 20 years. This premature failure affects wind turbine gearbox bearings among other mechanical components from other industrial sectors. Hydrogen is one of the main drivers triggering subsurface cracks and consequently WEC. Nevertheless, it has not been established so far how hydrogen acts when it comes to steel embrittlement in this specific case. According to literature, hydrogen can act by the following mechanisms: HELP, HEDE and HESIV [1]. In the present study, the authors put effort into trying to understand which HE mechanism plays a key role in pores and micro-cracks initiation. Transgranular and intergranular crack morphologies were examined in order to shed light on how hydrogen enhances steel embrittlement. 2. Experimental methodology Disc-on-disc tribometer configuration with spall lubrication was used. The specimens were 20 and 40 mm in outer diameter and 3 mm of contact line was used. The tested lubricant was a poly-α-olefine synthetic oil (ISO VG320). Premature subsurface cracks and WEC were reproduced through a transient condition test to simulate the actual wind turbine gearbox bearing working conditions. The maximum calculated Hertzian stress did not exceed 1,9 GPa and the maximum SRR was set to 45% while the mean value was 21% SRR. For hydrogen uptake, the specimen was put into a solution (sulfuric acid (H2SO4) (0,1 mol/ l) solution and potassium thiocyanate (KSCN) (1 g/ l)) under a −1,2 V potential (this potential was determined by making a previous polarization curve) for 4 h. This method ensures cathodic protection of the discs so that possible corrosion is prevented. After testing specimens were analysed using optical microscopy and SEM. The corresponding metallographic preparations were carried out prior to the analyses. These included cutting, grinding, and polishing. 3. Results and discussion The specimens not precharged did not show any failure. It is of the authors opinion the specimens were not subjected to enough cycles to generate subsurface fatigue. In the case of the precharged specimens, two scenarios can be distinguished, those specimens that were precharged twice, once at the beginning of the test and once in the middle of the test and those that were precharged just once, before testing. Specimens precharged twice were tested until the spalling occurs while the test with specimens precharged once was stopped before spalling. WECs and cracks without microstructural alteration were found at subsurface level in the spalled discs. Some of the cracks were connected to the surface while others were oriented parallel to the raceway without reaching the surface. WEAs formed because of crack face rubbing were found [2]. Likewise, WEAs whose formation was not possible through this mechanism were identified. Crack face rubbing in these cases was not feasible because of the lack of an adjacent crack. Nevertheless, these microstructural alterations were surrounded by micro-cracks. It is hypothesized that regions of material where micro-cracks develop are more prone to trigger 264 23rd International Colloquium Tribology - January 2022 Study of the early stages of subsurface cracks and microstructural alterations in 100Cr6 under hydrogen and RCF influence plastic deformation since the matrix has been weakened. This, in conjunction with hydrogen embrittlement favours WEAs formation [3]. The belief in the need for the existence of a crack prior to the formation of WEAs comes from what was found in the test where premature stages of WEC formation were studied. In this test, where no spalling developed, numerous subsurface micro-cracks appeared. These were sometimes accompanied by small volumes of WEA. No isolated WEA was found without adjacent or surrounding cracks. These results suggest that under the influence of hydrogen and RCF conditions WEC occurs because of the presence of subsurface cracks. Figure 1: WEA surrounded by micro-cracks. Through the detailed analysis of the cross-sections, we tried to interpret how hydrogen affects the generation of subsurface cracks and microstructural alterations. The modes of hydrogen embrittlement commonly presented in the literature seem to have a synergistic effect on the generation of this failure mode. On the one hand, HEDE favours the presence of pores that eventually coalesce with cycling to generate cracks [4]. On the other hand, HELP favours the movement of dislocations which in turn promote plastic deformation phenomena in regions of material under high stress [5]. One of the ways to find out how hydrogen acts in the formation of cracks is to study the morphology of the cracks, i.e., to analyse whether they are transgranular or intergranular cracks. In the present study, both transgranular cracks and WEAs were found. Although the presence of hydrogen has generally been associated with intergranular fracture, the results shown here prove that under certain conditions (RCF) and HE transgranular fracture is promoted. Figure 2: Transgranular WEA crossing grain boundary. 4. Conclusions The following conclusions can be drawn from the present study: • Under the influence of RCF and HE cracks tend to initiate in the subsurface. • With cycling, microstructural alterations develop in regions where micro-cracks were formed. • Hydrogen acts according to the two most proposed mechanisms in literature: HELP and HEDE. • Cracks are formed by the coalescence of pores generated in regions of maximum shear stress. • With cycling, both transgranular cracks accompanied by WEAs and transgranular WEAs surrounded by cracks develop. References [1] Hussein A, Krom AHM, Dey P, Sunnardianto GK, Moultos OA, Walters CL. The effect of hydrogen content and yield strength on the distribution of hydrogen in steel: a diffusion coupled micromechanical FEM study. Acta Mater 2021; 209: 116799. doi: 10.1016/ j.actamat.2021.116799. [2] Lai J, Stadler K. Investigation on the mechanisms of white etching crack (WEC) formation in rolling contact fatigue and identification of a root cause for bearing premature failure. Wear 2016; 364- 365: 244-56. doi: 10.1016/ J.WEAR.2016.08.001. [3] Kürten D, Khader I, Raga R, Casajús P, Winzer N, Kailer A, et al. Hydrogen assisted rolling contact fatigue due to lubricant degradation and formation of white etching areas. Eng Fail Anal 2019; 99: 330- 42. doi: 10.1016/ J.ENGFAILANAL.2019.02.030. [4] Spille J, Wranik J, Barteldes S, Mayer J, Schwedt A, Zürcher M, et al. A study on the initiation processes of white etching cracks (WECs) in AISI 52100 23rd International Colloquium Tribology - January 2022 265 Study of the early stages of subsurface cracks and microstructural alterations in 100Cr6 under hydrogen and RCF influence bearing steel. Wear 2021: 203864. doi: 10.1016/ j. wear.2021.203864. [5] Connolly M, Martin M, Bradley P, Lauria D, Slifka A, Amaro R, et al. In situ high energy X-ray diffraction measurement of strain and dislocation density ahead of crack tips grown in hydrogen. Acta Mater 2019; 180: 272-86. doi: 10.1016/ j.actamat.2019.09.020. Coatings, Surfaces and Underlying Mechanisms Lubricant-Surface Interaction 23rd International Colloquium Tribology - January 2022 271 Physical and Numerical Investigation of the Friction Behavior of Graphite Lubricated Axial Ball Bearings Arn Joerger Karlsruhe Institute of Technology (KIT)/ IPEK - Institute of Product Engineering, Karlsruhe, Germany Corresponding author: arn.joerger@kit.edu Markus Spadinger, Katharina Bause, Sascha Ott, Albert Albers Karlsruhe Institute of Technology (KIT)/ IPEK - Institute of Product Engineering, Karlsruhe, Germany 1. Introduction Even though graphite is known for centuries as lubricant, not much information about its applicability in technical systems is available in regular mechanical construction literature (cf. [1]). Especially at high temperatures, graphite has high potential for the lubrication due to the carbon bond energy. Rolling bearings are being used in many mechanical systems. Temperature limits of regular (considered here to be without additives) used oils or greases are at approx. 100°C. In context of the carbon bond energy, graphite has potential for the lubrication of rolling bearings in high temperature environments. However, before analyzing rolling bearings at high temperature, the friction behavior at regular conditions has to be investigated. For this reason, the first aim of this investigation is the experimental analysis of the friction behavior of graphite lubricated rolling bearings. For the transfer of these results to simulation models, a first approach for describing graphite lubrication in numeric simulation models is presented. The further aim of the project is the preparation of a demonstrator bearing, which includes a relubrication unit. 2. Physical testing of axial ball bearings 2.1 Method Axial ball bearings of type 51208 have been chosen for testing. The lubrication has been done by graphite dispersion, which has been sprayed on the bearings before and during the test runs. For the initial lubrication, the bearings were disassembled and the rings and cage (with balls) have been coated with graphite dispersion with an airbrush spray gun. The graphite forms a matt black surface on the rings and balls, the thinner immediately evaporates. The tests have been conducted on an IPEK rotational test bench, which was extended with a relubrication unit. This unit consists of mechanical clamps for its fixation in the test chamber and a commercial airbrush gun. Within this test setup, the inner bearing ring is driven. Above the bearing arranged sensors have measured the axial force and the torque, which has been transferred from the inner (driven) to the outer ring. The axial force has been applied by a pneumatic cylinder on top of the measure chamber. For testing, the bearings have been driven with rotational velocities of 250 rpm ( 6.75 m/ s), 375 rpm ( 10.125 m/ s) and 500 rpm ( 13.5 m/ s). Axial loads for the comparable Hertzian pressures between ring and one ball of 1 GPa (C/ P = 47), 1.5 GPa (C/ P = 14) and 2 GPa (C/ P = 6) have been applied. Eight specimens have been tested, each one at a constant velocity but with cyclic changing loads. This means, that with one bearing the first applied pressure has been 1 GPa, followed by 1.5 GPa and 2 GPa. This cycle is repeated two times for gaining nine test runs each 15 min per bearing. The evaluation has been done by the computed coefficient of friction µ = M measured / (F axial r Bearing ) 2.2 Results Before placing the bearings in the test chamber, the rings and cage (including balls) have been reassembled. Immediately, much of the graphite spalls from the surfaces, which contact the mutual parts. Thus, not much of the graphite stays on the surfaces but still small amounts of graphite are kept in the roughness valleys of the race. On the flat ring areas next to the races, the thickness measuring of the graphite coating reveals a layer thickness of approx. 75 µm. The spalling of the graphite shows the necessity of relubrication and that the thickness can be neglected. 272 23rd International Colloquium Tribology - January 2022 Physical and Numerical Investigation of the Friction Behavior of Graphite Lubricated Axial Ball Bearings Figure 1: The left picture shows the spalled graphite on the ring-shaped area next to the race of the inner ring. The race is focused on the right picture with scattered graphite spots. The test runs have been conducted for eight bearings with each nine tests. So, in total 72 time series are available for the evaluation. For each test run, the average coefficient of friction is computed and plotted by its pressure as box plot in Figure 2. The median value (red line) decreases with the pressure. So, by increasing the pressure, less rotational resistance occurs in the bearings. The values show, that for graphite lubrication in axial ball bearings coefficients of friction of approx. 0.005 can be expected. This is about three times more than for regular lubrication. So, graphite is capable of lubricating ball bearings, but not at the same reduction of the resistance than regular oil and grease lubrication. Regular lubricated bearings have coefficients of friction of approx.0.0015 for C/ P = 10 for [2]. Figure 2: The three boxes show the resulting coefficients of friction per pressure velocity. 3. Computational approach for the depiction of graphite lubrication 3.1 Computational approach Multi body simulations (MBS) are being used in bearing development processes because e. g. the system geometry can be easily replaced. Hereby, a modelling and computational approach for the depiction of a contact is required. For the relation between the normal and shear forces in contacts, the coefficient of friction is a suitable parameter. However, being a system dependent variable, the determination of it as single value is not suitable. Further approaches are necessary to depict the tribological behavior. For regular oil and grease lubrication, computation formulas are available for the determination of the frictional torque in bearings, which split the torque to a load dependent and load independent term [2]. But for the description of solid graphite lubrication in rolling bearings, no approach for multi-body simulations is available. In contrast to oil and grease, graphite has no viscous material properties. Therefore, the split of the computation of the bearing resistance torque with regarding the viscosity (cf. [2]) seems unsuitable. However, since graphite sliding experiments show [3] that graphite is shifted out by sliding motions, an approach, which splits sliding and rolling friction is presented. The application of the friction computation is applied in a multi-body model of the axial ball bearing 51208. For reducing the computational time, the model consists of the two rings and three balls. The cage is modelled as spring-damper systems between the balls. The frictional force in each of the six contacts is computed with the Amontons-Coulomb friction law F fric = µ MBS F normal The coefficient of friction is split in a sliding, rolling and rotating term µ MBS = µ slide + µ roll + µ rot The value for µ slide calculates as a share of the literature values [3] of sliding graphite friction. The share is computed by the slide-to-roll ratio (SRR). µ slide = µ slide,lit · k SRR The hereby presented simulation, conducted in MSC Adams, results are conducted without rolling or rotating resistance (µ roll = µ rot = 0). Since the SRR is hereby the main parameter, three initial simulations with Hertzian pressures of 1 GPa and SRRs of 1 %, 2 % and 10 % are considered. 23rd International Colloquium Tribology - January 2022 273 Physical and Numerical Investigation of the Friction Behavior of Graphite Lubricated Axial Ball Bearings 3.2 Numerical results Table 1: In the MBS, the coefficient of friction rises with an increasing SRR. SRR 1 % 2 % 10 % 0.0023 0.0024 0.0056 In Table 1, the results of the MBS illustrate that the results are in the same scale as the physically measured coefficients. Since the SRR are assumed values and the rolling and rotating resistance are neglected, further analysis is necessary to create the entire computational model for the depiction of graphite lubrication in MB software. 4. Conclusion and Outlook The results from the physical experiments have indicated a relation of the coefficient of friction and the applied pressure. A clear relation between the rotational velocity and the coefficient of friction has not been found. The coefficients of friction have shown that graphite has potential for the fluid free lubrication of rolling bearings. However, the lubrication is dependent on the relubrication since the graphite does not get to the contact on its own or due to system behavior. A relubrication mechanism is necessary to secure the lubricant supply. The results from the early stage computational model for the description of graphite lubrication in rolling bearings on base of a sliding coefficient of friction have illustrated right scale values, which requires extensive elaboration. Since especially the SRR is estimated to strongly influence the coefficient of friction in solid lubricant systems, solutions for measuring it will be analyzed with the aim of extending the test bench. Further, the variation of the amount of graphite for lubrication will show the durability of a lubrication and what amounts of graphite would be necessary for a lifetime lubrication. 5. Acknowledgment The authors thank the Deutsche Forschungsgemeinschaft (DFG) for the funding of the project “Mechanism of Graphite Lubrication in Rolling Contact” (“Mechanismen der Graphitschmierung in Wälzkontakten”), grant numbers AL533/ 37-1. The project is part of the priority program “SPP 2074: Fluidless Lubricationsystems with high mechanical Load” (“SPP 2074: Fluidfreie Schmiersysteme mit hoher mechanischer Belastung”). References [1] B. Sauer, Konstruktionselemente des Maschinenbaus 2, Springer Berlin Heidelberg, Berlin, Heidelberg, 2018. [2] Brändlin, H. Eschmann, Weigand, Die Wälzlagerpraxis: Handbuch für die Berechnung und Gestaltung von Lagerungen, korrig. Nachdr. der third. Aufl., Vereinigte Fachverl., Mainz, 1998. [3] C.E. Morstein, M. Dienwiebel, Graphite lubrication mechanisms under high mechanical load, Wear 477 (2021) 203794. 23rd International Colloquium Tribology - January 2022 275 Influence of Humidity on Graphite Lubrication: the Road to Turbostratic Carbon Carina Morstein Karlsruhe Institute of Technology KIT, IAM-CMS Institute for Applied Materials - Computational Materials Science, MicroTribology Center µTC, Karlsruhe, Germany Fraunhofer-Institute for Mechanics of Materials IWM, MicroTribology Center µTC, Freiburg, Germany Corresponding author: carina.morstein@kit.edu Andreas Klemenz Fraunhofer-Institute for Mechanics of Materials IWM, MicroTribology Center µTC, Freiburg, Germany Martin Dienwiebel Karlsruhe Institute of Technology KIT, IAM-CMS Institute for Applied Materials - Computational Materials Science, MicroTribology Center µTC, Karlsruhe, Germany Fraunhofer-Institute for Mechanics of Materials IWM, MicroTribology Center µTC, Freiburg, Germany Michael Moseler Fraunhofer-Institute for Mechanics of Materials IWM, MicroTribology Center µTC, Freiburg, Germany University of Freiburg, Institute of Physics, Freiburg, Germany 1. Introduction Solid lubricants are used in applications where conventional liquid lubricants reach their limits. One of the well-known solid lubricants is graphite, showing distinct lubrication properties in normal atmosphere but severe wear and friction in vacuum. Currently, two main explanations for the good lubrication behavior of graphite are present: The first one is the deck-of-cards-model postulated by Bragg et al. [1], according to which the graphene layers are easily sheared against each other due to the weak Van-der-Waals-forces between layers. However, this model does not explain the humidity dependence of graphite’s lubrication properties and has already been disproven by experiments, e.g. X-ray diffraction [2]. The second model is the “adsorption model” postulated by Savage [3]. He suggested that water adsorbs as a layer on top of graphite and thus acts as a boundary lubrication film. One has to mention that both models have been mainly investigated under low loads and on surfaces with a nanoscale roughness. This work aims to investigate the graphite lubrication mechanisms and humidity dependence under high loads and on technical surfaces. 2. Experimental Procedure For friction and wear experiments, polished iron plates were coated with a graphite dispersion using an airbrush spray gun. In a microtribometer, the samples were tested against a small steel sphere in a linear-reversible fashion for 500 cycles. The normal force was 402 mN, resulting in a high Hertzian pressure of 1 GPa. To investigate humidity influence on friction and wear, the experimental chamber was continuously flooded with pressurized air, which was humidified to the desired values (between 0.24-44% rH). After the experiments, the wear volume and thus wear coefficient was quantified by confocal microscopy. For the investigation of structural changes and sp 2 content of the graphite, detailed scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HR-TEM), as well as electron energy loss spectra (EELS) analyses were conducted before and after the experiments. 3. Results and Discussion 3.1 Friction and Wear Generally, an influence of the humidity on the steadystate coefficient of friction (COF) is observed even at the high loads investigated in this work. With an increase in humidity from 0.24% to 24%, a slight decrease in friction from μ = 0.14 to 0.10 is observed, followed by a plateau at μ ≈ 0.10 for all higher humidities. Comparable literature experiments with graphite or graphene often do not specify the exact environmental conditions the experiment has been conducted in. However, when summarizing different publications on graphite and graphene lubrication, typical values for the COF vary between 0.08-0.25 [4-8]. Evidently, the friction yielded with the 276 23rd International Colloquium Tribology - January 2022 Influence of Humidity on Graphite Lubrication: the Road to Turbostratic Carbon presented graphite lubrication lies on the lower end of this range. When analyzing the wear coefficient of the plate, a parabolic trend is observed, with the highest value yielded with dry pressurized air (RH = 0.24%) and with highly humidified air (RH = 44%). At intermediate humidity, the wear coefficient shows only little variation and is an order of magnitude smaller. At high humidity, the rapid material transport could be due to the formation of capillary necks between the asperities of the tribopartners. This would result in an additional normal force component and consequently, an increase in adhesion of the graphite to the steel sphere. Hence, graphite transportation during sliding will be observed due to easier delamination of the coating from the substrate. The high wear coefficient at low humidity (dry pressurized air) can be explained with beginning “dusting” mechanisms, which are known to dominate the wear of graphite in vacuum [7]. 3.2 Structural changes For an analysis of the graphite structure, two TEM lamellae were prepared: one in the middle of the wear track after an experiment and one in an unworn area as a reference point. HR-TEM analysis of the unworn reference sample revealed that the graphite coating is a 3.5 µm thick, porous layer built out of randomly oriented graphene bundles. The content of sp 2 -hybridized carbon was analyzed with EELS measurements and determined to be at 98% for the whole layer. Hence, the airbrush coating process yields purely graphitic carbon. After sliding wear, the structure of the graphite coating is distinctly different: a gradient in regards of the sp 2 -content has developed. At the iron substrate, the content of sp 2 -hypridization is 77%, whereas at the sliding interface it is only 70%. This observation is also visible in the HR-TEM images themselves; at the iron substrate interface, the graphene layers are parallel to each other and to the substrate. At the sliding interface, the graphene bundles completely disappeared and a turbostratic structure is observed instead. In conclusion, shearing does not take place between the individual graphene layers at the top of the coating. If this was the case, a high sp 2 content and parallel graphene layers would be observed at the sliding interface. Instead, shearing at these high loads takes place in the bulk of the material, leading to the formation of turbostratic carbon. This contradicts both the deck-of cards-model and the adsorption model. As a result, a new model mechanism is needed for the lubrication mechanism under high loads. The experimental data hints to the fact that low friction with graphite under high load is achieved due to the shear-induced formation of turbostratic carbon. 4. Conclusion In summary, our results have shown that neither the popular deck-of-cards model nor the adsorption model is suitable for the explaination of the tribological properties of graphite under high loads. Sliding of individual graphene layers might be true for experiments under low loads with a basal plane as sliding interface. In technical graphite coatings as presented in this work, a gradual decrease of sp 2 -content is observed towards the sliding interface. This demonstrates that shear takes mainly place within the graphite layer, leading to a shear-induced formation of turbostratic carbon. References [1] Bragg, W. H.: An introduction to crystal analysis, (G. Bell and Sons, Ltd., London, 1928). [2] Arnell, R. & Teer, D. Lattice Parameters of Graphite in relation to Friction and Wear, Nature 218, 1155-1156 (1968). [3] Savage, R. H. Graphite Lubrication, Journal of Applied Physics 19, 1-10 (1948). [4] Berman, D., Erdemir, A., Sumant, A. V., Reduced wear and friction enabled by graphene layers on sliding steel surfaces in dry nitrogen, Carbon 59, 167-175 (2013). [5] Berman, D., Erdemir, A., Sumant, A. V., Few layer graphene to reduce wear and friction on sliding steel surfaces, Carbon 54, 454-459 (2013). [6] Bowden, F. P. and Young J. E., Friction of diamond, graphite, and carbon and the influence of surface films, Proc. R. Soc. Lond. A 208, 444-455 (1951). [7] Lancaster, K. K. and Pritchard, J. R., On the ‘dusting’ wear regime of graphite sliding against carbon, Journal of Physics D: Applied Physics, 13, 1551 (1980). [8] Buckley, D. H.; Johnson, R. L., Mechanism of Lubrication for Solid Carbon Materials in Vacuum to 10 −9 Millimeter of Mercury, ASLE Transcations 7, 91-100 (1964). 23rd International Colloquium Tribology - January 2022 277 Effect of Lubricants on Hydrogen Permeation under Rolling Contact of Steel Yoji Sunagawa Idemitsu Kosan Co., Ltd., Chiba, Japan Corresponding author: yoji.sunagawa.0470@idemitsu.com Hiroyoshi Tanaka Kyushu University, Fukuoka, Japan Joichi Sugimura Kyushu University, Fukuoka, Japan 1. Introduction In rolling bearings used in automotive electrical instruments, power transmission parts such as CVT (Continuously Variable Transmission) and wind turbines, early bearing failure accompanied by white microstructures below the raceway subsurface occurs. The main cause is often thought to be the effect of hydrogen embrittlement. Hydrogen embrittlement is the process by which steel materials become brittle and fracture due to the introduction and subsequent diffusion of hydrogen into the metal. In rolling bearings, since active nascent metal surface is exposed, lubricant oils between metal surfaces is decomposed, and hydrogen is generated and penetrates into steels. 2. Experimental This study describes the effects of lubricant additives on the generation and permeation of hydrogen into AISI 52100 bearing steel in rolling contact. Lubricated tests were conducted in a nitrogen atmosphere. PAO was used as the base oil. Sample A and sample B were formulated with representative detergent additives. Oil decomposition test (Test 1) and rolling contact fatigue test (Test 2) were conducted. 3. Results In Test 1, the lubricant oil was decomposed by the effect of catalyst (Fe) and the amount of hydrogen generation was measured by gas chromatograph. Sample A showed two times higher hydrogen generation rate than that of the base oil, whereas Sample B reduced the hydrogen generation rate, as shown in Fig. 2. In Test 2, the fatigue life was evaluated using a thrust bearing type rolling test apparatus. Thermal desorption spectrometry (TDS) was used to measure the amount of permeated hydrogen immediately after the rolling test. The test revealed that the fatigue life increased in order of base oil, Oil B, Oil A, as shown in Fig. 4. TDS analysis revealed that the amount of permeated hydrogen was in the order of Oil A, Oil B, base oil. These results suggested that the amount of permeated hydrogen and the fatigue life were inversely correlated. Table 1: Test samples Figure 1: Hydrogen generation test apparatus (Test 1) 278 23rd International Colloquium Tribology - January 2022 Effect of Lubricants on Hydrogen Permeation under Rolling Contact of Steel Figure 2: Hydrogen generation test results The process of hydrogen permeation can be broken down into mainly two phases at nascent metal surface. One is dissociation at C-H bond in oil skeleton. The other is diffusion of hydrogen atoms on the metal surface. In the second phase, a part of atomic and/ or ionic hydrogen recombine to produce gaseous hydrogen. The others may permeate into the steel. The balance of the two processes may cause hydrogen content in the steel under rolling contact. The detail which effect of the two detergent additives on the hydrogen permeation process will be discussed. Figure 3: Fatigue life test apparatus (Test 2) Figure 4: Fatigue life test results References [1] Sadeghi, F., Jalalahmadi, B., Slack, T.S. Raje, N., and Arakere, N.K., “A Review of Rolling Contact Fatigue”, J. Tribol., 131, 4, 2009, 041403-1. [2] Tanaka, H., Niste, V.B., Abe, Y., and Sugimura, J., “The effect of lubricant additives on hydrogen permeation under rolling contact”, Tribol. Lett., 65, 3, 2017, 94. Tribologiy Behaviour 23rd International Colloquium Tribology - January 2022 281 Tribological and microstructural analysis of PVD coatings: deposited on high chromium steel substrates for cold rolling applications A. Carabillò Politechnic Department of Engineering and Architecture (DPIA), University of Udine, via delle Scienze 208, 33100, Udine, Italy. EUROLLS S.p.A., Udine, Italy carabillo.antonio@spes.uniud.it, Tel. number: (+39) 0433 750500 A. Lanzutti Politechnic Department of Engineering and Architecture (DPIA), University of Udine, via delle Scienze 208, 33100, Udine, Italy. alex.lanzutti@uniud.it F. Sordetti Politechnic Department of Engineering and Architecture (DPIA), University of Udine, via delle Scienze 208, 33100, Udine, Italy. francesco.sordetti@uniud.it M. Magnan Politechnic Department of Engineering and Architecture (DPIA), University of Udine, via delle Scienze 208, 33100, Udine, Italy. michele.magnan@uniud.it M. Querini EUROLLS S.p.A., Udine, Italy matteo.querini@eurolls.com, Tel. number: (+39) 0432796511 O. Azzolini Laboratori Nazionali di Legnaro (INFN), Viale dell’Università, 2, 35020 Legnaro (PD), Italy oscar.azzolini@lnl.infn.it, Tel. number: (+39) 0498068665 L. Fedrizzi Politechnic Department of Engineering and Architecture (DPIA), University of Udine, via delle Scienze 208, 33100, Udine, Italy. lorenzo.fedrizzi@uniud.it, Tel. number: (+39) 0432 558839 1. Introduction Cold rolling is performed on about 30% of the world metal production [1]. The rolls undergo to a rolling-sliding tribo-contact at very hertzian loads. The main wear mechanisms observed for this kind of applications are mainly abrasive and triboxidative, in the worst case it occurs cracking and spalling phenomena [2]. The use of thin films, in particular PVD coatings, is widespread in many technological fields thanks to the improvement of surface properties of the coated components (wear) [3]. This study aims to determine the tribological performances of many coatings deposited on W.Nr. 1.2344 and W.Nr. 1.2379 steels. In detail, the coatings (CrN, CrCN or TiN, TiON, TiCN, AlTiN-Si 3 N 4 ) studied in this work are produced by a combination of magnetron sputtering and cathodic arc evaporation techniques, in order to match high deposition rates, high energetic and ionized plasmas with low structural residual stress and low growth defects. To obtain a high-quality coating, the PDC-SBV (Pulsed Direct Current Substrate Bias Voltage) was varied and its effect on mechanical properties was investigated. 2. Experimental The study is therefore broken down into a first phase of sample preparation and coatings deposition by using an industrial PVD prototype plant. The second phase involves the chemical and microstructural characterization of the samples. A third phase instead investigates the mechanical properties of the samples as microhardness 282 23rd International Colloquium Tribology - January 2022 Tribological and microstructural analysis of PVD coatings: deposited on high chromium steel substrates for cold rolling applications and coating/ substrate adhesion. Finally, the last phase includes the tribological test. In particular the microstructure of the coatings was characterized by means of Scanning Electron Microscope and Energy Dispersive X-ray Spectrometry (SEM+EDXS) in both top view and cross section. The elemental distribution along the coating thickness was evaluated by means of Radio Frequency Glow Discharge Optical Emission Spectroscopy (Rf-GDOES). The mechanical properties of the coating were evaluated through micro-hardness tests with variable load, while the adhesion was evaluated with scratch test performed at variable load using a HRC indenter (0-90 N in 90 sec for a length of 10mm). Figure 1: top and cross section of a 1,2344 sample coated The samples underwent to ball on flat tests at high Hertzian loads (80 and 40N with a stroke length of 10 mm and 10 Hz of frequency), using an alumina sphere (9mm in diameter). The high Hertzian loads are used to roughly simulate the typical loads of cold rolling process. During the tests, the COF was acquired continuously. Afterwards, the wear rate (WR) was measured by stylus profilometer, while the wear mechanism was evaluated by means of SEM+EDXS analysis of the worn area in both cross section and top view. Figure 2: scheme of the ball on flat test 3. Results In this part of the document, only the results obtained on 1.2344 steel substrate are presented. As shown in the HV graphs (Fig.3), the microhardness for low load is close to what has been found in the literature [4], while as the load increases, the contribution of the substrate becomes more and more evident, while obtaining an always higher value. The adhesion is evaluated by two critical lengths, Lc 1 is the first cohesive defect of the coating and Lc 2 is the first coating delamination. The low bias sample has the best mechanical properties. Figure 3: HV of the coated and uncoated 1,2344 samples Figure 4: scratch s of the 1,2344 coated samples As shown in the COF graphs (Fig.3), the coated sample, tested with an applied load of 40N, presents lower COF respect to the bare steel, while the load increase (80N) showed a similar COF between the coated and uncoated specimen. In this case, the COF presents a less noisy signal. The wear mechanism, in specimens tested at 40N (Fig.4), is abrasive with sporadic delamination between substrate and coating. These delaminations can occur from poor local adhesion due to surface defects. The width of the trace is reduced by approximately 50% compared to the uncoated case. At high load (80N) the coating is completely removed and the delaminations are present on wear track side. In this case, the substrate exposed by coating removal is subject to abrasive and triboxidative wear, as in the bare steel. The wear rate (fig.5) shows a decrease in the wear rate of 97% compared to the case of the sample not coated, for the samples tested at 40N. The delaminations does not affect the wear performances of the coating. At high loads (80N) the wear rate reduction is only of the 10%, compared to the bare steel. This is probably due to the fact that the coating is removed and does not protect the underneath substrate. The results showed how the use of multilayer coatings, high bias deposited with the combination of the magnetron sputtering and cathodic arc techniques, improved the wear resistance of the material. This result was also achieved by the control of surface defects. 23rd International Colloquium Tribology - January 2022 283 Tribological and microstructural analysis of PVD coatings: deposited on high chromium steel substrates for cold rolling applications Figure 5: COF for the coated and uncoated 1,2344 samples. Figure 6: SEM analysis of the worn areas for the specimen tested at 40 N and 80 N Figure 7: wear rates of the tested samples coated and uncoated. Bibliography [1] P. Montmitonnet, Y.E. Khalfalla, K.Y. Benyounis , “Metal Working: Cold Rolling”, Encyclopedia of Materials : Science and Technology, 2001, Pages 5500 5506 [2] A. Lanzutti, J.Srnec Novak, F. De Bona, D. Bearzi, M. Magnan, L. Fedrizzi, “ Failure analysis of cemented carbide roller for cold rolling : Material characterisation, numerical analysis, and material modelling”, Engineering Failure Analysis 116 (2020) 104755 [3] Bemporad, E., Pecchio, C., De Rossi, S., & Carassiti, F. (2001). Characterization and hardness modelling of alternate TIN/ TICN multilayer cathodic arc PVD coating on tool steel. Surface and Coatings Technology, 146 147, 363 370. [4] S.J Bull, D.G Bhat, M.H Staia, Properties and performance of commercial TiCN coatings. Part 1: coating architecture and hardness modelling, Surface and Coatings Technology, 2003, Pag. 499-506, Vol. 163-164. 23rd International Colloquium Tribology - January 2022 285 Nanoscale wear behavior of CVD grown monolayer WS 2 Himanshu Rai Department of Materials Science and Engineering, Indian Institute of Technology Delhi, Hauz Khas, New Delhi, India 110016 Corresponding author: himanshu.rai@mse.iitd.ac.in Deepa Thakur School of Engineering, Indian Institute of Technology Mandi, Himachal Pradesh, India 175075 Deepak Kumar Department of Materials Science and Engineering, Indian Institute of Technology Delhi, Hauz Khas, New Delhi, India 110016 Zhijiang Ye Department of Mechanical and Manufacturing Engineering, Miami University, Oxford, OH 45056 Viswanath Balakrishnan School of Engineering, Indian Institute of Technology Mandi, Himachal Pradesh, India 175075 Nitya Nand Gosvami Department of Materials Science and Engineering, Indian Institute of Technology Delhi, Hauz Khas, New Delhi, India 110016 Abstract In this study, the nanoscale wear behavior of chemical vapor deposition (CVD) grown tungsten disulfide (WS 2 ) was examined using atomic force microscopy (AFM). Load-dependent controlled experiments were performed in the interior and at the edge of monolayer WS 2 flakes using a diamond-like-carbon (DLC) coated silicon AFM probe. The critical load to initiate wear in the interior region of WS 2 flake was found to be significantly higher than the edge regions. Experimental findings also elucidated significant variability in critical load values in both regions where particularly near the edge regions the different wear modes were observed including either sudden removal or gradual removal of the monolayer. The observed difference in wear behavior can be attributed to the presence of structural defects as confirmed via molecular dynamics simulations. Keywords: WS 2 , Solid lubricant, 2D materials, Tribology, Atomic force microscopy 1. Introduction Friction and wear are a major concern as they result in significant energy loss and removal of materials, and eventually mechanical failures. Advanced sensing devices such as micro-electromechanical systems (MEMS) and nano-electromechanical systems (NEMS) has led to the development of various modern devices. For these devices surface related issues including friction and wear are a crucial concern [1]. Tribological properties of these small-scale devices has an important role in achieving desired lifespan but unfortunately conventional lubricants have certain limitations at small-scale [2]. Therefore, solid lubricants are suitable in small-scale devices such as MEMS to achieve the desired tribological properties. Solid lubricants are more efficient under harsh conditions to a great extent [3]. Among various solid lubricants, two-dimensional (2D) materials have great potential due to their superior mechanical, chemical, and thermal properties [4]. 2D materials such as graphene and transition metal dichalcogenides (TMDs) are used extensively in tribological applications. But, graphene has poor lubrication behavior under dry conditions [5] which provides a way to explore TMDs including MoS 2 and WS 2 . Therefore, in the present study nanoscale wear behavior of CVD grown monolayer WS 2 has been explored and it was observed that the edge has lower load carrying capacity than the interior. Inconsistency in the wear behavior is attributed to the presence of structural defects as confirmed using molecular dynamics simulation study. 286 23rd International Colloquium Tribology - January 2022 Nanoscale wear behavior of CVD grown monolayer WS 2 2. Experimental methodology Atmospheric pressure chemical vapor deposition (AP- CVD) was used to grow the monolayer WS 2 on SiO 2 / Si substrate (300 nm SiO 2 on Si). WO 3 nanorods and sulfur powder (99.5% Alfa Aesar) were utilized as precursors and placed in a tube furnace. Further, the synthesis of monolayer WS 2 was accomplished at 850 °C (heating rate 8.5 °C/ min) for 10 min. To investigate the wear behavior of WS 2 , an atomic force microscopy (AFM, Flex Axiom, Nanosurf, Switzerland) was used. Experiments were performed using a sharp AFM probe (Multi75DLC, Budget-sensors, Bulgaria). Raman and photoluminescence (PL) microscopy (LabRAM HR evolution, Horiba Jobin Vyon, France) were used with a laser of 532 nm and spot size 1-2 micron (objective 100x, power ~ 0.2 mW8). 3. Results and discussion 3.1 Initial characterization CVD grown monolayer WS 2 flakes were identified by optical microscopy as shown in Figure 1a. Monolayer nature of the WS 2 flakes was confirmed by performing Raman and PL emission and the results are shown in Figure 1b & c. Figure 1: (a) Optical micrograph showing the monolayer WS 2 flakes (b) Raman intensity, and (c) corresponding PL intensity spectra. 3.2 Nanoscale friction and wear measurements To observe the wear behavior, load-dependent (~ 0.02 µN to ~ 1.35) sliding experiments were performed using AFM. When the experiment was performed within the interior of the WS 2 flake, complete removal of the flake was observed after a certain normal load which leads to the abrupt increase in friction as shown in Figure 2a. Figure 2b & c are the zoomed-out topographic image and its line profile, respectively, which confirms the wear in the experimental region. Zoomed-out friction force maps and its line profile are shown in Figure 2d & e, respec- 23rd International Colloquium Tribology - January 2022 287 Nanoscale wear behavior of CVD grown monolayer WS 2 tively, which shows an increase in the friction force in the experimental region. Figure 2: (a) Friction force variation with the applied normal force measured on the CVD grown monolayer WS 2 . (b) Zoomed-out topographic image of the experiment region and (c) its line profile. (d) Zoomed-out friction map of the experiment region and (e) its line profile. These experiments were performed in the interior of WS 2 . When the experiment was performed at the edge of the WS 2 flake, most experiments revealed gradual removal of the flake initiating at much lower load as shown in Figure 3a. Figure 3b & c are the zoomed-out topographic image and its line profile, respectively, that shows the removal in the form of small fragments. Zoomed-out friction force maps and its line profile are shown in Figure 3d & e, respectively. Figure 3: (a) Friction force variation with the applied normal force measured on the CVD grown monolayer WS 2 . (b) Zoomed-out topographic image of the experiment region and (c) its line profile. (d) Zoomed-out friction map of the experiment region and (e) its line profile. These experiments were performed at the edge of WS 2 . In this work, two distinct wear behavior were observed i) complete removal of the WS 2 flake when the experiments were performed within the interior of WS 2 flake, ii) gradual removal of the WS 2 flake with the increasing load when the experiments were performed at the edge of the flake. Removal of the flake at the edge was initiated at a significantly lower load and persisted up to the maximum applied normal load. Qi et al. [6] systematically studied the wear behavior of mechanically exfoliated monolayer graphene and noticed different wear behavior within the interior and at the edge, similar to present work. They also observed comparatively low load-carrying capacity at the edge than the interior. However, in contrast to exfoliated graphene, buckling of the monolayer near the edge region was not observed. Moreover, experiments in the present work were carried out in the air, so the anticipation of a certain level of organics and adsorbed water on the surface cannot be neglected [7]. 288 23rd International Colloquium Tribology - January 2022 Nanoscale wear behavior of CVD grown monolayer WS 2 4. Conclusions In conclusion, wear behavior of CVD grown WS 2 on a SiO 2 / Si substrate was investigated using AFM. Our experiments revealed that monolayer WS 2 is significantly stronger in the interior region than the edge of the WS 2 . In the interior region, below a critical normal load wear of monolayer WS 2 was not observed. Beyond this load, there is sudden removal of the WS 2 layer and leads to the abrupt increase in the friction. At the edge gradual removal of the WS 2 layer with the increasing normal load was observed in majority of experiments. However, it was also observed that partially removed WS 2 layer can still provide lubrication efficiently. Significantly low wear strength at the edge can be due to the easy bond formation between the DLC coated tip and the edge of WS 2 or due to the presence of structural defects. This study throws light on the wear behaviour of the CVD grown monolayer WS 2 , which is critical for various tribological applications of this atomically thin 2D material as a solid lubricant. References [1] D. Boer, T.M. Mayer, Society 26 (2001) 302-304. [2] A. Erdemir, C.D.-J. of P.D.A. Physics, undefined 2006, Iopscience.Iop.Org (n.d.). [3] P. Sutor, MRS Bull. 16 (1991) 24-30. [4] S. Zhang, T. Ma, A. Erdemir, Q. Li, Mater. Today 26 (2019) 67-86. [5] B.Y.- Wear, undefined 1996, Elsevier (n.d.). [6] Y. Qi, J. Liu, J. Zhang, Y. Dong, Q. Li, ACS Appl. Mater. Interfaces 9 (2017) 1099-1106. [7] J. Gao, B. Li, J. Tan, P. Chow, T.M. Lu, N. Koratkar, ACS Nano 10 (2016) 2628-2635. 23rd International Colloquium Tribology - January 2022 289 Tribological behaviour of W-S-C coated ceramics in a vacuum environment K. Simonovic Czech Technical University in Prague, Faculty of Electrical Engineering, Advanced Materials Group, Prague, Czech Republic Corresponding author: kosta.simonovic@fel.cvut.cz, simonovic.kosta@gmail.com T. Vitu Czech Technical University in Prague, Faculty of Electrical Engineering, Advanced Materials Group, Prague, Czech Republic A. Cammarata Czech Technical University in Prague, Faculty of Electrical Engineering, Advanced Materials Group, Prague, Czech Republic A. Cavaleiro SEG-CEMUC, Department of Mechanical Engineering, University of Coimbra, Portugal T. Polcar Czech Technical University in Prague, Faculty of Electrical Engineering, Advanced Materials Group, Prague, Czech Republic 1. Introduction In extreme environments such as high vacuum (pressure below ), extremely low or high temperatures (below 200 K and above 500 K), or those with high level of radiation exposure (dose equivalent above ), liquid lubricants and greases become ineffective and solid lubricants remain the only possible choice for reducing friction. From the application point of view, they are characterised by their low weight, making equipment lighter and cheaper; moreover, their long service life is advantageous for locations where service access is difficult or impossible [1]. Transition metal dichalcogenides (TMD) are a group of elements known for their excellent self-lubricating properties. The low friction related to TMD originates from the high anisotropy of the hexagonal crystal structure, which combines strong intra-planar bonds between chalcogenides and metal atoms, and weak bonding between the adjacent metal-chalcogenide layers. These easily breakable interlayer bonds facilitate sliding, and are responsible for the low coefficient of friction, while the strong intra-planar bonds give durability to the material [2]. In tribological applications, TMDs are used either as lubricant additives [3] or as solid coatings [4]. The unique frictional properties of TMD-based coatings are due to the formation of a thin tribolayer composed of pure crystalline TMD with basal planes oriented parallel to the sliding direction. The formation of such a tribolayer depends on contact conditions, where the contact pressure is the critical factor [5, 6]. However, tests under vacuum are often limited to single load investigations. Therefore, we investigated the tribological behaviour of magnetron sputtered W-S-C coatings over a range of applied loads, followed by detailed physicochemical surface characterisation. As the testing was done in a vacuum environment, we can exclude external contamination and better understand the factors underpinning the measured tribological properties (i.e., friction and wear). Moreover, considering TMD-based solid lubricant coatings are primarily used as lubricants for high-accuracy moving components and advanced controlling mechanisms in the aerospace industry, we decided to use lightweight ceramic substrates instead of steel or other high-density materials. 2. Experimental Tribological tests were performed using multiple loads (2 - 18 N), whereby the load was increased by 2 N in each subsequent experiment. Overall, nine individual loads were applied, and each test was repeated three times to ensure the repeatability of the results. Counter body for all the tests was 100Cr6 ball (∅ = 6 mm). Sliding speed and number of cycles were kept constant at 0.05 and 5000, respectively. The working pressure of the tribometer was . Each tribological test was followed by detailed Raman and SEM analysis. Moreover, obtained Raman spectra were complemented with Density Functional Theory calculations. 290 23rd International Colloquium Tribology - January 2022 Tribological behaviour of W-S-C coated ceramics in a vacuum environment 3. Results The coefficient of friction (COF), calculated from the last 30% of sliding cycles (1500 cycles), is shown in Figure 1. The coefficient of friction (Figure 3) does not follow a simple trend as a function of load. Specifically, there are two distinct regions: 1) up to 10 N of normal load, at which the coefficient of friction steadily decreases with the increase of load, with a sudden drop at 8 N, and 2) above 10 N of normal load at which the coefficient of friction is significantly higher. The wear volume and wear rate of the coated rings are presented in Figure 2. Note that the sliding distances varied over the loads as the number of cycles was kept constant. Figure 1: Average values of the coefficient of friction Two wear regimes are immediately distinguishable. Up to 10 N, the wear volume is almost constant, and, consequently, the wear rate steadily decreases. Once the load is higher than 10 N, we see an increase of 68% in the wear volume, indicating that wear behaviour enters a different regime. Again, the wear volume in this load region is almost independent of load. Moreover, SEM images (not shown) reveal that up to 10 N wear is polishing, while above 10 N it transitions to abrasive. Figure 2: Wear volume and wear rate of the disc for the investigated loads. Dashed lines are a guide for the eye. 3.1 Raman analysis summary Spectra taken from the wear scar of the ball are shown in figure 3. Following deconvolution of the spectra, and analysis (not shown), it was found that: 1) Compared to the as-deposited surface, the G peak position is significantly shifted upward (10 - 25 cm -1 ). However, until 8 N of normal load the upward shift of the G peak is increasing with the load. For loads above 8 N, the G peak position returns to lower values; 2) the D peak is shifted downwards by 10 - 30 cm -1 (compared to the as-deposited surface), with the highest shifts observed for loads of 8 N and 10 N; 3) the Full-Width-Half-Maximum (FWHM) of the G peak remained constant, and 4) the I D / I G intensity ratio was significantly lower compared to the as-deposited surface and reached a minimum value of 0.83 at 8 N. 23rd International Colloquium Tribology - January 2022 291 Tribological behaviour of W-S-C coated ceramics in a vacuum environment Figure 3: Raman spectra taken from the centre of the wear scar. 4. Conclusion Trough complex Raman analysis we have been able to understand mechanism that are behind measured friction and wear data. Moreover, we have supported our results with DFT calculation linking theory, and macroscopic tribology. Finally, we have differentiated individual roles of the coating components. References [1] Miyoshi K. Solid Lubricants. In: Wang QJ, Chung Y-W, editors. Encyclopedia of Tribology. Boston, MA: Springer US; 2013. p. 3159-65. [2] Pimentel JV, Danek M, Polcar T, Cavaleiro A. Effect of rough surface patterning on the tribology of W-S-C-Cr self-lubricant coatings. Tribology International. 2014; 69: 77-83. [3] Totolin V, Rodríguez Ripoll M, Jech M, Podgornik B. Enhanced tribological performance of tungsten carbide functionalized surfaces via in-situ formation of low-friction tribofilms. Tribology International. 2016; 94: 269-78. [4] Scharf TW, Prasad SV. Solid lubricants: a review. Journal of Materials Science. 2012; 48: 511-31. [5] Vitu T, Huminiuc T, Doll G, Bousser E, Matthews A, Polcar T. Tribological properties of Mo-S-C coating deposited by pulsed d.c. magnetron sputtering. Wear. 2021; 480-481: 203939. [6] Vuchkov T, Evaristo M, Yaqub TB, Polcar T, Cavaleiro A. Synthesis, microstructure and mechanical properties of W-S-C self-lubricant thin films deposited by magnetron sputtering. Tribology International. 2020; 150: 106363. Surfaces Reactions 23rd International Colloquium Tribology - January 2022 295 Investigation of friction surfaces during a preconditioning process concerning the behavior of surface parameters and friction coefficient stability Rüdiger Fehrenbacher IPEK - Institute of Product Engineering at Karlsruhe Institute of Technology (KIT), Karlsruhe, Germany Corresponding author: ruediger.fehrenbacher@kit.edu Arn Joerger IPEK - Institute of Product Engineering at Karlsruhe Institute of Technology (KIT), Karlsruhe, Germany Katharina Bause IPEK - Institute of Product Engineering at Karlsruhe Institute of Technology (KIT), Karlsruhe, Germany Sascha Ott IPEK - Institute of Product Engineering at Karlsruhe Institute of Technology (KIT), Karlsruhe, Germany Albert Albers IPEK - Institute of Product Engineering at Karlsruhe Institute of Technology (KIT), Karlsruhe, Germany 1. Introduction The demand for compact clutch and brake systems is increasing. These systems fulfill safetyand reliability-relevant functions, for example, in machine tools, production lines, mining, and especially in passenger transportation division. Furthermore, clutch and brake systems must fulfill high requirements in energy conversion by wind power, wastewater, or medical technology. For a safe and reliable operation, stable behavior over a working life is an essential aspect of reliability. Factory-new friction combinations, in particular, are exposed to tolerances due to manufacturing tolerances, storage and transport, and the surrounding construction, which makes preconditioning processes essential from a functional point of view. However, the evaluation of such processes is generally indicated only unclearly by evaluations based on friction coefficient curves over various types o f energy input into the friction pairing. Standardization exists neither for the type and amount of energy input nor for the evaluation of successfully completed preconditioning. In the latter case, the evaluation of the progression of friction coefficient and its approximation to a constant value over numbers of circuits has become established. That, however, without the knowledge of the mechanisms behind it. This research aims to take a first step towards investigating the processes happening on friction surfaces during preconditioning. We drew the correlations of friction coefficient, topology changes, and the calculated values of surface parameters by analyzing the friction surfaces of several system variants under different load collectives during a typical preconditioning process. 2. Infrastructure of Measurement and testing, methodology We used a test environment at a test bench of the IPEK - Institute of Product Engineering for preconditioning during this research work. In addition to a rigid structural design, all sensors are positioned near the friction contact to minimize measurement errors. An electric machine converts electrical energy into rotational energy. Coincident a mass inertia simulation controls the rotational speed. We analyzed the friction surfaces using a white light interferometer during the preconditioning process in specific time steps. The collected Data on this instrument builds a base for different evaluation methods and the calculation of typical surface profile parameters. In addition, we can set up a FEM simulation based on the recorded details to enable an in-situ analysis of the frictional contact. Due to the large volume of data, we decided to create a method for visualizing the measurement data by operationalizing relevant functions in a practical software tool among a background database for storing the surface data. In addition to a chronological sequence of the surface structures, the engineer assisted by the software can evaluate all measured surface characteristics and their relations to their minimum and maximum values. The tool further has an input mask, which displays desired scans 296 23rd International Colloquium Tribology - January 2022 Investigation of friction surfaces during a preconditioning process concerning the behavior of surface parameters and friction coefficient stability to the operator, considering the position and progress of the preconditioning process. In addition, it can calculate relevant surface characteristics via measurement clouds and show abott-curves (material ratio curves) of the measured areas. Fig. 1: The Software tool for Visualizing and calculating To support a systematic analysis, we split the methodology into several sub-areas. First, we start the preconditioning process on the test bench by performing brake circuits. The number of circuits and thus the ranges of the investigation intervals are different during the preconditioning process. Second, the engineers inspected neuralgic phases at the beginning of the process in short measuring intervals. In contrast, there were no significant changes after further energy input expectable, so we increased the number of successive brakings between surface scans. The tests were carried out on several systems with identical properties with the same input parameter combination to achieve a higher validity of the results. Then, high-resolution measurements follow each test interval by a white-light interferometer. We localized the measurement points of the surfaces concerning expected inhomogeneous load distributions over the complete friction lining width [1]. Finally, different friction materials with identical dimensions, varying mainly in their stiffnesses, were investigated. The initial load parameters (energy input, speed, surface pressure) by tests in similar projects with corresponding friction materials and evaluations of the results of preliminary tests have to be defined at the beginning of the research work by us. 3. Results The software tool can also display the results. In addition, it can organize surface parameters based on matrices to offer a direct comparison between different coatings and load collectives based on diagrams. Fig. 2: Arithmetic average roughness value (Ra) (different energy loads) The evaluations of the surface parameters show that the surface smooths out during the preconditioning process. The arithmetic (exemplified in Fig. 1) or the quadratic average roughness value (Ra, Rq) indicate that. Furthermore, the progression of the friction coefficient tends to increase with an increase in energy input overall power stages (Fig. 2). Fig. 3: friction coefficient (different energy loads) A significant value for evaluating these processes is the reduced peak height Rpk; it offers an excellent informative value regarding the tip combing of a profile, which can also be relevant for evaluating the material ratio curve [2]. Fig. 4: reduced peak high (Rpk) (different energy loads) We figured out that the curves of the reduced peak height correlate with those of the friction coefficient. However, the reader can see differences between the series with various energy inputs. Also noticeable are substantial changes in the characteristic values with an increase in the number of continuous braking cycles. In this case, there are indications of a change in the surface area associated with increasing temperature at friction surfaces [3]. In this regard, correlations between some surface characteristics and friction coefficients are observable. A change in the type of pavement also affects the gradients here. For example, the expression of the gradient for stiffer linings is more significant than for soft ones. 23rd International Colloquium Tribology - January 2022 297 Investigation of friction surfaces during a preconditioning process concerning the behavior of surface parameters and friction coefficient stability 4. Conclusion In this research, we developed a new investigation methodology for determining the progress of a preconditioning process. The extension by new evaluation criteria for the success of preconditioning by surface characteristics shows correlations with the friction coefficient progression. In this context, first experiences for evaluating mechanisms on the friction surface, which influence the progression of the friction coefficients, are shown. In addition, the parallel recording of surfaces in 3-D offers the possibility of validating the calculated surface characteristics and a deep insight into the structure of surface topographies and their changes. References [1] Albers, A., Ott, S., Merkel, P.: Kupplungsmodell zur Beschreibung der Übertragbarkeit tribologischer Prüfergebnisse von Teilbelagauf Bauteiluntersuchungen. Abschlussbericht FVA Forschungsvorhaben 607. Karlsruhe 2013 [2] Mahr GmbH. 2015. MarSurf. Oberflächenkenngrößen. [3] Severin, D., Musiol, F.: Der Reibprozess in trockenlaufenden mechanischen Bremsen und Kupplungen, Artikel. Konstruktion 47. Berlin 1995 23rd International Colloquium Tribology - January 2022 299 Improving the Tribological and NHV Behavior of Gears by Mechanochemical Surface Finishing Linus Everlid Applied Nano Surfaces Sweden AB, Uppsala, Sweden Martin Bengtsson Applied Nano Surfaces Sweden AB, Uppsala, Sweden Morteza Najjari Xtrapid Innovations, Toronto, Canada Florian Reinle OTEC Präzisionsfinish GmbH, Straubenhardt-Conweiler, Germany Andreas Storz Applied Nano Surfaces Sweden AB, Uppsala, Sweden Boris Zhmud Applied Nano Surfaces Sweden AB, Uppsala, Sweden Corresponding author: boris.zhmud@appliednanosurfaces.com 1. Introduction Powertrain electrification has been a growing trend in the automotive industry. While having multiple advantages over traditional powertrains, the drivetrains of hybrid (HEV) and full electric vehicles (EV) also bring up some new challenges, such as increased requirements for NVH performance in high speed e-drives, the need to deal with higher torques and loads while keeping an eye on the vehicle weight, and compatibility issues with some common lubricant additives. One challenging requirement is the increased sensitivity related to the NVH behaviour. Surface specifications and tooth geometry have a big impact on the noise originating from the gear mesh excitation. Improving energy efficiency is another important topic: while in ICE powered vehicles, friction power losses run in of kilowatts, for BEVs, each watt makes a difference. The mechanochemical surface finishing technology pioneered and developed by Applied Nano Surfaces in Sweden opens up new possibilities for gear tribology optimization. The technology combines elements of mechanical burnishing with a tribochemical deposition of a solid lubricant tribofilm. Despite significant differences in the process flow and hardware, the treatment results in the development of a progressively plateaued roughness profile with reduced gradient roughness and increasingly negative skewness, incorporating doping elements from the process fluid. Mechanochemically finished gears are expected to reveal improved scuffing resistance, reduced friction and wear, and less noise. In this study, some early experimental findings and simulation data are presented. 2. Experimental 2.1 Sample preparation Ground steel pins and standard FZG gear sets have been finished using the ANS Triboconditioning ® CG finishing method implemented on two different machining platforms: centrifugal finishing and stream finishing. Fig. 1: Centrifugal barrel finishing process (Courtesy Tipton Corp, Japan) 300 23rd International Colloquium Tribology - January 2022 Improving the Tribological and NHV Behavior of Gears by Mechanochemical Surface Finishing Fig. 2: Stream finishing process (after V. Schulze et al., CIRP Annal, 66 (2017) 523) A wet finishing process was used with water-based and neat-oil-type process fluids. Several different media types were compared: cemented tungsten carbide beads, sintered silicon nitride beads, and traditional bauxite media. 2.2 GD&T controls and tribological studies Changes in the surface roughness profile and form of the test pieces were evaluated under different process conditions using Zygo NewView 5032 and Alicona G5+ optical instruments. Gradient surface roughness was characterized using angle-resolved light scattering (OptoSurf). Elemental surface analysis was carried our using X-ray fluorescence (Niton XL3t Goldd+, ThermoFisher Scientific). Besides that, FZG scuffing and efficiency tests have also been carried out, comparing mechanochemically finished gears with standard ones. 3. Results and Discussion 3.1 Surface characteristics The Triboconditioning ® treatment brings about a triad of effects: (i) a modified surface roughness profile with increasingly negative skewness and reduced gradient roughness, (ii) compressive residual stress build-up; and (iii) tribofilm formation. Fig. 3: Surface finishes produced by conventional grinding (left) and mechanochemical finishing (right) 23rd International Colloquium Tribology - January 2022 301 Improving the Tribological and NHV Behavior of Gears by Mechanochemical Surface Finishing Fig. 4: Compressive residual stress profiles produced by shot peening and mechanochemical finishing using two different mass-finishing platforms. Fig. 5: Tungsten carbide particles embedded into the surface after barrel finishing with WC beads. Gear tribology simulations comparing conventional ground and mechanochemically finished gears were carried out using the thermal EHD model [2]. The simulations predict reduced friction shear and higher lubricant film strength for mechanochemically finished gears. Fig. 6: Gear tribology simulations References [1] B. Zhmud, Mechanochemical surface finishing and the Triboconditioning ® process, MPR034: Manufacturing Processes, Chalmers, October 1, 2021. [2] M. Najjari, R. Guilbault, Edge contact effect on thermal elastohydrodynamic lubrication of finite contact lines. Tribology International 71 (2013) 50. 23rd International Colloquium Tribology - January 2022 303 Influence of Black Oxide Coating on Micropitting and ZDDP Tribofilm Formation Mao Ueda Technology Centre Research & development Team, Shell Lubricants Japan K.K., Japan Tribology Group, Department of Mechanical Engineering, Imperial College London, London, United Kingdom Corresponding author: mao.ueda@shell-lubes.co.jp Hugh Spikes Tribology Group, Department of Mechanical Engineering, Imperial College London, London, United Kingdom Amir Kadiric Tribology Group, Department of Mechanical Engineering, Imperial College London, London, United Kingdom 1. Introduction Micropitting is a common type of surface fatigue damage caused by stress fluctuations that occur due to asperity interactions as the contacting bodies move over each other. These asperity stress cycles result in initiation of numerous tiny surface fatigue cracks which then propagate until small fragments of material detach from the surface. Recently, Brizmer et al. [1] reported that Black Oxide (BO) coating can reduce micropitting damage when it is applied on the rougher of the two bodies in rolling-sliding contact. They suggested that the mechanism by which BO reduces micropitting is related to enhanced running-in of the BO-coated surfaces that is at least partly brought about by BO suppressing the formation of ZDDP antiwear tribofilms. The consequences of the low hardness of the BO coatings in relation to running-in are now relatively well-established [1]; however the potential enhancement of the running-in process, and hence reduced micropitting, via chemical effects of the BO coating in suppressing the antiwear film buildup has not been directly observed and warrants further investigation. This research aims to establish the effect of BO on micropitting and, more importantly, clarify the mechanisms by which BO influences micropitting performance. 2. Test methods 2.1 Test conditions and procedures All micropitting tests were conducted using the same method as described in our study [2]. A mini-traction machine (MTM) ball-on-disc tribometer with a spacer layer imaging attachment (SLIM) was employed both to generate micropitting on the ball specimen and to monitor ZDDP tribofilm formation. BO coating was applied to both the ball and the disc, and four tribopair combinations of a steel ball/ steel disc, a steel ball/ BO-coated steel disc, a BO-coated steel ball/ steel disc, and a BO-coated steel ball/ BO-coated steel disc were studied. 2.2 Test lubricants The solution of primary-secondary mixed ZDDP in a PAO base oil at a concentration of 0.08 wt.% P was studied. The base oil was PAO 10 having viscosity 62.8 mm 2 / s at 40 °C and 9.9 mm 2 / s at 100 °C. 3. Results 3.1 Evolution of surface damage on balls Fig. 1 shows representative optical micrographs of the wear tracks on the balls of the four tribopairs after 0.1, 1, 4 and 8 million. The tribopairs of steel/ steel and BO/ steel formed cracks on the balls after 0.1 million cycles. As the test progressed, the number of cracks significantly increased. After 4 million cycles, small pits associated with these cracks became apparent. After 8 million cycles, these micropits covered large areas of the wear tracks. By contrast, cracks and micropits were not observed on the balls of the tribopairs of steel/ BO and BO/ BO at any time throughout the 8 million cycle tests. These results confirm that a BO coating on the rough counterface prevents micropitting. 304 23rd International Colloquium Tribology - January 2022 Influence of Black Oxide Coating on Micropitting and ZDDP Tribofilm Formation Figure 1: Optical micrographs of wear tracks on balls at different number of loading cycles from mcropitting tests with steel-steel, steel/ BO, BO/ steel and BO/ BO tribopairs Fig. 2 shows the corresponding depth of the rubbed ball tracks measured using a stylus profilometer. The tribopairs of steel/ steel and steel/ BO gave low levels of material loss after each cycle. By contrast, the triopairs of BO/ steel and BO/ BO generated high amount of material loss from the BO-coated balls after 1000 cycle. This material loss occurred mainly in the first 1000 cycles and after that, the rate of loss of material from the balls of BO/ steel and BO/ BO contacts was similar to that of steel/ steel and steel/ BO contacts respectively. Considering that BO coating has approximately 1 µm thickness, this suggests that most BO coating on the balls was removed in the first 1000 cycles. This implies that since blue-coloured ZDDP tribofilms were observed in all tribopairs (Fig. 1), ZDDP tribofilms grew on the steel substrates after removal of BO coating. Figure 2: Measured depth of ball wear track of the tribopairs with BO coating 3.2 Evolution of surface roughness of counterface discs Fig. 3 shows the evolution of the disc roughness during tests. In all cases the disc roughness reduced in the initial stages of the test and then remained relatively stable - behaviour indicative of running-in. The tribopairs of steel/ steel and BO/ steel gave disc roughness reduction from the initial Ra value of 0.44 µm to approximately 0.30 µm after 1000 cycles and staying constant at this level for the rest of the test. By contrast, the tribopairs of steel/ BO and BO/ BO reduced disc roughness from 0.42 µm to approximately 0.18 µm after the first 1000 cycles, and then reached approximately 0.13 µm at the end of the tests. This result shows that steel discs coated with BO experience a very considerable roughness reduction during the first 1000 cycles. Figure 3: Disc roughness evolution of the tribopairs with BO coating 3.3 Friction behaviour Fig. 4 shows the evolution of friction coefficient in tests conducted with the four tribopair combinations. The friction coefficient obtained from the tribopairs of steel/ steel and BO/ steel was initially ca. 0.1, and gradually decreased to reach 0.08 at the end of the test. By contrast, the friction coefficient obtained from steel/ BO and BO/ BO contacts immediately decreased to approximately 0.05 after the start of tests, and then stabilized at this value through to the end of the tests. Since high surface roughness generates high friction in mixed lubrication conditions, this result suggests that when BO coating was applied to rough countersurface steel discs, their roughness decreased almost immediately after the tests started, resulting in an increase in lambda ratio and thus a significant drop in friction coefficient. 23rd International Colloquium Tribology - January 2022 305 Influence of Black Oxide Coating on Micropitting and ZDDP Tribofilm Formation Figure 4: Friction behaviour in tests of the tribopairs with BO coating 4. Conclusion This study provides new understanding of the impact of BO reaction coatings on micropitting and suggests the relevant mechanisms by which BO coatings mitigate micropitting. Key conclusions are as follows. This study has been published in 2021 [3]. • Micropitting of balls is completely prevented by applying a BO coating to rough counterface steel discs. • BO coatings on rough steel discs are very rapidly removed from the surface asperities shortly after the onset of rubbing, and this results in an almost immediate and very significant reduction of disc surface roughness. This reduction in roughness produces an overall reduction in friction coefficient. • Because BO coating is removed from the asperities at the beginning of the tests, a ZDDP tribofilm then forms mainly on the steel surfaces. This tribofilm suppresses further surface roughness reduction of BO-coated discs. • The immediate reduction in roughness of the rough counterface removes the high asperity stresses that would otherwise initiate and propagate the microcracks needed to produce micropitting. • The key to this behaviour is the low hardness of BO coating, which is only one quarter that of the steel substrate. Hence, it is easily worn during rubbing to reduce surface roughness. Reference [1] Brizmer, V., et al. (2017). Tribology Transactions, 60(3), 557-574. [2] Ueda, M., et al. (2019). Tribology International, 138, 342-352. [3] Ueda, M., et al. (2021). Tribology Transactions, 1-21. Oxidation & Wear 23rd International Colloquium Tribology - January 2022 309 Mechanisms of tribo-oxidation in high-purity copper Julia S. Rau Institute for Applied Materials (IAM), Karlsruhe Institute of Technology (KIT), Karlsruhe, Germany IAM-CMS MicroTribology Center µTC, Karlsruhe, Germany Shanoob Balachandran Max-Planck-Institut für Eisenforschung GmbH, Department of Microstructure Physics and Alloy Design, Düsseldorf, Germany Reinhard Schneider Laboratory for Electron Microscopy (LEM), Karlsruhe Institute of Technology (KIT), Karlsruhe, Germany Peter Gumbsch Institute for Applied Materials (IAM), Karlsruhe Institute of Technology (KIT), Karlsruhe, Germany Fraunhofer IWM, Freiburg, Germany Baptiste Gault Max-Planck-Institut für Eisenforschung GmbH, Department of Microstructure Physics and Alloy Design, Düsseldorf, Germany Department of Materials, Royal School of Mines, Imperial College London, London, UK Christian Greiner Institute for Applied Materials (IAM), Karlsruhe Institute of Technology (KIT), Karlsruhe, Germany IAM-CMS MicroTribology Center µTC, Karlsruhe, Germany Corresponding author: greiner@kit.edu 1. Introduction Metals’ surfaces subjected to tribological loading often show a limited lifetime due to accelerated oxidation a critical issue in many applications such as wind turbines, hip implants or micro-mechanical systems. Tribo-oxidation takes place by chemical reactions of the sliding partners or the surrounding medium. Such reactions may alter the friction and wear behaviour drastically. Yet, the mechanisms and pathways for tribo-oxidation, particularly in the very early stages of sliding, are insufficiently understood. Our goal is to identify the elementary mechanisms by paring sapphire spheres with polyand single crystalline high-purity copper plates. In earlier investigations the formation of copper oxides (Cu 2 O) during tribological loading was reported in this setup[1]. Here, tribo-oxidation took place at rates order of magnitudes faster than the native oxidation of copper under the same environmental conditions. Although tribo-oxidation was studied for many years, it stays overall elusive why and how oxides grow so quickly under tribological loading. 2. Materials and methods Using copper as a model system, tribologically-induced oxidation is systematically investigated by varying the sliding speed (0.1 - 50 mm/ s, 12 mm stroke) and test duration (13.5 - 67 h, 0.1 mm/ s) under mild tribological loading. Under theses low loads of 1.5 N and slow sliding speeds, a significant temperature increase in the contact can safely be excluded. In addition, loaded samples were exposed to the ambient environment for different exposure times (0 - 48 h). Experiments were performed in a strictly controlled atmosphere with a reciprocating linear sliding setup at room temperature and a constant number of sliding cycles (1,000). Sample preparation including heat treatment, grinding and (electro-) polishing are described in detail in [2], [3]. The final electro-polishing step was performed right before the tribological tests to achieve a sample surface with minimal native oxidation and plastic deformation. State of the art scanning and transmission electron microscopy (SEM and TEM) techniques as well as atom probe tomography (APT) were used to investigate and characterize the resulting oxides within the plastically deformed subsurface. To protect the loaded surfaces from ion beam damage when milling, two protective platinum 310 23rd International Colloquium Tribology - January 2022 Mechanisms of tribo-oxidation in high-purity copper layers (electron and ion beam) were deposited. Except the samples for the exposure time tests, all samples were constantly evacuated to a pressure below 1 mbar immediately after the end of each experiment. 3. Results and Discussion Figure 1 depicts the oxide thickness after 1,000 cycles for different sliding speeds, test durations and exposure times, measured in cross sectional scanning electron microscopy images. Figure 1b shows that the oxide thickness is controlled by the test duration rather than the sliding speed. After sliding stopped, almost no further oxide growth took place (Figure 1c). Hence, the oxide formation and growth is almost entirely associated with the tribological loading. Chemical interactions of sphere and plate are not detectable: XPS measurements of the sapphire sphere did not detect any Cu on the sphere and APT measurements of the copper plate did not find any Al. The atom probe tomography dataset in Figure 2 shows a pipe-like oxygen-rich feature within the tribologically deformed subsurface. Such features are associated with dislocations, decorated with oxygen along the dislocation line. Plastic deformation from sliding creates defects, such as these dislocations as well as grain and later also phase boundaries between the oxide and the copper matrix that act as high diffusivity pathways. Oxygen diffusion into the bulk as well as of copper towards the free surface along these defects control the oxide formation kinetics. We speculate that the origin of the linear oxide growth law with test duration (Figure 1b) lies in the trapping-effect of the dislocation for the diffusing species: Once a pipe is clogged, the diffusion along its core will decrease. However, the ongoing movement of the sphere ‘frees’ the dislocation from the trapped atoms and provides a fresh pathway, while the subsurface is supersaturated with oxygen. Figure 1: Quantified oxide thickness as a function of increasing (a) sliding speed, (b) test duration and (c) exposure time to the ambient environment after the tribological loading of copper polycrystals. Each data point represents one experiment. The standard deviation stems from the evaluation of multiple SEM images within one cross-section. [4] 23rd International Colloquium Tribology - January 2022 311 Mechanisms of tribo-oxidation in high-purity copper Figure 2: Atom probe tomography (APT) analysis from the middle of the wear track after 5,000 sliding cycles on a high purity copper single crystal with (111) outof-plane orientation and ±<0-11> sliding direction. (a) Three-dimensional reconstruction within the tribologically deformed subsurface shows an oxygen pipe feature with 11 at% of oxygen in the Cu matrix. [4] 4. Conclusion Investigating the fundamental mechanisms of tribo-oxidation with high purity copper as a model system systematically, allowed to draw the following conclusion: The oxidation process is governed by diffusion processes along defects generated while sliding such as dislocations, phase and grain boundaries. Diffusion along dislocations together with the sliding sphere results in a linear oxide growth law with time which is different from the parabolic law observed in native oxidation. Understanding the fundamental mechanisms of tribo-oxidation will eventually help for tailoring materials properties for little wear and low friction. References [1] C. Greiner, Z. Liu, R. Schneider, L. Pastewka, and P. Gumbsch, “The origin of surface microstructure evolution in sliding friction,” Scr. Mater., vol. 153, pp. 63-67, 2018. [2] C. Greiner, Z. Liu, L. Strassberger, and P. Gumbsch, “Sequence of Stages in the Microstructure Evolution in Copper under Mild Reciprocating Tribological Loading,” ACS Appl. Mater. Interfaces, vol. 8, no. 24, pp. 15809-15819, 2016. [3] Z. Liu, T. Höche, P. Gumbsch, and C. Greiner, “Stages in the tribologically-induced oxidation of high-purity copper,” Scr. Mater., vol. 153, pp. 114- 117, 2018. [4] J. S. Rau, S. Balachandran, R. Schneider, P. Gumbsch, B. Gault, and C. Greiner, “High diffusivity pathways govern massively enhanced oxidation during tribological sliding,” Acta Mater., accepted Sept 2021. 23rd International Colloquium Tribology - January 2022 313 Wear of electrical contacts of equal motion amplitude and equal force in different directions Dirk Hilmert Precision Engineering Laboratory, Ostwestfalen-Lippe University of Applied Sciences and Arts, Campusallee 12, 32657 Lemgo, Germany Kevin Krüger Precision Engineering Laboratory, Ostwestfalen-Lippe University of Applied Sciences and Arts, Campusallee 12, 32657 Lemgo, Germany Haomiao Yuan Precision Engineering Laboratory, Ostwestfalen-Lippe University of Applied Sciences and Arts, Campusallee 12, 32657 Lemgo, Germany Jian Song Precision Engineering Laboratory, Ostwestfalen-Lippe University of Applied Sciences and Arts, Campusallee 12, 32657 Lemgo, Germany Corresponding author: jian.song@th-owl.de 1. Introduction With regard to the growing market of electric cars and connected production systems, reliable electrical connectors are becoming increasingly important. In these automotive applications and industrial production systems, electrical contacts experience various types of loads. Among these, thermal and vibrational stresses are critical loads which subsequently cause micro motions and result in the fretting wear of coatings. Also, since the connectors are mounted in various positions, these motions occur in different directions. This leads to translational relative motion and rocking motions in the mating direction and the directions orthogonal to mating direction respectively. The aim of this study is to analyse the fretting wear of silver coated electrical contacts in three different orthogonal directions. 2. Theory Electrical connectors that need to maintain low contact resistance in long term applications are often used with silver coatings. This protects the base material from atmospheric gas diffusion and thus prevents oxidation of the connector [1]. However, vibrations and different thermal expansion rates can lead to fretting wear of the coating which can result in a wear through of the protective layer. This eventually leads to the corrosion of the base material and the electrical failure of the contact. To ensure the safe design and validation of electrical connectors, test specifications and standards are available that define fretting wear tests [2]. Although failures can be observed due to rocking motions, former investigations mainly consider the mating direction [3, 4]. Therefore, initial studies of the motion in orthogonal directions to the mating direction have been conducted and a definition of directions for fretting wear tests has been proposed, as shown in Fig. 1 [5]. Fig. 1: Fretting directions according to [5] 3. Experimental Setup For this study silver coated electrical connectors with 5.5 µm silver coating and 2 µm nickel underlayer are used. In preparation for the tests, the receptacle and blade are mated which leads to an overlapping of the contact partners by 2 mm. The contact pairs are then mounted in the test rig with different mounting directions for each test. While the receptacle is clamped on a linear actuator, the blade of the connector is fixed in the test rig. In direction 1, the receptacle is clamped directly at the crimp. For directions 5 and 6 the electrical conductor is clamped with a distance of 2 mm from the crimp to take into effect the flexibility of the attached 314 23rd International Colloquium Tribology - January 2022 Wear of electrical contacts of equal motion amplitude and equal force in different directions cable. In the tests a displacement of 50 µm is given to the specimen at 1 Hz in these setups. To analyse the change of the fretting wear with respect to time, a series of 1000 cycles is conducted and the frictional energies for the 1st, 50th and 1000th cycle are calculated. These energies are then compared to determine the critical directions and displacements. 4. Results and Discussion The force-displacement curves of direction 1 for a total displacement of 50 µm are shown in Fig. 2. It can be observed that the curve changes over the course of 1000 cycles from a flat curve with a maximum force of 1.2 N to a thinner curve at about 6.7 N. Hence the curve is increasing in force while the hysteresis decreases. Fig. 2: Force-displacement curves of direction 1 for equal amplitudes of 50 µm The curves for the directions 5 and 6 are shown in Fig. 3. In comparison to direction 1 not only the maximum forces in the first cycle are lower, but also the hysteresis of the curves are lower. However, when conducting the tests with 1000 cycles it is also shown that the overall force increases for direction 5 as well as for direction 6 and that the general shape of the curve is not changing as in the case of direction 1. Fig. 3: Force-displacement curves of direction 5 and 6 for equal amplitudes of 50 µm As shown at a displacement of 50 µm in each direction for one cycle, the motion force in direction 1 is the highest with a maximum of about 1.2 N. In the orthogonal directions 5 and 6, smaller forces of 0.4 and 0.8 N are measured. Also, the maximum displacements in the orthogonal directions for a force of 1.2 N are examined in preliminary tests. Displacements of 250 µm for direction 6 and 600 µm for direction 5 are observed. Therefore, the wear behaviour corresponding to equal forces is also investigated by applying a total displacement of 1200 µm and 500 µm for directions 5 and 6 respectively. The results are shown in Fig. 4. In comparison to the displacement curves at 50 µm, the maximum forces are increased. Also, the hysteresis of the curves is increased and the overall shape is more comparable to direction 1. Comparing the 1 st , 50 th and 1000 th cycle of directions 5 and 6 at high displacements shows that the force increases while the hysteresis decreases. Fig. 4: Force-displacement curves of direction 5 and 6 for equal forces The calculation of the frictional energies for these diagrams is shown in Tab. 1. Comparing the 50 µm displacements, it can be observed that direction 1 shows the highest amount of frictional energy while direction 5 shows the lowest energies. It can also be noticed, that at equal amplitudes the frictional energies decrease over the course of 1000 cycles. In comparison to the equal amplitudes, the frictional energies of equal forces show, the highest amount of energy for direction 5. Due to the higher amplitude of displacement, these forces exceed the forces in direction 1. This comparison shows that the attached cable has a significant influence on the fretting wear of the connector. Tab. 1: Frictional energies of different directions (D1, D5, D6) and displacements Frictional Energy [µJ] 1st Cycle 50th Cycle 1000th Cycle 23rd International Colloquium Tribology - January 2022 315 Wear of electrical contacts of equal motion amplitude and equal force in different directions equal amplitude D1 50 µm 76.9 75.6 41.1 D5 50 µm 0.3 0.2 0.3 D6 50 µm 3.1 2.4 1.5 equal force D1 50 µm 76.9 75.6 41.1 D5 1200 µm 1320.5 1049.0 822.7 D6 500 µm 608.3 629.5 630.4 5. Conclusion In this study, the force-displacement curves of silver coated contacts at different displacement amplitudes are compared. In general, an increase of the overall force over the course of 1000 cycles and the corresponding change in curve shapes is observed. For an amplitude of 50 µm the mating direction (D1) is most severe and shows the highest frictional energies and forces. Therefore, this is the critical direction of motion. However, when the frictional forces are equal to direction 1, the frictional energy and the hysteresis of D5 and D6 increase compared to the equal amplitude tests. This shows a major influence of the attached cable to the electrical connector when subjected to vibrational or thermal loads. 6. Acknowledgement This study is financed by the German Federal Ministry for Economic Affairs and Energy (BMWi, IGF, 20139 N) References [1] Song, J., Wang, L., Zibart, A. et al.: Corrosion Protection of Electrically Conductive Surfaces, 2012. [2] N.N.: TechnischerLeitfaden-TLF0214: Validierung von Automotive-Niedervolt-Steckverbindern. [3] Perrinet, O., Laporte, J., Fouvry, S. et al.: The electrical contact resistance endurance of heterogeneous Ag/ Sn interfaces subjected to fretting wear, 2014. [4] Queffelec J.L., Ben Jemaa N., Travers D.: Materials and contact shape studies for automobile connector development, 1990. [5] Hilmert, D., Krüger, K., Song, J.: Vergleichende Untersuchung der Verschleißbilder von Steckverbindern aus Reibverschleiß- und Vibrationsprüfungen mit unterschiedlichen Prüfrichtungen, 2021. 23rd International Colloquium Tribology - January 2022 317 Improving abrasive wear performance of polymers Helena Ronkainen VTT Technical Research Centre of Finland, Espoo, Finland Corresponding author: helena.ronkainen@vtt.fi Jani Pelto VTT Technical Research Centre of Finland, Espoo, Finland Vuokko Heino VTT Technical Research Centre of Finland, Espoo, Finland Mikko Karttunen VTT Technical Research Centre of Finland, Espoo, Finland 1. Introduction Interest for thermoplastic polymers in engineering applications has increased due to their lightweighness and low cost, combined with ease of manufacturing as compared to metals and ceramics. The range of polymeric materials is vast and by blending and by using reinforcements, composites with widely different properties can be generated [1, 2]. Thermally resistant and mechanically strong polymers are available for demanding engineering applications, but they still often lack sufficient abrasive wear resistance causing material loss or aesthetic deficiencies. At VTT different strategies have been used to improve the abrasive wear performance of neat polymers. In this study, two semicrystalline thermoplastics, a commodity polymer high density polyethylene (HDPE) and a biobased engineering polyamide (PA1010), were used as matrix polymers with differed strategies to improve their wear performance. 2. Materials High density polyethylene HDPE powder was used as the matrix polymer and the commercially available nanopowders were used for polymer composites, namely graphene oxide (GO), halloysite aluminosilicate clay hollow nanotubes (HNT), fumed alumina (f-Al 2 O 3 ), and gamma-alumina (nano-γ-Al 2 O 3 ). Vinyltrimethoxy silane and organic peroxide were used for the chemical surface treatment of the fillers. Besides using different fillers, the HDPE was also blended with the ultrahigh molecular weights polyethylene (UHMWPE). The bio-based polyamide PA1010 was used for PA composites and different microand nano-scale fillers were used as filler reinforcements. The nano-scale reinforcements studied were GO, HNT, hydrophilic fumed silica (SiO2), hydrophopic fumed silica, and the micro-scale fillers were glass beads and glass flakes (1 µm in size). The fillers were chemically surface treated to improve the dispersion and the adhesion of the fillers to the polymer matrix. The compounding of polymer composites was carried out with DSM Xplore micro-compounder and the test samples were moulded with ThermoHaake MiniJet injection moulding machine. 3. Experimental The filler surface treatment was characterised by FT-IR and SEM. The abrasive wear of polymers was evaluated with a three-body sand abrasion test, where the abrading sand particles are introduced into the sliding contact of the rubber-coated wheel and the polymer sample. The sand (grain size about 0.32 mm) was flowing into the contact point with the flow rate of 320 gmin -1 . The tests followed the ASTM 65-04 standard, and besides the standard test parameters, also lower level of loading parameters was applied to verify the influence of loading on polymer wear. In the lower loading level tests, the load and the speed were reduced to decrease the heating effect of polymers, and to provide same amount of sliding distance compared to the higher load level, the test duration was increased. The test parameters used in the tests are shown in Table 1. As a reference material for the developed polymer composites the polyether ether ketone (PEEK) was used. The wear surfaces were studied by optical and scanning electron (SEM) microscopy after the tests to reveal the wear mechanisms. The indentation modulus and hardness of polymer composites were also measured by using CSM Micro Combi Tester (Anton Paar). Table 1: The test parameters with two loading levels used in sand abrasion tests. Load level 1 Load level 2 Normal load 19 N 45 N Velocity 50 rpm ~ 0.62 ms -1 100 rpm ~ 1.23 ms -1 Test time 6 minutes 3 minutes 318 23rd International Colloquium Tribology - January 2022 Improving abrasive wear performance of polymers 4. Results The abrasive war volumes measured for the polymers and polymer composites are presented in Figure 1. The PEEK polymer showed reasonable wear in abrasive test conditions and it was used as a reference for the developed polymer composites. The neat HDPE shows high wear volumes with both loading levels. The wear could be reduced dramatically by blending the HDPE with UHMWPE and by using the fillers as reinforcements. The improvement in performance is apparent under the harsher, more destructive abrasive loading conditions. HNT composite showed reduced wear and particularly composites with GO fillers provided 50 to 60 % reduction in wear for the studied HDPE/ UHMWPE blends. The lowest wear was achieved with UHMWPE/ HDPE blend with as high as 80% of UHMWPE and 0.5 wt.-% GO, a composition which was still well processible by standard injection moulding. The neat PA1010 polymer had a rather good wear performance, comparable to PEEK as presented in Figure 1. The abrasive wear performance of PA could be further improved by adding microand nano-scale fillers. The micro-scale GFL and the combination of micro and nano-scale-fillers GB+GO reduced the wear significantly. However, even more significant improvement in performance was achieved by nano-scale fillers. HNT, GO and silica fillers could reduce the wear about 10 % for the lower load level (PA1010/ 15wt-% HNT) and up to 50 % for the upper load level tests (PA1010/ 3wt-% SiO2). Figure 1: The abrasive wear volumes of PEEK, HDPE, PA1010 and the developed polymer composites. The abrasive wear was evaluated in sand abrasion tests with two different sets of test parameters. The wear surfaces studied by optical and SEM revealed change in wear mechanisms with different filler additions. As an example, the wear surface of PA showed scratched and plasticly deformed surface whereas the composite with the addition of silica fillers showed fractured features as presented in Figure 2. 23rd International Colloquium Tribology - January 2022 319 Improving abrasive wear performance of polymers Figure 2: The wear surfaces of PA1010 and PA1010/ hydrophilic fumed silica (3 wt-%) with the load level 1 and load level tests. When comparing the abrasive wear of HDPE and PA composites to PEEK, several composited were developed with improved wear resistance compared to PEEK. Since PEEK is rather expensive specialty polymer designed for high temperature environment from +140°C up to +200°C, the HDPE and PA composites can be considered as good and reasonably priced option for many applications that require high abrasive wear resistance, however, at lower temperature range < +100°C. 5. Conclusion The abrasive wear resistance of HDPE and PA could be significantly improved by nano-scale filler reinforcements, particularly with GO and HNT. The composites also provided lower wear compared to the reference PEEK polymer. 6. Acknowledgement This project has received funding from the Finnish Academy and VTT Technical Research Centre of Finland. References [1] Briscoe, B.J., Sinha, S.K., Tribological applicationsmof polymers and their composites - past, present and future prospects. In: Tribology of Polymeric nanocomposites. pp- 1-21. [2] Friedrich, K., Fakirov, S., Zhang, Z., Polymer composites, from nanoto micro-scale. Springer 2005. Test Methodologies and Measurement Technologies Seals & Polymer Testing 23rd International Colloquium Tribology - January 2022 325 Development and verification of a test method for determining the compatibility of elastomers with cooling lubricants Dr. Stephan Baumgärtel German Lubricant Manufacturers Association, Hamburg, Germany corresponding author: stephan.baumgaertel@vsi-schmierstoffe.de 1. Introduction Numerous functional elements are used in machine tools and their peropherie, which are conveniently made of elastomers. These are, among other things: • Seals in the machine tool and on piping • Drives of auxiliary units (e.B timing belts, etc.) • Covers and panels (e.B. Bellows etc.) • Connections and connections (e.B hoses, cables (sheaths) etc.) • Other parts in the periphery of machine tools (brackets, fasteners, etc.) The parts come into contact with cooling lubricants both as planned (seals) or accidentally/ unavoidably - both with the fluid and with mists that settle on parts. As long as there is no operational or safety-relevant interference and the components perform the intended functions, operation runs smoothly. The situation only becomes critical when malfunctions occur as a result of malfunctions and solutions have to be found. Therfore, the VSI developed a test method to asses the compatibitlity between coolandt and elastomers. 2. Selection of elastomers by machine/ plant manufacturers It is interesting to see who makes the selection of the respective components and determines their materials. Essentially, 3 parties are eligible: • The designer of the machine tool • The installer of the machine tool in operation • The maintenance technician of the system at the operator MWF producers are rarely asked for comments. According to an internal survey by the VDW (Verein Deutscher Werkzeugmaschinenfabriken e. V.), the followingmaterials for functional parts are mainly used: 1. FKM seals; O-rings 2. PU seals; timing belts; groove rings; 3. NBR wipers and profiles; sealings The selection is made either on the basis of empirical values (evolutionary) or on the basis of the manufacturer‘s specifications. It cannot be ruled out that „what is currently there“ will also be used - otherwise some gross malfunctions cannot be explained. From practice and experience, a prediction on compatibility is not easily possible. The materials and the concepts used are too different for the behaviour to be predictable. In the data sheets, only compatibility with substances is often indicated - but coolants are very complex mixtures! As already described, the range of elastomers used in a processing plant can be very large. When a compatibility assessment takes place, the concept and construction of the plant is usually well advanced - changes are only possible with great effort. Unfortunately, there is usually no suitable material available for this check - with which usually only „laboratory-specific“ tests are undertaken. In order to make an assessment, you need a method that is uniformly applicable and a scale. The methods can be based on standardized tests carried out for similar applications (testing the compatibility of elastomers with motors, transmissions and hydraulic oils). 3. VSI - Method In order to take into account the different types of coolant, model cooling lubricants were selected on the basis of the basic components used - polyalkylene glycols,esters and mineral oil - which act as reference cooling lubricants. In each case, 3 variants were created for the water-miscible MWF,which represent typical concepts: boron-containing, boron-free and boron-free with a high pH value. In addition, two non-water-miscible coolants and two forming lubricants were defined. A laboratory method (DIN ISO 1817: 2008-08) was chosen for the test, in which the test rods - S 2 test specimen (shoulder rod S 2 according to DIN 53504) are immersed in the medium for the test duration. Through preliminary tests and consultation with elastomer manufacturers, the duration and extent of storage per KSS were determined and determined. The duration is uniformly 1000 h, the storage temperature is 60 °C. For water-miscible products, 3 tests are carried out in par- 326 23rd International Colloquium Tribology - January 2022 Development and verification of a test method for determining the compatibility of elastomers with cooling lubricants allel: with water, with the MWF concentrate and with a 10% emulsion. In each case 5 test rods are used per test. The scope of the test includes the following parameters: • Volume change • Shore A Hardness - Change • Tensile strength (change) • Elongation at break (change) • pH value change • Conductivity Change • Sensory testing 4. Verification of the test method with elastomers In the next step, the method was used to carry out tests with a commonly used elastomer group - the PU materials. Both etherand ester-based PU grades have been tested. Especially with products of this group intolerances have been observed in use. Overall, the project has great support from the industry (elastomer, machine tool manufacturers, users). This has been expressed both in the provision of materials and in the execution of tests and communication of the results. The project identified and made available results on more than 30 materials - commercially available and also material under development. 5. Outlook and recommendations The described method allows an assessment of the compatibility of elastomers with cooling lubricants. The generic formulations of the reference cooling lubricants represent the coolant types available on the market. In any case, it is recommended to carry out a test before the use of an elastomer in a MWF-exposed environment in order toavoid unnecessary risks and costs. The VSI test method will be also incorporated into an ISO 1817 standard. 23rd International Colloquium Tribology - January 2022 327 Accelerated compatibility test of sealing material lubricant in a dynamic stress collective Ameneh Schneider Optimol Instruments Prüftechnik GmbH, D-81639 Munich, Germany Corresponding author: ameneh.schneider@optimol-instruments.de Josef Brenner AC2T Research GmbH, A-2700 Wiener Neustadt, Austria Felix Zak Optimol Instruments Prüftechnik GmbH, D-81639 Munich, Germany Summary The aim of this work was to develop a parameter set on the SRV ® tribometer to simulate dynamic degradation of polymers in short measurement times and to enable a ranking of polymer/ lubricant combinations based on residual mechanical properties after test and the coefficient of friction. For this purpose, the extent of the induced dynamic damage was compared with static insertion tests according to ISO 1817 as well as the original condition as a reference. Keywords: Tribological tests, dynamic load, elastomer compatibility, degradation, seal material, lubricant 1. Introduction The ISO 1817 standard (“Rubber, vulcanized or thermoplastic - Determination of the effect of liquids”) is a method by which the resistance of vulcanized or thermoplastic elastomers to liquids is tested [1]. Sealing’s damages caused by tribological-dynamic issues can often be observed in machineries. These damages result among others also from the counter surface, the lubrication and type of lubricant, the sliding speed as well as the temperature [2]. Braun described the challenges of static test very well [3]. This work represents added value to static compatibility test with conditions near to applications, the test setup is illustrated in figure 1. 2. Materials and method The following polymers (seal materials) and oils were selected for the feasibility of the tribological-dynamic investigation: Table 1: Investigated Materials Code Description Elastomers NBR Nitrile Butadiene Rubber NBR Semperit P 559 (70 Shore A, 2 mm) EPDM Ethylen-Propylen-Dien; M-group EPDM Semperit E 9566 (70 Shore A, 2 mm) Oils L32 Mineral base oil ISO VG 32 ES Ester oil Trioctyltrimellitat 99 % Figure 1: Clamped elastomeric tensile bar sample in the SRV®5 328 23rd International Colloquium Tribology - January 2022 Accelerated compatibility test of sealing material lubricant in a dynamic stress collective The test parameters were investigated as follows: • Normal force: 20 N à Pressing: → 1.6 MPa • Duration: 30 min • Temperature: 80 °C • Frequency: 40 Hz • Stroke: 4 mm 3. Results and discussions Figure 2 shows the comparison of coefficient of friction values after testing the different combinations of oils and elastomer with SRV ® 5 under the parameters mentioned above. Figure 2: COF from SRV ® 5 tests The EPDM/ mineral base oil L32 pairing had a significantly higher friction level (between 0.4 and 0.5) than the other (0.14 to 0.2). This combination shows a clear swelling of the elastomer (sample approx. 2 mm longer after testing, as can be seen in Figure 3). Figure 3: Samples after the dynamic tests The SRV ® 5 test confirms the incompatibility of EPDM with mineral base oil, as to be expected, in very short testing times, i.e., 30 min. Using HRA (High Resolution Analysis) of friction signal makes it possible to identify this incompatibility during the test online. Figure 4: COF hysteresis curves at 900 s of test In parallel to the dynamic investigations of the elastomers, static insertion tests were also carried out as a reference. Table 2 lists the chosen insertion times and temperatures: Table 2: Insertion parameters Sample code Temperature Insertion time 0,5 h 80 °C 80 °C 0.5 h 168 h 80 °C 80 °C 168 h 320 h RT RT 320 h original untreated The insertion test of 30 min at 80 °C served as a direct benchmark to the SRV ® tests. In this way, temperature influence and tribological-dynamic influence on the mechanical properties (e.g., tensile tests) of the elastomer samples were separated. Three samples of each elastomer type were insert in each oil under the chosen temperature and time. The following mechanical properties were evaluated after each insertion. • tensile strength • elongation at break 23rd International Colloquium Tribology - January 2022 329 Accelerated compatibility test of sealing material lubricant in a dynamic stress collective Figure 5 represents the results of tensile strength for NBR after treatment with oils L32 and ES. Figure 5: comparison of tensile strength after static and dynamic test condition Figure 6 shows the results of elongation break for NBR after treatment with oils L32 and ES Figure 6: comparison of elongation at break after static and dynamic test condition In this combination static thermal stress of 0.5 h at 80 °C hardly effected the NBR. SRV® tribo-tests of 0.5 h at 80 °C led to a light reduction in tensile strength but significant increase in elongation at break. Most changes are observed in the case of 168 h at 80 °C insertion time. The results of 320 h at RT static insertion and 0.5 h at 80 °C under dynamic insertion are in good agreement. Results of tensile tests for EPDM after treatment with oils L32 and ES show similar tendencies. 4. Summarized conclusions • As part of a feasibility study, a parameter set was developed on the SRV ® tribometer for dynamic polymer liquid compatibility testing • The method allows a ranking of elastomer/ lubricant combinations based on mechanical properties and the coefficient of friction • The elastomers from the SRV® tests (0.5 h at 80 °C), had significant different mechanical properties, when compared to the untested • The results indicate good agreement with the results of static insertion tests (320 h RT) 5. Outlook As these results are promising, this work will be extended and continued in new projects with variations in testing time and temperature (168 h 100 °C). The definition of criteria for elastomer compatibility based on mathematical calculation of hysteresis values of COF results will be further elaborated. This short dynamic test time and its defined criteria will save cost and time and give a quick ranking of polymer liquid compatibility. This method can be used for evaluation the fully formulated lubricants as well to screen, e.g., effects of additives. References [1] ISO 1817 standard “Rubber, vulcanized or thermoplastic - Determination of the effect of liquids” [2] M. Rinnbauer,“ Technische Elastomerwerkstoffe”, Verlag Moderne Industrie, Band 293, 2006 [3] Braun, „Elastomerverträglichkeitsuntersuchungen von Schmierstoffen - Reicht die bestehende Normung aus? “, Schmierstoffe und Schmierungstechnik, 2007 23rd International Colloquium Tribology - January 2022 331 Influences of roughness, moisture content and lubrication on friction of polymers against 100Cr6 Joel Voyer V-Research GmbH, Dornbirn, Austria Corresponding author: joel.voyer@v-research.at Heinz Haider Austrian Research Institute for Chemistry and Technology, Vienna, Austria Claudia Mayrhofer Austrian Research Institute for Chemistry and Technology, Vienna, Austria Igor Velkavrh V-Research GmbH, Dornbirn, Austria Tom Wright V-Research GmbH, Dornbirn, Austria 1. Introduction The interactions in dry and lubricated tribological polymer systems on smooth metal surfaces (Rz < 4 µm) were previously extensively investigated and published, and the main parameters influencing their friction behaviour are well known: the main mechanisms determining friction forces are adhesion and deformation. Depending on the polymer and on its adhesive and mechanical properties, friction may have a strong dependency on both surface roughness and normal load. Generally speaking, adhesive friction is predominant at low normal loads, but deformative friction becomes more important at higher loads. For specific polymers having high load bearing capabilities, an increase of the normal load usually results in a decrease of the friction coefficient (COF), due to a change in the main friction mechanism. For some industrial applications, tribologically optimized smooth surfaces cannot be economically produced and therefore, rough surfaces have to be used, which produces a change of the main tribological mechanisms. In this study, the influence of surface roughness coupled with modifications of the polymer’s moisture content and test temperature will be investigated and analysed. 2. Materials and Experimental Procedure Tribological investigations were undergone using 3 different polymers (POM, PA6-GF30 and PK) against 100Cr6 steel with different surface roughness (smooth or rough) (details in Table 1). To change the polymers’ moisture content, some were dried in a furnace at 70°C while others were immersed in water at 70°C until a weight change equilibrium was reached (~10 days). Table 1: Details on investigated materials. Parameter Unit Value Polymers - POM / PA6-GF30 / PK Moisture % rel. H. 0 / 100 Steel Plate hardened 100Cr6 Rz µm Rz ~ 1 (smooth) Rz ~ 20 (rough) 2.1 Friction theory for smooth and rough surfaces For smooth surfaces, the main friction mechanism is based on adhesion effects, which are mostly influenced by surface energy and real contact area of the tribological system [1]. By introducing a lubricant, this adhesion mechanism tends to be minimized due to a decreased in the surface energy. For rough (and especially rough-lubricated) plastic-metal contacts, where surface roughness has a major significance on friction behaviour [1], adhesion effects may be neglected, since deformation becomes the predominant friction mechanism. For instance, for soft polymers under normal loads against metallic partners, roughness asperities of the metal penetrate in the polymer without any metallic asperity’s deformation [1]. 332 23rd International Colloquium Tribology - January 2022 Influences of roughness, moisture content and lubrication on friction of polymers against 100Cr6 2.2 Tribological Experiments To evaluate static and dynamic COF, tribo-tests using different surface pressures (stepwise change from 20 to 0,5 N/ mm 2 ), two different polymer moisture contents (0%/ 100%) and two lubrication conditions (unlubricated/ lightly greased) were performed. Table 2 lists general tests parameters and Figure 1a shows the test setup and sample geometry. Static and dynamic COF were calculated from 4 cycles of the raw signals. Static COF was determined as first peaks after the sample’s motion (red dots in Figure 1b) and dynamic COF was an average of raw COF values using a window of 80% of a half-cycle (Figure 1c). a) b) c) Figure 1: a) Test setup and sample geometry, b),c) determination of static and dynamic COF. Table 2: Test parameters. Parameter Unit Value Surface Pressure N/ mm 2 0,5 / 1 / 2,5 / 5 / 7,5 / 10 / 15 / 20 Stroke per Cycle mm 20 Speed mm/ s 83 Temperature °C 20 / 70 Lubricant Condition - Dry / Grease 3. Results and Discussions The pre-treatments showed clearly that the water absorption capacity of the polymers differs drastically: - POM (water absorption = 1,5 wt%) - PA6-GF30 (water absorption = 5,9 wt%) - PK (water absorption = 3,2 wt%) Thus, it is expected that the polymers’ tribological properties may be influenced by the moisture contents. 3.1 Tribological Experiments Figures 2 and 3 present static and dynamic COF for all polymers but only for 20°C. Similar results for 70°C were obtained but not presented here. First, for some of the friction curves (especially for PA6 and PK), a load dependency of COF may be observed, as previously described in [1], and is due to a nonlinear behaviour between friction and normal force, which reduces COF with increasing normal load [2]. For low loads, lower COF were usually measured for polymers with low moisture contents than for polymers with high contents. Usually, a low moisture content leads to higher E-modulus and compressive yield stress, which causes a lower penetration depth and therefore at low loads, a lower COF. For polymers with high moisture, inverse observations are encountered: lower E-modulus and compressive yield stress results in higher COF at low loads. Although roughness asperities under high loads may penetrate deeper into polymers with higher moisture, resulting shear forces may be lower, due to lower mechanical properties. The introduction of a lubricant on a smooth surface eliminates any load dependency of COF, resulting in flattened COF curves over the whole surface pressure range independently of the moisture (Figure 2), due to a reduction of adhesion combined with a separation of the contact surfaces (decrease of asperity penetration). For rough surfaces, the presented investigations have shown that independent of polymer moisture, mechanical properties determine static COF, due to the fact that the metal asperities are more pronounced, even though although lubrication is used (Figure 3). 23rd International Colloquium Tribology - January 2022 333 Influences of roughness, moisture content and lubrication on friction of polymers against 100Cr6 Figure 2: COFs of dried and water saturated polymers, smooth plate (Rz ~1 µm), dry / lubricated, 20°C. Figure 3: COFs of dried and water saturated polymers, smooth / rough plates (Rz 1 / 20 µm), lubricated, 20°C. 4. Conclusion No general conclusions but only main observations may be drawn from the results: Dry conditions - POM: no influence of temperature or moisture. - PA6: strong influence of temperature and moisture. - PK: light influence of temperature and moisture. - COF mostly determined by adhesion effects. Lubricated Smooth Surfaces - Elimination of load dependency of COF. - reduction of static and dynamic COF. - almost no influences of moisture and temperature. - asperities effects not predominant. Lubricated Rough Surfaces - roughness and deformative friction are determinant. - asperities effects predominant: polymer mechanical properties determine the friction behaviour. References [1] Erhart G.: Zum Reibungs- und Verschleißverhalten von Polymerwerkstoffen. Diss. TH Karlsruhe, 1980. [2] Sujeet S.: Polymer Tribology. Imperial College Press, ISBN-10 1-84816-202-2, 2009. 23rd International Colloquium Tribology - January 2022 335 A novel measurement procedure to analyse the friction of rod seals in relation to pre-defined shear rates and starved lubrication conditions Oliver Feuchtmüller Institute of Machine Components, University of Stuttgart, Stuttgart, Germany Corresponding author: oliver.feuchtmueller@ima.uni-stuttgart.de Lothar Hörl Institute of Machine Components, University of Stuttgart, Stuttgart, Germany Frank Bauer Institute of Machine Components, University of Stuttgart, Stuttgart, Germany 1. Introduction Linear actuators such as hydraulic or pneumatic cylinders are used in a variety of applications. One critical component of every hydraulic or pneumatic cylinder is the rod seal, since it influences the performance of the whole machinery. If a rod seal fails, leakage or machine downtime is unavoidable. Moreover, modern applications demand friction-optimized sealing solutions. Low friction rod seals are required to optimize the efficiency and remain competitive. In high precision positioning actuators, the seal’s friction is of crucial importance, since its influence on the dynamic performance and precision of linear actuators. Consequently, friction properties of rod seals shall be considered when designing actuators for certain operating parameters. Despite decades of research, predicting a seal’s friction remains a challenging task due to numerous influence parameters. One main factor influencing the friction is the lubrication condition in the sealing gap. At outstroke and instroke, the hydraulic rod drags oil into the sealing gap resulting in a thin lubricant film in the nanometer range [1], [2]numerically, and experimentally. The analyzed sealing system consists of an unmodified, commercially available U-cup, a polished rod, and mineral oil. The inverse theory of hydrodynamic lubrication (IHL. A serious drawback of conventional test rigs for analysing friction of rod seals is that the film thickness remains unknown. This limits conclusion which can be drawn on actual tribological mechanisms in the sealing gap. We developed a novel measurement procedure to analyse the influence of film thickness and shear rate on the friction of reciprocating rod seals directly. It is possible to analyse the friction of almost every rod seal and lubricant in relation to the fluid shear and thin film lubrication conditions. The procedure offers a deep insight into the influence of parameters such as the seals material, geometry, surface roughness or rheological properties of the lubricant on the friction. One unique feature of the procedure is that a pre-defined lubricant film in the nanometer range is generated on the rod to achieve certain lubrication conditions and shear rates in the sealing gap. 2. Novel measurement procedure The procedure is based on a film thickness measurement technique using ellipsometry and a recently-developed test rig. The test rig was built to simulate the outstroke and measure the dynamic friction of the seal. The main advantage of the new test rig is that the rod and seal can be removed easily and without effort. Ellipsometry is a technique for measuring thin films in the nanometer range. Ellipsometry was employed to achieve the required accuracy for the film thickness measurements in the nanometer range. Due to the use of the ellipsometer, the hydraulic rod must be polished to a smooth surface finish. The novel measurement procedure contains several steps, which are illustrated in Figure 1. After outstroke at certain operating conditions , the film thickness on the hydraulic rod is measured using ellipsometry as described in previous studies [1], [3]. Therefore, the seal is removed from the rod carefully. Then, the same rod with the measured oil film is used for a second outstroke with increased rod speed . Since the speed is increased at the second outstroke, the oil film on the rod cannot be wiped off by the seal and remains constant. This is proofed by a second film thickness measurement afterwards. 336 23rd International Colloquium Tribology - January 2022 A novel measurement procedure to analyse the friction of rod seals in relation to pre-defined shear rates and starved lubrication conditions Figure 1: Illustration of the measurement procedure Assuming full fluid lubrication conditions, friction depends on the fluid shear in the sealing gap. Then, fluid friction F fluid is a function of the film thickness , speed u, dynamic viscosity η and contact area A as defined in Eq. 1. (1) The outstroke speed u can easily be controlled by the test rig and the film thickness h O on the rod is measured using ellipsometry. Assuming a linear Couette-flow in the sealing gap, the gap height is twice the measured film thickness on the rod. Thus, the shear rate in the sealing gap can be determined. Considering the viscosity η of the lubricant, the shear stress τ in the sealing gap can be calculated. The product of the shear stress τ and the contact area A between the seal and the rod results in the fluid friction F fluid as defined in Eq. 1. Aside, the apparent friction at outstroke is measured by a force transducer. For further discussion and comparison of various sealing systems, the measured apparent friction of rod seals can be analysed as a function of fundamental parameters such as the shear rate, film thickness and viscosity. 3. Results of the empirical study In a first empirical study, the friction of a typical polyurethan U-cup was analysed at different operating and lubrication conditions using the new measurement procedure. The friction was measured at shear rates in the range from approximately 10 5 to 10 7 s -1 which were achieved due to the combination of various pre-defined film thicknesses (1 to 200 nm) and rod speeds (10 to 200 mms -1 ). Furthermore, mineral oils of various viscosity classes (ISO VG 15 to 460) were used for variation of fluid shear stress in the sealing gap. The contact area between the U-cup and the rod was measured using a hollow glass rod in advance. All measurements were carried out at room temperature. The measurement results indicate a significant influence of the analysed parameters on the measured friction. In Figure 2, the measured friction F R,O at outstroke is plotted against the calculated fluid friction F fluid in accordance with Eq. 1. As demonstrated in Figure 2, it was possible to confirm a linear influence of the shear rate and viscosity in the sealing gap on the measured friction for a wide range of viscosities and shear rates. However, the directly measured friction was somewhat higher than the calculated fluid friction based on the speed, film thickness, viscosity and contact area. A possible reason for those discrepancies is the assumption of pure Newtonian fluid friction without considering boundary friction or asperity contacts which may appear in such thin gaps. 23rd International Colloquium Tribology - January 2022 337 A novel measurement procedure to analyse the friction of rod seals in relation to pre-defined shear rates and starved lubrication conditions Figure 2: Measured friction as a function of rod speed, gap height , dynamic viscosity and contact area of a urethane U cup at starved lubrication conditions 4. Conclusions The originality of the new measurement procedure is that friction of commercially available rod seals can be analysed as a function of film thickness, rod speed and viscosity. Moreover, the new procedure can be used to analyse further sealing systems with different components. For example, the tribological properties of hydraulic fluids based on different base oils with different chemical and rheological properties can be analysed in narrow gaps at high shear rates. The novel measurement procedure can be adopted in the development process of new rod seals for fine-tuning of the seal’s geometry, surface topography and the resulting lubrication conditions. Furthermore, the procedure can be used for the validation of soft EHL-simulation models in general. In conclusion, a new perspective on thin film lubrication and friction of practical relevant rod seals is provided by the empirical analysis of pre-defined lubrication conditions. References [1] O. Feuchtmüller, L. Hörl, and F. Bauer, “Oil film generation of a hydraulic rod seal: an experimental study using ellipsometry,” Tribol. Int., vol. 162, p. 107102, May 2021, doi: 10.1016/ j.triboint.2021.107102. [2] O. Feuchtmüller, N. Dakov, L. Hörl, and F. Bauer, “Remarks on Modeling the Oil Film Generation of Rod Seals,” Lubricants, vol. 9, no. 9, p. 95, 2021, doi: 10.3390/ lubricants9090095. [3] L. Hörl, W. Haas, and U. Nißler, “A comparison of test methods for hydraulic rod seals,” Seal. Technol., vol. 2009, no. 12, pp. 8-13, Dec. 2009, doi: 10.1016/ S1350-4789(09)70594-X. 23rd International Colloquium Tribology - January 2022 339 A new approach for the friction and wear characterisation of polymer fibres under dry, mixed and hydrodynamic sliding Justus Rüthing Hamm-Lippstadt University of Applied Science, Lippstadt, Germany Corresponding author: justus.ruething@hshl.de Regine Schmitz Hamm-Lippstadt University of Applied Science, Lippstadt, Germany Frank Haupert Hamm-Lippstadt University of Applied Science, Lippstadt, Germany Michael Sigrüner Rosenheim University of Applied Science, Rosenheim, Germany Nicole Strübbe Rosenheim University of Applied Science, Rosenheim, Germany 1. Introduction A new approach for the friction and wear characterisation of polymer fibres for the application in fibre reinforced concrete is developed. The abrasive conditions, similar to the ones found in an industrial concrete mixing process, are simulated using an optimised pin-on-disc test rig to conduct tests under dry, mixed and hydrodynamic sliding conditions. Using this test method, it is shown, that it is possible to differentiate the friction and wear characteristics of polymer fibres based on their dimension and sliding condition. 2. Materials 2.1 Specimen - Polypropylene Fibres For this study, three polypropylene [PP] fibres, produced by a single screw extruder and post treated in a stretching unit described in [1], where characterised. By variation of the processing parameter of the stretching unit, three fibres with the draw ratios from 1: 10, 1: 14 and 1: 17 were created and used in this study. Because of the different values for the vertical and across diameters, an elliptical fibre shape is assumed. The dimensions of the fibres are shown in Table 1. For the tribotest itself, the polymer fibre is fixed to a specifically designed specimen-holder. Within this configuration a fibre-area of 20 mm in length is tested against the abrasive counterpart. Table 1 Dimensions of the tested polypropylene fibres Draw Ratio Diameter Across [µm] Diameter Vertical [µm] 1: 10 670 (± 17) 627 (± 22) 1: 14 639 (± 10) 500 (± 15) 1: 17 575 (± 36) 552 (± 34) 2.2 Counterpart - Alumina-Disc The counterpart used consists of an Alumina (Al 2 O 3 ) disc with a surface roughness [R a ] of 1,59 µm (see Figure 1). To ensure the same surface properties apply for each measurement, the surface is grinded down using a diamond grinding disc (Schmitz Metallography, grain size 0080) before each tribotest. 2.3 Pin-on-Disc Test Rig The optimised test rig, described in [2], consists of an inhouse designed and built pin-on-disc tribometer, a programmable peristaltic pump (see Figure 1) as well as an 340 23rd International Colloquium Tribology - January 2022 A new approach for the friction and wear characterisation of polymer fibres under dry, mixed and hydrodynamic sliding Figure 1: Optimised Pin-on-Disc Test Rig optimised specimen holder. Within this test rig, normal force can be applied in the range of a few Newtons to 200 Newtons (± 0,3 N) through a mechatronic controlled load unit. With a force sensor, friction force is measured. Using a stepper motor, the counterpart disc is rotated to speeds of up to 5,0 m/ s. Applied load, friction force and rotational speed are measured, recorded and analysed in real time using an in-house designed software. The programmable peristaltic-pump is capable of supplying lubricants to the discs surface using an injection attachment in the defined rates of 0,01 to 5,7 ml/ min. 3. Experimental Method The testing procedure consists of a dry-sliding-phase, in which the tested fibre is abraded to a depth of 150 µm. Thereafter, water as a lubricant is constantly added over the water injection attachment to the discs surface. To model the different sliding conditions, similar to the ones found in an industrial concrete mixing process, two lubrication rates are used: 0,5 ml/ min for 25 min to model mixed sliding conditions, and 4,0 ml/ min for 25 min to model hydrodynamic sliding conditions. To compare the tribological properties of the fibres between each other, the loading force was adjusted for each fibre to keep an equal pv-product of 0.16 MPa m/ s for each test. The counterparts disc speed was kept at a constant 0,4 m/ s. The normal forces used were 5.3 N for 1: 10, 5.1 N for 1: 14 and 4.6 1: 17. The dry sliding friction and wear data of the tested fibers were taken in the defined steady state from 100 to 150 µm of absolute wear. For the mixed and hydrodynamic sliding conditions, the wear data was taken in the last 10 min of each lubrication rate. 4. Findings The findings of the tribological characterisation of three PP fibres in this study show, that the friction and wear behaviour of the tested fibres can be determined under dry, mixed and hydrodynamic sliding using the described test method. The wear and friction data gathered in this study are presented in Figure 2. 4.1 Friction The results of the tribological characterisation of three different fibres show, that the diameters impact the coefficient of friction [COF] as the fibre with the largest diameter (1: 10) demonstrating the highest and 1: 17, with the lowest diameter, demonstrating the smallest COF. Further, a reduction in the COF can be examined across all fibers with rising addition of lubricant. The dry sliding phase resulting in the highest and the hydrodynamic sliding phase resulting in the lowest COF out of every fibre tested. The friction results are presented in Figure 2. 4.2 Wear The wear behaviour of the tested fibres show a reduction in the steady-state wear rate due to the sliding conditions. The fibre with the lowest wear rate under dry sliding, tested in this study, is the fibre 1: 10. Considering the mean error, fibres 1: 14 and 1: 17 cannot clearly be differentiated between each other. However, a difference in the wear behaviour between the fibre 1: 10 and the fibres 1: 14 and 1: 17 can be examined. For the mixed sliding conditions, fibre 1: 10 shows a higher wear compared to fibres 1: 14 and 1: 17. No difference in wear behaviour can be examined between the fibres 1: 14 and 1: 17. With further increase in the lubrication rate and therefor hydrodynamic sliding, fibre 1: 10 stills show the highest wear rate compared to the fibres 1: 14 and 1: 17. As with the wear behaviour under mixed sliding, no difference in wear behaviour can be examined between the fibres 1: 14 and 1: 17. 23rd International Colloquium Tribology - January 2022 341 A new approach for the friction and wear characterisation of polymer fibres under dry, mixed and hydrodynamic sliding Figure 2: Steady-State wear rate and coefficient of friction of the fibres 1: 10, 1: 14 and 1: 17 in variation of the lubrication rate 5. Conclusion The results show, that the fibre with the smallest draw ratio (1: 10) exhibits the better wear-resistance under dry conditions whereas the fibres with the medium (1: 14) and high (1: 17) draw ratios show superior wear-resistance under mixed and hydrodynamic sliding. For the COF, the fibre with the smallest draw ratio has the highest COF under dry sliding. The COF for fibres with the medium and highest draw ratios is comparable across all tested sliding conditions. Using this optimised pin-on-disc test equipment, it is shown, that tribotests can be performed under various lubrication rates to characterize the tribological behaviour of polymer fibres. 6. Acknowledgement The authors thank the German federal ministry of education and research (BMBF) for the funding of this study as part of the project 13FH068PB6. References [1] M. Sigrüner, D. Muscat und N. Strübbe, „Investigation on pull-out behavior and interface critical parameters of polymer fibers embedded in concrete and their correlation with particular fiber properties“, J. Appl. Polym. Sci., 2021 [2] R. Schmitz, F. Haupert, J. Rüthing, M. Sigrüner und N. Strübbe, „Tribologische Charakterisierung von Polymerfasern unter Trockenreibung, Mischreibung und Hydrodynamik mittels einer optimierten Pin-on-Disc-Prüfmethode“, TuS, 2021 Lubricant Stability 23rd International Colloquium Tribology - January 2022 345 Novel electrical current feed apparatus for aging simulation of lubricants Controlled electrical current feed and analytical analysis of lubricants and additives Yasmin Korth Dr. Tillwich GmbH Werner Stehr, Horb-Ahldorf, Germany Corresponding author: yasmin.korth@tillwich-stehr.com Susanne Beyer-Faiss Dr. Tillwich GmbH Werner Stehr, Horb-Ahldorf, Germany 1. Introduction Lubricants used in industrial applications consisting of baseoils and additive packages are mostly insulators and therefore not suitable to lead off electrical currents from e.g., friction bearings in cars. Adding conductive additives as ionic liquids has already been used in industrial applications [1]. But until now it is not clarified what will happen to the chemical structures exposed to these electrical currents. In this applied joint research approach [2] different ionic liquids with different conductivities and different model lubricants where exposed to well defined electrical currents using a new constructed equipment to examine the impacts of different voltages and exposing times using IR spectroscopy, rheology and conductivity measurements of the liquids. 2. Methods The ionic liquids and model lubricants were exposed to the shown current feed equipment (test chamber and oven), Figure 1. In the apparatus voltages from 0 to 25V are possible with different selectable polarization. The test chamber may be heated and the occurring conductivity can be metered. Figure 1: Test chamber and current feed apparatus 2.1 Infrared spectroscopy: The current feed samples were analyzed by using this spectroscopical method to characterize rearrangement and decomposition processes, example Figure 2. 2.2 Rheology: Measuring the changes in viscosity to determine the degradation progress have been performed. 2.3 Conductivity: Identifying the changes during the current feed operation was mapped. Figure 2: IR example spectra of a current feed ionic liquid and pictures of the current feed test chambers after 4 hrs, 24 hrs and 288 hrs. 3. Results The examined ionic liquids, chemically described as molten salts with no measurable vapor pressure are electrically conductive. Depending on their own conductivity they react on the applied voltage by degradation of 346 23rd International Colloquium Tribology - January 2022 Novel electrical current feed apparatus for aging simulation of lubricants their chemical structure and attacking the steel sample chambers depending on the composition of the used steel parts, even the PTFE distance ring can be affected. The conductivity decreases during the process as well as the measured viscosity afterwards leading to the assumption that the ionic liquids have been degraded by the voltage, Figures 3,4. Figure 3: Measured conductivies of different ILs before and after current feed. Figure 4: Measured viscosities of different ILs before and after current feed. Adding ILs to conventional lubricant baseoils in additive like concentrations, no corrosion at the steel parts are visible. In the IR-Spectra the ILs seems to “disappear” dissipated by the current feed. Conductivies are measurable and confirm the conductivies of the model lubricants, Figures 5. Figure 5: Measured conductivies of different ILs before and after current feed. Using 5% of the IL, the viscosity of the model lubricants are not influenced significantly, Figure 6. Figure 6: Measured viscosities of different model lubricants before and after current feed. 4. Conclusion Depending on their chemical structure, the ILs have been decomposed differently, taking also into account their viscosity and resulting conductivity. The corrosion potential only depends on the chemical structure of the ILs. Dissolving ILs into base oils in additive like concentration leads to conductivity of the fluid, depending on their solubility. The ILs are consumed without leading to corrosion. References [1] Khazalpour, S.et al., “Applications of phosphonium-based ionic liquids in chemical processes,” Journal of the Iranian Chemical Society, Review, Springer, 2020 [2] Joint research project EPiG: Development of electrically conductive lubricants and adapted nanocomposites for sliding bearings by use of ionic liquids and graphene. BMBF support code 03XP0220A. Duration 01.05.2019 to 30.04.2022 347 23rd International Colloquium Tribology - January 2022 347 Laboratory-based reproduction of shear-degraded greases by use of a grease worker Christoph Schneidhofer AC2T research GmbH, Wiener Neustadt, Austria Corresponding author: Christoph.Schneidhofer@ac2t.at Michael Schandl AC2T research GmbH, Wiener Neustadt, Austria Nicole Dörr AC2T research GmbH, Wiener Neustadt, Austria Thomas Macheiner Siemens Mobility Austria GmbH, Graz, Austria Lukas Fritzer Siemens Mobility Austria GmbH, Graz, Austria 1. Introduction Grease is a system component, which is essential for the functionality and reliability of rolling bearings. Thermal, oxidative, and mechanical stress during oper-ation are major reasons for loss of lubrication perfor-mance of a grease. Thus, knowing its long-term per-formance is crucial. In typical bearing applications, chemical grease degradation is mostly induced by high operating temperature, whereas mechanically induced grease degradation is caused by the applied forces (shear stress) and velocities (shear rate). The breakdown of the thickener structure results in increased oil bleed-ing and consequently in reduced service life of rolling bearings. [1, 2] To properly correlate grease degradation with grease performance, e.g. lubricity, aged greases with defined condition and in sufficient amounts are required. There-fore, a laboratory-based method of grease degradation using a modified grease worker was developed. This method of artificial alteration aimed at significantly accelerated mechanical degradation compared to the field. In this work, greases sampled from axle box bearings on wheelsets for railway application were characterized as basis for the laboratory simulation of grease degrada-tion. Artificially stressed greases obtained after 500 000 and 1 000 000 cycles in the modified grease work-er were compared to the respective greases from the field by qualitative analyses of the thickener structure, among others. Shear stability of three greases is discussed. 2. Experimental setup 2.1 Fresh and used greases Used greases were collected according to EN 12082 [3] from four axle box bearings from a railway application with a milage of around 1.6 Mio. km. For the laboratory investigations, three commercially available greases were used. Table 1 lists the grease properties extracted from the datasheets. 348 23rd International Colloquium Tribology - January 2022 Laboratory-based reproduction of shear-degraded greases by use of a grease worker Table 1: Overview of greases Properties Grease A Grease B Grease C Base oil Mineral oil Mineral oil Synthetic Thickener Lithium Lithium Lithium complex NLGI consistency 2.5 2.5 2 Base oil viscosity 40° C 100 40 100 [cSt] 100° C 11 8 14.5 Dropping point [° C] 180 >180 274 2.2 Analysing grease condition Following analyses were performed to investigate the greases deteriorated in the field and in the laboratory: • Cone penetration using one-quarter scale cone equipment according to ASTM D1403. • Bleeding tendency according to an in-house method to evaluate the amount of oil bleeding at 80 °C after 6 h. • Infrared spectra obtained by a Fourier trans-form infrared (FTIR) spectrometer equipped with an attenuated total reflection (ATR) unit. • Thickener structure by scanning electron mi-croscopy (SEM). Figure 1: Trend of consistency (unworked cone penetration) (TOP) and bleeding (BOTTOM) of used greases depending on the position in the bearing 2.3 Modified grease worker for artificial alteration The greases were artificially altered in the grease worker, as described in ASTM D217-10, for 500 000 and 1 000 000 cycles with a speed of around 1 double-stroke per second. The perforated plate was modified, where the diameter of the holes was reduced to increase the shear stress. Afterwards, the grease conditions were determined and compared to those of the used greases. 3. Results and discussion Figure 1 shows the analyses of used greases from the field. The sampling positions (A, B, C1, C2, D) are corresponding to the positions defined in EN 12082 [3]. The consistency (unworked cone penetration) shows a typical W-shape when drawn over sampling positions. Grease samples from the raceway zones (C1, C2) get stiffer, caused by increased bleeding due to progressed shear degradation. Greases from A and B get softer due to mechanical degradation of the thicken-er. Grease samples from position D showed similarities to the fresh grease condition. The same trend can be observed for the bleeding tendency. 23rd International Colloquium Tribology - January 2022 349 Laboratory-based reproduction of shear-degraded greases by use of a grease worker Figure 2: Trend of consistency (TOP) and bleeding (BOTTOM) of artificially stressed greases in the modified grease worker The results from mechanical degradation in the grease worker are shown in Figure 2. Generally, the higher the number of strokes the higher the consistency (cone penetration) and, therefore, the softer the grease. How-ever, a certain saturation effect (flattened curves) can be detected. Grease A and B showed very similar trends during alteration, both based on a Li thickener. Grease C based on a Li-complex thickener with synthetic base oil exhibited a higher shear stability in comparison to grease A and B. Also, the bleeding tendency of grease A and B are similarly characterized by a slight increase. By contrast, grease C shows a slight decrease in artifi-cial alteration. Analyses of the thickener structure by SEM clearly illustrate a breakup of the thickener fibres in the used and artificially altered greases in comparison to the fresh grease (see Figure 3). The artificially altered grease after 1 Mio. cycles can be well correlated to the structure of the used grease sample from position A. Furthermore, the consistency of these samples is very similar. The modified grease worker is a useful tool to simulate shear degradation of greases and benchmark the shear stability of greases. Its application reproduces shear degraded greases in a rapid manner for further investi-gation of the influence of shear degradation on the functionality of greases in field operation. Figure 3: Qualitative optical comparison of thickener structures; a) fresh grease B; b) used grease sampled from position A c) artificially altered grease after 1 Mio. cycles 4. Conclusion Analyses of greases sampled from axle box bearings for railway application revealed mechanical stress as main grease degradation mechanism. A laboratory method developed to simulate shear degradation using a modi- 350 23rd International Colloquium Tribology - January 2022 Laboratory-based reproduction of shear-degraded greases by use of a grease worker fied grease worker provided greases that were compared to respective greases from the field. A good correlation between mechanically induced grease degradation in the laboratory and in the real application was confirmed. Therefore, laboratory-generated greases allow the accel-eration of investigation of grease performance. References [1] P. M. Cann, M. N. Webster, J. P. Donner, V. Wikstrom and P. Lugt, “Grease Degradation in R0F Bearing Tests,” Tribology Transactions, no. 50: 2, pp. 187-197, 2007. [2] A. Rezasoltani and M. M. Khonsari, “On Monitoring Physical and Chemical Degradation and Life Estimation Models for Lubricating Greases,” Lubricants, vol. 4, no. 34, 2016. [3] EN 12082: Railway applications - Axleboxes - Performance testing, CEN, 1 September 2017. 23rd International Colloquium Tribology - January 2022 351 Application of the Non-linear Behaviour of Longitudinal Ultrasonic Waves in Lubricants Monitoring S. Taghizadeh Leonardo Centre for Tribology, Department of Mechanical Engineering, University of Sheffield, Mappin Street, Sheffield S1 3JD, UK Corresponding author: staghizadeh1@sheffield.ac.uk R.S. Dwyer-Joyce Leonardo Centre for Tribology, Department of Mechanical Engineering, University of Sheffield, Mappin Street, Sheffield S1 3JD, UK The performance of lubricants directly effects the energy efficiency and level of environmental pollution. Oxidation due to high operating temperature, wear particles and contamination by fuel are factors that degrade lubricants and reduce their functionality. There are several techniques to determine the state of degradation such as infrared spectroscopy or chemical constituent examination. One of the limitations of these methods is being offline measurement and so an oil sample is required to be measured in a laboratory environment. Non-destructive methods using ultrasound have been widely used in tribology to detect contact and measure oil film thickness. In this method, longitudinal or shear ultrasonic waves are emitted by piezoelements. Ultrasonic waves propagate in a medium and are reflected at boundaries between a solid-lubricant or solid-air contact. The amplitude of the reflected or transmitted signal is decreased which contains information about the interface. Usually, ultrasonic waves are low power and elastic and the interface response is linear. However, when a high-amplitude ultrasonic waved is propagated in a linear or non-linear medium, or incident at an imperfect contact, the reflected or transmitted wave is distorted, and higher harmonics are generated. Some studies [1-4] showed the relevance of higher harmonics to the third order elastic constant in solids and pressure-density relationship in fluids. In the present work, the authors used a finite-amplitude method to measure the non-linear ultrasonic behaviour of a lubricant and related this to degradation. In this approach, high-power longitudinal waves propagate in the lubricant. The amplitude of fundamental frequency and second order harmonics were captured by the second transducer (receiver). A non-linear ultrasonic coefficient is then measured [1,2,5]: (1) where k is wavenumber, x distance between transducers (emitter and receiver), A 1 and A 2 are the amplitude of the fundamental frequency and 2 nd order harmonic. Eq. 1 can be represented considering only the amplitude of fundamental frequency and second harmonic [5]: (2) Four samples of lubricant were examined: fresh and degraded diesel engine oil Cat Deo 10W-30, fresh PAO 40 and fresh PAO 100. Table 1 shows the density and dynamic viscosity (measured using a rheometer TA Instruments Rheometer HR10) of the lubricants. Table 1: Density and dynamic viscosity of the lubricants. Lubricant Density (g/ m 3 ) Dynamic Viscosity (Pa. s) at Temperature 25 Degraded Cat Deo 10W-30 0.86 0.122 Fresh Cat Deo 10W-30 0.86 0.146 Fresh PAO 40 0.85 0.765 Fresh PAO 100 0.85 2.92 Fig. 1 compares the variation of nonlinear coefficient β′ with the distance between the transducers. The distance between the transducers is classified as near field and far field. In the near field, β′ is less sensitive to the variation of density and viscosity of the lubricants. For example, although the viscosity of degraded and fresh Cat Deo 10W-30 are varied, β′ cannot distinguish the difference. However, it was observed in the far field (specifically at the distance longer than twice the near field), β′ is clearly dependent on the viscosity of the lubricant. As the viscosity of the lubricant decreases, β′ increases. However, 352 23rd International Colloquium Tribology - January 2022 Application of the Non-linear Behaviour of Longitudinal Ultrasonic Waves in Lubricants Monitoring their densities are quite similar, and a densitometer hardly can measure the difference. This method has the potential to be used in the on-line measurement of degradation of the lubricants. Figure 1: Variation of β′ of the lubricats with the distance. References [1] A. Hikata, B.B. Chick, C. Elbaum, Dislocation contribution to the second harmonic generation of ultrasonic waves, J. Appl. Phys. 36 (1965) 229-236. https: / / doi.org/ 10.1063/ 1.1713881. [2] K.E. Van Den Abeele, Elastic pulsed wave propagation in media with secondor higher-order nonlinearity. Part I. Theoretical framework, J. Acoust. Soc. Am. 99 (1996) 3334-3345. https: / / doi.org/ 10.1121/ 1.414890. [3] R.T. Beyer, Parameter of Nonlinearity in Fluids, J. Acoust. Soc. Am. 32 (1960) 719-721. https: / / doi. org/ 10.1121/ 1.1908195. [4] R.T. Beyer, The parameter B/ A, in: M.F. Hamilton, D.T. Blackstock (Eds.), Nonlinear Acoustics, Academic Press, 1998. [5] C. Pantea, C.F. Osterhoudt, D.N. Sinha, Determination of acoustical nonlinear parameter β of water using the finite amplitude method, Ultrasonics. 53 (2013) 1012-1019. https: / / doi.org/ 10.1016/ j.ultras.2013.01.008. Rheology 23rd International Colloquium Tribology - January 2022 355 Observation of Grease Flow by Particle Image Velocimetry Haruka Iki Lubricants R&D Dept., ENEOS Corporation, Yokohama, Japan Department of Mechanical Engineering, Graduate School of Engineering, Kanto Gakuin University, Japan Kazumi Sakai Lubricants R&D Dept., ENEOS Corporation, Yokohama, Japan Reo Miwa Department of Mechanical Engineering, Graduate School of Engineering, Kanto Gakuin University, Japan Ryosuke Sato Department of Mechanical Engineering, Graduate School of Engineering, Kanto Gakuin University, Japan Norifumi Miyanaga Department of Mechanical Engineering, Graduate School of Engineering, Kanto Gakuin University, Japan 1. Introduction Grease characteristics are one of the most important factors that determine performances of rolling bearings. For example, it is known that bearing torque is influenced by grease flow on raceways as well as by viscosity of the base oil[1]. Furthermore, bearing noise is occurred when the thickener passing over the raceway and homogeneous dispersion of thickener is indispensable for effective noise reduction in bearings[2]. Thus, it is important to understand the flow properties for grasping the bearing performance and designing grease formulation logically and efficiently. Sakai et al. [3], visualised grease fluidity and large scale distribution in ball bearings by neutron imaging technology. However, there are few methods that could reveal grease microscopic behavior on raceways, and consequently it is difficult to grasp the complicated behavior of grease accurately. Therefore, in this study, using Particle Image Velocimetry (PIV), the observation method of flow property was established and the difference in grease flow depending on the thickener type was investigated. 2. Methodology PIV is an optical method of flow visualizations. Tracer particles are added in fluids, and speed and direction of the flow are calculated from the motion of tracer particles. Fig.1 shows the schematic image of experimental device used in the PIV analysis. By using a ball-on-disk type lubrication tester (steel ball and glass disk), the flow of grease was observed by taking pictures from above the disk with a high-speed camera after ball passing. Tested greases were composed of poly-α-olefin as base oil and urea-based thickeners. As for the urea-based thickeners, different types of thickeners -alicyclic, aliphatic (C8, C18)were also examined. 3. Results and discussion By the PIV method, grease flow towards outside of the raceway and flow back on the raceway after ball rolling were observed. Furthermore, aliphatic urea greases adhered less and were actively flowing on the raceway, whereas the flow of the alicyclic type was slow when the rotation speed is low. These results suggest that the grease flow strongly depends on the thickener type and that these differences affect bearing performance. References [1] M. Nitta, T. Tsuda, H. Arai, K. Sakamoto and K. Sakai, “Effect of Transition Point of Viscoelasticity of Diurea Grease and Molecular Structure of Thickner on Running Torque of the Ball Bearing” Tribologist, 61, 10 (2015) 699-708. [2] K. Matsubara, D. Dong and T. Endo, “Low Noise Greases for Bearings”, NLGI Spokesman, 72, 6 (2008) 25-34. [3] K. Sakai, Y. Ayame, Y. Iwanami, N. Kimura and Y. Matsumoto, “Observation of Grease Fluidity in a Ball Bearing Using Neutron Imaging Technology”, Tribology Online, 16, 2 (2021) 146-150. 356 23rd International Colloquium Tribology - January 2022 Observation of Grease Flow by Particle Image Velocimetry Fig. 1: Schematic of experimental device 23rd International Colloquium Tribology - January 2022 357 High pressure, high shear viscometry - Lubricant characterization for highly loaded contacts Lukas Mebus Institute for machine elements and systems engineering, RWTH Aachen University, Aachen, Germany Corresponding author: Lukas.mebus@imse.rwth-aachen.de Georg Jacobs Institute for machine elements and systems engineering, RWTH Aachen University, Aachen, Germany Clément Larriere TotalEnergies, OneTech, Centre de Recherches de Solaize, France Arnaud Riss TotalEnergies, OneTech, Centre de Recherches de Solaize, France Jonathan Raisin TotalEnergies, OneTech, Centre de Recherches de Solaize, France Florian König Institute for machine elements and systems engineering, RWTH Aachen University, Aachen, Germany 1. Introduction Lubricants play a major role in reducing friction and preventing wear inside various applications. In general, these phenomena are responsible for yearly losses equalling up to 5% of the gross domestic product [1]. Tribological optimization has been identified as one possibility to reduce friction and wear of tribological systems, with a potential avoidance of up to 40% of these losses over the next years [2]. Whilst significant attention has been given to the optimization of lubricants for common applications like internal combustion engines, upcoming applications have to be considered as well. The challenge for both common and upcoming applications remains the same: Reduction of friction of moving surfaces without the increase of wear by using lubricating oils. They, on the one hand, separate the contact bodies from each other and, on the other hand, ensure minimum frictional losses in the tribological system. For this a lubricant is chosen based on the lubricant’s properties, mainly the viscosity, and its dependency on the applied strains inside the contact. The viscosity is measured in so called viscometers, which can be divided by concept into falling body, capillary, rotational or quartz viscometers. However, these viscometers are currently not able to recreate the simultaneous acting lubricant strains of pressures up to 3 GPa, shear rates up to 10 6 s -1 and temperatures up to 150°C, which are commonly observed for example in gearboxes and roller bearings in E-Mobility drive trains [3,4]. Hence, to this date, additional component and system level test are necessary for a sophisticated lubricant evaluation and selection. To solve this problem, a new viscometer has been developed at MSE, which is presented in this work. It is capable of measuring the viscosity under simultaneous application of pressure, shear and temperature leading for better understanding of lubricants and an improved application oriented lubricant selection. 2. Material and method 2.1 High pressure high shear viscometer The new viscometer concept for high-pressure and highshear developed at MSE is shown in Figure 2-1. This viscometer uses a rotational viscometer concept with a rotating inner cylinder, a so-called Searle-type viscometer. The viscometer is composed of the electrical drive, viscometer stator and rotor, velocity sensor, temperature sensor and torque sensor. In between viscometer stator and rotor, the measurement gap forms with a defined gap width. For shear rate adjustment the rotational speed of the motor or the gap width can be adjusted. This setup is submerged in a lubricant specimen and inserted into the pressure chamber during the measurement. For proof of concept a prototype viscometer was built and tested inside an existing high-pressure test rig capable of pressures up to 800 MPa. Based on the positive results of the prototype a new High-Pressure-High-Shear (HPHS)-vis- 358 23rd International Colloquium Tribology - January 2022 High pressure, high shear viscometry - Lubricant characterization for highly loaded contacts cometer using the same concept was developed. With this, measurements under conditions similar to the effective lubricant strains inside tribological contacts can be conducted. Figure 2-1: Schematic presentation of viscometer con-cept 2.2 Measurement procedure For measurements, the pressure vessel is heated below the desired measurement temperature to enable the compensation of viscous heating due to fluid friction during the measurement. Afterwards, the viscometer is inserted into the vessel and is allowed to heat up to the pressure vessel temperature. As soon as the temperature is equalized, a pressure is applied and the electrical motor is started. During measurement, the inner cylinder is rotating shearing the pressurized lubricant inside the measurement gap leading to a measurable torque at the torque sensor. In combination with the temperature measurement at the measurement gap and the velocity measurement of the viscometer rotor the necessary data for viscosity determination is generated. 2.3 Evaluation Based on the results of the viscometer the dynamic viscosity of the specimen is calculated with the generalized Newtonian fluid model . For calculation, the measured torque is converted into the applied shear stress based on the geometry of the measurement gap. To calculate the correct viscosity only the torque produced inside the measurement gap has to be considered. Therefore, a Computational Fluid Dynamics (CFD-) simulation is used to obtain a correction factor to reduce the measured torque to the torque generated inside the measurement gap. This factor is comparable to the correction factor applied by known viscometer standards e.g. DIN EN ISO 3219-2 [5]. For this CFD model, a 120° wedge of the viscometer including parts of the housing were modelled and simulated. This wedge is chosen due to possible influences of the torque sensor on the measurement results and the torque sensor symmetry. The chosen wedge and the simulated fluid domain are shown in Figure 2 2. In addition to this the temperature influence of the sensor is compensated by measurement-based correction factor for each temperature. This approach’s advantage is a reduced amount of calibration measurements to determine the correction factor of the viscometer. Figure 2 2: CFD model generation from viscometer to fluid domain: viscometer (left), stator (center), surface of the fluid domain without solid-body structure (right) 3. Results The prototype viscometer, described in chapter 2.1-2.2 and evaluated via the methods described in chapter 2.3, is used as a reference for the HPHS Viscometer measurements. To ensure the validity of the results a comparison between results conducted in the prototype and a falling body viscometer is used, which is shown in figure 2-3. The measurements presented were conducted at a desired temperature of 60°C and shear rates of at different pressures levels between ambient pressure and 200 MPa. A mineral group III base oil with Newtonian behaviour was used for validation. The measurement data was compared with the results obtained in a high-pressure falling body viscometer at 60°C at various pressures. The prototype results show a good accordance to the trend of the falling body viscometer measurements, shown in Figure 2-3. In addition to this, the trend of the prototype measurements corresponds to the trend of the falling body viscometer accurately with an error over the complete pressure range < 2%. Comparison of deviations of the individual measurements shows a higher deviation (up to 10%) of the prototype measurements compared to the falling body viscometer measurements (up to 4.5%). This can be explained by the dynamic of the rotational viscometer compared to the gravity driven falling body viscometer. 23rd International Colloquium Tribology - January 2022 359 High pressure, high shear viscometry - Lubricant characterization for highly loaded contacts Figure 2 3: Measurement results of group III base oil 4. Summary and conclusion A performance evaluation of lubricants is necessary for selecting a suitable lubricant. The evaluation should be performed under realistic load conditions. For this purpose, a new rotational viscometer concept for lubricant characterization was developed. The viscometer concept has been prototyped and a new HPHS-viscometer was developed. For evaluation of the measurement results a new evaluation approach has been developed, based on CFD simulation and measurement results. The shown prototype results of the measured lubricant show good accordance compared to the measurements conducted with falling body viscometers, validating the prototype results. These measurements also show, that for this concept a further reduction of the deviation of individual measurements to < 5% is desirable for better measurement quality. This improvement in combination with the increased measurement range of the HPHS-viscometer leads to further understanding and quantitative description of lubricants under realistic operational conditions. 5. Acknowledgement The authors would like to thank TotalEnergies for the funding and support of this project. References [1] Czichos, H. , Habig, K-H.: Tribologie-Handbuch 4th edn., Springer Vieweg, Wiesbaden (2015). [2] Holmberg, K., Erdemir, A.: Influence of tribology on global energy consumption, costs and emissions. Friction 5(3): 263-284 (2017) [3] Morhard, B., Schweigert, D., Mileti, M. et al.: Efficient lubrication of a high-speed electromechanical powertrain with holistic thermal management. Forsch Ingenieurwes 85, 443-456 (2021). https: / / doi.org/ 10.1007/ s10010-020-00423-0 [4] Schröter, J., Jacobs, G., Straßburger, F.: Schnelldrehende Elektrische Antriebe für Bau- und Landmaschinen. Antriebssysteme 2015 : Elektrik, Mechanik, Fluidtechnik in der Anwendung ; Aachen, 11. und 12. November 2015 / VDI Produkt- und Prozessgestaltung, Seiten/ Artikel-Nr: 27-37. DOI: 10.18154/ RWTH-2015-06857 [5] DIN EN ISO 3219-2: 2021-08, Rheologie - Teil 2: Allgemeine Grundlagen der Rotations- und Oszillationsrheometrie (ISO 3219-2: 2021) Tribometry 23rd International Colloquium Tribology - January 2022 363 Investigation of Rolling and Lateral Slip on the MopeD Qs2STg500 (Modellprüfstand erster Designentwurf Querschlupf 2 Scheiben Testgerät 500 N) K.-O. Karlson Hochschule Mannheim, Kompetenzzentrum Tribologie Mannheim (KTM), Paul-Wittsack-Straße 10, 68163 Mannheim Corresponding author: k.karlson@hs-mannheim.de H. Buse Hochschule Mannheim, Kompetenzzentrum Tribologie Mannheim (KTM), Paul-Wittsack-Straße 10, 68163 Mannheim J. Molter Hochschule Mannheim, Kompetenzzentrum Tribologie Mannheim (KTM), Paul-Wittsack-Straße 10, 68163 Mannheim 1. Introduction As part of a publicly funded project (PFP) [1], the KTM developed a test bench for rolling slip tests. The primary use of the MopeD test bench is to record frictional forces with variable slip amount and direction settings. The theme of the PFP was to investigate the frictional forces and the cross slip of worm gears. 2. MopeD Mechanics, Drives and Applications To make the slip conditions in the test setup as variable as possible, the tribometer has five axes. Four of them are electromechanically controlled and one is operated manually. The sample geometry consists of two disks, which are in rolling contact with each other. There is one electric direct servo-drive for each sample disk. One linear axis moves the samples into contact and applies a normal force. To investigate the cross slip, there is an axis to set an angle for the vertical sample. Figure 1 shows the MopeD test bench. Figure 1: MopeD Qs2STg 500 test bench [KTM] The MopeD is able to log data for the applied load, the circumferential frictional force at each sample disk and the axial force at the vertical sample disk as shown in figure 2. The MopeD offers high sliding speeds, high normal force application, high sample-rates, an automatic angle adjustment and the capability to test large specimens. Table 1 lists some machine data of the MopeD. 364 23rd International Colloquium Tribology - January 2022 Investigation of Rolling and Lateral Slip on the MopeD Qs2STg500 Figure 2: Measurable forces at the samples Due to its design the MopeD can be utilised to analyse a multitude of systems, some of which are listed below: • For friction, wear and traction properties among others: Tires, drills, screws, planetary roller screw drives and fluids • General 2-Disk material and coating tests with pure to variable rolling slip together with superimposed cross slip Table 1: Operating data of the MopeD test bench Value Unit Maximum normal force F N 500 N Typical pressure with spherical disk with R = ∞ and r = 26.5 mm; pmax 1240 Maximum sliding speed at the vertical sample disk v vsd 7 Maximum sliding speed at the horizontal sample disk v hsd 19 Adjustable swivel range for the vertical sample disk α 180 ° 3. Traction - and wear curves of Tires Two different kinds of rubber as tires are tested to determine the wear amount. In addition, the influence of the wheel load is measured to show variations in wear behavior due to weight differences in combustion engine and electrical engine cars. The tests have shown that the difference of the wear mass between the model tire and the PU tire amounts to 94 %. In addition, experiments with 10 N normal force have shown that there is a variance in the type of wear between the model and the PU tire. The PU tire has much finer particles than the model tire. Figure 3 shows both tires after their test runs. Figure 3: Model and PU tire after the tests Testing different wheel loads (15/ 20 N) has shown that the torque at the tire is increasing and a larger amount of wear particles is detectable. In this case, it makes sense to think about, how we can reduce the mass of a vehicle and its batteries. Figure 4: Tests with zero slip, various forces, and various materials In order to assess the toxicology of the wear particles, it is planned to count the particles with a scattered light sensor and to collect them, fractioned according to size, in a cascade impactor. After the fractionated collection of the particles, there could be a toxicological study to investigate the environmental impact of different rubber compounds. 4. Lubricated 2-Disk Setup For testing lubricants, the 2-Disk test bench by Optimol-Instruments has been the method of choice. The samples for this test, two disks with a typical diameter of 45 mm, are pressed against each other, forming a linear contact under rotation. Additionally spherical discs can be utilized in order to create a point contact if higher contact pressure is desired during testing. The contact is on the shell surface of the two disks [2]. Similar to the classic 2-Disk test we conducted a feasibility study on the MopeD. 23rd International Colloquium Tribology - January 2022 365 Investigation of Rolling and Lateral Slip on the MopeD Qs2STg500 During this study a spherical, vertically arranged disk is pressed on a horizontally fixed disk as shown in figure 5. Figure 5: Lubricated 2-Disk-Setup Figure 6: Angular COF-Data of a 2-Disk test During the test the normal force is 230 N (911 MPa) and the slip is changing linearly from 0 to 20% and then to -20 %. The system remains at the positive and negative slip extremes for 8 minutes each before alternating back for a test total runtime of 40 hours. Furthermore, the oil (Klübersynth GEM 4320N) temperature is set to 60 °C. The contact surfaces of the samples are sanded until an average roughness depth of 3 ± 10 μm is achieved. Figure 6 shows the amount and the direction of the friction coefficient of the vertically arranged disk in relation to the circumferentialand the axial-force as a distribution histogram. This visualization shows that the most commonly measured COF lies around 0.05. Future studys will also use an additional lateral slip to investigate different materials and lubricants. References [1] Panther GmbH, Hochschule Mannheim Kompetenzzentrum Tribologie, Förderzeichen: ZF4008703, Mannheim, 2020. [1] M. Grebe, Tribometrie, Tübingen: expert verlag GmbH, 2021. 23rd International Colloquium Tribology - January 2022 367 The use of the MTM rig for wear testing Matthew Smeeth PCS Instruments, London, UK Corresponding author: matt.smeeth@pcs-instruments.com Clive Hamer PCS Instruments, London, UK 1. Introduction The wear rate of any lubricated contact is dependent on many factors, including, surface roughness, lubricant composition, environment, operating conditions, temperatures, etc. There are also many different wear mechanisms, often operating in parallel. Since wear in itself is not an intrinsic property of a system, different wear tests can give very different results. Despite their popularity and widespread use, all wear bench test methods all have some shortcomings when used to investigate complex lubricant additive combinations. However sophisticated the test method, they are inevitably unable to directly mimic real lubricated contacts conditions of machine elements. Interpretation of different bench test results can be difficult and misleading conclusions can sometimes be drawn. A new pure sliding wear test is described which can produce measurable wear withing a reasonable period of time. The repeatability and merits of the test method is discussed. 1.1 Background The thickness and distribution of reaction layers formed by ZDDP and other antiwear additives is controlled by several factors including load, temperature, sliding speed and additive concentration. Invariably, the thickness formed will increase at higher temperatures and higher pressures The chemical antiwear film formed between running surfaces is complex in composition and has been examined using a large number of different analytical techniques; however the exact mechanism by which they form is still not clearly understood. Spikes et al (1,2) and others has showed that antiwear additives form a film which is initially an amorphous glassy structure, which then converts to a nanocrystalline structure during prolonged rubbing. The nanocrystalline structure is relatively weak in comparison to the more crystalline structures, since they inherently possess greater obstruction to dislocation movement For this reason, short wear tests must be very carefully controlled, since the running in period at the start of the test (when the antiwear film is initiated) is critical. Cleanliness and complete lack of contamination is also critical, since this can adversely affect the repeatability of the test. Conversely, longer tests are less susceptible to these variations but obviously suffer the (considerable) disadvantage that the duration may be excessively long, to the point where gathering and meaningful amount of reliable test data is impractical. 1.2 Test procedure A series of tests were carried out using the MTM test rig under the following conditions Configuration Pure sliding, reciprocating Lower specimen 52100 steel disc, 760Hv Upper specimen 52100 steel ball, 3mm diameter, 800Hv Load 20N (2.74 GPa max Hertzian pressure) Temperature 100°C Frequency 20 Hz Stroke length 4mm Duration 16 hours Table 1: Test conditions A pure sliding test was chosen since the wear rate was relatively high. This allowed the wear scar formed on the ball to be measured as the primary wear indicator. Although mixed sliding and rolling wear tests have been carried out in previous studies the wear rates are considerably lower and have therefore required additional instrumentation to fully evaluate the wear. Using the reciprocating mechanism allowed a measurable wear track to form on the disc. Over the 16 hour period, 1.15 million contact cycles were run, which produced an easily measurable and clearly defined wear scar for all the fluids tested. 368 23rd International Colloquium Tribology - January 2022 The use of the MTM rig for wear testing Figure 1: Typical wear scar showing clearly defined boundary 1.3 Test fluids A group 2 mineral base oil with various concentrations of antiwear additive was tested. The viscometric properties of the base oil are shown below KV 40V 67.3 cSt KV 100C 8.8 cSt VI 103 Table 2: Base oil properties Different concentrations of the same additive was used in the base oil. 1.4 Results The graph in figure 2 shows the average wear scar dimension, taken as the average of the sliding the orthogonal direction. In all cases the wear scar boundary was clearly defined and repeat measurements were always within 20 microns of each other. The results are presented as the wear scar diameter as a function of P content. Figure 2: Variation of wear scar with blend P content Measurements were also taken of the disc using a while light interferometer, which can be used to calculate the wear volume lost during the test. The discs from 3 tests at different concentrations were measured and showed excellent correlation with the wear scar measured on the ball. As expected, relatively low concentrations of additive showed lower wear with a relatively smooth transition between the high and very low additive concentration regions The initial results indicated that the wear test was highly repeatable. To investigate this further, a series of tests were carried out on a commercial 0w-20 engine oil with the following properties Moly 60 Zinc 710 Phosphorous 633 Calcium 1344 Boron 250 Table 3: Formulated oil composition The test was very repeatable with a mean wear scar of 325 microns and standard deviation of 7 microns, shown in figure 3. 23rd International Colloquium Tribology - January 2022 369 The use of the MTM rig for wear testing Figure 3: Repeat wear scar measurements on formulated oil sample 2. Conclusion The test showed that a highly repeatable wear test could be carried out over a reasonable time scale. The test was proven to be robust using both base oil/ individual additive mixtures and fully formulated blends. The tests were carried out on Ph and Zinc containing oil,s but can be used as base line tests for ashless and other novel antiwear chemistries as a compassion. References [1] Luiz, J.F., Spikes, H. Tribofilm Formation, Friction and Wear-Reducing Properties of Some Phosphorus-Containing Antiwear Additives. Tribology Letters 68, 75 (2020) [2] Spikes, H. The History and Mechanisms of ZDDP. Tribology Letters 17, 469-489 (2004) 23rd International Colloquium Tribology - January 2022 371 Tribological Assessment of Marine Distillate Fuels under a variant HFRR Method Theodora Tyrovola Laboratory of Fuels and Lubricants, Chemical Engineering Department, National Technical University of Athens. Corresponding author: theodoratirovola@gmail.com Fanourios Zannikos Laboratory of Fuels and Lubricants, Chemical Engineering Department, National Technical University of Athens. 1. Introduction: Negative Environmental Effect of Maritime Industry Maritime transport consists an integral part of global economy, as it accounts for around 80% of worldwide trade. Per mass of cargo and per distance travelled, ships are the most energy efficient means of transportation. In recent years thought, the consumption of large amounts of fossil fuels has turned shipping industry into an emerging source of greenhouse gas emissions and a growing source of air pollution. In the context of the massive effort to reduce hazardous pollutants from maritime transport and improve air quality, the environmental regulations adopted by the International Maritime Organization (IMO) on 1 January 2020 in Annex VI of MARPOL73/ 78 convention (Marine Pollution), pose stricter limitations on sulphur oxide (SOx) emissions from ships. The IMO2020 rule limits the sulphur content of the fuel used on board ships either operating outside designated emission control areas (ECAs) to 0.50% m/ m or within ECAs to 0.10% m/ m -. IMO aims to mandate cleaner-burning fuels at sea by 2020 and to curb greenhouse gas e1missions (GHG) from ships by 2050. With the ever-changing technology in shipping industry, the fuel that is used to run marine engines is also changing rapidly. Stakeholders now focus on inherently low or zero sulphur marine gasoils (MGO) and predominantly to marine distillates (DM), in order to achieve compliance with the Sulphur Cap 2020. 2. Low-Sulphur Marine Gasoils 2.1 Tribological Properties of Marine Distillates Marine distillates carry five per cent more energy per unit volume than high sulphur fuel oil and require no major up-front investment nor costly modification or retrofitting of the vessel. Distillates are considered the most viable solution to date; however, they are accompanied by a huge range of side effects related to their storage, combustion, ignition and lubricity. Marine engines are basically compression ignited twoand four-stroke diesel engines. The operation of the vessel’s fuel injection system (pumps, injectors, etc.) depends directly on the lubricating capacity of the fuel. Marine distillates undergo a refining process (desulphurisation), where apart from sulphur and nitrogen compounds, a significant proportion of oxygenated and polyaromatic (polar) compounds, are removed. Loss of the polar compounds is considered to be responsible for the limited tribological abilities of low sulphur marine gasoils. The new desulphurized fuels are interwoven with a high decline in the engine’s lubricating properties, leading to excessive wear and scarring on the engine’s components. 2.2 High Frequency Reciprocating Rig (HFRR) Test The lubricating capacity of marine distillates is determined by the High Frequency Reciprocating Rig (HFRR) test according to ISO 12156-1 and ASTM D6079 international standards. The parameters of HFRR test method simulate marginal lubrication and welding wear conditions. Lubricating capacity is determined by measuring the wear scar diameter, expressed in micrometers (μm). For all seven types of distillate marine fuels, according to ISO 8217: 2017 fuel standard, the maximum limit of wear scar diameter (WSD) is 520 μm [1] . HFRR test consists the global standard for the lubricity assessment of automotive diesel fuel, providing high-precision results. It was established when ultra-low sulphur diesel (ULSD) fuels became the common type of diesel, used in automotive diesel engines in the mid-2000s. Lubricity is of paramount importance when operating in low-sulphur marine gasoils, nevertheless is not yet sufficiently understood in the marine sector. After the implementation of the IMO2020 sulphur regulation, more and more insufficient knowledge and inaccuracies related to lubricity, came to light. 3. Measurement and Evaluation of Wear In order to increase the sensitivity and accurateness of HFRR over marine distillates, we rely firstly on the basic parameters of ISO 12156-1 standard and subsequently on the modification of them. The modification of the basic parameters of ISO 12156-1 is made so as to identify the poor lubricating capabilities of low-sulphur marine 372 23rd International Colloquium Tribology - January 2022 Tribological Assessment of Marine Distillate Fuels under a variant HFRR Method gasoils and to track wear on the metallic parts of the engine’s equipment that cannot be detected by the original method. Base Fuels: 1. Distillate marine DM 1 (grade DMA): Fuel’s properties comply with EN ISO 8217: 2017. 2. Distillate marine DM 2 (grade DMA): Fuel’s properties comply with EN ISO 8217: 2017. Properties of both fuels are similar. The sulphur content in DM 1 is 900 ppm and in DM 2 is 850 ppm. Case 1: Following the test conditions of HFRR method as determined in ISO 12156-1. An upper spherical specimen (test ball) with 6 mm diameter is subject to reciprocating motion, with frequency of 50Hz and oscillation width of 1mm, with the help of an electromagnetic oscillator. The spherical specimen is tangent to a flat specimen under a weight of 200 g while the point of contact is immersed into 2 ml of the tested fuel. The fuel is preheated to 60°C and the test lasts 75 minutes. The test ball is grade 28 (G28) according to ISO 3290 of steel ISO 683-17-100Cr6. It has a Rockwell Hardness “C” scale (HRC) number of 58 to 66 according to ISO 6508-1 [2] . Case 2: Altering only the load imposed on the spherical specimen and keeping all the rest parameters unchanged. The permissible load that HFRR PCS Instruments device (mechanical unit) can bear is 1000g. Wear diameter is measured per 100 grams added, starting from the base load (200g). Case 3: Altering both the imposed load and the type of the upper specimen (test ball). The modified test ball is grade 25 (G25). It has a Rockwell Hardness “C” scale (HRC) number of 55 to 60. The spherical specimen meets the requirements of ASTM D7688, ISO 12156-1, ASTM D6079, CEC F-06-A, EN 590, JPI-5S-50 & IP 450. Wear diameter is measured per 100 grams added, starting from the base load (200g). Table 1: Wear Scar Diameter with variable load. Table 2: Wear Scar Diameter with variable load and variable test ball. Diagram 1: Wear Scar Diameter vs Imposed Load (*mod: modified test ball type) Under no modification both fuels have excellent tribological properties. The imposed load can challenge the efficacy of marine distillates. By keeping all parameters immutable, only changing the load and always taking into account the repeatability R & r of the method, there is a slight but significant limitation in fuel’s lubricity. Τhe replacement of standard specimens with mοre sensitive and vulnerable to reciprocating motion, reveals an increased wear on their surfaces, which eventually leads to excessive friction. Τhe most significant increase in wear scar diameter occurs when both load and upper specimen are altered. When using the more vulnerable and less hard upper specimens, as soon as the imposed load increases, wear scar diameter is maximized. When increasing the load, wear in DM 2 is remarkably substantial than the corresponding one in DM 1 . This finding indicates that as sulphur content diminishes it induces lack of lubricity and consists a prominent factor for the malfunction of fuel’s injection system. 4. Conclusion: The Next Step in Lubrication Assessment Poor lubricating capacity may result in blocking fuel lines, damaging fuel pumps, injectors and even contribute to the loss of engine power (LOP), but it is not the only factor that provokes a failure. Great and thorough 23rd International Colloquium Tribology - January 2022 373 Tribological Assessment of Marine Distillate Fuels under a variant HFRR Method research must be done so as to identify sources of variability in the HFRR test method and to improve its precision to marine distillates, in order to avoid future breakdowns [3] . The need to establish an innovative perspective on the evaluation of the lubricating capacity of such fuels is imperative, since the already existing equipment might be unsatisfactory for protecting naval fuel systems. References [1] Petroleum Products-Fuels (Class F)-Specifications of Marine Fuels, International Standard ISO/ FDIS 8217: 2017. [2] Diesel Fuel-Assessment of Lubricity using the high-frequency reciprocating rig (HFRR)-ISO/ DIS 12156-1: 2018. [3] Nikanjam M. and Rutherford J.,“Improving the Precision of the HFRR Lubricity Test”, SAE 16- 10-06. 23rd International Colloquium Tribology - January 2022 375 Conductive Layer Deposits and the Development of Bench Test Technology for Electric Vehicle Drivetrains Greg Miiller, John Bucci Savant Group, Midland, MI, United States Gunther Mueller, Rico Pelz APL, Landau, Germany Timothy Newcomb Lubrizol, Wickliffe, OH, United States 1. Introduction The EV industry is continuously evolving with new technologies leading the way for improved lubricants. Both electric and hybrid vehicles, with various types of drivetrain designs, are operating around the world under diverse conditions. As real-world experience accumulates, opportunities to increase efficiency and improve reliability are being revealed. One such opportunity to improve reliability involves enhanced protection of the electric motor and electronics from corrosion. One way to accomplish this is through enhancing the protection provided by the lubricant. However, the current tests employed to assess this key lubricant characteristic were designed with mechanical parts in mind, not electric motors and electronics. To ensure improved reliability of electrified hardware, new methods are needed. This paper describes the development of two such tests designed to address this challenge. 1.1 Deposit Tests Electric motor burn out has occurred from time to time in electrified vehicles, some of which have been caused by the accumulation of conductive corrosion byproducts formed around the motor coils. In addition, electric sensors occasionally malfunction due to corrosion of wires or contacts. In these cases, the lubricants in use were believed appropriate to the application as all performed well in versions of the ASTM D130 “Standard Test Method for Corrosiveness to Copper from Petroleum Products by Copper Strip Test.” Clearly a more robust assessment of the corrosion protection, more attuned to electrified hardware, is needed. To help resolve this, a group of industry experts gathered from across the globe to develop a bench test to predict the potential to form conductive deposits. Corrosion is the chemical process that converts metal into oxides, hydroxides, carbonates or sulfides. Though the copper wires of the electric motor windings are insulated with a polymer film, the integrity of the insulation can be compromised allowing contact with the lubricant. In addition, not all metal connections from the electric motor to the power supply are insulated, nor are all the electrical connections within other electrical devices. Corrosion can lead to the removal of metal leading to an open circuit. The corrosion process itself can vary nonuniformly with temperature. A test has been developed, the wire corrosion test (WCT), to determine the rate of corrosion and copper depletion over time in both solution and vapor states [1]. Whereas removal of copper can lead to a failure through the creation of an open circuit, a failure caused by the formation of solid corrosion byproducts, conductive deposits, can be a bit more traumatic. These deposits can provide a new electrical path, essentially enabling the shorting of the electric motor leading to thermal runaway ending in motor burn out. A test to specifically determine this risk is needed. Several examples of such tests have been presented at various industry meetings. The conductive deposit test (CDT) described here assesses the formation of conductive deposits forming from the chemical reaction of the lubricating fluid and copper. It operates at elevated temperatures under low voltage electrified conditions and evaluates the tendency of deposits to form in both the solution and vapor states. In actual electric drive units (EDUs), where the lubricant led to failures attributed to electrical short circuits, deposit formation started within smaller spaces, typically within crevices around the mounting sections and gaps around the electric motors. To mimic these confined spaces, the test uses stacked uncoated circuit boards with repeatable spacing between the copper traces. A voltage of 5 vdc is placed onto the traces and monitored, via resistance, over time. Because the reaction with the lubricant and ensuing deposit formation is different between the solution and vapor in the powertrain, they are also separated in this test. Each are tracked independently ensuring the capture of a failing condition. A diagram of the test board is shown in Figure 1. To ensure the test was applicable to EDUs in real world operation, two lubricants associated with real field fail- 376 23rd International Colloquium Tribology - January 2022 Conductive Layer Deposits and the Development of Bench Test Technology for Electric Vehicle Drivetrains ure were selected as bad references. Lubricants used to replace these, that is correct the field problems, were selected as good references. Though 150°C was selected as the standard setpoint to encourage failure, consideration has been taken so that this equipment can ramp potentially from a lower temperature around 130°C and include temperature spikes up to 160°C if desired (full range is room temperature to 180°C). Figure 1 Figure 2: Field Failing Fluids The test results are shown in Ohms, which is a measurement of the resistance naturally occurring within the copper traces. If the traces on the test board are bridged by conductive deposits, the resistance will decrease, ultimately resulting in a short circuit in the extreme case. Figure 2 shows the results of the two bad reference lubricants. The results are indicative of what occurred within the motor windings and ensuing failure. These have been reproduced on multiple units with several laboratory operators. Passing oils show no such degradation. The test can potentially operate for as long as 1000 hours but efforts to shorten this timeframe are showing promise with failures routinely observed at 650 hours or less. Repeatability for the apparatus has been less than 16% of the mean and in most cases less than 8% of the mean. 2. Conclusion Failures have been shown in EV motors relating to corrosion and the formation of conductive deposits. Tests have been developed in the form of a conductive deposit test (CDT) and a wire corrosion test (WCT). Research shows that the mechanism for failure between the lubricant and vapor states can be different. Therefore, both lubricant and vapor states are assessed within these tests for accuracy reasons. Both tests have proven to be effective in predicting these failure modes. The separation between passing and failing fluids is evident and proven. References [1] Hunt, G., “New Perspectives on Lubricant Additive Corrosion: Comparison of Methods and Metallurgy”. SAE Technical Paper 2018-01-0656, 2018. 23rd International Colloquium Tribology - January 2022 377 Tribological simulation of Friction Torque Test using SRV and EHD tribometer - A new approach for performance evaluation of energy efficient engine lubricant Rameshwar Chaudhary Indian Oil Corporation Ltd., R & D Centre, Faridabad, India Inder Singh Indian Oil Corporation Ltd., R & D Centre, Faridabad, India Punit Kumar Singh Indian Oil Corporation Ltd., R & D Centre, Faridabad, India S. Bhadhavath Indian Oil Corporation Ltd., R & D Centre, Faridabad, India Dr. S. Seth, R. Mahapatra Indian Oil Corporation Ltd., R & D Centre, Faridabad, India Corresponding author: mahapatrar@indianoil.in M. Sithananthan Indian Oil Corporation Ltd., R & D Centre, Faridabad, India A.K. Harinarain Indian Oil Corporation Ltd., R & D Centre, Faridabad, India Dr. P. Bhatnagar Indian Oil Corporation Ltd., R & D Centre, Faridabad, India Dr. D. Saxena Indian Oil Corporation Ltd., R & D Centre, Faridabad, India Dr. SSV Ramakumar Indian Oil Corporation Ltd., R & D Centre, Faridabad, India 1. Introduction This present study describes this approach to evaluate the frictional losses under hydrodynamic losses and boundary regimes of lubrication under simulated conditions present in IC Engines, and also validating it with a friction torque test in an engine configuration. Fuel efficient low viscosity candidate oil of 0W16 viscosity grade offering better fuel efficiency and long life was selected and compared against an industry reference product for the studies. A friction torque test (FTT) was carried out in a motorized gasoline engine under a wide range of speeds and lubricant temperatures. For validation of FTT results, simulated tribo tests under different regimes and conditions existing in the engine using EHD film thickness test apparatus and SRV tribometer were conducted. The frictional property under different lubrication regimes experienced in engine components was mapped in these simulated tribo tests. The EHD film thickness apparatus confirmed the fuel economy benefit on account of lower viscometrics simulating the FTT test result. However, the standard test protocol in SRV could not discriminate the oils in terms of coefficient of friction, therefore an extended test in SRV was carried out to find the wear track. Not only the wear volume with candidate oil was found to be lower than the reference oils, but also during the long duration test the friction coefficient was found to be significantly lower than the reference oils due to activation of surfaceactive additives. The results with the developed test protocol correlates well with the FTT test result with candidate oil showing lower friction in both hydrodynamic and boundary regimes as experienced in 378 23rd International Colloquium Tribology - January 2022 Tribological simulation of Friction Torque Test using SRV and EHD tribometer an engine configuration. Besides, lower wear volume in a long duration SRV test with candidate oil is expected to provide a better durability characteristic as compared to reference oil of same viscometrics. 2. Experimental Detail The comparative viscometrics of the candidate oil A visà-vis another candidate oil B and industry reference oil C is given below in Table 1. A full FTT test carried out under a wide range of speed and lubricant temperature showed lower friction torque with candidate oil A w.r.t. candidate B and reference oil C. Further, Tribo tests were carried out using SRV tribometer and EHD interferometry based film thickness test rig to investigate the friction and wear reduction capability of the candidate oil A visà-vis Oil B and Oil C of same viscosity grade. Table 1: Comparative viscometrics of the oils. Properties Candidate Oil A Candidate Oil B Reference Oil C K.V@ 100°C, cSt ASTM D 445 7.27 6.58 6.65 K.V@ 40°C, cSt ASTM D 445 34.14 28.15 25.95 VI ASTM D 2270 185 208 232 A) EHD Film thickness system The EHD interferometry based tribometer measures film thickness in the EHL contact formed between a 3/ 4 inch steel ball and a rotating 100 mm diameter disc. Tests were carried out at 10N and 20N load which corresponds to a contact pressure between the ball and disc of approximately 0.4 and 0.5 GPa respectively. The lubricant film thickness is measured by optical interferometry. B) SRV test Two test specimens (e.g., a cylinder and disk) are installed in the test chamber and pressed together with a specified normal force. The top specimen oscillates on the bottom specimen. Friction force is continually measured by a sensor. This test gives an indication of the boundary film forming tendency or lubricity of the lubricating oil under a simulated contact geometry 3. Result and Discussion EHD film thickness measurements have been done of the three candidates’ oils at two different temperatures 40 °C and 100 °C (Refer Fig.1 and Fig.2). These test conditions cover the range of temperature, load, and speed of the FTT. The oil film thickness increases with increase in speed and decrease in oil temperature and follows Stribeck curve. There is a significant difference in film thickness with the 3 oils with oil A giving lowest film thickness. This clearly indicates that due to lower viscometrics, high VI and suitable additive chemistry of oil A, the film thickness is lowest which will give lowest churning loss in hydrodynamic regime resulting in fuel efficiency for the engine components such as main and crank shaft bearing working in hydrodynamic regimes. Fig. 1: EHD Results at 10N load Fig. 2: EHD Results at 20N load Fig. 3: SRV friction trace in extended endurance test SRV test to measure the friction coefficient was conducted on the 3 oils using line contact (cylinder on flat steel 23rd International Colloquium Tribology - January 2022 379 Tribological simulation of Friction Torque Test using SRV and EHD tribometer disc) geometry at 400 N, 90 0C, for 45 minutes as per standard test condition. During the 45 minutes test, there was no difference in frictional behaviour of the oils. However, when the test was further extended for 2 hours to find out the wear track and to check whether there is any difference in the friction behavior a significant difference in friction coefficient was found as shown in Fig. 3. As shown in the figure, an interesting finding was observed with candidate oil A giving lower coefficient of friction as compared to oil B and C during the extended test. This may be because of the activation time required for the activation of surface-active additives. Further, the wear volume of worn part of cylinder after test was calculated. The results of cylinder worn volume along with the wear image of cylinder wear is shown in Fig.4. These results clearly indicate that the candidate oil A is having good frictional characteristics under boundary regime and is expected to give fuel efficiency for engine components working in boundary and mixed lubrication regime. Fig. 4: Wear volume of worn-out cylinder 4. Conclusions • Standard short duration test in SRV tribometer could not differentiate the candidate oil from the reference oils. However, the extended test could clearly differentiate the oils showing lower coefficient of friction and lower wear volume with candidate oil A vis a vis oil B and oil C. • The tribological test result with the developed test protocol is correlating the FTT test result with candidate oil A showing lower friction in both hydrodynamic and boundary regime due to the lower viscometrics along suitable additive chemistries. • Further lower wear volume in long duration SRV test with candidate oil A is in correlation with the lower COF and the oil is expected to provide a better endurance compared to oil B and C. References [1] Holmberg, K.; Andersson, P.; Erdemir, A. Global energy consumption due to friction in passenger cars. Tribol. Int. 47(0), 221−234, 2012. [2] Spikes, H.A.: Friction modifier additives. Tribol. Lett. 60, 5(2015). [3] Kenbeek D, Buenemann T, Rieffe H. Review of organic friction modifiers—Contribution to fuel efficiency? SAE Technical Paper 2000-01-1792, Society of Automotive Engineers, Warrendale, PA, 2000. 23rd International Colloquium Tribology - January 2022 381 Investigation into the effect of lubricant viscosity in engine bearing-film-thickness-using-embedded-ultrasonic-transducers Henry-Brunskill Corresponding author: henry@pktopk.co.uk Peak to Peak Measurement Solutions ltd., Sheffield, UK Andy-Hunter Peak to Peak Measurement Solutions ltd., Sheffield, UK Am-Ho-Sung- Hyundai Motor Company, Seoul, S. Korea Junsik-Park- Hyundai Motor Company, Seoul, S. Korea Rob Dwyer-Joyce Leonardo Centre for Tribology, University of Sheffield, Sheffield, UK 1. Introduction With the introduction of the new Euro 7 emmission standard, the automotive industry is under increased pressure to reduce CO2 emissions to lessen the impact on global warming and climate change. This has led to a trend in reducing viscosity of the engine oil to improve fuel economy and emissions. In doing so, there is a risk that the engine bearing lubricant films become too thin and scuffing/ film breakdown can occur, leading to decreased service intervals and in some cases, engine failure. In this work, non-invasive ultrasonic sensors were installed in a fired engine dyno test to measure the film thicknesses in the main and big-end bearings. The results were compared to models. 2. Ultrasonic-Measurement-of-Lubricant-Film- Thickness The micro-ultrasonic sensors are mounted on the rear of a component and a high-frequency pressure wave is generated that reflects of the lubricated interface. The reflected wave amplitude is proportional to the stiffness of the interface, K, which can be related to the lubricant film thickness, h, via and a series of know parameters: the transducer frequency, ω, the lubricant bulk modulus, B, and the acoustic impedance of the materials either side of the contact, z1, z2. More detail on the method is given in [1, 2]. A small form factor ultrasonic DAQ hardware system was developed and implemented to capture ultrasonic data 14kHz per channel. 3. Engine,-Instrumentation,-and-Test-Details 3.1 Engine Details A diesel engine with the following specification was used for testing: • Displacement (cc): 1598 • Engine speed (rpm): 750~5200 • Rated power (ps): 136@4000rpm • Maximum torque (kgfm): 32@1750rpm 3.2 Main Bearing Film Thickness Instrumentation A linear array of 4 off 0.7 × 2.5mm ultrasonic transducers was mounted on the rear surface of the 2nd and 3rd unmodified main bearing shells for the measurement of lubricant film thickness. At each transducer location, a K-type thermocouple was also bonded to the bearing. Small holes were machined in the bed-plate to eject the 0.4mm micro-coaxial and 0.6mm thermocouple cables. Images describing the instrumentation can be seen in Figure 1. 382 23rd International Colloquium Tribology - January 2022 Investigation into the effect of lubricant viscosity in engine bearing film thickness using embedded ultrasonic transducers Figure 1: Photographs of the instrumented bearing shell and modified bed plate and a sketch showing the measurement concept. 3.3 Big End Bearing Instrumentation A linear array made up of 5 identical transducers and 2 in-built thermocouples were embedded in a slot machined in the 1st big end journal pin in the crankshaft. The slot was positioned at the estimated angular position so that the transducers where measuring at the point of the minimum film thickness considering the complex engine cycle. A 3mm hole was machined in the centre of the shaft to eject the transducer and thermocouple cables. A slip-ring was mounted on the end of the crankshaft to eject the rotating signal cables. Images describing the crankshaft instrumentation can be seen in Figure 2. Figure 2: Photograph of the instrumented big-end pin on the crankshaft shell and a sketch showing the measurement concept. 3.4 Fired Engine Test Conditions Tests were conducted to establish the oil film thickness between different lubricants and engine operating parameters. During testing, the engine parameters were modified and held until steady state thermal conditions were reached before sensor measurements were logged. Three different lubricants were used for testing. Table 3 shows the different test conditions to be presented in this paper. Speeds (RPM): 1000, 1500, 2000, 2500, 3000, 3500, 4000 Loads (Nm): Unfired, 50, 100, 150 Nm, Full load (exact Nm varies by test condition) Lubricants: 0W20, 0W30, 0W16 4. Results This section shows some example results from the different sensor configurations. 4.1 Main Bearing Measurements An example main bearing lubricant film thickness measurement is shown in Figure 3. Also shown are the simulated results modelled using Gamma Technologies GT-Suite v.2016. Figure 3: Example measured and simulated main bearing lubricant film thicknesses with 0W20 lubricant, 4000RPM, and full load. Figure 4: Measured and simulated main bearing film temperatures for 3 lubricants at full load, and various speeds. 4.2 Big End Bearing Measurements An example big end minimum lubricant film thickness measurement is shown in Figure 5. The calculated total power loss for two different lubricants can be seen in Figure 6. 23rd International Colloquium Tribology - January 2022 383 Investigation into the effect of lubricant viscosity in engine bearing film thickness using embedded ultrasonic transducers Figure 5: Example measured big-end lubricant film thicknesses with 0W20 lubricant, 100 Nm, and various speeds. Figure 6: Calculated power loss for two lubricants at 100 Nm and various speed conditions. 5. Discussion-and-Conclusion In this project, the ultrasonic lubricant film thickness measurement method has been successfully demonstrated in automotive engine main and big end bearings. The results consistently showed that lower viscosity oils reported thinner films and reduced total power loss, proving that viscosity reduction is one viable approach to work towards meeting the new regulatory standards. None of the results reported reached critically thin levels below the combined component surface roughness (approx. Ra = 0.35 µm). The measured main bearing results consistently reported good correlation with the simulations, although in all cases, slightly thicker films. This is most likely because the sensors were in fixed positions and the minimum film location is dynamic. Additional work could be performed to extrrapolate minimum films To increase confidence in new lubricants, on-road duration testing is planned. References [1] Dwyer-Joyce R. S.; Drinkwater B. W.; Donohoe C. J.: The measurement of lubricant-film thickness using ultrasound. In: Proc. R. Soc. Lond. 459957- 976. 2003 [2] Beamish, S. L.; X. Brunskill, H.; Hunter, A.; Dwyer-Joyce, R.: Circumferential film thickness measurement in journal bearings via the ultrasonic technique. In: Tribology International, 148/ 2020 23rd International Colloquium Tribology - January 2022 385 Investigation of the Ball Motion Behavior in Spindle Bearings under Dynamic Loads Hans-Martin Eckel Laboratory of Machine Tools and Production Engineering (WZL) of RWTH Aachen University, Aachen, Germany Corresponding author: h.eckel@wzl.rwth-aachen.de Christian Brecher Laboratory of Machine Tools and Production Engineering (WZL) of RWTH Aachen University, Aachen, Germany Stephan Neus Laboratory of Machine Tools and Production Engineering (WZL) of RWTH Aachen University, Aachen, Germany 1. Introduction In case of high-speed applications, bearings are subjected to a complex static and dynamic load conditions. Typical excitation sources are cutter edge engagements during machining or tooth engagements in gears. Under the influence of radial forces and moment loads, a modulation of the balls orbital velocity around the bearing axis occurs. The result is a leading and trailing motion of the balls in the cage pockets, the so-called ball advance and ball retardation (BaBr). If this value exceeds the clearance of the balls, formed by their clearances in the cage pockets and the cage guidance, significant contact forces arise between balls and cage. The risk of a cage and bearing failure increases. The motions of the balls cannot be described unambiguously with analytic kinematic formulas. It is subject to the load-dependent friction condition in the rolling contacts. Even under static loads, common calculation approaches show completely different ball kinematics. So far, experimentally validated results under dynamic load at high speeds are not available. 2. Ball kinematics A rolling and drilling motion occurs superimposed at the inner and outer rolling contact at high speeds and loads. The ratio of these motions influences the ball pitch angle with which the ball rotates around the bearing axis. In the influence of different kinematic hypotheses on the axial bearing stiffness and the pitch angle is calculated. The most common hypotheses are the innerand outer-race control (IRC/ ORC). At high speeds, the calculated pitch angles and thus the orbital velocity of the balls differ significantly between the hypotheses. In the operating behavior of rolling bearings under dynamic load is investigated. Calculations for a deep groove ball bearing (size 6220) at 1,000 rpm show that a significant change in ball rotational speed occurs only under axial load. In the stress of the cage caused by the BaBr under static loads is investigated for a deep groove ball bearing (size 6310) in the speed range up to 1,600 rpm. For higher speeds, presents a system for measuring the ball and cage motions by means of high-speed videography, results at radial load are not given. 3. Test Equipment and measuring method The metrological investigations under dynamic load are carried out on the test stand already presented in for the investigation of ball kinematics under static loads and high speeds (30,000 rpm), extended by a dynamic actuation system (Figure 1). The test bearing of size 7014 in hybrid design is elastically preloaded with a second spindle bearing with 1,000 N in an O-arrangement. The contact angle is 19°, the pitch circle diameter 90 mm and the ball diameter 11.906 mm. A photoelectric measuring system records the ball positions. For this purpose, the bearing is illuminated by 21 LED between the inner ring and the cage. Opposite to the LED mounted photodetectors detect the light signals that are intermittently blocked by the balls. 386 23rd International Colloquium Tribology - January 2022 Investigation of the Ball Motion Behavior in Spindle Bearings under Dynamic Loads Figure 1: Test bench for dynamic bearing excitation Two preloaded piezoelectric actuators with a relative angle of 90° generate the dynamic forces. The forces are applied via a load unit, which decouples the rotation of the spindle shaft with another bearing, into the shaft. The actuators are coupled to the load unit with specially developed solid-state joints with applied strain gauges, so that tensile and compressive forces can be applied with high amplitudes. 4. Results Measurements at stationary, static loads are the basis to understand the balls behavior under dynamic load. Figure 2 shows the measured deviations of a ball along the bearing circumference for different radial forces and speeds. The load acts in the direction of 0° and the ball position is equal to the direction of cage rotation. The modulation of the ball movement at 1,000 N is small and rises with increasing speed. A trailing deviation builds up after the load zone, which kinematically corresponds to an predominant ORC. At 2,000 N, a strong modulation occurs in the middle speed range, where the balls show a leading motion after the load zone. This behavior indicates a predominant IRC. Figure 2: Measured deviations of orbital ball motion The BaBr reaches significant values above a certain radial force at which a high deviation of the contact angles occurs between the inner and outer rolling contacts. Above this force, the BaBr increases progressively with increasing load. Under high dynamic loads, load conditions can arise within a force period, which, according to the results under static load, cause a slight and a strong increased modulation of the ball velocities. The interaction of dynamic and static force components is relevant for the formation of the BaBr. Figure 3 shows the measured BaBr values for four static load conditions with superimposed dynamic, stationary loading with harmonics of the shaft rotation frequency. In the purely alternating load case (F stat = 0 N), no significant BaBr appears at any load case. Figure 3: BaBr under dynamic load at 12,000 rpm The BaBr reaches higher values only under the influence of static force components. In the range of medium static force, the highest BaBr values are found with a dynamic excitation at the rotational frequency. A significant increase of the BaBr due to increased excitation frequencies does not occur. The BaBr is saturated at the load case with F stat = 2,000 N, where the dynamic loading has no influence. In the case of dynamic load, the relative position of the ball to the acting force determines the load and thus the kinematics. A recurring load on the ball over the bearing circumference, as in the static case, does not occur due to the odd cage speed. In the case of an unbalanced load, the balls experience a smaller change in load due to the rotating force over a larger angle of rotation of the cage. As an extreme example, Figure 4 shows the deviations of the ball motions with circulating forces of 250 N dynamic amplitude corresponding to the cage and shaft rotational frequencies. In the case of the cage rotational frequency, the load condition for a ball remains constant over a long period of time, so that individual balls build up a very high leading or trailing deviation. In contrast, the dynamic excitation at rotational frequency shows low BaBr values. 23rd International Colloquium Tribology - January 2022 387 Investigation of the Ball Motion Behavior in Spindle Bearings under Dynamic Loads Figure 4: BaBr with circulating forces 5. Conclusion The results show, that contrary to previous assumptions, high speeds and high load forces are not necessarily critical for high BaBr values. Dynamic forces with harmonics of the shaft rotational frequency do not cause a significant increase in BaBr. A purely unbalanced load does not lead to critical BaBr values. A dynamic load with the rotational frequency increases BaBr values only under the influence of a static force component. 6. Acknowledgement Supported by Federal Ministry for Economic Affairs and Energy on the basis of a decision by the German Bundestag. The authors would like to thank the German Federation of Industrial Research Associations (AiF) and the German Machine Tool Builders’ Association (VDW) for financial support of the project 21640 N/ 1. References [1] Noel, D.; Ritou, M.; Furet, B.; Le Loch, S.: Complete Analytical Expression of the Stiffness Matrix of Angular Contact Ball Bearings. In: Journal of Tribology. 135. Jg., 2013, Nr. 4 [2] FVA: Einfluss von Vibrationsanregung auf Wälzlager. Abschlussbericht zum Forschungsvorhaben Nr. 589 I, 2014. [3] Kakuta, K.: The Effects of Misalignment on the Forces Acting on the Retainer of Ball Bearings. In: Journal of Basis Engineering, 1964, Nr. 86. S. 449-456 [4] Holland, L.: Analyse des Bewegungsverhaltens der Komponenten in Spindellagern mittels Hochgeschwindigkeitsvideographie. Dissertation Technische Hochschule Darmstadt, 2018 [5] Brecher, C.; Eckel, H.-M.; Fey, M.; Neus, S.: Measuring the Kinematic Behavior of the Rolling Elements in a Spindle Bearing under Axial and Radial Loads. In: Bearing World Journal. 2020, S. 159- 167 Lubricant Analysis 23rd International Colloquium Tribology - January 2022 391 Improved Oil Condition Monitoring of Industrial Gear Oils Dipl.-Ing. Rüdiger Krethe OilDoc GmbH, Kerschelweg 28, 83098 Brannenburg, OELCHECK GmbH, Kerschelweg 28, 83098 Brannenburg Dr. Thomas Fischer OilDoc GmbH, Kerschelweg 28, 83098 Brannenburg, OELCHECK GmbH, Kerschelweg 28, 83098 Brannenburg Summary Oil oxidation is the most important process in oil aging for almost all industrial lubricants. New application areas and requirements for much longer oil drain intervals lead to a strong increase in the use of synthetic gear oils. Typical test patterns like viscosity, acid content and IR oxidation are not sufficient for a reliable oil condition monitoring of synthetic gear oils particularly in large industrial gearboxes. The paper demonstrates the principle and application of new methods in oil condition monitoring. It includes a number of field examples from different applications to demonstrate the value of the new methods and to give a basic evaluation guide for application. 1. New lab methods of Oil Condition Monitoring 1.1 Oxidation Index FT-IR based methods are used to detect oxidation in mineral oils for decades. In Europe this method is standardised in DIN 51543 / 6/ . The oxidation level in industrial applications like gearboxes is appr. 10 - 20 times lower than in combustion engines. Therefore, a single wave-number based oxidation test methods like standardised in DIN 51453 is not able to detect oxidation in industrial applications reliable and on an early stage. The Oxidation Index is based on the monitoring of an area instead of a single wavenumber, like shown in figure 1. Figure 1: Oxidation detection using FT-IR. Single wavenumber based versus area-based. The oxidation process generates different species of products. Especially when ongoing on a low level, a single wave-number based methods becomes unreliable. This way, the area-based method produces much more reliable results. It allows the oxidation detection on an early stage and a trend evaluation when sampling on regular basis. 1.2 Additive depletion Much more stable synthetic base oils move the focus from the oxidation detection more to the additional monitoring of additive condition to provide a reliable forecast for scheduling the oil drain interval. For the detection of additive condition are different methods suitable, for example: • Infrared spectroscopy (FT-IR, antioxidants, antiwear, EP) / 7/ • Linear voltammetry (RULER, antioxidants) / 4/ • High-pressure liquid chromatography (HPLC) for the thiazoles (anti-corrosion) / 8/ In order not to go beyond the scope of this publication, we refer in this respect to the literature references 1.3 Deposit potential testing The MPC (Membrane Patch Colorimetry) was initially developed to monitor the tendency of deposit generation of turbine oils / 9/ . A special membrane patch is generated. The deposits on the membrane patch are evaluated by colorimetry (reflected light). The MPC test result is calculated by luminance and special color distribution. This test was adopted to detect the tendency of deposit generation for other applications like hydraulic systems, gear boxes or other XXL lubrication systems with success. 392 23rd International Colloquium Tribology - January 2022 Improved Oil Condition Monitoring of Industrial Gear Oils 2. Conclusion The reliable oil condition monitoring of modern industrial gear oils needs more detailed analysis methods and evaluation rules. Typical test patterns like viscosity, acid content and IR oxidation are not sufficient for a reliable oil condition monitoring of synthetic gear oils particularly in large industrial gearboxes. Oil oxidation is the most important process in oil aging for almost all industrial lubricants. Due to the higher saturation level of modern mineral oil based, but much more synthetic base oils the ongoing of oil oxidation is harder to detect reliable. The Oxidation Index, a new area-based IR-method provides more reliable results, even when measuring PAO based, ester containing oils. Additive depletion is not only a sign of reduced useful life of the oil filling, but often the cause of significant deposit generation in gearboxes and higher effort to clean up the gearbox during oil change. Considering the increased use of synthetic base oils the monitoring of additive depletion becomes much more important. References [1] Krethe, R., Handbuch Ölanalysen (Manual of oil analysis, German), expert-Verlag, Tübingen, 2020, ISBN 978-3816934998 [2] Jensen et al, Initiation in hydrocarbon autooxidation at elevated temperatures. International Journal of Chemical Kinetics 22, (1990) [3] Krethe, Fischer, New Method for oxidation detection in industrial lubricants, International Colloquium of Industrial and Automotive Lubrication, Ostfildern, 2020 [4] Ameye, Jo, Krethe Rüdiger: Linear Sweep Voltammetry (RULER©) - An innovative approach for Looking Forward to Lubricant Oxidation. Part I: Fundamentals, Part II: Determination of Remaining Useful Lifetime of Lubricating Oils, Application and Examples. 15th International Colloquium Tribology, Ostfildern, 2006 [5] OELCHECK: Oil analysis reports (internal). www. oelcheck.de. [6] DIN 51453: 2004-10. Testing of lubricants - Determination of oxidation and nitration of used motor oils - Infrared spectrometric method (Prüfung von Schmierstoffen - Bestimmung der Oxidation und Nitration von gebrauchten Motorenölen - Infrarotspektrometrisches Verfahren). Beuth-Verlag. www.beuth.de [7] OilDoc GmbH: Additives in lubricating oils and their condition monitoring. 2020, online-training in 2 modules. www.oildoc.com or https: / / elopage. com/ s/ oildoc [8] Monitoring of nonferrous metal passivators in gear oils - Proactive copper wear detection in wind turbine. (part I and II), Dr. T. Fischer, Dipl.-Ing. S. Mitterer, OilDoc Conference, Rosenheim, 2019 [9] ASTM D7843-18. Standard Test Method for Measurement of Lubricant Generated Insoluble Color Bodies in In-Service Turbine Oils using Membrane Patch Colorimetry [10] Krethe, Rüdiger; Bots, Steffen: Particle Counting of In-service lubricants: Lab analysis meets reality. Reliable Plant Conference, Louisville, April 5 - 7, 2016 23rd International Colloquium Tribology - January 2022 393 Study of the Capacity of Spectroscopy UV-Vis and NIR to Quantify Fuel Dilution on used engine oil Bernardo Tormos CMT - Motores Térmicos, Universitat Politècnica de València, Valencia, Spain. Vicente Macián CMT - Motores Térmicos, Universitat Politècnica de València, Valencia, Spain. Benjamín Pla CMT - Motores Térmicos, Universitat Politècnica de València, Valencia, Spain. Adbeel Balaguer CMT - Motores Térmicos, Universitat Politècnica de València, Valencia, Spain. Corresponding author: abalrey@mot.upv.es. 1. Introduction Fuel dilution of engine oil is a common problem for both diesel and gasoline internal combustion engines: when the fuel contaminates the oil, it modifies its properties, mainly viscosity, reducing lubrication film strength. The quantification of fuel in oil (FiO) is an important parameter in the ICE’s condition monitoring, as it allows performance prediction and to take proper actions. The standard method (e.g., ASTM D3524 - 14) for assessing the content of fuel in oil require high-cost equipment, as chromatographer and solvents, while this work evaluates the capacity of UV-Vis and FT-NIR spectroscopy to quantify fuel dilution, considering them as techniques with simple operation and reduced cost, able to produce accurate and significant results. This work evaluated both spectroscopic techniques and the results proved that is possible to quantify diesel dilution by FT-NIR spectroscopy using the spectral peak area at 4600 cm -1 (BL: 4635-4558 cm -1 ). 2. Methods and Results To study the capability of the spectroscopy for FiO quantification, the first step in this work was to prepare diluted samples using fresh oil for analysis, in order to avoid interference from contaminants, as soot and other typical impurities, in the spectrum. The first test samples were prepared using SAE 5W-30 fresh engine oil contaminated with diesel in a concentration ranging from 0-10.0% (w/ w) and then analyzed in both, UV-Vis and NIR. The second phase of the work was to use the spectroscopic method that have provided the best results in previous step, to analyze used oil samples with different fuel dilution rate. 2.1 Fresh oil samples analyzed in UV-Vis The UV-Vis data (700-200nm) for the fresh oil samples contaminated with diesel was acquired in a Perkin Elmer UV-Vis Lambda 365 using an optical path length of 10 mm. Due to the similarities between the spectra of the oil and the fuel it was not possible to differentiate a specific peak or area where the quantification could be done directly, therefore the possibility of using a fuel dye to improve quantification in this region was studied as in the work of Neupane et al when using laser induced florescence spectroscopy. The technique consisted in dying the fuel used to prepare the samples at different concentration rates and then obtaining the spectra, eight samples were used, and the spectra were collected by triplicate. The use of the dye in the fuel (600 ppm) allowed to identify an area that could be used for quantification, between 415-435 nm, after preforming a spectral peak area analysis for the collected spectra the coefficient of linear correlation obtained was R² = 0.8240. 2.2 Fresh oil samples analyzed in FT-NIR The NIR spectra for the fresh oil samples contaminated with diesel was acquired in a Perkin Elmer FT-NIR Spectrum Two N between 11500-4500 cm -1 also using an optical path length of 10 mm. The first step was to obtain and compare the spectra of the fresh oil and the diesel fuel, it was possible to identify a specific peak, as shown in Figure 1, at the wave number 4600 cm -1 where the diesel could be quantified. 394 23rd International Colloquium Tribology - January 2022 Study of the Capacity of Spectroscopy UV-Vis and NIR to Quantify Fuel Dilution on used engine oil Figure 1: Fresh engine oil and diesel NIR spectra Following, the spectra of the prepared samples were collected by triplicate. The quantitative analysis technique chosen was peak height at 4600 cm -1 , it proved the existence of a linear relationship according to the Beer-Lamber Law, between the peak height at 4600 cm -1 and the concentration of diesel in the sample, the fitting equation displayed a good regression coefficient of R 2 =0.98368, in the studied range, as shown in Figure 2. Comparing the results of both methods, the FT-NIR let to the obtention of significantly better results for quantification in the fresh oil samples whit a simpler procedure, therefore it was the chosen spectroscopic alternative to continue the analysis in used oil samples. Figure 2: Linear fitting for fresh oil samples 2.3 Used oil samples analyzed in FT-NIR Samples for this stage were prepared gravimetrically from used oil from diesel engines and contaminated with fuel, 9 samples were used to build the model, in a concentration ranging from 0-10.0% (w/ w). The first attempt to record the spectra of the used samples was not effective because the soot content generated noise in all the spectrum range, therefore it was required to dilute the samples. Various solvents were put on trial and finally the heptane was chosen, as well, several dilution ratios were evaluated, for this group of samples that was prepared from a used oil containing 0.067% of soot, the selected ratio was 3.4 g of heptane per each gram of sample since it produced a clean spectrum to work on the analysis stage. To record the spectra, the reference cell was filled with heptane, triplicate measurements were made, and the spectra were collected between 11500- 4500 cm -1 . For this case the quantitative analysis measurement technique chosen was spectral peak area analysis at the peak previously identified in the fresh samples, the area was measured over the range of 4635-4558 cm -1 . The areas were calculated using the own Perkin Elmer equipment software. For the construction of the calibration model, the area corresponding to each sample was the difference after subtracting the area of the sample without added diesel from the area of the contaminated sample. Using that peak area of the samples over the range of 4635 cm -1 to 4558 cm -1 as the arguments, and the fuel concentration as the dependent variable, the fitting equation of peak area with fuel concentration is obtained. The equation presented a regression coefficient was R 2 = 0.92068, which indicates a good correlation between predicted value and known value, therefore this method could be used to assess the content of fuel as a first approximation. The same procedure was applied on another group of samples prepared from the same type of engine oil but having a higher content of soot, and it was noticed that it required a higher dilution ratio to eliminate the noise in the recorded spectra. The results obtained were analogues to the previous one, for this the fitting equation presented a regression coefficient R 2 = 0.93240, similar to the previous one. Figure 3: Linear fitting for used oil samples 2.4 Determination of the dilution factor To apply this method is required to dilute the used oil sample with heptane in a proportion that varies according 23rd International Colloquium Tribology - January 2022 395 Study of the Capacity of Spectroscopy UV-Vis and NIR to Quantify Fuel Dilution on used engine oil to the sample’s soot content, towards reducing the noise in the measured spectrum. This work studied used oils in a range of soot concentration from 0.067% to 0.282%, that concentration was measured with FTIR. The following table presents the dilution ratios used in this work: Soot (%) g heptane/ g sample 0.067 3.40 0.115 6.33 0.174 11.11 0.282 13.33 3. Conclusion This work proposes a methodology for quantifying fuel dilution particularly focused on diesel engines using spectral peak area analysis that has been shown as a viable method in the near-infrared region. Although full spectrum features can be used when working with multivariate methods, it is important to remark the identification of a unique spectral region that describes accurately the fuel dilution concentration providing a simple method for measuring it. References [1] ASTM Standard D3524 - 14, 2020, “Standard Test Method for Diesel Fuel Diluent in Used Diesel Engine Oils by Gas Chromatography”, ASTM International, DOI: 10.1520/ D3524-14R20, www.astm. org. [2] S. Neupane, V. Boronat Colomer, D. Splitter, et al. “Measurement of Engine-Oil Fuel Dilution Using Laser Induced Fluorescence Spectroscopy”. 2020 Spring Technical Meeting of the Central States Section of the Combustion Institute Proceedings. Center States Combustion Institute (CSSCI) 2020. Acknowledgments This work has been partially supported by grant PID2020-11969RB-100 funded by MCIN/ AEI/ 10.13039/ 501100011033. 23rd International Colloquium Tribology - January 2022 397 On the role of microorganisms for lubricants - Sometimes good, sometimes bad Peter Lohmann Hermann Bantleon GmbH, Ulm, Germany Corresponding author: plohmann@bantleon.de Gerhard Gaule Hermann Bantleon GmbH, Ulm, Germany 1. Introduction Biodegradation is the breakdown of organic material by microorganisms e.g., bacteria and fungi. Lubricants usually are hydrocarbonic substances of organic origin. Accordingly, there are microorganisms having the capability of breaking down lubricants. On the one hand, we welcome microorganisms and their biological degradation processes, namely when it comes to the fact that untraceable or unreachable residues of oily leaks in the environment are to be eliminated. On the other hand, we curse microorganisms that undesirably drive the decomposition and degradation of important components in emulsions of metalworking machines and thus cause quality losses. 2. Microorganisms There is a huge variety of hydrocarbonoclastic microorganisms having the ability to biodegrade hydrocarbons. These ubiquitous microorganisms include bacteria, yeast, and fungi. There are freshwater bacteria, such as e.g., Pseudomonas and Acinetobacter. Others are adapted to a marine environment e.g., Alcanivorax [Fig. 1] and Marinobacter. Aromatic hydrocarbons are mainly degraded by marine Neptunomonas and Cycloclasticus species, while some methane-oxidizing and phototrophic bacteria are partially capable of oxidation of aliphatic hydrocarbons. The bacteria that dominate soils include for example Mycobacterium or Rhodococcus [Fig. 1]. Among the fungi, it is usually geobiontic representatives such as Aspergillus, Fusarium or Penicillium [Fig. 1], which can decompose hydrocarbons. Alkane-oxidizing yeasts can be found, for example especially in the genera Candida [Fig. 1] and Lodderomyces. 3. Mechanisms There are both oil-positive microorganisms that can enter directly into the oil phase and oil-negative microorganisms that remain suspended in the water phase and excrete emulsifying substances for an effective absorption of oil microdrops. Others are equipped with a waxy surface to attach to lipophilic substrates and to facilitate the assimilation into the cell [1]. The subsequent degradation process most frequently starts with a monoor diterminal [2] or, more rarely, subterminal [3] attack on the hydrocarbon by special enzymes. A chain of complex biochemical reactions is ending up in the final degradation via β-oxidation [4, 5, 6]. The corresponding result is that organically bound carbon is converted into carbon dioxide. To put it simple, one can summarize all these reactions as follows: Organic substance + Oxygen → Carbon dioxide + Water + (microbial biomass). Figure 1. Oil-degrading microorganisms. A Candida maltose, B Penicillium spec., C Alcanivorax borkumensis, D Rhodococcus ruber. 4. Conclusion N-alkanes and monoaromatic substances can be degraded relatively easy by microorganisms. In contrast, branched and aliphatic hydrocarbons are hard to degrade, sometimes only by microbial specialists. As a rule, biodegradation of lubricants is a concerted action of various microorganisms having different characteristics. 398 23rd International Colloquium Tribology - January 2022 On the role of microorganisms for lubricants - Sometimes good, sometimes bad References [1] Fuchs, G. 2006 Allgemeine Mikrobiologie. 8. Auflage. Georg Thieme Verlag, Stuttgart, Germany [2] Watkinson, R. J. and P. Morgan. 1991. Physiology of Aliphatic Hydrocarbon-Degrading Microorganisms. In Physiology of Biodegradative Microorganisms, ed. C. Ratledge, 79-92. Springer, Netherlands. [3] Forney, F. W. and A. J. Markovetz. 1970. Subterminal oxidation of aliphatic hydrocarbons. J Bacteriol 102(1): 281-282. [4] Coon, M. J. 2005. Omega oxygenases: nonheme-iron enzymes and P450 cytochromes. Biochem Biophys Res Commun 338(1): 378-385. [5] Krauel, H., R. Kunze, and H. Weide. 1973. Bildung von Dicarbonsäuren durch Candida guilliermondii, Stamm H 17, aus n-Alkanen. Z Allg Mikrobiol 13(1): 55-58. [6] Kester, A. and J. Foster. 1963. Diterminal oxidation of long-chain alkanes by bacteria. J Bacteriol 85(4), 859-869. 23rd International Colloquium Tribology - January 2022 399 Studying the action of surface active lubricant additives by surface analytical methods T. Rühle BASF SE, Carl-Bosch-Straße 38, 67036, Ludwigshafen, Germany Corresponding author: Thomas.ruehle@basf.com J. Eickworth Fraunhofer IWM MikroTribologie Centrum, Wöhlerstraße 11, 79108 Freiburg, Germany M. Dienwiebel Karlsruher Institut für Technologie KIT, Kaiserstraße 12, 76131 Karlsruhe, Germany 1. Introduction Lubricant formulations typically contain >95 % of a mineral or synthetic base stock and up to 5 % of lubricant additives. Some of these additives are surface active like e.g. corrosion inhibitors or antiwear additives. It is important to understand the action of these additives on the metal surface to be able to develop an optimized formulation for each application. Besides understanding the adsorption behavior of a single additive, it is also important to understand the interaction (synergistic or antagonistic) between two or more additives on a metal surface. The antagonistic interaction between corrosion inhibitors and antiwear additives is a prominent example. Other kinds of additive interactions are described elsewhere [1]. 2. Surface Analytical Methods for Tribology Surface analytical methods are widely used in heterogeneous catalysis to better understand the molecular mechanism of catalytic processes [2]. Since in catalysis as well as in tribology similar systems are considered, a chemical substance adsorbed on a solid, the use of selected analytical tools established in catalysis could also be beneficial to better understand tribological processes. Suitable surface analytical methods are e.g.: • Morphological / Surface Roughness: • White light interferometry (WLI) • Scanning electron microscopy (SEM) • Contact angle / surface energy • Atomic force microscopy (AFM) • Laser fluorescence microscopy (LFM) • Chemical Information: • X-ray photoelectron spectroscopy (XPS) • Diffuse reflectance infrared Fourier transform spectroscopy (DRIFT) • SEM plus energy dispersive x-ray analysis (EDX) • Mass spectrometry (MS) • Secondary ion mass spectroscopy (SIMS) • Thermal stability: • Thermal desorption spectroscopy (TDS) • Calorimetry (DSC) • Gravimetric Methods: • Thermogravimetric analysis (TGA) • Quartz crystal microbalance (QCM) 3. Examples to be addressed by surface analytical methods The surface of machine parts based upon iron alloys typically are terminated by iron oxide and/ or iron hydroxide layers. In this context the question arises how the lubricant additives are coordinated on the surfaces. In principle, there are different modes possible (see Figure 1). Figure 1: Different modes of coordination of additives on iron oxide terminated metals surfaces (Taken from [3]) This kind of chemical information can be derived from XPS spectra. Another question is about the surface coverage of additives on a metal surface. E.g., for friction modifiers it is known, that the coefficient of friction could strongly correlate inversely with the surface coverage (see Figure 2). For this reason, it is of high interest to measure the adsorbed amount of additive and derive the surface coverage from these data. This can be achieved using a highly sensitive gravimetric method like QCM [5]. 400 23rd International Colloquium Tribology - January 2022 Studying the action of surface active lubricant additives by surface analytical methods Another question concerns the question whether friction modifiers are adsorbed as mono-or multilayers on a metal surface. The model of an adsorbed monolayer not always explains the tribological behaviour accurately. Figure 2: Surface coverage (FractCov) of cotton seed oil and the corresponding coefficient of friction (COF) measured in hexane (Taken from [4]) It must be considered that only one or a few layers of friction modifiers on the metal surface could be sheared off over time in the tribosystem. As a consequence, this causes an increase of the coefficient of friction. In a specific example1, the sufficient number of layers to be adsorbed on a surface in order to ensure a stable coefficient of friction over time was determined to be 53 [6]. How the structure of these multilayers might look like is described elsewhere [7] It can be determined by combining the information gained from different methods, like XPS, QCM, MS or SIMS. 4. Ashless dialkyl-dithiophosphate (DTP) + friction modifier In our own study, investigations of 1 % glycerol monooleate (GMO) and 1% of an organic friction modifier (OFM) in combination with an ashless dithiophosphate (DTP) in a mineral oil (MO) and a synthetic base oil (SBO), i.e. poly alpha olefin revealed antagonistic and synergistic effects. Using QCM adsorption measurements, it was possible to determine the amount of adsorbed additive and via the dissipation shift to judge whether the adsorbed layer rather is hard or viscoelastic. By combining with tribometry data, the synergy effect was linked to the adsorption behaviour. In order to get more information, XPS depth profiles for have been measured. Figure 3: Synergistic, intermediate and antagonistic interaction of an ashless DTP and a friction modifier (Taken from [5]) The results are summarized in Figure 3. The combination of dithiophosphate and an organic friction modifier (OFM) revealed a synergistic effect in terms of wear. If the initially formed films are viscoelastic, wear also can be reduced. Also taking data from a XPS depth profile analysis into account, as a mechanism, the adsorption of the OFM on the formed antiwear layer is proposed. 5. Conclusion Surface analytical methods are a powerful tool to better understand tribological processes. The adsorption modes of additives and their action on the surface either as a single additive or in combination/ competition with other additives can be investigated: Lubricant formulators can use these findings in order to further optimize their formulations and therefore save resources. References [1] H.A. Spikes: Additive-Additive and Additive-Surface Interactions in: Lubrication Scienc, Volume 2, Issue 1, pages 3-23, October 1989 [2] J.W. Niemantsverdriet: Spectroscopy in Catalysis - An Introduction; VCH Weinheim (1993). [3] R.M. Cornell, U. Schwertmann: The Iron Oxides - Structure, Properties, Reactions, Occurence and Uses. VCH Verlagsgesellschaft Weinheim (1996) p. 245. [4] G. Biresaw: “Surfactants in Lubrication” in: Lubricant Additives - Chemistry and Applications”, CRC Press, Boca Raton, (2009) 411. [5] L Eickworth, E. Aydin, M. Dienwiebel, T. Rühle, T. Wilke, T.R. Umbach: „Synergistic effects of antiwear and friction modifier additives”, Industrial Lubrication & Tribology, Vol 72, Issue 8, pages 1019-1025 (2020). [6] Gellman, Andrew J. and Spencer, Nicholas D., “Surface Chemistry in Tribology” (2002). Department of Chemical Engineering. Paper 22. http: / / repository.cmu.edu/ cheme/ 22 [7] Crawford, A. Psaila, S.T. Orszulik: “Miscellaneous Additives and Vegetable Oils“ in: R.M. Mortier, M.F. Fox, S.T. Orszulik (Eds.): Chemistry and Technology of Lubricants. Springer Dordecht Heidelberg London New York (2010) S. 189 ff. Metrology in Tribology (Wear) 23rd International Colloquium Tribology - January 2022 403 Continuous wear measurements of diamond-like carbon (DLC) based on radioactive isotopes Manuel Zellhofer AC2T research GmbH, Wiener Neustadt, Austria Corresponding author: manuel.zellhofer@ac2t.at Martin Jech AC2T research GmbH, Wiener Neustadt, Austria Ewald Badisch AC2T research GmbH, Wiener Neustadt, Austria Ferenc Ditrói Institute of Nuclear Research of the Hungarian Academy of Sciences, Debrecen, Hungary Andreas Kuebler Robert Bosch GmbH Feuerbach, Germany Paul Heinz Mayrhofer Institute of Materials Science and Technology, Vienna University of Technology, Austria 1. Introduction Diamond-like carbon (DLC) coatings are being developed to protect engine parts from wear and create low-friction systems to save energy in applications. For combustion engines and electric cars, the thickness of DLC coatings is usually between 1 to 4 µm. Nevertheless, unintended failure of DLC coatings has been observed in many engine applications. In the automotive industry in particular, delamination processes caused by abrasive wear particles lead to failures [1]. However, it is not yet clear whether the delamination in the presence of abrasive particles is a result of a spontaneous burst of the coating or a continuous wear progress. Such an investigation requires a continuous wear measurement method to monitor wear. Radioactive tracer methods (especially the radioactive isotope concentration method - RIC) have proven to be effective indicators for monitoring the progress of wear, e.g. on metallic engine components [2]. Irradiation methods such as thin layer activation (TLA) are used for these wear measurement methods [3]. However, previous studies have shown that irradiation similar to the RIC method can affect the tribological behaviour of DLC [4]. Thus, at tribometer level, we investigate the application of the RIC method (influence of irradiation) to subsequently determine the wear behaviour of DLC coatings under abrasive particles. 2. Methods Within this study, two different tribocontacts were experimentally studied using tribometers in order to generate various loading conditions typical for automotive applications: an oscillating ball-on-plate contact (Universal Mechanical Tester - UMT), and an unidirectional journal-bearing contact (Sintered Bearing Tester - SLPG). The samples consisting of a ~2.3 µm thick DLC coating on a steel substrate (100Cr6) were provided by the partner. DLC was activated by 3 He irradiation to generate 7 Be isotopes [5]. As a result of the irradiation method, the steel substrate underneath the DLC coating was activated too. In the RIC wear measurements performed during the tribological experiment, the wear particles containing the isotopes are transported to a detector via the lubricant circuit, see Figure 1. A filter with a mesh size of 1 µm was placed in the detector to trap the wear particles in the measurable zone of the detector. Tribological tests performed under high contact stress in ball-on-plate configuration (UMT, DLC plate against 100Cr6 ball, 2750 MPa hertzian contact stress, 30 min, 45,000 cycles) were used to investigate the influence of the irradiation on the tribological behaviour of the DLC coating. For comparison of irradiated and original DLC, the worn areas (3 experiments respectively) were measured using a chromatic confocal profiler (Jr25, Nanovea). In addition, nanoindentation experiments and a structure analysis with transmission electron microscopy were 404 23rd International Colloquium Tribology - January 2022 Continuous wear measurements of diamond-like carbon (DLC) based on radioactive isotopes performed to evaluate the difference between irradiated and original DLC. To investigate the influence of abrasive particles, tribological tests were conducted well below the critical contact stress at which DLC fails (SLPG, DLC liner against X90CrMoV18 shaft, 275 MPa). Three experiments (SLPG-A to -C) were performed using different abrasive particle concentrations at a particle size < 1 µm collected from previous tests on engine test benches. Figure 1: Simplified representation of the RIC-circle containing detector with filter, pump, and tribo-contact. 3. Results and discussion 3.1 Influence of irradiation No significant difference was found between the irradiated and the original samples, see Table 1. In addition, no significant failure or delamination of the DLC was observed during the performed tribological tests at high contract stress. Table 1: Summarized results of material analyses and tribometrical investigations comparing irradiated and original DLC coating. Sample/ condition (material analyses) Irradiated unworn Original unworn Roughness Ra, µm 0.18 ± 0.02 0.18 ± 0.02 sp2-content, % 55 ± 2 55 ± 3 Hardness, GPa 20 ± 3 19 ± 3 Young´s modulus, GPa 175 ± 14 172 ± 12 Sample/ condition (tribometrical invest.) Irradiated and worn Original and worn DLC wear, 105 µm³ 4.4 ± 2.4 4.5 ± 2.1 COF 0.247 ± 0.011 0.245 ± 0.010 3.2 Influence of abrasive particles The wear of the DLC coating and the wear of the co-activated steel-substrate of experiment SLPG-A are displayed in Figure 2. The results show that DLC wear starts immediately, while steel-substrate wear is observed with a delay of ~3.5 hours (50,400 revolutions). A continuous slightly progressive increase of the DLC wear can be observed before the steel-substrate wear is detected, which leads to the assumption that the DLC coating is continuously worn in a mild abrasive wear regime. Test SLBG-B and C show similar results. Figure 2: DLC wear (blue up-triangles) and steel-substrate wear (green down-triangles) at a particle concentration of 7 × 10 6 particles per ml (experiment SLPG-A, sliding contact). Table 2: Summary of test duration, abrasive particle concentration, and total wear volume of experiment SLPG-A to C. Experiment Total test duration, hours (revolutions) Abrasive particle concentration, 10 6 p/ ml 1) Wear volume, 10 6 µm³ 2) SLPG-A 6 (86,400) 7 4.5 SLPG-B 5 (72,000) 4 3.3 SLPG-C 5 (72,000) 1 2.0 1 ) The abrasive particle concentration is given in particles/ ml (p/ ml) ± 50 %. 2 ) Wear volume as sum of DLC and substrate wear with a total uncertainty of ± 0.6 × 10 6 µm³. The results from the SLPG tests indicate that increased wear occurs at higher abrasive particle concentrations (measured with the particle measurement device [6]), see Table 2. Subsequently, in the presence of abrasive particles, which possibly originate from another tribo-contact, the wear increases significantly, which can lead to early failures. 23rd International Colloquium Tribology - January 2022 405 Continuous wear measurements of diamond-like carbon (DLC) based on radioactive isotopes 4. Conclusion The irradiation method specifically applied for RIC measurements within this study does not significantly affect the DLC structure and consequently the tribological behaviour. Therefore, this procedure is well suited for investigating the nanoscopic wear behaviour of DLC coatings. Throw the use of the RIC method a continuous wear behaviour was found in contrast to a spontaneous burst of the DLC coating. In addition, a correlation between the DLC wear and the abrasive particle concentration was indicated. During the tribotests performed under high contact stress the DLC coating did not fail. However, lower contact stresses and the presence of abrasive particles can become critical parameters limiting lifetime in automotive applications. 5. Acknowledgements This work was funded by the Austrian COMET Program (project K2 InTribology1, no. 872176). The work has been carried out within the TU Vienna (Austria) and the “Excellence Centre of Tribology” (AC2T research GmbH). TEM investigations were carried out using the USTEM facilities at the TU Vienna, Austria. References [1] T. Haque, D. Ertas, A. Ozekcin, H. W. Jin, and R. Srinivasan, “The role of abrasive particle size on the wear of diamond-like carbon coatings,” Wear, vol. 302, no. 1-2, pp. 882-889, Apr. 2013, doi: 10.1016/ j.wear.2013.01.080. [2] P. Brisset et al., “Radiotracer Technologies for Wear, Erosion and Corrosion Measurement,” 2020. [3] T. Wopelka et al., “Wear of different material pairings for the cylinder liner piston ring contact,” Industrial Lubrication and Tribology, vol. 70, no. 4, pp. 687-699, 2018, doi: 10.1108/ ILT-07-2017- 0218. [4] N. Zhang, L. Lin, B. Liu, G. Wu, W. Xu, and T. Peng, “Tribological properties improvement of H-DLC films through reconstruction of microstructure and surface morphology by low-energy helium ion irradiation,” Diamond and Related Materials, vol. 109, Nov. 2020. [5] F. Ditrói, S. Takh, F. Th-Khyi, and I. Mahunka, “Study of the nat-C(3He,2α) 7Be and 9Be(3He,αn) 7Be nuclear reactions and their applications for wear measurements,” 1995. [6] C. Haiden, “Dissertation Optical Microand Nanoparticle Characterization in Microfluidics,” 2016. 23rd International Colloquium Tribology - January 2022 407 Quantifying Wet Brake Chatter Using an Accelerometer Michael Botkin Southwest Research Institute, San Antonio, Texas, USA Corresponding author: michael.botkin@swri.org Caroline Mueller Southwest Research Institute, San Antonio, Texas, USA 1. Introduction Wet brakes are common in off-road equipment and other high-torque applications where high levels of heat must be dispersed. Under the right conditions, wet brakes are susceptible to brake chatter caused by a “stick-slip” action which induces noise and vibration in the machine. For many years, this action was thought to be a result of the ratio of static to dynamic coefficient of friction [1]; however, research has shown that this action may also be triggered by a sufficiently negative friction velocity curve and/ or machine design [2]. Brake chatter, defined as an audible noise induced under braking, can be quantified via sound pressure level, variations in braking torque, or vibration measured using an accelerometer [1]. To measure sound, a technician listens for brake chatter in the audible range, or a microphone is used. This provides a good indication of what a driver would experience, but is sensitive to differences in observer and environment, resulting in poor repeatability. Strain gauges on the shaft driving the brake can be installed to measure braking torque. When chatter occurs, it is seen in the measurement as a variation in the measured torque [3,4]. Larger variations in torque produce more severe chatter, and there is a threshold torque variation value below which no audible chatter occurs. For a more accurate measurement, the strain gauges should be placed as close to the brake as possible, but this requires extensive modifications and maintenance since the brake is an internal, rotating component. Using an accelerometer to measure brake chatter allows for an easy test setup, as it can be mounted on the external surface of the machine. Furthermore, the accelerometer can pick up vibrations that occur even when little or no noise is produced—this provides a potential method to differentiate between fluids based on non-audible vibration. 2. Test Rig and Method To develop an accelerometer-based measurement of brake chatter, an off-road axle test installed at Southwest Research Institute was selected. The test rig was already fitted with internally mounted strain gauges to measure torque variation at the brake. An accelerometer was mounted on the external casing of the axle, directly above the brake disk, measuring in a direction tangent to brake disk rotation at that point. The accelerometer output was recorded at a DAQ rate of 2,000 Hz. A Fourier Transform was conducted on the accelerometer data during brake engagement to convert it into the frequency domain; for engagements that produced audible brake chatter, a resonant frequency of 340 Hz to 420 Hz was identified for this system. To quantify the severity of the chatter event for a single brake engagement, the integral of the frequency domain data from 340 Hz to 420 Hz was approximated using a midpoint Riemann sum. These values were then plotted against the magnitude of torque variation during the same engagement to establish a correlation between the two measurements. For an individual system, threshold values may be established through repeated testing to indicate when brake chatter occurs. 3. Data and Analysis 1,200 brake engagements were performed on various test fluids at different axle speeds, brake application pressures, fluid temperatures, and states of disk wear. The resulting dataset, shown in Figure 1, was generated by concurrently recording data through the strain gauges and the accelerometer. The magnitude of torque variation measured by the strain gauges is plotted against the magnitude of the integral of the resonant frequency range measured by the accelerometer. From historical testing, it is known that audible chatter on this test rig occurs if the magnitude of torque variation during a brake engagement exceeds 875 Nm. This is shown as a horizontal dashed line in Figure 1 and is known as the threshold value. Values above this horizontal line are understood to produce audible chatter, while values below this line do not. The audibility threshold value for the accelerometer is represented by the vertical dashed line on the plot. Its location was determined by minimizing the number of points that fell within regions of disagreement between the strain gauges and the accelerometer. The areas marked Type 1 and Type 2 in Figure 1 indicate a disagreement between the strain gauges and the accelerometer and differentiate between types of disagreement—a false positive chatter identification by the accelerometer or a false negative. For this test rig, the audibility threshold value for the accelerometer was determined to be 2.10. Using this threshold, the strain gauges and accelerometer were in agreement for 97.8% of brake applications. 408 23rd International Colloquium Tribology - January 2022 Quantifying Wet Brake Chatter Using an Accelerometer Figure 1: The magnitude of torque variation during a brake engagement on a text axle was plotted against the magnitude of the integral of the resonant frequency range measured by the accelerometer. Each marker color represents a test run. The dashed lines represent the threshold values above which audible chatter occurs, determined by repeated experiment. 4. Conclusions The method described above can reliably differentiate audible brake chatter from quiet brake engagements in a wet brake off-highway axle stand at different wheel hub speeds, brake engagement pressures, fluid sump temperatures, and states of disk wear. The integral area under the frequency-domain curve in the resonant frequency range is characteristic of brake chatter intensity and independent of fluid or operational conditions tested. A threshold value can be determined from experimentation that distinguishes audible brake chatter from quiet brake engagements. Finally, the method described herein is a suitable replacement for the strain gauge method used previously on the described axle. References [1] Anleitner, M.A., “Vibration and Noise in Oil- Immersed Friction Couples-A Basic Discussion,” SAE Technical Paper 861202, 1986, https: / / doi.org/ 10.4271/ 861202. [2] Friesen, T.V., “Chatter in Wet Brakes,” SAE Technical Paper 831318, 1983, https: / / doi.org/ 10.4271/ 831318. [3] Cave, W. and Lochte, M., “Development of an Updated Brake Chatter Test for Anti-Brake Chatter Transmission/ Hydraulic Fluids,” SAE Technical Paper 961817, 1996, https: / / doi.org/ 10.4271/ 961817. [4] Michael, R.A., “Key Elements of Wet Brake and Clutch Design,” SAE Technical Paper 921660, 1992, https: / / doi.org/ 10.4271/ 921660. 23rd International Colloquium Tribology - January 2022 409 The Identification of an Adequate Stressing Level to Find the Proper Running-In Conditions of a Lubricated DLC-Metal-System Joachim Faller Fraunhofer IWM MikroTribologie Centrum, Karlsruhe, Germany Corresponding author: joachim.faller@iwm.fraunhofer.de Matthias Scherge Fraunhofer IWM MikroTribologie Centrum, Karlsruhe, Germany 1. Introduction Until today there is no straightforward method to achieve a proper running-in of a tribological system (except for trial-and-error) [1,2]. This contribution therefor presents an analysis of a lubricated DLC-metal-system. Initial experiments served to identify the critical stressing levels, this means critical normal forces and/ or sliding velocities that trigger significant responses of the friction and wear signal. These stressing levels are called key levels and were used to construct a dedicated running-in procedure. 2. Methods Experiments were conducted on a pin-on-disk using a flat pin made from iron-plated aluminum and a DLC coated steel disk. The wear behavior was determined with a radionuclide wear measuring unit using a radioactively marked pin. The lubricant (fully formulated engine oil) was applied continuously to the disk. The experimental conditions are stated in table 1. Table 1: Experimental conditions parameter set point unit oil temperature 80 °C velocities 0.5-4.2 m/ s applied load 500/ 700/ 900/ 980 N nominal pressure 26/ 38/ 48/ 52 MPa level duration 4 h 3. Results and Discussion Starting with an initial parameter field covering the velocity-pressure-plane (see figure 1) leads to an overall linear wear behaviour and significant decrease in COF during the single stress levels. The identified key levels were combined to a new parameter field (figure 2) starting with high pressure and low velocity in order to achieve a high-power stressing of the tribological system. With this procedure, the significantly higher initial wear rates (150 nm/ h) were reduced to around 5 nm/ h after running-in along with a decrease in COF to 0.02. Figure 1: Initial parameter field with COF (green), wear (black) and linearized wear rate (yellow) High-power stressing leads to a degressive wear behavior. High wear rates at the beginning are linked to a topographical running-in, while the slow decrease in COF with small wear rates is caused by tribo-chemical running-in. The latter is closely related to third body formation. In order to achieve a successful running-in, high initial stress proves to be advantageous. Figure 2: Derived parameter field with COF (green), wear (black) and linearized wear rate (yellow) 410 23rd International Colloquium Tribology - January 2022 The Identification of an Adequate Stressing Level to Find the Proper Running-In Conditions of a Lubricated DLC-Metal-System References [1] Dowson, D.; Taylor, C.; Godet,M.; Berthe, D. (Eds.) The Running-in Process in Tribology; Butterworth- Heinemann: Oxford, UK, 1982; p. iv. [2] Blau, P.J. Running-in: Art or engineering? J. Mater. Eng. 1991, 13, 47-53. Digitisation in Tribology Rolling Contact 23rd International Colloquium Tribology - January 2022 415 Contact and Lubrication Aspects on Predicting the Contact Area in Lubricated Hot Rolling André Rudnytskyj AC2T research GmbH, Wiener Neustadt, Austria TU Wien, Vienna, Austria Corresponding author: andre.rudnytskyj@ac2t.at Martin Jech AC2T research GmbH, Wiener Neustadt, Austria Josef Leimhofer AMAG rolling GmbH, Ranshofen, Austria Stefan Krenn AC2T research GmbH, Wiener Neustadt, Austria Georg Vorlaufer AC2T research GmbH, Wiener Neustadt, Austria Markus Varga AC2T research GmbH, Wiener Neustadt, Austria Carsten Gachot TU Wien, Vienna, Austria 1. Introduction In the context of metal forming, bulk forming processes such as lubricated hot rolling involve a series of physical and chemical events in the contact zone between roll and workpiece [1]. In order to optimize such processes in terms of energy consumption, it is desirable to quantify and predict the friction forces due to the tribological aspects of the contact. For a sound tribological understanding of the friction conditions, it is required to estimate the real contact area [2,3]. In turn, the quantification of real contact area requires an accurate description of the material deformation behaviour, characterization of the surface topography, and defining the role of the lubricant. 2. Materials and Methods Timeand temperature-dependent plastic deformation is an important aspect of hot rolling of aluminium alloys of the 6xxx material grade. Assisted by high temperature tests on aluminium alloys 6061 and 6016, the material properties were modelled through advanced thermo-viscoplastic constitutive equations such as Eq. (1), calculating the material parameters (Q,A,a,nʹ) using Python programming language and its numerical libraries. Despite having similar properties at room temperature, the two alloys significantly differ with varying temperature and strain rate. The material laws of flow stress (σ f ) as a function of strain, strain rate, and temperature (ε,ἑ,T) were implemented in the numerical analysis of a contact applying the Finite Element Method (FEM), by use of the commercial software COMSOL Multiphysics ® . In order to investigate whether equation (1), which was derived from compression experiments, is appropriate to be used in a contact analysis, hardness tests at room and elevated temperatures were performed and compared to a FE indentation model. A contact patches approach in conjunction with a FE database [4] allows customized treatment of the surface and user-defined material models to be included in a contact analysis (Figure 1). 416 23rd International Colloquium Tribology - January 2022 Contact and Lubrication Aspects on Predicting the Contact Area in Lubricated Hot Rolling Figure 1: Surface topography is evaluated at chosen separation and contact patches are identified. Each individual contact patch (or asperity) is analysed in a FE simulation with the implemented material model. The presence of the lubricant and the characteristics of the topography may lead to a limitation in the real contact area if the lubricant is entrapped between asperities. Along with the development of an inlet film thickness, entrapped lubricant in so-called lubricant pockets could provide normal support, thus decreasing the real contact area. 3. Results The contact patches approach along with the user-defined material model allows to calculate the real contact area and contact load under tribological conditions of interest. These can be a set temperature or an approaching velocity, which can be related to actual rolling process parameters. The importance of correctly setting the appropriate temperature of the contact is evidenced by the FE database results, which is a consequence of the temperature-dependent material properties. Figure 2: Contact load of different sized asperities at different temperatures [5]. Additionally, different sizes of asperities resulted in different mean contact pressures (Figure 2). Such results indicate that not only the right operating conditions such as temperature and speeds must be well defined, but also the representation of the surface topography plays an important role. 4. Acknowledgments Part of this work was supported by the Austrian COM- ET-Program (K2 Project InTribology, no. 872176) and carried out at the “Excellence Centre of Tribology” (AC2T research GmbH). The government of Lower Austria supported the endowed professorship tribology at the TU Vienna (grant no. WST3-F-5031370/ 001-2017). References [1] Schey, J.A. “Tribology in metalworking: friction, lubrication, and wear”. American Society for Metals, 1983. [2] Nielsen, C. V., and N. Bay. “Review of friction modeling in metal forming processes.” Journal of Materials Processing Technology 255: 234-241; 2018. [3] Wilson, W., et al. “Real area of contact and boundary friction in metal forming.” Int. J. Mech. Sci. 30: 475-489; 1988. [4] Shisode, M.P., et al. “ Semi-analytical contact model to determine the flattening behavior of coated sheets under normal load.” Tribology International 146: 106-182; 2020 [5] Rudnytskyj, A., et al. “Influence of the 6061 aluminium alloy thermo-viscoplastic behaviour on the load-area relation of a contact”. Materials 14, 1352, 2021. 23rd International Colloquium Tribology - January 2022 417 Wear Modeling of non-conformal Rolling Contacts subjected to Boundary and Mixed Lubrication Andreas Winkler Corresponding author: winkler@mfk.fau.de Engineering Design, Friedrich-Alexander-University Erlangen-Nürnberg (FAU), Erlangen, Germany Marcel Bartz Engineering Design, Friedrich-Alexander-University Erlangen-Nürnberg (FAU), Erlangen, Germany Sandro Wartzack Engineering Design, Friedrich-Alexander-University Erlangen-Nürnberg (FAU), Erlangen, Germany 1. Introduction The striving for frictionand wear-optimized machine elements and the associated increasing use of low-viscosity lubricants leads to a shift of operating conditions from full film lubrication to the mixed lubrication or even the boundary lubrication regime. Therefore, detailed wear simulations offer great potential for the design of machine elements: On the one hand, operating conditions with an undesirably high wear rate can be systematically avoided. On the other hand, it enables the optimization of running-in processes, which have a decisive influence on the service life of machine elements subjected to mixed lubrication or boundary lubrication. 2. Numerical Wear Modeling Within this contribution, a general method for numerical wear modeling of machine elements operated under mixed and boundary lubrication is briefly described. The entire wear-modeling scheme is implemented using a commercial FEM software. 2.1 Mixed Lubrication Model Wear simulation of the mixed lubrication regime, as depicted in Figure 1, is implemented by the application of an FEM-based EHL-Model according to H abcHi [1] to solve for the R eynolds equation: A statistical contact model of rough surfaces (e.g. G Reen wood / w illiamson -model [2]) is used to calculate the asperity contact pressure. Moreover, the surface topography model of s uGimuRa and K imuRa [3] is used to consider the time-dependent change of the surface height distribution function, which is in turn required as an input for the applied statistical asperity contact model. EHL simulation and the asperity contact model are coupled in order to fulfil the equilibrium of the load balance equation: The Profile variation is calculated by means of a RcHaRd ’s wear model [4]. Figure 1: Wear Modeling (Mixed Lubrication) 418 23rd International Colloquium Tribology - January 2022 Wear Modeling of non-conformal Rolling Contacts subjected to Boundary and Mixed Lubrication 2.2 Boundary Lubrication Model In contrast to the first mentioned approach, wear simulation of the boundary lubrication regime relies on a FEMbased contact pressure calculation, see Figure 2. This modification was implemented since EHL simulations tends to become numerically unstable in the boundary lubrication regime. Figure 2: Wear Modeling (Boundary Lubrication) In analogy to the FEM-based EHL model according to H abcHi [1], a substitute body is defined which possesses equivalent mechanical properties of the base and counter body. This substitute body is contacted with a rigid surface, which in turn possesses the equivalent geometry of the base body and the counter body, see Figure 3. Figure 3: Contact Model (Boundary Lubrication) The remaining simulation procedure is based on the mixed lubrication model as described in section 2.1. 3. Experimental Determination of the wear coefficient The aim of this wear modeling approach is to utilize a universal wear coefficient that is valid for both the boundary lubrication and the mixed lubrication wear simulations. Therefore, the wear coefficient needs to be determined in the boundary lubrication regime. But since in the mixed lubrication regime only a part of the total load is carried by the asperities, the asperity contact pressure - not the total contact pressure - is used to calculate the wear volume by means of a RcHaRd ’s wear law: A two-disc tribometer was chosen as the experimental setup for the determination the boundary lubricated wear coefficient, see Figure 4. Figure 4: Two-Disc Tribometer The material of the discs as well as their surface roughness and the lubricant ought to match the conditions of the application to be investigated. However, the geometry of the discs, the kinematics and the lubricant film thickness should be selected so as to ensure that the two-disc contact operates within the boundary lubrication regime. On the one hand, the wear volume can be determined gravimetrically and converted via the density of the disc material: On the other hand, the wear volume can also be determined by profile measurement of the worn disc. In this case, the worn cross-sectional area A wear must be determined: Finally, the wear coefficient can be calculated: 4. Conclusion and Outlook The presented wear modeling approach offers the possibility to calculate the surface profile evolution as well as the time-dependent change of the surface height distribution in any lubrication regime. Commercial FEM software is used to calculate contact pressures. Moreover, an experimental setup for the determination of the wear coefficient for a RcHaRd ’s wear law was presented. Since lubricant additives and the chemical processes at the interfaces can strongly influence the wear behavior, future research should focus to a greater extent on the influence of interface chemistry on the wear of tribological systems. 23rd International Colloquium Tribology - January 2022 419 Wear Modeling of non-conformal Rolling Contacts subjected to Boundary and Mixed Lubrication References [1] H abcHi , W., “Finite Element Modeling of Elastohydrodynamic Lubrication Problems”, John Wiley & Sons Incorporated, 2018. [2] Greenwood, J.A. et al., “Contact of nominally flat surfaces”, Proc. R. Soc. A: Math. Phys. Eng. Sci., 295, 1442, 1966, 300-319. [3] Sugimura, J. et al., “Analysis of the topographical changes due to wear”, J. Jpn. Soc. Lubr. Eng., 31, 11, 1986, 813-820. [4] Archard, J.F., “Contact and Rubbing of Flat Surfaces”, J. Appl. Phys., 24, 8, 1953, 981-988. Digitisation 23rd International Colloquium Tribology - January 2022 423 Artificial Intelligence in Tribology: Design of new dispersants using artificial intelligence tools Nuria E. Campillo ICMAT (CSIC). Nicolás Cabrera, nº 13-15. Campus de Cantoblanco, UAM. 28049, Madrid, Spain. CoFounder of AItenea Biotech. CIB Margarita Salas (CSIC) Ramiro de Maeztu, 9. 28740, Madrid, Spain Corresponding author: nuria.campillo@csic.es Pablo Talavante AItenea Biotech. Parque Científico de Madrid. Ciudad Univer.de Cantoblanco. Calle Faraday, 7. 28049, Madrid, Spain. Ignacio Ponzoni Institute for Computer Science and Engineering (UNS-CONICET), Bahía Blanca, Argentina. Department of Computer Science and Engineering, Universidad Nacional del Sur, Bahía Blanca, Argentina. Axel J. Soto Institute for Computer Science and Engineering (UNS-CONICET), Bahía Blanca, Argentina. Department of Computer Science and Engineering, Universidad Nacional del Sur, Bahía Blanca, Argentina. María J. Martínez ISISTAN (CONICET - UNCPBA) Campus Universitario - Paraje Arroyo Seco, Tandil, Argentina. Roí Naveiro ICMAT (CSIC). Nicolás Cabrera, nº 13-15. Campus de Cantoblanco, UAM. 28049, Madrid, Spain. Ramón Gómez-Arrayas Dep. of Organic Chemistry and Institute for Advanced Research in Chemical Sciences, UAM. 28049, Madrid, Spain. CoFounder of AItenea Biotech. Mario Franco Dep. of Organic Chemistry and Institute for Advanced Research in Chemical Sciences, UAM. 28049, Madrid, Spain. Shin-Ho Kim Lee AItenea Biotech. Parque Científico de Madrid. Ciudad Univer.de Cantoblanco. Calle Faraday, 7. 28049, Madrid, Spain. Pablo Mauleón Dep. of Organic Chemistry and Institute for Advanced Research in Chemical Sciences, UAM. 28049, Madrid, Spain. Guillermo Revilla-Lopez Repsol Technology Lab DC Tech. & Corporate Venturing, Agustín de Betancourt s/ n, 28935 Móstoles, Madrid, Spain. Marco Bernabei Repsol Technology Lab DC Tech. & Corporate Venturing, Agustín de Betancourt s/ n, 28935 Móstoles, Madrid, Spain. 1. Introduction Dispersants are the main additives in oils and lubricants to help keep engines clean and free of deposits. These polymeric surfactant-like molecules are characterized by at least one hydrophobic, oil soluble ‘tail’ polymer backbone component, often polyisobutylene (PIB), and at least one hydrophilic, polar ‘head’ unit that adsorbs onto the carbon deposit precursors (mainly sludge soot particles). An efficient dispersant design requires tailoring the nature of the chemical interactions to meet the performance characteristics of a particular engine, for which a number of parameters need to be fine-tuned. Despite the knowledge available, the chemistry for production of 424 23rd International Colloquium Tribology - January 2022 Artificial Intelligence in Tribology: Design of new dispersants using artificial intelligence tools dispersants in use today remains limited. The design of dispersants is typically carried out through trial and error, coupled with chemical intuition, but this process is expensive and time-consuming. In sharp contrast, artificial intelligence (AI) has the potential to guide the design of next generation materials, allowing both economic and time savings. Herein we describe an AI framework for dispersant design and optimization. Two complementary strategies were developed using unsupervised and supervised learning, dimensionality reduction methods and data visualization approaches. This framework predicts performance properties of new dispersants as part of virtual screening (VS) strategies to identify the most promising candidates. 2. Computational Modelling Framework A dataset with 83 PIB derivatives was collected from the literature, and a wide range of molecular descriptors were computed using Mordred library for each chemical structure. In addition, SMILES embeddings were also computed using a Transformer-based model. Then, two AI models were learned providing different approaches to rank candidate compounds during virtual screening. Therefore, the best candidate is selected by a consensus. 2.1 Model based on structural similarity distances The first step was to conduct a feature selection procedure to identify a reduced set of molecular descriptors statistically related to the target property. This procedure was carried out by analyzing the outputs of several feature selection techniques using VIDEAN [1]. The selected descriptors are used to study the structural similarity between the compounds in the database, and to visually project those molecules on two-dimensional spaces, using for example tSNE[2]. Subsequently, to rank the candidates during the VS stage, the k-nearest-neighbors method is used in the original representation space to identify the projected regions where each candidate is located, and to infer from their locations which of them are the most promising chemical structures. Simultaneously with the visualization of the two-dimensional projections, a pairwise analysis of the relationship between the selected descriptors is also shown by means of a scatter plot matrix. The pairwise analysis enables a better interpretation of the low-dimensional projection in terms of the structural similarity defined by the descriptors. Finally, for each candidate, a numerical estimation of its target property value and its closeness to the chemical space represented by the database molecules is provided. 2.2 Supervised model To identify the single best probabilistic model, comparisons between different models, hyperparameter tuning and feature selection were carried out. Mean Absolute Error estimated via cross validation was used as a performance metric. The features included came from both, molecular descriptors and SMILES embeddings. The best resulting model was BART[3] including 14 features, half of them being molecular descriptors, while the other half being SMILES embeddings. Variable selection was performed using the procedure described by Bleich et al. [4]. Given a new candidate molecule, the model produces samples from the posterior predictive dispersancy. These samples are then used to compute different metrics to evaluate the candidate. In particular, the expected improvement with respect to the best available molecule is computed to identify which candidates for further development. Other helpful metrics are: mean predictive dispersancy, predictive standard deviation and probability of improvement. Finally, to gain some interpretability, the model is used to compute partial dependence plots. These serve to illustrate how each of the features affects dispersancy, on average. Additionally, to give some interpretation to the covariates coming from SMILES embeddings, molecular descriptors highly correlated with each of the embedding-based variables are computed. 3. Conclusion The use of AI is having a growing impact on the design of new molecular compounds. Although it does not replace some of the traditional wet-lab experimentation, it is playing a key role in accelerating discovery/ design of new materials such as dispersants. In this work, we have illustrated how unsupervised and supervised learning can be successfully combined for virtual screening in the design of new dispersants. We also concluded that visual analytical strategies help to chemical experts with the outputs produced by the machine learning models, contributing to the interpretability of the results. In brief, our AI methodology gives useful insights to material designers beyond the limits of a classical Edisonian approach to materials discovery. References [1] Martínez, M.J., Ponzoni, I., Díaz, M. et al. “Visual analytics in cheminformatics: user-supervised descriptor selection for QSAR methods”. J Cheminform 7, 39, 2015. [2] van der Maaten, L. & Hinton, G. “Visualizing Data Using t-SNE”. J Mach Learn Res 9: 2579-2605, 2008. [3] Chipman, H., George, E., & McCulloch, R. “BART: Bayesian additive regression trees.” The Annals of Applied Statistics, 4(1), 266-298, 2010. [4] Bleich, J., Kapelner, A., Jensen, S. & George, E. “Variable selection inference for bayesian additive regression trees”. arXiv: 1310.4887v1, 2013. 23rd International Colloquium Tribology - January 2022 425 Preparation of measured engineering surfaces for digital twins in tribology Yuechang Wang Institute of Functional Surfaces, University of Leeds, Leeds, UK Corresponding author: y.wang1@leeds.ac.uk Abdullah Azam Institute of Functional Surfaces, University of Leeds, Leeds, UK Mark C.T Wilson Institute of Functional Surfaces, University of Leeds, Leeds, UK 1. Introduction Digital twins in tribology are precise, virtual copies to predict the tribologcial performance, e.g., friction, wear, and tribofilm formation of laboratory apparatus, machine components. or even engineering systems. Surface topography, evolving during the tribological processes, plays an essential role in building digital twins in tribology. Although measurement, characterization, and modeling of surface topography have been well studied, the application of surface topography in constructing digital twins in tribology is still rudimentary. Some published works only use several classic roughness parameters to incorporate the surface topography. Although many researchers report that measured surface topography is used, the necessary preparation of measured engineering surfaces is rarely mentioned. As yet there appears to be no general guidance on preparing measured engineering surfaces for digital twins in tribology. Therefore, the authors attempt to establish such a framework by the latest progress of surface modeling in this report. 2. Proposed framework The proposed framework consists of characterization, filtration and resampling, and reconstruction of rough surfaces. The three parts are not independent but related to each other. This framework aims to generate rough surfaces that contain the surface features of interest and are ready to use in further numerical models. 2.1 Characterization of rough surfaces Unlike other works on characterizing rough surfaces by various roughness parameters, the current study considers them based on the reconstruction requirements of rough surfaces. The recent work of Pérez-Ràfols and Almqvist provided a new technique to generate rough surfaces with a given surface height probability distribution (HPD) and power spectral density (PSD). Following their method, the current study proposes to use the HPD and PSD to characterize the measured rough surfaces. For the HPD, the empirical cumulative distribution function (CDF) with generalized Pareto distributions (GPDs) in the tails is used to estimate the CDF of measured surfaces. The Pareto tails can improve the smoothness of the distribution in the tails where data might be sparse. The PSD is directly calculated from the surface heigh matrix z by the following equation. (1) The S z is a real centrosymmetric matrix, which illustrates the double-sided power spectrum. 2.2 Filtration and resampling of rough surfaces The size and resolution of the measured rough surfaces are determined by the specific measurement equipment and corresponding measurement settings. Thus, the measured surface data usually cannot be directly input into numerical models of specific tribology systems. According to the specific application scenarios, the measured surfaces usually need to be filtered or decomposed to specific frequency ranges. Moreover, the measured surfaces usually have dense mesh grids, such as 1024×1024 points. Such grid sizes result in substantial computational cost in running numerical models of tribological problems. Therefore, after the filtration of measured surfaces, it is necessary to resample the surfaces to coarse grids while keeping the essential roughness features. The current work proposes a solution for resampling the filtered rough surfaces based on the characterization and reconstruction of rough surfaces. The HPD and PSD of the filtered rough surfaces are calculated. Then the PSD is resampled. The resampled PSD and the HPD are used 426 23rd International Colloquium Tribology - January 2022 Preparation of measured engineering surfaces for digital twins in tribology to reconstruct rough surfaces, which can be directly used in subsequent numerical simulations. 2.3 Reconstruction of rough surfaces The reconstruction procedures developed by Pérez-Ràfols and Almqvist are used. Random series following the estimated HPD of rough surfaces and the target PSD are the inputs of the reconstruction method. Then the simulated rough surface is iteratively updated to approach the desired HPD and PSD until the predetermined criteria are reached. Detailed descriptions of the reconstruction procedures can be seen in Ref [1]. In summary, the proposed framework to prepare the measured rough surfaces for tribological digital twins can be illustrated by the schematic diagram Figure 1. Figure 1: Schematic diagram of the proposed framework 3. Results and discussions In this extended abstract, measured honing and lapping surfaces were used to illustrate the proposed framework. The size of measured surfaces is 833mm×833mm with grid size 1024×1024. Figure 2 shows the results for a measured honing surface. 23rd International Colloquium Tribology - January 2022 427 Preparation of measured engineering surfaces for digital twins in tribology Figure 2: (a) Measured honing surface, (b) Simulated honing surface, (c) HPD, (d) PSD It can be seen that the simulated honing surface has similar patterns to the measured one. The HPD and PSD of the simulated surface agree with the measured one. Figure 3 shows the results for a measured lapping surface, which has filtered out the high-frequency components and resampled to 256×256 grids. The simulated surface is based on the filtered lapping surface and is resampled to 256×256 grids. 428 23rd International Colloquium Tribology - January 2022 Preparation of measured engineering surfaces for digital twins in tribology Figure 3: (a) Measured lapping surface, (b) Filtered lapping surface, (c) Simulated surface with resampling (256×256 points), (d) HPD, (e) PSD The results show that the simulated one has similar features to the filtered one. Moreover, the HPD and PSD curves show a good match between the simulated and filtered surfaces, although they have different grid sizes. The preliminary results above prove that the proposed framework can characterize and reconstruct the measured rough surfaces with different features by HPD and PSD. Moreover, the resampling procedures are also proved preliminarily. One interesting finding is that the simulated honing surface does not show the significant grooves in the measured one, although the HPD and PSD of the measured surface are kept in the reconstruction. This result indicates that HPD and PSD cannot fully characterize some features, and other characterization methods should be used. 4. Conclusion A framework for preparing the measured engineering surfaces for digital twins in tribology is proposed. The framework includes characterization, filtration, resampling, and reconstruction procedures, which have been proved to be valid preliminarily. Reference [1] Pérez-Ràfols F, Almqvist A. Generating randomly rough surfaces with given height probability distribution and power spectrum. Tribology International. 2019; 131: 591-604. 23rd International Colloquium Tribology - January 2022 429 Tribological Experiments in the Age of Big Data Nikolay T. Garabedian Institute for Applied Materials (IAM), Karlsruhe Institute of Technology (KIT), Karlsruhe, Germany Paul J. Schreiber Institute for Applied Materials (IAM), Karlsruhe Institute of Technology (KIT), Karlsruhe, Germany Christian Greiner Institute for Applied Materials (IAM), Karlsruhe Institute of Technology (KIT), Karlsruhe, Germany Corresponding author: christian.greiner@kit.edu 1. Introduction Among the many reasons for implementing robust data management of scientific results, there are two that stand out: i) the increasing demand put forward by public funding agencies, and ii) the potential for accelerated scientific discovery by integrating machine learning (ML) into tribology research. Due to higher computing and storage capabilities, ML has evolved to rely heavily on large pools of data that can serve to train predictive or analytical algorithms. Such an approach sits in the core of the “big data” idea. Establishing a database which can be treated as “big data in tribology” presents multiple challenges. First, in an experimental lab setting exact tribological properties of a particular system are often unique to the specific test itself; this presupposes that in order to cover a broad range of testing conditions, a large number of tests need to be performed. Second, the field of tribology is inherently multidisciplinary, an artefact related to the diversity of scientific interrogations that could be conducted during the analysis of an entire system of bodies in motion. These two challenges can be addressed by constructing protocols for the fully digital collection and manipulation of data and metadata. The principles of producing findable, accessible, interoperable, and reusable (FAIR) [1] data were suggested as a set of strategies, which when observed enable the exchange and efficient utilization of scientific results. Since tribological properties are a function of entire systems, making data interoperable requires that enough details are attached to any shared data. These details usually need to include not just the features confined to the time frame of the experiment (e.g., base and counter bodies, tribometer, environment, etc.), but they must extend to the processes that produced the specimens of interest. This information is essential for the interpretability, traceability and repeatability of the scientific outcomes. In order to satisfy the FAIR principles, a certain degree of standardization is needed. This does not necessarily call for coordinating global standards, but rather the construction of local standards, which are interoperable between each other. Constructing such standards via ontologies provides a scalable way for knowledge formalization. This was already recognized in the field and a general tribology ontology (called tribAIn) was proposed [2]. Additionally, ontological schemas offer the systematic input of details about objects from different angles. Therefore, such an approach seems like a viable strategy for including the myriad of aspects in which a tribological system can be analyzed. However, just having standards defined is not enough for the digital transformation of tribological experiments. It is also essential that data is automatically recorded within the constructed schema, in order to minimize the effect of human intervention; it is also necessary that the new methods for data storage do not slow down existing scientific workflows. Thus, a viable solution could be the integration of virtual lab environments which ease the communication chain between equipment, data storage, and researchers. One such environment is Kadi4Mat [3], which among other benefits features an electronic lab notebook (ELN) functionality. Connecting tribological equipment and ELN’s, however, is only possible by involving both software developers and tribologists. This paper describes the reimplementation of an experiment, which was part of a past publication by the lab. By striving to digitize each step of the process, we had a chance to develop the necessary tools that can serve as the basis for expanding to system to the rest of experimental protocols in the lab. 430 23rd International Colloquium Tribology - January 2022 Tribological Experiments in the Age of Big Data Figure 1: A simplified overview of the route taken to digitizing one exemplary showcase pin-on-disk tribological experiment. The results are the proposed “FAIR Data Package” and set of tools for its assembly, described below. 2. Methods This project commenced by assembling a team of ten doctoral and postdoctoral researchers who collaboratively listed all objects, processes, and relevant input parameters that constitute typical laboratory experiments. In order to collaborate, a local “TriboWiki” was installed using an instance of MediaWiki, chosen for its wellknown and intuitive environment. Once the lists of terms were established, to narrow down the scope of the project, a “showcase” experiment was selected. It is based on a previous publication [4] and represents a typical lubricated pin-on-disk experiment on a commercial tribometer. The motivation for this particular experiment came from the availability of the same materials, machines and lab protocols. The terms describing the lifecycle of this experiment were organized within an ontology (called TriboData- FAIR Ontology), which was developed using the Protégé software, and the upper SUMO and EXPO ontologies were used, with tribAIn to a limited extent. The three major technical solutions developed during this project aimed at easing tribologists’ interaction with Kadi4Mat with the aim of ensuring that data was recorded observing the FAIR principles, while not requiring extended training or time. The first solution (called SurfTheOWL) is a program that converts the ontological class structure into a hierarchical list of descriptions for each procedure and instrument used in the showcase experiment; it is operated within a web interface, and offers a machine-readable export of the list, which could be utilized as a pre-assembled template directly into an ELN. The second solution came in the form of a guided user interface, which was mounted on a tablet computer; this software offers the collection of details about analogue processes (without computer control, such as polishing, cleaning, etc.) and aims to replace the paper lab journals with its flexible but still systematic event logging. The third solution comes in the form of a generic LabVIEW code, which attaches to the final parts of tribometer programs. This implementation establishes a connection with Kadi4Mat, creates a record within it, and then uploads the collected data, metadata, and descriptions. 3. Results The major outcome of this project (shown schematically in Figure 1) is the so-called “FAIR Data Package” of a tribological experiment. The main feature of the package is the availability of descriptions, data, and metadata in both a machineand human-operable structure. The package contains the necessary information for conducting inquiries about data provenance (e.g., converting raw into processed data), or to explore the relations between machines, operators, and processes. The documentation associated with the meaning of each entry in the package is contained within the TriboDataFAIR Ontology, which is publicly hosted on GitHub; the various records within the FAIR package are referenced to the specific version of the ontology through GitHub commit hashes. All of these features make the data that was collected during this project interoperable and reusable. The entire FAIR data package is uploaded to Zenodo where it becomes findable and accessible. 4. Conclusions and Outlook By going through an entire chain of sub-projects needed for the production of FAIR tribological data, we developed a possible approach and a set of tools for the future integration of such a system in experimentalists’ daily lab routine. Not surprisingly, to complete such a project three core teams needed to work simultaneously: a large group of domain experts in tribology, a team of virtual research environment developers, and a coordinating body of project managers. Looking into the future, once more similar systems are suggested by other labs, there will be a need for software solutions (again developed by tribologists and computer scientists), which will enable automatic remapping of knowledge graphs given the specificities of each individual research group. References [1] M. D. Wilkinson et al., “Comment: The FAIR Guiding Principles for scientific data management and stewardship,” Sci. Data, vol. 3, no. 1, p. 160018, Dec. 2016. 23rd International Colloquium Tribology - January 2022 431 Tribological Experiments in the Age of Big Data [2] P. Kügler, M. Marian, B. Schleich, S. Tremmel, and S. Wartzack, “tribAIn-Towards an explicit specification of shared tribological understanding,” Appl. Sci., vol. 10, no. 13, 2020. [3] N. Brandt et al., “Kadi4mat: A research data infrastructure for materials science,” Data Sci. J., vol. 20, no. 1, pp. 1-14, Feb. 2021. [4] A. Codrignani, B. Frohnapfel, F. Magagnato, P. Schreiber, J. Schneider, and P. Gumbsch, “Numerical and experimental investigation of texture shape and position in the macroscopic contact,” Tribol. Int., vol. 122, pp. 46-57, Jun. 2018. 433 Digitalization and lubricant analyses - an efficient partnership Stefan Mitterer OELCHECK GmbH, Brannenburg Michael Linnerer OELCHECK GmbH, Brannenburg 1. Introduction Oil analyses are quite rightly a central topic in condition monitoring of the lubricating oil and the machine. They provide reliable values for setting an ideal oil change interval, contamination control and show abnormal wear situations at an early stage. Rapid technological progress sets significantly higher demands on lubrication, which can only be met by new special lubricants, which increasingly developed for particular applications. 1.1 Big Data Big Data represents another central point in the field of industrial development. Thanks to newer and faster systems and algorithms, the data will hardly be detectable by humans. Nevertheless, Big Data will permanently change many areas, as the algorithms can often react and act within a few seconds due to the sheer volume of data. With Big Data, one gains insights from the abundance of data. The mountain of data is getting bigger and bigger. As much as possible is being stored in the search for benefit and advantage. The bigger the mountain, the more difficult it is to derive connections and statements from it. However, the bigger the mass of data, the richer the data, the greater the benefit that can be derived from it. For this, however, it is also a prerequisite to have new and powerful IT systems available with which to process the information. 1.2 Significance for lubricant analysis Various tests are available for the analysis of lubricants and operating fluids. It is essential to define the appropriate tests for the respective fluids and the corresponding application. This selection of analyses is used to check whether there are any abnormalities in the fluid which also allow conclusions to be drawn about the condition of the machine. Thus, in addition to element analysis, viscosity measurement or FTIR spectroscopy for a hydraulic application, particle counting can also provide important information. In an engine, on the other hand, conclusions about the acid number (AN) or base number (BN) are decisive for the customer. The topics of data analysis are also becoming increasingly important for the analyses of lubricants and operating fluids. A large and sustainable database is an important prerequisite for obtaining detailed information from the data. The demands on analytics now go far beyond the assessment of individual samples. In addition to monitoring individual machines and their trendlines, customers often want to draw more information content from the analyses carried out. The monitoring of both the individual machine and the operating lubricant are only one reason. Questions arise such as: Do the analysis values in several identical machines with different load profiles behave identically or where are differences and why? Are deviations evident in different regions in relation to an entire fleet of machines and why do they occur? These are just two of countless questions that indicate what expectations are placed on the large amounts of data generated in lubricant analysis. 2. Possibilities of data collection In order to be able to assign the data to the lubricant samples, a correct transfer of the information is the basic prerequisite. There are various options available for this purpose: 1. Filling out the paper sample form 2. Entering the data electronically in the customer portal 3. Sending the information via app 4. Importing the data via a connection of the systems from the customer to the laboratory After the analysis kits have been ordered, they are delivered to the customer. The customer takes the samples and sends them back to the laboratory with the corresponding information. After the analysis has been carried out, the analysis values and thus the laboratory report are passed on to the customer. 2.1 Information path from the client to the laboratory First of all, the information path from the customer to the laboratory. Here, electronic data collection offers decisive advantages compared to the paper version of the sample information form: 434 23rd International Colloquium Tribology - January 2022 Digitalization and lubricant analyses - an efficient partnership - Basic data already implemented - Avoiding data input errors - Plausibility checks (operation time) - Definition of mandatory fields - Automated allocation of sample to machine There are therefore no ambiguities as can occur with illegible handwriting. In addition, a lot of information about the machines and the lubricant is already implemented and makes data collection much easier, faster and thus more efficient for the customer. 2.2 Information path from the laboratory to the customer After the analysis in the laboratory has been completed and the values have been evaluated, the data and laboratory reports are to be sent back to the customer. There are now also various options for sending the laboratory report and its data: - In paper form by post - or electronically - As a PDF file via E-mail - Export of the sample data in various formats - Storage of the data on a FTP server - Retrieval of analysis data via API connection Diagram 1: Options for sending lab data When looking at individual samples or trendlines, it is sufficient to summarize the respective analysis data in a laboratory report. However, considering that a single laboratory report can contain up to 40 individual values, the preparation of the analysis data for a larger number of laboratory reports is a challenge. Consequently, the complete path of data transmission from the customer to the laboratory and back again must be optimized accordingly. This is where specially set up data exports or linking the IT systems come into play. With a data export, the analysis results can be transmitted in the desired form and thus processed directly at the customer’s site in their software. The export of data can be carried out in the customer portal of the laboratory by the customer himself. Another possibility is to send a daily, automated export to the customer. This can be done in the form of e-mails, but also by making the analysis data available on an FTP server. FTP stands for “File Transfer Protocol”, which is a way of transferring data. It is a communication protocol that allows different systems to communicate with each other. In this way, the analysis data from the laboratory are made available to the customer at a defined point in time and the customer can pick them up and process them accordingly. A direct connection between the customer’s and the laboratory’s systems is even more elegant. A direct system coupling can take place via so-called API interfaces. An API (Application Programming Interface) is used to exchange information between an application and individual programs in a standardized manner. The transfer of data and commands is structured according to a previously defined syntax. This makes it possible to access all data at any time. In addition to current analysis data, analyses from the history can also be used, as the interface allows a permanent and continuous exchange of information. In summary, the API interface offers the following advantages for the customer: • Digital data transfer (Input/ Output) • Full integration of lab systems into customer systems • Improvement of the data quality The presentation will show the possibilities of digital data transfer and the advantages for the operator. The whole chain of transferring data is described and how the analysis parameters can be prepared. Using the example of some applications, the benefit of digital significance is represented and which technical and thus financial advantages can be derived from it. Simulation 23rd International Colloquium Tribology - January 2022 437 Molecular dynamics simulation on the behavior of viscosity modifying polymers in oil Shuhei Yamamoto Mitsui chemicals, Inc., Sodegaura, Japan Corresponding author: Shuhei.Yamamoto@mitsuichemicals.com Kazunori Kamio Mitsui chemicals, Inc., Sodegaura, Japan Yoshiki Ishii Graduate School of Information Science, University of Hyogo, Kobe, Japan Deboprasad Talukdar Graduate School of Information Science, University of Hyogo, Kobe, Japan Kosar Khajeh Graduate School of Information Science, University of Hyogo, Kobe, Japan Gentaro Sawai Graduate School of Information Science, University of Hyogo, Kobe, Japan Kyosuke Kawakita Graduate School of Information Science, University of Hyogo, Kobe, Japan Eiji Tomiyama Graduate School of Information Science, University of Hyogo, Kobe, Japan Hitoshi Washizu Graduate School of Information Science, University of Hyogo, Kobe, Japan 1. Introduction Increasing global concern about the environment requires industry to develop better fuel economy tech-nologies, not only automotives but also construction machineries, agricultural machines, injection molding machines, and so on. Liquid olefin copolymer (L-OCP) is one type of viscos-ity modifying polymer, derived from ethylene and α-olefin, used for drive system lubricants due to the better shear stability based on the lower molecular weight than conventional olefin copolymer used for engine oil. Application of L-OCP to hydraulic fluids is now being studied. Recently, energy efficiency improvement of hydraulic fluid formulated with L-OCP in the field and on the bench tests are reported [1]. Secondary-flow suppression effect of L-OCP in hydraulic fluid has been proposed as a mechanism of the phenomenon [2]. In this study, two types of simulations are done to investigate the mechanism of the phenomenon from the points of view of molecular dynamics (MD) and hydro-dynamics. First one is, the all-atom MD simulation is utilized to examine the behavior and the adsorption process onto the Fe surface of two polymers, L-OCP and polyalkyl-methacrylate (PMA) in hydraulic fluid. Second one is, here we show our multi-physics numeri-cal simulation approach to investigate the dynamics of polymer solution. The numerical scheme is to provide the dynamics of suspensions of Brownian particles, coupling molecular motion treated by Langevin equa-tion and hydro-dynamics treated by lattice Boltzmann method. The motion of polymer segments are simulated under the flow in confined geometry. In order to simu-late chemical feature of realistic polymers, we modify each polymer segment as polar and non-polar particles. Point dipoles are added as the polar segments. Since the relative permittivity is very low in oil condition, the structure and dynamics of the polymer is strongly af-fected by the distribution of the polar segments. 438 23rd International Colloquium Tribology - January 2022 Molecular dynamics simulation on the behavior of viscosity modifying polymers in oil 2. Simulation Methods 2.1 MD simulation All-atom MD simulations of the adsorption process of polymers (L-OCP, PMA) in base oil are done in the following manner [3]. Simplified molecules of L-OCP, PMA, 3, 5-diethyldodecane (DED) taken from the structure of the poly α-olefin used as base oil, and schematic picture of the simulation model confined by two solid layers, placed a neutral Fe wall at the top and a charged Fe wall at the bottom is illustrated in Figure 1, 2. In this MD simulation, the partial atomic charges on the organic molecules are assigned by the MOPAC6 semi-empirical molecular orbital calculation with the Hamil-tonian: AM1, the organic molecules are dynamically treated using the Dreiding force field. By means of LAMMPS (Large-Scale Atomic/ Molecular Massively Parallel Simulator), adsorbing behaviour of each simpli-fied molecule to the charged Fe wall in 299 base oil molecules is examined at the constant temperature of 473 K for 10 ns. Figure 1: Schematic molecular structures of base oil, and L-OCP, PMA 2.2 BD (Brownian Dynamics) and LBM (Lattice Boltzmann) Coupling scheme Figure 2: Schematic picture of the MD simulation The motion of the Brownian particles (polymer segments) are tracked by the Langevin equation, whereas the Navier-Stokes equation governing the behavior of the host fluid is analyzed by using the lattice Boltz-mann method [4]. The two equations are coupled through the friction between the particle and surround-ing fluid. The friction force is proportional to the veloc-ity of a particle relative to the host fluid. The lattice Boltzmann method is employed for the flow simulation, which is compatible with massive parallel computing, and is easy to apply various types of boundary condi-tions such as the periodical shear boundary, and com-plex structure. The polymers are described as bead-spring model, i.e. each polymer segment described as a points are tied together with springs. The polymer segments have van der Waals interaction described by Lennard-Jones poten-tial. Then the interaction between functional groups are calculated by dipole-dipole interaction. 3. Results and Discussions 3.1 MD simulation Simulation results of the adsorption process onto the Fe surface of L-OCP and PMA initially placed at the bottom of liquid phase are shown in Figure 3. We observe that PMA interacts with Fe surface more frequently than L-OCP, besides the adsorbing duration of PMA is longer than that of L-OCP. After approaching the Fe surface from a terminal of molecule affected by base oil molecules’ diffusion/ aggregation, PMA tends to strongly ad- 23rd International Colloquium Tribology - January 2022 439 Molecular dynamics simulation on the behavior of viscosity modifying polymers in oil sorb onto the Fe surface due to the polar groups, while L-OCP does temporarily and easily de-sorb from the Fe surface. In addition, simulation results also imply that base oil molecules form thin layer onto the Fe surface, which has an influence on the adsorption process that L-OCP and PMA molecules’ approach the Fe surface does not always result in the adsorption. Figure 3: Snapshots of the adsorption process. 3.2 BD (Brownian Dynamics) and LBM (Lattice Boltzmann) Coupling scheme Figure 4 shows the thermal equilibrium structure of non-polar and partially polar polymers. Segment number are 128 for each polymer and the polar segments are set in every 4 segments. The stretched structure in non-polar polymer and aggregated structure in polar polymer are clearly distinguished. The steady state structure of 2 polymer (each 128 non-polar beads) under shear are shown in Figure 5. Upper boundary is sliding in each sliding velocity and the width between upper and lower boundary is 96 nm. Under very high shear (100 m/ s), each polymer is stretched and the velocity field are almost as given. In middle shear (10 m/ s), the velocity field made by the polymer motion become actual, and in low shear (1 m/ s), the velocity fields are disordered even in very low Reynolds number. This mean the effect of polymer structure strongly affect the flow dy-namics in low flow speed region. 4. Conclusion Two types of simulations were conducted to investigate the influence of viscosity modifying polymers on the secondary-flow in hydraulic fluid. These simulations revealed that the polymer structure difference affects the adsorption tendency onto the Fe surface and the flow dynamics, which may result in the secondary-flow pat-terns. Figure 4: Snapshots of polymer of non-polar (dark gray) and polar (light gray) polymers. The polar seg-ments are described by red sphere. Figure 5: Snapshots of polymers under shear calculated by BD-LBM simulation. This study provides a methodology for simulating secondary-flow suppression effect of viscosity modifying polymers, and contributes to establishment of a novel fuel economy technology for lubricants. 5. Acknowledgments The authors thank Dr. Hiroaki Yoshida for useful help. References [1] M. Moon, Lubes ‘n’ Greases, 25 (No. 10), 20 (2019) 34. [2] I.K. Karathanassis, E. Pashkovski, M. Heidari-Koochi, et al., J. Nonnewton. Fluid Mech. 275, (2020) 104221. [3] M. Konishi, H. Washizu, Trib. Intl. 149, (2020) 105568. [4] H. Yoshida, T. Kinjo, H. Washizu, Chem. Phys. Lett., 737 (2019) 136809. 23rd International Colloquium Tribology - January 2022 441 Molecular Dynamics Study of the Adsorption of Organic Friction Modifiers on Iron Oxide Surfaces Pablo Navarro Acero Nextmol (Bytelab Solutions SL), Carrer de Roc Boronat 117, 08018 Barcelona, Spain Barcelona Supercomputing Center (BSC-CNS), Carrer Jordi Girona 29, 08034 Barcelona, Spain Stephan Mohr Nextmol (Bytelab Solutions SL), Carrer de Roc Boronat 117, 08018 Barcelona, Spain Barcelona Supercomputing Center (BSC-CNS), Carrer Jordi Girona 29, 08034 Barcelona, Spain Corresponding author: stephan.mohr@nextmol.com Marco Bernabei Repsol Technology Lab, DC Technology & Corporate Venturing, Agustín de Betancourt s/ n, 28935 Mostoles, Madrid, Spain Carlos Fernández Repsol Technology Lab, DC Technology & Corporate Venturing, Agustín de Betancourt s/ n, 28935 Mostoles, Madrid, Spain Beatriz Dominguez Repsol Technology Lab, DC Technology & Corporate Venturing, Agustín de Betancourt s/ n, 28935 Mostoles, Madrid, Spain James Ewen Department of Mechanical Engineering, Imperial College London, South Kensington Campus, London, SW7 2AZ, U.K 1. Introduction The adsorption and self-assembly of surfactants at solid-liquid interfaces plays a key role in a wide range of technological processes. In boundary lubrication conditions, lubricant additives that reduce friction are vital to increase the energy efficiency of moving engine components. However, due to concerns with respect to detrimental side effects caused by certain chemical elements found in conventional friction modifier additives, there is an increasing interest in so-called organic friction modifiers (OFM) that only contain C, H, O and N atoms. The performance of OFMs, as well as other additives, depends critically on their ability to adsorb onto the metal surface of the engine components and to form self-assembled layers that then result in the desired friction reduction. Therefore, understanding the relation between the initial concentration of the additive in the lubricant and the resulting surface coverage is extremely important for lubricant formulations and other surfactant applications in general. 2. Computational Modelling Approach In recent years, molecular simulations have provided additional insights into the nanoscale behavior of a wide range of lubricant additives, including OFMs. These insights at the atomic scale are essential to develop new additives with improved performance. Thanks to considerable advances in both theory and algorithmic development seen in recent years, combined with the steadily increasing power of modern supercomputers, it is now possible to simulate complex systems and phenomena with high accuracy and within reasonable time. In the current study, we used Molecular Dynamics (MD) to study the adsorption isotherm of three different OFMs (stearic acid, glycerol monooleate and glycerol monoostearate) onto a hematite surface with hydrogenated 1-decene trimer (main constituent of PAO 4 base oil) acting as bulk solvent. 2.1 Adsorption PMF First, we calculated the potential of mean force (PMF) of the adsorption process using the adaptive biasing force (ABF) importance sampling method [1]. We found that the adsorption strength of GMO is 442 23rd International Colloquium Tribology - January 2022 Molecular Dynamics Study of the Adsorption of Organic Friction Modifiers on Iron Oxide Surfaces considerably higher compared to GMS, which in turn is comparable to SA. Moreover, the PMF profiles are interpreted in terms of headgroup-surface and tail-solvent interactions, in order to explain the differences in the adsorption energies (Figure 1 shows as illustrative example the case of GMS). Additionally, we show that the PMF calculation using ABF is more efficient than the analogous calculation with Umbrella Sampling. Figure 1: Adsorption PMF for GMS. 2.2 Hard-disk area Second, we estimated the area occupied by each molecule on the surface in the high coverage limit. To this end, we carried out simulated annealing simulations for films of various densities of OFMs pre-adsorbed onto the surface, with the objective of determining the maximum coverage and thus the area occupied by each molecule. The results are shown in Figure 2. We obtained a similar (hard-disk) surface area for GMS and GMO (0.23 nm 2 ), whereas the result is smaller for SA (0.16 nm 2 ). 2.3 Adsorption isotherms from MTT Finally, we combined the adsorption energy and the surface area of each OFM to determine the respective adsorption isotherms using the Molecular Thermodynamic Theory (MTT) model developed by Blankschtein et al. [2]. The results are shown in Figure 3. Out of the three OFMs that have been studied, SA yields the highest maximum coverage (3.6 nm -2 ) due to its smaller headgroup size compared to GMO and GMS. Since both GMO and GMS have the same headgroup, they yield a very similar maximum coverage at high concentrations, where the surface coverage is mostly determined by the packing efficiency of the molecules. GMO yields the highest coverage of the three OFMs at low concentration, which is due to its larger adsorption energy. GMS has a coverage between GMO and SA at low concentration because of its intermediate adsorption energy. Overall, the results are in good agreement with reported experiments, even though there are some slight deviations, in particular concerning the difference between the experimental results for saturated and unsaturated surfactants and our computational results for GMO and GMS. We propose that these deviations are mainly due to differences in the kinetic barriers to the formation of high coverage monolayers. These kinetic barriers can be understood in terms of the steric hindrance for molecules adsorbing into partially formed monolayers, whereas lateral interactions between the tail groups and differences in aggregation (inverse micelle formation) play probably a secondary role. We discuss possible ways of taking these factors into account in future studies. Figure 2: Inital and final surface coverage of the OFMs following the annealing simulations. Figure 3: Adsorption isotherms for the studied OFMs calculated with the MTT model. 23rd International Colloquium Tribology - January 2022 443 Molecular Dynamics Study of the Adsorption of Organic Friction Modifiers on Iron Oxide Surfaces 3. Experimental validation We validated the calculated adsorption energies through high frequency reciprocating rig (HFRR) friction measurements. First, we measured the friction coefficient in boundary lubrication conditions as a function of the molar fraction of OFM added to the base oil. Subsequently, we applied the Jahanmir and Beltzer model [3] to relate the friction coefficient in boundary lubrication conditions with surface coverage. In this way, we obtain the surface coverage as a function of the OFM concentration. Finally, fitting these results with the Temkin adsorption isotherm yields an experimental estimate of the adsorption energy. The obtained values are in very good agreement with the predictions made by the simulations for SA and GMS, whereas for GMO they are slightly worse (Table 1). We attribute this discrepancy once again to the steric hindrance for molecules adsorbing into partially formed monolayers, which is larger for GMO due to the kink in the unsaturated tail group. SA GMS GMO Simulation -27.8 -34.2 -41.8 Experiment -26.4 *) -33.2 -24.9 Table 1: Adsorption energies (in kJ/ mol) calculated from simulation and experiment. *) taken from [4]. 4. Conclusion We have used both computational and experimental methods to assess the adsorption of three OFM molecules onto an iron oxide surface. The overall good agreement between simulation and experiments demonstrates that MD is an accurate and efficient tool to study the adsorption of OFMs at interfaces. Moreover, the possibility to evaluate OFM molecules in silico allows to develop automated high-throughput workflows to perform a virtual screening of many molecules, out of which only the best candidates will eventually be synthetized and tested experimentally. This approach can accelerate the development of new additives and chemicals, also beyond the area of tribology. References [1] Darve, E.; Rodríguez-Gómez, D.; Pohorille, A. Adaptive biasing force method for scalar and vector free energy calculations. Journal of Chemical Physics 2008, 128. [2] Nikas, Y. J.; Puvvada, S.; Blankschtein, D. Surface Tensions of Aqueous Nonionic Surfactant Mixtures. Langmuir 1992, 8, 2680. [3] Jahanmir, S.; Beltzer, M. An adsorption model for friction in boundary lubrication. ASLE Transactions 1986, 29, 423. [4] Jaishankar, A.; Jusufi, A.; Vreeland, J. L.; Deighton, S.; Pellettiere, J.; Schilowitz, A. M. Adsorption of Stearic Acid at the Iron Oxide/ Oil Interface: Theory, Experiments, and Modeling. Langmuir 2019, 35, 2033. 445 23rd International Colloquium Tribology - January 2022 445 Diversification of Evaluation Options for Tribological Measuring Results Using Origin and Phyton Thomas Witt Dr. Tillwich GmbH Werner Stehr, Horb, Germany, twitt@4advancedtechnologies.de 1. Introduction In today’s industry, as well as in the field of tribologi-cal testing, the amount of data that is acquired prior, during and post machine runs is phenomenal. This amount of data needs to be monitored, processed, sent and analysed. Therefore, the analysis of data needs to be optimised, simplified and analysed in much more detail in order to understand the process better. In an ideal world these data could enabled us to react, before things occur. 2. Current situation in the field of tribology and data analysis In our area, the field of friction and wear testing, we are facing the same problem - more data. Let’s have a look at our testings of e.g. radial sliding bearings. We are collecting loads of measurement data, especially when we talk about long term / life time testing. We are talking here of up to 1,000 testing cycles with up to 1,000 Hz data acquisition sampling rate per second on various channels. For data analysis we are using Origin / Phyton since long for two reasons. Reason one is, that the analysis of the raw data is faster and we face no limits in the amount of data. The second reason is that we can get more details out of the raw data. By nature of Origin / Phyton, it’s relatively easy to implement and add addi-tional features, to generate further key figures and graphs based on our raw data. 3. Stages in data analysis When using first time the origin system we pre-selected the raw data, manually, in order to reduce the import time as a quick pre-check of the measured data. When the data looked plausible the entire set of raw data got imported. We analysed the COF and temperatures of the radial bearing (back side of the bearing). In the next evolution step we have implemented vari-ous add ons. E.g. we are able to split the 1,000 cycles into three areas. For each area we are able to freely import different numbers of individual testing cycle. Meaning that we can import every testing cycle during the run in phase and e.g. every 20th cycle after the run in phase. Next thing we have done is that we are able to convert the 3D waterfall diagram into XY diagrams. Also a table of COF values is generated for definable sliding speeds. In a third evolution step the moving average of the COF curve got implemented. Reason for this is that we have seen different levels of noise and vibrations in the tribological testing system due to different loads, different sinter bearing alloys, bearing clearances, etc. Fig.1 shows the COFdiagram before processing the raw data and fig. 2 shows the XY diagram of individual testing cycles. Figure 1: Diagram COF - raw data Figure 2: Diagram of individual cycles - raw data 446 23rd International Colloquium Tribology - January 2022 Diversification of Evaluation Options for Tribological Measuring Results Using Origin and Phyton In fig.3 and fig. 4 the same diagrams are shown as in fig.1 and fig. 2 but processed and smoothed with a moving average of 100 values. Figure 3: Diagram COF - smoothed Figure 4: Diagram of individual cycles - smoothed 4. Conclusion History teaches us that the amount of data is growing and it’s growing exponentially. The same trend we are facing in tribological testing as data acquisition rates are increasing, more data channels and so on. The analysis tool Origin / Phyton enables us to handle these large data volumes we receive of our testing rigs. For processing the data we are absolutely free to add and adjust process steps, additional diagrams are easy to generate, statistics evaluations can be enlarged or shrinked. Since Phyton can be used within the Origin environ-ment the link has now been made between the famous programing language Phyton and the Origin LabTalk world. References [1] 2021-10-13: https: / / www.additive-net.de/ en/ software/ produkte/ originlab/ public-relations/ screencasts/ programmierung/ 9427-originpro-2021-python-beispiele Modelling 23rd International Colloquium Tribology - January 2022 449 Designing a REACH Conform Small Conrod Bearing of a Plunger Pump with the Help of EHD Simulation Vincent Hoffmann Tribo Technologies GmbH, Barleben, Germany Corresponding author: vincent.hoffmann@tribo-technologies.com Felix Hartmann Hammelmann GmbH, Oelde, Germany Christian Stelzer CADFEM GmbH, Grafing bei München, Germany 1. Introduction Plunger pumps from Hammelmann are often used in the chemical, oil and gas as well as the food industry. The pumps can reach a performance of 1100kW, generate a volume flow of 3000 l/ min and maximum pressure values of up to 3000 bar. The pressure build-up of the pump is generated by plungers which are set in motion by a crankshaft in combination with conrods. A typical plunger pump and conrod of Hammelmann are depicted in Figure 1. Figure 1: Hammelmann plunger pump and conrod Due to the regulation 1907/ 1906 concerning the registration, evaluation, authorization and restriction of chemicals (REACH) manufacturers are obligated to avoid the usage of any dangerous materials like lead in their products [1]. Motivated by this regulation a material change of the bearing shell of the small conrod bearing of a plunger pump is analysed. Here a bearing layer structure with a sliding surface made of a leaded bronze on a steel back is replaced by a REACH conform bronze without a steel back, see Figure 2. Previous Bearing Layer Structure REACH conform Bearing Layer Structure Figure 2: Analysed bearing shell layer structures The load carrying capacity is analysed with the help of elasto-hydrodynamic simulations of both conrod bearing designs. 2. EHD Simulation For this investigation the operating behaviour of the small conrod bearing is analysed with the help of the simulation tool Tribo-X inside Ansys. 450 23rd International Colloquium Tribology - January 2022 Designing a REACH Conform Small Conrod Bearing of a Plunger Pump with the Help of EHD Simulation Figure 3: Process for the determination of a reliable REACH conform bearing design Therefore, due to a load surge resulting from the operation of the plunger pump it is of great importance to consider transient load conditions including the panning motion of the small conrod bearing which results from the transformation of the rotational movement of the crankshaft into the translational movement of the plunger [4]. Furthermore the small conrod bearing has to carry loads up to 200 kN during a load cycle of the pump. This generates high hydrodynamic pressure values in the lubricating gap, which makes the consideration of elastic deformations necessary to generate reliable results [2] [3]. In case wear affected areas occur in the lubricating gap a mixed friction model is used to identify those areas. The input quantities for the mixed friction model are deduced with the help of measured surfaces of the conrod and pin of the previous bearing design [3]. Therefore, the new bearing layer structure is expected to have a similar surface topography. In order to introduce a REACH conform bearing design for the plunger pump the previous leaded bronze bearing is analysed as a reference. Based on the acquired results a material change and a design modification of the supply pockets of the small conrod bearing are investigated. The main goal here is to improve the operating behaviour compared to the previous bearing design. The process is depicted in Figure 3. 3. Results Due to the operating conditions of the pump, which consist of a low pressure phase at the beginning and a high pressure phase at the end, the minimum film thickness changes significantly during one load cycle, see Figure 4. Therefore, the minimum film thicknesses are about 3.5 µm at the first half of the operating cycle. And it reaches values below 1 µm for the second half of the load cycle. In consequence for both bearing designs the simulation shows a contact between bearing shell and pin. Minimum Film Thickness Figure 4: Calculated minimum film thicknesses for previous and REACH conform bearing layer structure In conclusion the material change from the leaded bronze to the REACH conform material resulted in a worsened bearing performance. The analysis of the hydrodynamic pressure distribution of the bearings showed that the positioning of the lubricant supply pockets has a significant influence on the pressure build up. Due to a centric positioning of the supply pockets the sliding surface for a hydrodynamic pressure build up is limited. This results in a narrow hydrodynamic pressure field including high absolute pressure values. In this investigation it could be shown that the bearing performance could be significantly improved when the supply pockets are positioned non-centrically, farther to the bearing top. In consequence wear can be completely avoided after this modification. Furthermore the evaluated hydrodynamic pressure values are significantly smaller. A comparison between the hydrodynamic pressure values in dependence from the supply pocket positioning is shown in Figure 5. 23rd International Colloquium Tribology - January 2022 451 Designing a REACH Conform Small Conrod Bearing of a Plunger Pump with the Help of EHD Simulation Centric Positioning of Supply Pockets Non-centric Positioning of Supply Pockets Figure 5: Influence of supply pocket positioning on the hydrodynamic pressure at 340 degree crankshaft 4. Conclusion A material change of a small conrod bearing is analysed with the help of EHD simulation. It could be shown that the bearing performance of a REACH conform bearing design is worse compared to the previous bearing design. By evaluating the pressure distribution of the bearing it was possible to identify a significant design improvement. Therefore, it could be shown that a new positioning of the supply pocket leads to a heavily improved bearing performance. References [1] “Regulation (EG) Nr. 1907/ 2006: Registration, Evaluation, Authorization and Restriction of chemicals (REACH)”, 2006. [2] “ISO 7902 - 1…3: Hydrodynamic plain journal bearings under steady-state conditions - Circular cylindrical bearings”, 2013. [3] Bartel, D., “Simulation von Tribosystemen - Grundlagen und Anwendungen“, Vieweg+Teubner, Wiesbaden, 2010. 453 23rd International Colloquium Tribology - January 2022 453 Predicting Electric Vehicle Transmission Efficiency Using a Thermally Coupled Lubrication Model Joseph F. Shore Imperial College London, London, UK Corresponding author: joseph.shore15@imperial.ac.uk Athanasios I. Christodoulias Imperial College London, London, UK Anant S. Kolekar Valvoline, Lexington KY, USA Frances E. Lockwood Valvoline, Lexington KY, USA Amir Kadiric Imperial College London, London, UK 1. Introduction Range anxiety remains a primary concern for electric vehicle (EV) consumers, therefore, increasing vehicle efficiency is an important focus for manufacturers. Since electric motors (EMs) have far greater efficiency than internal combustion engines (ICEs), power losses in the transmission account for a greater percentage of the overall losses than in an equivalent ICE vehicle. Thus, reduction in these losses could lead to significant gains in overall vehicle efficiency. Since EV gearboxes are required to operate at high torque, low speed conditions at one extreme and very high speed and low torque at the other extreme, there are competing requirements on lubricant performance. This work presents an efficient numerical model to predict power losses and hence efficiency in a typical EV transmission. The model considers the gear meshing losses, bearing losses and gear churning losses. Importantly, the model accounts for the evolution of lubricant temperature in the gearbox during a drive cycle accounting for heat transfers to the surroundings as well as oil cooling the EM, thereby allowing an entire drive cycle to be analyzed. The model is able to identify inefficiencies within the gearbox design and can distinguish nominally similar lubricants by accounting for differences in lubricant rheology. 2. Model Description 2.1 Gear Meshing Losses Similarly to [1], the path of contact between the gear teeth is discretized into many points and the local gear geometry at each point is used to determine the contact pressure. At each point, the thermal coupling between coefficient of friction (COF), film thickness, oil film and gear bulk temperatures is accounted for by using an iterative procedure. The COF is determined by considering the rheology of the lubricant based on the Eyring stress using an algorithm developed by Olver and Spikes [2]. The value of the Eyring stress is determined by interpolating between experimentally derived values from tribometer tests on the lubricant, further discussed in section 3. By accounting for the lubricant’s rheology, this method allows for nominally similar lubricants to be compared in terms of their impact on EV gearbox efficiency. Since gears frequently operate in the mixed lubrication regime, it is necessary to consider the boundary COF as well as the EHL COF. The overall gear mesh COF is calculated as an average of the fluid COF and the experimentally determined boundary COF, weighted by the lambda ratio, as described in [2,3]. 454 23rd International Colloquium Tribology - January 2022 Predicting Electric Vehicle Transmission Efficiency Using a Thermally Coupled Lubrication Model 2.2 Bearing and Churning Losses The gear loss model is combined with existing numerical model for bearing losses developed by Morales-Espejel [4] at SKF and gear churning losses described by Changenet et al. [5] to create a complete efficiency model of the gearbox. 2.3 Thermal Coupling to the Environment To analyze a gearbox over an entire drive cycle, it is necessary to account for the evolution of lubricant temperature over the course of the cycle. To do this, a thermal model of the transmission has been devised which accounts for heat lost through a heat exchanger and the heating of the lubricant by losses in the transmission and EM. EM losses are estimated from an efficiency map and the heat exchanger is accounted for by using coolant and oil flowrates and coolant temperature through the heat exchanger measured from the real vehicle. 3. Determination of Lubricant Parameters The Eyring stress was found at various contact pressures and temperatures by implementing the procedure developed by Lafountain et al. [6]. Traction tests were performed using a PCS ETM rig to obtain the COF at various slide-roll ratios at several temperatures and pressures representative of EV gear conditions. The results were combined with film thickness measurements to create a plots of shear stress against strain rate from which the Eyring stress could be determined. The boundary COF of the oil was determined via a series of Stribeck curves produced from traction tests performed on a PCS MTM rig. 4. Model Validation The accuracy of the model’s predictions was assessed by comparing predicted evolution of temperatures within the gearbox to experimental temperature measurements on a real-world road test with an EV installed with a similar gearbox. The temperature evolution predicted by the model showed good agreement with the temperature measurements, as shown in Figure 1. Figure 1: Predicted temperatures compared to measurements for a real-world EV road test 5. Breakdown of Power Losses Figure 2 shows the sources of losses within a typical EV gearbox with varying torque and speed at a constant input power of 15 kW. Figure 2: Breakdown of losses with varying speed at constant 15kW power This figure allows us to identify the major contributors to power losses within the transmission and thereby identify inefficiencies in the transmission design. Bearing losses are the greatest contributor to power losses, especially at higher speeds. Churning losses are negligible at low speed but account for significant losses as speed increases, emphasizing the importance of lubricant selection to minimize this loss type. Gear losses make up a substantial proportion of the total power losses under high torque, low speed conditions but reduce as the speed increases in this example, primarily due to the increase in specific film thickness. 23rd International Colloquium Tribology - January 2022 455 Predicting Electric Vehicle Transmission Efficiency Using a Thermally Coupled Lubrication Model Considering the total powertrain losses, with an EM efficiency of around 90%, the total transmission losses account for between 15 to 25% of the total powertrain losses under these conditions, underlining the potential for improving vehicle efficiency and range by optimizing transmission design and lubricant selection. 6. Conclusion • A thermally coupled model of a full EV transmission has been presented. The model accounts for lubricant rheology and is computationally efficient enough to allow an entire drive cycle to be analyzed • Predictions using the model show good agreement with results from real world drive cycle tests on a real EV • The model allows for the sources of losses to be analyzed, allowing inefficient components to be identified, aiding gearbox design • The model is able to distinguish between two nominally identical lubricants in terms of their impact on transmission efficiency and hence can aid in early lubricant selection. References [1] A. Christodoulias, “Prediction of Power Losses in an Automotive Gearbox,” PhD Thesis, Imperial College London, 2017. [2] A. V. Olver and H. A. Spikes, “Prediction of traction in elastohydrodynamic lubrication,” Proc. Inst. Mech. Eng. Part J J. Eng. Tribol., vol. 212, no. 5, pp. 321-332, 1998, doi: 10.1243/ 1350650981542137. [3] M. Smeeth and H. A. Spikes, “The influence of slide roll ratio on the film thickness of an EHD contact operating within the mixed lubrication regime.” Presented at the Twenty-second Leeds-Lyon Symposium on Tribology, The Third Body Concept, Lyon, France, 5-8 September 1995 [4] G. Morales-Espejel, “Using a friction model as an engineering tool,” Evolution SKF, vol. 2, pp. 27- 30, 2006. [5] C. Changenet and P. Velex, “A model for the prediction of churning losses in geared transmissions - Preliminary results,” J. Mech. Des. Trans. ASME, vol. 129, no. 1, pp. 128-133, 2007, doi: 10.1115/ 1.2403727. [6] A. R. Lafountain, G. J. Johnston, and H. A. Spikes, “The elastohydrodynamic traction of synthetic base oil blends,” Tribol. Trans., vol. 44, no. 4, pp. 648- 656, 2001, doi: 10.1080/ 10402000108982506. 23rd International Colloquium Tribology - January 2022 457 Polymer-coated plain bearings during start-stop operation - an experimental and numerical assessment Florian König Institute for Machine Elements and Systems Engineering, RWTH Aachen University, Aachen, Germany Corresponding author: florian.koenig@imse.rwth-aachen.de Georg Jacobs Institute for Machine Elements and Systems Engineering, RWTH Aachen University, Aachen, Germany 1. Introduction Plain bearing applications such as gearboxes in wind turbines and operating strategies such as automatic startstop systems lead to an increased proportion of mixedfriction operation. The resulting wear limits the service life of a plain bearing, which makes wear resistance utterly important. In addition to wear resistance, high demands are placed on the efficiency of a plain bearing. Low friction losses are thus important for the selection of a plain bearing material. In order to ensure low wear and low friction, even under mixed-friction conditions, self-lubricating materials are often used in the bearings including metal backing composite materials, polymer and filled polymer composite materials. The use of anti-friction coatings for plain bearings, such as for example polyamide-imide (PAI) [1], has emerged, e.g. for automotive crank train bearings, due to their promising anti-friction performance [2]. In a direct comparison to conventional bimetallic bearings, anti-friction coatings show lower wear during running-in and during the subsequent start-stop cycles [2]. However, high friction losses may be found in the first few start-stop cycles, which can be attributed to the adhesive forces of the polymer/ steel interface. The question arises, whether running-in leads to reduced frictional losses in subsequent star-stop cycles. Therefore, the aim of this study is to experimentally investigate the tribological behaviour of PAI-coated bearings during start-stop operation. Additionally, the behaviour during start-stop operation was studied in a mixed-elasto-hydrodynamic lubrication (mixed-EHL) simulation model for further elucidation of running-in effects. 2. Materials and methods 2.1 Polymer-coated plain bearing experiments In this study, plain bearings from bronze CuSn12Ni2-C were coated with a f 10 µm thick layer of polyamide-imide (PAI). These bearings were subjected to varying number of start-stop cycles under stationary load in a plain bearing test rig. The aim was to study the frictional behaviour and the wear caused by starting and stopping. The PAI-coated plain bearings, test rig and test method are shown in Figure 2-1. In this study, the bearing housing was heated to a temperature of 90 °C with circumferentially positioned heating cartridges to ensure isothermal conditions. The oil supply temperature was set to 80 °C with an electrically heated hose. After this steady state was reached, the bearings were subjected to 5,000 start-stop cycles at specific pressures of 2 MPa, where the radial load was applied to the bearing housing using a flexible load unit. Afterwards the bearing was removed from the test rig and the contour and roughness was analysed. The speed profile is shown in Figure 2-1. It consists of start-up ramp (2 seconds) to the nominal speed, a plateau phase of 2 seconds and a stopping ramp of 3 seconds to standstill. The standstill period between two cycles was 10 seconds to ensure the displacement of oil between the shaft and the bearing. A friction gauge, which is connected directly to the housing of the bearing, was used to determine the frictional force and friction coefficient. Further details on the test rig can be found in [3,4]. 458 23rd International Colloquium Tribology - January 2022 Polymer-coated plain bearings during start-stop operation - an experimental and numerical assessment Figure 2-1: A PAI-coated plain bearing, schematic presentation of the plain bearing test rig and test method 2.2 Numerical simulation The contact conditions in plain bearings during startstop operation were calculated using a transient mixed-elasto-hydrodynamic lubrication (mixed-EHL) simulation model, which was previous generated in AVL Excite Power Unit for metallic bearings [4]. However, for PAI-coated bearings with a surface layer with a low Young’s modulus, the existing transient elastohydrodynamic simulation model was extended. In this study, the elastic and frictional behaviour of the polymer coating was considered according to the approach by O ffner and K naus [5]. 3. Results In screening tests, PAI-coated plain bearings with further filler materials have shown a superior wear performance during start-stop operation, when compared to non-coated bearing systems [4]. However, high friction losses were found in the first few start-up procedures, which can be attributed to the adhesive forces of the polymer/ steel interface. With increasing number of start-stop cycles, running-in of the coated bearing shells was observed which lead to a slightly improved frictional performance as shown in Figure 2-2. Figure 2-2: Experimental frictional performance of a bearing during 5,000 start-stop cycles The black line at a CoF of 0.02 marks the expected transition between mixed lubrication and hydrodynamic lubrication. Thus, slight running-in effects in terms of transition speed can be observed during the operation at 2 MPa. However, due to the missing wearing-in effects, the frictional losses in terms of CoF remained nearly constant at values of 0.2 during starting and stopping. After the experiment, the bearing was taken from the test rig and wear analysis was performed. Very low wear losses in terms of profile change were observed. However, the anti-friction coating initially showed Rz and Ra values in the range of 4…7 µm and 0.7…1.2 µm, respectively. Due to the starting and stopping, a reduction of Rz and Ra to values of 4 µm and 0.6 µm was overserved, respectively. To further study the tribological performance of plain bearings with PAI-coatings during start-stop operation, the new and worn system with reduced roughness were compared in a mixed-EHL simulation. The results are shown in Figure 2-3. Figure 2-3: Simulated frictional performance of a bearing during the 1 st and 5’000 th start-stop cycle The direct comparison between experimental and numerical results shows a good agreement in terms of frictional performance. 4. Summary and conclusion The aim of this study was to elucidate the tribological performance of plain bearings with anti-friction coatings made out of polyamide-imide (PAI) during start-stop operation. Based upon the experimental results of the friction and wear behavior and the simulation results, the following conclusions can be drawn: At low speeds, high friction losses were observed in the starting and stopping phase, which can be attributed to the adhesive forces of the polymer/ steel interface. The PAI coating showed a high wear resistance with negligible wear losses during 5,000 start-stop cycles. Consequently, negligible wearing-in was observed in terms of profile change. Nonetheless, the roughness of the PAI coating reduced significantly, which was further considered in a mixed-EHL simulation model of the startstop cycle. The simulation model demonstrates that it is important to ensure wearing-in of anti-friction coatings at increased loads to achieve low friction losses during start-stop operation throughout a bearings service life as 23rd International Colloquium Tribology - January 2022 459 Polymer-coated plain bearings during start-stop operation - an experimental and numerical assessment well as move the transition speed between the mixed and hydrodynamic lubrication regime towards lower speeds. Modelling the tribological behavior of such a coated bearing still continues to be a major challenge that should be tackled in the future. 5. Acknowledgement Funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) - GRK 1856. References [1] Ligier J-L, Noel B. Friction Reduction and Reliability for Engines Bearings. Lubricants. 2015; 3(3): 569-596. https: / / doi.org/ 10.3390/ lubricants3030569 [2] Gudin D, Mian O, Sanders S. Experimental measurement and modelling of plain bearing wear in start-stop applications. Proceedings of the Institution of Mechanical Engineers, Part J: Journal of Engineering Tribology. 2013; 227(5): 433-446. doi: 10.1177/ 1350650112471287 [3] König F., Ouald Chaib A., Jacobs G., Sous C.: A multiscale-approach for wear prediction in journal bearing systems - from wearing-in towards steadystate wear. Wear 2019; 426-427: 1203-11. https: / / doi.org/ 10.1016/ j.wear.2019.01.036. [4] König, F., Sous, C., Jacobs, G. Numerical prediction of the frictional losses in sliding bearings during start-stop operation. Friction 9, 583-597 (2021). https: / / doi.org/ 10.1007/ s40544-020-0417- 9 [5] Offner G, Knaus O. A Generic Friction Model for Radial Slider Bearing Simulation Considering Elastic and Plastic Deformation. Lubricants. 2015; 3(3): 522-538. https: / / doi.org/ 10.3390/ lubricants3030522 Sliding Contact 23rd International Colloquium Tribology - January 2022 463 An experimental study and numerical modelling of nanocomposite coating wear in sliding contact Professor Zulfiqar A Khan NanoCorr, Energy & Modelling Research (NCEM) Group, Department of Design & Engineering, Bournemouth university UK 1. Abstract This paper presents an experimental investigation and numerical modelling of reciprocating wear behaviour of nanocomposite coatings. This study employed u-shaped geometrical profiles to assess and calculate energy distribution along the interfacial contact by incorporating the Archard density factor. Both energy and mechanics equations were utilised to develop a mechano-wear model for characterisation of sliding wear behaviour in nanocomposite coatings. This study found that Nickel-Graphene demonstrated higher wear resistance compared to other composite coatings. These models are presented and are significant for predicting wear failures to mitigate machine idle time and reduce maintenance costs. Several coating failure mechanisms have been reported [1] including electrochemical decay. Earlier work considered optimisation of materials to include thickness of thin coating and surface texture at the interface during interactive components to avoid and mitigate electrochemical induced coating failures. Further a summary of significant models which have incorporated elastic energy release in relation to pressure and a new Khan-Nazir I model, shown below, with inclusion of mechanistic approach has been presented [1]. Where v c = Poisson ratio of coating, E c = young’s modulus of coating, = film thickness, Mc = blistering induced film-substrate system bending moment, p = blister pressure, = critical pressure. Khan-Nazir II model has been proposed and reported [2] for advanced numerical predictions in reciprocating contacts with incorporated effects of hardness of material and load configuration and has shown higher accuracy in compared to classical models [3]. Where = corrosion current density, F = Faraday’s constant, ρ = coating density, K = specimen material’s electrochemical equivalent, A s = area of the specimen, = corrosive wear volume loss, = wear rate, = Archard factor density, S = synergistic factor. In this work a reciprocating tribo-test configuration is employed to investigate newly developed nanocomposite coatings. Four selected composite coatings and test parameter are presented with experimental observation and discussion alongside their pre and post-test surface texture. Scanning Electron Microscopy and Energy Dispersive Spectroscopy were employed for both surface and constituents’ analyses. Grain sizes have been noted to corelate to coatings’ tribo performance. This study included surface quality in terms of roughness characteristics, co-efficient of friction and rate of wear in conjunction with energy attribute for the development of numerical models. Simulation results in terms of wear volume and friction coefficient and Archard loading factor are presented. A kinetic depth profile approach has been adapted to study and develop corresponding wear depth kinetics profiles (WDKP) [4]. New equations for mechano-wear analysis of nanocomposite coatings have been developed [4] and are discussed within the context of 2D predictive modelling. 2. Keywords Nanocomposite coatings, sliding contact, wear, simulation, modelling References [1] Nazir, M.H. and Khan, Z.A., 2017. A review of theoretical analysis techniques for cracking and corrosive degradation of film-substrate systems. Engineering Failure Analysis, 72, 80-113. [2] Kasar,A.K., Bhutta, M.U., Khan, Z.A. and Menezes, P.L., 2020. Corrosion performance ofnanocomposite coatings in moist SO2 environment. International Journal of Advanced Manufacturing Technology, 106 (11-12), 4769-4776. 464 23rd International Colloquium Tribology - January 2022 An experimental study and numerical modelling of nanocomposite coating wear in sliding contact [3] Nazir, M.H., Khan, Z.A., Saeed, A., Siddaiah, A. and Menezes, P.L., 2018. Synergistic wear-corrosion analysis and modelling of nanocomposite coatings. Tribology International, 121, 30-44. [4] Nazir, M.H., Khan, Z.A., Saeed, A., Bakolas, V., Braun, W. and Bajwa, R., 2018. Experimental analysis and modelling for reciprocating wear behaviour of nanocomposite coatings. Wear, 416-417, 89-102. Links https: / / www.researchgate.net/ lab/ NanoCorr-Energy-and- Modelling-NCEM-Research-Group-Zulfiqar-A-Khan 465 23rd International Colloquium Tribology - January 2022 465 Effect of Thermal Conductivity of Bearing on the Thermal Wedge in Parallel Slider Bearing Tae-Jo Park School of Mechanical Engineering, Gyeongsang Nation University, Jinju, Korea Corresponding author: tjpark@gnu.ac.kr Jeong-Guk Kang School of Mechanical Engineering, Gyeongsang Nation University, Jinju, Korea 1. Introduction Temperature rise due to viscous shear of the lubricating oil generates hydrodynamic pressure even if the lubri-cating surfaces are parallel [1-2]. This is known as the thermal wedge effect and varies significantly with film-temperature boundary conditions [3]. The bearing con-ducts a part of the heat generated; hence, the film tem-perature varies with the thermal conductivity (ks) of the bearing. This study numerically investigates the effect of thermal conductivity on the thermohydrodynamic (THD) lubrication of parallel slider bearings. 2. Numerical Analysis Figure 1: Schematic of 2D parallel slider bearing. Table 1. Bearing size and operating condition. Symbol Value Bearing length, Effect of Thermal Conductivity of Bearing on the Thermal Wedge in Parallel Slider Bearing Tae-Jo Park 1)* , Jeong-Guk Kang 1) 1) School of Mechanical Engineering, Gyeongsang Nation University, Jinju, Korea * Corresponding author: tjpark@gnu.ac.kr 1. Introduction Temperature rise due to viscous shear of the lubricating oil generates hydrodynamic pressure even if the lubricating surfaces are parallel [1-2]. This is known as the thermal wedge effect and varies significantly with filmtemperature boundary conditions [3]. The bearing conducts a part of the heat generated; hence, the film temperature varies with the thermal conductivity (k s ) of the bearing. This study numerically investigates the effect of thermal conductivity on the thermohydrodynamic (THD) lubrication of parallel slider bearings. 2. Numerical Analysis Figure 1 Schematic of 2D parallel slider bearing. Table 1. Bearing size and operating condition. Symbol Value Bearing length, ㎛ L 450 Pad thickness, ㎛ h s 100 Film thickness, ㎛ c 1 Ambient temperature, K T 0 310 Sliding speed, m/ s U 10 Table 2. Thermal properties of bearing material. k s , W/ m∙K C ps , J/ kg∙K Carbon 167.36 707 Steel 16.27 502.48 SiO 2 1.4 700 Figure 1 shows a 2D micro-bearing model used. The continuity, Navier-Stokes, energy equations, temperature-viscosity-density relations for lubricant, and conduction equations for bearing are analyzed using a commercial CFD software, FLUENT. Tables 1 3. Results and Discussion Figure 2 shows the contour plot of film temperature and pressure distributions for three different pad materials, and Fig. 3 compares load-carrying capacity (LCC) and friction force acting on the slider. The thermal conductivity significantly influences the THD lubrication characteristics of parallel slider bearings. The lower the thermal conductivity, the greater the pressure generation due to the thermal wedge effect, so the LCC increased, and the frictional force decreased. Figure 2 Film-temperature and pressure distributions. (a) h s = 0 ㎛ , (b) Carbon, (c) Steel, (d) SiO 2 . (a) (b) Figure 3 Effect of bearing thermal conductivity on the (a) LCC, (b) friction force. 4. References [1] Cameron, A., "The viscosity wedge", ASLE Trans., 1, 2, 1958, 248-253. [2] Khonsari, M. M., "A review of thermal effects in hydrodynamic bearings. Part I: Slider and thrust bearings", ASLE Trans., 30, 1, 1987. 19-25. [3] Cui, J. et al., "The relation between thermal wedge and thermal boundary conditions for the L 450 Pad thickness, Effect of Thermal Conductivity of Bearing on the Thermal Wedge in Parallel Slider Bearing Tae-Jo Park 1)* , Jeong-Guk Kang 1) 1) School of Mechanical Engineering, Gyeongsang Nation University, Jinju, Korea * Corresponding author: tjpark@gnu.ac.kr 1. Introduction Temperature rise due to viscous shear of the lubricating oil generates hydrodynamic pressure even if the lubricating surfaces are parallel [1-2]. This is known as the thermal wedge effect and varies significantly with filmtemperature boundary conditions [3]. The bearing conducts a part of the heat generated; hence, the film temperature varies with the thermal conductivity (k s ) of the bearing. This study numerically investigates the effect of thermal conductivity on the thermohydrodynamic (THD) lubrication of parallel slider bearings. 2. Numerical Analysis Figure 1 Schematic of 2D parallel slider bearing. Table 1. Bearing size and operating condition. Symbol Value Bearing length, ㎛ L 450 Pad thickness, ㎛ h s 100 Film thickness, ㎛ c 1 Ambient temperature, K T 0 310 Sliding speed, m/ s U 10 Table 2. Thermal properties of bearing material. k s , W/ m∙K C ps , J/ kg∙K Carbon 167.36 707 Steel 16.27 502.48 SiO 2 1.4 700 Figure 1 shows a 2D micro-bearing model used. The continuity, Navier-Stokes, energy equations, temperature-viscosity-density relations for lubricant, and conduction equations for bearing are analyzed 3. Results and Discussion Figure 2 shows the contour plot of film temperature and pressure distributions for three different pad materials, and Fig. 3 compares load-carrying capacity (LCC) and friction force acting on the slider. The thermal conductivity significantly influences the THD lubrication characteristics of parallel slider bearings. The lower the thermal conductivity, the greater the pressure generation due to the thermal wedge effect, so the LCC increased, and the frictional force decreased. Figure 2 Film-temperature and pressure distributions. (a) h s = 0 ㎛ , (b) Carbon, (c) Steel, (d) SiO 2 . (a) (b) Figure 3 Effect of bearing thermal conductivity on the (a) LCC, (b) friction force. 4. References [1] Cameron, A., "The viscosity wedge", ASLE Trans., 1, 2, 1958, 248-253. [2] Khonsari, M. M., "A review of thermal effects in hydrodynamic bearings. Part I: Slider and thrust bearings", ASLE Trans., 30, 1, 1987. 19-25. [3] Cui, J. et al. "The relation between thermal h s 100 Film thickness, Effect of Thermal Conductivity of Bearing on the Thermal Wedge in Parallel Slider Bearing Tae-Jo Park 1)* , Jeong-Guk Kang 1) 1) School of Mechanical Engineering, Gyeongsang Nation University, Jinju, Korea * Corresponding author: tjpark@gnu.ac.kr 1. Introduction Temperature rise due to viscous shear of the lubricating oil generates hydrodynamic pressure even if the lubricating surfaces are parallel [1-2]. This is known as the thermal wedge effect and varies significantly with filmtemperature boundary conditions [3]. The bearing conducts a part of the heat generated; hence, the film temperature varies with the thermal conductivity (k s ) of the bearing. This study numerically investigates the effect of thermal conductivity on the thermohydrodynamic (THD) lubrication of parallel slider bearings. 2. Numerical Analysis Figure 1 Schematic of 2D parallel slider bearing. Table 1. Bearing size and operating condition. Symbol Value Bearing length, ㎛ L 450 Pad thickness, ㎛ h s 100 Film thickness, ㎛ c 1 Ambient temperature, K T 0 310 Sliding speed, m/ s U 10 Table 2. Thermal properties of bearing material. k s , W/ m∙K C ps , J/ kg∙K Carbon 167.36 707 Steel 16.27 502.48 SiO 2 1.4 700 Figure 1 shows a 2D micro-bearing model used. The continuity, Navier-Stokes, energy equations, 3. Results and Discussion Figure 2 shows the contour plot of film temperature and pressure distributions for three different pad materials, and Fig. 3 compares load-carrying capacity (LCC) and friction force acting on the slider. The thermal conductivity significantly influences the THD lubrication characteristics of parallel slider bearings. The lower the thermal conductivity, the greater the pressure generation due to the thermal wedge effect, so the LCC increased, and the frictional force decreased. Figure 2 Film-temperature and pressure distributions. (a) h s = 0 ㎛ , (b) Carbon, (c) Steel, (d) SiO 2 . (a) (b) Figure 3 Effect of bearing thermal conductivity on the (a) LCC, (b) friction force. 4. References [1] Cameron, A., "The viscosity wedge", ASLE Trans., 1, 2, 1958, 248-253. [2] Khonsari, M. M., "A review of thermal effects in hydrodynamic bearings. Part I: Slider and thrust c 1 Ambient temperature, K T 0 310 Sliding speed, m/ s U 10 Table 2. Thermal properties of bearing material. k s , W/ m∙K C ps , J/ kg∙K Carbon 167.36 707 Steel 16.27 502.48 SiO 2 1.4 700 Figure 1 shows a 2D micro-bearing model used. The continuity, Navier-Stokes, energy equations, temperature-viscosity-density relations for lubricant, and conduction equations for bearing are analyzed using a commercial CFD software, FLUENT. Tables 1 & 2 show bearing size and operating condition, and thermal properties of bearing material used. The ther-mal properties of oil used are nearly the same as Ref. [3]. 3. Results and Discussion Figure 2 shows the contour plot of film temperature and pressure distributions for three different pad mate-rials, and Fig. 3 compares load-carrying capacity (LCC) and friction force acting on the slider. The thermal conductivity significantly influences the THD lubrication characteristics of parallel slider bearings. The lower the thermal conductivity, the greater the pressure generation due to the thermal wedge effect, so the LCC increased, and the frictional force decreased. 466 23rd International Colloquium Tribology - January 2022 Effect of Thermal Conductivity of Bearing on the Thermal Wedge in Parallel Slider Bearing Figure 2: Film-temperature and pressure distributions. (a) hs = 0 cating surfaces are parallel [1 2]. This is known as the thermal wedge effect and varies significantly with filmtemperature boundary conditions [3]. The bearing conducts a part of the heat generated; hence, the film temperature varies with the thermal conductivity (k s ) of the bearing. This study numerically investigates the effect of thermal conductivity on the thermohydrodynamic (THD) lubrication of parallel slider bearings. 2. Numerical Analysis Figure 1 Schematic of 2D parallel slider bearing. Table 1. Bearing size and operating condition. Symbol Value Bearing length, ㎛ L 450 Pad thickness, ㎛ h s 100 Film thickness, ㎛ c 1 Ambient temperature, K T 0 310 Sliding speed, m/ s U 10 Table 2. Thermal properties of bearing material. k s , W/ m∙K C ps , J/ kg∙K Carbon 167.36 707 Steel 16.27 502.48 SiO 2 1.4 700 Figure 1 shows a 2D micro-bearing model used. The continuity, Navier-Stokes, energy equations, temperature-viscosity-density relations for lubricant, and conduction equations for bearing are analyzed using a commercial CFD software, FLUENT. Tables 1 & 2 show bearing size and operating condition, and thermal properties of bearing material used. The thermal properties of oil used are nearly the same as Ref. [3]. rials, and Fig. 3 compares load carrying capacity (LCC) and friction force acting on the slider. The thermal conductivity significantly influences the THD lubrication characteristics of parallel slider bearings. The lower the thermal conductivity, the greater the pressure generation due to the thermal wedge effect, so the LCC increased, and the frictional force decreased. Figure 2 Film-temperature and pressure distributions. (a) h s = 0 ㎛ , (b) Carbon, (c) Steel, (d) SiO 2 . (a) (b) Figure 3 Effect of bearing thermal conductivity on the (a) LCC, (b) friction force. 4. References [1] Cameron, A., "The viscosity wedge", ASLE Trans., 1, 2, 1958, 248-253. [2] Khonsari, M. M., "A review of thermal effects in hydrodynamic bearings. Part I: Slider and thrust bearings", ASLE Trans., 30, 1, 1987. 19-25. [3] Cui, J. et al., "The relation between thermal wedge and thermal boundary conditions for the load-carrying capacity of a rectangular pad and a slider with parallel gaps", ASME J. Tribology, 138, 2, 2016, 024502-1~6. , (b) Carbon, (c) Steel, (d) SiO2. Figure 3: Effect of bearing thermal conductivity on the (a) LCC, (b) friction force. References [1] Cameron, A., „The viscosity wedge“, ASLE Trans., 1, 2, 1958, 248-253. [2] Khonsari, M. M., „A review of thermal effects in hydrodynamic bearings. Part I: Slider and thrust bearings“, ASLE Trans., 30, 1, 1987. 19-25. [3] Cui, J. et al., „The relation between thermal wedge and thermal boundary conditions for the load-carrying capacity of a rectangular pad and a slider with parallel gaps“, ASME J. Tribology, 138, 2, 2016, 024502-1~6. 23rd International Colloquium Tribology - January 2022 467 Slender EHL contacts under high sliding conditions Marko Tošić Technical University of Munich, Germany; School of Engineering & Design, Department of Mechanical Engineering, Gear Research Centre (FZG) Thomas Lohner Technical University of Munich, Germany; School of Engineering & Design, Department of Mechanical Engineering, Gear Research Centre (FZG) Roland Larsson Division of Machine Elements, Luleå University of Technology, Luleå, Sweden 1. Introduction This study deals with experimental and numerical analysis of slender elastohydrodynamically lubricated (EHL) elliptical point contacts under high sliding. Thereby, the entrainment direction is orientated along the major axis of the contact ellipse. Such contact geometries can appear in worm gears [1]. Film thick-ness measurements were carried out on an optical EHL tribometer. Numerical solutions were obtained by solv-ing the EHL contact considering non-Newtonian rheol-ogy and thermal effects. 2. Methodology For experimental investigation, an optical EHL tribometer based on thin film colorimetric interferometry is used [2]. To investigate slender EHL contacts, test specimens with a radius of curvature in gap length direction of R y =12.7 mm and gap width direction of R x =12.7 were manufactured. The steel roller was polished and paired with a glass disk. A mineral oil ISO VG 100 (MIN100) is used as a lubricant. Experiments are per-formed at a normal force resulting in a Hertzian pressure of Slender EHL contacts under high sliding conditions Marko Tošić 1)* , Thomas Lohner 1) , Roland Larsson 2) 1) Technical University of Munich, Germany; School of Engineering & Design, Department of Mechanical Engineering, Gear Research Centre (FZG) 2) Division of Machine Elements, Luleå University of Technology, Luleå, Sweden 1. Introduction This study deals with experimental and numerical analysis of slender elastohydrodynamically lubricated (EHL) elliptical point contacts under high sliding. Thereby, the entrainment direction is orientated along the major axis of the contact ellipse. Such contact geometries can appear in worm gears [1]. Film thickness measurements were carried out on an optical EHL tribometer. Numerical solutions were obtained by solving the EHL contact considering non-Newtonian rheology and thermal effects. 2. Methodology For experimental investigation, an optical EHL tribometer based on thin film colorimetric interferometry is used [2]. To investigate slender EHL contacts, test specimens with a radius of curvature in gap length direction of 𝑅𝑅 ! = 12.7 𝑚𝑚𝑚𝑚 and gap width direction of 𝑅𝑅 " = 4 𝑚𝑚𝑚𝑚 were manufactured. The steel roller was polished and paired with a glass disk. A mineral oil ISO VG 100 (MIN100) is used as a lubricant. Experiments are performed at a normal force resulting in a Hertzian pressure of 𝑝𝑝 # = 0.63 𝐺𝐺𝐺𝐺𝐺𝐺 and an oil temperature of 𝜗𝜗 $%& = 40 ± 0.5 ℃ . The entrainment speed was varied as 𝑣𝑣 ' = {0.6,1.2,1.8} 𝑚𝑚 𝑠𝑠 ⁄ and the slide-to-roll ratio as 𝑆𝑆𝑅𝑅𝑅𝑅 = ()! "#$$*)$%&&"+ )' = {0, +1.5, −1.5} . The experimental investigations are accompanied by numerical modelling. Thereby, the generalized Reynolds equation for elliptical contacts with unidirectional lubricant entrainment is considered [3]. Elastic deformation of an equivalent body is obtained by solving linear elasticity equation. Applied load and generated fluid pressure are balanced via the force-balance equation. The Vogel and Roelands model describe the pressure and temperature dependence of the considered oil and the Ree-Eyring model describes its rheological behaviour. Reynolds, energy and linear elasticity equations are written in a weak form, as a convection-diffusion type of equation. Due to high Peclet numbers, SUPG and GLS stabilization terms are applied to the Reynolds and energy equation. The equations are written in dimensionless form and solved by the finite element method, using the full-system approach for the generalized Reynolds’ equation and the linear elasticity equation with strong coupling of this system of equations with the energy equation. More details on the used equations, material properties and numerical procedure is given in references [4, 5]. 3. Results and Discussion Fig. 1 shows exemplarily for v m = 1.8 m/ s experimental and numerical results for the film thickness along the gap length direction (top) and film thickness interferograms (bottom) for different sliding conditions. Fig. 2 shows the corresponding calculated temperature and dynamic viscosity contours for 𝑆𝑆𝑅𝑅𝑅𝑅 = −1.5 and SRR = 1.5. Fig. 3 shows the derived results for h m and h c over the entrainment speed v m . In general, the experi- 0 1µm 0.05 0.85µm 0 1µm 0.05 0.85µm 0 1µm 0.05 0.85µm Figure 1. Experimental and numerical results for film thickness along the gap length direction (top) and film thickness 0,0 0,1 0,2 0,3 0,4 0,5 0,6 0,7 -0,2 -0,1 0,0 0,1 0,2 h in µm Gap length direction x in mm v_m_exp=1.8 m/ s v_m_num=1.8 m/ s 0,0 0,1 0,2 0,3 0,4 0,5 0,6 0,7 -0,2 -0,1 0,0 0,1 0,2 h in µm Gap length direction x in mm vm_exp=1.8 m/ s vm_num=1.8 m/ s 0,0 0,1 0,2 0,3 0,4 0,5 0,6 0,7 -0,2 -0,1 0,0 0,1 0,2 h in µm Gap length direction x in mm vm_exp=1.8 m/ s vm_num=1.8 m/ s SRR=-1.5 v m =1.8 m/ s SRR=0 v m =1.8 m/ s SRR=-1.5 v m =1.8 m/ s SRR=0 v m =1.8 m/ s v m =1.8 m/ s SRR=1.5 SRR=1.5 v m =1.8 m/ s b) a) c) v m|exp = 1.8 m/ s v m|num = 1.8 m/ s v m|exp = 1.8 m/ s v m|num = 1.8 m/ s v m|exp = 1.8 m/ s v m|num = 1.8 m/ s and an oil temperature of Slender EHL contacts under high sliding conditions Marko Tošić 1)* , Thomas Lohner 1) , Roland Larsson 2) 1) Technical University of Munich, Germany; School of Engineering & Design, Department of Mechanical Engineering, Gear Research Centre (FZG) 2) Division of Machine Elements, Luleå University of Technology, Luleå, Sweden 1. Introduction This study deals with experimental and numerical analysis of slender elastohydrodynamically lubricated (EHL) elliptical point contacts under high sliding. Thereby, the entrainment direction is orientated along the major axis of the contact ellipse. Such contact geometries can appear in worm gears [1]. Film thickness measurements were carried out on an optical EHL tribometer. Numerical solutions were obtained by solving the EHL contact considering non-Newtonian rheology and thermal effects. 2. Methodology For experimental investigation, an optical EHL tribometer based on thin film colorimetric interferometry is used [2]. To investigate slender EHL contacts, test specimens with a radius of curvature in gap length direction of 𝑅𝑅 ! = 12.7 𝑚𝑚𝑚𝑚 and gap width direction of 𝑅𝑅 " = 4 𝑚𝑚𝑚𝑚 were manufactured. The steel roller was polished and paired with a glass disk. A mineral oil ISO VG 100 (MIN100) is used as a lubricant. Experiments are performed at a normal force resulting in a Hertzian pressure of 𝑝𝑝 # = 0.63 𝐺𝐺𝐺𝐺𝐺𝐺 and an oil temperature of 𝜗𝜗 $%& = 40 ± 0.5 ℃ . The entrainment speed was varied as 𝑣𝑣 ' = {0.6,1.2,1.8} 𝑚𝑚 𝑠𝑠 ⁄ and the slide-to-roll ratio as 𝑆𝑆𝑅𝑅𝑅𝑅 = ()! "#$$*)$%&&"+ )' = {0, +1.5, −1.5} . The experimental investigations are accompanied by numerical modelling. Thereby, the generalized Reynolds equation for elliptical contacts with unidirectional lubricant entrainment is considered [3]. Elastic deformation of an equivalent body is obtained by solving linear elasticity equation. Applied load and generated fluid pressure are balanced via the force-balance equation. The Vogel and Roelands model describe the pressure and temperature dependence of the considered oil and the Ree-Eyring model describes its rheological behaviour. Reynolds, energy and linear elasticity equations are written in a weak form, as a convection-diffusion type of equation. Due to high Peclet numbers, SUPG and GLS stabilization terms are applied to the Reynolds and energy equation. The equations are written in dimensionless form and solved by the finite element method, using the full-system approach for the generalized Reynolds’ equation and the linear elasticity equation with strong coupling of this system of equations with the energy equation. More details on the used equations, material properties and numerical procedure is given in references [4, 5]. 3. Results and Discussion Fig. 1 shows exemplarily for v m = 1.8 m/ s experimental and numerical results for the film thickness along the gap length direction (top) and film thickness interferograms (bottom) for different sliding conditions. Fig. 2 shows the corresponding calculated temperature and dynamic viscosity contours for 𝑆𝑆𝑅𝑅𝑅𝑅 = −1.5 and SRR = 1.5. Fig. 3 shows the derived results for h m and h c over the entrainment speed v m . In general, the experi- 0 1µm 0.05 0.85µm 0 1µm 0.05 0.85µm 0 1µm 0.05 0.85µm Figure 1. Experimental and numerical results for film thickness along the gap length direction (top) and film thickness 0,0 0,1 0,2 0,3 0,4 0,5 0,6 0,7 -0,2 -0,1 0,0 0,1 0,2 h in µm Gap length direction x in mm v_m_exp=1.8 m/ s v_m_num=1.8 m/ s 0,0 0,1 0,2 0,3 0,4 0,5 0,6 0,7 -0,2 -0,1 0,0 0,1 0,2 h in µm Gap length direction x in mm vm_exp=1.8 m/ s vm_num=1.8 m/ s 0,0 0,1 0,2 0,3 0,4 0,5 0,6 0,7 -0,2 -0,1 0,0 0,1 0,2 h in µm Gap length direction x in mm vm_exp=1.8 m/ s vm_num=1.8 m/ s SRR=-1.5 v m =1.8 m/ s SRR=0 v m =1.8 m/ s SRR=-1.5 v m =1.8 m/ s SRR=0 v m =1.8 m/ s v m =1.8 m/ s SRR=1.5 SRR=1.5 v m =1.8 m/ s b) a) c) v m|exp = 1.8 m/ s v m|num = 1.8 m/ s v m|exp = 1.8 m/ s v m|num = 1.8 m/ s v m|exp = 1.8 m/ s v m|num = 1.8 m/ s . The entrainment speed was varied as 2) Division of Machine Elements, Luleå University of Techno 1. Introduction This study deals with experimental and numerical analysis of slender elastohydrodynamically lubricated (EHL) elliptical point contacts under high sliding Thereby, the entrainment direction is orientated along the major axis of the contact ellipse. Such contact geometries can appear in worm gears [1]. Film thickness measurements were carried out on an optical EHL tribometer. Numerical solutions were obtained by solving the EHL contact considering non-Newtonian rheology and thermal effects. 2. Methodology For experimental investigation, an optical EHL tribometer based on thin film colorimetric interferometry used [2]. To investigate slender EHL contacts, test specimens with a radius of curvature in gap length direction of 𝑅𝑅 ! = 12.7 𝑚𝑚𝑚𝑚 and gap width direction of 𝑅𝑅 " = 4 𝑚𝑚𝑚𝑚 were manufactured. The steel roller was polished and paired with a glass disk. A mineral oil ISO VG 100 (MIN100) is used as a lubricant. Experiments are performed at a normal force resulting in Hertzian pressure of 𝑝𝑝 # = 0.63 𝐺𝐺𝐺𝐺𝐺𝐺 and an oil temperature of 𝜗𝜗 $%& = 40 ± 0.5 ℃ . The entrainment speed was varied as 𝑣𝑣 ' = {0.6,1.2,1.8} 𝑚𝑚 𝑠𝑠 ⁄ and the slide-to-roll ratio as 𝑆𝑆𝑅𝑅𝑅𝑅 = ()! "#$$*)$%&&"+ )' = {0, +1.5, −1.5} . The experimental investigations are accompanied by numerical modelling. Thereby, the generalized Reynolds equation for elliptical contacts with unidirectional lubricant 0 1µm 0.05 0.85µm 0 Figure 1. Experimental and numerical results for film thickness along the gap length direction (top) and film thickness interferograms (bottom) for 𝑆𝑆𝑅𝑅𝑅𝑅 = −1.5 0,0 0,1 0,2 0,3 0,4 0,5 0,6 0,7 -0,2 -0,1 0,0 0,1 0,2 h in µm Gap length direction x in mm v_m_exp=1.8 m/ s v_m_num=1.8 m/ s 0,0 0,1 0,2 0,3 0,4 0,5 0,6 0,7 -0,2 h in µm Gap length direction x in mm SRR=-1.5 v m =1.8 m/ s SRR=-1.5 SRR=0 v m =1.8 m/ s v m =1.8 m/ s b) a) v m|exp = 1.8 m/ s v m|num = 1.8 m/ s and the slide-to-roll ratio as Slender EHL contacts under high sliding conditions Marko Tošić 1)* , Thomas Lohner 1) , Roland Larsson 2) 1) Technical University of Munich, Germany; School of Engineering & Design, Department of Mechanical Engineering, Gear Research Centre (FZG) 2) Division of Machine Elements, Luleå University of Technology, Luleå, Sweden 1. Introduction This study deals with experimental and numerical analysis of slender elastohydrodynamically lubricated (EHL) elliptical point contacts under high sliding. Thereby, the entrainment direction is orientated along the major axis of the contact ellipse. Such contact geometries can appear in worm gears [1]. Film thickness measurements were carried out on an optical EHL tribometer. Numerical solutions were obtained by solving the EHL contact considering non-Newtonian rheology and thermal effects. 2. Methodology For experimental investigation, an optical EHL tribometer based on thin film colorimetric interferometry is used [2]. To investigate slender EHL contacts, test specimens with a radius of curvature in gap length direction of 𝑅𝑅 ! = 12.7 𝑚𝑚𝑚𝑚 and gap width direction of 𝑅𝑅 " = 4 𝑚𝑚𝑚𝑚 were manufactured. The steel roller was polished and paired with a glass disk. A mineral oil ISO VG 100 (MIN100) is used as a lubricant. Experiments are performed at a normal force resulting in a Hertzian pressure of 𝑝𝑝 # = 0.63 𝐺𝐺𝐺𝐺𝐺𝐺 and an oil temperature of 𝜗𝜗 $%& = 40 ± 0.5 ℃ . The entrainment speed was varied as 𝑣𝑣 ' = {0.6,1.2,1.8} 𝑚𝑚 𝑠𝑠 ⁄ and the slide-to-roll ratio as 𝑆𝑆𝑅𝑅𝑅𝑅 = ()! "#$$*)$%&&"+ )' = {0, +1.5, −1.5} . The experimental investigations are accompanied by numerical modelling. Thereby, the generalized Reynolds equation for elliptical contacts with unidirectional lubricant entrainment is equivalent body is obtained by solving linear elasticity equation. Applied load and generated fluid pressure are balanced via the Roelands model dependence of the considered oil model descr Reynolds, energy and linear elasticity written in a of equation. Due to high Peclet numbers, SUPG GLS stabilization terms are applied energy equation. The equations are sionless form and solved by the using the full olds’ equation and the strong coupling of this system of equations with the energy equation terial properties and numerical procedure is given in erences [4, 5 3. Results and Discussion Fig. 1 shows exemplarily for and numerical results for the film thickness along the gap length direction (top) and film thickness interferograms (bottom) for shows the corresponding calculated temperature and dynamic viscosity contours for SRR = 1.5. h c over the entrainment speed v 0 1µm 0.05 0.85µm 0 1µm 0.05 0.85µ Figure 1. Experimental and numerical results for film thickness along the gap length direction (top) and film thickness interferograms (bottom) for 𝑆𝑆𝑅𝑅𝑅𝑅 = −1.5 (a), 𝑆𝑆𝑅𝑅𝑅𝑅 = 0 (b) and 𝑆𝑆 0,0 0,1 0,2 0,3 0,4 0,5 0,6 0,7 -0,2 -0,1 0,0 0,1 0,2 h in µm Gap length direction x in mm v_m_exp=1.8 m/ s v_m_num=1.8 m/ s 0,0 0,1 0,2 0,3 0,4 0,5 0,6 0,7 -0,2 -0,1 0,0 0,1 0,2 h in µm Gap length direction x in mm vm_exp=1.8 m/ s vm_num=1.8 m/ s SRR=-1.5 v m =1.8 m/ s SRR=0 v m =1.8 m/ s SRR=-1.5 SRR=0 v m =1.8 m/ s v m =1.8 m/ s b) a) v m|exp = 1.8 m/ s v m|num = 1.8 m/ s v m|exp = 1.8 m/ s v m|num = 1.8 m/ s . The experimental investigations are accompanied by numerical modelling. Thereby, the generalized Reyn-olds equation for elliptical contacts with unidirectional lubricant entrainment is considered [3]. Elastic deformation of an equivalent body is obtained by solving linear elasticity equation. Applied load and generated fluid pressure are balanced via the force-balance equation. The Vogel and Roelands model describe the pressure and temperature dependence of the considered oil and the Ree-Eyring model describes its rheological behaviour. Reynolds, energy and linear elasticity equations are written in a weak form, as a convection-diffusion type of equation. Due to high Peclet numbers, SUPG and GLS stabilization terms are applied to the Reynolds and energy equation. The equations are written in di-mensionless form and solved by the finite element method, using the full-system approach for the general-ized Reynolds’ equation and the linear elasticity equa-tion with strong coupling of this system of equations with the energy equation. More details on the used equations, material properties and numerical procedure is given in references [4, 5]. 468 23rd International Colloquium Tribology - January 2022 Slender EHL contacts under high sliding conditions Figure 1: Experimental and numerical results for film thickness along the gap length direction (top) and film thickness interferograms (bottom) for SRR = -1.5 (a), SRR = 0 (b) and SRR = 1.5 (c) for v m = 1.8 m/ s Figure 2: Numerical results for temperature distribution and viscosity for (a) and (b) for vm = 1.8 m/ s 3. Results and Discussion Fig. 1 shows exemplarily for v m = 1.8 m/ s experimental and numerical results for the film thickness along the gap length direction (top) and film thickness interferograms (bottom) for different sliding conditions. Fig. 2 shows the corresponding calculated temperature and dynamic viscosity contours for SRR = -1.5 and SRR = 1.5. Fig. 3 shows the derived results for h m and h c over the entrainment speed v m . In general, the experimental and numerical results for the considered slender EHL contacts are in good accordance. By comparing all three graphs shown in Fig. 1 (top), it can be concluded that there is the highest film thickness at pure rolling with SRR=0, which is expected since there is no significant oil shearing and consequently temperature generation inside the oil film. Additionally, it can be seen that at SRR = 0 and SRR = -1.5, the film thickness in the central contact region has a flat shape, while at SRR = 1.5 it shows a decreasing trend along the gap length direction. The film thickness interferograms in Fig. 1 (bottom) show that at SRR = 0 and SRR = -1.5 the film thickness in the central contact region has a “U-shape”, while at SRR = 1.5 the shape reminds more of a “V-shape”. Figure 3: Experimental and numerical results for h m and h c over entrainment speed v m for SRR = -1.5 and SRR = 1.5 23rd International Colloquium Tribology - January 2022 469 Slender EHL contacts under high sliding conditions This shape of the film thickness in the central region is mainly caused by very different thermal effusivities. Since glass has a much lower thermal effusivity than steel, in both positive and negative sliding conditions the glass surface has a higher temperature than the steel one, resulting in more viscous oil in the vicinity of the steel surface (see Fig. 2). When the steel surface moves faster than the glass surface (SRR = -1.5), the viscous oil is moved through the contact with higher speed, resulting in lower central film thickness. When the steel surface moves slower than the glass surface (SRR = 1.5), the viscous oil “accumulates” in the contact, causing an obstacle for passing the oil through the contact, increasing the side flow and ultimately changing the film thickness shape in the central region. The trends of minimum and central film thickness h m and h c over the entrainment speed v m in Fig. 3 show that h c is higher and increases stronger with v m at SRR = 1.5 than at SRR = -1.5. On the other hand, h m is higher and increases faster with v m at SRR = -1.5 than at SRR = 1.5. In fact, it seems that at SRR = -1.5 increasing v m has almost no effect on h m . This means that in slender EHL contacts with positive SRR, increasing entrainment speed cannot help much in preventing very low values of h m and eventually lubricant breakdown, particularly if the ratio of R x and R y is more severe than considered in this study. 4. Conclusion The results presented in this study show for the considered slender EHL contacts with high positive sliding a continuous decrease of the lubricant film thickness in the central contact region. This is in context with the different thermal effusivity of the rolling-sliding pairing considered. The influence of the entrainment speed on the minimum film thickness is small. References [1] Sharif K et al.; Journal of Mechanical Engineering Science, 215(7), 831: 46; https: / / doi. org/ 10.1243/ 0954406011524180 (2001) [2] Yilmaz M et al.; Lubricants, 7(5), 46; https: / / doi. org/ 10.3390/ lubricants7050046 (2019) [3] Habchi W. ISBN: 978-1-119-22512-6. Wiley, Chichester, UK. 2018. [4] Ziegltrum A. et al.; Lubricants, 6(1), 17; https: / / doi. org/ 10.3390/ lubricants6010017 (2018) [5] Ziegltrum A. et al.; Tribology Letters, 68: 71; https: / / doi.org/ 10.1007/ s11249-020-01309-6 (2020) 23rd International Colloquium Tribology - January 2022 471 Opportunities and Applications for Artificial Intelligence in Sealing Technology Matthias Baumann University of Stuttgart, Institute of Machine Components, Stuttgart, Germany Corresponding author: matthias.baumann@ima.uni-stuttgart.de Lukas Merkle University of Stuttgart, Institute of Machine Components, Stuttgart, Germany Frank Bauer University of Stuttgart, Institute of Machine Components, Stuttgart, Germany 1. Introduction Sealing technology is an expert science in which the experience and the expertise of the players are important in many respects. In the case of failure analysis, it is often the small things that reveal the causes of failure and the damage mechanisms. In many places, a great deal of effort is therefore being expended to optimize the methods used for the analysis of sealing systems, [1]. Specialized equipment has even been developed, for example to produce the best possible images of the components of a sealing system or to measure relevant parameters user independently [2-4]. Despite considerable effort in failure analysis and the use of standardized evaluation matrices (see Figure 1), interlaboratory tests with several participants regularly show scattered evaluation results. This is a delicate matter in standardized seal test procedures, which potentially aim for the release of an oil for a given application. Of course, the inherent scatter of tribological tests contributes to these results, [5]. However, when the measurement data of all participants are considered together as a team, there is usually a clear unification of the evaluation results. This is ultimately due to the different levels of knowledge and the individual subjective evaluation of the experts performing the tests. One way of standardizing the evaluation of tribological tests and reducing the influence of the single user is to use artificial intelligence methods. Assistance systems that are trained with previously coordinated and appropriately classified image data can preserve and transfer expert knowledge. Furthermore, they can help to keep the track about the sometimes hundreds of involved images and analysis results. 2. Failure Analysis Methodology for Rotary Shaft Seals Standardized test specifications for evaluating e.g. the oil-elastomer compatibility of newly developed oils with rotary shaft seals made of standard elastomers have become established in the industry, [6]. Systematic procedures form the basis for the evaluation and, associated with this, the release of the tested oils for the respective application. In addition to measuring the wear width, the radial load and the inner diameter of the tested seals, such approvals also include a visual inspection of the elastomeric sealing edges of the rotary shaft seals. To ensure consistent results over a longer period of time and a higher number of tests, an evaluation matrix was developed at the institute. The so-called IMA-MARS (Matrix for the Advanced Rating of Seals, ) has been iteratively improved ever since then, Figure 1. Methodically, the evaluation includes an examination of the sealing edges in the uncleaned and cleaned condition. 472 23rd International Colloquium Tribology - January 2022 Opportunities and Applications for Artificial Intelligence in Sealing Technology Figure 1: Matrix for the Advanced Rating of Seals - MARS [1] Based on 4 groups (Mechanical Failure, Thermal Attack, Oil Carbon Deposits, Chemical Attack), the condition of the elastomer sealing edge is systematically rated in terms of the sealing function. But however, a systematic approach alone does not lead to fully consistent results. Carried out individually, there are usually always certain deviations in the ratings due to the individual subjective influence of the user. Therefore, comparison tables are used and the ratings are carried out in large expert teams at joint meetings. All this represents a not inconsiderable effort. In order to work efficiently and consistently, good preparation and coordination is required. This has led to the development of intelligent assistance software at the institute, which supports the raters in their work. 3. Image Classification Part of the evaluation criteria, which are determined in the course of the visual analysis of sealing edges described above, are determined on uncleaned images of the sealing edge and the other part on cleaned images of the sealing edge, both taken e.g. with the IMA Sealobserver [7]. The following rating can be done conveniently if the rater is specifically shown the correct image data in each case. To make this possible in an automated way, Convolutional Neural Networks (CNNs) from the field of machine learning can be used. These are particularly well suited for classifying images and can thus distinguish undeclared image data. Such a CNN is roughly composed of an image input layer, a combination of different convolutional and pooling layers and a classification layer. It converts an image file into a classification vector via previously trained computing operations. We trained a CNN with the image data of sealing edges, obtained from past research projects of the institute. The image data were previously divided manually (supervised machine learning) into the classes: uncleaned, undamaged and damaged, whereas damaged was mainly focused on the group thermal attack to the sealing edge. A split of the data into 80 % training data and 20 % validation data led to a validation accuracy of 99 % after the training procedure. The resulting classification network was transferred into a graphical user interface and now allows a targeted display of the image data. The tool is used in rater meetings, which have since become much more efficient and less time consuming. Figure 2: Graphical user interface for the rating seals according to the IMA-MARS 4. Image Regression In addition to classification problems, CNNs can also be used to calculate regressions. This is of interest when image data must be converted into parameters, as is also required here in the case of the individual evaluation criteria. The otherwise manually performed evaluation is is therefore automated. The rater receives an evaluation proposal from an intelligent assistance system and can use this as a basis for checking the image data and, if necessary, taking corrective action. The problem here is that the evaluation criteria presented above are based on a global view of a large number of images. Accordingly, a complete derivation of all evaluation criteria cannot be made on the basis of a single image, which is the way CNNs work. Several images have to be linked to get a result. For this purpose, a Long Short-Term Memory (LSTM) [8] network was implemented. This 23rd International Colloquium Tribology - January 2022 473 Opportunities and Applications for Artificial Intelligence in Sealing Technology network architecture belongs to the Recurrent Neural Networks (RNN) and was developed for the analysis of data sequences such as videos or speech. Series of images can be processed sequentially, whereby information about arbitrary intervals is stored in a LSTM cell. Through this procedure it is possible to transform a set of image data into a regression of the evaluation criteria. An LSTM network was trained with the previously mentioned image data. The evaluation required for this using the IMA MARS was previously carried out in an expert team meeting. The network was integrated into the graphical user interface and now supports the user in the evaluation of the image data. However, an interlaboratory test among several users is still pending. The aim is to investigate whether the user-dependent variation in the evaluation can be reduced by means of such assistance systems and whether consistent results are obtained overall. 5. Conclusion The field of artificial intelligence is growing at a tremendous rate. The tools that have already been developed enable a wide range of applications in almost all technical areas. There are also many possible applications in sealing technology. Convolutional Neural Networks can be used for classification of image data in damage analysis to make the evaluation process more comfortable for the user. LSTM networks also permit the creation of systemic evaluation matrices from image data sets. These can serve as a basis guess for a user, they preserve expert knowledge and are intended to make results user-independent and even more consistent in the future. Both examples show the benefits of the application of machine learning methods for application within the sealing technology. Many other applications are further conceivable, as for example artefact detection on sealing counterfaces, classification of manufacturing methods and much more. References [1] Bauer, F.: Federvorgespannte-Elastomer-Radial- Wellendichtungen, Wiesbaden: Springer Fachmedien Wiesbaden, 2021, - ISBN 978-3-658-32921-1. [2] Baumann, M.; Bauer, F.: Moderne visuelle Untersuchungsmethoden für die Verschleißanalyse am Beispiel Radial-Wellendichtring. 20th International Sealing Conference (ISC), Stuttgart, 10.-11. Oktober 2018; Fluidtechnik; Frankfurt am Main: Fachverband Fluidtechnik im VDMA e.V, 2018, S. 93-104 - ISBN 978-3-8163-0727-3. [3] Schollmayer, T.; Burkhart, C.; Kassem, W.; Thielen, S.; Sauer, B.: Verschleißanalyse an Radialwellendichtringen und weiteren Maschinenelementen mittels Laserprofilometrie. Tribologie-Fachtagung. 2021, 62 , 70/ 1-70/ 10. [4] Fehrenbacher, C.; Hörl, L.; Bauer, F.; Haas, W.: Description of the Pumping Rate of Shaft Counterfaces in the Sealing System Radial Lip Seal Using the 3D Parameters of ISO 25178. Tribology Online. 2016, 11 (2), S. 69-74. [5] Bauer, F.: Tribologie, Wiesbaden: Springer Fachmedien Wiesbaden, 2021, - ISBN 978-3-658-32919-8. [6] Hüttinger, A.; Hermes, J.; Wöppermann, M.; Prem, E.: Neues Prüfverfahren für dynamische Dichtungen von Getriebemotoren. Erschienen in: Jahrbuch Dichtungstechnik 2016, Friedrich Berger; Sandra Kiefer; Mannheim: ISGATEC GmbH, 2015 - ISBN 978-3-9811509-9-5. [7] Universität Stuttgart, Institut für Maschinenelemente: IMA-Sealobserver. Universität Stuttgart, Institut für Maschinenelemente (Hrsg.), IMA- TechSheet, V1, #102070, Stuttgart, URL: https: / / www.ima.uni-stuttgart.de/ dokumente/ forschung/ dichtungstechnik/ einrichtungen/ 102070.pdf. [8] Hochreiter, S.; Schmidhuber, J.: Long short-term memory. Neural computation. 1997, 9 (8), S. 1735- 1780. Soft Contacts 23rd International Colloquium Tribology - January 2022 477 Improved design process of dry-running radial plastic plain bearings by coupling laboratory tests and component simulation Marc Fickert Leibniz-Institut für Verbundwerkstoffe GmbH, Erwin-Schrödinger-Straße 58, 67663 Kaiserslautern, Germany Corresponding author: marc.fickert@ivw.uni-kl.de Andreas Gebhard Leibniz-Institut für Verbundwerkstoffe GmbH, Erwin-Schrödinger-Straße 58, 67663 Kaiserslautern, Germany 1. State of the art and daily practice While comprehensive standards, design guidelines [1] and professional calculation tools [2-4] are available for hydrostatically and dynamically operated radial plain bearings, the design process of dry-running radial plain bearings made of plastic for demanding applications has so far not been possible without cost-intensive component tests. The reason for this is the currently available calculation methods which are of a highly approximate nature and cannot be readily applied to other materials due to the necessary transfer functions in the form of diagrams. There are significant methodological gaps, particularly with regard to the consideration of the sliding surface temperatures occurring in the respective installation situation, since the natural interdependence between the temperature-dependent coefficient of friction and the temperature dependent on the coefficient of friction, in combination with the heat conduction dependent on the installation situation, cannot be solved without further ado. But even with the use of individual and high-resolution calculation methods, such as the FEM method, a lot of material characteristics are required, the determination of which in the form of tribological material maps by means of model tests such as the block-on-ring wear test involve an enormous amount of work. 2. New concept “aBoR” Because of the above reasons, a novel method for the design of dry-running radial plain bearings is currently being developed at Leibniz-Institut für Verbundwerkstoffe GmbH. By building a computer-aided calculation model of a plain bearing and coupling it with a block-on-ring wear test rig, a control loop (“hardware-in-the-loop”) is created that simulates the real behavior of a plain bearing. The plastic block used in this process corresponds to a segment of a plain bearing at its most heavily loaded point. On the basis of the test rig measurement variables of sliding friction coefficient and block height, which are continuously transmitted to a simulation during an ongoing test, the simulation calculates the current operating state of a virtual plain bearing on the basis of all the measurement data transmitted to date. A thermal calculation model is used to calculate the temperature of the virtual shaft from the coefficient of sliding friction and the geometric and material-specific boundary conditions entered. The wear-related change in block height is used to calculate the wear-related change in geometry of the virtual bearing which in turn is used to calculate the current surface pressure distribution in the virtual bearing. These two calculation results more precisely, the representative normal force resulting from the surface pressure and the counter-body temperature are transmitted to the test rig and adjusted accordingly. This procedure is carried out iteratively and continuously. Thus, both the surface pressure prevailing in the further course of the aBoR test and the temperature of the ring test specimen no longer result, as before, only from the frictional power of the block-ring test specimen pair and the heat dissipation dependent on the respective test rig design, but are set according to the results of the simulation of a plain bearing running during the test. A patent application has been filed for the “aBoR” (advanced Block-on-Ring) method (DE 10 2021 109 854), which is intended to significantly optimize the informative value and processing time of a plain bearing design. 3. First results of early-stage prototype The described hardware-in-the-loop control loop, i.e. the communication between the wear test rig and the separately running simulation, was prototypically set up using a blockon-ring test rig. A thermal network model was used to calculate the temperature development and distribution of a virtual plain bearing on the basis of the measured coefficient of sliding friction (see Figure 1). In the example shown the coefficient of friction starts at a high level of almost 0.3, but quickly drops to a value below 0.1 after running-in. With the time-delayed increase in the friction surface temperature (shaft temperature) it then rises again rapidly to a maximum value of 0.31 and then falls to a steady-state value of 0.16. The shaft temperature then rises again to a maximum value of 0.31 and then falls to a steady-state value of 0.16. The shaft temperature rises temporarily to up to 170 °C. Knowledge of the operating temperatures of the individual plain bearing components was used to optimize the clearance of the plain bearing application. Based on the component temperatures, their thermal expansions are continu- 478 23rd International Colloquium Tribology - January 2022 Improved design process of dry-running radial plastic plain bearings by coupling laboratory tests and component simulation ously calculated (see Figure 2). The difference between the bearing inner diameter and the shaft diameter is the operating clearance (see Figure 3) which is set to its smallest value of 2.2 ‰ in the range of the highest shaft temperature. Figure 1: Simulated temperature curves based on the measured coefficient of friction (COF) Figure 2: Shaft and bearing diameter Figure 3: Operational clearance If this value is now reduced to the smallest possible radial clearance of, for example, 0.5 ‰ [5], the plain bearing clearance can be reduced by 52 µm, thus extending the service life accordingly. Table 1: Results of clearance optimization 4. Summary and outlook The currently available design methods for dry-running radial plain bearings are inaccurate with regard to the prediction of sliding surface temperature, dimensioning and lifetime, and inflexible with regard to the influence of the installation situation on the temperature distribution. As a remedy, a hardware-in-the-loop process called “aBoR” was developed. A first prototype, which uses a thermal network model to calculate the transient component temperatures, is already capable of continuously calculating the operating clearance and thus optimizing the geometric design of a bearing. The next development goals are the correlation of the model with the results of component tests, the implementation of FEM-based simulation methods for heat conduction and distribution and the development of a wear progress model. References [1] VDI-Fachbereich Produktentwicklung und Mechatronik, „Gleitlagerberechnung - Hydrodynamische Gleitlager für stationäre Belastung,“ in VDI-Handbuch Produktentwicklung und Konstruktion, Berlin, Beuth Verlag GmbH, 1992, p. 59. [2] Tribo Technologies GmbH, „Software for higher efficiency - Radialgleitlager,“ o. J.. [Online]. Available: https: / / www.tribotechnologies.com/ de/ tribox/ basismodule/ radialgleitlager. [access on 30.06.2021]. [3] TU Clausthal - Institut für Tribologie und Energiewandlungsmaschinen, „COMBROS R - Simulation des Radialglleitlagerbetriebsverhaltens,“ o. J.. [Online]. Available: https: / / www.itr.tuclausthal.de/ forschung/ tribosimulation/ combros-r. [access on 29.06.2021]. [4] KISSsoft AG, „KISSsoft Spezifikationen - Wellen und Lager,“ o. J.. [Online]. Available: https: / / www. kisssoft.com/ de/ products/ productoverview/ kisssoftr-elements. [access on 30.06.2021]. [5] M. Mäurer, Tribologische Untersuchungen an Radialgleitlagern aus Kunststoffen, TU Chemnitz, 2002. 23rd International Colloquium Tribology - January 2022 479 Tribological behavior study of elastomer - hard substrate contact in marine environment Claire Robin, Ahmad Al Khatib ECAM RENNES, Bruz, France Corresponding author: ahmad.al-khatib@ecam-rennes.fr Jean-Marie Malhaire ECAM RENNES, Bruz, France Jean-François Coulon ECAM RENNES, Bruz, France 1. Introduction and state of art A lot of machines and equipment (pumps, open hydraulic drive system and blades of ships, etc.) are used in seawater environment for several applications like transportation, offshore naval missions and oil drilling. Thus, friction and wear studies under seawater conditions is an important topic in tribology [1]. In this environment, seawater plays the role of lubricant and modify the tribological behavior between the mechanical parts. However, these parts should be resistant for high corrosive nature of seawater. For this reason, recent studies involve testing the friction and wear behavior of several materials with anti-corrosive and anti-wear properties like some polymers, ceramics metals and metal alloys in marine environment [2, 3, 4]. The Nitrile butadiene rubber (NBR) is known as an elastomer with good chemical and corrosive resistance for seawater [5]. It is commonly used in industry and especially for marine applications like seals on boats’ propeller shafts. So, we are focusing in this work on the study of tribological behaviour between NBR and hard substrate in marine environment. In the case of elastomers, the phenomenon of friction can be defined as the sum of four main components [6]. We note that the friction force F f as being: F f = F adhesion + F hysteresis + F viscosity + F cohesion . F adhesion represents the frictional force required to break the molecular chains between the surface of the elastomer and the surface of the substrate. It is proportional to the real contact surface. F hysteresis represents the dissipation of energy due to the viscoelasticity of the elastomer. It defines the friction force due to the pressure difference between charge and discharge [7]. F viscosity appears in the case of lubricated friction. It results from the viscosity of the lubricant. Finally, F cohesion corresponds to the initiation of cracks and the wear of the elastomer. These four components are not independent of each other, which complicates the analysis. In lubricated conditions, several researchers show the link between wettability and friction coefficient. Wettability is the ability of a substrate to be wetted by a liquid when they come into contact. It is not characteristic of the substrate or the liquid, but rather of the combination of the two. This is characterized by the shape of the gout of liquid in the materiel surface [8]. In their study, Pawlak et al. (2011) [9] studied the link between the wettability of the material and the resulting coefficient of friction in the case of hydrophilic-hydrophilic, hydrophilic-hydrophobic and hydrophobic-hydrophobic tribological couples with water lubrication. For a hydrophilic-hydrophilic couple, the coefficient of friction increases significantly when the wettability increases. The water then plays a bonding role. For a hydrophobic-hydrophobic couple, the coefficient does not change if the wettability increases. In the case of hydrophilic-hydrophobic contact, the coefficient of friction decreases significantly with wettability. The wettability of the surface of material can be modified by several treatments and coatings (Plasma, DLC). Kim et al. (2011) [10] studied the relationship between the decrease in the wettability of the substrate and the friction coefficient in the case of plasma treatments on NBR. The tribological tests were carried out with grease lubrication. Decreasing the contact angle from 100° to 50° leads to a decrease in the coefficient of friction from 0.25 to 0.15. Our state of the art leads us to focus our study of master degree on the link between the wettability and the tribological behavior of NBR in friction against a hard substrate in a marine lubrication environment. The NBR samples will be in friction with a glass plate but also with a stainless steel plate, this to bring us closer to industrial reality. 2. Material and methods NBR samples (60 ±7 Shore A; Ra=0.6μm) are cut in the form of pellets with a diameter of 6mm and a thickness of 1.5mm. The used hard substrates are a glass plate (80mm×40mm×3mm; Ra =0.06 μm) and tow stainless 480 23rd International Colloquium Tribology - January 2022 Tribological behavior study of elastomer - hard substrate contact in marine environment steel plates with tow roughness (80mm×40mm×3mm; Ra 1 = 2μm; Ra 2 =0.03μm). A sliding tribometer developed in our university is used. The speed of sliding is of 2mm/ s. We set the normal load on NBR samples during the tests at 140 grams. The tests are realized in three conditions: a) dry condition; b) demineralized water lubrication condition; c) artificial seawater lubrication condition. For the third condition, it is difficult to have repeatable measurements with natural seawater. Indeed, the composition of this water is varying significantly depending on the geographical area but also on temperature and sea currents. For this reason, we decided to use so-called artificial seawater by adopting a seawater synthesis using the standard D1141 - 98 [11]. In addition to the standard concentration seawater, we used doubled concentration seawater in order to study the coefficient of friction as a function of the salinity of the water. To modify the wettability of NBR samples, atmospheric-pressure plasm is used. The plasma treatment is carried out at a height of 20mm from the sample, the speed is 300 mm/ s. The torch is set at a frequency of 200 kHz and the flow rate is 40 l/ min. These parameters are determined to not exceed the temperature of deterioration of the elastomer while having a treatment that allows a significant change in the contact angle. To measure the wettability of different surfaces, a contact angle test is performed using the Owens-Wendt method [8]. The liquids used to measure the contact angle are demineralized water, diazomethane as well as artificial seawater. 3. Results and discussion In the case of NBR/ glass friction (Figure 1), seawater allows a reduction in the coefficient of friction which drops from 0.62 for demineralized water to 0.305 for standard seawater. This reduction is less important for doubled concentration seawater. The reduction of friction coefficient is valid for treated and untreated NBR. This result is in agreement with the work of Wang et al (2009) [12]. In fact, seawater is a lubricant that significantly reduces the coefficient of friction. However, this depends on the concentration of salts in seawater. In the case of NBR/ stainless steel (Ra: 2µm) friction (figure 2), this difference is less significant. This can be explained by an influence of roughness more important. Indeed, the figure (3) shows that the friction coefficient increases when the roughness of the steel plate is less important. This is explained by the effect of the real contact surface between NBR and hard substrate. Thus, the NBR sample does not fully fit into the interstices created by the increase in roughness as shown by the work of et Ido al., (2019) [7]. The plasma treatment, as we carried out, made it possible to reduce the contact angle for the three lubrication conditions (demineralized water, standard seawater and doubled seawater). Reducing the contact angle by plasma treatment leads to a significant increase in the coefficient of friction for both standard concentration seawater and doubled concentration seawater. We find this effect for NBR/ glass and NBR/ steel frictions. However, we couldn’t find this effect with demineralized seawater NBR/ glass friction. If we reconsider the equation developed by Kummer [6], F cohesion can be identified by tensile tests but also by a numerical simulation that we carried out on Abaqus commercial solution (figure 4). By comparing the results of stress from the simulation with tensile strength, it can be considered that wear does not exist. Between demineralized water and seawater, the difference in viscosity is 0.059 centipoise at room temperature. However, we have not investigated the role of such a small difference in viscosity on F viscosity and consequently on the friction coefficient. F hysteresis is due to energy dissipation due to the viscoelasticity of the elastomer which does not change between the different conditions. However, when the roughness changes, the hysteresis is also modified. Finally, F adhesion was related to the couple of material in friction but also to the plasma treatment. Figure 1: coefficient of friction on glass with and without plasma treatment for different lubrication conditions 23rd International Colloquium Tribology - January 2022 481 Tribological behavior study of elastomer - hard substrate contact in marine environment Figure 2 : coefficient of friction on steel with and without plasma treatment for different lubrication conditions Figure 3: coefficient of friction of steel for two roughness Figure 4 : finite elements simulation for friction NBR/ hard substrate References [1] Haq, M. I. U., Raina, A., Vohra, K., Kumar, R., & Anand, A. (2018). An assessment of tribological characteristics of different materials under sea water environment. Materials Today: Proceedings, 5(2), 3602-3609. [2] Dong, C. L., Bai, X. Q., Yan, X. P., & Yuan, C. Q. (2013). Research status and advances on tribological study of materials under ocean environment. Tribology, 33(3), 312-320. [3] Wang, D., Li, Z. Y., & Zhu, Y. Q. (2003). Lubrication and tribology in seawater hydraulic piston pump. Journal of Marine Science and Application, 2(1), 35-40. [4] Shan, L., Wang, Y., Li, J., Li, H., Wu, X., & Chen, J. (2013). Tribological behaviours of PVD TiN and TiCN coatings in artificial seawater. Surface and Coatings Technology, 226, 40-50. [5] ZHAI, Z. S., ZHONG, X., ZHANG, Y. P., & HU, G. (2011). Predicting the service lifetime of O-rings in sea water. Synthetic Materials Aging and Applicationg, 6, 39-43. [6] Kummer, H. W. (1966). Unified theory of rubber and tire friction. Engineering research bulletin, 94, p. 152. [7] Ido, T., Yamaguchi, T., Shibata, K., Matsuki, K., Yumii, K., & Hokkirigawa, K. (2019). Sliding friction characteristics of styrene butadiene rubbers with varied surface roughness under water lubrication. Tribology International, 133, 230-235. [8] Owens, D. K., & Wendt, R. C. (1969). Estimation of the surface free energy of polymers. Journal of applied polymer science, 13(8), 1741-1747. [9] Pawlak, Z., Urbaniak, W., & Oloyede, A. (2011). The relationship between friction and wettability in aqueous environment. Wear, 271(9-10), 1745- 1749. [10] Kim, J. H., Kim, S. S., Choi, S. G., & Lee, S. H. (2011). The friction behavior of NBR surface modified by argon plasma treatment. International Journal of Modern Physics B, 25(31), 4249-4252. [11] ASTM (2003). Standard Practice for the Preparation of Substitute Ocean Water D1141-98. ASTM international. [12] Wang, J., Yan, F., & Xue, Q. (2009). Tribological behavior of PTFE sliding against steel in sea water. Wear, 267(9-10), 1634-1641. Sustainable Lubrication 23rd International Colloquium Tribology - January 2022 485 Sustainability by Design using Tribological and Lifecycle Assessment Tools Amaya Igartua Fundación TEKNIKER, Eibar, Spain Corresponding author: amaya.igartua@tekniker.es Raquel Bayon Fundación TEKNIKER, Eibar, Spain Gemma Mendoza Fundación TEKNIKER, Eibar, Spain B. Zabala Fundación TEKNIKER, Eibar, Spain Mathias Woydt MATRILUB, Berlin-Dahlem, Germany 1. Introduction Tribological research and developments are substantial and hidden contributors to climate protection and sus-tainability through friction reduction and wear protec-tion. Techniques, like condition monitoring, repair and reuse as well as recycling extend longevity and limit the material hunger with its embedded CO 2 . The consequent reduction of friction and improvement of longevity contributes on the long run to reduce 6-10 gigatons of CO 2eq emissions [1-2] out of 33.6 gigatons of direct or energy related CO 2 emissions (fossil or anthropogenic) in 2019. It was recently illuminated, that 20-33% [U.S. Congress [2] & Holmberg [3]] of the total primary energy consumption is consumed by friction! By assuming savings between 30-40% in a mid-/ long-term perspective, friction reduction will contribute to saving 8-13% of pri-mary energy consumption, irrespective it is CO 2 -neutral or fossil based, whereas wear protection and condition monitoring offer an extended service life of machines and their components generating less material consumption and reducing there embedded CO 2eq . emissions from mining, extraction and conversion of raw materials. Further investigation is needed to allocate the material streams to in different applications. Tribology is a property of the system and occurs everywhere in the total value chain and material streams over all industrial sectors (transportation, energy, construction, medical, etc) and private uses (consumer goods, appliances) [3-9]. Figure 1: Testing tribological configuration to reproduce at laboratory the failure mechanism of the tribological system, ©TEKNIKER. Tribology is the tool to design sustainable usage of materials and processes in systems submitted to relative movement. [7]. Materials solutions (including coatings and lubricants) can help to reduce friction and increase lifetime of materials and Coatings. On the other hand, the energy consumption during operation by friction losses dominates the CO 2 emissions during a lifecycle and countermeasures are needed to minimize the carbon footprint impact. Corrosion and tribology both are surface properties and two key degradation mechanisms. The simultaneous occurrence of both phenomena is called tribocorrosion. Corrosion and wear cause irreversible material and functional losses and thus increase fuel and primary materials consumption. The material volume saved by extended service life cycles lowers CO 2 emissions, material streams and wastes. Combination of modelling and characterization needs to be optimized to achieve this goal [1, 3, 10]. 486 23rd International Colloquium Tribology - January 2022 Sustainability by Design using Tribological and Lifecycle Assessment Tools 2. Proposed solutions The white paper “The Role of the Materials for Post Covid Society” edited by EUMAT-A4M and published by EU Commission is a reflection on how Materials will enable solutions for society and citizen’s demands. [4] contains positioning, potential solutions, and recommendations from the European Materials community (A4M) towards Horizon Europe. Compiles Strategic Research Agendas (SRAs) from Materials stakeholders, addressing lessons learned in current COVID19 pandemic, and aligned with Green Deal Priorities and Recovery Plan. 3. Impact Quantification The global population is still growing, including its wealth. The resource consumption will increase from 92,1 gigatons (2017) plus 8,6 gigatons of cycled prod-ucts to 165-190 gigatons in 2050, if no action is taken [1,2, 13]. With one ton of primary material/ metal are associated 1,36-1,83 tons of CO 2eq . The consumption of primary energy, either fossil or CO2-neutral ones, will increase accordingly. The Tribology is a key interdisciplinary technology to reduce CO 2 emissions through friction reduction and to achieve resources conservation: - doubling the service life results in average savings of 1.06-3.70 gigatons in mass of resources per year or of embedded 1.68-6.77 gigatons CO 2eq . per year [1, 10]. - A reduction of 30% in friction losses reduce global CO 2 emissions by 2.27-4.55 gigatons of CO 2 per year [2, 13]. Document Chapters Proposed solutions Circular economy, sustainable raw materials, materials cycles Use secondary materials, Coatings to enhance durability, biobased materials, Green and Clean Energy Energy efficiency, materials durability for renewable energy, low carbon footprint, Lifecycle environmental assessment, lifecycle cost CO 2 emissions reduction and Climate impacts Recycle, reuse, repair, condition monitoring Digitalization and Artificial Intelligence Sensor, drones, smart maintenance, virtual vision Resilience against future emergencies, less critical dependencies “by design” Design for recycling, for durability, for energy efficiency, substitute critical raw materials by coatings Enabling efficient, prudent, frugal quick response and innovation in emergency solutions Flexible and tailored manufacturing (eg. Additive manufacturing, 3D printing) Social, societal, education and political impacts in post COVID times e-training, e-LUBMAT, S-LCA 4. Recommendations • Use for low carbon footprint processes and products sustainable design approaches by tribology. • Use secondary materials or (re)cycled materials to assure raw materials availability and limit material hunger as well as enhance functionalities by surface treatments. • Circular economy (recycle, reuse, repair…) to extend lifetime • Use advanced sensors and drones for predictive mainte-nance taking the advantages of artificial intelligence 5. Conclusions The use of Tribology at the design phase of the products and processes allows to predict at the laboratory, materials durability and friction (linked with energy efficiency), simulating working conditions and main failure mechanism during their use. Materials solutions (including coatings and lubricants) can help to reduce friction and increase lifetime of materials and Coatings. Environmental, Economic and Social Lifecycle impact evaluations (LCA, LCC, LCS) can help to optimize the processes and products and minimize their impact. The wear and corrosion protection has an economic saving potential of 3-5% of the Gross National Product. 6. Acknowledgements The authors would like to acknowledge the EU Commission, German, Basque and Spanish research financing organizations to support the research highlighted in this document. 23rd International Colloquium Tribology - January 2022 487 Sustainability by Design using Tribological and Lifecycle Assessment Tools References [1] “CO2 & Friction” (2019) https: / / www.gft-ev.de/ en/ tribology-study/ , available in DE/ FR/ EN [2] “Sustainability & Wear Protection” (2021) h tt p s : / / www. gfte v. d e / w p c o n t e n t/ u plo a d s / GfT-Studie-Verschlei%C3%9Fschutz-und-Nachhaltigkeit.pdf . [3] K. Holmberg et al., The Impact of Tribology on Energy Use and CO2 Emission globally and in Combustion Engine and Electric Cars, Tribology International, Volume 135, July 2019, p. 389-396, [4] ‘The role of Materials in the post-covid society’, |European Commission (europa.eu), 22.09.2020 [5] 2019_02_a4m_position_paper_v44.pdf (eumat.eu) [6] K. Holmberg, A. Erdemir, “Influence of tribology on global energy consumption, costs and Emissions”, Friction 5 (3): 263-284 (2017); https: / / doi. org/ 10.1007/ s40544-017-0183-5. [7] A. Igartua et al., “Tribology, the tool to design materials for energy efficient and durable products & process”, IntechOpen, April 2019, ISBN 978-1-78984-288-3, http: / / dx.doi.org/ 10.5772/ intechopen.85616; [8] https: / / doi.org/ 10.1016/ j.triboint.2019.03.024 [9] LUBMAT 2020 Video Conference, https: / / www. lubmat.org [10] M. Woydt, “Material efficiency through wear pro-tecttion- The contribution of Tribology for reducing CO2 emissions”, WEAR, Vol. 488-489, 25 January 2022, 204134, https: / / doi.org/ 10.1016/ j. wear.2021.204134 [11] https: / / inspectione ering.com/ news/ 2016-03- 08/ 5202/ nace-study-estimates-global-cost-of-corrosion-at-25-trillion-ann; http: / / corrosion.org/ [12] Role of Green Tribology in Sustainability of Mecha-nical Systems: A State of the Art Survey, Materials Today, Vol. 4(2), Part A, 2017, p. 3659-3665 [13] M. Woydt, “The importance of Tribology for redu-cing CO2 emissions and for sustainability”, WEAR, Vol. 474-475, 15 June 2021, 203768, https: / / doi.org/ 10.1016/ j.wear.2021.203768. 489 23rd International Colloquium Tribology - January 2022 489 Addressing sustainability needs of the lubricants industry: Innovative base stocks with significant greenhouse gas emissions reduction potential Sabrina Stark BASF SE, Ludwigshafen, Germany Edith Tuzyna BASF SE, Ludwigshafen, Germany Christian Prokop BASF SE, Ludwigshafen, Germany Cristina Vilabrille Paz BASF SE, Ludwigshafen, Germany 1. Introduction Sustainability has become a major driver in the lubricant industry. The topic of sustainability encompasses many aspects like toxicity, biodegradability, renewable raw materials, energy efficiency, lifetime improvements and product carbon footprint (PCF). Lubricants will have a big impact on the overall decarbonization journey of the industry, with synthetic base stocks and lubricant oil additives offering high potential to reduce the overall greenhouse gas (GHG) emissions and PCFs of lubricant formulations. This paper covers sustainability criteria at the individual product level and give an insight into a new portfolio of biomass balanced base stocks and lubricant oil additives with significantly reduced carbon footprint. 2. Biomass Balance Methodology Driven by the need to reduce GHG emissions and dependence on fossil resources, the chemical and other industries are gradually starting to develop products derived from renewable feed-stocks. For the introduction of renewable feedstocks in existing production pathways in a cost-effective way, a simplified approach based on a feedstock accounting principle has been proposed by BASF [1]. This concept is known as the biomass balance (BMB) approach (Fig. 1) and the resulting products are called BMB products. The main fossil feedstocks in the chemical industry are naphtha and natural gas, which are further processed either by cracking or part-oxidation at high temperatures. For the production of BMB products, these feedstocks are replaced by renewable feedstocks, i.e. bio-naphtha and/ or bio-methane at certain amounts calculated through a material flow analysis [1]. BMB products are chemicals that are produced using both fossil and renewable feedstocks in an integrated chemical production facility. The output is a mix of fossiland renewable based products which are not distinguishable based on their composition or technical characteristics. As the renewable feedstock is processed together with fossil feedstock, it might not be physically traceable throughout the production processes. Therefore, there is a need to attribute the applied renewable feedstock volumes to an end-product in a fully transparent and auditable way, which is achieved by a certification according to the requirements of the RedCert2 scheme. Figure 1: The biomass balance (BMB) approach This solution enables the use of renewable feedstocks to produce products with the same properties as those manufactured from fossil feedstock while saving fossil resources and reducing CO2 emissions. This methodology offers hundreds of BMB products across various industries, including components for the lubricants industry. 490 23rd International Colloquium Tribology - January 2022 Addressing sustainability needs of the lubricants industry: 3. Calculation of product carbon footprint (cradleto-gate) of biomass balanced products Cradle-to-gate PCF assessments cover part of a product life cycle, from material acquisition (“cradle”) to the factory gate (i.e., before it is transported to the customer). Subsequent production steps at the customer, the use phase and disposal phase of the product are not considered. BASF calculates the PCFs in alignment with the GHG Protocol Product Standard and based on the global warming potential for a 100-year evaluation period (GWP100) using characterization factors from the 2013 IPCC Assessment Report (AR5) including climate carbon cycle feedback [2]. When co-producing chemical products with varying proportions of bioand fossil feedstocks in integrated production facilities, collection of all the required data for life cycle assessment (LCA) for a segregated product becomes challenging. As a result, such data are often obtained based on simulation models. To conduct an LCA of a BMB product, an existing ISO 14040 compliant LCA model [3] for the fossil-based product is used as a starting point and estimations of the environmental burdens of the BMB product are calculated. The life cycle impact assessment (LCIA) modelling in this study has been carried out in GaBi Software-System and Database for Life Cycle Engineering by thinkstep [4] using BASF’s primary data combined with GaBi’s cradle-togate background. Life cycle inventory (LCI) data for biomethane have been also sourced from the GaBi database [4]. Biomethane produced from food (kitchen) waste via anaerobic digestion, according to BASF responsible procurement policies, which follow the sustainability criteria as in EU RED (Renewable Energy Directive of EU Commission) was considered. In this model, food waste is considered as burden-free. If the bio-feedstocks have the same chemical properties as their fossil counterparts, hence being totally interchangeable, the life cycle environmental burdens of natural gas are subtracted from the total burdens of the fossil-based product and the burdens of biogas are added to the model. However, some bio-feedstocks may have different carbon content, energetic value, or other chemical properties from the fossil feedstocks to be replaced. In such situations, it is necessary to consider the equivalent quantities of bio-feedstocks. For these purposes, it is suggested to use an equivalent factor, based on the lower heating value (LHV) of fossil and bio-feedstocks as an approximation of the chemical properties [5]. Although LCIA addresses only the environmental issues that are specified in the scope and is therefore not a complete assessment of all environmental issues of the product system under study, its results quantify and make transparent benefits such as significant CO2eq. savings of the biomass balanced products compared to the fossil counterparts. Two examples from the BASF portfolio on biomass balanced products that bring such sustainability benefits for the lubricants industry are the high performance water-soluble polyalkylene glycol (PAG) base stocks (Breox® 60 D BMBcert™ series) and the polyisobutene (PIB) portfolio (Glissopal® BMBcert™). In the case of the PAG base stocks, a product carbon footprint reduction of up to 81% is achieved in comparison to a standard Breox® 60 D product by using biomethane as feedstock in a biomass balance approach. The Breox® 60 D products find use in a variety of industrial lubricant applications, due to their low friction coefficient and excellent lubricity (low wear scar), offering energy savings and durability benefits, combined with biodegradability and a strong health and safety profile. In addition to all proven benefits mentioned above, the biomass balanced Breox® BMBcert™ product family with significantly lower PCF and 100% sustainably sourced renewable feedstocks is a unique solution and a sustainability leader on the market today. Another example for BMB products is BASF’s polyisobutene (PIB) portfolio of PIB homopolymers that has been designed to meet the demanding requirements of the lubricant industry as cost attractive high viscosity components for thickening or co-thickening of lubricants. The high performance PIB grades are suitable for thickening mineral oil base stocks and are also compatible with Poly Alpha Olefins and Ester base stocks. They can be used in a variety of industrial, driveline and grease applications, e.g., axle and transmission lubricants, hydraulic and gear lubricants as well as metalworking fluids (MWF). They do not contain any chlorine and are thus not promoting any corrosion. Glissopal® BMBcert™ grades show a PCF reduction of 100% in comparison to the corresponding non-BMB product. With the same principle, further PAG and ester base stocks, MWF components and lubricant oil additives are being launched by BASF and providing the lubricant industry with solutions for a sustainable future. 4. Conclusion Based on an established and independently certified method, the biomass balanced products enable transparency for sustainable purchasing decisions and a faster transition to a carbon-neutral circular economy. Providing the benefits of sustainably sourced renewable feedstock, flexible scale-up and identical product quality, the new biomass balanced product range BMBcert™ provide base stocks and lubricant oil additives that help save fossil resources and reduce overall greenhouse gas emissions, while maintaining the same performance. The biomass balance approach creates unique solutions for the lubricant industry, enabling customers to differentiate their lubricant solutions from competition and helps towards achieving industry sustainability goals. 23rd International Colloquium Tribology - January 2022 491 Addressing sustainability needs of the lubricants industry: References [1] Krüger, C., Kicherer, A., Kormann, C., Raupp, N., “Biomass balance: An innovative and complementary method for using biomass as feedstock in the chemical industry”. In: “Designing Sustainable Technologies, Products and Policies: From Science to Innovation”. Benetto, E., Gericke, K., Guiton, M. (Eds.), Springer International Publishing, Cham, 2018. [2] Stocker, T.F., Qin D., Plattner G.-K., Tignor M., Allen S.K., Boschung J., Nauels A., Xia Y., Bex V. and Midgley P.M. (Eds.), “IPCC Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change”, Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, 2013. [3] ISO, “ISO 14040: Environmental Management - Life Cycle Assessment - Principles and Framework (Geneva, Switzerland)”, 2006a. [4] Thinkstep, GaBi ts (Software version 9.2, SP 37 Database 2019). https: / / www.thinkstep.com/ . [5] Jeswani H.K., Krüger C., Kicherer A., Antony F., Azapagic A., “A methodology for integrating the biomass balance approach into life cycle assessment with an application in the chemicals sector”, Science of The Total Environment, 687, 2019. 23rd International Colloquium Tribology - January 2022 493 Novel, bio-based Group V basestocks for EV applications: customizable performance with reduced CO 2 footprint Arthur Coen Oleon NV, Ertvelde, Belgium Corresponding author: arthur.coen@oleon.com Ben Deweert Oleon NV, Ertvelde, Belgium Anne-Elise Lescoffit Oleon SAS, Venette, France Marion Kerbrat Oleon SAS, Venette, France 1. Introduction Strengthening fuel economy and emission control regulations are steering the automotive industry to look at electric vehicles to reduce CO 2 and other GHG emissions. OEMs are continuously optimizing electric drivetrain designs to increase drive range, accelerate charging rates and improve transmission efficiency. Performance characteristics of EV fluids can be enhanced by selecting the right base stock. Because of specific challenges, like the need to lower fluid viscosity and decreasing the additives treat rate, the base oil must largely carry the many technical EV requirements by itself. By optimizing viscosity profiles, increasing heat transfer capacity, lowering volatility and improving electrical and material compatibility, multi-purpose basestocks like Group V oils can help address many of the industrial requirements. Simultaneously, the awareness for the carbon intensity of the different automotive components themselves is increasing. Eco-design is a valuable tool to design sustainable solutions right from the start, considering both the product footprint and handprint in a full life cycle. By designing new Group V base oils from renewable, sustainably sourced building blocks, LCA studies (ISO 14040 & 14044) showed that these fluids may reduce the product carbon footprint, in particular when biogenic carbon is subtracted, compared to petrochemical alternatives. 2. Novel Group V basestock for EV Group V base stocks and in particular esters are an incredibly versatile product group. Customizable to a very high degree as they provide a mean to create complex organic structures from simple building blocks like acids and alcohols. The complexity is to strike the right balance between sometimes opposing properties, both from a technical as an environmental perspective. 2.1 Eco-design and Product Carbon Footprint Eco-design is the integration of environmental aspects into the product development process, by balancing ecological and economic requirements. Eco-design considers environmental aspects at all stages of the product development process. We used life cycle analysis as a methodology to select the most sustainable new developments. The analysis highlighted the contribution of the different steps in the process on the product carbon footprint. The main contributors, in a cradle to gate scenario, are the origin of the raw materials and the production step, so efforts have been focusing on these contributors first. It was shown that with careful selection of sustainably sourced raw materials and by exploring new production methods significant improvements are possible. 2.2 Technical performance and product handprint Embedding the assessment of the product carbon footprint in product development is a fundamental first step to lay a strong and credible basis for future innovation. Maybe even more important however is the contribution a product can have during use-phase, this is generally referred to as the handprint of the product. What positive contribution can a product make in terms of efficiency improvements or fuel economy improvements compared to an alternative technology or solution? Many challenges come with the development of electrical vehicles but reducing the size and weight of the e-motor is the main driver of e-motor development currently. By doing so, heat dissipation area is decreased, so the im- 494 23rd International Colloquium Tribology - January 2022 Novel, bio-based Group V basestocks for EV applications: customizable performance with reduced CO 2 footprint provement of e-motor cooling becomes crucial in order to achieve increasing power density. This led to the concept of oil cooling for the electric motor, instead of the standard water jacket cooling. This creates a need to design a multipurpose fluid that functions as lubricant for the transmission and bearings as always, and at the same time is a coolant for the electric motor. The following performance characteristics have been reviewed in the search for a suitable base oil for such a multipurpose fluid: 2.2.1 Thermal properties Studies have demonstrated that there is little differentiation in the thermal properties (specific heat capacity, thermal conductivity) between the main different base oil technologies. Also within the ester product group our analysis has shown equivalent conclusions. This means the cooling power is mainly determined by the viscosity and can be significantly improved by lowering the viscosity of the fluid. Esters demonstrate a high customizable nature with wide flexibility in viscosity design, whilst maintaining a low volatility and strong lubricant film formation. The heat transfer capacity in our study has been characterized by the Mouromtseff number: (1) Figure 1: Relationship between viscosity, cooling power and flash point 2.2.2 Dielectric properties The electrical compatibility of fluids with the e-motor and other drivetrain components is key for EV performance. Some research showed the dielectric properties of finished fluids is strongly impacted by the formulation and types of additives used, while the base oil seems to play a secondary role. The typical range of the electrical volume resistivity (ASTM D1169 at 20°C) for the Group V esters in our research is between 0.5 and 200 GΩ.m and varied with the viscosity. Figure 2: Electrical volume resistivity of different esters 2.2.3 Material compatibility The requirement for copper compatibility has strongly increased for electric vehicles, especially when the copper windings are in direct contact with the cooling fluid. An extended copper corrosion test (ASTM D130) was performed for 400h at 100°C to better mimic the EV conditions. The research proved excellent compatibility of Group V esters, with minimal impact on the copper strip and no copper leaching (ICP). The elastomer compatibility of esters needs special attention. By selecting suitable seals, coatings and plastics in combination with the right Group V base oil or/ and blending with other base stocks, strategies can be developed to eliminate compatibility issues. 2.2.4 Transmission Efficiency Transmission efficiency is a key focus area for the industry. MTM traction curves were used to simulate powertrain efficiency by mimicking the behavior in the elasto-hydrodynamic lubrication regime of gears. Results showed superior lubricity performance for the Group V esters. Figure 3: MTM traction curves - 75°C, 16N, 2 m/ s 23rd International Colloquium Tribology - January 2022 495 Novel, bio-based Group V basestocks for EV applications: customizable performance with reduced CO 2 footprint 3. Conclusion Our study has shown that newly developed low viscous Group V ester base stocks can possibly play an important role in the development of multipurpose driveline and battery fluids for future electrical vehicles. These new developments have the potential to improve both the handprint through optimized viscosity profiles, more efficient cooling and higher transmission efficiencies as well as having a positive impact on the product carbon footprint through careful selection of renewable, sustainably sourced and produced building blocks. References [1] Boyde, S., “Esters”, Synthetics, Mineral Oils, and Bio-Based Lubricants, Chemistry and Technology, 3 rd Ed. CRC Press, 2021 [2] El Bahi, H., “ Comprehensive study of cooling and lubrication of electric drive units based on an innovative MP fluid”, SAE powertrains, fuels and lubricants summit, September 2021 [3] Murr, T., “Lubricants solutions for combined thermal cycles of electrirfied powertrains”, SAE powertrains, fuels and lubricants summit, September 2021 497 23rd International Colloquium Tribology - January 2022 497 CO 2 ZERO - How Lubricants Contribute to Climate Neutrality Apurva Gosalia Senate of Economy, Bonn/ Berlin, Germany Corresponding author: a.gosalia@senat-deutschland.de 1. Introduction After tumultuous years in 2020 and 2021, stuck between corona crises, climate change and cultural conflicts, industry players may be wondering whether sustainability is still a priority in a post-Covid world. I think that it is now more of a priority than ever, as sustainability can bridge the gap between recovery from the pandemic and innovation in the industry. This paper looks at the contribution from the lubricants industry to sustainability and climate neutrality and also provides examples and solutions on successful sustainable business models and new ideas for the future of the sector. 2. The “5F”-Model To reduce CO 2 emissions, lubricant companies must first take a detailed look at each aspect of the processes directly and indirectly under their control and search for ways to reduce their carbon footprint, when producing lubricants. While this is a vital step, companies must also examine what comes before and after the blending process that may have an effect on the environment. This is known in life cycle assessment terminology as a cradle-to-cradle approach, which can be achieved by using what I like to call the 5F-Principle. The first of the five F’s is the “footprint”, which is the impact of a company’s own lubricant production. This follows lubricants during the production phase, known as gate-to-gate. The second F is the “feedprint”, which follows lubricants from cradle-to-gate and requires companies to be mindful of the sustainability characteristics of their raw materials. On the whole, lube manufacturers operate at the end of the value chain and have to bring in 100% of the raw materials to produce their lubricants. About 90% of the carbon footprint of a lubricant comes from the raw materials. The name of the game is to work closely with the suppliers, so that they’re bringing the carbon footprint of their raw materials down. The third F is the “fingerprint” - commonly called the handprint - which follows a lubricant from cradle-tograve. The fingerprint refers to the positive effects in customer application, i.e. the CO 2 savings that a lubricant generates in the use phase at customer operations. This can be calculated. If it is a specialized lubricant, it saves more CO 2 in customer applications thanks to higher reduced friction and ability to protect against wear and corrosion compared to a conventional alternative such as a standard-type lubricant. The fourth F is the “fining-print”, a play on the word rerefining. To be completely circular, the end-of life treatment of a lubricant product must be considered. The waste oil that can be collected and rerefined into feedstock and ultimately becomes a new lubricant — and also the CO 2 savings associated with that process — can be calculated. Here we are talking about cradle-to-cradle and circular economy. The final F is the “firing-print”, which refers to used oils that cannot be regenerated because of their high content of additives or pollutants being incinerated to generate power. At this point, CO 2 is emitted again, but it can be captured, stored or utilized and turned into a feed-stock for lubricants again. 3. The “CarbFix”-Project An example of carbon capture storage is a project being carried out in Iceland by CarbFix together with Climeworks, a Switzerland-based company. In this project, CO 2 can be captured from emissions or directly from the air and converted into solid mineral rocks. The method provides a complete carbon capture and storage solution where water with dissolved CO 2 is ejected into sub-surface rock formations where natural processes transform CO 2 into solid carbon and minerals within a couple of years. This process can be applied wherever favorable rock formations, water and a source of CO 2 come together. 4. The “CO 2 Lubricants”-Project Along a similar vein, a project specific to the lubricants industry - the CO 2 Lubricants Project - was aimed at converting CO 2 into lubricants. It was funded for nearly 2 million euros and carried out from 2016 to 2019 by the Federal Ministry of Education and Research in Germany and five other partners. In the project, carbon dioxide was captured from industrial emissions or from the atmosphere and converted into lubricants using chemical and biotechnological processes. Various microorganisms 498 23rd International Colloquium Tribology - January 2022 CO2ZERO - How Lubricants Contribute to Climate Neutrality such as yeast and algae use CO 2 as a nutrient and can convert it into new products such as lipids. For the production of high-performance lubricants, these lipids are then extracted from the microorganisms and used either purely or in a further processed form. Microalgae fed with CO2 can achieve a lipid fraction of up to 80% of their weight. Thus, it is possible to capture the already-emitted CO 2 and to either store it forever or utilize it to make a new feedstock for lubricants. 5. The “3C”-Approach However, we cannot rely only on high-performance lubricants to reduce emissions in the use phase. Working toward sustainability must be a three-step approach of calculating, cutting down and compensating for CO 2 emissions that the lubricants industry generates. The first step is to calculate the corporate carbon footprint and the product carbon footprint. The next step is to search for opportunities to avoid and reduce CO 2 emissions. For instance, about 80% of the emissions of a typical lube manufacturer are caused by heat and electricity consumption, so energy efficiency is certainly an important lever in avoiding or reducing CO 2 . Offsetting unavoidable carbon emissions through compensation measures is also critical to achieving carbon neutrality. Since emissions impact the climate at a global level, it is ultimately irrelevant where on the planet they originate and where they are saved. Compensation measures occur through the voluntary promotion and investment in climate protection projects in socially, politically or economically disadvantaged countries. Typically, projects used for compensation measures target six project sectors: biomass, cookstoves, solar energy, forest conservation, hydropower and wind energy. 6. Conclusion The lubricants industry as a whole can contribute to the “CO 2 ZERO”-journey, while lubricants as products can contribute to climate neutrality. References [1] Technische Universität München (n.d.): CO 2 Lubricants, available at https: / / www.department.ch.tum. de/ wssb/ forschung/ abgeschlossene-projekte/ co2lubricants/ ,accessed 10 Mai 2021. [2] Umweltbundesamt (2014): Altöl, available at https: / / www.umweltbundesamt.de/ themen/ abfallressourcen/ abfallwirtschaft/ abfallarten/ gefaehrliche-abfaelle/ altoel,accessed 10 Mai 2021. Digital Tribological Services: i-Tribomat 501 23rd International Colloquium Tribology - January 2022 501 From service request to standardized tribological data sets Alvaro Garcia TEKNIKER, Eibar, Spain Corresponding author: *alvaro.garcia@tekniker.es 1. Introduction Advances on technologies regarding acquisition, communication, storage and processing of data and information are providing a great impact on the way tribological experiments can be managed, and tribological results and data can be integrated and enriched with new services. This paper will introduce one of the advances made in this direction within the i-TRIBOMAT project, with respect to tribology tests and data management. It will describe all the defined data entities used to cover tribological data. It will also introduce the tools and infrastructure developed to manage the data sets. 2. Aim The approach of the i-TRIBOMAT project is to create a portal where a group of tribological labs collaborate to offer their services in a single portal. This way clients are given access to a shared pool of equipment, making it possible to offer a greater range of services in the same endpoint. To achieve this a well-defined data management system is necessary. Each tribology lab partner has an internal way of describing, naming, identifying, and storing tribological tests and their results. A common and harmonized data management system is thus necessary to make data coming from all partners shareable and integrable. An extensive data model is the cornerstone of this, along with software components to manage and exploit it. 3. Data model The data model includes all the necessary entities to describe the different elements involved in tribological testing. These entities are the following: - Equipment: Defines any equipment capable of being used in a tribological tests. It includes some basic information about itself (name, description, ... ) a list of configurable traits and a list of expected results or data signals. - Materials: This entity defines any material used in the samples, including core materials and coatings. Is defined by attributes such as identifiers, designations, chemical composition and physical properties. - Samples: Define any sample, body or interbody involved in a tribological test. It includes a list of characteristics (shape, size, materials/ composition, coatings/ additives...). - Tribological tests: A tribological test includes basic information (name, description...) and references to involved equipment and samples. It is composed by a series of steps, which will have the specific configuration values for the involved equipment. An attribute will keep track of the status of the test and their inner steps: Requested, In progress, Completed... - Results: A completed test step will have associated results which can be multivalued functional data, single annotations and associated files or images. Figure 1: Major data model entities Some of these entities have sub-entities (e.g. samples have batches and coatings), but the five introduced are the major ones. 3.1 Variable types and key-value pairs The variable-types is a predefined list of any measurable or configurable attribute, which will be referenced in all the other entities. They include a unique identifier, descriptive name, magnitude and measuring unit. The reason to have the list is to avoid possible misnomers and conflicts between similar names. All of the entities are based on lists or sets of variable type-value pairs (equipment characteristics, sample attributes, test conditions, test results...). This approach makes it possible to modify the entities as it is needed, while new variable types can be added to extend the model to new use cases. 502 23rd International Colloquium Tribology - January 2022 From service request to standardized tribological data sets The values can include references to external entities, making it possible to create relationships with external entities. E.g: The tool uses a software called KeyCloak to manage users and roles. There exists an attribute to reference operators performing the test, which could take the value of users defined in KeyCloak. 3.2 Additional data entities The presented entities focus on the technical aspect of the tribological service, those aimed at the definition and characterization of tribological tests. But a tribological service also includes other business-related data entities: requests, orders, contacts, clients, invoices, reports… While a specific software has been developed to manage the technical data entities, existing Enterprise Resource Planning (ERP) solutions are used to manage the business aspect of the services. 4. Extracting information from a service request Prior to the service request the partners will have a list of their existing equipment, which will have a range of operations and configurations. Once the service request arrives tribological experts will assess the petition. If the proposed outcome is to perform a tribological test , the following will be defined: - The materials to be used in the samples. Novel materials will be added to the data set, defining the composition and known characteristics. - Samples to be used, with references to their materials, physical characteristics, coatings and any other trait. - Type of test to be performed, along with the desired configurations: movement type, loads, environmental conditions... More than one test can be defined per service request. Once defined, the software tool will look for available equipment that can perform the request test(s). The partner owner of the equipment will receive the description of the test to perform. Once the tribological test is performed the results will be uploaded. The collected data can be used to provide additional services. The results can provide insight into how different materials behave in similar conditions, or how the same material performs in different conditions and configurations. More available data can reduce the need to perform tribological tests, using previous ones as reference instead. 5. Software components The data management system is composed of two software tools. The first tool is the triboconector. It will act as a local management system for the different partner labs. It will relay the requested services and tests to perform and keep track of their status, as well as collect and upload their result data. This tool is designed in a modular manner making it possible to add new characteristics, such as the analysis of topographical images or search for scientific articles from federated databases The second tool is a centralized data platform. It will be used as an entry point for customers to request services, as well as a central data repository. Most of the “business” related functionalities will take place on the data platform, while the triboconector will be more “technical” related. 6. Conclusions The introduced data model allows for a detailed description of all the involved information needed when defining a tribological service. This has several benefits: - The harmonized information allows different partners to perform the requested test without the risk of missing details out or mixing conditions due to misnomers, translation errors or difference in namings. - The data collected from different partners can be integrated and exploited for additional service value. The i-TRIBOMAT project has received funding from the European Union’s Horizon 2020 research and innovation programme (innovation action) under grant agreement No. 814494 (Call: H2020-NMBP-TO-IND-2018) 23rd International Colloquium Tribology - January 2022 503 Trusted tribological materials characterisation services Mirco Kröll Bundesanstalt für Materialforschung und -prüfung (BAM), Berlin, Germany Corresponding author: mirco.kroell@bam.de Reinhard Grundtner AC2T research GmbH, Wiener Neustadt, Austria Katharina Newrkla AC2T research GmbH, Wiener Neustadt, Austria Dirk Spaltmann Bundesanstalt für Materialforschung und -prüfung (BAM), Berlin, Germany Francesco Pagano Fundación Tekniker, Eibar Guipuzcoa, Spain Bihotz Pinedo Fundación Tekniker, Eibar Guipuzcoa, Spain Erik Nyberg Luleå Tekniska Universitet, Luleå, Sweden Markus Söderfjäll Luleå Tekniska Universitet, Luleå, Sweden Vuokko Heino Teknologian tutkimuskeskus VTT Oy, Espoo, Finland Helena Ronkainen Teknologian tutkimuskeskus VTT Oy, Espoo, Finland 1. Introduction Renowned institutions in various European countries combine their tribo-testing as well as analytical and characterisation capabilities for the European Tribology Centre. This foundation of one of the largest Open Innovative Test Beds for tribological services, the aim of the European Horizon 2020 project i-TRIBOMAT, places certain demands on the comparability of the test equipment and execution process. Combining more than 100 tribometers, including commercial and in-house built ones, allows to cover the widest possible ranges of parameters, atmospheres, and motions for all types of materials and lubricants. Additionally, tribological characterisations can be accelerated when having a large number of testing equipment available, also increasing the expertise offered to the customer by the different institutes. This is complemented by a huge variety of characterisation methods for the samples before and after the tests. Irrespective of the challenges emerging from the fact that results are coming from different countries, various operators, and different ways of analysing the results, the customer expects trusted, comparable, and reproducible data. Exemplarily, results will be provided for the determination of roughness, hardness, wear volume and the coefficient of friction when improved standards, new evaluation techniques, and quality management mechanisms are applied, all of them developed for the European Tribology Centre founded within i-TRIBOMAT. 2. Quality of data This testbed needs procedures which ensure the results of these tribological services to be characteristic as well as descriptive, trustworthy, comparable, and reproducible. At the same time, these results need to be valid regardless of the institute, equipment, evaluation techniques 504 23rd International Colloquium Tribology - January 2022 Trusted tribological materials characterisation services and operators. It goes without saying that by being stored in a database, the FAIR principles must be applicable on them. Those quality demands on the data are even more critical, because (component) simulations and other services rely on them. 3. Minimising influences on the quality The quality (e.g., certainty) of tribological data is influenced by many aspects. In order to improve the quality, it is necessary to clarify the impact of these influences on the results and output signals. Tribometers for example were designed and constructed to mimic contact situations of the respective applications. Comparing them is challenging since standards for doing so are missing, but beneficial because unstandardised parameters can be covered with them. This also affects the evaluation of the coefficient of friction, for which at least four different calculation methods of reciprocating movements exist. It is an important result given by software of tribometers and mentioned in some standards, but its calculation is often not specified. It is essential to accurately describe the surface roughness of the bodies of a tribological system when comparing tribological data. For measuring the roughness, the methodology of ascertaining the topography as well as the proper application of the calculations laid out in standards are important. The application of the cut-off defined in current standards (e.g., ISO 21920) leaves room for interpretation by the operator. Different software solutions, often provided by the manufacturer of the equipment, generate different results of roughness parameters, although they had the same input of raw data and work with the same standard specifications. Most of these software tools are “black boxes”; an understanding for the different outcomes is usually hidden in the dark. Among other things, a documented and web-based in-house tool to calculate roughness parameters was developed. It is made available to all partners of the project and guarantees a uniform, traceable and verified calculation. After having harmonised the determination, the surface roughness of the samples provided becomes crucial. A tribological test can only be as good as the input for it. If the roughness of samples differ, friction and wear will differ. Hence a careful manufacturing of samples needs to be considered. The very same comes true for the hardness of samples. Nevertheless, these are only some examples of differences in tribological characterisations, their execution and evaluation, and how they influence the comparability and quality of data. 4. Continuous improvement process as part of tribological characterisations Via improved interlaboratory tests (round robin tests) with the partners of i-TRIBOMAT, the current methods applied were gathered. The results of these tests have been analysed, particularly regarding the influences mentioned above. Methods and measures of the quality management followed to minimise those influences. Best practices were described at the end, which are at the centre of the harmonised procedure of trusted tribological characterisation services. PDCA (Plan, Do, Check, Act) is the main tool used in the continuous improvement process described. The four steps are identified as 1. Round Robin tests 2. Gathering methods used 3. Analysis of results 4. Responses and best practices. Thus, harmonised procedures, improved methods and application of best practices can lead to a significant reduction of the repeatability and reproducibility standard deviation (see figure 1). This is mandatory when creating a combined test bed of more than 100 tribometers and aligning multiple characterisation techniques to measure as well as describe tribological systems. Figure 1: Exemplary result of an evaluation of the coefficient of friction of a round robin test on differently designed and manufactured tribometers according to standard and improved methods (100Cr6 vs. 100Cr6, lubricated) 23rd International Colloquium Tribology - January 2022 505 Trusted tribological materials characterisation services 5. Conclusion The PDCA process will be part of the quality management system, which is required for trusted tribological characterisation services of materials for the European Tribology Centre and ensures a constant comparison of methods used. In the same way new and improved techniques are implemented and harmonised. References [1] Wilkinson, M., Dumontier, M., Aalbersberg, I. et al. The FAIR Guiding Principles for scientific data management and stewardship. Sci Data 3, 160018 (2016). https: / / doi.org/ 10.1038/ sdata.2016.18 [2] I. Llavori, et al., Critical Analysis of Coefficient of Friction Derivation Methods for Fretting under Gross Slip Regime, Tribology International, Volume 143, 2020, 105988, ISSN 0301-679X, https: / / doi.org/ 10.1016/ j.triboint.2019.105988. Acknowledgement This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No. 814494, project iTRIBOMAT. More details: https: / / www.i-tribomat.eu/ . 23rd International Colloquium Tribology - January 2022 507 Upscaling Materials Performance Ulrike Cihak-Bayr AC2T research GmbH, Wiener Neustadt, Austria Corresponding author: franz.pirker@ac2t.at Marin Herr, Franz Pirker AC2T research GmbH, Wiener Neustadt, Austria 1. Introduction The design process of tribological systems usually involve expensive and time-consuming experimental tests on full component scale to ensure efficient and reliable operation on system scale. Within the European test-bed project i-TRIBOMAT („Intelligent Open Test Bed for Tribological Materials Characterisation“) we present an approach to upscale material performance from simple model tests to component scale behaviour and predict the product performance at an early development stage and significantly reduce costs and time-to-market for new materials. The current study investigates the influence of the tribological properties of self-lubricating polymer seals on system performance of a pneumatic actuator and represents one of three i-TRIBOMAT use cases. 2. Digital Services The centrepiece of the digital service provided by i-TRI- BOMAT are numerical simulations predicting material performance. Figure 1 shows the simulation for reciprocating seals under dry conditions, exemplarily. The simulation is fed with the mechanical material models taken from an extensive database including the tribological properties of the material of interest in an appropriate tribological model test. The requirements of the industrial system, where the seal is meant to operate, define the boundary conditions of the upscaling simulation, such as environmental temperature, velocity profile, and chamber pressure. Thus, the simulation expert, who designs the new component, can consult the database (service 2) for model-test results fulfilling these requirements. If some additional parameter variations of the model test are needed, these will be performed within the service 1, the shared tribological test infrastructure. Figure 1: Overview services and integrated workflow The target values of the upscaling simulation such as frictional force and wear volume indicate the new seal material performance in terms of efficiency and reliability of the system. 3. Trusted input data Flexibly, new materials can be characterised in the standardized model set-up and be evaluated for their performance in the up-scaling simulation. This requires absolute control of the input data quality. While the mechanical testing procedure is quite straight forward, the tribological testing remains a challenge and slightly different testing procedures [1] and different evaluation processes [2] lead to a significant variation of the final result. To ensure stable conditions at model tests and reliable results the test was standardized during the i-TRIBOMAT project to provide trusted experimental data for the up-scaling from model test to component performance. The validation of the model with the results from component test-rig on system level (Figure 2) ensures trustworthy up-scaling model simulation outputs. Figure 2: Component test-rig on system level 508 23rd International Colloquium Tribology - January 2022 Upscaling Materials Performance 4. Workflow The workflow starts with the industrials users` needs with a new material and the operation conditions (Figure 3). In order to find the appropriate model test parameters, the simulation model is used to “down-scale” the operational conditions on component level to an appropriate model test set-up and parameter field. So, the input conditions such as chamber pressure, ambient temperature, velocity, and stroke determine the range of contact pressure, velocity, and temperature for the model test. At the end of the down-scaling process it is possible to define a tribological test matrix for the standardized model test that will closely represent conditions in the contact on component level. The results of the model tests are subsequently used as input values in the up-scaling model to predict target values like frictional force on system level and change of the seal profile due to wear. Figure 3: Workflow of the upscaling simulation model 5. Influence of tribological input parameters on seal upscaling model A sensitivity study is the basis to detect the essential level of accuracy of the experimental input data to ensure robust predictions on friction and wear on the system level. Figure 4 shows the results of a parameter study performed with a wide range of CoF input-values, ranging from typically suggested values of 0.2 to values obtained in tribological tests for the current material in contact with a given counter-body surface. The diagram in Figure 4 shows the frictional force for a chamber pressure of 0, 10 and 60 bar. The frictional force does not relate linearly to the coefficient of friction but increases following a power law relation. The red circle in Figure 4 shows a CoF value typically suggested in the simulation community. If the predicted frictional forces are compared with the measured CoF of 0.6 for the current seal material (see green circle in Figure 4), there will be a deviation between predicted friction of 75 % compared to the values based on an assumed CoF taken e. g. from literature. Figure 4: Influence of coefficient of friction (CoF) on frictional force of seal model Figure 5 shows the cross section of the seal in operation with different values for CoF and chamber pressure. In specific operation conditions the seal loses its grip to the housing, which leads to an increased contact area between seal and shaft. Naturally, the seal cannot operate under such unstable conditions and is prone to early failure. These fatal conditions are difficult to predict experimentally on system level beforehand but can reset the whole design process back to its start. Figure 5: Contour plots of seal for different chamber pressures and coefficient of frictions 6. Conclusion The presented materials upscaling model can predict the system performance of self-lubricating seals based on well-designed model tests. The sensitivity study reveals a strong dependence on the CoF value chosen as input parameter. As small changes in the model test-set up or evaluation process can have significant influence on the results, a standardization of the model test is done. With a strong linkage between simulation and experimental tribological testing of the material and full control over the quality of the data i-TRIBOMAT provides a platform for prediction of material performance on system level. 23rd International Colloquium Tribology - January 2022 509 Upscaling Materials Performance i-TRIBOMAT captures the industrial need for drastically reduced development processes by providing validated numerical up-scaling models, an extensive material library, and tribological testing service on a web-based platform. Thus, the optimal material solution can be determined at an early stage of the development, which significantly reduces the costs and time to market. References [1] Gee, M. G. “VAMAS report: Towards standardization for friction and wear testing.” Tribology International 26.2 (1993): 143-146. [2] Llavori, I., et al. “Critical analysis of coefficient of friction derivation methods for fretting under gross slip regime.” Tribology International 143 (2020): 105988. 7. Acknowledgement This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No. 814494, project i-TRIBO- MAT. More details: https: / / www.i-tribomat.eu/ . 23rd International Colloquium Tribology - January 2022 511 Friction control by surface texturing in Internal Combustion Engines Konstantinos Gkagkas Toyota Motor Europe NV/ SA, Zaventem, Belgium Corresponding author: Konstantinos.Gkagkas@toyota-europe.com Franz Pirker AC2T research GmbH, Wiener Neustadt, Austria András Vernes AC2T research GmbH, Wiener Neustadt, Austria also Technische Universität Wien, Vienna, Austria 1. Introduction In light of the European Green Deal, which targets to make Europe climate neutral in 2050 [1], current targets call for reductions of -37.5% for the tailpipe CO2 emissions of newly registered passenger cars for 2030. Sales of electrified and other alternatively powered passenger cars need to pick up strongly to achieve targets [2]. In the same direction, Toyota has announced the “New Vehicle Zero CO2 Emissions Challenge” with the aim to reduce global average CO2 emissions from new vehicles by 90% by 2050, compared to Toyota’s 2010 level [3]. The automotive industry needs, therefore, to keep advancing technologies for internal combustion engines, which will remain widely adopted in the context of hybrid, and plugin hybrid electrified vehicles. Friction accounts approximately for one-third of the fuel energy consumed in passenger cars [4]. Minimization of the environmental impact via the reduction of friction losses is therefore a significant focus point in the automotive sector. Additionally, the demand for low-viscosity oils further increases the importance of the surface topography. Accordingly, this study represents an industrial request where the up-scaling of the frictional performance via numerical simulations is performed with the main goal to optimize the texture of interacting surfaces, while the pairing of materials and the lubricant is kept fixed. 2. Methodology The computational strategy followed here (Fig. 1) will aim at the numerical estimation of the friction coefficient on the macro-scale passing through all length scales below, i.e., from ab-initio calculations, e.g., on additives in the lubricant, molecular dynamics simulation for revealing the ordering of molecules in the lubricant and fluid dynamics to determine the roughness-dependent flow factors. Since this numerical framework is planned to be used for various textures, e.g., either computer-generated or experimental ones, the results are expected to be transferable to larger, say component length scales, by applying proper machine learning (ML) techniques. Experimental data will be obtained using pin-on-disctype as well as properly adapted SRV tribometers by closely following the contact situation of the engine components of interest. The surface topography will be measured before and after each test to use these surface data as input for various numerical simulations. Figure 1: Computational framework for studying frictional losses in internal combustion engines. 3. Results 3.1 Macroscopic scale On the macroscopic scale, the impact of roughness on the lubricant flow will be described by flow factors. Accordingly, the mean lubrication gap for given operating conditions, such as the normal pressure, sliding speed and 512 23rd International Colloquium Tribology - January 2022 Friction control by surface texturing in Internal Combustion Engines temperature, will be calculated on the micro-to-macro scale by using advanced homogenisation techniques [5]. On these scales the numerical findings will be compared with the output of laboratory tests (either pin-on-disc or adapted SRV). Unfortunately, the contact as seen numerically and illustrated in Fig. 2 cannot be directly observed experimentally. Therefore, the relevant tribo-rheological properties of the lubricant molecules or additives, e.g., their layering and viscosity within real operating conditions at high temperatures and pressures, must be numerically determined. 3.2 Microscopic scale At this length scale, where the topography of textures is of crucial importance for the frictional performance, the impact of various geometrical features, such as those of the grooves, on the surface roughness parameters (SRPs) is separately studied by computer generating a large variety of surfaces. This is then completed by similar analyses of the used samples before and after the tribological testing at both laboratory and component level. Finally, an attempt is made in a machine-learning fashion to predict the frictional losses of the computer-generated surfaces based on their calculated SRPs and hence to select the presumably best performing textured surface. For this, those system parameters will be considered which are resulting from the performed laboratory and component-level tests and correlate to the flow factors, recall Sec. 3.1, calculated for each textured surface of interest by taking also into account the numerical tribo-rheological data obtained from the nanoscopic simulations, see Sec. 3.3. Figure 2: Dependence of oil flow on texture and lubrication gap. [6] 3.3 Nanoscopic scale For the simulation of the lubricated contacts at the nano-scale. we employ a coarse-grained model for the description of lubricant molecules that interact with metallic solids, see Fig. 3. Previous studies have shown that strong layering can occur in the case of confined molecules with charged atoms, especially close to the walls [7, 8, 9]. We study the impact of Coulomb interactions on the liquid structure by adjusting the charge of the lubricant molecules, as well as the polarizability of the solid surfaces. In addition, we study the impact of molecule shape on the lubricant layering and the resulting friction forces. Figure 3: Near-wall layering of confined lubricants. [9] 4. Conclusion To speed up materials upscaling and bring new technologies like surface structuring, i-TRIBOMAT develops a wide range of services. The services are standardized tribological model tests, data driven services and various multiscale materials up-scaling tools. In this paper the workflow is presented how to characterize new surface structures and predict their performance on component level using a multi-scale approach which combines simulations, experiments, and ML techniques for the material design of lubricated surfaces in internal combustion engines. We expect that such results will help us to describe the physico-chemical mechanisms that control lubrication and guide us towards the efficient design of novel tribological systems with significantly lower friction losses. This workflow is expected to significantly decrease the costs and time of the development process within Toyota. References [1] COM(2019) 640 final; COMMUNICATION FROM THE COMMISSION TO THE EUROPE- AN PARLIAMENT, THE EUROPEAN COUN- CIL, THE COUNCIL, THE EUROPEAN ECO- NOMIC AND SOCIAL COMMITTEE AND THE COMMITTEE OF THE REGIONS; The European Green Deal, European Commission 23rd International Colloquium Tribology - January 2022 513 Friction control by surface texturing in Internal Combustion Engines [2] European Automotive Manufacturers Association, Making the Transition to Zero-Emission Mobility - 2019 progress report, (2019) [3] Toyota Motor Corporation, Environmental Report 2020, (2020) [4] K. Holmberg, P. Andersson and A. Erdemir, “Global energy consumption due to friction in passenger cars” Trib. Int. 47 (2012) 221-234. [5] A. Almqvist, J. Fabricius, A. Spencer and P. Wall, “Similarities and differences between the flow factos method by Patir and Cheng and homogenization”, ASME. J. of Tribology 133(3) (2011) 031702. [6] S. Sanda, H. Nagakura, N. Katsumi, S. Hotta, K. Kawai and M. Murakami, “Analysis of piston frictional force under engine firing condition”, J. Soc. Auto. Eng. 45(5) (2014) 799-804. [7] R. Capozza, A. Vanossi, A. Benassi and E. Tosatti, “Squeezout phenomena and boundary layer formation of a model ionic liquid under confinement and charging”, J. Chem. Phys. 142 (2015) 064707. [8] A. E. Somers, P. C. Howlett, et al., “A Review of Ionic Liquid Lubricants”, Lubricants 1 (2013), 3-21. [9] M. Dašić, I. Stanković, K. Gkagkas, “Molecular dynamics investigation of the influence of the shape of the cation on the structure and lubrication properties of ionic liquids”, Phys. Chem. Chem. Phys. 21 (2019) 4375-4386 Acknowledgement This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No. 814494, project iTRIBO- MAT. More details: https: / / www.i-tribomat.eu/ . 23rd International Colloquium Tribology - January 2022 515 Novel journal bearing materials for wind turbine gearboxes Taneli Rantala Moventas Gears, Jyväskylä, Finland Corresponding author: Taneli.rantala@moventas.com Kaisu Soivio Moventas Gears, Jyväskylä, Finland 1. Introduction Bearings have a marked influence on levelized cost of energy (LCoE) in wind industry. Both capital and operational expenses are influenced by bearings. [1] As the size of wind turbines is growing, the rolling element bearings become more expensive, and their performance becomes challenged due to increased load transmission requirement. One recognized opportunity to solve this issue is the implementation of journal bearings. However, traditional journal bearing materials do not provide reliable solution for the wind turbine lifetime requirements due to relatively slow sliding speeds and high, constantly changing load conditions. In standards, one can find limit values for projection pressure for traditional materials, such as Al-Sn alloys, which are in range of 5 to 7 MPa, whereas in wind turbine gearbox, specific bearing loads are generally in range from 10 to 20 MPa. Before introducing new constructional and material solutions to a wind turbine gearbox, it is necessary to investigate and prove the reliability of the selected solutions. Because it is not feasible to be done on full-scale for expected lifetime of 20 to 30 years, intelligent testing methods combining different testing size and complexity scales with developed modeling practices were chosen as approach to verify novel journal bearing materials to be used in wind turbine gearbox. This novel methodology has been developed under the i-TRIBOMAT open innovation test bed initiative as one of the three use cases. 2. Approaches 2.1 Field-2-Lab down-scaling (2 columns) First, relevant parameters and operation conditions for small scale testing need to be identified and quantified. i-TRIBO- MAT focuses on study of continuous load conditions on planet wheel radial journal bearings, so transient phenomena, mainly start-up and shut-down of turbine are not considered here. Load duration distribution (LDD) data of specific wind site acts as a basis for analysis. Input load data, desired ratio for gearbox, fixed geometrical values of bearing parts and operation mode data of a turbine can be used to define operational window for journal bearings as a function of projection pressure and sliding speed. Projection pressure and sliding speed can be selected as suitable parameters when down-scaling from product scale to laboratory scale material tests. In a similar fashion, Hertzian contact pressure can be used if all required parameters are known. Figure 1: Example of operation window, used for downscaling operation conditions With identified critical operation conditions, tests can be defined and criteria for material performance set. In combination with these input load parameters, environmental parameters such as oil pressure and temperature are set to present realistic operation conditions for sliding contact. All input values can be transferred to test setups of different scales, and viability of test method can be then considered. As time spent in critical point of operation window can be very long, continuous wear due to asperity contact is not allowed, and good run-in properties are preferred. Properties like self-lubrication during oil starvation and low wear rate are also considered to be beneficial. Objective of Moventas is to select and test possible journal bearing material candidates in product scale, and provide test results and performance data for i-TRIBOMAT Single Entry Point (SEP) members. This data is then used by the SEP members to develop laboratory scale testing environment and up-scaling tools for i-TRIBOMAT. 516 23rd International Colloquium Tribology - January 2022 Novel journal bearing materials for wind turbine gearboxes 2.2 EHD simulation Due to simplicity of definition of projection pressure, it was assumed that results it yields are not realistic enough, and more sophisticated method is needed to achieve more accurate representation of loading of journal bearing. For this goal, EHD-simulation capability was developed. Multiple simulation models of test gearbox with journal bearings were built. As expected, local hydrodynamic pressure values differ greatly from simple projection pressure values. Comparability of laboratory tests and product scale tests can be improved by constructing simulation model of both test rigs, and replacing projection pressure by local hydrodynamic pressure. Laboratory scale test conditions can be updated accordingly to represent operation conditions observed in actual product. 2.3 Product scale test (2 columns) Product scale test runs were conducted with test gearbox. First to study the limits of journal bearing system and ability to simulate the performance accurately, and second to test complete operation window of a gearbox with journal bearings. During first test run, operation conditions with clear mixed lubrication in journal bearing was found. When transitioning to slower sliding speed after that, a bearing seizure occurred. Simulation model indicated high asperity contact next to oil inlet of the journal bearing, and disassembly of the gearbox confirmed this to be the root cause for seizure. After optimizing the journal bearing geometry based on this information and modelling updates, asperity contact pressure was minimized, and complete operation window, including safety margins, was tested successfully. During disassembly of the gearbox after test run, no issues were observed in any journal bearings. Figure 2: Hydrodynamic and asperity contact pressure of journal bearing after geometry optimization 3. Conclusion Laboratory scale material tests and comparison to fullscale test results are still on-going. Initial results for selected bearing material indicate good wear resistance and sliding properties even in oil starved conditions, which are in line with gearbox test results. Results indicate the importance of advanced field-to-lab down-scaling practice. Generally implemented simplifications of tribological contacts lead to difficulties in drawing conclusions of material performance in real application, and during whole lifetime. Generally known tribological tests can put material pairs in tribological contact to performance order by certain parameters, but the prediction, i.e. up-scaling capability for system level performance is still limited and under further development. Up-scaling capable tribological testing can increase the likelihood of finding optimal material solution and simultaneously decrease the time and monetary effort related to the testing required for selection, as good performance is secured, but selected solution is not overly expensive leaving capacity half-used. Acknowledgement This project has received funding from the European Union’s Horizon 2020 research and innovation programme (innovation action) under grant agreement No. 814494 (Call: H2020-NMBP-TO-IND-2018) More details: https: / / www.i-tribomat.eu/ . References [1] Dao, C, Kazemtabrizi, B, Crabtree, C. Wind turbine reliability data review and impacts on levelised cost of energy. Wind Energy. 2019; 22: 1848-1871. https: / / doi.org/ 10.1002/ we.2404 Appendix 23rd International Colloquium Tribology - January 2022 519 Committees - 23 rd International Colloquium Tribology The program committee for the International Colloquium Tribology is made up of recognized experts from research and development, industry and practice. Its tasks include the formulation of the objectives and the definition of the main topics of the conference, the assessment and selection of the submitted proposals for the conference program and the technical advice of the organizer. Steering Committee Dr.-Ing. A. Fatemi Robert Bosch GmbH Stuttgart, Germany Prof. Dipl.-Ing. Dr. techn. A. Pauschitz AC2T Research GmbH Wiener Neustadt, Austria Dr. K. Topolovec-Miklozic Powertrib Ltd Oxford, United Kingdom Program Planning Committee Prof. Dr.-Ing. h.c. A. Albers Karlsruhe Institute of Technology Karlsruhe, Germany Prof. Dr.-Ing. habil D. Bartel University of Magdeburg Magdeburg, Germany Dr. rer. nat. M. Dienwiebel Karlsruhe Institute of Technology Karlsruhe, Germany Priv.-Doz. Dipl.-Ing. Dr. techn. N. Dörr AC2T Research GmbH Wiener Neustadt, Austria Univ.-Prof. Dr.-Ing. C. Gachot Vienna University of Technology Vienna, Austria Dipl.-Ing. G. Gaule Hermann Bantleon GmbH Ulm, Germany Dr.-Ing. M. Gleß ContactEngineering Stuttgart, Germany Univ.-Prof. Dr.-Ing. G. Jacobs RWTH Aachen University Aachen, Germany Dr. M. Jungk LUBEVISIO GmbH Brannenburg, Germany Dr. T. Kilthau Klüber Lubrication SE & Co. KG Munich, Germany Dipl.-Ing. R. Krethe OilDoc GmbH Brannenburg, Germany Dr. L. Lindemann Fuchs Petrolub SE Mannheim, Germany Dr. M. Matzke Robert Bosch GmbH Stuttgart, Germany Prof. Dr.-Ing. J. Molter Mannheim University of Applied Sciences Mannheim, Germany Dr. J. Müllers Robert Bosch GmbH Stuttgart, Germany 23rd International Colloquium Tribology - January 2022 521 Index of Authors AAcero, Pablo Navarro 441 Adam, Pierre 77 Adam, Karl 251 Agocs, Adam 97, 105 Aguirrebeitia, Josu 263 Albers, Albert 239, 271, 295 Alenezi, Abdullah 207 Almqvist, Andreas 255 Alumą, Marc 101 Amann, Tobias 33 Aranzabe, Estibaliz 141 Ayame, Noriko 157 Azam, Abdullah 425 Azzolini, O. 281 BBadisch, Ewald 403 Balachandran, Shanoob 309 Balaguer, Adbeel 393 Balakrishnan, Viswanath 285 Bardin, Franc 251 Bartz, Marcel 417 Bauer, Frank 335, 471 Baumann, Matthias 471 Baumgärtel, Stephan 325 Bause, Katharina 239, 271, 295 Bayon, Raquel 485 Belin, Michel 137 Bellini, Marco 87 Bengtsson, Martin 299 Bernabei, Marco 423, 441 Besser, Charlotte 97 Beyer-Faiss, Susanne 33, 345 Bhadhavath, S. 377 Bhatnagar, Pankaj 73, 377 Biboulet, Nans 209, 213 Bill, Stefan 133 Bischofberger, Arne 239 Björling, Marcus 27 Blach, Philippe 161 Böhle, Martin 259 Botkin, Michael 407 Boyer, Chantal 77 Brecher, Christian 385 Brenner, Josef 327 Brunskill, Henry 381 Bucci, John 375 Buse, H. 363 CCammarata, A. 289 Campillo, Nuria E. 423 Cañellas, Gerard 101 Cann, Philippa 63 Carabillė, A. 281 Cavaleiro, A. 289 Cayer-Barrioz, Juliette 45 Charles, Pierre 209 Chaudhary, Rameshwar 377 Chen, Jiaqi 187 Chommeloux, Claire 191 Chretien, Christelle 115 Christodoulias, Athanasios I. 453 Cihak-Bayr, Ulrike 507 Coen, Arthur 161, 493 Combarros, Mar 101 Cooper, Clayton 93 Cornel, Daniel 67 Coulon, Jean-Franćois 479 DDahdah, Simona 209 Delic, Ivan 251 Dellis, Polychronis 203 Deweert, Ben 493 Dienwiebel, Martin 65, 275, 399 Diloyan, George 125 Ditrói, Ferenc 403 Dominguez, Beatriz 141, 441 Dörr, Sebastian 25 Dörr, Nicole 97, 347 Dubreuil, Frederic 137 Dufils, Johnny 213, 229 Dwyer-Joyce, R.S. 351, 381 EEckel, Hans-Martin 385 Ehara, Taro 101 Eickworth, J. 399 Elexpe, Iker 141 Emeric, Ariadna 101 Espejo, Cayetano 207 Everlid, Linus 299 Ewen, James 441 FFaller, Joachim 409 Fatemi, Arshia 247 Fath-Najafi, Mehdi 125 Fedorov, Sergey Vasiliy 81 Fedrizzi, L. 281 Fehrenbacher, Rüdiger 295 Fernández, Carlos 441 Fernandez-Diaz, Beatriz 263 Feuchtmüller, Oliver 335 Fickert, Marc 477 Fischer, Thomas 391 Fox, M. F. 197 Franco, Mario 423 Franke, Jörg 71 Frauscher, Marcella 97, 105 Fritzer, Lukas 347 GGäbert, Chris 65 Gachot, Carsten 415 Garabedian, Nikolay T. 429 Garcia, Alvaro 501 Gaule, Gerhard 397 Gault, Baptiste 309 Gebhard, Andreas 477 Gkagkas, Konstantinos 511 Glänzer, Steffen 41 Gless, Michael 225 Gómez-Arrayas, Ramón 423 Gosalia, Apurva 497 Gosvami, Nitya Nand 285 Goyal, Arjun 145, 149 Grebe, Markus 109 Greiner, Christian 309, 429 Grundei, Stefan 71 Grundtner, Reinhard 503 Gudi, Dennis 259 Gumbsch, Peter 309 Gutierrez, Tomas Pérez 141 Guzmán, Francisco Gutiérrez 67 HHaider, Heinz 331 Hamer, Clive 367 Hanson, Gregory A.T. 199 Harinarain, A.K. 377 Hartmann, Felix 449 Härtwig, Fabian 43 Haupert, Frank 339 Héau, Christophe 229 Hees, Andreas 169 Heino, Vuokko 317, 503 Hernaiz, Marta 141 Herr, Marin 507 Herrmann, Inga 25 Hilmert, Dirk 219, 313 Hoffmann, Vincent 449 Holub, Florian 105 Hope, Ken 31 Hörl, Lothar 335 Huang, Haipeng 187 Hue, Laura 127 Hunter, Andy 381 Huybrechts, Ward 161 522 23rd International Colloquium Tribology - January 2022 IIgartua, Amaya 485 Iki, Haruka 355 Ishii, Yoshiki 437 JJacobs, Georg 67, 357, 457 Jech, Martin 403, 415 Joerger, Arn 271, 295 Joshi, Ratnadeep 73 KKadiric, Amir 183, 303, 453 Kailer, Andreas 71 Kamio, Kazunori 437 Kang, Jeong-Guk 465 Karlson, K.-O. 363 Karttunen, Mikko 317 Katta, Lakshmi 73 Kaulfuß, Frank 43 Kawakita, Kyosuke 437 Kerbrat, Marion 493 Khajeh, Kosar 437 Khan, Zulfiqar 463 Khatib, Ahmad Al 479 Kiw, Yu Min 77 Kleijwegt, Peter 191 Klemenz, Andreas 275 Kolekar, Anant S. 453 König, Florian 357, 457 Korth, Yasmin 33, 345 Kossoko, Nasrya F. 137 Krenn, Stefan 415 Krethe, Rüdiger 391 Kröll, Mirco 503 Krüger, Kevin 219, 313 Kuebler, Andreas 403 Kumar, Deepak 285 Kürten, Dominik 71 LLanzutti, A. 281 Larriere, Clément 357 Larsson, Roland 27, 467 Lee, Peter M. 199, 233 Lee, Shin-Ho Kim 423 Leimhofer, Josef 415 Lescoffit, Anne-Elise 161, 493 Li, Jinxia 89, 125 Lindemann, Lutz 23 Linnerer, Michael 433 Linsler, Dominic 65 Liu, Hong 187 Liwicki, Marcus 255 Lockwood, Frances E. 453 Lohmann, Peter 397 Lohner, Thomas 467 López-Uruñuela, Fernando José 263 Lorenz, Lars 43 Lotfi, Babak 177 Lubrecht, Antonius 209, 213 Lubrecht, Thomas 213 Lucazeau, Siegfried 113 MMacheiner, Thomas 347 Macián, Vicente 393 MacLaren, Alexander 183 Macron, Etienne 229 Maddukuri, Chowdary 247 Magnan, M. 281 Mahapatra, R. 377 Makowski, Stefan 43 Malhaire, Jean-Marie 479 Malm, Linda 89 Martínez, María J. 423 Masen, Marc A. 63 Mauleón, Pablo 423 Maurin-Perrier, Philippe 229 Mayrhofer, Claudia 331 Mayrhofer, Paul Heinz 403 Mazuyer, Denis 45 McClure, Ted G. 53 Mebus, Lukas 357 Mendoza, Gemma 485 Merkle, Lukas 471 Michael, Adler 251 Michaelis, Klaus 57 Miiller, Greg 375 Mikitisin, Adrian 67 Minfray, Clotilde 137 Mitterer, Stefan 433 Miwa, Reo 355 Miyanaga, Norifumi 355 Mohr, Stephan 441 Molter, J. 363 Moody, Gareth 165 Morgan, Alexes 53 Morgan, David 191 Morina, Ardian 187, 207 Morstein, Carina 275 Moseler, Michael 275 Mosher, Donna 145, 149 Mourhatch, Ramoun 191 Mueller, Gunther 375 Mueller, Caroline 407 Murali, Manoj 63 NNajjari, Morteza 299 Narita, Keiichi 173 Navarro, Ángel 101 Naveiro, Roí 423 Neus, Stephan 385 Neville, Anne 187 Newcomb, Timothy 375 Newrkla, Katharina 503 Norrby, Thomas 89 Notheaux, Guillaume 127 Nyberg, Erik 503 OOrtelt, Markus 259 Ott, Sascha 239, 271, 295 PPagano, Francesco 503 Park, Chan IL 243 Park, Junsik 381 Park, Tae-Jo 465 Passman, Frederick J. 91 Payer, Wolfgang 105 Paz, Cristina Vilabrille 489 Pelto, Jani 317 Pelz, Rico 375 Pettersson, Anders 27 Pinedo, Bihotz 263, 503 Pirker, Franz 37, 507, 511 Pla, Benjamín 393 Plebst, Sebastian 33, 61, 71 Polcar, T. 289 Ponzoni, Ignacio 423 Pota, Simone 87 Potnis, Harish 93 Priest, M. 197 Prokop, Christian 489 QQuerini, M. 281 RRai, Himanshu 285 Raisin, Jonathan 357 Ramakumar, SSV 73, 377 Rangova, Theodora 65 Rantala, Taneli 515 Rau, Julia S. 309 Regauer, Simon 153 Reinicke, Stefan 65 Reinle, Florian 299 Revilla-Lopez, Guillermo 423 Riss, Arnaud 357 Ristic, Andjelka 105 Robin, Claire 479 Rohbogner, Christoph 153 Ronkainen, Helena 317, 503 Rudnytskyj, André 415 Rühle, T. 399 Ruland, Michael 109 Rüthing, Justus 339 23rd International Colloquium Tribology - January 2022 523 SSakai, Kazumi 355 Sanchez, Carlos J. 233 Satish, Poorna 247 Sato, Ryosuke 355 Sawai, Gentaro 437 Saxena, Deepak 73, 377 Schaeffer, Philippe 77 Schandl, Michael 347 Scherge, Matthias 409 Schimpf, Artur 259 Schitco, Cristina 121 Schlüter, Florian 65 Schmitz, Regine 339 Schneider, Reinhard 309 Schneider, Ameneh 327 Schneidhofer, Christoph 347 Schreiber, Paul J. 429 Schubert, Thomas 33, 61 Schulz, Michael 159 Schwarz, Anette 225 Seiler, Helge 259 Sepehr, Maryam 191 Seth, Sarita 73, 377 Shakhvorostov, Dmitriy 169 Shi, Yijun 27 Shore, Joseph F. 453 Sigrüner, Michael 339 Simonovic, K. 289 Singh, Inder 377 Singh, Punit Kumar 377 Sithananthan, M. 377 Smeeth, Matthew 367 Söderfjäll, Markus 503 Soivio, Kaisu 515 Song, Jian 219, 313 Sordetti, F. 281 Soto, Axel J. 423 Spadinger, Markus 271 Spaltmann, Dirk 503 Spikes, Hugh 303 Stahl, Karsten 57 Stark, Sabrina 489 Steinweg, Florian 67 Stelzer, Christian 449 Storz, Andreas 299 Strübbe, Nicole 339 Stubbs, Robert 53 Sugimura, Joichi 277 Sunagawa, Yoji 277 Sung, am Ho 381 TTaghizadeh, S. 351 Takagi, Akira 157 Talavante, Pablo 423 Talukdar, Deboprasad 437 Tanaka, Hiroyoshi 277 Tatsumi, Go 157 Thakur, Deepa 285 Thiébaut, Benoît 77, 137, 207 Thornley, Aaron 187 Tobie, Thomas 57 Tomiyama, Eiji 437 Tormos, Bernardo 393 Tortora, Angela 153 Tošić, Marko 467 Tuzyna, Edith 489 Tyrovola, Theodora 371 UUeda, Mao 303 Usman, Ali 255 VVarga, Markus 415 Veeregowda, Deepak H. 153 Velkavrh, Igor 331 Vernes, András 511 Vitu, T. 289 Vorlaufer, Georg 415 Voyer, Joel 331 WWang, Yuechang 187, 425 Wang, Chun 187 Ward, Claire 51 Warren, Bethan 165 Wartzack, Sandro 417 Washizu, Hitoshi 437 Weihnacht, Volker 43 Weldon, Nicholas 165 Wieber, Stephan 169 Wilkens, Roland 169 Wilson, Mark C.T 425 Winkler, Karl Jakob 57 Winkler, Andreas 417 Witt, Thomas 445 Wopelka, Thomas 105 Woydt, Mathias 485 Wright, Tom 331 YYamamoto, Shuhei 437 Ye, Zhijiang 285 Yuan, Haomiao 313 ZZabala, B. 485 Zak, Felix 327 Zannikos, Fanourios 371 Zellhofer, Manuel 403 Zhang, Sara 191 Zhmud, Boris 161, 299 Zitouni, Karima 161 The conference provides an international exchange forum for the industry and the academia. Leading university researchers present their latest findings, and representatives of the industry inspire scientists to develop new solutions. Main Topics Trends lubricants and additives Automotive and transport industry Industrial machine elements and wind turbine industry Coatings, surfaces and underlying mechanisms Test methodologies and measurement technologies Digitalisation in tribology Digital tribological services: i-TRIBOMAT Sustainable lubrication Target Groups Companies in the field of of lubrication, additives and tribology Research facilities www.tae.de ISBN 978-3-8169-3547-6