eJournals International Colloquium Tribology 23/1

International Colloquium Tribology
ict
expert verlag Tübingen
125
2022
231

Trusted tribological materials characterisation services

125
2022
Mirco Kröll
Reinhard Grundtner
Katharina Newrkla
Dirk Spaltmann
Francesco Pagano
Bihotz Pinedo
Markus Söderfjäll
Erik Nyberg
Vuokko Heino
Helena Ronkainen
ict2310503
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/ .