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.