Efficient numerical models for the tribological analysis of textured journal bearing systems

滑动轴承系统中摩擦和磨损的减少可以极大地促进传动系统的高效设计。表面纹理是一种减少摩擦和磨损的新兴技术。用于混合摩擦条件下顺序运行的滑动轴承系统设计的数值模型通常只考虑表面粗糙度对摩擦和磨损的影响。将这些模型应用于纹理系统会导致严重的建模错误，或者需要使用高分辨率的表面纹理离散化进行耗时的模拟。因此，确定在特定应用中减少摩擦和磨损的最佳纹理设计几乎是不可能的。因此，该项目的主要目标是开发、实施和验证一种有效的数值方法，以优化具有粗糙、纹理轴面的轴承系统。与现有软件解决方案包含Patir和程的经验平均流量模型不同，本项目中的建模基于均化的数学概念。均化是基于渐近展开的，与平均流动模型不同，它为任何表面粗糙度或纹理的配置提供了正确的结果。此外，对平均解的简单放大允许捕捉局部效应。这个概念可以通过重复的均匀化来扩展，这样就可以考虑粗糙度和纹理，而不需要通过精细的计算网格来分解纹理。通过开发和实现单独的模块，组装了一个综合的暂态仿真模型。该模型考虑了(I)考虑空化的流体动力学，(Ii)通过计算弹塑性粗糙面接触压力和弹性变形(EHL)来计算混合摩擦，以及(Iii)通过流体和固体的能量方程来计算温度效应。由此得到的热-弹流/混合摩擦模型最终被用于预测磨损的物理模型所扩展。后者被加强，以说明在粗糙接触天平上磨合过程中发展的轴和轴承的一致性。除了数值研究外，还进行了实验以验证数值模型，并系统地研究了粗糙度和织构对滑动轴承系统摩擦学特性的解耦和协同效应。此外，还对表面纹理的耐久性进行了研究。这涉及到使用不同的倾向于涂抹的轴承材料，以及在混合摩擦条件下的测试。研究了混合润滑转变为流体动力润滑时的磨合/磨合效应。

The reduction of friction and wear in sliding bearing systems can significantly contribute to the efficient design of a drivetrain. Surface texturing is an emerging technique to reduce friction and wear. Numerical models for the design of sliding bearing systems for applications with sequential operation under mixed friction conditions, e.g., wind power drives or internal combustion engines, commonly only incorporate the effect of surface roughness on friction and wear. The application of these models to textured systems leads to significant modeling errors or requires time-consuming simulations with highly-resolved surface-texture discretizations. Consequently, determining the optimal texture design for the reduction of friction and wear in a given application is nearly impossible. The main objective of this project therefore is the development, implementation and validation of an efficient numerical method for the optimal design of bearing systems with rough, textured shaft surfaces. In contrast to existing software solutions that incorporate Patir and Cheng’s empirical average flow model, the modeling in this project is based on the mathematical concept of homogenization. Homogenization is based on an asymptotic expansion, which - in contrast to the average flow model - provides correct results for any configuration of surface roughness or texturing. In addition, a simple upscaling of the averaged solution allows for capturing local effects. The concept can be extended by reiterated homogenization in such a way that roughness and textures can be taken into account without resolving the textures by fine computational meshes. By developing and implementing individual modules, a comprehensive model for transient simulations is assembled. This model incorporates (i) hydrodynamics taking into account cavitation, (ii) mixed friction by computing the elastic-plastic asperity contact pressure and elastic deformations (EHL) and (iii) temperature effects through energy equations for the fluid and the two solids. The resulting thermo-elastohydrodynamic/mixed friction model is finally extended by physical models for the prediction of wear. The latter are enhanced to account for the conformity of shaft and bearing developing during running-in on asperity contact scale. In addition to the numerical studies, experiments are conducted to validate the numerical model and to systematically investigate the uncoupled and synergistic effects of roughness and texture on the tribological characteristics of sliding bearing systems. Furthermore, the durability of surface textures is studied. This involves the use of different bearing materials that tend to smearing as well as tests under mixed friction conditions. Running-in/wearing-in effects such as the shift of the transition speed from mixed to hydrodynamic lubrication are studied as well.