Three-dimensional finite element modeling of rolling contact fatigue.

摘要

Rolling contact fatigue is a stochastic mode of material failure experienced in tribological machine components such as rolling element bearings. The fatigue lives of effected components are significantly dispersed on account of the interaction of highly localized contact loading with heterogeneous microstructure features. Contact conditions often warrant the use of two-dimensional simplifications of the applied loading in investigations of rolling contact fatigue. However, finite three-dimensional characteristics of the microstructure can significantly influence the failure initiation and progression, thereby impacting the resulting fatigue lives. Recognizing this connection, this dissertation presents a three-dimensional modeling approach for investigating rolling contact fatigue in the framework of finite element analysis. The approach directly considers the internal microstructure topology by modeling assemblies of material grains as randomly constructed Voronoi tessellations. These topological models are utilized in conjunction with damage mechanics and a novel mesh partitioning algorithm to simulate the gradual material degradation from crack initiation through propagation to final failure. Two additional sources of randomness are studied: (1) spatial variation of material properties and (2) the presence of inherent material flaws. Constructing the model in a three-dimensional framework incurs a substantial increase in computational expense; however, several solution strategies are developed and implemented to offset these costs. The results are demonstrated to be in good qualitative and quantitative agreement with published empirical data. The failure progression begins at multiple isolated subsurface locations prior to the linking and branching of fatigue cracks that breach the contact surface. The scatter in the resulting fatigue lives is shown to be consistent with experimental findings and is well characterized by two and three-parameter Weibull distributions. Fatigue lives are found to follow an inverse power law relationship with the maximum contact pressure and parametric studies with input material parameters is carried out to develop a new rolling contact fatigue life equation for three-dimensional line contacts.