EHL modeling of nonhomogeneous materials: The effects of polycrystalline anisotropy on RCF

Bearing steel is comprised of a polycrystalline aggregate of anisotropic crystals which affects the stress distribution and subsurface fatigue crack formation. In the present investigation an approach is proposed to determine the contact pressure, film thickness and subsurface stresses in a polycrystalline anisotropic aggregate material operating under elastohydrodynamic lubrication (EHL). The approach is based on a fully coupled finite element EHL model which uses 1D finite elements to solve the Reynolds equation and 2D finite elements to resolve the deformations for a line contact EHL problem. The polycrystalline material is simulated using a Voronoi polygon discretization with each Voronoi polygon receiving a unique crystallographic orientation. The anisotropic material definition used for this model has a cubic crystal structure. Results from the FE Voronoi EHL model show that the contact pressures vary due to crystallographic orientation and stress concentrations occur at the polycrystalline grain boundaries. EHL film thickness profiles were not significantly affected by the addition of crystal anisotropy effects to the microstructural model. However, relative life prediction obtained from the model with the anisotropic stress profiles showed that significant life scatter is generated by the addition of crystal anisotropy into the microstructural model. The results obtained from the FE Voronoi EHL model show much closer agreement to experimental results than models that assume isotropic material models.