Effects of microstructure on rolling contact fatigue of a wind turbine gear based on crystal plasticity modeling

With the increases of the power densities and loading capacity of heavy duty machines such as wind turbines, rolling contact fatigue (RCF) problems of gears have become key problems limiting the reliabilities of those machines. The RCF analysis of gear has been widely studied from the perspective of the geometrical aspect and working conditions. However, the underlying mechanism of gear RCF remains unclear, especially the influence of material micro-structure on fatigue behavior is to be discovered. In this work, an integrated methodology considering the microstructure and crystal plasticity is proposed to evaluate the RCF performance of a wind turbine gear. The Voronoi tessellations are used to construct the virtual microstructure of the gear material. The crystal plasticity constitutive model considering the kinematic hardening and the isotropic hardening is established. The crystal plasticity constitutive is implemented in ABAQUS/Standard using a user material subroutine (UMAT). The Fatemi-Socie multiaxial fatigue criterion (FS) is applied to study the contact fatigue behavior of this heavy-duty gear considering the normal stress and shear strain of crystallographic slip systems. The influence of the crystal anisotropy of gear material on the RCF performance is investigated. The results indicate that the randomness of grain orientation and the anisotropy of crystal properties lead to the discretization of maximum FIP and the distinction of the failure position. Among the results of fifteen sets of models with randomly distributed grain orientations, compared with the mean value, the maximal fluctuating of magnitude and the depth position of maximum FIP are up to 15.8% and 20%, respectively. The effect of the grain orientation on FIP is explored. The predicted results reveal that the anisotropy and randomness of crystal orientation lead to the discretization of magnitude of FIP and the variation of crack initiation position. The rolling fatigue cracks tend to initiate along the direction having angles between 20 degrees to 45 degrees relative to the rolling direction.