A microstructure sensitive contact fatigue model of a carburized gear

Rolling contact fatigue (RCF) issues of carburized gears are not fully understood and relate to many factors, such as gradients of mechanical properties, the multiaxial stress state and the complex stress-strain response due to the polycrystalline anisotropy. In this work, a numerical model for RCF performance evaluation of a carburized gear is proposed by considering the anisotropy of carburized material microstructure and the hardness gradient. The crystal plasticity framework is adopted by using a user material subroutine. The effects of mechanical property gradients induced by carburizing are considered and introduced on the grain level. The Fatemi-Socie fatigue criterion is implemented to capture the RCF performance on crystallographic slip systems during the gear meshing process. The RCF performance of carburized gear is evaluated and compared with a non-carburized gear. The simulation results reveal that the influence of microstructure anisotropy on the maximum contact pressure is the most significant at the pitch point meshing position. The plasticity accumulates at a certain depth of non-carburized gear, and this accumulated plasticity leads to more scattered and larger values of a fatigue indicator parameter. Several sets of random grain orientations are developed, and the result shows that the RCF indicator parameter of non-carburized gear is more sensitive to the grain orientation.