On the effect of microplasticity on crack initiation from subsurface defects in rolling contact fatigue

This work demonstrates numerically how microplasticity, i.e. the yielding behavior below the conventional 0.2% plastic strain threshold, can lead to initiation of cracks at subsurface defects, in rolling contact applications operating under realistic loads. A 3D elasto-plastic finite element model is employed to perform shakedown analysis of the bearing steel around a small spherical void with two different approximations of the steel constitutive behavior at the plastic micro-strain regime. When non-linear kinematic hardening is used to model a fast but smooth onset of plasticity, the fields of plastic strains and micro-residual stresses around the void evolve very distinctly to the case where a sharp transition is assumed. To further investigate the role of the tensile micro-residual stresses occurring in the former case on crack initiation, a planar circular crack is inserted at the equator of the void and an entire overrolling cycle is investigated by means of linear elastic fracture mechanics (LEFM). This analysis is repeated for different crack sizes and the respective stress intensity factors and their amplitudes, relevant for crack growth, are reported. The work also reports implementation details for the coupling of a 3D elasto-plastic model for shakedown analysis to a subsequent LEFM analysis model.