CONTRIBUTION OF SURFACE IRREGULARITIES TO ROLLING-CONTACT PLASTICITY IN BEARING STEELS

A ''two-body'' elasto-plastic finite element model of two-dimensional rolling and rolling-plus-sliding has been developed to treat the effec t of surface irregularities. The model consists of a smooth cylinder i n contact with a semi-infinite half-space that is either smooth or fit ted with one of two irregularities: a 0.4 mu m deep groove, or a 7 mu m deep groove. The model incorporates elastic-linear-kinernatic-harden ing-plastic (ELKP) and nonlinear-kinematic-hardening-plastic (NLKP) ma terial constitutive relations appropriate for hardened bearing steel a nd the 440C grade. The calculated contact pressure distribution is Her tzian for smooth body contact, and it displays intense, stationary, pr essure spikes superposed on the Hertzian pressure for contact with the grooved and ridged surface. The results obtained for the 0.4 mu m dee p groove are consistent with those reported by Elsharkawy and Hamrock (1991)for an EHD lubricated contact. The effect of translating the cou nterface on the halfspace, as opposed to indenting the counterface on the half-space with no translation, is studied. The stress and strain values near the surface are found to be similar for the two cases, whe reas they are significantly different in the subsurface. Efforts have been made to identify the material constitutive relations which best d escribe the deformation characteristics of the bearing steels in the i nitial few cycles. ELKP material constitutive relations produce less n et plastic deformation in the initial stages, for a given stress, than seen in experiments. NLKP model produces more plasticity than the ELK P model and shows promise for treating the net distortions in the earl y stages. Artificial indents were inserted on the running track of the cylindrical rolling elements and profilometer measurements of these i ndents were made, before and after rolling. These preliminary measurem ents show that substantial plastic deformation takes place in the proc ess of rolling. The deformations of the groove calculated with the fin ite element model are compared to those measured experimentally.