Modeling of Surface Modified Layers in the Presence of Surface Irregularities

Finite element calculations that examine the effects of surface modification on the deformation produced by pure rolling contact are presented. The model simulates the repeated, two-dimensional (line) contact of a cylinder that is rolling over a semi-infinite half space. The half space is treated as an elastic-linear-kinematic-hardening-plastic (ELKP) material with the cyclic flow properties of a hardened, HRC-62, bearing steel. Two different cases are examined : (i) a smooth half space is studied using a one-body model, and (ii) a half space with a 100 μm wide and 7 μm deep surface asperity is studied using a two-body model. In both cases, calculations are performed for a homogeneous body and a body with a shallow, surface modified layer. The surface modified layer is alternately : (a) stiffer, (b) harder, (c) softer, and (d) harder and stiffer as compared to the substrate. Consistent with the earlier studies of surface modification (Bhargava, 1987), the present findings indicate that the benefits of the mechanical property modifications are confined to the altered layer itself. This may explain the improvement in performance realized by relatively thin modified layers (5 μm).