MODELING OF SURFACE-MODIFIED LAYERS IN THE PRESENCE OF SURFACE IRREGULARITIES

Finite element calculations that examine the effects of surface modifi cation on the deformation produced by pure rolling contact are present ed. The model simulates the repeated, two-dimensional (line) contact o f a cylinder that is rolling over a semi-infinite half space. The half space is treated as an elastic-linear-kinematic-hardening-plastic (EL KP) material with the cyclic flow properties of a hardened, HRC-62, be aring 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 m u m wide and 7 mu m deep surface asperity is studied using a two-body model. In both cases, calculations are performed for a homogeneous bod y and a body with a shallow, surface modified layer. The surface modif ied 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 modifications (Bhargava, 1987), the present findings indicate that the benefits of the mechanical property modifi cations are confined to the altered layer itself. This may explain the improvement in performance realized by relatively thin modified layer s (approximate to 5 mu m).