FINITE-ELEMENT ANALYSIS OF REPEATED INDENTATION OF AN ELASTIC-PLASTIC LAYERED MEDIUM BY A RIGID SPHERE .1. SURFACE RESULTS

A comprehensive elastic-plastic finite element analysis is presented for the axisymmetric problem of a frictionless rigid sphere indenting a half-space with a harder and stiffer layer. The indenter is modeled by contact elements, thereby avoiding a priori assumptions for the pressure profile. Two layer thicknesses are examined, with layer elastic modulus and yield stress both two and four times greater than those of the substrate. Perfectly plastic and isotropic strain-hardening behavior of the layer and substrate media are investigated, At least three complete load-unload cycles are applied to a peak load of 300 times the load necessary to initiate yielding in a half-space of the substrate material, The effect of hardening properties on the loaded and residual stresses is presented and the consequences for crack initiation at the surface are discussed, Results for the contact pressure and surface stresses and deformations are presented, and the influence of residual displacements and load cycles on the contact pressure and the loaded and residual surface stresses is investigated.