Analysis of subsurface crack initiation under rolling contact

This dissertation presents studies of different aspects of rolling contact. Analysis of the effects of boundary conditions and mesh refinement of finite element models of elasto-plastic 2-dimensional pure rolling contact are presented in Chapter I. The pure rolling of a cylinder is simulated by incrementally translating a semi-elliptical Hertzian pressure distribution over a finite element model of a semi-infinite half space. The calculations evaluate the effects of rigid and elastic boundary conditions and two degrees of mesh refinement on the steady state residual stresses, the continuing cyclic plasticity, and the residual displacements.;Chapter II describes the rolling and sliding calculations for bearing steel assuming an idealized elastic-linear-kinematic hardening-plastic (ELKP) material behavior, an idealization that closely approaches the behavior of low, medium, and high hardness steels. The calculations treat Hertzian contact pressures in the range 2500 MPa ;Finite element calculations that examine the effects of surface modification on the deformation produced by pure rolling contact are presented in Chapter III. The half space is treated as an ELKP material with the cyclic flow properties of a hardened, HRC-62, bearing steel. A homogeneous body and one with a shallow, y = 0.4w ;Crack initiation studies on 7075-T6 aluminum are presented in Chapter IV. The ELKP cyclic flow properties of 7075-T6 aluminum determined by means of simple push-pull fatigue tests are incorporated in a three dimensional finite element model simulating the test conditions of 3 ball/rod rolling contact fatigue tester. The plastic strains and the residual stresses obtained from the analysis are compared with the actual microstructural changes and the location of sub-surface cracks produced in the rolling tests. The results show that a combination of plastic strains and low values of residual stresses is conducive to sub-surface crack initiation and growth.