Elastic-plastic analysis of hardened layers in rims subjected to repeated rolling contacts

Abstract

This paper examines the effects of shallow, surface, and subsurface hardened layers on the response of rims to repeated, 2-dimensional (plane strain) rolling contacts. The rolling is simulated by translating a Hertzian pressure distribution across a finite element model of an elastic-plastic half-space. Four cases are examined: (1) a homogeneous rim, (2) and (3) rims with 0.2w-deep and 0.4w-deep (2w is the Hertzian contact width) hardened surface layers, and (4) a rim with a 0.4w-deep subsurface layer. The dimension 2w can be viewed as either the macrocontact width or the microasperity contact width. The calculations treat elastic-perfectly plastic, cycle and amplitude independent, Von Mises material behavior with the yield strength of the hardened layers twice the value of the surrounding material. The effects of pure rolling at a peak contact pressure-to-shear yield strength ratiop0/k = 5 are examined. The calculations describe the effects of the layers on the displacements of the rim surface, the extent of the plastic zone, the residual stresses, and incremental plastic strains. The results indicate that the response of the material at different depths is weakly coupled. Cyclic plasticity is eliminated in the hardened layers, but is not substantially altered in the adjacent material. The hardened layer must occupy a large part of the respective active plastic zones of the macrocontact and microasperity contact to prevent continuing cyclic plastic deformation in the two regions.