Tension and shear cracking during indentation of ductile materials by opposed wedges

Abstract

Kudo and Tamura [1] indented ductile solids with opposed wedges until cracks appeared. Depending on the conditions, cracks initiated either at the center of the specimen in the line of action of the wedges, or immediately below the tips of the wedges; furthermore cracks propagated either in tension or in shear. The principal controlling factors that determined where, and in what mode, cracks initiated and propagated were wedge angle, friction, axial loading of the specimen, and specimen orientation (metal anisotropy).This paper simulates the formation of these different types of crack using work-hardening plasticity and the damage accumulation model developed by Bai and Wierzbicki [2] which is able to predict shear fractures by including the stress triaxiality, the third invariant of the deviatoric stress tensor (Lode angle parameter), and the material post-failure softening. The damage model is extended to account for the anisotropy under plane strain conditions. Since the wedges cutting is a plane strain dominated process, the Lode angle parameter is a constant. It is found that the material fracture strain dependency on stress triaxiality, fracture limit anisotropy and post-failure softening are three key features affecting the crack prediction in cutting. The paper demonstrates the applicability of cutting process finite element simulation for anisotropic materials using a ductile fracture model.