A Finite Element Study of Stable Crack Growth Under Plane Stress Conditions: Part II—Influence of Hardening

A detailed finite element analysis is performed to model quasi-static crack growth under plane stress, small-scale yielding conditions in elastic-plastic materials characterized by isotropic power law hardening and the Huber-Von Mises yield surface. A nodal release procedure is used to simulate crack extension. Results pertaining to the influence of hardening on the extent of active yielding and the near-tip stress and deformation fields are presented. Clear evidence of an elastic unloading wake following the active plastic zone is found, but no secondary (plastic) reloading along the crack flank is numerically observed for any level of hardening. A ductile crack growth criterion based on the attainment of a critical crack opening displacement at a small microstructural distance behind the tip, is employed to investigate the nature of the J resistance curves under plane stress. In addition, the same criterion is employed to investigate the influence of hardening on the potential for stable crack growth under plane stress. It is found that predictions based on a perfectly plastic model may be unconservative in this respect, which is qualitatively similar to the conclusions reached in antiplane shear and Mode I plane strain.