This paper summarizes the work we conducted in recent years on modeling plastic response of metallic alloys and ductile fracture of engineering components, with the emphasis on the effect of the stress state. It is shown that the classical J2 plasticity theory cannot correctly describe the plasticity behavior of many materials. The experimental and numerical studies of a variety of structural alloys result in a general form of plasticity model for isotropic materials, where the yield function and the flow potential are expressed as functions of the first invariant of the stress tensor and the second and third invariants of the deviatoric stress tensor. Several mechanism-based models have been developed to capture the ductile fracture process of metallic alloys. Two of such models are described in this paper. The first one is a cumulative strain damage model where the damage parameter is dependent on the stress triaxiality and the Lode parameter. The second one is a modification to the Gurson-type porous plasticity models, where two damage parameters, representing void damage and shear damage respectively, are coupled into the yield function and flow potential. These models are shown to be able to predict fracture initiation and propagation in various specimens experiencing a wide range of stress states.
