Models for Compressible Elasto-Plasticity Based on Internal State Variables

A general constitutive framework is presented for rate-independent porous plasticity. This framework is formulated using combined nonlinear isotropic-kinematic hardening rules along with void growth models which can be either implicitly embedded within a pressure dependent yield function or explicitly established based on a micromechanical model. A void nucleation criterion is also introduced in the framework. An associative flow rule is first set forth which implicitly introduces general void growth models. Correlations are presented with experimentally determined porosity evolution in circumferentially notched specimens subjected to various superimposed hydrostatic pressures. The framework is then generalized to include explicit void growth models with plastic flow which are either associative or non-associative with the yield function. Single element computations are carried out using these model frameworks to compare the behavior predicted by specific implicit and explicit void growth models.