Damage Evolution in Elasto-Plastic Materials - Material Response Due to Different Concepts

The purpose of this paper is to show that shortcomings exist in the plasticity induced damage theories. Existing phenomenological thermodynamic approaches used for describing elasto-plasticity coupled with damage are therefore evaluated. Within the concept of effective stress both the postulate of strain equivalence and the postulate of (complementary) energy equivalence, as well as extensions of the postulates, are considered. As a prototype model the von Mises plasticity model coupled with isotropic damage is considered. Simulations of a strain-controlled uniaxial model are also performed. The results reveal that a mapping, similar to that of the stress, of both the kinematic and isotropic hardening variables is to be preferred. More interesting is that, irrespective of the postulate employed, the elastic strain will not equal zero when failure takes place, i.e. the interpretation of elastic strain is lost. From the results it is also concluded that (complementary) energy equivalence have some undesirable properties.