On stress integration of coupled viscodamage-viscoplasticity models with separate yield/loading surfaces

This paper deals with numerical integration of stresses, inelastic strains and internal variables related to coupled viscodamage-viscoplasticity models. The class of models considered here is the one where the viscodamage and viscoplasticity parts are described independently based on their specific loading/yield criteria and evolutions laws. Moreover, in the viscodamage part, an anisotropic compliance damage formulation is adopted. Both the viscodmage and the viscoplasticity components are formulated in terms of the consistency model by Wang (1997). Two methods for coupling the damage and the plasticity parts are presented. In the first more traditional method, both models are solved simultaneously returning the trial stress onto the intersection of the criteria while updating the internal variables. The second, nonstandard method exploits the damage strain to impose iteratively the stress equality on the stress vectors returned independently on the respective, viscodamage and viscoplasticity surfaces. A special emphasis is laid on the treatment of the corner point plasticity case. After the general treatment, the two methods are illustrated with an application to the Mohr-Coulomb viscoplasticity model combined with Rankine viscodamage model.