Modified formulation of a rate-dependent damage model for ductile materials

A modification to the rate-dependent damage and failure model developed by Addessio and Johnson [J. Appl. Phys. 74, 1640 (1993)] for ductile materials under high-rate loading is presented. In the current formulation the equilibrium stress, which is used to calculate the plastic strain rate and damage in the material, is defined as the orthogonal projection of the final stress onto an equilibrium yield surface, instead of being a projection of the trial stress onto the yield surface as is done in the original formulation. The modification makes the current formulation fully consistent with the viscoplasticity theory. An implicit algorithm is also presented for the modified model and numerical results of copper under uniaxial strain loading are given to show the features of the model and the algorithm. Comparisons with the results of the original formulation are also presented. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3326939]