Effect of stress triaxiality corrected plastic flow on ductile damage evolution in the framework of continuum damage mechanics

Most of the damage models derived from the theory of Lemaitre have been dev eloped using the hypothesis based on "proportional loading" for the determi nation of some material parameters. This hypothesis is adopted in such a wa y that a material coefficient (a scale factor for damage values) can be eva luated from tensile tests on unnotched specimens, considering the triaxiali ty of the stress state to be that corresponding to perfect uniaxiality, ove r the entire load history, and so ignoring necking induced variations in th e triaxiality. The present paper analyses the response of some continuum damage mechanics models which incorporate a correlation between the triaxiality factor and l ogarithmic plastic strain. These correlation laws: affecting also the true stress-true strain material curve, were derived from experimental data proc essed using the Bridgman method. Due to the lack of experimental data speci fically related to damage evolution, the aim of the study was to evaluate t he sensitivity of these models to the variability of the triaxiality parame ter during the deformation history. (C) 2001 Elsevier Science Ltd. All righ ts reserved.