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

Abstract

Most of the damage models derived from the theory of Lemaı̂tre have been developed using the hypothesis based on “proportional loading” for the determination of some material parameters. This hypothesis is adopted in such a way that a material coefficient (a scale factor for damage values) can be evaluated from tensile tests on unnotched specimens, considering the triaxiality of the stress state to be that corresponding to perfect uniaxiality, over the entire load history, and so ignoring necking induced variations in the triaxiality. The present paper analyses the response of some continuum damage mechanics models which incorporate a correlation between the triaxiality factor and logarithmic plastic strain. These correlation laws, affecting also the true stress–true strain material curve, were derived from experimental data processed using the Bridgman method. Due to the lack of experimental data specifically related to damage evolution, the aim of the study was to evaluate the sensitivity of these models to the variability of the triaxiality parameter during the deformation history.