A KINETIC-EQUATION FOR DAMAGE DURING SUPERPLASTIC DEFORMATION

In this paper a kinetic equation for the isotropic damage during super plastic deformation is proposed, based on the thermodynamic theory of irreversible processes with internal state variables and the normality criterion. The damage variable D during superplastic deformation is n on-linear with the equivalent plastic strain epsilon(p), and it is sho wn that D is affected strongly by the triaxiality stress ratio (sigma( m)/sigma(eq)). Furthermore, in order to demonstrate the efficiency of the proposed equation, superplastic deformation experiments were perfo rmed on aluminium alloy LY12CZ and brass H62 without any pre-treatment . The comparision with the experimental results is presented on the in fluence of the triaxiality stress ratio on the equivalent strain to ru pture: good correlation is found between the theoretical and experimen tal results. Therefore, this equation for damage may reflect successfu lly superplastic damage behaviour during superplastic deformation proc esses.