Prediction of the forming limit diagram on the basis of the damage criterion under non-proportional loading

Based on the theory of damage mechanics, a recently developed anisotropic p lastic damage model for the prediction of forming limit diagrams (FLDs) is extended to take into account the effect of rotation of the principal damag e coordinates on the deformation and damage behaviour. With the aid of the damage plastic potential, the damage evolution equations are established. A damage criterion for localized necking under arbitrary loading history is proposed. The model is employed to predict the FLDs of AL6111-T4 alloy. The predicted results agree well with those determined experimentally.