Abstract：A novel criterion for predicting forming limit diagram （FLD） is presented, namely, thickness gradient criterion. This criterion is based on the critical thickness gradient C which occurs perpendicular to the necking when the failure develops. During forming process, when the ratio of thickness in neighboring regions of a deforming sheet metal drops below the critical magnitude C, necking develops. The process of Nakazima experiment was simulated by eat/Dynaform. FLD was obtained by finite element cal- culation based on thickness gradient criterion. FLD obtained in this way was compared with those obtained from theoretical calculation and experimental method. Results show that FLD obtained by this method is more consistent with the experimental results than those obtained by the theoretical calculations. Good correlation between the simulation and experimental results is indicated.
2008, Vol. 29 
