FLD of AZ31 sheet under warm stretching and its prediction

Forming Limit Diagrams (FLDs) of a magnesium alloy (AZ31) sheet at various forming speeds (3 to 300 mm·mm^-1) at several temperatures of 100-250°C were investigated by performing a punch stretch-forming test. The forming limit strains increased with temperature rise and with decreasing forming speed, where the effect of forming speed was stronger at higher temperatures. To describe such a characteristic of FLD of AZ31, the Marciniak-Kucznski type forming limit analysis was conducted using the Backofen-type constitutive equation (c = Cεⁿε^m). In this analysis, the damage evolution in the necking zone was taken into account based on Oyane's ductile fracture criterion. The numerical results of the FLD show a good agreement with the corresponding experimental observations.