Abstract:A modified MK model combined with ductile fracture criterion (DFC-MK model) is proposed to compute the forming limit diagrams (FLDs) of 5A06-O aluminum alloy sheet at different temperatures. The material constant (C) of ductile fracture criterion and initial thickness imperfection parameter (f₀) at various temperatures are determined by using a new computing method based on wide sheet bending test. The FLDs at 20and 200°C are calculated through the DFC-MK model. The DFC-MK model, which includes the influence of through-thickness normal stress, is written into the subroutine VUMAT embedded in Abaqus/Explicit. The cylindrical cup hydroforming tests are carried out to verify the model. The results show thatcompared with experimental observations, the predicted FLDs based on DFC-MK model are more accurate than the conventional MK model;the errors between the simulations and experiments in warm hydroforming are 8.23% at 20°C and 9.24% at 200°C, which verify the effectiveness of the proposed model.

Key words: MK model; ductile fracture criteria; warm hydroforming; through-thickness normal stress