Inverse identification method for determining stress–strain curves of sheet metals at high temperatures

•The effects of the parameters in the damage evolution model on stress–strain curve and force–displacement curve is revealed, and an inverse identification method considering work hardening, softening, damage and strain rate sensitivity is presented.•A coupled viscoplastic-damage constitutive model is determined, which can characterize the analytical curve. Moreover, when the damage variable in the model is shielded, the non-damage curve can also be characterized. This model is the object of reverse modification.•The inverse identification procedure is demonstrated using 7075 aluminum alloy, and the complete high temperature flow curve prior to fracture is obtained.•The obtained flow curves by the inverse identification method are used for finite element analysis of hot tensile and isothermal bulging of 7075 aluminum alloy to proving the validity. Because of the strong dynamic softening effect of sheet metals at high temperatures, necking occurs early and continues for longer periods. Therefore, obtaining a flow curve after necking has occurred is necessary. The high-temperature flow behavior of materials typically exhibits the coupled effects of work hardening, softening, strain-rate sensitivity, and damage, and using the traditional inverse identification method is quite challenging. This study presents a finite element (FE) inverse identification method that considers work hardening, softening, damage, and strain-rate sensitivity. The method uses a coupled viscoplastic-damage constitutive model as the modified object, and the parameters of the damage equation are iteratively modified by the FE method until the simulated force–displacement curve is consistent with that of the experiment. The identification procedure is demonstrated using 7075 aluminum alloy, and a complete high-temperature flow curve prior to fracture is obtained. The obtained flow curve is applied to analyze the strain field distribution in a hot tensile process and to predict the fracture occurrence and thickness distribution under an isothermal bulging test. Experimental and simulation results are shown to be in good agreement, thus proving the validity of the proposed method.