Damage and fracture prediction of 7075 high-strength aluminum alloy during cryogenic stamping process

In order to accurately predict the damage and fracture behaviors of a 7075 aluminum alloy during cryogenic stamping, a nonlinear damage model taking into account stress triaxiality and cryogenic temperature was established to access the formability of the alloy. Seven types of specimens with various stress triaxialities were tested and simulated to define a triaxial-failure curve, and the damage parameters of the model for 7075 alloy deformation at room temperature and liquid nitrogen temperature were determined by the inverse calibration method. Moreover, finite element simulations combined with this model were used to analyse the damage and fracture behavior of a U-shaped part stamped at low temperature. The results indicated that the alloy at −196 °C showed a remarkable improvement in failure strain. The damage value of the cryogenic deformed specimens was smaller than that at room temperature. It was found that the model was capable of predicting the nonlinear damage accumulation and cracking process of the cryogenic stamped part. A good agreement of the fracture onset and position were found between experiments and simulations. The cryogenic samples presented a combination of ductile-fracture modes and transgranular brittle fracture modes, which was significantly different from those at RT.