Influence of ductile damage on springback prediction of aluminum alloy sheet under changing loading paths

Abstract

Springback prediction during the metal forming, especially under complex loading paths, is always one big issue in industry, which is also attracting attentions of many researchers. The accuracy of simulation prediction depends not only the forming conditions, but also the chosen material model. In the classical model, the yield function and Young’s modulus both play important roles in the springback prediction. Normally, the yield function represents initial anisotropy, and ignores the subsequent anisotropy. Since the yield surface shape, especially its evolution are difficult to measure. At the same time, the average Young’s modulus decreases with the plastic deformation, which will highly affect the final springback values. In this study, a recently proposed damage model concerning Lode angle parameter, stress triaxiality and also micro-cracks is employed to simulate the fracture phenomena of chosen AA7055. A mixed hardening anisotropic finite plasticity has also been added to the fully coupled isotropic ductile damage in the given constitutive equations. The aluminium alloy sheet metal AA7055 is chosen as the test material. In order to investigate its springback phenomena under variable strain paths, the three point bending tests are conducted with three different pre-strains. Through the comparisons between numerical results and experimental observations, it can be found that the great influence of ductile damage on the springback.