Anisotropic failure modes of high-strength aluminium alloy under various stress states

The influence of stress state and plastic anisotropy on the fracture behaviour of a rolled AA7075-T651 aluminium plate under quasi-static loading conditions is studied both experimentally and numerically. Material tests in different directions of the plate were carried out using specimens with various shapes to provide a wide range of stress states. The strain to failure and the failure modes were found to vary strongly with the stress state, but also with the loading direction due to the complex microstructure of the alloy. Finite element simulations adopting an anisotropic plasticity model were used to obtain local values of stresses and strains and to define the strains at fracture for the various stress states. The numerical simulations show that due to the heterogeneous stress and strain fields in the specimens, it is very difficult to accurately locate the point where fracture initiates and thus to determine the local fracture strain as a function of stress state and loading direction.