Study of the constitutive behavior of 7075-T651 aluminum alloy

The flow and fracture behavior of 7075-T651 aluminum alloy has been studied under different stress-states, strain rate and temperature in order to explore the characteristics of the material under extreme situations developed in aerospace and armor structures. Influence of stress state was studied by performing quasi-static tension tests on notched specimens of different initial notch radii, 0.44 - 6 mm. Strain rate sensitivity was studied by carrying out tension test in the range 5 × 10−4 s−1 - 800 s−1. Thermal sensitivity of the material was studied by performing quasi static tension tests in the range 25 - 600 °C. The increase in stress triaxility described increase in strength while reducing ductility. Increase in temperature on the other hand, stimulated opposite characteristics in the material. The variation in strain rate could not influence the flow and fracture behavior of material. Anisotropy observed in the material has been carefully investigated by carrying out tests in different in-plane and out of plane orientations. The stress-strain relations obtained through these tests were employed for calibrating Johnson-Cook (JC) flow and fracture model in different orientations. The Hill's stress potentials were also obtained to incorporate the anisotropy in the material flow. Four different sets of parameters were calibrated and employed for numerically simulating the ballistic performance of 20 mm thick 7075-T651 aluminum targets against 12.7 and 7.62 API projectiles. The results thus reproduced through each set of parameters were compared with the experimental findings and the limitation and accuracy of each calibrated model have been discussed.