On the dynamic behavior of A5 aluminum. Two thermally activated deformation mechanisms and high strain modeling

Abstract
In order to improve dynamic behavior modeling of metallic materials, a semi physical constitutive relation was investigated for a fcc metal, A5 aluminum. Mechanical characterization tests appropriate to the model and the material were performed. Parameters were calculated through a specific optimization technique from quasi static and dynamic compression tests. In the experimental domain of loading, the model reproduces the stress-strain curves. But, basic validation tests exhibit two consistent points : the model, in its first form, failed to reproduce higher strains and a second deformation micromechanism was activated at high strain rates or low temperatures. Relevance of model to high strain domain can be solved using specific tests and different optimization technique. Concerning the second mechanism, we proved that it is thermally activated. In order to respect observed physical phenomena, we introduce, in the constitutive equations, another term which is insignificant only at low and medium strain rates or at high temperature. This new formulation of the model can describe high strain, low and high strain rate, low and high temperature. Usefulness of dynamic tests at 77 K is emphasized. They give valuable data needed for dynamic behavior modeling : high stress levels obtained correspond to very high strain rate tests at the room temperature (10⁴ s^-1), which are difficult to perfonn actually.