Determination of the Origin for the Dissymmetry Observed between Tensile and Compression Tests on Shape Memory Alloys

Abstract
Experimental observations performed on polycrystalline Cu-based Shape memory alloys exhibit assymmetrical responses for tensile or compressive test. We used a micromechanical point of view to determine the physical origin of this dissymmetry. At first approximation, we assume that the stress field is uniform inside the material and equals to the applied stress. This modelling gives some differences in the transformation slope and in the transformation strain associated to these two loading conditions. Using this approach we established that the volume change associated to the phase transformation exerts no influence upon this phenomenon. It appears that the low symmetry of the martensite is the major physical origin of this assymmetry. Finally, we improve the accuracy of these results using a self-consistent approach to determine the macroscopic behavior from the definition of the local constitutive equations. This modelling is able to determine the internal stress field developed by the phase transition. This approach gives different critical transformation stress and different hysteresis size for tensile or compressive test. Results obtained by this modelling are in good agreement with experimental features observed on Cu-based Shape Memory alloys. Multiaxial loading are then numerically performed and used to determine a macroscopic transformation criterion.