STRESS-STRAIN RELATION FOR MATERIALS WHICH UNDERGO 2-PATH STRESS-INDUCED DISPLACIVE PHASE-TRANSITION

CuAlNi alloy subjected to loading undergoes subsequent phase transitions with increase of stresses: first from the gamma'-phase to the beta'-phase then from the beta'-phase to the alpha-phase. During unloading, however, it changes from the alpha-phase to the gamma'-phase through the beta"-phase, which is different from beta'. This paper suggests an analytical explanation of this phenomenon. We assume that the deformation occurring in this material is micro-nonhomogeneous. We employ internal variables to describe this deformation. In particular, we use them to postulate expressions for the energy density and the stress-strain relation. The shape of the energy density function is so chosen that if the deformation in the loading process exceeds a certain level it cannot return to the starting point along the original path with a decrease in loading.