SIMPLE-MODEL OF HYSTERESIS IN THERMOELASTIC MARTENSITIC TRANSFORMATIONS

To attain a better understanding of the hysteretic behaviour in shape memory alloys we present in this work a simple phenomenological model based on the thermoelastic balance that must be fulfilled at every step of transformation. The model is built on the simplest choice for the chemical and non-chemical free energies, that is, a first order dependence of these functions on T and x (transformed fraction) respectively. From this choice, some considerations are made on the contributions to the non-chemical energy that should be taken and their physical meaning. Apart from the global hysteresis loop, the model is able to describe the subloop behaviour which, in spite of its interest from the point of view of many applications, is not well known. The study of subloops in the frame of the model leads to discuss the location of the starting temperatures for the forward and reverse partial transformations in relation to the dissipative terms.