Energy balance of thermoelastic martensite transformation under stress

Energy balances of pseudoelastic behaviour of a shape memory alloy are experimentally determined using IR techniques. In fact, these balances, established for Cu-Zn-Al alloy at constant room temperature and under quasi-static tensile conditions, allow us to study the relative importance of the intrinsic (mechanical) dissipation involved in austenite-martensite phase changes compared with thermomechancial couplings. An analysis of the experimental data shows that the thermoelastic austenite-martensite phase transition can be considered as a non-isothermal process involving no or little (hardly measureable) mechanical dissipation. Assuming a non-dissipative phase transition, numerical simulations are done in the case of non-isothermal processes using two existing models. This numerical exercise gives mechanical, thermal and energetic responses that can be qualitatively compared with those obtained experimentally. These results evidence that an intrinsic dissipation is not necessary to describe the pseudoelastic behaviour. In general, this example emphasizes once again that thermal and mechanical analyses should be carried out jointly to characterize properties of materials.