Analysis of thermomechanical behaviour of Nitinol wires with high strain rates

From experimental evidence it has been possible to conclude that the strain rate has a great effect on the shape memory alloy load-displacement response. Because in some applications, for example the case for dissipative devices, the strain rate varies over a wide range, it is very important to be able to predict the mechanical behaviour of these materials. As regards this aspect of shape memory alloys, there are many analytical models able to predict the stress field related to deformations that the material is subjected to, but they are valid only in static loading cases. In the case of high strain rates, it is necessary to couple to a mechanical model an equation able to account for internal heat produced both as phase transition latent heat and by mechanical dissipation. In this paper, on the basis of Tanaka's model, we try to predict the mechanical behaviour of NiTi wires subjected to tensile tests with various strain rates (ε = 0.0001,0.001,0.1, 0.5 s-1); numerical results are compared with experimental results.