On the thermomechanics of shape memory wires

The thermomechanical behavior of a shape memory wire is modeled based on a theory that takes cognizance of the fact that the body can possess multiple natural configurations [1]. The constitutive equations are developed by fi rst constructing the form of the Helmholtz potential (based on different mo des of energy storage), and dissipation mechanisms. The internal energy inc ludes contributions from the strain energy, the latent energy, the interfac ial energy and thermal energy. The entropy of the system includes the "entr opy jump" associated with the phase transition. The role of the rate of mechanical dissipation as a mechanism for entropy g eneration and its importance in describing the hysteretic behavior is broug ht out by considering the difference between hysteretic and non-hysteretic (dissipation-less) behavior. Finally, simple linear or quadratic forms are assumed for the various const itutive functions and the full shape memory response is modeled. A procedur e for the determination of the constants is also indicated and the constant s for two systems (CuZnAl and NiTi) are calculated from published experimen tal data (see [2, 3]). The predictions of the theory show remarkable agreem ent with the experimental data. However, some of the results predicted by t he theory are different from the experimental results reported in Huo and M uller [2] We discuss some of the issues regarding this discrepancy and show that there appears to be some internal inconsistency between the experimen tal data reported in Figure 6 and Figure 9 of Huo and Muller [2] (provided they represent the same sample).