A macroscopic multi-mechanism based constitutive model for the thermo-mechanical cyclic degeneration of shape memory effect of NiTi shape memory alloy

A macroscopic based multi-mechanism constitu-tive model is constructed in the framework of irreversible thermodynamics to describe the degeneration of shape mem-ory effect occurring in the thermo-mechanical cyclic defor-mation of NiTi shape memory alloys (SMAs). Three phases, austenite A, twinned martensite M t and detwinned marten-site M d , as well as the phase transitions occurring between each pair of phases (A → Mt, Mt → A, A → Md, Md → A, and Mt → Md) are considered in the pro-posed model. Meanwhile, two kinds of inelastic deformation mechanisms, martensite transformation-induced plasticity and reorientation-induced plasticity, are used to explain the degeneration of shape memory effects of NiTi SMAs. The evolution equations of internal variables are proposed by attributing the degeneration of shape memory effect to the interaction between the three phases (A, M t , and M d ) and plastic deformation. Finally, the capability of the proposed model is verified by comparing the predictions with the experimental results of NiTi SMAs. It is shown that the degeneration of shape memory effect and its dependence on the loading level can be reasonably described by the proposed model.