Phase-field theory based finite element simulation on thermo-mechanical cyclic deformation of polycrystalline super-elastic NiTi shape memory alloy

Based on the previously developed isothermal phase field model [1], the thermo-mechanical cyclic deformation of polycrystalline super-elastic NiTi shape memory alloy (SMA) was simulated by a newly proposed thermomechanical phase filed based finite element method. To ensure the efficiency of numerical simulation, a twodimensional (2D) phase field based finite element method was proposed. From the simulations, it is concluded that the cyclic super-elasticity degradation and related phase transition mode of polycrystalline NiTi SMA and their dependence on the loading rate and loading level are reasonably modeled. Furthermore, correspondent physical mechanism is summarized, that is, the cyclic degradation of super-elasticity and the localization of phase transition (especially for that in the stable cycle) become more significant by increasing loading level and loading rate, but the physical mechanisms of them are different: they are attributed to the increase of residual martensite bands resulted from the expansion of relatively large plastic deformation domain in the polycrystalline NiTi SMA if increasing the loading level; while, if increasing the loading rate, they are attributed to the increase of residual martensite bands resulted from the impediment of thermo-mechanical coupled effect to the phase transition.