Micromechanical constitutive model considering plasticity for super-elastic NiTi shape memory alloy

Experimental results show that, for super-elastic NiTi shape memory alloy, the transformation start stress from austenitic to stress-induced martensitic phase increases with the increase of ambient temperature. When the ambient temperature increases to a critical value, a residual strain occurs after tensile test with one loading–unloading cycle due to the dislocation slip in austenitic phase. Based on the experimental observation, a single crystal constitutive model considering both transformation and plasticity is first established in the framework of thermodynamics, and interaction energy is introduced into the Helmholtz free energy in order to consider the effect of plasticity on the transformation. Then, an explicit scale-transition rule is adopted in the proposed micromechanical constitutive model to obtain the polycrystalline behavior of super-elastic NiTi alloy. Finally, the capability of the proposed micromechanical model to describe the temperature-dependent super-elasticity of NiTi alloy is verified by comparing the predictions with corresponding experiments.