Crystal plasticity based constitutive model of NiTi shape memory alloy considering different mechanisms of inelastic deformation

To comprehensively describe the deformation behaviors of polycrystalline NiTi shape memory alloy under various thermo-mechanical loading conditions, a micromechanical constitutive model is constructed based on crystal plasticity. At the scale of single crystal, 24 martensite variants are introduced. Different mechanisms of inelastic deformation in the NiTi shape memory alloy, including martensite transformation, martensite reorientation and detwinning, dislocation slipping in the austenite and twinning in the martensite, are considered in the proposed model. The Helmholtz free energy for the representative volume element of a single crystal is constructed and the thermodynamic driving forces of internal variables are obtained from the dissipative inequalities. The evolution equations of internal variables are deduced in power-law forms. The differences of elastic properties between the austenite and martensite phases, as well as the restraint effect of twinning in the martensite on the reverse transformation, are considered. A simplified explicit scale-transition rule is adopted to extend the single crystal model to a polycrystalline version. Finally, the capability of proposed model to describe the various thermo-mechanical deformation behaviors of polycrystalline NiTi alloy is verified by comparing the simulated results with the experimental ones.