Micromechanical modelling on thermomechanical coupling of superelastic NiTi alloy

In the present study, a micromechanical constitutive model is proposed to account for the thermomechanical coupling of superelastic NiTi alloy. Martensitic transformation is treated as the shrinkage and expansion of martensite domain which is embedded in austenite matrix. The model is first constructed in the single crystal scale based on Mori-Tanaka homogenization, and is then extended to polycrystalline version via Taylor approximation. The energy balance equation and the driving force for martensitic transformation are derived from the first law and the second law of thermodynamics, respectively. The difference of elastic properties between austenite and martensite is taken into consideration, which makes the model generalized and physically robust. The thermomechanical response of NiTi deformed at various temperatures and strain rates under uniaxial and multiaxial loadings can be reproduced by the proposed approach to good accuracy.