A micromechanical constitutive model for unusual temperature-dependent deformation of Mg–NiTi composites

Based on the mean-field approach, a micromechanical constitutive model is established to describe the unusual temperature-dependent deformation of Mg–NiTi composites. Firstly, the constitutive equations of two phases are proposed: for NiTi shape memory alloy (SMA), a simplified Hartl–Lagoudas model (Hartl and Lagoudas, 2009)which considering the martensite transformation and plastic deformation is adopted; while, for magnesium (Mg), an elastic-plastic model including a new nonlinear plastic hardening law is employed. The dependence of elastic moduli and yield surfaces of two phases at ambient temperature is addressed. Then, a non-isothermal incremental Mori–Tanaka homogenization method is employed and further extended to describe the interaction between two phases and calculate the macroscopic overall stress-strain response of Mg–NiTi composites. Finally, comparisons between the simulated results and the corresponding experimental ones show that the temperature-dependent deformation of the composites with different volume fractions of NiTi SMA phase can be well captured by the proposed model. Predicted results demonstrate that the unusual temperature-dependent deformation of Mg–NiTi composites originates from the change in the inelastic deformation mechanism of NiTi SMA with the variation of temperature.