Macroscopic constitutive law of shape memory alloy thermomechanical behaviour. Application to structure computation by FEM

In this study, a phenomenological model describing superelasticity, shape memory effect under constant stress and the reorientation process in the martensitic phase is proposed. This model is based on a thermodynamical description of the phase transformation which involves two internal variables: the overall martensite volume fraction and the mean transformation strain. An explicit Gibbs free energy expression is deduced from micromechanical considerations. The evolution laws of the internal variables are derived from this potential, assuming a symmetry of the behaviour between tension and compression and considering only proportional loadings. The behaviour of a representative volume element (RVE) of SMA is deduced and the model is implemented in the ABAQUS finite elements software. Results for uniaxial tensile loadings and a three-point bending test are analysed.