Constitutive modelling of transformation pattern in superelastic NiTi shape memory alloy under cyclic loading

In this paper, multiple cases of cyclic loadings on superelastic NiTi are studied experimentally and then numerically by means of finite element simulations. A novel constitutive framework is proposed to account for cyclic response of superelastic NiTi shape memory alloy. Martensitic transformation and degradation of mechanical properties are taken into consideration. The mechanical instability is involved in the model to reproduce transformation pattern under primarily tensile stress states. The Helmholtz free energy of the representative volume element is derived and the evolutions of internal variables are obtained keeping to dissipative inequality. Based on backward Euler integration scheme, the model is implemented implicitly into a finite element code. By comparing the simulation results with the experimental ones, it is verified that the proposed approach captures the features of the cyclic response and the associated strain pattern reasonably.