Analysis and simulation on cyclic superelastical deformation behavior of TiNi shape memory alloy subjected to loading and unloading

Superelasticity is one of the important mechanical properties of shape memory alloy (SMA). In the present paper, the superelastic deformation behavior of TiNi SMA under various loading conditions with different experimental temperatures and strain rates was discussed based on the experimental studies. The change of transformation stress and the modulus of elasticity during cyclic deformation was analyzed from the continuum mechanical point of view. The cyclic superelastic deformation of TiNi SMA subjected to loading and unloading is characterized by introducing three internal variables, that is, the residual stress and strain which are accumulated during cycling and the residual martensite phase which is also accumulated. The method of simulating cyclic superelastic behavior deformation was proposed. The modulus of elasticity during the internal loop is expressed by the mixed rule with the function of transformation strain. It is important to design perfect SMA working elements and to evaluate their reliability.