3D Thermomechanical Model for SMA Behaviors Under Different Type of Cyclic Loadings Enriched by an Experimental Study of the Transformation Kinetic

Shape memory alloys present a phase transformation under thermomechanical loadings leading to a large reversible strain. This reversibility permits the development of original applications in various domains like biomedical, aerospace, transport, civil engineering, etc.

In order to dimension correctly these applications, a macroscopic model which permits to describe the thermo­mechanical behaviors of SMA under complex cyclic loadings has been developed. It is the extension of the previous models of Saint-­Sulpice et al. [1,2]. In this model, at the macroscopic scale, three states of the material have been defined: the austenite, the thermally induced martensite and the stress induced martensite. Different transformation surfaces [1,3] have been used to define correctly all the possible transformations introduced in the material during the different thermo­mechanical loadings. This model describes also the cyclic effects. As it is known, a residual strain under cyclic loadings is developed in these materials like ratcheting effect in plasticity. The origin of the evolution of the residual strain can be the jammed martensite or the plasticity [2,4].The evolution of the developed residual strain has been described according to the two possible origins.

The material parameters of the developed model have been identified using some tensile cyclic tests realized on a superelastic SMA. Then it has been validated using various thermomechanical cyclic tests as assisted shape memory effect at low and high stress level and complex multiaxial non-proportional loadings. In all these cases, a particular attention has been paid to the transformation kinetics obtained by the model and also by the realized tests.