Shear and tensile thermomechanical behavior of near equiatomic NiTi alloy

The industrial development of devices using the intriguing properties of shape memory alloys involves accurate prediction of their thermomechanical behavior. This may be achieved using Computer Aided Design together with Finite Element programs. Reliable constitutive laws are needed for the execution of such programs. Several tensorial constitutive laws have been proposed to model the unusual thermomechanical properties of shape memory alloys. However, for all these tensorial models, it is necessary to make assumptions which cannot be verified when only tensile property data are available. The purpose of this paper is to present a new set of experimental mechanical data, including tensile and simple shear tests performed on sheet samples of near equiatomic NiTi alloy. Both mechanical behaviors are compared for a large temperature range (from below Mf to above Af). It is shown that the von Mises assumptions usually made in the establishment of tensorial constitutive equations are not always valid. Other yield locus forms are proposed to model the typical tension and simple shear thermomechanical behavior of shape memory alloys.