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 thermomec hanical behavior. This may be achieved using Computer Aided Design tog ether with Finite Element programs. Reliable constitutive laws are nee ded for the execution of such programs. Several tensorial constitutive laws have been proposed to model the unusual thermomechanical propert ies of shape memory alloys. However, for all these tensorial models, i t is necessary to make assumptions which cannot be verified when only tensile property data are available. The purpose of this paper is to p resent a new set of experimental mechanical data, including tensile an d simple shear tests performed on sheet samples of near equiatomic NiT i alloy. Both mechanical behaviors are compared for a large temperatur e range (from below Mf to above Af). It is shown that the von Mises as sumptions usually made in the establishment of tensorial constitutive equations are not always valid. Other yield locus forms are proposed t o model the typical tension and simple shear thermomechanical behavior of shape memory alloys.