Transient Thermal Stresses in a Superelastic Shape Memory Alloy Strip.

Abstract

The austenitic Shape Memory Alloy (SMA) can be loaded up to a large strain without any plastic deformation and behaves superelastically (pseudelastically) above its characteristic transition temperature. When loaded, the superelastic SMA undergoes a stress-induced martensitic transformation that will result in a large recoverable strain up to 8%. On unloading, the superelastic SMA experiences a large hysteresis loop that makes the alloy an useful candidate for strain energy absorption. By taking advantage of this effect, SMA is used in various fields. The SMA can be used to improve the impact damage tolerance of composite materials and to induce the relaxation of stress distribution. This investigation deals with the transient thermoelastic problem for a superelastic SMA strip under the heat exchange. In order to simplify the SMA model, a linearization of one dimensional constitutive equations is made. The piecewise linear stress-strain relation is separated into two parts : before and after the stress-induced martensitic phase transformation. Another assumption is the identical SMA stress-strain relation in tension and in compression. Results for the temperature and stresses distributions are obtained numerically. We discuss about the variation of the martensitic phase and the thermal stress relaxation.