RELAXATION IN SHAPE-MEMORY ALLOYS .1. MECHANICAL MODEL

A variety of relaxation phenomena such as the stabilization of martens ite, rubber-like behavior, evolving hysteresis loops and stabilization of interfaces have been observed in various shape-memory alloys. Thes e effects adversely impact technological applications. Despite a great deal of experimental evidence, there is no consensus on the mechanism . However, there is universal agreement on certain fundamental aspects of these phenomena. Based on these areas of agreement, we propose a p henomenological, but predictive, model in this paper. This model is ba sed on the framework of thermoelasticity augmented with an internal va riable. In this part, we discuss the basic mechanical model and show t hat it reproduces the experimental observations remarkably well. In Pa rt II of this paper, we extend this model to include thermal effects a nd use these models to propose new experiments in order to clarify lon gstanding issues. (C) 1997 Acta Metallurgica Inc.