Determination of Shape Memory Alloys Fatigue Properties by Classic and Self-Heating Techniques

Shape Memory Alloys (SMA) are materials which are able to recover a large inelastic deformation (up to 8%) under thermomechanical loadings. It is due to a solid-solid diffusionless phase transformation called martensitic transformation. This interesting property makes these alloys suitable for the development of original applications in various domains like biomedical, transport, etc. The thermomechanical behavior of these alloys has been studied more and more since last years. These materials can generate different types of behavior. Superelasticity is one of these behaviors which is obtained under isothermal mechanical loading. This effect is widely used in applications. In recent years, many models have been developed to describe the behavior of these materials. But their fatigue is still a relatively unexplored area. Currently in the design phase of structures based on these materials, fatigue is not considered. In this study, we focus on superelastic SMA fatigue and also the self-heating phenomena. This study begins with a primary phase based on fatigue tests at low and high number of cycles under different loading. We look after two types of loading first we make classical tensile test and secondly we study rotating bending on SMA wires. By this way, Wöhler curves are obtained for different SMA. These tests permit to determine the fatigue mechanisms in these alloys and also to determine the phase transformation or process effects on the fatigue properties. In parallel, self-heating tests are carried out on the same materials to determine the fatigue properties of these materials by fast techniques. This fast characterization of fatigue properties is validated by comparing results of the two techniques.