Generation of Recovery Stresses : Thermodynamic Modelling and Experimental Verification

Shape memory elements generate significant recovery stresses when the shape recovery associated with the reverse martensitic transformation is impeded during heating. This process of stress generation is influenced by many parameters. A fundamental model has been developed to describe this generation of recovery stresses. The model is based on a generalised thermodynamic analysis of shape memory behaviour. The mathematical approach and the assumptions in this model are selected in such a way that the calculations yield close approximations of the real behaviour and that the final mathematical equations are relatively simple. The paper presents also experimental measurements of recovery stress generation for complex restraining conditions. Comparison of the experimental results with the calculated results confm that this model can be used to predict quantitatively the generation of recovery stresses.