Phase proportioning in CuAlBe shape memory alloys under thermomechanical loadings using electric resistance measurements

The microstructure of shape memory alloys changes with the thermomechanical history of the material. Under thermomechanical loadings there can be at most three phases present in the material: austenite, autoaccommodated martensite or oriented martensite. In applications integrating SMA parts, utilization conditions affect seriously the present phases and can generate macroscopic strain or stress. Consequently, under different shapes of thermomechanical loading, it is important to be able to proportion the different phases and to understand the kinetic of phase transformation. This is very useful in the development of constitutive equations of behavior models. In this study, we propose a simple method based on the measurement of the variation of electric resistance of CuAlBe wires to evaluate the volume fraction of austenite, oriented martensite and also autoaccommodated martensite. This method is generalized to the most common loadings used in the applications: pseudoplasticity, recovery stress and assisted memory effect. The proportioning method is based on a mixture law integrating the resistivity of pure phases present in the SMA.