Effect of variable material properties and environmental conditions on thermomechanical phase transformations in shape memory alloy wires

This paper reports a computational study of the impact of variable material properties and environmental conditions (thermal boundary conditions and convection coefficients) on shape memory alloy wires undergoing (i) zero-stress, thermally-induced phase transformations, and (ii) stress-induced phase transformations at constant stress rates. A finite difference numerical approach has been employed, and has been validated by comparing with two analytical solutions. The results have been all given in non-dimensional form, and within the context of the range of parameters that have been studied, the following recommendations can be made for shape memory alloys (SMA) actuator design: (i) an uncertainty in the thermal boundary condition is not as important as long as the design process allows for a full transformation back to martensite at the end of a cycle of martensite–austenite–martensite thermal transformation, (ii) uncertainties in the thermal boundary condition, convection coefficient and thermal material properties are not as important when the phase transformation in a SMA is induced by stress.