Effects of thermo-mechanical cycling on the strain response of Ni–Ti–Cu shape memory alloy wire actuator

The present paper deals with the strain response of Ni–Ti–Cu shape memory alloy (SMA) wire actuators on thermo-mechanical cycling (TMC). The characteristics of the actuators such as austenite (hot shape) remnant deformation and recovery strain undergo changes upon TMC. These changes are significant in the initial few cycles and the properties of SMA tend to reach a steady state on further cycling. It is believed that TMC induces defects in the microstructure and stabilizes the martensite/austenite phase. These in turn result in continuous change in strain response with the progress of TMC. It has been shown that for a stable strain response, the wire actuators need to be subjected to TMC at a higher stress than the working stress prior to application. Experiments were also conducted in order to minimize the number of TMC required for achieving stable strain response.