SMAs under applied stress generate a recovery stress and strain due to heating of them.  Developments of SMA actuators using this property are being carried out.  SMAs allow reduction in size and weight, and construction simplification of actuators because SMA actuators require no sensor. Also, SMA actuators have the advantage of being high power even if they are light.

Ti-Ni-Cu alloys are being expected to be used in SMA actuators, because the recovery stress increases and the stress hysteresis and transformation temperature hysteresis decrease with increasing copper content in the alloys. However, it is reported that the recovery stress and the transformation temperature of SMAs are influenced by manufacturing processes such as processing rate and aging treatment.

This study carried out heating-cooling tests under constrained strain using the aged specimen, for studying the effect of aging on thermomechanical properties of Ti-Ni-Cu alloy. Furthermore, the variation of electric resistivity during the heating-cooling test was measured, and the effect of aging on electric characteristic of Ti-Ni-Cu alloy was also discussed.

The recovery stress decreases with increasing aging temperature. Also, the temperature response increases with increasing aging temperature. However, there has been little effect of aging temperature on the transformation temperature hysteresis.