Free Response of a Thermally Driven, Composite Actuator

A thermally driven force/displacement actuator may be fabricated from a composite consisting of a shape memory alloy (SMA) and an elastomer. A simple onedimensional device is described where a thin layer of SMA overlays an elastomer which is in turn bonded to a heat sink. A thermal response model is developed which includes the martensite fraction of the SMA, in addition to the effects of heat capacity of the composite and conductive resistance of the elastomer. Solutions, in terms of temperature-composition-time trajectories, for free response are obtained using different phase transition models. Calculations for a device consisting of Nitinol overlaying a typical elastomer show that rapid response, coupled with small power consumption, may be achieved if device size is kept small.