Experimental analysis of cooling time reduction in SMA actuator through tuning of wire geometry and heat transfer process

Abstract Shape memory alloys (SMAs) are commonly used as linear actuators due to their capacity of achieving large excitation forces and displacements. These materials undergo phase transformation at specific temperatures related to austenite and martensite phase transformations, in which SMA shows a large change in modulus of elasticity when heated above or cooled below the phase transformation temperatures. However, the main drawback of current SMA actuators is their low actuation frequency, which makes the actuators unsuitable for controlling the response of dynamic systems. The frequency of the actuator is inversely associated with the total time taken by the actuator to complete a cycle. Decreasing the total time can lead to an increase in the actuator frequency, which can be reduced by either decreasing the heating or the cooling time. Typically, the cooling time is significantly longer than the associated heating time in SMA. The response of SMA actuators would be faster if the cooling time is reduced substantially. This work explains some effective techniques to decrease the cooling time of SMA-based actuators. To reduce actuator cooling time and improve actuation frequency, multiple thin SMA wires can be arranged in pennate configurations with varying cross-sectional areas, thereby enhancing heat dissipation and accelerating the cooling rate. In addition, the effect of various cooling agents is investigated with the objective of achieving reduced cooling times. It is envisaged that the combined implementation of these techniques could significantly enhance the cooling efficiency, thereby improving the frequency range applicability of SMA based actuators.