A study on high-speed actuation of Shape Memory Alloy

The main problem with Shape Memory Alloy (SMA) actuators is their slow response speed. Current SMA actuators work in tens of seconds though they can generate large force and displacement outputs. The objective of the research in this paper is to improve the response speed of SMA actuators to 10 milliseconds or less. SMA actuators are driven by thermal energy and their slow response is attributed to the inefficient heat transfer. To improve the response, direct Ohmic heating was used in the experiments. The SMA actuators used in this study are Ti-Ni-Cu columns of phi 5x50 mm with residual strain produced upon unloading after 5.3% axial compression. The transient displacement response of the SMA actuators without axial constraint and the transient force response of the actuators under axial constraint were measured with direct heating. The shortest response time achieved for unconstrained actuators is 4.6 ms and that for constrained actuators is 6.5 ms. The average value of maximum recovery force is 10.8kN, which corresponds to 550MPa of recovery stress. It was also found that constrained actuators need about 50% more energy for heating than unconstrained actuators.