Design, Development and Validation of an Experimental Test Bed for SMA Actuators

Abstract

The actuation behavior of Shape Memory Alloy (SMA) is not yet fully understood due to their nonlinear and hysteretic behavior. Moreover, the data provided by the manufacturers are not exhaustive and can therefore, only be used as a guideline. The SMA actuation behavior depends on environmental temperature, bias load, cycle time and actuation current. Hence measurement of actuation characteristics is required in order to effectively utilize these actuators for a particular application. An experimental test bed was designed and developed to characterize SMA actuators. The test bed was validated by conducting the tests on a commercially available SMA actuator of diameter 0.15 mm. The strain during actuation was measured with Laser displacement sensor. Load cell was used to measure bias load on SMA wire. National Instruments FPGA based controller myRio with LabVIEW software was used for cyclic actuation. The tests were conducted using constant current circuit specially developed for the test bed. The SMA actuator was actuated with 200-400mA currents for 1 second. A bias load resulting in the recommended stress of 100 MPa was used. Actuation strains recorded were within the guidelines provided by the manufacturer.