Mechanical properties and contractile force mechanism of shape memory alloy knitted fabric actuator

The purpose of this research is to clarify the contractile force mechanism of a shape memory alloy (SMA) knitted fabric actuator. We knitted SMA yarn with plain stitches. We then determined the limit up to which SMA plain knitted fabric can be uniaxially elongated and thereafter the original dimensions can be recovered through its repeated heating. Moreover, the temperature dependence of SMA plain knitted fabric in the case of contractile force is quantitatively evaluated experimentally by heating it and then measuring its tension after it is extended to a certain length and fixed at both ends. The results show that, in its wale direction, the maximum tension by heating exceeds the tension corresponding to the extension. Furthermore, it is confirmed that theoretical calculations for the tensile properties of the knitted fabric of spun yarn and filament yarn can be applied to plain knitted fabric of SMA yarn. Using this theoretical calculation, and the flexural rigidity measured by KES system, it is clarified the contractile force of the SMA knitted fabric actuator is affected not only by contraction of SMA yarn but also an increase in its flexural rigidity. © 2019 The Textile Machinery Society of Japan.