Contractile Force and Stitch Modeling of Shape Memory Alloy Knitted Fabric Actuators

To improve the calculation accuracy of the contractile force in a shape memory alloy (SMA) knitted fabric actuator, which was developed in a previous study, we measured the Young's modulus, E , and wire diameter, d , of a SMA yarn in unheated (20 °C) and heated (100 °C) environments. Subsequently, the contractile force in the heated environment was calculated in terms of bending rigidity ( EI ) using the measured values of E and d . The accuracy of the theoretical contractile force, considering contraction and increment in EI , was improved when compared with that in the former one, which only considered contraction of the SMA yarn. Furthermore, to enhance calculation accuracy, we proposed a 2 dimensional stitch model for SMA plain knitted fabric. This model consisted of clothoid curves through four contact points, where each yarn crosses the other stitches and act forces. Further, this model could show the change in the curvature via the contraction of the yarn as well as the increase in its potential energy. Therefore, it was confirmed that this model is useful for calculating the contractile force of the SMA knitted fabric.