Spatially Distributed Actuation of Shape Memory Alloy Knitted Composites

Shape Memory Alloy (SMA) knitted structures provide complex distributed three-dimensional actuation motions. The kinematic actuation performance is tailorable through the continuous network of loops called knit patterns. By varying the knit pattern, many complex actuation motions are possible (contraction, furling, coiling, arching, etc.). One knit pattern, rib knit pattern, is of particular interest because it actuates to form a corrugated surface, which has potential use in boundary layer flow control applications. Current SMA rib knit pattern actuators rely on environmental heating for actuation, prohibiting localized actuation and limiting the types of applications. Additionally, the open structure of the knitted actuator cannot be used as an aerodynamic surface. This work addresses implementation-related research issues to enable the spatially distributed actuation of SMA knitted composites. Actuation of individual ribs within the corrugated structure is achieved by Joule heating regions of the knitted structure above the Austenite finish temperature. The geometric parameters of the interlacing network of adjacent loops are used to create a geometric model consisting of the loop height, loop width, and interlacing loop lengths. The lengths in the geometric model are converted to a linear segment resistive model with state-based resistivity. The model predicts the number of rows activated by a single electrical contact and informs the selection of positive and negative terminals to achieve distributed actuation of the rib knit. The SMA knit and electrical terminals were embedded in a flexible composite. Spatially distributed actuation of SMA knitted composites provide unique surface actuation motions for diverse applications.