| dc.description.abstract | The properties of shape memory alloy (SMA) wires have long been leveraged in a variety of industries. Straight wires using the shape memory effect have been used as linear actuators in applications that range from valve actuation to robotic grippers, while wires using the pseudoelastic effect have been used in medical devices such as guidewires and stents for years. While properties of straight wire-formed SMA are well understood, complex geometries developed from SMA wire such as knits are less explored. Early experimental results indicate that such geometries have structural advantages in bending and are more flexible than weaves and meshes (which use mostly straight wire). SMA knits are therefore a good candidate for medical and bio-compatible devices, as the human body often demands flexibility, particularly in limbs and joints. In addition, knitted structures have the unique ability to be tailorable in both structure and material for improved shaping and variation structural response compared with weave-based fabrics. Knitting techniques and patterns developed in the textile industry allow for variable materials and geometries in the same structure, allowing for a large range of tailored macro-structure responses based on knit pattern alone.
Current models for these types of smart structures are simplistic, however. Out of plane deformation and 3D geometry of stitches are ignored, and contact interactions between stitches are considered only as constraints on stitch motion. This work seeks to develop and validate a finite element model for SMA knitted structures incorporating the Boyd-Lagoudas SMA transformation model. A representative volume element (RVE) is developed for a common knit pattern, and macro-structure response is explored and experimentally validated. This research provides a foundation for better understanding fundamental capabilities and responses of knitted SMA structures, allowing for better design, functionality, and customizability of the existing devices that use them and enabling new designs. | en |
