Chelsea Knittel2 1 Oana Ghita3 Ken Evans3 Genevieve Dion1 4

2, Drexel University, Philadelphia, Pennsylvania, United States
1, Drexel University, Philadelphia, Pennsylvania, United States
3, University of Exeter, Exeter, , United Kingdom
4, Drexel University, Philadelphia, Pennsylvania, United States

Traditional textile fabrication technologies, such as weft knitting machines, have existed for over 400 years, providing automated methods of producing textiles both in the form of continuous cloth or as shaped 3D forms. The versatility of this production process is being used as a tool for development of the next generation of fabrics: smart textiles and garment devices. While this platform offers efficiency in production, the design and development stages are lacking the modeling sophistication found in modern manufacturing techniques such as 3D printing and composite fabrication.
In weft knitting specifically, basic building blocks, the knit and purl stitch, can be combined into a limitless number of patterns to produce novel textile structures with tunable properties. The interaction of these two stitch types in varying geometric patterns produces relief structures that self-fold due to yarn relaxation, producing highly dimensional and variable textiles architectures. The complexity and range of forms that can be achieved with this technique lend themselves to a variety of engineering and design applications. Several researchers have begun investigating the use of weft knit structures for textile property enhancement. This has included increased impact resistance, sound absorption and auxetic behavior. The variable dimensionality of these structures combined with new active materials could be applied to smart textile innovations including fabrics with engineered moisture or heat transfer properties, origami-inspired folding structures such as those used in satellite design, and assistive garments that could enhance movement or strength through use of articulated segments. These textiles could also be used to add structural design elements in architecture and interiors. However, before these novel textiles can be efficiently designed and produced, we must develop means of predicting their formation. Current textile modeling software can accurately render stitch patterns and yarns, but cannot provide predictions regarding the physical behavior of the structures due to yarn relaxation. This leaves the design of complex relief structures to the process of trial and error, slowing production and leading to material waste.
Here we investigate methods of predicting the relaxation and self-folding behavior of complex weft knit patterns through study of mechanical properties of basic self-folding structures. On the stitch level, all knit-purl structure designs are produced using combinations of four variations of transition between knit and purl, defined by their relationship to the axis of manufacture. By assigning magnitudes of forces to these fundamental building blocks, we can correlate measured mechanical properties to basic self-folding behavior. In this work, we demonstrate methods of measuring the forces driving self-folding and discuss how this information will be used to predict more complex behaviors.