Capturing corrugation, folding, and multi-stability in knit materials with an elastic continuum finite element model

Weft knitting is a method of fabric production in which a continuous horizontal yarn is interlooped with itself. Each loop is connected to its neighboring loops, forming a fabric. Notably, the individual stitches are asymmetric through the plane, which introduces internal stresses in the finished fabric and results in curling at the boundaries. Additionally, during manufacturing, stitches can either be added in the front-facing or back-facing directions, creating localized regions of opposite curvature. By designing where we use both types of stitches, we can realize a diverse array of resultant fabrics, some of which exhibit self-folding or multistability. While this complex behavior arises from interactions at the yarn level, continuum finite element simulations with well-known material models can accurately capture the experimentally observed behaviors, including out-of-plane curvature and a multi-welled energy landscape. We use this model to explore the vast geometric space, and expect it to allow us to design fabrics with particular target properties.