Curling Morphology of Knitted Fabrics: Structure and Mechanics

The plain stitch consists of periodic lattices of characteristic Ω-shaped yarns, with 3D curling emerging at the edges. While previous studies have focused on 2D models, the relation between 3D geometry and mechanics remains unclear. Through experiments and simulations, we show that the curling behavior emerges through the elasticity and geometry of the knitted loops. By changing the knitting numbers, three types of curl shapes emerge: side curl and top/bottom curl shapes, which are curled only horizontally and vertically, and double curl shape, in which both curl shapes appear together. We uncover that the knit is side-curled when the knitted loop is vertically elongated, while double and top/bottom curl as the loop becomes horizontally elongated. Furthermore, this characteristic loop shape affects the mechanical properties of knitted fabrics. To simplify the 3D deformation of the knitted loop shape, we performed a compression test for half of the single knitted loop by modeling the knitting yarn as an elastic rod. The constrained rod undergoes the pop-up transition, depending on the aspect ratio of the knitted loop shape. Our results imply that the change in shape per a single knitted loop has the potential to control the 3D shape of knitted fabrics.