Quantifying the Elastic Nature of Knitted Materials

Knitted materials involve the manipulation of a 1D material into a complex 2D sheet. We manipulate yarn into a lattice of slip-knots, known as stitches, where the types of stitches have significant impact on the resulting fabric and its elastic properties. The constituent yarn is normally inextensible, yet when manipulated into these stitches, the fabric possesses emergent elastic behavior. We show through uniaxial applied strain experiments that the bulk stress-strain relationship of knitted fabrics have two key regimes: a linear response in the low stress regime and a nonlinear response with increasing stress. The length of the low stress regime corresponds to the softness of the fabrics and how extensile the stitch patterns are from their topology. The nonlinear regime stems from the yarn to yarn interactions; eventually as the stitches are stretched, they reach a point where the stitch can no longer deform and the yarn must stretch. We characterize the non-affine deformation of the fabrics by tracking a 5 by 5 grid of points while undergoing deformation. We quantify the programmable nature of knitting and extract parameters to create a continuum model of knitted materials.