The effect of yarn mechanics on the non-linear elasticity of knitted textiles

Knitted fabrics are composed of single strands of yarn manipulated into complex lattices of slipknots. These fabrics exhibit emergent elastic properties. Their stress-strain relationships indicate the existence of a linear, low-stress regime and a non-linear, high-stress regime. Prior study has determined that the low-stress behavior can largely be explained by the stitch composition of the fabric: which stitches are used, their topology, and how they are patterned. Under high-stress however, the stitches themselves quickly reach their maximum deformation. At this point, the constituent yarn’s material properties, particularly its compressibility and, to a lesser extent, bending modulus, dictate these elastic properties. Additionally, simulations have shown that the property dominating fabric behavior may be influenced by the direction of applied stress on the fabrics. In order to understand the effect of yarn type on fabric behavior, we perform uniaxial applied strain experiments on fabrics of the same structure, but varying constituent yarn types. We further characterize the effects of yarn compression and bending by performing similar experiments in alternate directions on an array of yarn types and analyzing their stress-strain relationship. This will enable us to develop a constitutive model for knitted fabrics based on both the stitch pattern topology and the underlying mechanics of the yarn itself.