Tying Together Yarn Compression and Knit Fabric Jamming

The mechanical response of knitted fabrics is typically characterized by a soft, bending-dominated linear elastic response at low strain, followed by strain-stiffening due to yarn compression and contacts. However, when a fabric is very tightly knit, we see an additional response in the very low strain region where the modulus starts out stiff and then softens. This low-strain high-modulus behavior in knitted fabrics is known as jamming. Using computational simulations of stockinette fabric, we present a new energy marker for jammed knit fabrics that shows that the rest state of the fabric is not a minimum contact energy state. Instead, the stitches reach a contact energy minima when the fabric is stretched and leaves the jammed regime. This contact energy marker shows how the jammed regime changes as a function of yarn compressibility; yarns close to the incompressible limit show a sharp jamming transition while yarns further from the in-compressible limit have a soft transition. *This work is funded by NSF 1847172