Pulling apart the mechanisms that lead to jammed knitted fabrics

TL;DR

This paper explores how geometric confinement causes jammed knitted fabrics to initially resist deformation and then soften, with fabric jamming influenced by yarn properties and manufacturing parameters, revealing mechanisms behind their mechanical behavior.

Contribution

It uncovers the geometric and contact rearrangement mechanisms that lead to fabric jamming and demonstrates how manufacturing parameters can control this behavior.

Findings

Jammed fabrics exhibit a transition from stiff to soft response due to yarn geometry changes.

Adjusting stitch size affects yarn radius and length, influencing jamming behavior.

Rearrangements in yarn contacts facilitate relaxation of residual forces.

Abstract

We investigate the mechanical behavior of jammed knitted fabrics, where geometric confinement leads to an initially stiff mechanical response that softens into low stiffness behavior with additional applied stress. We show that the jammed regime is distinguished by changes in yarn geometry and contact rearrangement that must occur to allow the individual stitches to stretch. These rearrangements allow for the relaxation of high residual contact forces that are present within jammed fabric, altering the low-strain response. We demonstrate that fabric jamming can be induced or reduced by changing either the constituent yarn or the fabric manufacturing parameters. Analysis of experimental samples shows that changing the "stitch size" in manufacturing affects both the in situ yarn radius and the length of yarn per stitch, both of which affect jamming.