Laddering of a knitted fabric: a topology-induced failure

TL;DR

This study investigates laddering in knitted fabrics, revealing how initial tension influences defect propagation, with findings on velocity scaling and damage prediction relevant for damage mitigation.

Contribution

It introduces a combined experimental and simulation approach to understand the mechanics of laddering and proposes a model for damage prediction based on tension and wave velocity.

Findings

Laddering velocity scales linearly with fabric tension.

A force threshold due to stitch curvature controls defect propagation.

Damage can be predicted at moderate tension levels.

Abstract

Laddering is the propagation of a topological defect in an everyday-life material: weft knitted fabrics, following a broken thread or a dropped stitch. What is a minor frustration when damaging a pair of tights is a more serious issue for industrial-scale production, but might inspire new solutions to limit and mitigate damage to architected materials. In this work, laddering is investigated in a pre-stressed model knit through experiments and Discrete Element Rod simulations. The control parameter is the initial tension applied on the fabric. A force threshold due to the stitch's natural curvature is evidenced. It controls both the propagation onset and arrest, as tension is relaxed by the thread length freed by ladder growth, and enables damage prediction at moderate tension. Furthermore, we uncovered that the laddering velocity is of the order of the velocity of bending waves and exhibits an unexpected linear scaling with the fabric tension, that arises from a complex combination of elastic and friction forces. Finally, we discuss the implications of our results from the perspective of damage control and mitigation.