Composite of knitted fabric and soft matrix. II. Laddering

Knitted fabrics are widely used in artificial tissues and flexible electronics. Understanding the failure of knitted fabrics is vital for their applications. Laddering is a common failure mode of knitted fabrics, where a broken yarn can unravel to form a ladder-like pattern. However, the underlying mechanics of laddering remain poorly understood. Here, we study the laddering process in knitted fabrics and their soft composites. For a knitted fabric with a pre-crack in the wale direction, yarns disentangle loop by loop ahead of the crack to initiate laddering. We find that the critical laddering stretch does not depend on the fabric height or loading speed, but on the yarn friction and fabric density. A higher yarn friction leads to a higher critical laddering stretch, and a sparser fabric density leads to a lower critical laddering stretch. We further explore how matrix toughness affects laddering in soft composites of knitted fabrics. Laddering occurs in the composite with a brittle matrix, but is suppressed in the composite with a tough matrix. This work may provide insights for designing knitted-fabric reinforced composites with improved structural reliability.