Physicists often think of socks and other knitted fabrics as ‘metamaterials’ — that is, their macroscopic properties are determined by patterning at intermediate, rather than microscopic, scales. This is why scarves and socks are stretchy even if the yarn they are made of is not. But predicting the elasticity and other physical properties of knits from first principles has been a long-standing challenge.
Samuel Poincloux at the École Normale Supérieure in Paris and his collaborators created a mathematical model of a common type of knit as it is deformed. In the model, a knitted fabric placed under tension reacts in a way that minimizes the energy needed to displace its fibres.
The researchers then used their model to make quantitative predictions, which matched the team’s measurements of knitted nylon fishing line as it was stretched. The authors say that a better understanding of these metamaterials could facilitate the development of ‘smart’, self-shaping materials for building robots.