Plastic fluctuations in a knitted fabric

A knitted fabric is a topologically constrained elastic yarn following a periodic path. The mechanical behavior of the fabric appears to be drastically different from the yarn it is made of. To explain this discrepancy, we introduced a network model which features three ingredients, a dominant bending energy, an unaltered topology and yarn length conservation. This model provides a quantitative comparison with experiments done on a model knitted fabric, both in the force-elongation relation and in the deformation field. However, yarn-yarn friction at the crossing points induces fluctuations around elasticity in the force response and deformation field. The fluctuations are identified as sudden drops of the force correlated with localized lines of deformation in the network, and are caused by the propagation of stick-slip events at contact points. The plastic events are characterized and their properties predicted owing to the network constraints that still apply. A good understanding of the friction induced plastic events allows quantitative comparison with similar plastic events arising in other a-thermal soft amorphous solids.