Extensions, displacements and forces associated with pulling a single yarn from a fabric

Abstract

This paper describes some of the yarn deformations and relative movements between yarns which occur when an isolated yarn is pulled through 20 crossover yarns out of an untreated cotton weave which has a relatively open and regular structure. The described deformations are of two kinds: linear extension in the selected yarn and the bending of the yarns which intersect its path. These processes occur at relatively low-tensile forces (50*10^-2 N) produce irreversible deformations where the pulled yarn begins to progressively slide over the crossover yarns. As the pulled yarn is drawn from the weave the associated force decreases in discrete steps in proportion to the number of residual crossover points. The paper does not deal with the movement of the yarns normal to the direction of the tensile force. A simple linear elastic model is developed to describe the interrelationship between the extensibility of the pull-out yarn and the effective elastic shear resistance of the neighbouring yarns prior to inter-yarn junction slip. The tensile stiffness of the yarn is significantly greater than the stiffness in shear of the locally deformed yarn. The maximum pull-out force is a measure of the static friction or adhesive rupture force of one contact and the decreasing force values after this point provide a value for the sliding friction of one junction; the former is approximately three times bigger than the latter.