THE TORSIONAL BEHAVIOR OF SINGLES YARNS .1. THEORY

The same fundamental approach that has previously been found reasonabl y accurate in predicting the tensile behaviour of bulky singles yarns at small extensions of up to 10 % is used here to model yarn torsion. The theoretical analysis is based on discrete-fibre-modelling principl es, an energy method, and a 'shortest-path' hypothesis. It is applied to the twisting behaviour of bulky singles yarns which may have non-un iform fibre-packing-density across their cross-sections. The twisting of a yam both under constant yarn length and under constant yarn tensi on is modelled. The contributions to yarn torque due to fibre tension, fibre torsion, and fibre-bending can all be calculated, Comparison of the theoretical models with some experimental data will be presented in Part II.