ANALYSIS OF THE TENSILE-STRENGTH OF PARALLEL-LAY ROPES AND BUNDLES OF PARALLEL ELEMENTS BY PROBABILITY-THEORY

A model for determining the tensile strength of parallel-lay ropes and bundles of parallel elements by means of a probability theory is presented. Ropes of a characteristic length are modelled from the knowledge of the statistical properties of the constituent elements and the weakest-link concept is employed to extend the results to long ropes. From the model, analysis of parallel-lay ropes with non-linear stress-strain relationships can be carried out and the study of the variability effects on the ropes, due to the scatter in elements' characteristics, is permitted. The variability in the element stiffness has a profound effect on the bundle strength. The scatter in the element cross-sectional area increases the bundle strength slightly, albeit by an insignificant amount. The results From the model are contrasted with classical bundle theory, and experimental data from parallel-lay ropes made from Kevlar-49 aramid and high tenacity polyester yarns have been used to predict, with reasonable accuracy, the tensile strength behaviour of the ropes.