Effect of Twisting on Tensile Failure of Impregnated Yarns with Broken Filaments

Abstract

The tensile strength of impregnated strand/unidirectional composite depends on many factors including the strength of the interface. Recent efforts in trying to increase the strength of composites have been directed towards increasing the strength of the interface through fiber surface treatment and better resin systems that give better interfacial shear strength. However, the role of frictional forces and analysis of twisted impregnated yarns have largely been ignored. Twisted geometry gives rise to lateral pressure that contributes to the frictional shear stress; therefore, for a twisted yarn, interfacial shear strength would be higher than that of a impregnated strand/unidirectional composite. Twisted yarns have the obvious disadvantage that their unidirectional strength suffers because of fiber obliquity. This work examines the effect of the lateral pressure on the tensile strength of twisted yarns with broken filaments. Studies have been carried out on both the helical wound impregnated yarns and helical twisted impregnated yarns.