Effect of twisting on tensile failure of impregnated yarns with broken filaments

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 i ncreasing 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 yams hav e largely been ignored. Twisted geometry gives rise to lateral pressure tha t contributes to the frictional shear stress; therefore, for a twisted yam, interfacial shear strength would be higher than that of a impregnated stra nd/unidirectional composite. Twisted yams have the obvious disadvantage tha t their unidirectional strength suffers because of fiber obliquity. This wo rk examines the effect of the lateral pressure on the tensile strength of t wisted yams with broken filaments. Studies have been carried out on both th e helical wound impregnated yams and helical twisted impregnated yams.