Influence of weaving on the mechanical response of aramid yarns subjected to high-speed loading

Abstract

Aramid fibres are used in high performance fabrics and yarns for dynamic loading applications, because of their high strength and stiffness, and good energy absorption. This investigation explores the influence of the weaving process on the mechanical response of aramid yarns. The quasi-static and dynamic properties of virgin T1040 Twaron® yarns and their woven counterparts, extracted from plain-woven T717 Twaron® fabric, are characterized and compared, to examine the effect of the weaving process. In particular, the phenomenon of yarn uncrimping is examined. A Split Hopkinson Tensile Bar device, with a specially-designed fixture to attach specimens to the loading bars, is used to apply high-speed tension to yarn specimens. High-speed photography is employed to observe deformation and failure, and to measure specimen strain. Experimental results show that virgin and woven yarns exhibit similar rate sensitivity – an increase in strain rate makes both stiffer, increases their tensile strength, and decreases the failure strain. Virgin yarns possess a lower failure strain compared to woven yarns, but a higher strength and stiffness. Observation of broken fibres shows this may be due to the damage of the fibre during the weaving process, which affects the cohesion of the fibrils at the micro-level. Consequently, the yarn strength and stiffness are degraded, and this decreases the overall energy absorption capacity.