Directionality in tensile behavior of woven fabrics and strain hardening of warp yarns

In this paper, the phenomenon of strain hardening of woven fabrics in the warp direction is demonstrated and discussed. This is the plastic deformation in woven fabric manufacturing. A direct image of this phenomenon is that the shape of tensile stress-strain curve of a woven fabric is usually steeper in the warp direction, that is, the warp direction is harder to stretch in physical terms. One of the evidences of the effects of the plastic strain on different directions of a woven fabric is that the areas of warp yarns are generally smaller than those of weft when they are made of the same yarns. Based on the plastic strain principle, the plastic stratic strains in the longitudinal direction of yarns in a fabric have been calculated. The results statistically show that the warp yarns in a woven fabric have positive or extended plastic strain before testing and the weft yarns negative one, which causes warp yarns in a woven fabric harder to stretch than the weft yarns. The difference of plastic strains in warp and weft directions are shown to have linear relationships with ΔEMT, ΔWT and ΔRT.