The Low-Stress Mechanical Properties of Wool and Wool-Blend Woven Fabrics

Abstract

The uniaxial-tensile and bending properties have been examined for a series of wool and wool/polyester woven apparel outerwear fabrics. The fabrics tested include a wide range of laboratory-produced woven materials (varying systematically in weave structure and the ratio of the two yarn curvilinear lengths) and also a range of commercially-produced woven fabrics. The fabric load-extension curves and yarn- decrimping curves are analyzed and discussed in terms of the following dimensionless parameters: the normalized tension per thread (the applied tension divided by the yarn-bending rigidity and multiplied by the square of curvilinear length in the extended direction); the relative yarn or fabric extension (the yarn or fabric extension divided by the yarn crimp); the initial fabric tensile modulus (i.e., initial slope of the normalized tension vs. relative extension curves); the yarn-decrimping modulus; the relative energy of stretching (i.e., area under the normalized load-extension curve); and the energy loss due to hysteresis (i.e., area of the hysteresis loop of the normalized load-extension curve during tensile-recovery measurements). Inelastic and elastic parameters are described for the fabric-bending hysteresis curves. Fabric tensile and bending properties are shown to depend largely on the yarn linear density, the crimp value of yarns, under deformation, and the ratio of the two yarn curvilinear lengths in the structural repeat unit of the fabric. It is shown that there are considerable constraints imposed on the yarn curvature within the fabric, resulting in increased resistance to fabric stretching and bending compared to the results measured on yarns removed from the fabric. A study is made of the effect of yarn extensibility on the decrimping behavior of yarns unravelled from fabric. The effect of weave construction is prominent on the tensile behavior of fabric; its effect on the decrimping behavior of yarn and bending properties of fabrics is only marginal. The effect of blend composi tion on these mechanical properties has been examined for a series of wool/polyester woven fabrics produced from yarns of the same linear density and was found not to be significant.