Uniaxial Tensile Properties of Yarns: Effects of Moisture Level on the Shape of Stress-Strain Curves

摘要

With the aim of clarifying the complex shapes of the stress-strain curves of yarns such as wool and silk and improving the reproducibility of the experimental results achieved through their mechanical characterization, nylon 6,6 yarns consisting of one, three, nine, and thirty filaments are selected as a modeling system. Moreover, the uniaxial tensile properties of commercial nylon 6,6 yarns are investigated and compared with the corresponding properties of commercial wool and silk yarns. Moisture level plays a very relevant role in determining the mechanical behavior of yarns. With an increasing moisture level of conditioning, in fact, nylon 6,6, wool, and silk yarns show neat breaking points, and their stress-strain curves tend to assume the typical shape of the curve shown by respective single fibres. This suggests that high moisture levels minimize the multiple breakage phenomena occurring in the yarn. Moreover, for all the yarns investigated and, in particular, for wool, the process of conditioning at 100% RH reduces the variability of the experimental results, thus inducing a significant improvement in the precision and reproducibility of uniaxial tensile tests.