Role of Fabric Structure on the Second Tensile Elastic Modulus of Net Warp-Knitted Fabrics

This work aimed to study the second elastic modulus of net warp-knitted fabrics (NWKF) experimentally and theoretically. Net knitted fabrics were selected to study owing to their wide practical application and also lack of enough attention. Knitted fabrics have two regions of tensile elastic behavior which the initial one refers to the displacement of the elements of fabrics before jamming of the yarns. As soon as jamming takes place completely, the constituent yarns in the structure of fabrics go through tension. In other words, yarns in their spatial configuration resist the applied loads. This resistance is important in the ultimate strength of the fabrics and also in the composite materials reinforced with knitted fabrics. NWKFs were produced using a Raschel knitting machine. Uniaxial tensile tests were conducted in the course and wale directions. The second elastic modulus was measured using a statistical approach. In the theoretical part, a mechanical model based on the configuration of elements of fabrics after jamming status and using Energy method and Castigliano’s Theorem was proposed. The proposed model was used to calculate the second elastic modulus. To validate the model, the authors’ experimental data along with the collected data from the other researches were compared with the calculated values, and the results showed that the proposed model can predict the modulus reasonably. The results showed that the fabric structure including wale spacing, course spacing, and the number of lapping movements creating the holes affects the second elastic modulus despite the accepted concept, but the mechanical properties of yarns only influence the second elastic modulus of the fabrics.