Evaluating the tensile stress relaxation of rib weft-knitted fabrics using viscoelastic models

Stress relaxation phenomenon occurs in various textiles, especially in medical textiles such as varicose socks, pressure garments, and compression bandages, in which keeping a definite level of pressure on the damaged organ is vital. Stress relaxation can cause disorders in the function of these garments, and subsequently, their longevity and durability. Therefore, the effectiveness of these textiles will be reduced over time. This research aims to predict the stress relaxation behavior of weft-knitted fabrics using viscoelastic analysis. Rib-knitted fabrics with different numbers of miss stitches in successive wales were fabricated, and their stress relaxation was assessed under two strain levels in the course direction. It was observed that increasing the number of miss stitches in the fabric structure enhances the stress relaxation of the fabric. Consequently, the use of miss stitches in the structure of compression garments, varicose stockings, and pressure bandages is not proposed. Furthermore, all fabric structures were found to exhibit more stress relaxation under higher tensile strain, and the stress relaxation increment of the fabrics due to an increase in the applied strain was dependent on the fabric structure. Among the investigated viscoelastic models, the three-component Maxwell model with a nonlinear spring is appropriate to describe accurately the stress relaxation behavior of all considered fabric structures.