Study On Structures And Mechanical Propenies Of Knitted Fabric And Its Influence On The Clothing Pressure

Knitted fabrics play a more and more important role in every kinds of tight or sports garments, because of their good elasticity. Clothing pressure comfort of knitted fabric is one of the important factors for evaluation of wearing comfort. Currently, more study on the nature of contact pressure needs to be done and prediction model hasn’t been utterly completed. Evaluation on wearing touch and pressure comfort mainly depends on wearing tests, which takes a lot of time and labor and could easily be affected by environment as well as attitude, psychological and physiological. Therefore, it is very important to have research the evaluation indicator and establish scientific evaluation system of clothing pressure comfort, which will give out significant effort on the comfort research of garments.This paper studies on the basic structural characteristics of elastic knitted fabric, mechanical properties and formation mechanism of pressure garments, clothing pressure prediction theory and method, aims to establish the elastic properties of the knitted fabric design theory and method system, realize the rational use and scientific prediction of elastic knitting. Following are the main work and contribution.(1) Weft-elastic knitted fabric structure model. Knitted fabric’s loop structure is a complex space curve, so the loop structures with elastic yarn have taken significant changes, resulting in many performances of the knitted fabrics. In this chapter, the density and density contrast coefficients of10kinds of inelastic weft-knitted fabrics and8kinds of weft-elastic knitted fabric are analyzed. Results show that density contrast coefficients of weft-elastic knitted fabric are significantly reduced, the cross density has virtually remained unchanged, the longitudinal density has significantly increased, the average density contrast coefficient of the inelastic weft-knitted fabrics is0.89, while the density contrast coefficient of the elastic weft-knitted fabrics0.80. The loop structure model of elastic weft-knitted fabrics has built, and the functional relationships between loop length and yarn diameter has set up. By verifying the model established based on the measured loop length values of8kinds of weft-elastic knitted fabric, and comparing with the three commonly used model, Pierce model, Leaf model, b-spline model. Results indicate that the loop lengths calculated by the three models has larger errors compared with the measured values, the average errors are more than10%, which means that the three models does not appropriate for elastic weft knitted fabric, and the loop lengths calculated by this model has error less than5%, indicating that the loop form built by this model has good match with the actual loop form.(2) Weft-knitted fabrics structure, mechanics influence on clothing pressure. The tensile tests at constant elongation and extension tests at constant load of four typical weft-elastic knitted fabrics at a low stress state in the horizontal and vertical direction are carried out in this study. Test results show that the four typical tensile curves of elastic weft-knitted fabrics have similar characteristics, which exhibit three obvious phases, that is, low strength and high elongation, high strength and high elongation and high strength and low elongation. In addition, the organization structure of knitted fabric, content of spandex, fabric density and weight per square meter are important factors affecting the elasticity of fabrics. elastic yarn has negative contribution to the fabric in horizontal direction, the negative contribution rate is inversely proportional with spandex content, and the overall effect is not significant affected, the average contribution rate was3.52%, while elastic yarns have a marked influence on fabric in vertical direction, and the average elastic contribution rate15.24%. When the spandex content is below a certain value, the contribution rate will decline rapidly. Load at specified elongation test has shown that the greater the longitudinal load, the smaller the zonal load, which exhibits inversely proportional law and longitudinal load value is significantly higher than lateral load value. In addition, clothing pressure of three types of elastic weft-knitted fabrics has been tested by fabric garment pressure testing device. Test results show that the vertical and horizontal clothing pressure is gradually increasing with fabric elongation increase. Spandex content tensile has significant impact on fabric in the early stage, and with the tension increased, the impact of spandex content increase on garment pressure gradually reduced. In addition, the longitudinal clothing pressure is higher than zonal clothing pressure and the higher growth rate as well.(3) Warp-knitted fabrics structure, mechanical influence on clothing pressure. This chapter study on the mechanical property of6kinds of elastic warp knitted fabric with different structures and spandex content. The elasticity contribution rate of spandex in6kinds of warp-knitted elastic knitted fabric is tested respectively. The average lateral elastic contribution rate is14.94%, while the average longitudinal elastic contribution rate is28.88%), indicating that the longitudinal elastic contribution rate given to fabric by elastic yarn is higher than the lateral elastic contribution rate. It shows that after adding the elastic yarn in warp knitted fabrics, the loop is compressed, so that the vertical fabric density has significant increase. Tensile properties testing indicates that its tensile curve showing non-elastic yarns and knitted fabric characteristics of different, the curve as with weft-elastic knitted fabrics have obvious three different stages. By comparison analysis, fabric stretch performance and fabric structure is closely related, both the stretch curve of elastic weft-knitted fabric and elastic warp-knitted fabric have low strength high stretch features at early stage, but warp-knitted fabric has smaller elastic elongation and larger tensile strength than weft-knitted fabric, which is the specific performance of obvious ammonia fiber content differences. Clothing pressure of6types of elastic weft-knitted fabrics have been tested by fabric garment pressure testing device, test results show that clothing pressure of warp-knitted fabric increase with the elongation of knitted fabric at low stress state. This is because the elastic fibers play a leading role and contribution in clothing pressure of warp knitted fabric. Through comparative analysis of clothing pressure value of the weft-knitted fabric and warp knitted fabrics, weft-knitted fabrics have smaller clothing pressure value than warp knitted fabrics. For weft-knitted fabrics, elastic fibers only have a certain impact on clothing pressure at the initial stretch stage, with tensile elongation increasing; the overall fabric clothing pressure is quite similar finally.(4) Forecast of knitted fabrics clothing pressure. Using the finite element analysis method on the simulation of knitting structure and tensile behavior is very advanced. Since knitted fabric structure is very complex, this study only focused on weft plain fabric structure and its tensile behavior, the loop structure model of weft plain fabric is built. By simulating the clothing pressure formation under the weft plain tension, the clothing pressure curve at simulated state is obtained, showing simulating curves have good consistency with measured curves.