Compressive mechanics of warp-knitted spacer fabrics. Part I: a constitutive model

This paper presents a theoretical study of the compressive mechanics of warp-knitted spacer fabrics. The first part, as presented in the current paper, focuses on the establishment of a constitutive model that can give accurate compressive stress-strain relationships of warp-knitted spacer fabrics. Based on the analysis of three existing models for polymeric or metallic foams, a constitutive model consisting of seven parameters was firstly proposed for spacer fabrics. The effect of each parameter on the regressive stress-strain curves was then parametrically studied. Experimental validation was finally conducted by using 12 warp-knitted spacer fabrics produced with different spacer monofilament diameters and inclination angles, fabric thicknesses, and outer layer structures to identify the physical sense of the parameters. The analysis has showed that an excellent agreement exists between the regressive and experimental results, and all seven parameters have a quantitative effect on a particular phase of the resultant compressive stress-strain curves of warp-knitted spacer fabrics. The change of each parameter makes a clear physical sense on the stress-strain curve. Therefore, the proposed constitutive model can be used as a useful tool to engineer the cushioning properties of warp-knitted spacer fabrics. The adoption of the constitutive model to develop a dynamic model for predicting the impact compressive responses of warp-knitted spacer fabrics under various loading conditions will be presented in Part II.