Trapezoidal tearing propagation mechanisms of biaxial-warp-knitted fabric composites and tensile-shear coupling behaviors involved

Considering the yarn orientation and microscopic structure of the biaxial-warp-knitted fabric, a series of experimental and numerical studies on trapezoidal tearing under off-axis and crack parameters were conducted at first. Then, the influences of parameters on the tearing strength and mechanical properties were investigated. Finally, the crack propagation mechanisms and the characteristics of tensile-shear coupling behavior involved were demonstrated. Results show that there is a significant correlation between crack propagation and the evolution of the main yarn delta zone as well as the X-shaped shear stress region, and the typical stages in the tearing history can be defined. Also, the tensile-shear coupling of the material and the cooperative deformation between warp and weft yarns are the main factors that cause tearing properties to show a dependence on yarn orientation. In addition, both factors vary regularly as the off-axis angle tends to 45° and cause mixed propagation of cracks in both directions and the "ridge" pattern of tearing strength. The conclusions obtained can provide references for damage analysis of related fabric composites and safety assessment of membrane structures.