Shear performance and mechanism analysis of warp-knitted non-crimp fabric composites under combined shear and tension loading

Abstract

In order to further clarify the shear mechanisms and shear-tension coupling effects of warp-knitted non-crimp fabric (NCF) composites under the combined shear and tension loading, biaxial bias extension tests with three tensile stress levels (TSLs) and four shear stress levels (SSLs) were conducted. The shear stiffness was calculated by three methods to obtain accurate variation characteristics, and the shear stiffness’s nonlinearity for the first positive loading curves was analyzed based on the shear stiffness-strain curve method. The shear deformations and mechanisms of NCF and plain-woven fabric composites were discussed. Results show that, the shear deformations and plasticity of NCF composites are mainly related to the SSL, and tend to saturate with the increasing TSL when the SSL is constant, which is probably due to shear-tension coupling effects. The shear stiffness is stress-state specific, and its stable variation characteristics could only appear for some particular TSLs. Due to different internal micro-structures, the shear stiffness variation characteristics of NCF composites are different from those of plain-woven fabric composites. The used methods and conclusions obtained can provide useful references for the determination of accurate shear properties for fabric composites, as well as the design and analysis of membrane structures.