Characterizing and modelling the coupled in-plane shear-biaxial tension deformation response of unidirectional non-crimp fabrics

The coupled biaxial tension and shear-biaxial tension deformation responses of a unidirectional non-crimp fabric (UD-NCF) was explored using a novel experimental test setup. A custom multiaxial loading system was used to subject multibranched fabric specimens to combined in-plane tension loads. Biaxial tension tests conducted with varying ratios of deformation along the orthogonal carbon fiber tow and supporting glass fiber yarn directions revealed minor tension-tension deformation coupling over the deformation range considered. Combined shear-equibiaxial tension tests were also conducted with different deformation rates along the fabric diagonal direction, where variations in the force-strain response revealed notable shear-extension coupling. A macroscopic finite element simulation model was developed for the fabric, which employed an available constitutive model that captured the anisotropic hyperelastic response of the fibers. The simulation model accurately predicted the fabric coupled shear-extension deformation for the combined shear-equibiaxial test cases and revealed that the shear angle at the specimen center was limited by the applied tension along the orthogonal fibers. The simulation model was also used to predict shear angle contours for multibranched specimens with different fiber orientations. It was demonstrated that the extent of shear deformation is sensitive to the direction of tension loads. These important findings provide an improved understanding of the coupled deformation modes for UD-NCFs, which will aid in future studies focused on their formability.