Assessing the coupled in-plane shear-biaxial tension deformation response of unidirectional non-crimp fabrics in support of macroscopic forming simulations

Liquid molded composites comprising layers of unidirectional non-crimp fabric (UDNCF) offer high lightweighting potential owing to their high in-plane properties and tailorability. Nevertheless, during forming the complex interactions between the fabric constituents can result in undesirable defects such as out-of-plane wrinkling. Forming processes can be optimized to reduce the severity of these defects by manipulating the inherently coupled macroscopic in-plane shear and tension deformation modes of the fabric, which has not been widely studied for UD-NCFs. The aim of this paper is to assess the coupled in-plane shear-biaxial tension deformation response of a heavy tow carbon fiber UD-NCF. A novel experimental test setup using a custom multiaxial loading system was used to subject multibranched fabric specimens to combined in-plane tension loads with varying ratios of deformation along the different specimen directions. Captured force-strain responses for different deformation ratios revealed strong shear-extension coupling. A macroscopic simulation model employing an anisotropic hyperelastic constitutive model was used for the fabric. Simulations revealed that the extent of shear deformation is sensitive to the direction of the applied 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.