Effect of strain rate on the in-plane orthotropic constitutive response and failure behaviour of a unidirectional non-crimp fabric composite

A comprehensive experimental campaign was performed to characterize the strain rate-dependent orthotropic constitutive response and failure behavior of a unidirectional non-crimp fabric (UD-NCF) carbon fiber/snap-cure epoxy composite. Shear and transverse compression strengths increased by 60% and 50%, respectively, over the range of strain rates considered, which is consistent with previously reported trends for unidirectional tape composites (UDTCs). The transverse tension strength increased by 18% with increasing strain rate, which is different from UDTCs. Owing to the distinct microstructure of UD-NCF composites, local damage mechanisms such as pullout of transverse supporting glass fibers and stitching were observed and are deemed to contribute to the rate dependency of transverse tension strength. The longitudinal compression strength increased by 35% with increasing strain rate. Observation of failed specimens revealed widespread inter-tow axial splitting and localized tow kinking, distinct from UDTCs. This important finding will aid in the development of failure criteria for UD-NCF composites.