Understanding and modelling the effect of stitching on the geometry of non-crimp fabrics

Abstract: Internal geometry of multiaxial multi-ply warp-knitted non-crimp fabrics (NCFs) and their composites is described in this chapter, based on the understanding of the production process of NCF, experimental studies of the internal structure of NCF composites and models of the same. The internal geometry of NCF is treated as geometry of cross-ply laminate of unidirectional fibrous plies, with fibres in the plies distorted due to interaction with the knitting needles and the stitching thread. The positions and dimensions of the distortions are characterised for different types of NCF in their relaxed state and after consolidation into composite material. This characterisation includes changes of NCF geometry due to shearing of the reinforcement during composite forming. A ‘virtual NCF’ model implemented in a software tool is described.