Mechanical properties of structurally stitched non-crimp fabric composites

Abstract: The mechanical performance of polymer matrix composites perpendicular to the laminate plane can be improved by the insertion of local through-thickness reinforcements into dry fibre preforms by structural stitching. On the other hand, the in-plane stiffness and strength properties of the laminate may be reduced by this process though the induction of in-plane fibre undulations and the formation of voids in the vicinity of stitches after resin infusion. In this chapter the effect of structural stitching on in-plane and out-of-plane properties of multidirectional non-crimp fabric (NCF) carbon fibre/epoxy laminates is illustrated. Ambivalent effects of the various stitching parameters on the mechanical properties were observed. A finite element based unit cell model was developed to estimate in-plane elasticity and strength coefficients of structurally stitched NCF laminates. Comparison with experimental results shows that stiffness and strength properties of structurally stitched NCF laminates can be predicted with satisfying accuracy.