Structurally stitched NCF preforms: Quasi-static response

Experimental data are presented for a typical structurally stitched preform, composed of carbon fibre non-crimp fabrics (NCFs) and impregnated with an epoxy resin. The term 'structural' presumes here that the stitching yarn does not only consolidate the layers (as the non-structural one does for NCF plies) but forms also a through-the-thickness reinforcement. One stitching technique-tufting-is studied, with 67 tex carbon yarn and several stitching lengths. The test results (in-plane tension, out-plane compression, and 3-point bending) are compared and discussed revealing an influence of stitching and specifics of damage development. The stitching, on the one hand, decreases delaminations and increases the ultimate load. On the other hand, the stitching creates stress-strain concentrators which lead to earlier damage initiation.