Damage Tolerance Behaviour of Carbon Fibre Multi-Axial Warp Knit Fabric Composites

The stitch formation in Multi-axial Warp Knit Fabric (MWKF) is different to that found in traditional overstitching. The effect of such stitching is investigated and reported in this paper. Three different variants of stitch architectures in carbon MWKF, used in an epoxy matrix, were considered to investigate the effect of stitch density. Low energy impact, through penetration impact and compression strength testing were carried out. During low energy impact, a higher stitch density offered more damage resistance, being directly influenced by the through-thickness stitches, which have been shown to stop or deviate crack propagation. Similar results were also found during through penetration impacts. Compression after Impact properties were found to vary directly with the damage area. Whilst a high stitch density resulted in better residual strength properties, the percentage retention of the compression after impact strength was superior for low stitch density MWKF.