Stitched mendable composites: Balancing healing performance against mechanical performance

The effect of through-the-thickness stitching with thermoplastic filaments on the healing efficiency and mechanical properties of mendable carbon-epoxy composites is investigated. Stitching with filaments of polyethylene-co-methacrylic acid (EMAA) provides composite materials with high delamination resistance and self-healing efficiency, but at the expense of reduced mechanical properties. The modes I and II interlaminar fracture toughness properties and healing performance are improved greatly by thermoplastic stitching. However, stitching reduces the tensile and compressive properties of mendable composites. Experimental research reveals that the delamination toughness and healing properties increase whereas the mechanical properties decrease with increasing areal density or size of the mendable stitches. However, the percentage improvements to the interlaminar fracture toughness (in the order of 35-650%) and healing efficiency (50-250%) are much greater than the reductions to the mechanical properties (less than 50%) caused by thermoplastic stitching.