Healing of carbon fibre-epoxy composite T-joints using mendable polymer fibre stitching

This paper presents an experimental investigation into a novel stitching technique for the toughening and healing of composite T-joints. Carbon fibre-epoxy T-joints were stitched using mendable poly(ethylene-co-methacrylic acid) (EMAA) thermoplastic filaments to form a three-dimensional healing polymer network in the stiffener, web and flange sections. The stitched network created a unique composite joint having the synergistic combination of high toughness and multiple healing repair of delamination and matrix cracks. The stitched network increased the delamination toughness of the T-joint under tension (stiffener pull-off) loading by the thermoplastic filaments bridging the fractured sections and thereby generating bridging traction (crack closure) loads. The delamination toughening induced by the mendable stitched network was determined using mode I interlaminar fracture testing. It was discovered that thermal activation of the stitched network resulted in partial repair of delamination and matrix cracks and substantial recoveries (more than 50%) in the stiffness, ultimate load and energy absorption properties of the fractured T-joint. The healing and partial property restoration of the mendable T-joint was repeatable for multiple healing processes