Z-Pinned composites with combined delamination toughness and delamination Self-Repair properties

Damage to z-pinned laminates and other types of composite materials with through-the-thickness fibre reinforcement (e.g. 3D woven yarns, stitches, tufts) cannot be repaired using conventional methods. To overcome this problem, we have developed a new type of z-pinned composite that uniquely incorporates thin thermoplastic mendable filaments which, upon activation using heat, can repair delamination damage. We demonstrate this technology using a z-pinned composite material containing carbon fibre based ply layers containing a low fraction of thermoplastic filaments composed of poly[ethylene-co-(methacrylic acid)] (EMAA). The inclusion of mendable EMAA filaments in the carbon plies increased the mode I interlaminar fracture toughness of the z-pinned composite material due to their capacity to pin, deflect and branch delamination cracks. The mode I interlaminar toughness values for crack initiation and crack propagation were increased greatly (by over 230% and 750% respectively) by the inclusion of EMAA in the carbon fabric to the z-pinned composite relative to the control specimen. Upon moderate heating, the EMAA activated a mendable healing process that repaired the delamination damage and partially restored the mode I toughness properties. This novel repair process has potential application for any type of composite containing through-thickness reinforcement, including 3D woven, stitched, tufted and z-anchored materials.