Vitrimer based composite laminates with shape memory alloy Z-pins for repeated healing of impact induced delamination

Owing to their unique and outstanding in-plane properties and high specific strength and stiffness, fiberreinforced polymer composite laminates are being used widely for many structural applications, such as aircrafts, infrastructure, and automobiles. Notwithstanding, they are normally susceptible and vulnerable to damage from out-of-plane impact events. Low velocity impact of fiber-reinforced composite laminates often results in damages that are invisible, but would progressively propagate and later results in a catastrophic failure. This study focused on developing a self-healing composite laminate with improved transverse strength and cyclic healing capabilities that would address the problem of delamination. A novel self-healable and recyclable vitrimer-based shape memory polymer (VSMP) was used as the matrix, unidirectional Saertex glass fiber as the reinforcing fibers, and tension programmed shape memory alloy (SMA) wires (Flexinol) as z-pins. This design followed the strategy of close-then-heal (CTH) for delamination healing. Low velocity impact tests, compression after impact tests, and self-healing of impact induced delamination were investigated. The tension programmed SMA z-pins helped resist delamination during impact; the shape memory effect of the vitrimer and SMA z-pins, together with the external pressure used, helped narrow/close the delamination through constrained shape recovery during heating, so that the narrowed/closed delamination can be healed repeatedly by the VSMP itself. The novel hybrid composite laminate provides a promising sustainable multifunctional material system for structural application.