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

Abstract

Owing to their unique and outstanding in-plane properties and high specific strength and stiffness, fiber-reinforced 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.