Experimental study on the mode Ι interlaminar properties of self-healable vitrimeric CFRP with various interfaces

Despite decades of development, the delamination damage of multidirectional laminates still accounts for a considerable proportion of the failure problems encountered in the actual industrial field. The internal cracks that are difficult to be repaired make composites show a disposable essence. Thus, self-healable carbon fiber-reinforced polymer (CFRP) has attracted the attentions in recent years. Vitrimer is a polymer containing dynamic cross-linking networks, which could be repaired after damage without using extrinsic healing agents. However, vitrimeric CFRP (vCFRP) laminates are also inevitably susceptible to delamination damage like traditional thermosetting composites owing to the lack of reinforcements in the thickness direction, whereas the reports about delamination healing of vCFRP remains limited. In this study, a triepoxy was introduced into an existing epoxy system to synthesize the self-healable vitrimer based on transesterification. It showed that the polyfunctional groups could improve the mechanical properties and glass transition temperature (Tg) of cured vitrimer, and laid a groundwork for engineering application. Then the effects of stacking interfaces on the interlaminar properties and the twice interlaminar healing efficiency of the unidirectional vCFRP were studied. The results indicated that the load-displacement curves, R-curves, fracture toughness, fiber bridging length, fiber bridging effect and crack growth behaviour were strongly influenced by the stacking interfaces. The interlaminar healing efficiencies of the specimens after two complete delamination failure exceeded 80%. Development of such dynamic polymer composites could provide meaningful guidelines for improving the reliability, safety and maintainability of structural materials.