Self-healing of transverse crack damage in carbon fiber composites

Laminated fiber-reinforced composites are susceptible to transverse cracking at relatively low stresses. These cracks cause a reduction in stiffness and can lead to premature and dangerous failure modes. Here, we investigate the self-healing efficiency of carbon fiber composites in isolated transverse crack events. The composites contain solvent-filled microcapsules in an epoxy matrix toughened with 20 wt% of thermoplastic poly(bisphenol A-co-epichlorohydrin) (PBAE). Self-healing is triggered upon release of the encapsulated solvent and subsequent transport of dissolved thermoplastic into the damaged volumes. Following solvent evaporation, redistributed thermoplastic re-bonds the crack faces to heal the damage. To evaluate self-healing efficiency, we develop a new protocol which leverages digital image correlation (DIC) to compare the stress required to open and re-open a transverse crack before and after healing. Self-healing is evaluated after 2, 4, and 6 days and compared to control specimens that are healed thermally. We report a self-healing efficiency of up to 57% after 6 days with just 1 vol% microcapsule concentration in a high glass transition temperature (179 °C) carbon fiber-reinforced composite.