Toughening and healing of continuous fibre reinforced composites by supramolecular polymers

Interleaves comprising self-healing materials based on hydrogen bonded supramolecular polymers (SP) were successfully incorporated in the mid-plane of unidirectional (UD) carbon fibre reinforced polymers (CFRPs). The fracture toughness of these hybrid composites and their healing capability were measured under mode I loading. The fracture toughness appeared to have increased considerably since the maximum load (P_max) of the hybrid composite had increased approximately 5 times, and the fracture energy I (G_IC) displayed a dramatic increase by almost one order of magnitude when compared to the reference composite without the SP. Furthermore, the double cantilever beam (DCB) hybrid composites displayed a healing efficiency (H.E.) value for the mode I interlaminar characteristics around 60% for the P_max and the G_IC after the first healing cycle, dropping to 20-30% after the seventh cycle. During the mode I interlaminar fracture toughness tests the acoustic emission (AE) activity of the samples was also monitored. It was found that AE-activity strongly reduced due to the presence of the SP. Moreover, optical microscopy not only showed that the epoxy matrix at the interface is partly infiltrated by the SP, but it also revealed that cross-sections of both fractured surfaces were covered with the SP comprising pulled-out carbon fibres, indicating a strong interfacial adhesion. Finally it was shown that the SP fractured surfaces were partially covered with pulled-out carbon fibres emanating from the edges of the SP film in which the epoxy system exists.