Adhesively bonded healable composite joint

In a previous study, a biomimetic two-step self-healing scheme (close-then-heal (CTH)) by mimicking self-healing of human skin has been proposed by Li and Uppu (Li G, Uppu N. Shape memory polymer based self-healing syntactic foam: 3-D confined thermomechanical characterization, Compos Sci Technol 2010;70:1419–1427.) for self-healing structural-length scale damage. In this study, the CTH concept was applied to repeatedly heal adhesively bonded joints. Adhesively bonded composite joints were prepared. A thermosetting adhesive was modified by incorporating thermoplastic particles. The prepared joints were fractured per the peel testing of double cantilever beam (DCB) configurations. The fractured specimens were healed in terms of the CTH scheme. This fracture-healing cycle was repeated up to three cycles. Energy release rate, local peel strength, and cohesive law were measured for each fracture-healing cycle and the ratio of the energy release rate of the healed specimen over that of the virgin specimen was used to determine the healing efficiency. SEM, FTIR, and EDS tests were performed to understand the healing mechanisms. It is found that the CTH scheme can repeatedly heal the joint with a considerable healing efficiency; also, healing was at molecular-length scale through physical entanglement of the thermoplastic molecules and thermosetting molecules.