Recovery of Mode I self-healing interlaminar fracture toughness of fiber metal laminate by modified double cantilever beam test

Abstract

Fiber metal laminate (FML) is a sandwich combination of thin metal and a composite layer which possess high fatigue, creep, and corrosion resistance. The performance of FML depends on the bonding behavior between the metal and composite interface (MCI). Introducing Redux 335k polymer interleaf can improve MCI, but cannot retain the mechanical properties after its first delamination. Toughened self-healing co-polymer film EMAA (Ethylene-methacrylic acid) can be used as an alternative due to its self-healing property which can recover the mechanical property after each delamination. Double-cantilever-beam (DCB) test is carried out by supporting a thick CFRP composite as a backing beam to avoid the yielding of thin metal in FML to estimate the interlaminar fracture toughness (G1C) at the MCI. Results from the DCB test shows that the incorporation of EMAA thin film improves G1C at the MCI. However, G1C gradually decreases despite recovering its fracture toughness after each delamination when the self-healing reaction is thermally activated. The Mode I fracture toughness of EMAA before the first heal is 1.95 kJ/m2, which is higher due to its thermoplastic nature. This article emphasizes only on the recovery of Mode I self-healing efficiency of EMAA at MCI. However, the article also shows the fracture toughness at MCI by using non-self-healing film adhesive at MCI. This comparison is to understand that the standard structural adhesive (Redux 335K) cannot retain the mechanical properties after its first delamination, and also to understand the failure modes of both thermosetting and thermoplastic interleaf at MCI.