Research and development on a composite material named as Fiber-Metal Laminates (FML) for its airplane structural applications have been focused on in recent years. These materials laminate FRP (Fiber Reinforced Plastic) of susceptibility to out-of-plane loads and metal of high impact resistance together to mutually compensating the weaknesses of FRP and metals. To date, a typical one of FML is GLARE (Glass Laminate Aluminum Reinforced Epoxy) which laminates the aluminum alloy (Al) and the

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... -fiber reinforced plastic (GFRP) together. In this work, interlaminar mechanical properties, e.g., fracture toughness, of GLARE are improved by acid treatment to Al and adding Vapor Grown Carbon Fiber (VGCF) between Al and GFRP layers. The influence of VGCF addition and acid treatment on the mechanical properties of GLARE is examined by End Notched Flexure (ENF) tests. On the surface of an Al plate, the "line" induced during rolling manufacturing process appears clearly by acid treatment. Furthermore, VGCF addition amount is changed as 0, 10, 20 and 30 g/m 2 . From the results of ENF tests for Mode-Ⅱ properties, when 10g/m 2 of VGCF are added between Al with acid treatment and GFRP layers in GLARE, critical load (P C ) and critical strain energy release rate in Mode-Ⅱ(G ⅡC ) increase most significantly due to the fiber bridging effect, i.e., 118% and 345%, respectively. The present results also reveal that properly adding VGCF, e.g., 10g/m 2 , has an effect on deterrence of crack growth. However, G ⅡC decreases when the VGCF loading is too high due to poor VGCF dispersion, e.g., 30 g/m 2 here. Moreover, the anisotropy of interlaminar mechanical properties depending on the "line" and fiber directions appears more obviously by adding VGCF.