The interlaminar fracture toughness is a critical property for the damage tolerance, impact resistance, and delamination of fiber-reinforced polymer (FRP) composites. To enhance this property, various strategies have been explored, from introducing through the thickness reinforcement, strengthening the fiber-matrix interface, to improving the fracture toughness of the matrix resins. This research examines the effects of Graphene Nanoplatelet (xGnP) on the fracture toughness of epoxy resins commonly used in FRPs. Two epoxy systems were examined: EPON 862 and SC-15. xGnP was added into the epoxy resins at two weight fractions: 0.1wt% and 0.5wt%. The fracture toughness of the reinforced resins was investigated with the compact tension (CT) experiment. It was observed that xGnP resulted in a greater enhancement in the fracture toughness of EPON 862 than that of SC-15. For EPON 862, the GIC value had an improvement of 87% and 156% for the reinforced 0.1wt% and 0.5wt%, respectively. For SC-15, the improvement was 21% and 14% for the reinforced 0.1wt% and 0.5wt%, respectively. SC-15 is already rubber toughened. For comparison purpose, EPON 862 was also reinforced with nano-silica particles. At 0.1wt% and 0.5wt%, the improvement in GIC was 49% and 87%, respectively. In summary, adding xGnP can significantly improve the fracture toughness of a relatively brittle epoxy system. At a low concentration, xGnP is much more efficient than nano-silica in terms of improving the fracture toughness. Finally, in fracture experiment, the method of introducing pre-crack was found to have a significant effect on the measured fracture toughness value.
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