Fracture toughness tests were conducted for carbon composite scarf joints with and without carbon nanotube (CNT) reinforcement in order to study the effect of CNT on enhancing the fracture toughness of the scarf joint interface. Both mode I (i.e., opening mode) and mode II (i.e., shear mode) fracture tests were undertaken with and without CNT applied locally at the joint interface. During the study, the image correlation technique was used to examine the fracture mechanisms altered by the introduction of CNT. The experimental study showed that CNT increased the fracture toughness of the composite interface significantly, especially for the mode II fracture, with altering the fracture mechanism. On the other hand, there was no significant change on mode I fracture caused by CNT reinforcement. The enhancement of mode II fracture toughness was considered to result from the mechanical interlocking between polymers and CNT at the scarf joint interface.

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