The interlaminar fracture toughness of composite laminates have been evaluated mainly with unidirectional or cross-ply laminates. However, it is difficult to estimate the realistic interlaminar fracture toughness and failure process with these laminates, since quasi-isotropic or angle-ply CFRP laminates consisting of various fiber orientation angles are mainly used in industrial structures such as aircraft. In this paper, we focused on the effects of fiber orientation angle on the interlaminar fracture toughness. The static mode I interlaminar fracture toughness was measured by using three types of CFRP laminate, in which the neutral interlaminar consisted of 0º/45, ±22.5º and 0º/0º layers. The results were evaluated by both experimental and analytical approaches. Both the (0º/45º) and (±22.5º) laminates exhibited an energy release rate almost twice larger than that of the unidirectional laminate. Moreover, the fracture mechanism between (0º/45º) and (±22.5º) laminates was significantly different due to the effect of fiber bridging.
