MODE I INTERLAMINAR FRACTURE TOUGHNESS AND FRACTOGRAPHIC OBSERVATION OF MULTIDIRECTIONAL CARBON FIBER/EPOXY COMPOSITES

Mode I interlaminar fracture toughness was evaluated and fracture surfaces were observed to investigate crack propagation behaviors and establish the relationship between fracture toughness and fracture surface morphology in multidirectional carbon fiber/epoxy composites. Double cantilever beam specimens, with artificial cracks made of Teflon film embedded in the middle plane, were prepared. Six crack lengths were considered (25–50 mm). The slopes of the load displacement curves depend on the initial crack length. The mode I interlaminar fracture toughness at crack initiation is approximately constant, regardless of the initial crack length, but fluctuates with crack propagation. The fracture surface morphology indicates that the R-curve is closely related to the crack propagation mechanism. The fracture surface exhibits damage, such as crack migration, fiber bridging, crack branching, double cracking, and ply splits. These results provide insight into interlaminar fracture toughness assessment and the crack propagation behavior of multidirectional carbon fiber/epoxy composites.