Effect of Fiber Strength on Notch Bending Fracture of Unidirectional Long Carbon Fiber–Reinforced Epoxy Composites

The unidirectional long carbon fibers with 3.5 and 5.5GPa average tensile strength reinforced epoxy matrix composites (designated as 3.5 and 5.5 CF composites, respectively) were studied to determine the effect of fiber strength on notch bending fracture behavior of a CF composite. Three-point slow bend and instrumented Charpy impact tests were conducted. Two different V-notch subsize Charpy specimens with several different angles between the fibers and longitudinal direction of the specimen were used. Compared with the 3.5 CF composite with angles of 0 and 10 degrees, the 5.5 CF composite with the same angles exhibited higher fracture energies. However, slow bend and Charpy impact fracture energies of the composites decreased significantly at angles of 22.5 degrees and larger. Compared with the 3.5 CF composite, the 5.5 CF composite showed a greater anisotropy in fracture energy. The results are described and the fracture mechanism is briefly discussed on the basis of fractography.