Low cycle fatigue of CFRP laminated composites due to repeated out-of-plane loading

Fatigue of CFRP (Carbon Fiber Reinforced Plastics) laminated composites due to repeated out-of-plane loading was investigated using two testing methods. One is the four-point-bending fatigue test using L-shaped specimens and the other is the flatwise tension fatigue test. Interlayer-toughened unidirectional CFRP laminates were used as the specimens. Here, for reduction of the testing time, low cycle fatigue was focused on by setting cyclic loads not to be too small comparing with the static strength of the specimen. Fatigue fracture occurred in a brittle manner with almost no prior deformation in both tests. The fatigue life of the L-shaped specimen was much longer than that of the flatwise tension specimen. As the results of the fracture surface observation, it could be seen that the fracture at the CF (Carbon Fiber)/epoxy layer was predominant. However, regions of the toughened interlayers were also observed on the fracture surface at the curved section of the L-shaped specimen.