Mode I and II delamination fatigue crack growth behavior of alumina fiber/epoxy laminates in liquid nitrogen

Mode I and II interlaminar fracture toughness and delamination fatigue crack growth behavior were investigated with unidirectional alumina fiber (ALF)/epoxy laminates at 77 K in liquid nitrogen. The mode I fracture toughness values at 77 K were higher than those at room temperature in laboratory air (RT). Although initial values of the fracture toughness under mode II loading was higher at 77 K than those at RT, the propagation values of the fracture toughness was insensitive to the test temperature. The fatigue crack growth threshold at 77 K under mode I loading was higher than that at RT. The stress ratio dependency under mode II loading at 77 K was completely different from that at RT. Then, the increase of the fatigue crack growth resistance at 77 K from that at RT was observed only under stress ratio, R=0.1. The difference of the fracture mechanism due to the test temperature and the loading mode was discussed on the bases of fracture mechanics and microscopic fracture mechanism consideration.