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

Mode I and 11 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 11 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 11 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. (C) 2002 Elsevier Science Ltd. All rights reserved.