Mode I Interlaminar Fracture under Static and Fatigue Loadings of Alumina Fiber/Epoxy Laminates in Liquid Nitrogen

摘要

Laminate structures of alumina fiber (ALF)/epoxy composites have been applied to the struc- tural components of superconducting magnets because of their low thermal conductivity and higher specific strength and modulus. Since these structures are used as the load support system for superconducting magnets at cryogenic temperature, the evaluation of interlaminar strength both under static and fatigue loadings is important. In the present study, mode I interlaminar fracture toughness and delamination fatigue crack growth behavior were investigated with unidirectional ALF/epoxy laminates in liquid nitrogen (77 K). Tests were carried out using double cantilever beam specimens. Both the fracture toughness values and fatigue thresholds at 77 K were higher than those in laboratory air (RT). The analysis of the stress-ratio dependency showed that the fatigue mechanism in liquid nitrogen was only controlled by the maximum stress. The difference of the fracture mechanism owing to the test temperature was discussed on the bases of fractographic observation.