Comparison of interlaminar fracture toughness between CFRP and ALFRP laminates with common epoxy matrix at 77K in LN <inf>2</inf>
Mode I and II interlaminar fracture toughness was investigated with unidirectional carbon fiber (CF)/epoxy and alumina fiber (ALF)/epoxy laminates. A common bisphenol A type epoxy matrix was used to highlight the influence of the fiber physical and geometrical properties. The tests were carried out at 77K in liquid nitrogen (77K-LN 2 ), and the results were compared with those at room temperature in air (RT-air). The mode I fracture toughness of the neat epoxy matrix was also evaluated both in 77K-LN 2 and RT-air for comparison. The fracture toughness of the neat resin increased by 1.8 times by changing the test environment from RT-air to 77K-LN 2 . This increase was directly translated into the increase of the mode I fracture toughness values of ALF/epoxy where the toughness in 77K-LN 2 was 1.8 times higher than that in RT-air. This environmental effect for CF/epoxy laminates was smaller and the toughness in 77K-LN 2 was only 1.3 times higher than that in RT-air. On the other hand, the mode II interlaminar fracture toughness values of both CF and ALF/epoxy laminates were insensitive to the test environment. The ratios of the fracture toughness of ALF/epoxy to those of CF/epoxy were about two for both laminates in 77K-LN 2 and RT-air. The mechanism of the fiber and environmental effects were discussed from the mesoscopic view points on the bases of microscopic observation.
Interlaminar fracture toughness