Effect of Fiber Direction and Stress Ratio on Fatigue Property in Carbon Fiber Reinforced Epoxy Composites

Abstract

The fatigue limit and crack growth behavior of slit specimens of carbon fiber reinforced epoxy composites were investigated. The fatigue limit was defined by the maximum stress amplitude that the specimen endured 106 times repeated stress when S-N curve was used. The highest fatigue limit was obtained when all the fiber directions were parallel to the load axis. The fatigue limits were evaluated in the cases of composites using alternately parallel and perpendicular to the load axis and compared with the result of the specimen having all the carbon fiber orientations were parallel to the load axis. When the measured value of the fatigue limit was lower, shear damage to the epoxy resin and peeling of fiber from epoxy resin occurred clearly. According to those results, it was expected that the fatigue limit of smooth specimens of carbon composites with long fibers can be evaluated from the results of the slit specimens.