Effects of Stress Waveform and Water Absorption on Fatigue Fracture Behavior of Aramid/Epoxy Composites

Abstract

The influences of stress waveform and water absorption on the tension-tension fatigue fracture behavior were investigated using aramid fiber/epoxy matrix unidirectional composite (Kevlar49/#2500). The fatigue tests were performed for specimens preconditioned in dry air (dry specimen) and the ones that were immersed in deionized water at 80℃ (wet specimen). Negative and positive pulse waveforms were used for fatigue tests. For dry specimens, the fatigue strength under negative pulse waveform was lower than that under positive pulse waveform. At a high stress level, the fatigue strength under positive pulse waveform became hardly independent of applied stress, and therefore the S-N curve became flat. The fatigue strength of wet specimens was lower than that of dry specimens at high stress level. The fracture surface was closely examined using a scanning electron microscope (SEM).