Effects of low-energy impact on the fatigue behavior of carbon/epoxy composites

Abstract

The fatigue behavior of a [0/45/90/−45]2S carbon/epoxy laminate subjected to low-energy impact has been investigated. The strength, residual strength and penetration impact responses of the laminate are measured; the fatigue behavior of the impacted and unimpacted laminates is compared in this study. The fatigue tests were performed at various stress levels under tension–tension (T–T) loadings with a fatigue frequency of 3Hz. The median rank method and Weibull distribution are applied to predict the failure probabilities of the specimen under monotonic and fatigue testing. The S/N curves are obtained and the S/N curves of these two laminates (with and without impact loading) are compared. The tensile strength is reduced slightly when a relatively low-energy impact is applied; however, a significant decrease with wider data distribution in tensile strength is observed when a higher-energy impact is used. It is also found that both the spread and the cycles of fatigue life are reduced after low-energy impact. C-scanning is used to inspect the damage zone of the specimens subjected to low-energy impact, and it is found that the damage zone increases with an increase in impact energy. The delamination propagation is monitored, and the effect of impact damage on delamination propagation during fatigue testing is revealed in this work.