Modeling Stiffness Reduction of Graphite/Epoxy Composite Laminates

An investigation has been conducted into the effects of fatigue loading on the stiffness and strength degradation of composite laminates. An experimental test program using graphite/epoxy [±35]2 s laminates has been conducted to generate meaningful data for this evaluation. Based on this investigation, a model is proposed to relate the stiffness degrada tion to the fractional life expended at a given stress level and also to the residual strength degradation. These models are restricted to specimens subjected to constant amplitude fatigue loadings.