SEDL / STP / STP1012-EB / STP10415S

Predicting Interlaminar Fatigue Crack Growth Rates in Compressively Loaded Laminates

Russell, AJ
Research scientist and composites group leader, Defence Research Establishment Pacific, FMO Victoria, British Columbia,

Street, KN
Research scientist and composites group leader, Defence Research Establishment Pacific, FMO Victoria, British Columbia,

Pages: 17    Published: Jan 1989

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Abstract

The fatigue crack growth rates of delaminations under mixed mode (I and II) loading conditions were investigated. Double cracked-lap-shear specimens were used to obtain da/dN versus ΔG data for AS4/3501-6 graphite/epoxy. This, together with previously reported results for pure mode I and mode II made it possible to establish a mixed mode fatigue criterion. The validity of these findings was then tested by using them to predict the growth rates of through-the-width delaminations in laminates subject to constant amplitude compressive loadings. Symmetric honeycomb sandwich specimens with delaminations located at a depth of four, six, eight, or ten plies beneath the surface were loaded in compression at 2.5 Hz, and the fatigue crack growth rates were determined. The experimental results were generally in good agreement with the predicted behavior although fiber bridging and load-induced crack closure resulted in predicted rates being too high in some cases.