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Constant amplitude tension-tension fatigue tests were conducted on AS4/3501-6 graphite epoxy (02/θ2/-θ2)s laminates, where θ was 15, 20, 25, or 30°. Fatigue tests were conducted at a frequency of 5 Hz and an R-ratio of 0.1. Dye penetrant-enhanced X-radiography was used to document the onset of matrix cracking in the central - θ° plies and the subsequent onset of local delaminations in the θ/-θ interface at the intersection of the matrix cracks and the free edge.
Two strain energy release rate (G) solutions for local delamination from angle ply matrix cracks were derived: one for a uniform delamination front across the laminate width, and one for a triangular-shaped delamination area that extended only partially into the laminate width from the free edge. Plots of maximum cyclic G versus the number of cycles to local delamination onset (Gmax versus N) were generated to assess the accuracy of these G solutions. The influence of residual thermal and moisture stresses on G were also quantified.
composite material, graphite epoxy, delamination, matrix crack, fatigue
Directorate, NASA Langley Research Center, Hampton, VA