Published: Jan 1986
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Quasi-isotropic 32-ply graphite/epoxy specimens were tested in static tension and tension fatigue. Both dry specimens and specimens containing 1% moisture (by weight) were tested. The first type of damage observed under both static and cyclic loading was transverse matrix cracking in the 90-deg plies. Under continued static or cyclic loading the cracks propagated into the neighboring −45-deg plies. No delamination was observed under static loading. In fatigue the matrix cracks acted as initiators of delamination, which resulted in a marked reduction in stiffness and residual strength. For specimens which had been subjected to a tensile overload before fatigue cycling, delamination occurred earlier due to the formation of more transverse matrix cracks.
The major effect of moisture was to increase the stress level at which first-ply failure occurred and to delay damage development during fatigue at low stress levels. The leveling-off of the crack density at an approximately constant level during fatigue loading gives support to damage models which predict the occurrence of a characteristic damage state, independent of load history, before laminate failure.
composite materials, epoxy resin, fatigue (mechanics), fiber-reinforced composites, test methods
Section head, Materials, The Aeronautical Research Institute of Sweden (FFA), Bromma,
The Defence Material Administration, Stockholm,
The Aeronautical Research Institute of Sweden (FFA), Bromma,