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This investigation demonstrates how moisture absorbed in [0/±45/90]s and [0/90/±45]s graphite epoxy laminates significantly alters the stress state and chronology of damage development along the laminate edge during static tension and tension-tension cyclic loading.
Emphasis is placed on using reasonable approximations for wet and dry elastic properties, including out-of-plane properties (v23 and G23), since these properties are required by finite element and shear lag models to predict the stress state at the laminate edge.
Moisture was observed to alter the dry edge stress state in the 90-deg plies of the [0/±45/90]s laminate such that delaminations occurred at a lower load and transverse cracks occurred at a higher load. A model was developed which predicted the differences in loads required to initiate damage in the 90-deg plies of the two laminates in the wet and dry conditions.
Although moisture can alter the chronology of damage development, the damage state in each laminate observed prior to fracture appeared to be independent of moisture content.
composite materials, graphite epoxy, damage, characteristic damage state, moisture absorption
Postdoctoral research associate, Fracture and Deformation Division, Department of Commerce, National Bureau of Standards, Boulder, Colo.
Professor, Virginia Polytechnic Institute and State University, Blacksburg, Va.