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Low-velocity instrumented dropweight impact tests were performed on carbon/ epoxy laminates. The composite plates were 8-ply (+45, 0, -45, 90)s laminates supported in a clamped-clamped/free-free configuration with varying amounts of in-plane load, Nx applied. The amount of damage induced into the specimen was evaluated using the instrumented impact data and X-ray inspection. Results showed that for a given impact energy level, more damage was induced into the specimen as the external in-plane load, Nx, was increased. The majorityof damage observed consisted of backface splitting of the matrix parallel to the fibers in that ply, associated with delaminations emanating from these splits. A free-edge delamination model was used to explain the type and extent of the major delaminations caused by the preload/impact combinations.
composites, damage resistance, preload, instrumented impact, toughened epoxy, nondestructive evaluation, delamination
Materials research engineer, NASA Langley Research Center, Hampton, VA