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This paper extends two ideas that have been used in the study of straight free edges to the case of curved free edges. The first idea is based on the notion that it is the differences in material properties of adjacent laminae that are responsible for initial free-edge interlaminar damage. To extend this to curved free edges the idea must be interpreted in terms of differences in shear and elongation strains of adjacent laminae. This interpretation involves both the material property differences and the spatial distribution of laminate strain at the hole edge. It is shown that a large strain level and a small difference in material properties can be as damaging as a small strain level and a large difference. From this it is evident interlaminar damage will probably begin at some circumferential location other than the net section. To explore these findings, the second extension was necessary. Specifically, the edge replication technique, using acetate film, was extended to record damage at a curved free edge. For a curved free edge the standard polishing technique was modified, as were the steps necessary to actually make a replica. These points are discussed in the paper. Finally, the damage recorded from uniaxially loaded plates containing central circular holes and semicircular edge notches are compared with the predictions of the difference theory.
composite laminates, notched laminates, free-edge effects, replication techniques, test methods
University of Illinois, Champaign-Urbana, IL
Virginia Polytechnic Institute and State University, Blacksburg, VA