The purpose of this investigation was to observe and document the details of edge damage initiation, growth, and interaction as a function of load history and determine the effect of the damage state on material properties. Quasi-isotropic graphite/epoxy specimens with two different stacking sequences were selected to study the damage behavior under both tensile and compressive out-of-plane normal stresses. Observations were made using a replication technique which allows for recording the damage detail along the edge of the stressed specimen.

Specimens were tested in tension-tension fatigue (R = 0.1) at maximum stresses of 234, 290, and 393 MPa (34, 42, and 57 ksi). At selected intervals between 1/2 and 10⁴ cycles, replicas of the edge damage were made. A chronological order of damage events was established for each cyclic stress level and type of laminate. Micromechanical damage in the form of transverse cracks and delaminations initiated at stresses below the proportional limit on the static stress-strain curve and increased with additional cyclic loading in a manner dependent upon the type of laminate. A stable crack density was measured which was dependent on the type of laminate but not on the cyclic stress level. The fracture modes of each laminate were also different. Residual strength and stiffness data are also reported.