Open hole and mechanically fastened joint specimens employing three different symmetric stacking sequences were used for this project. Replicates for each specimen type and stacking sequence were loaded to ultimate and four load levels below ultimate to produce specimens containing progressive amounts of damage. During loading of each specimen Acoustic Emissions (AE) were monitored as a function of load. Specimens from each of the four load levels were inspected for matrix cracking, delamination and fiber bundle fractures using penetrant enhanced X-ray radiography and the deply technique. The deply technique, a unique but destructive inspection method, was used to separate the graphite-epoxy composite into its individual laminae while maintaining the integrity of each lamina. With the application of a gold chloride penetrant before deplying, the internal matrix damage as well as fiber bundle fracture could be readily observed on the surface of the individual laminae. These damage observations were recorded on a Lamina Damage Characterization Chart for each specimen. These charts contain pictorial sketches, with fiber orientations shown, for each lamina of the specimen segment deplied. A summary of the inspection results including photomacrographs of typical observed damage along with examples of charted damage is presented in the main body of the report.

The applicability of the acoustic emission (AE) technique to detect and locate damage initiation, monitor its progression and accumulation and to identify the major modes of damage associated with the failure process in cross- ply AS4/3502 graphite/epoxy laminates has been investigated. Six pairs of different laminate configurations were studied, having different stacking sequences and containing different ratios of ply thickness. Each pair included one laminate with external 90 deg plies and one with external 0 deg plies, e.g. (902/02/90)s, and (02/902/0)s, respectively. The testing program included determination of mechanical properties and monitoring of failure mechanisms and processes using optical observations, X-radiography, deplying, and scanning electron microscopy. Special efforts were directed toward establishing a correlation between the failure process and the AE results. Acoustic emission was monitored during quasi-static loading to failure in all cross-ply laminates. Results indicate that stacking sequence strongly affects the events intensities, e. g. amplitude energy, duration, and counts per event. Also, stacking sequence has a significant effect on damage initiation load and on rate of damage accumulation.

The applicability of the acoustic emission (AE) technique to detect and locate damage initiation, monitor its progression and accumulation and to identify the major modes of damage associated with the failure process in cross- ply AS4/3502 graphite/epoxy laminates has been investigated. Six pairs of different laminate configurations were studied, having different stacking sequences and containing different ratios of ply thickness. Each pair included one laminate with external 90 deg plies and one with external 0 deg plies, e.g. (902/02/90)s, and (02/902/0)s, respectively. The testing program included determination of mechanical properties and monitoring of failure mechanisms and processes using optical observations, X-radiography, deplying, and scanning electron microscopy. Special efforts were directed toward establishing a correlation between the failure process and the AE results. Acoustic emission was monitored during quasi-static loading to failure in all cross-ply laminates. Results indicate that stacking sequence strongly affects the events intensities, e. g. amplitude energy, duration, and counts per event. Also, stacking sequence has a significant effect on damage initiation load and on rate of damage accumulation.