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Electron microscopy was used to analyze the fracture surfaces of T300/934 graphite/epoxy, unidirectional, off-axis tensile coupons which were subjected to 1.0 MeV electron radiation at a rate of 5.0 × 107 rad/h for a total dose of 1.0 × 1010 rad. Fracture surfaces from irradiated and nonirradiated specimens tested at 116 K (−250°F), room temperature, and 394 K (+250°F) were analyzed to assess the influence of radiation and temperature on the mode of failure and variations in constituent material as a function of environmental exposure. Micrographs of fracture surfaces indicate that irradiated specimens are more brittle than nonirradiated specimens at low temperatures. However, at elevated temperatures the irradiated specimens exhibit significantly more plasticity than nonirradiated specimens. The increased plasticity in irradiated specimens tested at elevated temperature is much more evident in 10° offaxis specimens. This is the result of the high shear stresses in these specimens. The same high degree of plasticity is not observed in the 90° specimens which fail at a much lower ultimate strain. Little difference in fracture surfaces and material behavior for irradiated and nonirradiated specimens is noted for room temperature specimens. The analysis of the photomicrographs is shown to correspond well with mechanical behavior of the specimen.
composites, electron radiation, microscopy, fracture, graphite-epoxy
Senior member, Technical Staff, Northrop Defense System Division, IL
Research scientist, NASA Langley Research Center, Hampton, VA
Professor of engineering science and mechanics, Virginia Polytechnic Institute and State University, Blacksburg, VA