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A commercially obtained glass/epoxy composite material has been exposed to a wide variety of actual outdoor and accelerated climates at different test sites around the world. Portions of this sample population are returned at various intervals for an extensive laboratory characterization aimed at determining the effect of exposure on engineering properties and elucidating the nature of the deterioration mechanism as well. In spite of clear visual and chemical evidence of severe photolytic degradation of the resin surface layers, test values of tensile and flexural strength do not show a clearly defined correlation with this deterioration. Reasoning that the structural effect of photolytic molecular scission might be to interrupt the three-dimensional network of resin bonds and increase the effective molecular weight between crosslinks, the glass transition temperature of the laminates has been determined by torsional pendulum analysis as a function of exposure time. The molecular weight between crosslinks, as determined from these data, is then shown to correlate strongly with laser pyrolysis observations of chemical degradation.
composite materials, environmental tests, weathering, mechanical properties, chemical analysis
Associate professor, Massachusetts Institute of Technology, Cambridge, Mass.
Research physicist, Organic Materials Laboratory, Army Materials and Mechanics Research Center, Watertown, Mass.