Detection of Environmental Deterioration in Fiber-Reinforced Composites by FT-Raman Spectroscopy

A number of advanced fiber-reinforced organic matrix composites employed in a variety of Army systems are exposed to environmental weathering and/or in-service loading. This may induce chemical, physical, and mechanical changes in the composite material, and ultimately lead to component failure. This proposal will develop a fiber optic based Fourier transform Raman (FT-Raman) spectrometer for the nondestructive evaluation of composite material deterioration due to environmental weathering. This proposal will focus on the effect of photo induced oxidation occurring at the surface as a function of temperature and moisture. A series of composites employing graphite, fiberglass and Kevlar as reinforcement fibers in epoxy and polyimide matrices will be subjected to accelerated environmental deterioration. The FT-Raman system will correlate environmentally induced changes in Raman spectral features to changes in mechanical properties. These measurements will be used to quantify the degree of environmental durability of the various composites. During Phase II, this information will be used to develop a methodology to assess and predict in-use component performance. Also, during this phase a field-portable prototype will be developed which includes an extended fiber optic probe with the potential of assessing a full-scale composite structure employed in an Army system.