THE DEVELOPMENT OF AN OPTOMECHANICAL RAMAN STRAIN SENSOR FOR USE IN HIGH-TEMPERATURE-CURING CARBON COMPOSITE STRUCTURES

A novel technique for detecting internal strains at a point within hig h-temperature-curing carbon composite laminates is described and utili zes the Raman properties of an embedded polydiacetylene crystal. Raman shift/strain dependencies are significantly improved if the effects o f twinning and stress transference between the laminate and the crysta l are minimized and maximized, respectively, by applying a thin film o f room-temperature-curing epoxy resin along the length of the crystal first, before curing the laminate. Qualitative explanations for its ac tion are given. Results demonstrate a linear relationship between Rama n shift and applied strain and high strain sensitivities. Suggestions for future improvements are offered.