THERMAL DAMAGE DETECTION OF CFRP USING COATINGS DOPED WITH FLUORESCENT PROBES

摘要

Incipient thermal damage of CFRP composites is a serious problem as it can significantly reducernmechanical properties of a composite and it is not detectable by common inspection methodsrnsuch as ultrasound. To detect this incipient thermal damage, DGEBA-DETA epoxy coatingsrndoped with a thermally responsive fluorescent probe were applied to CFRP composite panels andrnsubjected to localized heating at 204 ℃ and 232 ℃. At short exposure times (5 min) a yelloworangernfluorescence from the probe is observed, but for longer exposure times the fluorescencernchanges to a blue-green color. This shift in fluorescence wavelength was attributed to thernsuperposition of the probe fluorescence and the matrix fluorescence, which was also found torngrow with thermal exposure. After 30 minute exposures at 232 ℃, the fluorescence begins torndecrease due to oxidation of the matrix; however, the areas surrounding the quenched region arernstill fluorescent enabling optical detection of the damage even with the quenching of thernfluorescence. Removing the thermally oxidized surface layer by sanding was found to restorernthe fluorescence.