CURE MONITORING OF THE LIQUID COMPOSITE MOLDING PROCESS USING FIBER OPTIC SENSORS

Fluorescence has been demonstrated to be an accurate tool for monitori ng resin cure. It is measured using an evanescent wave fiber-optic sen sor. An economical optical fiber sensor has been developed with a refr active index greater than 1.6, permitting evanescent wave monitoring o f epoxy resins. The fluorescence wavelength-shift, which has been corr elated with monomer conversion, is monitored during the liquid molding process. Unidirectional glass fabrics with volume fractions from 40% to 60% were injected with epoxy resin at a variety of driving pressure s and cured at several temperatures. Several composite parts were fabr icated to test the effects of vacuum pressure, injection rate, cure te mperature, and fiber fraction on the performance of the sensor. The se nsitivity of the evanescent wave fluorescence sensor to the condition of the resin system was also examined. Two sets of resin/hardener samp les were subjected to rigorous chemical analysis to determine the exte nt of their differences.