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The Use of Microdielectrometry in Monitoring the Cure of Carbon-Epoxy Prepreg.
Technical rept. no. 3 (Final) Sep 84-Sep 86,
WESTINGHOUSE RESEARCH AND DEVELOPMENT CENTER PITTSBURGH PA
Pagination or Media Count:
As thermosetting resins and composites made from them begin to be used in critical applications, it becomes necessary to monitor and analyze the cure of the resin within the confines of the processing equipment. Such measurements have been carried out using a dielectric technique called dielectrometry or dielectric analysis. Conventional dielectrometry has certain limitations associated with the use of parallel plate geometry for electrodes. For in situ measurement of cure, intrusiveness of electrodes is a problem which may require placement of electrodes in non-strategic areas. Since electrode spacing changes during cure, it is difficult to deduce permittivity and loss factor from the data. At lower frequencies the capacitive currents are small and signal-to-noise ratios are small, therefore, measurement at low frequencies 100 Hz typically require large electrode sizes. Results show that microdielectrometry can be used to follow the cure of the prepreg and absolute measurements of permittivity and loss factor can be made to provide information on the mechanisms that produce the observed changes. Data at 1 Hz can be obtained. For these systems prior to gelation at typical cure temperatures, the data is often out of range of the instrument, requiring the use of a high conductivity option which we do not have for monitoring that regime of cure. Lower than expected permittivity values at the end of cure indicate some problems with resin separation from the chip surface. Experiments with aged prepregs are also described.
APPROVED FOR PUBLIC RELEASE