The on-line cure monitoring of fiber reinforced thermosetting resin matrix composite material has been performed for improving quality and productivity during manufacturing. The dissipation factor measured by dielectrometry is dependent on both the degree of cure and temperature of resin. Therefore, in this study, a new method to obtain the degree of cure without temperature effect during on-line cure monitoring for glass/polyester and glass/epoxy composites was developed by employing a combination function of the temperature and the log dissipation factor. The elimination method removed the effects due to resistance and capacitance from the external cable, and consequently improved the sensitivity of cure monitoring. The temperature signal was measured with a K-type thermocouple and the dissipation factor signal was measured with an interdigital dielectric capacitance (IDC) sensor during curing process. Then the calculated degree of cure using the measured data from dielectrometry was compared to the measured value from DSC. The developed on-line cure monitoring method was applied to a 2-step cure cycle and a cooling-reheating cure cycle during the cure of planar thick composite laminates for the verification of the developed procedure.
Residual strains were measured using bore out experiment for axi-symmetric carbon/phenolic thick composites, and residual stresses were calculated from piecewise elimination of elements in FE analysis. The formation of wrinkle and void was eliminated by adapting radial expansion mechanism and modification of the cure cycle. In conclusion, the reliability of manufacturing of thick composites was improved from the application of cure monitoring technique during autoclave vacuum bag molding process.
