The on-line cure monitoring during the cure process of fiber reinforced resin matrix composite material is important for the better quality and productivity. In this study, a cure monitoring system which consists of an electric circuit, a sensor and a personal computer was developed to on-line monitor the dielectric properties of carbon fiber epoxy composite materials. Also, the cure kinetic model of carbon fiber epoxy composite materials was developed by curve fitting of differential scanning calorimetry (DSC) data and was used for the reference of the degree of cure.
The sensitivity of the dielectric sensor for the on-line cure monitoring was analyzed by finite element method. Using the analytical results, the equation for the capacitance of the sensor as well as the effective range that the electric field affects the medium were obtained. Also, more sensitive sensor design than usual planar interdigital capacitor was suggested using the three dimensional FE analysis and experiment on the sensor types. Also, the start and end points of cure and the relationship between the dissipation factor and the degree of cure were obtained by comparing the dissipation factor from the dielectric properties with the degree of cure from the DSC data. The relationship between the dissipation factor and the degree of cure was tested under various temperature profiles. In addition, an insitu viscosity measuring device was developed to match the measured dissipation factor to the viscosity of the thermosetting resin of the composite material.
The autoclave cure cycle to prevent thermal overshoot during the exothermic reaction of thick thermosetting resin composite materials was suggested from the modification of the conventional cure cycle. To modify the conventional cure cycle, the simulation program to predict the temperature distribution of thick thermosetting composite materials was used. The steps of cooling and reheating were introduced into the conventional cure cycle to prevent thermal overshoot during the exothermic reaction and were determined using the parameters of the cure rate and the center temperature of the laminate. From the experimental result, it was found that the modified cure cycle can reduce thermal overshoot effectively.
