Glass fibre epoxy composite sure monitoring using parallel plate dielectric analysis in comparison with thermal and mechanical testing techniques

This investigation considers dielectric response using a parallel plate arrangement, as opposed to the commonly used single surface sensor, in an attempt to monitor signal change during composite cure. Parallel plate arrangements provide the possibility of obtaining an average state of cure throughout the composite thickness without necessitating the inclusion of the sensor within the composite structure. To assess the suitability of this sensor arrangement, a Dielectric Analyser (DEA) was used to simulate the cycle conditions of a Resin Transfer Moulding (RTM) process. Arbitrary positions of the DEA analysis output were used to identify the conditions for various states of cure, to which several mouldings were subsequently manufactured and cured using an RTM system. Thermal and mechanical testing techniques were performed on these RTM mouldings in an attempt to determine the suitability of the parallel plate sensors for degree of curl detection and the influence of cure upon the final composite material properties. Results indicated that a correlation does exist between the DEA output using parallel plate sensors and the change in properties of the composite with cure time. This was additionally beneficial in that the optimum cure cycle was identified. Finally parallel plate DEA is discussed as a means not only for optimising cure cycles in the laboratory but as a potential means of process control. (C) 1998 Elsevier Science Ltd. All rights reserved.