Monitoring autoclave cure in commercial carbon fibre/epoxy composites

Embedded dielectric sensors and thermocouples have been used to monitor the state of cure, in real time, for a range of current commercial epoxy resin carbon fibre reinforced composites. This paper summarises the methodology and data analyses involved in the monitoring procedure and gives specific examples of the results obtained. The generic rules governing the relationships between dielectric properties and material transformations for epoxy-based resins are stated. The problem of reaction exotherms in thick sections and the resulting uneven temperature and property distributions are quantified for two specific resin types. The reduction in interlaminar shear strength, resulting from the presence of the embedded dielectric sensors, is shown to be 15% for a brittle resin system and 5% for a tough resin system. The results and information obtainable from the dielectric cure monitoring are set against the background of the development of a comprehensive overall model for composite cure. (C) 1998 Elsevier Science Limited. All rights reserved.