21st Congress of International Council of the Aeronautical Sciences, Melbourne, Australia, 13-18 September, 1998
Paper ICAS-98-4.4.3

THE EFFECT OF MATRIX MOISTURE CONTENT ON THE REPAIR OF CARBON FIBRE REINFORCED EPOXY

Bond D., Swan G., Bader M.*, Smith P.*
RAAF, Australia; * University of Surrey, United Kingdom

Keywords: matrix moisture content, repair, carbon fibre reinforced epoxy

Carbon fibre reinforced epoxy composites inevitably contain moisture absorbed from the atmosphere. Heating such composites to cure adhesively bonded repairs encourages diffusion of some of this moisture into the bonding adhesive. Here, the absorbed moisture may affect the integrity of the repair by causing; excessive adhesive voiding, adhesive plasticisation, interference to the adhesive cure and/or interference to the formation of an effective substrate-adhesive bond line. Thorough drying of composite substrates is usually recommended to avoid these possibilities. This research investigates the extent of drying required to restore substrate moisture free joint strengths. The strengths of joints constructed from substrates conditioned to various equilibrium moisture contents are compared to those of joints similarly conditioned, but which were dried for varying times prior to bonding. The pre-dried joints are shown to perform better (for a given substrate pre-join moisture content) than the undried joints. A model is developed to estimate the amount of moisture desorbed from the substrates to the joint adhesive and the strength of the joints is shown to be related to this quantity of moisture.

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