EFFECTS OF VACUUM AND PRESSURE IN AN AUTOCLAVE CURING PROCESS FOR A THERMOSETTING FIBER-REINFORCED COMPOSITE

The autoclave manufacturing of thermosetting composites involves several process parameters which affect, significantly, their two main physical properties - void content and glass-transition temperature, both of which latter determine the strength of the composites and their ability to maintain their strength at higher temperatures. This report analyses the effect of the bagging vacuum and the autoclave pressure on the void content, and subsequently on the bending strength and the modulus. Increase of the bagging vacuum was found to decrease the void content asymptotically, whilst increase of the pressure was found to decrease the void content exponentially. Both phenomena have been explained using a pressure/surface-tension void-stability approach involving a water-vapour diffusion mechanism. Post-curing treatment was found to increase the strength but not the modulus. The results indicate that to achieve process-optimisation, the vacuum should first be effected, to be followed by a minimum autoclave pressure of 4 bars, but optimally 12 bars. Post-curing treatment should follow for at least 12 hours thereafter. © 1990.