HUMIDITY AND AUTOCLAVE PRESSURE EFFECT ON THE INTERFACIAL SHEAR-STRENGTH OF A MICROWAVE CURED EPOXY-GLASS FIBER-COMPOSITE

Microwave radiation curing of thermoset composite has been shown to achieve higher strengths and stiffness than conventional thermal curing, due to a higher Interfacial Shear Strength (ISS). Industrial processing of critical composite components requires the application of additional pressure to reduce the final composite void content. The nucleation and growth of voids is dominantly driven by vaporisation of moisture content, which is particularly accelerated in the microwave process, due to the high dielectric constant of water. This paper examines the effect of humidity content and pressure on the Interfacial Shear Strength of a hot curing epoxy/fibre glass composite that was microwave cured. Results indicate that the ISS decreased with higher humidity % for different microwave power settings from 500-75 W. Application of a 8 bar pressure during cure increased the ISS values for all humidity levels significantly. This was attributed to the reduction in the interfacial voids, so that the effective interface between the fibre and matrix is increased.