Flexural and interlaminar shear strength properties of carbon fibre/epoxy composites cured thermally and with microwave radiation

The ease of heating an epoxy resin with microwaves depends, among other factors, on the dielectric properties of its components at the frequency of the radiation used. The majority of the papers published on the microwave curing of reinforced epoxy resin composites have used widely available DGEBA type resins and amine hardeners such as 4,4'-diaminodiphenylsulphone (DDS). This paper investigates the use of two epoxy systems where the choice of resin and hardener was based on their measured dielectric loss factors. System I contained a resin and hardener with higher loss factors than those used in System 2. The two systems are formulated with polyetherimide (PEI) as a toughening agent. Unidirectional carbon fibre prepregs were prepared from both systems. Composites were laid up from these prepregs, which were then cured in three different ways: autoclave curing, partial autoclave curing followed by microwave post-curing, and microwave curing. System I composites had greater flexural properties and interlaminar shear strengths than System 2 composites when autoclave cured. Flexural properties and interlaminar shear strengths were greater for System 2 in the microwave post-cured composites. When fully microwave-cured the properties were similar. In the microwave-cured composites the flexural and interlaminar shear properties were influenced by the structure of the phase separated PEI and the void content. (C) 2002 Elsevier Science Ltd. All rights reserved.