A STUDY OF THE INFLUENCE OF THE ENVIRONMENT ON THE MEASUREMENT OF INTERFACIAL PROPERTIES OF CARBON-FIBER EPOXY-RESIN COMPOSITES

The importance of understanding the interface and its reactions is paramount to determining optimum composite properties in service. However, many tests are not carried out at the temperatures and humidities which the component may be subjected to in service. The influences of resin type, hardener, cure time and temperature have been well established, although much work continues in ignorance of the precise details of the system being used. Additionally and perhaps more importantly, the temperature at which the composite part will be used and therefore the properties of the resin and the interface at this temperature should be ascertained for each system or well understood and therefore predicted. A specially designed environmental chamber has been built for the purpose of conducting high temperature fragmentation tests. Fractures of the resin at filament breaks in various systems and at various temperatures have also been studied. It is shown that small changes in the temperature of testing (relative to the T(g)) can alter the properties of the interface as much as any changes to the fibre treatment and matrix cure. The changes are found to involve not only a shift in the values of the fragment length but also their distribution, as well as the fracture morphology at fragmentation. All these factors must be considered in any analysis of the interface.