Study of Processing and Properties of Graphite Fiber/High Temperature Resin Composites.

The effect of processing conditions on the structure and properties of composites was examined using polyphenylquinoxaline and other high temperature resins as matrices and graphite fibers as reinforcement. It was observed that inadequate resin flow and volatile removal caused extensive voids in the laminnate. The size and number of voids were found to be reduced by increasing resin flow as long as adequate measures were taken for the removal of volatiles. Increasing resin flow could be achieved by increasing the volatile content of the prepeg or by using a higher postcure temperature. However, reduction of voids was accompanied by an increasing tendency towards microcrack formation. A certain level of compaction is apparently necessary for the development of sufficient residual stress to cause translaminar cracking. Since the residual stress derives from the inherent properties of the components differential thermal behavior of fiber and resin, elimination of crack formation problems may be impossible without modification of component properties.