Effects of interphase regions on performance of carbon fiber reinforced thermoset composites

The effects of systematically varied interphase materials on carbon fiber reinforced epoxy and vinyl ester matrix composites are under continuing investigation. Substantial differences in composite strength and fatigue durability have been observed between two composite material systems with epoxy matrices and contrasting interphases. The improvements were directly attributed to the application of a thermoplastic sizing miscible with the matrix resin, poly(vinylpyrrolidone), as opposed to a conventional epoxy sizing. In some cases, fiber dominated composite strength was improved by 50% and fatigue lives were increased by two orders of magnitude using the polyamide sizing. Distinct morphological differences resulted in the interphase regions using the different sizings, and thus, it was assumed that the local mechanical properties of the composites in this region were dissimilar. This work has now been extended to carbon fabric reinforced, vinyl ester/styrene matrix composites. Analogously, dramatically increased fatigue durability of these materials using poly(vinylpyrrolidone) sizings has also been observed.