FIBER-MATRIX LOAD-TRANSFER IN CYANATE RESIN CARBON-FIBER SYSTEMS

Comparative single fiber fragmentation test measurements are used to characterize cyanate and epoxy resin interface load transfer with high modulus (HMS4) and high strength (AS4) carbon fibers. The HMS4 fiber forms a weak interface with a fiber controlled failure mode, and the AS4 fiber forms a strong interface with the resin properties, apparently determining the level of load transfer. The resin properties examined are critical surface energy for wetting, cure shrinkage, thermal shrinkage, and mechanical modulus and strength. The cyanate and epoxy resins display no significant difference in critical surface energy. Cure shrinkage has a negligible effect on load transfer. The compressive force from thermal shrinkage is significant, but the larger Tg to testing temperature range of the cyanate resin is offset by the larger thermal expansion coefficient of the epoxy, resulting in a near equal compressive force for the two resins. There is little difference in modulus between the two resins but a significant difference in shear strength. This difference is reflected in the larger load transfer measurement for the cyanate resin. A comparison of simple one-dimensional elastic and plastic models for the fiber fragmentation experiment resulted in better conformity with the plastic model. This would indicate that interfacial failure occurs by plastic deformation of the resin for the systems of this study.