Effects of Cure and Sizing on Fiber-Matrix Bond Strength

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Abstract
Experiments were performed to evaluate the effects of cure and sizing on the bond strength between graphite fiber bundles and epoxy resins. Fiberite 976 and 934 resins and Thornel T300 (3K) fibers were used in the tests. The fibers were either uncoated (no siz ing) or coated with different types of sizing. Pure resin specimens and resin specimens containing a single coated or uncoated fiber bundle were prepared by curing in a mold at different temperatures. The specimens were subjected to three-point bending, and the load versus deflection curves were recorded. Photomicrographs of fiber bundles em bedded in the resin were also taken. The data show the influence of the cure temperature (and the corresponding degree of cure) on the fracture strain and on the stiffness of the pure resins. The data also indicate the effects of cure temperature and sizing on the fiber bundle-resin bond strength (as manifested by the specimen's fracture strain), and the effect of sizing on the geometry of the bundle and on the fiber density inside the bundle.