Correlation of the Rate Dependence of Fracture Toughness between Carbon-Fiber/Epoxy Composite and Neat Epoxy Resin.

Abstract

Mode I fracture behavior of modified epoxy (#133, Toho rayon) and carbon-fiber/modifiedepoxy composite (IM 600/133, Toho rayon) was examined over eight decades of loading rates from 0.01 mm/min to 15 m/sec to study the correlation of their rate dependence. Although the fracture toughness of both epoxy resin and composite laminates showed negative rate dependence, the epoxy resin was more rate-sensitive than the composite laminates especially at very low loading rates. Microscopic observation showed that the debonding of the interface between carbon fibers and matrix resin was dominant at low loading rates but that the fracture of matrix resin was dominant at high loading rates in composite laminates. This was considered to be the cause for the difference of the rate dependence between in the composite laminates and in the epoxy resin at very low loading rates. The crack growth behavior was unstable at low loading rates but stable at high loading rates in the epoxy resin. In the composite laminates, however, the crack growth behavior was almost stable over the range of loading rate tested in this study.