Study of interfaces of high‐performance glass fibers and DGEBA‐based epoxy resins using single‐fiber‐composite test

The single‐fiber‐composite (SFC) technique was used to study the interfacial behavior between two flexible blends of diglycidylether of bisphenol A (DGEBA)‐based epoxy and polyglycol epoxide and three glass fibers. Dog‐bone‐shaped SFC specimens were made and strained to obtain a distribution of fragment lengths. The fibers were tension‐tested at two different gauge lengths. The fragment length distributions, the fiber strength data, and a Monte Carlo simulation of a Poisson/Weibull model for fiber strength and flaws were used to obtain the effective interfacial shear strength values. The results show that the interface does not fail. Instead, penny‐shaped transverse cracks appear at every fiber break and grow as the specimen is strained. The interfacial shear strength values are many times higher than the yield shear strength values of bulk epoxy obtained from the tension test.