A Non-Saturation Approach for Obtaining the Fiber-Matrix Interfacial Shear Strength in Glass Fiber Composites

The single fiber fragmentation test (SFFT) as currently devised involves the repeated fracture of a fiber embedded in a matrix dogbone specimen until the fragmentation process ceases (saturation). The average fragment length (lƒ) obtained from this test procedure is then used in a shear-lag model to determine the fiber-matrix (F-M) interfacial shear strength (IFSS) (tIFSS). This testing methodology has many issues that have precluded it from becoming a standardized test method. In 1991 Galiotis et al. developed a model-independent non-saturation approach for obtaining the F-M IFSS in SFFT specimens composed of Raman active fibers by directly measuring the strain in the deformed fiber. In addition to showing that the fiber strain profile best fit the Cox shear-lag model, their F-M IFSS values, which they termed tISS exceeded the yield stress of the epoxy matrix. In this paper, a non-saturation approach is put forth to obtain the F-M IFSS for Raman inactive glass fiber composites based on the average strain in the fiber (t〈ISS〉). A slight modification of the Cox shear-lag model is required along with the observation that the thermoset matrix that is used deforms in a nonlinear anelastic manner.