Fiber interactions in the multi-fiber composite fragmentation test

The single-fiber fragmentation test has been extended to a multi-fiber fragmentation test that demonstrates the fiber/fiber interactions that are present in real composites. The model composites are of Nicalon fibers embedded in an epoxy resin and have a controlled inter-fiber separation. An important qualitative result is that the interfacial failure in each fiber in an array is correlated with that of its neighbors, even when the individual fiber breaks are not at the same location. The fiber bundle as a whole thus has well defined regions of interfacial failure. Quantitatively, fibers in an array have a larger mean fragment length than a single fiber, and the fragment length increases with smaller inter-fiber separation or more embedded fibers. Shear-lag theory predicts the opposite effect. The results suggest that the presence of neighboring fibers prevent failure at some flaws. The flaw density function changes as a result of fiber/fiber interactions and this affects the fiber fragmentation process. Multi-fiber fragmentation tests show that the embedded single fiber test is insufficient to model fiber behavior within real composites.