FIBER INTERACTIONS IN THE MULTIFIBER COMPOSITE FRAGMENTATION TEST

The single-fiber fragmentation test has been extended to a multi-fiber fragmentation test that demonstrates the fiber/fiber interactions tha t are present in real composites. The model composites are of Nicalon fibers embedded in an epoxy resin and have a controlled inter-fiber se paration. An important qualitative result is that the interfacial fail ure 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 interfaci al failure. Quantitatively, fibers in an army have a larger mean fragm ent length than a single fiber, and the fragment length increases with smaller inter-fiber separation or more embedded fibers. Shear-lag the ory predicts the opposite effect. The results suggest that the presenc e of neighboring fibers prevent failure at some flaws. The flaw densit y function changes as a result of fiber/fiber interactions and this af fects the fiber fragmentation process. Multi-fiber fragmentation tests show that the embedded single fiber test is insufficient to model fib er behavior within real composites.