Experimental investigation of intra-tow fluid storage mechanisms in dual-scale fiber reinforcements

Fiber reinforcements used for structural RTM applications feature dual-scale porous microstructures. During injections, these microstructures induce intra-tow resin storage that affects, significantly in fast curing cases, the distribution of temperature, viscosity and degree of cure. Storage is considered permanent in the literature; however, to optimize the process, a finer understanding of the storage and release mechanisms is required. To reach this goal, an experimental program has been implemented. Based on the injection of colored model and UV-curing fluids, the distribution of the colorant during the injection has been studied in a quantitative manner at the macroscopic and microscopic scales. It has been observed that storage is transient and that the release rate depends on the average FVF, the fiber orientation and the architecture of the reinforcement. Furthermore, the local intra-tow flow mechanisms have been identified. Finally the overall/tow permeability ratio has been identified as a good indicator to classify storage trends.