The influence of fiber wetting in resin transfer molding: Scale effects

Resin transfer molding (RTM) has become a popular technique for fabrication of composite parts. During the mold Ailing stage, the resin is forced to flow into pore spaces between tow filaments and the between the tows themselves. Voids trapped in the composite during the filling stage are believed to be the consequence of the non-uniform micro-flows inside fiber bundles and macro-flows between them. Thus, to minimize the void formation, the processing parameters should be determined to generate a uniform front. In this case, the flow inside tows Is driven by both the injection pressure and the capillarity forces and matches the flow outside the tows, which is driven only by pressure. To control such a flow, both viscous and capillarity flows have to be known at all scales of the fibrous structure. For this purpose, the wetting effects at the different scales (ranging ii-om the individual tow to the multi-layers reinforcements) are investigated. Original experiments are carried out to visualize micro-flows and to measure the capillarity flow rates. Wicking effects are quantified in terms of the overall and local effective permeabilities. A new parameter that accounts for interactions between flows splitting in macro- and micro-flows is introduced. Practical ways to reduce voids entrapment are also discussed.