Résumé
In LCM processes, the impregnation in fabric by resin is commonly driven by a pressure gradient. Moreprecisely, low pressure gradients are used to avoid fibre misalignment, meaning that all other forms ofpressure such as capillary pressure (Pcap) cannot be neglected. This is because such pressure cancontribute to the overall pressure gradient to drive flow front movement and an error in calculation ofthe overall pressure gradient can occur if the capillary pressure is not considered. Pcap is, here, ahomogenized representation of local wetting effects that depends on the morphology of the medium andits interaction with the liquid. The Pcap was fundamentally estimated using the Young-Laplace’sequation where some shape factors appear to consider the flow. The Young-Laplace’s equation was usedcoupled with the Darcy’s law, measuring simultaneously the Pcap with the permeability. Authors haveestimated the Pcap under a constant applied pressure gradient and at a constant flow rate, but shapefactors are difficult to measure, and results strongly dependent on such parameters [1].Other works focused on the spontaneous capillary wicking to determine the Pcap, where no externaldriving pressure was applied during impregnation. The test velocity was thus non-constant allowing todefine a homogenized value independent from the flow. In this case the Pcap is defined thanks to anequivalence between Washburn’s equation and Darcy’s law. The Pcap thus depends on parametersaccounting for the geometry of the porous medium, the fluid-solid interactions and the mediumpermeability. All parameters can be evaluated independently by experimental methods [2].On the other hand, natural fibres have not a stable morphology during wicking that makes difficult thedetermination of Pcap. In this work, a model was developed to predict the capillary wicking in flaxfabrics at different fibre volume fractions (Vf), considering the multi-scale swelling effects of theelementary fibres and the individual yarns [3]. Then the Pcap was estimated in carbon fabrics and inflax fabrics. The main novelty of this approach resides in two aspects: the study of Pcap in natural fabricsand the correlation between the Pcap and the Vf, for both types of fabrics (carbon vs flax) and withdifferent liquids (n-hexane vs water) (Figure 1).