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Capillary pressure estimation depending on fabric, liquid and fibre volume fraction for Liquid Composite Moulding (LCM) processes

Abstract : In LCM processes, the impregnation in fabric by resin is commonly driven by a pressure gradient. More precisely, low pressure gradients are used to avoid fibre misalignment, meaning that all other forms of pressure such as capillary pressure (Pcap) cannot be neglected. This is because such pressure can contribute to the overall pressure gradient to drive flow front movement and an error in calculation of the overall pressure gradient can occur if the capillary pressure is not considered. Pcap is, here, a homogenized representation of local wetting effects that depends on the morphology of the medium and its interaction with the liquid. The Pcap was fundamentally estimated using the Young-Laplace’s equation where some shape factors appear to consider the flow. The Young-Laplace’s equation was used coupled with the Darcy’s law, measuring simultaneously the Pcap with the permeability. Authors have estimated the Pcap under a constant applied pressure gradient and at a constant flow rate, but shape factors 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 external driving pressure was applied during impregnation. The test velocity was thus non-constant allowing to define a homogenized value independent from the flow. In this case the Pcap is defined thanks to an equivalence between Washburn’s equation and Darcy’s law. The Pcap thus depends on parameters accounting for the geometry of the porous medium, the fluid-solid interactions and the medium permeability. 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 the determination of Pcap. In this work, a model was developed to predict the capillary wicking in flax fabrics at different fibre volume fractions (Vf), considering the multi-scale swelling effects of the elementary fibres and the individual yarns [3]. Then the Pcap was estimated in carbon fabrics and in flax fabrics. The main novelty of this approach resides in two aspects: the study of Pcap in natural fabrics and the correlation between the Pcap and the Vf, for both types of fabrics (carbon vs flax) and with different liquids (n-hexane vs water) (Figure 1).
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https://hal.mines-ales.fr/hal-03716617
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Soumis le : jeudi 7 juillet 2022 - 16:01:09
Dernière modification le : vendredi 5 août 2022 - 14:44:08

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  • HAL Id : hal-03716617, version 1

Citation

Hong Nhan Vo, Sylvain Drapier, Monica Francesca Pucci, Pierre-Jacques Liotier. Capillary pressure estimation depending on fabric, liquid and fibre volume fraction for Liquid Composite Moulding (LCM) processes. ECCM20 - 20th European Conference on Composite Materials, Jun 2022, Lausanne, Switzerland. ⟨hal-03716617⟩

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