Résumé
During impregnation of a fibrous reinforcement in Liquid Composite Moulding (LCM) process, capillary effects have to be considered, in order to identify their influence on void formation in composite parts. Wicking in a fibrous medium described by Washburn equation was considered as equivalent to a flow under the effect of a capillary-pressure according to Darcy's law. Experimental tests for characterization of wicking in both flax and carbon fibers reinforcements were carried out in their three main directions for quasi-UD fabrics by means of a tensiometer. Then, through the equivalence between Washburn and Darcy laws, an "orthotropic capillary-pressure" was identified. However for flax fibers reinforcements, results of wicking tests are a superposition of different phenomena due to its sensitivity to humidity. In order to make fibers less sensitive to water sorption, a thermal treatment was carried out on flax reinforcements. Swelling tests proved that treated flax fibers are less sensitive to these effects and wicking has a similar trend to those found for carbon fabrics, allowing determination of capillary pressure.