Capillary rise affects void inclusion during the impregnation of fiber reinforcements in resin transfer molding. A new model of effective capillary radius has been developed to investigate the effect of pore size distribution on capillary flow in unidirectional fiber bundles. With the image analysis method, the statistical results showed that the pore size distribution could be very different even for the same fiber volume fraction. Then, the classical Washburn equation, in conjunction with different models for calculating effective capillary radius, was applied to predict the capillary rise rate. Compared with the experimental results, we found that the new model performed better than traditional models where the effective capillary radius was obtained using average pore radius or hydraulic radius.
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