Determination of the permeabilities of preforms is critical for an accurate analysis of mold filling during liquid composite molding processes. The complex labyrinth of the preform pore structures, however, presents a major challenge to a quantitative description of the microstructures, and conseqently, the evaluation of their permeabilities. Towards addressing this problem, a fundamental description of the disordered preform pore structures using fractal techniques is presented. A fractal permeation model is developed which relates the preform permeabilities to the actual microstructures in terms of two fractal dimensions-one relating the size of the capillary flow pathways to their population, and the other describing the tortuosity of the capillary pathways. The analytical model predictions are validated by experimentally-determined perme-abilities for a wide range of volume fractions and injection pressures. The model development, experimental studies and the model validation are presented and discussed.
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