A fractal geometry model for evaluating permeabilities of porous preforms used in liquid composite molding

Permeation of a net-shaped porous preform by a catalyzed thermosetting resin is an important step in the fabrication of fiber-reinforced composite materials using liquid molding techniques. Determination of the preform permeabilities is critical for an accurate analysis and design of these processes. The complex labyrinth of the preform pore structures, however, presents a major challenge to a quantitative description of the microstructures, and consequently, the evaluation of their permeabilities. Toward 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 permeabilities for a wide range of preform and process parameters. The model development, experimental studies and the model validation are presented and discussed. The methodology presented may be extended to analyzing transport through porous media arising in other application areas as well. (C) 1999 Elsevier Science Ltd. All rights reserved.