A nonlinear compaction model for fibrous preforms

Based on the mechanics of porous media and physical insight gained from experimental observation, a model for predicting the nonlinear compaction of fibrous preforms in the resin transfer molding process is developed. A key physical constant - namely, preform bulk compressibility - is proposed to establish the relationship between the applied pressure and the preform bulk volume. The preform bulk compressibility is a function of fiber volume fraction and five parameters - the initial fiber volume fraction, the final (maximum attainable) fiber volume fraction, the initial pore volume compressibility, the fiber compressibility, and an empirical index. Results of compaction experiments on plain-woven fabric preforms and unidirectional non-woven materials support the validity of the model. Excellent agreement between theory and experiments has been obtained. The present model provides for fibrous preforms a nonlinear constitutive law whose coefficients can be physically interpreted. (C) 2001 Elsevier Science Ltd. All rights reserved.