Investigation of microscale flow phenomena in determining permeabilities of fabrics for composites.

Abstract

An accurate model is needed for the flow of resin through fabric reinforcements, especially those that have been deformed, mainly in shear, when conforming to the shape of a curved part. The goal of this work was to develop such a model, based on the fabric microstructure. Experiments were carried out to determine the permeability of sheared fabric reinforcements. The trends observed could not be modeled by existing semi-empirical or empirical approaches. A three-dimensional fabric model was developed, as well as an algorithm to obtain cross-sections through fabric layers at any desired angle and through any desired point, for any shear angle. Those tools were used to interrogate the effect of layer nesting and to establish the geometry of the gaps that occur between fabric tows. After verifying that the assumptions for creeping flow were valid for cases of interest, a model based on gap size was developed. Results obtained with this variable-gap model for realistic production conditions bound the experimental permeability data, and give excellent predictions for the principal flow directions. Moreover, the techniques developed here use no fitting parameters.