Permeability and capillary effects in a channel-wise non-crimp fabric

Flow properties are investigated for a non-crimp glass fabric with large meso-channels designed for high-permeability, as compared to glass twill woven fabric. Saturated and unsaturated permeability are measured through in-plane, unidirectional, constant-pressure flow experiments. Capillary effects are evaluated following a novel approach based on the ratio of unsaturated and saturated permeability for a set of experiments conducted at capillary numbers varying over a large range from similar to 4.10(-5) to 4.10(-1). The mesoscopic pore-space of the compacted fabrics is imaged with X-ray Tomography, and analyzed to propose permeability predictions based on the channels geometry, which correspond well to experimental results. Permeability is governed by viscous flow in the meso-channels. As a result, provided that the capillary number exceeds a threshold value, the permeability can be rather accurately measured in these dual-scale fabrics by carrying out unsaturated measurements, neglecting micro-flow and capillary effects.