The permeability and compressibility of aligned and cross‐plied carbon fiber beds during processing of composites

Abstract Two of the most important input parameters needed to simulate the processing of continuous fiber laminated composites are the fiber bed permeability and the portion of the autoclave load borne by the consolidating fiber network (compressibility). In this study we have experimentally examined how both these parameter change with resin volume fraction as pressure is applied and consolidation proceeds. For a unidirectional fiber bed, the Kozeny‐Carman equation can be used to predict both the transverse (perpendicular to the laminate plies) permeability (Kozeny constant, K ′ z = 11) and the axial (parallel to the fibers) permeability (Kozeny constant, K ′ X = 0.57). The axial permeability was found to be dependent on the surface tension of the permeant. For a unidirectionally aligned fiber, the measured transverse permeabilities varied from 1.1 × 10 −10 cm 2 to 12. × 10 −9 cm 2 while the axial values varied from 2.1 × 10 −9 to 4.4 × 10 −8 cm 2 for a liquid volume fraction range of 0.25 to 0.5. Axial permeability measurements indicate that the permeability decreases with increasing off‐axis angle × (measured from the laminate axial direction). The off‐axis permeability behavior can be described by a modified Kozeny‐Carman equation. The fiber network compressibility can be described with a logarithmic relation which has been found valid for a large number of consolidated soils.