Resin Transfer Molding (RTM) involves the injection of liquid resin into a closed mold preloaded with dry preforms. For planar composite structures, the in-plane permeability should be determined prior to the injection process in order to predict the fluid flow and fill time progress. In this work, the in-plane permeability of multi-layer multi-directional warp knit (MMWK) laminates stitched using Kevlar fiber were measured using radial flow visualization experiments. The visualization demonstrated that the in-plane permeability of MMWK laminates is highly anisotropic and significantly influenced by the Kevlar stitches. Results showed that the major principal permeability, kx, decreased with an increase in stitch density. Although the stitches resulted in an increase in minor principal permeability, ky, it seems that the increase in stitch density did not result in an obvious change in ky.
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