Effective compressibility and permeability of multi-layer non-crimp fiberglass reinforcements

Liquid moulding processes, such as resin transfer moulding (RTM), utilize fiber reinforcements to produce composite parts. These reinforcements may comprise multiple layers of a particular fabric or an arrangement of different fabrics, depending on the structural and/or processability requirements. It is therefore important to study the effective compressibility and permeability of these multi-layer reinforcements. In the present work, compaction and radial flow tests were conducted on three different non-crimp fiberglass fabrics. The reinforcements used in the tests consisted of either multiple layers of the same non-crimp fabric or multiple layers of a combination of the fabrics (hybrids). The experimental results were processed to obtain the compressibility and in-plane permeability of the various reinforcements. It is shown that the effective compressibility of a hybrid reinforcement is predominantly determined by the compressibility and proportion of the constituent fabrics. However, the effective in-plane permeability of a multi-layer hybrid reinforcement is found to be dominated by the orientation and proportion of the fibers on the outer surface plies.