The effect of yarn length and diameter on permeability and compaction response of flax fibre mats

The manufacturing of fibre reinforced plastics using Liquid Composite Moulding (LCM) techniques requires compaction of fibrous reinforcements and flow of liquid resins through them before curing. In the modelling of LCM processes, an accurate description of compaction response and resin flow resistance through the fibrous media (also described as permeability) is required. Permeability and compaction response affect a number of important parameters, such as required tooling forces and mould fill-times. To study the influence of yarn diameter and length, on permeability and compaction characteristics of natural fibre reinforcements, six different types of flax yarn mats were manufactured. Compaction tests were carried out on both dry and saturated samples. Average in-plane permeability was also measured at different fibre volume fractions. It was found that increasing the yarn diameter reduced compaction forces and increased permeability. Long yarn length mats demonstrated higher permeability and compaction response than short yarn length mats.