Effective permeabilities of multilayer fabric preforms in liquid composite moulding

A homogenisation method was developed to predict effective permeabilities of multilayer fabric preforms by considering interlayer continuity and coupling between in-layer flow and trans-layer flow. A simplified approach was addressed first, from which the common approaches of arithmetic mean formation and harmonic mean formation can be deduced to define the effective permeability by neglecting coupling between in-layer flow and trans-layer flow. For multilayer preforms in liquid composite moulding, the permeability predicted by such an approach, however, is generally different from the actual one because of neglecting effects of micro-structure between layers and synchronisation between in-layer flow and interlayer flow. A conceptual model for interlayer flow, based on the hydraulic radius theory, was then proposed to quantitatively characterise the effect of interlayer micro-structure on the effective permeability of multilayer fabric preforms. The predictions show good agreement with experimental results available in literature.