On the variability of permeability induced by reinforcement distortions and dual scale flow in liquid composite moulding: A review

A comprehensive review of experimental and analytical studies since 1990 on the variability of permeability induced by fibrous media (reinforcement) distortions across the composite part manufacturing chain is presented. The review covers variability in as-supplied dry reinforcements, which include tow waviness, tow size and tow shape variations, interconnectedness of the pore space inside the tows (tortuosity), and changes during production, handling or storage, affected by the reinforcement deformation (non-uniform shearing, stretching and compression) and nesting of the layers in the laminate. The review clearly indicates that the interdependencies among these parameters is one of the root causes of the spatial variation of the permeability of the preform. This has spurred recent work to quantify flow front and filling time variabilities and development of optimal injection strategies using stochastic flow simulations. State-of-the-art experimental and theoretical approaches and modelling of this stochastic behaviour within numerical frameworks for the design of composite manufacturing processes are introduced and future outlook on the role of such variability at different scales is forecasted.