Permeability of 2D Woven Composite Textile Reinforcements: Textile Geometry and Compaction, and Flow Modelling

Abstract

Liquid Composite Moulding (LCM) is an important family of processes to manufacture high-performance fibre-reinforced composite parts. A typical LCM cycle involves the insertion and compaction of a textile reinforcement into a mould cavity, followed by the injection of liquid resin. Complete reinforcement-resin saturation is paramount to the fabrication of defect-free composite products, and LCM process simulations are powerful tools for effective process design. These simulations require the input of accurate reinforcement permeability data, which is a physical property that depends on the reinforcement’s flow architecture. Considering the wide variety of available textile reinforcements on the market and under development, the need for an efficient and versatile numerical tool to accurately predict the permeability of general engineering textiles was identified. A comprehensive permeability simulation chain has been developed and demonstrated to predict the permeability of a 2D woven reinforcement. A stacked sample of the studied textile has been non-destructively imaged using a laboratory-scale micro-computed tomography scanner. The individual tow information contained in such a scan was automatically identified using a novel image processing methodology, which combines 3D structural tensor analysis, unsupervised machine learning classification algorithms, and tow mapping-correction schemes. The extracted tow data was inputted to another novel modelling methodology to automatically construct realistic multi-layer textile unit cells. These textile unit cells were guaranteed to be periodic, free from non-physical inter-tow penetrations, and possess no simplifying geometrical assumptions. An in-house conformal meshing algorithm was implemented to convert these unit cells to highly structured finite-element meshes, which were numerically compacted to fibre volume fractions up to 0.60. The tow mechanics in the compaction simulations were modelled using a novel non-linear large-strain constitutive approach, capable of predicting the shape changes and stresses in deforming tows. Low Reynold-number flow simulations were then carried out on the compacted textile unit cells, followed by the computation of unit cells’ permeability using Darcy’s law. The predicted permeability values were compared with those obtained from flow permeability experiments. Strong agreement between the two permeability datasets was concluded, thus establishing the reliability of the proposed permeability simulation chain.