Through thickness permeability and compaction characterization of 3D preforms using in-situ μXCT

Compaction of composite reinforcement preform and resin infusion are two major steps in composite manufacturing by liquid composite molding processes. Understanding of the preform compaction and permeability characteristics is important for the process characterization and optimization. Existing methods either require a number of tedious experiments or numerical simulations using geometric models of the reinforcement preform. Geometric modeling approaches of the preforms fail to capture the real architecture as well as the effect of the compaction of the reinforcements. This study presents numerical computation of through thickness permeability of two types of 3D woven fabrics by in-situ compaction characterization using micro X-ray computed tomography (μXCT). The study involves extracting geometrical features of the fiber reinforcement, followed by detailed flow analysis using two different commercial software packages. The real-time 3D images obtained by in-situ compaction at four different fiber volume fractions. A bimodali segmentation was applied to separate the fiber tows from intra tow gaps. The gap analysis reveals significant changes in the meso-structure of the preform under applied compression. The conservation of mass and momentum equations were solved to obtain the flow field within the intra tow gaps for a representative volume element and Darcy's law was to obtain the preform permeability. The flow field analysis revealed three dimensional flow paths within the preform. The through thickness permeability values were in excellent agreement with the experimental data.