Prediction of permeability tensor for three dimensional circular braided preform by applying a finite volume method to a unit cell

Complete prediction of second order permeability tensor for three dimensional circular braided preform is critical to understand the resin transfer molding process of composites which are especially composed of thick or complex parts. The permeability can be predicted by considering resin flow through the multi-axial fiber structure. In this study, permeability tensor for a 3-D circular braided preform is calculated by solving a boundary problem of a periodic unit cell. Flow field through the unit cell is obtained by using a 3-D finite volume method and Darcy's law is utilized to obtain permeability tensor. The yarn is regarded as an impermeable solid because flow within the yarn can be neglected if inter-tow porosity is relatively high. To avoid checkerboard pressure field and improve the efficiency of numerical computation, a new interpolation function for velocity variation is proposed on the basis of analytic solutions. Permeability of the braided preform is measured through a radial flow experiment and compared with the permeability predicted numerically.