Characterisation of woven flax fibres reinforcements: Effect of the shear on the in-plane permeability

Abstract

International audienceThis paper describes a method to characterise the influence of in-plane shear on the permeability of fibrous preforms used in liquid composite moulding processes. An optical method for measuring the local shear variation of the woven textile is presented and used in conjunction with an in-plane permeability measurement system. Two flax fibre fabrics were tested and compared with a woven glass fibre fabric of similar architecture. The system presented here can be used either as a validation tool for permeability prediction models or to compile semi-empirical permeability models for the use in liquid composite moulding process simulation tools

Permeability characterization of sheared carbon fiber textile preform

“…This flow front tracking and analysis code has also been made freely available on the MathWorks file exchange website . Recently, other researchers have demonstrated similar automated tools for visual flow front tracking and local shear angles in deformed samples . Their work also observed increasing anisotropy with shear angle, along with a rotation of the principal permeability direction (relative to the twill‐weave fiber directions) that is similar to the results reported in this article.…”

Capillary wicking in a fibrous reinforcement – Orthotropic issues to determine the capillary pressure components

“…Measuring the permeability of fibrous preform is an important issue that is the aim of numerous ongoing studies all over the world [29][30][31][32]. To focus on capillary pressure in the present study, permeability measurements have not been performed.…”

“…For convenience values in the three principal fabric directions have been considered from literature. For later studies, these estimations can be replaced by measurements such as proposed for natural fibres [29] for instance. Values of transverse permeability of powdered carbon quasi-UD fabrics have been measured and found similar in at least two studies [38].…”

“…To make it possible, the tortuosity (c) and the mean average radius ( r) have to be characterised in the principal directions at constant fibre volume ratio (V f ¼ 40%). Those principal directions are the same that are commonly studied for non-sheared reinforcements [29]. Experiments using the sample holder described in Section 3.2.1 have been developed to allow measurements in:…”

“…In parallel, the liquid flow front motion in a porous medium was described by Darcy law [28], that relates the average velocity of a liquid to the pressure gradient, through the fluid dynamic viscosity g and the permeability tensor K. The permeability should be a physical parameter independent from the liquid used to measure it. It appears that the measurement of components of the permeability tensor is very sensitive to the method used [29][30][31][32]. Moreover permeability has to be considered depending on the degree of saturation of porous medium [33,34].…”