Elsevier Vernet, N.; Ruiz, E.; Advani, S.; Alms, JB.; Aubert, M.; Barburski, M.; Barari, B.... (2014) Abstract:In this second international permeability benchmark, the in-plane permeability values of a carbon fabric were determined by 12 participants worldwide. One other participant also investigated the deformation of this fabric. The aim of this work was to obtain comparable results in order to make a step towards standardization of permeability measurements of fibrous reinforcements. The procedures used by most participants were according to the guidelines defined for this exercise after the first benchmark. Unidirectional injections in three in-plane directions of the fabric were conducted to determine the unsaturated in-plane permeability tensor. Parameters such as fiber volume fraction, injection pressure and fluid viscosity have been fixed in order to minimize sources of scatter. The comparison of the results from each participant was encouraging. The scatter between data obtained while respecting the test guidelines was close to the scatter of the setups themselves. A slightly 2 higher dispersion was observed when some parameters differed from the recommendations.Overall, a good correlation is observed between all the results of this exercise.

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An analytical model has been created to estimate the in-plane and through-thickness permeability of three-dimensional Interlock fabrics. The model is based on the calculation of the pressure drop in the mesoscopic pores, i.e. in the inter-tow spaces of the fabric. Firstly, the dimensions and distribution of the mesopores are determined from the weaving parameters. A mesoscopic permeability model can then be inferred from the fabric structural data. The contribution of the microscopic flow inside the tows is also taken into account by introducing the concept of dual scale porosity. This additional feature is shown to improve the permeability model, which is validated by comparison with the experimental values of principal permeability measured for five different three-dimensional Interlock fabrics.

This paper reports an experimental investigation aiming to validate a predictive model of in-plane and transverse permeability for three-dimensional interlock fabrics as a function of fabric architecture. Composite specimens were fabricated and cut to conduct microscopic observations of pore dimensions for five three-dimensional interlock fabrics compressed to a fiber volume content of 58%. The pore cross-section height and width, the number of pores and the pore tortuosity were measured to evaluate an average pore size and distribution along the warp and weft directions for each fabric considered. The changes of these geometrical parameters are analyzed as a function of the fabric structure. A previously developed permeability analytical model is applied using the geometrical characteristics derived from the experimental observations. This allows comparing the experimental permeability to the theoretical predictions of the model and to the values calculated by the same model from the experimentally observed pore dimensions at the considered fiber volume content of 58%. The good agreement obtained in all cases between the measured and calculated values of permeability confirms the validity of the proposed analytical model.