Experimental characterization of the pore size distribution in fibrous reinforcements of composite materials

This study uses capillary flow porometry to investigate the porous structure of engineering fabrics used in high-performance polymer composites. This technique consists of applying air pressure to a previously wetted sample to progressively expel the liquid from the pores. A porometry testing device commonly employed to characterize filtration media was used as the principal tool for this investigation. Four types of fibrous fabrics made of glass and carbon fibers with different textile architectures have been experimentally characterized with a through-thickness setup. This allowed obtaining the pore size distribution inside the tested material. In all the cases studied, the porometry technique was able to detect in a reproducible way a bimodal pore size distribution reflecting the presence of both micropores (inside the fiber yarns) and mesopores (between the yarns). Moreover, experimental results indicate that the method can be used to study the influence of the textile pattern on the pore size distribution. Overall, the study shows that capillary flow porometry can give valuable information on the dual scale structure of fibrous reinforcements, which plays a critical role during the impregnation stage of Liquid Composite Molding processes. Because of its simplicity and speed of execution, the proposed approach appears to be a promising way to complement other sophisticated techniques already used for composites such as microscopy and X-ray microtomography.