Permeability characterization of braided fabrics made of hemp fibers

Abstract

Reinforcement permeability represents crucial parameters in the manufacturing of fiber reinforced composites by liquid composite molding processes (LCM) [1]. Evaluation of fabric permeability is usually challenging and it requires several flow experiments. Indeed, permeability usually presents different values due to the anisotropic nature of textiles and different values have to be evaluated to calculate the permeability tensor. In addition, different flow conditions could establish during the impregnation: macroscopic and microscopic flow through the inter- and intra-tow leading to unevenly wetted regions of the fabric. Finally, differently from synthetic fibers, natural fibers can absorb fluid, acting as a sink, drawing fluid from the main flow and causing swelling of the natural fibers. In this work unsaturated permeability of braided hemp fabrics are studied for different architectures. Two type of braided fabric were investigated: triaxial and biaxial braids. Three distinct values of braiding angle, namely 45°, 50° and 60° were adopted for the biaxial braid to assess the impact of the braiding angle on the reinforcement permeability. The relation between permeability, porosity and fabric architecture was obtained in the case of the Vacuum Assisted Resin Infusion process.