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Reinforcement permeability represents a crucial parameters in the manufacturing of fiber reinforced composites by liquid composite molding processes (LCM). 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. [ABSTRACT FROM AUTHOR]

Injection Pultrusion (IP) is one of the most effective processes, in terms of productivity and costs, to manufacture fiber reinforced polymers. In IP roving of fiber are driven through an injection chamber in which they are impregnated by the resin and then formed in a shaped die. The die is heated in order to cure the resin. Pultruded products are in most cases characterized by constant cross-section profile, whereas unidirectional long fibers are mainly used as reinforcing material. Two relevant phenomena occur within the injection chamber and the heated die, namely the impregnation of the fibers and the polymerization of the resin. Furthermore, thermal expansion, resin chemical shrinkage and the interaction between the die and the impregnated fibers strongly influence the process [1]. Clearly, thermal and mechanical fields significantly impact on these strictly chained behaviours. The use of thermocouples to evaluate temperature within pultrusion die is already widespread, but they are not capable to acquire any information concerning stress-strain levels. In the present work Fibers Bragg Gratings (FBG) sensors were used to measure thermal and strain profiles in selected material location within the injection chamber and the curing die. Being the differences among the spectres transmitted and received are related to the variations in both temperature and strain, commercial FBG sensors were opportunely modified and calibrated. The optical fibers were hooked to the fibers entering into the injection pultrusion die. Taking the pulling speed into account, each waveform acquired was correlated to a position within the die. Obtained data highlight the effect of the heat generation due to resin reaction as well as longitudinal strains related to the pulling force, the thermal expansion and the chemical shrinkage of the resin system. [ABSTRACT FROM AUTHOR]