Experimental characterization by fluorescence of capillary flows in dual-scale engineering fabrics

Abstract

Liquid composite molding (LCM) is an increasingly used family of processes to manufacture composite parts. In LCM, the fibrous reinforcement is first laid in a mold cavity. After closure of the mold or covering of the reinforcement with a plastic bag, a liquid polymer resin is injected or infused under vacuum through the fiber bed. A key issue and novel feature of this investigation lies in the dual-scale architecture of engineering fabrics: microscopic pores exist between the filaments of the fiber tows, while macroscopic pores are created between the tows as a result of the stitching/weaving process. On a microscopic scale, capillary flows in fiber tows and gaps between tows play a major role on the quality of impregnation of the fiber bed by the liquid resin. In order to better understand the mechanisms that govern the impregnation of fibrous reinforcements in LCM, an experimental study of wicking behavior was carried out based on capillary rise experiments. A new monitoring technique based on fluorescent dye penetration inspection (DPI) and digital imaging was implemented in this investigation to track the capillary flow front. Visual monitoring of the capillary front is coupled with Wilhelmy’s approach based on real-time fluid mass acquisition with a high resolution balance. Experimental observations of the height of the capillary front and the uptake fluid mass absorbed by the fabric were analyzed by two different imbibition models.