Optical measurement of voids in situ during infusion of carbon reinforcements

Abstract

Liquid composite molding (LCM) is growing in importance as an alternative to traditional prepreg-autoclave methods for manufacture high-performance composites. The most significant roadblock to industry’s implementation of LCM is the usually higher void content compared with prepreg processing. One tool for reducing void levels in LCM involves optimization of flow velocity, which requires models to be developed to describe void formation at a given velocity. To help solve this problem, the following research illustrates the first known method for optical void measurement in situ during infusion in a carbon fiber reinforcement. Similar to previous studies on glass fiber, this work utilizes fluorescent dye and a digital camera to produce sufficient contrast and resolution for image analysis. Visible bubbles are photographed against the opaque carbon fiber background. An automated method of image analysis is outlined, which was used to analyze 230 images for three different flow orientations of a single fabric, producing the highest amount of experimental data seen so far on in situ void measurement. The resulting data identifies a minimum velocity threshold for minimal macro-void formation. The resultant void characterization framework will better enable optimization of LCM processing for high-performance composites based on carbon reinforcements.