Experimental Investigation of Bubble Mobility in Porous Media During Resin Transfer Molding

Abstract

Liquid Composite Molding (LCM) is a class of manufacturing processes such as Resin Transfer Molding (RTM) and Vacuum Assisted Resin Transfer Molding (VARTM) used to produce composite materials. One of the challenges in LCM is elimination of voids or air pockets in the final composite part which can compromise its structural integrity. One source of voids are the bubbles that are present within the resin as it enters the closed mold and are trapped as the resin cures. The first step to eliminate such voids is to understand their flow behavior in a resin that is injected into a fabric. We have carried out an experimental study to characterize the bubble movement through the pore network formed by the fabric weave architecture. The movement of bubbles within the resin is tracked using a camera within a transparent mold for three different fabric types. The bubble diameter and its velocity are measured as it goes through the fibrous media. By introducing dimensionless numbers that characterize bubble mobility (how fast the bubble moves compared to the resin velocity) as a function of dimensionless channel within the fabric weave (ratio of bubble diameter to the spacing of fiber tows) it is demonstrated that bubble mobility is much higher for tighter weaves and larger bubbles. This can help to optimize the LCM processes and minimize the voids by tunning the bubble mobility during the manufacturing process.