In-site process monitoring using laser-based ultrasound

Manufacturers of polymer composite materials are seeking more economical methods for fabricating structures with complex contours. One such method is resin transfer molding (RTM). A method that uses a laser-based ultrasonic technique to monitor the resin flow front during transfer of the resin into the mold is described. The flow of a vinyl ester resin through a preform made from high density random chopped glass mats and an acrylic ester through a preform made from low density random chopped glass mat is studied. The essential features of these experiments are described, and sequences of ultrasonic images of the resin flow front during the transfer are presented. This monitoring technique provides an accurate measure of the progress of the resin through the mold, shows whether void areas develop, and provides an accurate measure of their elimination through continued resin transfer