Three-dimensional features of void morphology in resin transfer molded composites

Detailed analyses of shape, size, and spatial variations of void morphology are presented for a disk-shaped, resin transfer molded (RTM), E-glass/epoxy composite. The disk is molded at constant injection rate and contains 17.5% E-glass random fiber mats. Voids throughout the composite are evaluated by microscopic image analysis of through-the-thickness and planar surfaces obtained from adjacent radial samples. The void content of 2.15% is obtained from the analysis of through-the-thickness images and believed to be representative of the actual void content in the studied part. Relatively large cylindrical voids are observed in cigar shapes in the planar surfaces, whereas these voids only appear as small irregular or elliptical voids on through-the-thickness surfaces. Along the radial direction, combined effects of void formation by mechanical entrapment and void mobility are shown to yield a complex radial void distribution. It is shown that fewer voids are trapped mechanically with increasing distance from the inlet and most of the medium and small voids that are mobile migrate towards the exit during resin injection. These findings are believed to be applicable not only to RTM, but generally to liquid composite molding processes with varying fluid front velocities.