Effect of packing on void morphology in resin transfer molded E-glass/epoxy composites

Effects of applying a packing pressure on void content, void morphology, and void spatial distribution were investigated for resin transfer molding (RTM) E-glass/epoxy composites. Packing pressures of zero and 570 kPa were respectively applied to center-gated composites containing 17.5% randomly oriented, E-glass fiber preform. Radial samples of these disk-shaped composites were utilized to evaluate voidage via microscopic image analysis. Two adjacent surfaces were cut from each molded disk in order to evaluate void presence from both through-the-thickness and planar views. The packed composite was found to contain almost 92% less void content than the unpacked composite. While void fractions of 2.2 and 2.6% were measured, respectively, from the through-the-thickness and planar surfaces of the unpacked composite, only 0.2% void content was observed in the packed composite from both surfaces. Digital images obtained from through-the-thickness surface showed that average void size dropped from 59.3 mu m in the unpacked composite to 31.7 mu m in the packed composite. A similar reduction in average void size from 66.7 to 41.1 mu m was observed from the planar surfaces. Circular voids were found to experience higher removal rates at 99%, followed by cylindrical and elliptical voids at 83 and 81%, respectively; while irregular voids show slightly lower void removal rates at 67%. Void proximity to fiber bundles was also observed to affect void reduction as voids located inside fiber tows experience lower void reduction rates. Along the radial direction of the molded disks, removal of voids with different proximities to fibers seems to depend on their arrangement at the end of the filling stage. These findings are believed to ascertain packing as an effective void removal method for RTM and similar liquid composite molding processes.