Reduction of Voids in VARTM Composites by Magnetic Compaction of Preforms before Infusion

Abstract

The quality and performance of composites fabricated by vacuum assisted resin transfer molding (VARTM) are primarily characterized by their void content, often induced by the resin flow during impregnation. In this study, the effect of compacting 18-ply random mat and plain weave fabrics in a vacuum bag before the infusion was investigated as a possible low-cost method to substantially reduce or eliminate the process-induced voids in VARTM. The compaction of the fabrics was achieved by applying a set of Neodymium Iron Boron (NdFeB) permanent magnets on a vacuum bag lay-up. Laminates without magnetic compaction were also fabricated using identical parameters to demonstrate the effectiveness of this method. The impregnation of the compacted fabrics became much slower and took almost twice as long compared to the uncompacted parts. The final thickness of random mat and plain weave reinforced epoxy laminates did not change and remained at approximately 4 mm and 2.7 mm, respectively. The measurements indicate a relaxation of the compressed mat as the resin front progressed along the lay-up. Most interestingly, however, the void volume fractions of the compacted random mat and plain weave laminates were reduced to the very low 0.90% and 0.99%, respectively, from the relatively high 5.7% and 2.7% level observed for the uncompacted laminates. Finally, the flexural strength and modulus of the compacted random mat and plain weave laminates slightly improved compared to those manufactured by traditional VARTM. For instance, the flexural modulus of compacted woven/epoxy laminates is almost 6% higher than that of the uncompacted laminates.