Void reduction in VARTM composites by compaction of dry fiber preforms with stationary and moving magnets

Voids are the most common process-induced defects in composite laminates fabricated by vacuum assisted resin transfer molding (VARTM). Reduction or total elimination of these defects is essential for the improved performance and long-term durability of the structural composites. This study introduces a novel method that reduces the void content in VARTM laminates to below 1% by compacting the fibrous mat before infusion. The compaction is achieved by applying magnetic pressure on the vacuum bag by either stationary or moving magnets which are removed before the resin infusion. To assess the effectiveness of the proposed method, 6-, 12-, and 18-ply random mat glass/epoxy laminates are fabricated by VARTM using compacted and uncompacted mats and their properties are compared. In addition, different sets of magnets are used to investigate the effect of compaction levels on the resin flow and the quality of the final part. The placement of stationary magnets on the entire vacuum bag surface is practical for fabrication of small parts. For medium to large parts, however, magnets with a smaller footprint can be moved to apply the compaction pressure over a larger vacuum bag surface. The results show that by applying compaction pressure of 0.2 MPa or higher either by stationary or moving magnets on the dry preforms, the void volume fraction was decreased by 65%-95% to 0.1%-0.8% in all laminates.