Effect of external pressure and resin flushing on reduction of process-induced voids and enhancement of laminate quality in heated-VARTM

Applying external pressure on the vacuum bag in heated-Vacuum Assisted Resin Transfer Molding (heated-VARTM) is a new approach for manufacturing high quality composite laminates with minimal voids. The present study focuses on the effects of external pressure and resin flushing on the microstructural features of the laminates, including spatial variation and size distribution of the voids as well as the compaction of fiber tows. The microstructural analysis performed on glass/epoxy composites reveal that external pressure reduces void content and average void size, and leads to more uniform spatial distribution of voids. Significant increase in fiber volume fraction from similar to 50% up to similar to 62% and a low void content of less than 1% are achieved by applying modest gauge pressure levels up to 138 kPa on laminates with various thicknesses. The increase in fiber volume fraction coupled with low void content improves the flexural properties as much as 20%, while the short-beam shear strength of the laminates remains unchanged due to low void content in all laminates.