Void reduction of high-performance thermoplastic composites via oven vacuum bag processing

In this study, void reduction mechanisms during oven vacuum bag processing of high-performance carbon fiber thermoplastic composites are investigated. Entrapped air exists within the prepreg tape and between layers during lay-up and must be removed during processing to achieve aerospace quality (<1% void content) Key void reduction mechanisms during oven vacuum bag processing include through-thickness air diffusion and in-plane flow to the laminate edges through the permeable interlayer regions created by the prepreg surface roughness. Interlayer permeability between unidirectional and cross-ply laminates is measured experimentally and is sufficiently high for effective air removal during oven vacuum bag processing. Thick 72-layer carbon fiber/PEEK (poly (ether ether ketone)) laminates were fabricated with oven vacuum bag process under different edge sealing conditions. Void reduction in the laminate with sealed perimeter is dominated by air diffusion through the entire laminate thickness, and the laminate exhibits very high void content levels after oven vacuum bag processing. In the laminates with edges open to vacuum, air diffusion through a single layer and flow through the permeable interlayer lead to essentially void-free laminates. The findings show the importance of the interlayer permeability and edge conditions on the void reduction, and demonstrate that low void content can be achieved in thick section thermoplastic composite laminates via cost effective oven vacuum bag processing.