VACUUM-BAG-ONLY PREPREG PROCESSING OF HONEYCOMB STRUCTURES: FROM LAB-SCALE EXPERIMENTS TO AN AIRCRAFT DEMONSTRATOR

摘要

An aircraft demonstrator was manufactured using out-of-autoclave prepreg and vacuum-bagonlyrnprocessing techniques. The demonstrator featured flat, double-curvature, joggles, abruptrngeometry changes, and honeycomb inserts. The scientific literature was used to assess andrnmitigate the processing risks for this demonstrator. Low through-thickness gas permeability andrnply-bridging in small radii corners were thought to be the most significant risks. The throughthicknessrnpermeability of the target material was undetectable, therefore spiking was used tornincrease gas evacuation. Unfortunately, the available mould had small radii that could not bernincreased, as a result ply bridging was observed in these corners.rnMiniature pressure sensors were successfully embedded in the demonstrator to monitor thernhoneycomb core pressure throughout the lay-up, including intermittent de-bulking, the pre-curernvacuum hold, and the elevated temperature cure. The sensors identified two insightful processrnphenomena: 1) gas evacuation increased with additional plies, and 2) non-uniform pressurernresponse was observed in the part during cure. Visible part quality was acceptable, excludingrnsmall radii geometrical features. Internal part quality (voidage) was estimated using pulsedrninfrared thermography non-destructive-evaluation. While void contents are not exact, thernthermography revealed local voidage can vary significantly over the part.