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Gas transport in out-of-autoclave prepreg laminates Louis, Bryan Michael


Out-of-autoclave (OOA) pre-impregnated (prepreg) materials are a prospective alternative to traditional autoclave processing, with the potential to reduce processing costs and build structures without size limitations imposed by the autoclave. Gas transport pathways in prepreg laminates play an important role in the removal of entrapped gases and volatiles during processing. Removal of gases by vacuum evacuation is essential in order to produce composite laminates with low final void content. Gas pathways are of particular importance in OOA prepregs where the maximum applied pressure during processing is 1 atm. In this study, the gas transport of OOA prepreg MTM45-1/CF2426A (epoxy/carbon) laminates is examined. The gas permeability of laminates is carefully measured in the in-plane and through-thickness directions. The study examines the effect of the number of layers, the effect of internal ply terminations, and the effects of heat on laminate gas transport. Supplemental experiments such as laminate compaction, microscopy, and water visualization are conducted to gain additional understanding of laminate gas transport. The study shows that gas transport is strongly directional for the studied prepreg with significantly higher permeability in-plane than in the through-thickness direction. Counter-intuitively, the permeability of MTM45-1/CF2426A is not found to be greater than autoclave prepreg when compared to carbon/epoxy Toray 3900-2 (plain weave). The physical nature of gas transport pathways in MTM45-1/CF2426A prepreg laminates is found to change with processing state. Debulking was found to decrease in-plane gas transport from its as-laid-up permeability. Laminate heating is found to affect laminate gas transport. In-plane permeability decreased with increasing temperature, while through-thickness permeability increased with increasing temperature. Correlations between gas transport and laminate compaction is also evident. During debulking, laminate compaction is found to correlate to decreasing in-plane permeability. Additionally, laminate compaction is found to relate to the quality of edge breathing.

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