James Kratz

An experimental technique to characterize interply void formation in unidirectional prepregs

Out-of-autoclave prepreg processing requires evacuation of volatiles in the early stages of processing to achieve an acceptable final void content. In this study, single prepreg plies were laid-up onto a glass tool to simulate a ply–ply interface, to gain an understanding of initial air entrapment and eventual removal mechanisms. The contact was recorded during processing with various edge breathing configurations to identify the relationship between evacuation pathways and contact evolution. The existence of preferential flow channels along the fibre direction of the material was demonstrated by characterizing the prepreg surface. Gas evacuation in those channels prevented contact during an extended ambient temperature vacuum hold. The contact between the prepreg and glass tool equilibrated around 80% during the ambient vacuum hold, and reached full contact at elevated temperature after a brief loss in contact due to moisture vaporization, when the resin pressure decreased to below the water vapour pressure.

Resource-friendly carbon fiber composites: combining production waste with virgin feedstock

Abstract Reclaimed carbon fiber materials were studied in this paper with the aim of improving virgin fiber feedstock usage. Both processing and mechanical properties were investigated. The compaction response showed lower fiber volume fractions in reclaimed fiber materials than the virgin continuous reinforcement from which it was reclaimed. In addition, localized high-strain regions were observed during consolidation of the dry fiber and mechanical loading of cured laminates. These vulnerable failure points were mitigated by incorporating virgin continuous fiber feedstock into the laminate. A knock-down in mechanical properties was observed, however classical laminated plate theory identified a planar stiffness drop of 3.5 GPa for every 10% increase in reclaimed carbon fiber content in a continuous fiber laminate. Increased feedstock usage by combining both virgin and reclaimed carbon fibers was shown to be viable option to implement more resource efficient, but heavier, composite structures. Graphical abstract