Lab-based in-situ micro-CT observation of gaps in prepreg laminates during consolidation and cure

An experimental technique was developed to obtain 3D microstructural information on two typical lay-up features that often appear in automated fibre placement (AFP) or automated tape laying (ATL). Parallel-ply gaps between adjacent courses and ply-drop gaps needed to change the thickness of composite laminates were studied. Using a lab-based CT scanner, the different squeezing and bleeding mechanisms were obser ved while the manufacturing process was occurring. The initially large gaps were closed by fibre and/or resin flow, with the parallel-ply gap consolidating faster and reaching a lower porosity level than the ply-drop gap. However, after reaching a minimum porosity, previously consolidated voids reappeared and remained locked into the final microstructure. The in-situ CT data was helpful to identify opportunities for future process model developments. Overall, lab-based in-situ micro-CT was proven to be an effective and accessible technique to study how composite features evolve through the manufacturing process.

Automated summary

An experimental technique was developed to obtain 3D microstructural information on typical lay-up features in automated fibre placement or automated tape laying, with a focus on parallel-ply gaps and ply-drop gaps. Using lab-based CT scanning, different mechanisms of squeezing and bleeding during the manufacturing process were observed. The study found that parallel-ply gaps consolidate faster and reach lower porosity levels compared to ply-drop gaps, but previously consolidated voids may reappear and remain in the final microstructure.