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 observed 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.