Processing out-of-autoclave honeycomb structures: Internal core pressure measurements

A strong desire to reduce manufacturing costs in the aerospace industry, coupled with recent advancements in out-of-autoclave prepreg materials, has created the potential to manufacture composites with only vacuum pressure. As a step towards better manufacturing of sandwich structures, we focus on the behaviour of air inside a honeycomb core during vacuum bag processing. The pressure of the air inside the core was measured in a lab-scale test fixture to simulate full-scale manufacturing. The lab-scale tests revealed pressure fluctuations if the internal core pressure equalled atmospheric pressure during processing. Furthermore, an increasing number of pressure fluctuations were observed for increasing cure temperatures. Sandwich panels cured at higher temperatures had a higher void content and a worse bond between the skin and core.