Vacuum bag only co-bonding prepreg skins to aramid honeycomb core. Part I. Model and material properties for core pressure during processing

A process model was developed for the honeycomb core pressure during sandwich panel manufacturing. The model predicted the inflow of moisture from the cell walls into the cell void space using by Fick's law, and the outflow of moist air through the bag-side skin was governed by Darcy's law. The model required the core moisture content and honeycomb skin through-thickness air permeability to be experimentally measured. A partially saturated out-of-autoclave woven prepreg was used as the skin material in this study. In-order to accurately apply Darcy's law during elevated temperature processing, an incremental temperature measurement technique was proposed to maintain constant skin thickness during air permeability characterization. Micro-CT imaging was performed on cure quenched samples to confirm that the proposed characterization technique maintained the impregnation dynamics of the target cure cycle. Model predictions using the characterized material properties are compared to in-situ core pressure measurements in Part II.