The variation mechanism of core pressure and its influence on the surface quality of honeycomb sandwich composite with thin facesheets

This paper successfully achieves the in-situ monitoring on core pressure of honeycomb sandwich composite during hot-pressing process by using a self-designed pressure sensing system. The core pressure variation and surface quality of honeycomb sandwich com-posites were investigated under open or sealed conditions, where the edges of sandwich composites were exposed to air or sealed with sealant tape, respectively. The results show that the core pressure increases with the increase in temperature and then declines at the stable temperature platform and cooling stage under open condition. The core pressure at the central area is bigger than that at the edge areas, and the dimpling defects are most pronounced on the thin facesheets at the edge areas under open condition during hot -press process. Under sealed condition, the core pressure is greatly enhanced and main-tains at a higher pressure during the whole manufacturing process, and thus the dimpling defects are minimized. The maximum core pressure at the edge area and central area of 25 cm x 25 cm sandwich composite may reach 4 kPa and 13 kPa, respectively. Furthermore, by using a self-designed device, the air permeability of the whole sandwich structure is measured, and a two-dimensional model is built to simulate the air flow and core pressure variation inside sandwich composites during hot-pressing process. The simulated core pressure variation shows the same tendency with experimental results, which explains the mechanism of core pressure variation and guides the control of process quality. (c) 2021 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).