Geometric design and mechanical properties of cylindrical foldcore sandwich structures

Sandwich structures with foldcores are regarded as a promising alternative to conventional honeycomb sandwich structures as lightweight structural materials. One of the proposed applications of foldcore sandwich structures is on the aircraft fuselage and the interstage of a rocket. While flat foldcore sandwich structures have been intensively studied in the literature, there lacks a general design tool to create foldcores for a given cylindrical sandwich structure and the mechanical properties of such structures have not been well investigated. In this paper, a geometrical design protocol for foldcores that will fit into the space between the external and internal walls of a given cylindrical sandwich structure is developed based on the vertex method. A parametric study on the mechanical properties of several selected cylindrical foldcore models and a honeycomb core model virtually tested in axial compression, internal pressure and radial crush using the finite element method is performed. It is shown that foldcores outperform the honeycomb core model in axial compression and radial crush but have lower radial stiffness when subjected to internal pressure. The design protocol together with the virtual test results can serve as a useful tool for researchers to design cylindrical foldcore sandwich structures for many potential applications including but not limited to aircraft fuselage, submarine shell and other pressurized cylinders.