Quasi-static impact of indented foldcores

• Sub-folds are introduced into a standard foldcore to make an indented foldcore.
• The indented foldcore possessed a high-order travelling hinge line (THL) failure mode.
• The THL failure mode can absorb more energy in a more uniform manner than a standard failure mode.
• Improvements in energy absorption by up to 39% were seen, with a 35% improved uniformity.
• Good correlation is seen between numerical and experimental results.

A modified planar foldcore geometry was developed by introducing sub-folds into a standard foldcore pattern. It was demonstrated using numerical simulation that the new geometry, deemed the indented foldcore, successfully triggered a high-order travelling hinge line failure mode. This was found to have a much higher and more uniform energy absorption than the plate buckling failure mode seen in a standard foldcore structure. A numerical analysis also established optimum standard and indented geometries with maximum energy absorption. Prototypes were constructed to experimentally validate numerical findings. Prototypes with no visible geometric imperfections displayed the travelling hinge line behaviour as predicted. Prototypes with visibly-buckled plates showed no change in failure mode compared to a standard foldcore, confirming numerical findings that the travelling hinge line failure mode is highly sensitive to geometric imperfections.

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