Fig. 5: Energy absorption performance evaluation.

a 3D-printed CMCS metamaterial with 3 × 3 × 1 units. b Force-displacement curves of the CMCS (red line) and re-entrant (blue line) metamaterials by quasi-static compression experiments, where \(F\) and \(S\) are the force and pressure area, respectively. c Comparing CMCS (red bar) and re-entrant (blue bar) metamaterials in EEA, SEA, plateau phase (\({D}_{{{{\rm{P}}}}}\)), densification displacement (\({D}_{{{{\rm{D}}}}}\)), undulation of load-carrying (\({\chi }_{{{{\rm{ULC}}}}}\)), and relative density (\(\bar{\rho }\)) of which equations and values are provided in the Methods section and Supplementary Note 13, respectively, where \(h\) is the height. d The CMCS metamaterial attached to the hammer, where the hammer mass is 1 kg and the drop height is 1 m. e Force-time curves with (the red line) or without (the black line) the CMCS metamaterial. f Twenty drop tests are conducted with the same CMCS metamaterial and one without it; each red bar represents the peak force measured in the tests with the CMCS metamaterial, while the black bar represents the peak force without it.