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Metastructures have drawn extensive attention from researchers due to their excellent mechanical properties. In this paper, to further enhance the mechanical properties of the re-entrant origami honeycomb metastructure, the bio-inspired hierarchical design is introduced on the re-entrant origami honeycomb metastructure, a novel hierarchical re-entrant origami honeycomb (HROH) metastructure is proposed. The crashworthiness of the novel HROH is researched under low-velocity and high-velocity impact. The results indicate a significant improvement in the energy absorption capacity of the novel HROH compared to both the conventional hierarchical re-entrant honeycomb and the re-entrant origami honeycomb. The plateau stress of the novel HROH under different compression velocities are derived by the two-scale method. And the theoretical results are in good agreement with the numerical results. Moreover, the influences of the dihedral angles and wall thickness on impact resistance also are studied. To increase the wall thickness will improve the plateau stress and SEA–strain curve of the HROH, while increasing the dihedral angles will diminish the plateau stress and SEA–strain curve. In addition, to obtain the optimal structure of the HROH, a multi-objective optimization method based on surrogate models and the non-dominated sorting genetic algorithm II (NSGA-II) is employed. The results exhibit high accuracy in the crashworthiness optimization. This study provides a crucial reference for the design and application of buffer protection structure in fields such as automotive, aerospace and defense. • A novel re-entrant origami honeycomb is proposed by introducing hierarchical design. • The two-scale method is used to derive theoretical expression of the novel honeycomb. • Energy absorption and deformation mode of the novel honeycomb are studied. • A multi-objective optimization method is employed to obtain the optimal structure. [ABSTRACT FROM AUTHOR]

Recently, auxetic metamaterials have turned into an area of growing interest, because of their deformation uniqueness, design flexibility, and functional diversity. To achieve their programmable design of densification and energy absorption, the variable stiffness factor method (VSF) emerged. However, the energy absorption capacity of the metamaterials designed by this method has a significant reduction. In this work, to remedy this defect, several different lightweight specimens are proposed and fabricated to extend the stage of energy absorption and retain the tunability. Then quasi-static compression tests and finite element methods are carried out to analyze the mechanical properties of the designed boundary-constrained structure (BCS) and X-shape constrained structure (XCS). The accuracy of the densification points and energy absorption capacity of the two structures at different VSF values are also studied. The results show that the densification points of the designed structures can be adjusted quantitatively, and their deformation modes are more stable than conventional structures during compression. Furthermore, their specific energy absorption is four and five times higher than that of non-lightweight structures with VSF = 40%, respectively. These findings contribute to advancing the implementation of auxetics in applications of multistage protective structures. • A lightweight metamaterial based on the variable stiffness factor (VSF) method is proposed. • The proposed structures realize multi-level energy absorption and stable deformation. • The SEA of proposed structures was 4 and 5 times higher than that of VSF = 40% structure. [ABSTRACT FROM AUTHOR]