Dynamic Response of Programmable Mechanical Properties 3D Orthogonal U‐Shaped Multistep Metamaterial Honeycomb Structures and Sandwich Panels

This study investigates the low‐velocity impact response of a novel programmable 3D orthogonal U‐shaped accordion (3D‐OUA) multistep metamaterial sandwich panel. The structure embeds secondary unit cells within primary U‐shaped accordion cells, enabling tunable mechanical properties and multistep deformation. The deformation modes and multistep load‐bearing of the new multistep structure are verified by experiments and numerical simulations. Results demonstrate that the multistep metamaterial exhibits two distinct stress plateaus, with the second plateau stress increased by 134.59% compared to 3D‐OUA structure. The validity of the finite element model (FEM) is verified by low‐velocity impact experiments, and the effects of geometric parameters and impact energy on the dynamic response are systematically analyzed. Under low‐energy impacts, only primary cell collapse occurs, while higher energy activates secondary cell deformation, forming dual‐stage contact force profiles. Parametric studies reveal that reducing cosine amplitudes ( A ₁ , A ₂ ) or increasing wall thicknesses ( b ₁ , b ₂ , t ₁ , t ₂ ) enhance impact resistance and reduce transverse displacements. Programmable mechanical response by tuning geometric parameters. The proposed metamaterial effectively improves the impact resistance of sandwich panels through multistage load‐bearing. This work provides a design paradigm for tunable anti‐impact structures with multistage energy management capabilities, offering insights for engineering applications requiring adaptive impact protection.