Material-equivalent hierarchical thin-walled structures with enhanced energy absorption and stable crushing behavior

Bio-inspired hierarchical core designs have been widely explored to improve the impact resistance of sandwich structures; however, most existing configurations rely on additive manufacturing to realize complex geometries, which limits their manufacturability and cost-efficiency in large-scale structural applications. This study proposes a material-equivalent hierarchical strategy that preserves geometric simplicity while achieving substantial improvements in crashworthiness. The resulting hierarchical cubic core is compatible with both additive manufacturing and conventional sheet-metal fabrication, thereby satisfying practical requirements for low-cost and scalable structural impact protection. The mechanical behavior of the proposed structure is systematically investigated through quasi-static compression tests, dynamic impact experiments, and validated finite element simulations, with direct comparisons to a conventional cubic core possessing identical mass and wall thickness. Results demonstrate that the hierarchical design promotes more stable and spatially distributed plastic deformation. In particular, the second-level hierarchy enhances deformation stability, reduces sensitivity to load misalignment, and facilitates more uniform plastic hinge formation. Consequently, the specific energy absorption is improved by 2.1 times, whereas the crushing force efficiency decreases by only 4%, despite a 30% reduction in effective crushing stroke. Compared with conventional honeycomb cores, the proposed hierarchical cubic core exhibits a lower initial peak force and a higher plateau force, indicating superior crashworthiness performance. Under dynamic loading conditions, both the hierarchical core and its two-dimensional array configuration further enhance impact energy absorption. In addition, a simplified analytical model is established to predict the mean crushing force of the structure. This work presents a manufacturing-friendly and cost-effective hierarchical core architecture for high-performance sandwich structures with enhanced impact protection capability.