Crushing response of novel bionic bi-hexagonal hierarchical multicell tubes for energy absorption

Numerous studies have demonstrated the advantages of multicellular tubes in energy absorption, and hierarchical structure is one of the effective means to develop the cross-section of thin-walled tubes. However, the potential of dual hexagonal hierarchical tubes remains largely unexplored. This paper aims to develop bionic bi-hexagonal hierarchical multicell (BBHM) tubes, inspired by biological structures and featuring a tree-like, multicellular hierarchical design. The effects of tree-like hierarchical orders, oblique load, impact load, and axial thickness gradient on the energy absorption behaviour of BBHM tubes are investigated by numerical simulation. Results show that the 2nd-order BBHM tube achieves a 108% increase in specific energy absorption (SEA) and a 96% rise in mean crushing force (MCF) compared with conventional hexagonal tubes under quasi-static loading. At 80 m/s impact, SEA reaches 32.75 J/g, confirming strong robustness against dynamic loading, while axial thickness gradients effectively reduce initial peak force and stabilize progressive deformation. A theoretical model is developed to predict MCF, showing deviations within 10% of simulation results. Compared with twelve representative bio-inspired tubular designs, the BBHM tube demonstrates superior crashworthiness, with SEA up to 26.05 J/g and crushing force efficiency above 80%. These findings indicate that BBHM tubes are lightweight, high-performance alternatives for advanced energy-absorbing applications in automotive, rail, and aerospace engineering.