Energy absorption characteristics of bio-inspired hierarchical multi-cell bi-tubular tubes

Previous studies have shown that the multi-cell bi-tubular tubes exhibit superior energy absorption compared to the multi-cell tubes. To further improve the energy absorption of the multi-cell bi-tubular tubes, in this study, we propose new bio-inspired hierarchical multi-cell bi-tubular (BHMB) tubes mimicking the tree-like structures in nature. Unlike the conventional multi-cell bi-tubular tubes, the webs in the BHMB are innovatively constructed based on the tree-like structures found in natural structures such as giant water lily leaves. The energy absorption performances of the BHMB tubes with different hierarchical orders, inner diameters and loading angles are numerically investigated. The results demonstrate that the specific energy absorption (SEA) increases with the hierarchical order and inner diameters, and the SEA of the 2nd order BHMB tube is about 55% and 81% higher than that of the conventional multi-cell circular tube and circular tube under axial loading, respectively; 46% and 72% higher under oblique loading with the loading angle of 10 degrees. A theoretical analysis based on the simplified super folding element theory is also developed to determine the mean crushing force (MCF) of the proposed BHMB tubes. The theoretical predictions of the MCF agree well with the numerical results. The findings of this study provide an effective guide for the design of multi-cell bi-tubular tubes with high energy absorption efficiency.