Crashworthiness of bio-inspired hierarchical hybrid multi-cell tubes under axial crushing

Inspired by the gradient hierarchical structures from the wood and bamboo, a new bio-inspired hierarchical hybrid multi-cell tubes (named BHHMT) were proposed. A systematic investigation on the crashworthiness of BHHMT with structural hierarchy was conducted experimentally, numerically, and theoretically to obtain the optimal parameter configuration. The results indicated that the specific energy absorption (SEA) of the 3rd order BHHMT was 49.10% higher than that of the single square tube. Moreover, the initial peak crushing force (IPCF) and the undulation of load-carrying capacity (ULC) used for evaluating the stability of the BHHMT under dynamic crushing were also considered. The IPCF and ULC of the 3rd order BHHMT reduced up to 18.37% and 77.21% compared to the single square tube. It indicated that the BHHMT had a larger potential to improve energy absorption than the square tube and conventional multi-cell square tube. Subsequently, a theoretical model was developed to estimate the mean crushing force (MCF) of the proposed tubes, which was in good agreement with the numerical results. Finally, the influence of various additive manufacturing materials on the crashworthiness of the BHHMT was investigated. It indicated that the metal BHHMT-3 exhibited a significantly higher SEA and equivalent SEA compared to other popular cellular structures. This study provided valuable insights and guidelines for designing protective structures with mechanical safety performance, including understanding the failure process.