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Multi-wall tube has excellent crashworthiness therefore is widely used in energy absorption. The crashworthiness of multi-wall tube is not only related to shape but also materials. However, the specific value of some material parameters cannot be determined, instead, only interval can be confirmed. In this work, a novel multi-wall tube (NMT) that is composed of octagon and nested quadrilateral was designed and an interval uncertainty optimization method was proposed to improve the crashworthiness. Firstly, the crashworthiness of the NMT, octagonal multi-wall tube (OMT) and square double-wall tube (SDT) under axial load was compared and analyzed by experimental and numerical simulation. It indicated that NMT has obvious energy absorption advantages and good progressive deformation mode. Moreover, the energy absorption of NMT structure is more sensitive to wall thickness than wall spacing ratio and inner wall length. Then, based on the theory of simplified super folding element (SSFE), the theoretical model of NMT was proposed. The theoretical analysis is consistent with the simulation results. Finally, according to the interval number theory, the uncertain interval optimization problem was transformed into deterministic optimization and reliability analysis. Non-dominated sorting genetic algorithm II (NSGA-II) was used to seek superior crashworthiness of NMT. When considering interval uncertainty in optimization, the reliability of crashworthiness of the NMT can be further improved. The research results provide a good guidance and theoretical support for crashworthiness optimization design. [ABSTRACT FROM AUTHOR]

Multi-wall profile as one of the most widely approaches can enhance the crashworthiness properties in thin-walled tubular structures. In actual application process as energy absorbers, there may be a variety of circumstances including axial crushing and lateral crushing. However, the crashworthiness in the multi-wall tubular structure considering both axial crushing and lateral crushing circumstances has rarely been evaluated in the existing literature. In the study, a new tailored-property multi-wall thin-walled structure (TMTS) is put forward to increase the ultimate strength of this material in the region of corner to accommodate two conditions including lateral and axial crushing conditions. Finite element models verified from experiments were established in PAM-CRASH to analyse the crashworthiness performance for this structure. Under lateral and axial crushing, it was revealed that TMTSs exhibited obvious superiority to the corresponding traditional structures. It was concluded that wall thickness, tailoring length and other geometry parameters could effectively influence the crushing performance of the TMTSs. In addition, the progressive deformation mode could be exhibited by the well-designed TMTSs under axial impact. Furthermore, the theoretical model of the TMTS was proposed according to the Super-folding Element Theory. Theoretical analysis is consistent with simulation results, which proves that the deformation formula and the analytical model are all correct. Finally, according to the multi-objective optimisation method, the thicknesses of tailored and non-tailored regions of the TMTS were reasonably configured to further enhance crashworthiness. The research results provide good guidance and theoretical support for the development of novel lightweight energy-absorbing structures under various loading circumstances. [ABSTRACT FROM AUTHOR]