Improving the crashworthiness of bio-inspired multi-cell thin-walled tubes under axial loading: Experimental, numerical, and theoretical studies

Bio-inspired thin-walled structures are widely applied in the engineering field to improve energy-absorption performance. In this study, the axial crushing resistances with large plastic deformation of polygonal single cell (PSC) and novel bio-inspired polygonal multi-cell (BPMC) thin-walled tubes were investigated using comprehensive experimental, numerical, and theoretical methods. Combining the biological characteristics of plant stems and the mechanical properties of thin-walled structures, BPMC tubes were introduced based on the structural characteristics of horsetails formed from two straight polygonal tubes with the same crosssectional shapes, which were connected by several ribs at the corners. A total of 108 design conditions were considered, including nine cross-sectional shapes with different scales and two different thicknesses. Quasi-static experiments were performed to study the energy-absorption characteristics of thin-walled tubes with different multi-cell and multi-corner configurations. Nonlinear explicit finite element analysis (EFEA) was employed to simulate the crushing behavior. Theoretical models were established to analyze the large deformation mechanism, and expressions were derived to predict the mean crushing force (F-m), special energy absorption (SEA), crushing force efficiency (CFE), and corresponding normalized parameters. The results of the theoretical models were highly consistent with the experimental and numerical results. Finally, using the optimization function fmincon, a BPMC-20 tube with a scale number of 0.35 was selected as the better energy absorber. The normalized mean crushing force (N F-m) of the optimal BPMC-20 tube was 1.64 and 8.30 times larger than that of the BPMC-10 and PSC-10 tubes, respectively. In conclusion, the energy-absorption characteristics of the structure could be significantly improved by adding ribs at the corners. Furthermore, the introduction of the novel BPMC tube could effectively improve the crashworthiness of the structure, thereby serving as a potential candidate for future crashworthiness applications.