## 4 Conclusions  
This study investigated the mechanical properties and crashworthiness of a series of bionic thin-walled tubes inspired by sea stars and leaf beetles, using systematic experiments, numerical simulations, and theoretical analysis. The main findings are as follows:  
1. The maximum compression bearing capacity of each bionic structure (BS) is similar, with a lightweight compression value (LWN-C) of about 310 N/g. BS-4, BS-6, and BS-7 have relatively high maximum bearing capacities.
2. Increasing the number of polygonal structures inside the thin tube can effectively improve the torsional performance of BS. The torsional strengths of BS-4, BS-6, and BS-7 are significantly higher than those of BS-3 and BS-5.
3. Multi-layer quadrilateral and hexagonal column structures can improve the bending performance of BS. BS-4 has the highest maximum bending load and LWN-B.
4. Double-layer structures inside the thin tube generally have stronger energy absorption capacity than single-layer structures. BS-4, BS-6, and BS-7 have higher \(EA\) and \(SEA\) values, indicating their better energy absorption capacity compared to other BSs.  
Figure 11: Results of impact test. Panels (**a–e**) display the values of each BS sample for \(P_{\text{max}}\), \(EA\), \(SEA\), \(P_{m}\), and \(CLE\), respectively. Panels (**f–h**) illustrate the average values of \(P_{\text{max}}\) and \(P_{m}\), \(EA\) and \(SEA\), and \(CLE\) for each BS sample.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Types** & \(P_{\text{max}}\) **(kN)** & \(EA\) **(l)** & \(SEA\) **(l/kg)** & \(P_{m}\) **(kN)** & \(CLE\) \\ \hline BS-1 & 3.33 \(\pm\) 0.075 & 20.03 \(\pm\) 0.150 & 193.67 \(\pm\) 1.426 & 0.91 \(\pm\) 0.017 & 0.27 \(\pm\) 0.015 \\ BS-2 & 2.76 \(\pm\) 0.121 & 19.67 \(\pm\) 0.445 & 190.26 \(\pm\) 4.280 & 1.09 \(\pm\) 0.006 & 0.40 \(\pm\) 0.021 \\ BS-3 & 7.36 \(\pm\) 0.711 & 28.01 \(\pm\) 1.455 & 270.94 \(\pm\) 14.065 & 4.42 \(\pm\) 0.067 & 0.61 \(\pm\) 0.074 \\ BS-4 & 9.56 \(\pm\) 0.665 & 36.55 \(\pm\) 0.552 & 353.42 \(\pm\) 5.293 & 3.43 \(\pm\) 0.253 & 0.36 \(\pm\) 0.056 \\ BS-5 & 9.21 \(\pm\) 0.512 & 28.50 \(\pm\) 1.189 & 275.65 \(\pm\) 11.479 & 2.54 \(\pm\) 0.065 & 0.28 \(\pm\) 0.021 \\ BS-6 & 4.37 \(\pm\) 0.055 & 37.65 \(\pm\) 0.835 & 363.99 \(\pm\) 8.108 & 1.19 \(\pm\) 0.015 & 0.27 \(\pm\) 0.010 \\ BS-7 & 5.24 \(\pm\) 0.148 & 32.99 \(\pm\) 0.771 & 318.99 \(\pm\) 7.471 & 1.21 \(\pm\) 0.029 & 0.23 \(\pm\) 0 \\ \hline \hline \end{tabular}
\end{table}
Table 7: Crasworthiness indicators of each BS (Mean \(\pm\) SD).  
**Author Contributions:** Study design, [PERSON] ([PERSON]); conduct of the study, [PERSON] ([PERSON]) and C.G.; conceptualisation, C.G., Y.G. and L.Z.; methodology, L.L. ([PERSON]), Y.G. and L.Z.; writing--original draft preparation, [PERSON] ([PERSON]) and [PERSON] ([PERSON]). All authors have read and agreed to the published version of the manuscript.  
**Funding:** This work was supported by the National Natural Science Foundation of China (grant No. 51875282), the Natural Science Foundation of the Jiangsu Higher Education Institutions of China (grant No. 21 KJB460033), Science Research Project of Xuzhou University of Technology (grant No. KC21002), Jiangsu Industry University Research Cooperation Projects (BY2022774), and the National Defense Basic Scientific Research Project (grant No. JCKY2018605C010).  
**Institutional Review Board Statement:** Not applicable.  
**Infrared Consent Statement:** Not applicable.  
**Data Availability Statement:** Not applicable.  
**Acknowledgments:** We gratefully acknowledge the support of the Institute of Bio-inspired Structure and Surface Engineering at Nanjing University of Aeronautics and Astronautics.  
**Conflicts of Interest:** The authors declare that there is no conflict of interest regarding the publication of this article.