Mechanical behavior and energy absorption characteristics of a biomimetic multi-layer ring-stiffened thin-walled tube with density gradient under impact loading

Biomimetic design offers an effective pathway to enhance the impact resistance of lightweight thin-walled structures in automotive and aerospace engineering. In this study, a novel biomimetic tubular structure (BTS) inspired by the lotus stem's unique cross-section is proposed, and its mechanical response and energy absorption performance under impact loading are systematically investigated through finite element simulations. Various BTS models with different outer cross-sectional shapes and different numbers of radial ribs are constructed, and the reliability of the finite element model is validated based on mesh convergence and comparison with experimental data. The results indicate that increasing the number of ribs significantly improves the peak crushing force (PCF), mean crushing force (MCF), specific energy absorption (SEA), and crushing force efficiency (CFE), with the circular configuration showing the best energy-absorption performance. From Type A to Type D, the SEA nearly doubles, and the CFE increases from 0.62 to 0.84. Furthermore, introducing a three-layer thickness-graded design for the internal ribs shows that thickening the outer and middle layers can achieve higher energy-absorption efficiency, markedly outperforming the uniform-thickness configuration. Overall, the lotus-stem-inspired hierarchical thin-walled structures exhibit ordered folding, stable plateau stress, and high energy dissipation, providing new insights and theoretical guidance for the biomimetic design of lightweight, high-performance impact-resistant structures.