Crashworthiness of Bionic Fractal Multi-Cell Circular Tubes under Axial Load

A bio-inspired fractal multi-cell circular (BFMC) tube with embedded regular polygons is proposed to address the gap between the need for high absorption and the limited performance of traditional thin-walled circular tubes. Inspired by biological structures and fractal hierarchy theory, geometric models of BFMC tubes embedded with square, pentagonal, and hexagonal cells are constructed. Numerical simulations are carried out to systematically investigate the effects of mass, fractal dimension, and the number of sides of the embedded polygons on the axial crushing performance, and the results are compared with those of typical multi-tubes. The results indicate that, under approximately equal mass conditions, the BFMC tube can significantly enhance the specific energy absorption and the load-bearing capacity owing to its fractal hierarchical and bio-inspired configurations. Its crashworthiness increases with mass, first decreases and then rises as the fractal dimension increases, and improves further as the number of polygon sides increases, while the peak force is only weakly affected. A theoretical model for predicting the mean crushing force of BFMC tubes is developed based on the super folding element theory and is validated through numerical simulations. This study provides theoretical support and structural design guidelines for developing high performance thin-walled energy absorption structures.