Crashworthiness analysis of gradient fractal thin-walled structure

Inspired by the structure of bamboo, this study introduces a gradient fractal structure (GFS) design concept, which can be used in high-performance energy absorber. Crashworthiness performances of GFSs are investigated via numerical simulation. The 4-cell square thin-walled column with the cross-sectional dimensions of 36 mm × 36 mm reported in reference is used for the finite element model verification before the parametric analysis of GFS. Results show that the specific energy absorption (SEA) of 1st and 2nd order GFSs is 15% and 25% higher respectively compared to conventional square honeycombs under the same cell wall length and thickness. The gradient fractal distribution of materials not only increases the average folding number, but also lowers the force–displacement fluctuation and increases the crashworthiness performances of GFS. When the wall thickness increases, the SEA of GFS increases. However, large wall thickness will inevitably deteriorate the force–displacement fluctuation. Increasing the number of the outer components k also has similar tendency for crashworthiness performances. Simulations also suggest that reasonable wall thickness and height-side length ratio are two important factors for designing the GFSs with better energy absorption performances. • A gradient fractal structure (GFS) is proposed and investigated via numerical simulation. • The specific energy absorption of GFS is much higher than the conventional square honeycombs. • Gradient fractal distribution of materials significantly increases the specific energy absorption. • GFSs with small wall thickness and medium H / L 0 ratio tend to generate the compact deformation mode.