Crashworthiness design of functional gradient bionic structures under axial impact loading

•A novel thin-walled filled structure based on a combination of a gradient lattice and a square thin-walled tube.•The gradient lattice-filled tube increases the maximum energy absorption by 36.65% compared with the empty tube.•The gradient pattern with gradually decreasing radius outwards is more favourable for energy absorption than the inwards pattern.•Multi-objective optimization of structural gradient parameters is beneficial to improve crashworthiness.