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. Gradient structures have become a hot research topic because of their excellent crashworthiness. Inspired by the gradient distribution of human bone and the excellent energy absorption properties of thin-walled constructions, a novel biologically inspired functionally graded lattice-filled tube (FGLT) is proposed in this paper by combining a radial gradient lattice with a thin-walled structure. Lattice arrays with different gradient patterns were prepared by laser melting (SLM) technique and embedded in square thin-walled tubes for experimental crashworthiness study. It was found that there was a 25.47% increase in specific absorption energy of uniform lattice-filled tubes with respect to empty tubes, and a 36.65% increase in specific absorption energy of graded grating filled tubes with respect to empty tubes. It is noteworthy that the peak load of the structure is only improved by 3.95% compared to the empty tube for the gradient lattice as a filler embedded in the thin-walled tube. Finally, based on the response surface methodology (RSM) and the second-generation non-dominated ranking genetic algorithm (NSGA-II), the multi-objective optimization of the new bionic gradient structure with the maximum specific energy absorption and the minimum peak load is performed. The expression of the maximum standardized impact force is obtained by dimensionless processing, which can fully explore the influence of the structural parameters on the impact load. The functional gradient bionic structure provides new ideas for the design of more effective energy absorption structures and collision avoidance systems. [Display omitted]