Optimization of novel functionally graded FRD-filled crash box for enhanced crashworthiness

The frontal crumple zone of a vehicle, particularly the crash box, plays a crucial role in absorbing impact energy during collisions to mitigate passenger injuries. This study presents a novel approach to improve vehicle crashworthiness by incorporating an Förstner Random Dots (FRD) cellular structure as a filler component within a conventional square-hollow tube crash box. The finite element model of the crash box is employed to investigate the crashworthiness performance using nonlinear explicit dynamics analysis via LS-DYNA. Additionally, the functionally graded thickness (FGT) technique is applied in the design of the Triply Periodic Minimal Surface (TPMS)-filled crash box to reduce the initial peak crash force (IPF). The TPMS-filled crash box demonstrates superior energy-absorbing capabilities compared to conventional designs. To achieve the highest crashworthiness with a lightweight design, multi-objective particle swarm optimization is utilized to determine the optimal grading exponents of the outer and filler structures. The optimization process aims to maximize specific energy absorption and mean crushing force simultaneously. Pareto fronts of non-dominated solutions are generated, and optimal solutions are identified using multi-criteria decision-making with the Technique for Order Preference by Similarity to Ideal Solution (TOPSIS). Results suggest an optimal crash box design featuring a thickness gradient along its height, with a thinner profile from top to middle to facilitate progressive deformation and thicker sections at the bottom to prevent buckling. The optimized FGT model significantly reduces the IPF and controls the deformation behavior of the crash box, leading to progressive failure, especially under oblique impact scenarios, compared to the uniform thickness model.