Theoretical prediction and crashworthiness optimization of multi-cell polygonal tubes

Multi-cell polygonal tubes are highly efficient energy absorbers and widely used in vehicle engineering. There is no doubt that the structure designers have strong interest to know which kind of multi-cell polygonal tube has the best crashworthiness. However, the comparative study on the crashworthiness of multi-cell polygonal tubes with different edges was quite few. In this paper, the multi-cell polygonal single and bitubular tubes were investigated using the numerical simulation and theoretical prediction methods. Theoretical expressions of the mean crushing forces of the multi-cell polygonal single and bitubular tubes with arbitrary edge were derived by employing the simplified super folding element theory. The theoretical predictions well coincided with the numerical results. Based on the theoretical and numerical results, it can be found that the multi-cell polygonal bitubular tube with 18 edges had the best energy absorption capacity. In order to further improve the crashworthiness of multi-cell polygonal tube, a metamodel-based multi-objective optimization method which jointly employed the finite element simulation, metamodelling method and non-dominated sorting genetic algorithm ver. II multi-objective optimization algorithm was developed. Based on this metamodel-based optimization method, the multi-cell polygonal bitubular tube with 18 edges was optimized. The theoretical prediction also had good agreement with the numerical simulation result for the optimal design. The optimal multi-cell polygonal tube not only had excellent energy absorption capacity but also had stable collapse mode.