Crashworthiness performance and optimization of multi-cell aluminum tubes under axial loading

Abstract

Multi-cell thin-walled tubes have been proven to be an efficient energy absorber with well-controlled deformation stability and high energy absorption capability. Nevertheless, research on multi-cell tube energy absorbing structures mainly focused on the fields of small size and light energy absorption. The high cost and low crushing force significantly restrict their applications in practical engineering, especially for large-size equipment, such as train crashworthiness protection. To address this limitation, this paper presents a novel multi-cell tube energy absorption structure made of aluminum alloy for ultra-large energy absorption field with features of low cost (extrusion and welding processing), large size (450 mm × 280 mm × 280 mm), light weight (∼9 kg), high energy absorption capacity (>200 kJ) and large crushing force (>600 kN). The proposed multi-cell structure is composed of four extruded square tubes connected by welding. To demonstrate the feasibility of the proposed structure, the sample is fabricated and dynamic impact test is performed. Experimental results show that the tube buckles progressively and forms plastic folding lobes with a total absorbed energy of 235.6 kJ and a mean impact force of 668.7 kN, which are about 500% higher than that of previous reported multi-cell structures. Finite element simulation and theoretical model are developed and well-capture the experimental deformation process. The relative errors of theoretical and simulation mean crushing force, Effective crushing distance coefficient, energy absorption and maximum crushing distance in comparison experimental results are all within 10%. Based on the validated finite element model, the effect of geometrical parameters of the proposed structure on its crashworthiness performance is analyzed. Finally, we construct the response surface models of the multi-cell tube and optimize the absorbed energy under a mass constraint by Multi-objective Non-dominated Sorting Genetic Algorithm (NSGA-II). The Pareto front of structure energy absorption and mass is obtained. In particular, under the constraint of total mass M = 9 kg, the optimal solution with maxing energy absorption is t = 4.999 mm, α = 0.342 mm, and w = 281.5 mm. The proposed structure can be applied to ultra-large energy absorption fields such as train crashworthiness protection.