Crashworthiness performance and multiobjective optimization of a combined splitting circular tube energy absorber under eccentric impact for subway vehicles

Abstract This paper proposes a new type of combined splitting circular tube energy absorber for subway vehicles. An impact experiment is conducted to investigate the dynamic crushing performance of this combined splitting circular tube energy absorber. The results show that the combined tubes experience steady dynamic splitting deformation. The crush force efficiency (CFE) and effective stroke ratio (ESR) of the combined splitting circular tube energy absorber are 85.7% and 85.9%, respectively. A theoretical solution for the dynamic splitting crushing load is derived. Finite element (FE) models of the energy absorber are then established, and the dynamic crushing forces agree well with those of the impact experiment. The cumulative error and validation metrics of the crushing force obtained from the numerical simulation and impact experiment are 0.0938 and 0.9122, respectively. The effect of the strain rate of AISI 1020 steel on dynamic steady-state forces is analytically studied, and the results are compared with those of FE simulations and impact experiments. The numerical results show that the dynamic steady-state force of the combined splitting circular tubes under dynamic loading increases by 31.69% compared to that of the tubes under quasistatic loading. The effects of various structural parameters are discussed using the validated FE models. The results show that the combined splitting tube energy absorber has excellent crashworthiness under eccentric loading. The eccentric impact of the two absorbers has a significant influence on the crashworthiness performance of the structure. The specific energy absorption (SEA) increases by 15.2% as the eccentric distance increases from 20 to 80 mm. Compared with the influence of the wall thickness t of the combined splitting circular tubes, the tube radius and die angle have a more significant influence on the SEA. To improve the crashworthiness of combined splitting circular tubes under eccentric loading, a Pareto front of the SEA and average axial crushing force (AACF) under an eccentric distance of H = 40 mm was obtained after optimization by multiobjective particle swarm optimization (MOPSO). The results show that the SEA and AACF are positively correlated and that a balance between the SEA and AACF was obtained at optimal point B (SEA = 14.6 kJ/kg and AACF = 938 kN).