Crashworthiness optimisation of a step-like bi-tubular energy absorber for subway vehicles

This paper presents the crashworthiness optimisation of a step-like energy absorber which is composed of nested thin-walled rectangular tubes. The impact experiment and numerical simulation were carried out. The results had a good agreement and indicated that the collapse process is clearly divided into two phases. To investigate the effects of geometry parameters of the structure on essential crashworthiness characteristics, two groups of samples with different wall thickness and inner tube dimensions were simulated, respectively. The change in the outer tube and inner tube wall thickness has obvious influence on energy distribution and crashworthiness characteristics. The thickness of the diaphragms has little influence on these responses. The increase of inner tube dimensions leads to the interactive obstruction of outer tube and inner tube. The decrease of inner tube dimensions leads to the self-obstruction of inner tube. The above two results lead to the increase of EA1 and MCF2 values. Then, the design of experiments (DOE) based on simulations were established. Finally, based on the developed surrogate models, optimisation design for the absorber to maximize the specific energy absorption (SEA) under the constraint of two important indicators was carried out. It was clearly found that the optimal solution increased the value of SEA from 8.93 to 9.36 kJ/kg while satisfying the two constraints.