This study aims to provide important guidelines for the crashworthiness design of composite energy-absorbing structures, especially railway vehicles. An experimental and numerical investigation was carried out to explore the crushing response of circular composite tubes reinforced with plain woven carbon fiber-reinforced polymers (CFRP). Quasi-static and dynamic axial crushing tests were performed on CFRP tubes with an inner diameter of 100 mm and a nominal wall thickness of 12 mm. Experimental results showed that increasing loading velocity led to a 21.8% reduction in specific energy absorption (from 99.7 kJ/kg to 78.7 kJ/kg) but had negligible influence on failure modes. Finite element models were also established and validated against the experimental results using ABAQUS/Explicit software. The effects of several different parameters such as the number of shell layers, friction coefficient, and interface properties on the simulated results, were also investigated and analyzed. A small variation in these parameters could change the total energy absorption of CFRP tubes. The comparisons between the predicted and experimental results indicated that a finite element model with 10 shell layers could effectively replicate the crushing response. In addition, the simulated results indicated that the damage of tubal wall materials dominated the major energy-absorbing mechanisms of CFRP tubes under quasi-static loads, which was 69.1% of the total energy. The energy dissipated by friction effects between the loading platen and the crushed fronds was 24.1% of the total energy. The increase in the loading velocity led to a decrease in the composite damage energy except for friction energy, resulting in a decrease in the total energy absorption.

The transverse vibration test of bolts has been designed with adoption of the fatigue tester to study the features of the loosening life of bolts. Firstly, the transverse vibration frequency has been changed, the effects of the amplitudes of displacement, velocity, and acceleration on the loosening life of bolts have been compared, and it has been confirmed that the transverse displacement amplitude is the main factor that affects bolt loosening in low‐frequency vibration. Secondly, the loosening degree of the bolts preloaded standard under five displacement amplitude grades has been monitored and the bolt loosening situation has been expressed through the residual preload‐vibration times curve. The data of each stage of residual preload under each displacement amplitude were summarized, and the displacement‐life (D-N) curve of bolt loosening under different loosening situations (percentage of residual preload) which is referred to the material fatigue life S-N curve was drawn. Finally, the accumulation mechanism of bolt loosening has been studied and the linear accumulation model of bolt loosening has been set up through designing variable amplitude vibration tests at high‐low and low‐high displacement stages. Results show that, through the bolt loosening D-N curve, it can be found out that the bolt loosening life curve and the material fatigue life curve are with features of double line and high‐ and low‐cycle boundary under the logarithmic coordinate. Linear accumulation of bolt loosening is with similar principle of linear damage accumulation of material fatigue. Therefore, the bolt loosening life can be predicted through bolt displacement‐loosening life (D-N) curve attained from the experiment and the established linear accumulation model of bolt loosening.

To further enhance the crashworthiness of subway vehicle anti-climb energy-absorbing devices, this paper proposes a novel collapsible structure, which is embedded with honeycomb aluminum blocks and consists of an inner and outer double-layer square tube. An impact finite element model of the subway vehicle’s anti-climb energy-absorbing device was established using LS-DYNA (v.17.2). The effects of the connecting diaphragm thickness, the inner and outer tube thicknesses of the thin-walled tubes, and the yield strength of the honeycomb aluminum on the energy absorption and impact force of the anti-climb energy-absorbing device were investigated. The results indicate that changes in the inner and outer tube thicknesses of the thin-walled tubes significantly affect the energy absorption and impact force of the anti-climb energy-absorbing device. However, changes in the connecting diaphragm thickness only increase the maximum energy absorption by up to 7.5% but have a significant impact on the maximum peak force. It was also found that the difference in energy absorption due to changes in the yield strength of the honeycomb aluminum is only 3.6%, suggesting that the yield strength of the honeycomb aluminum and the connecting diaphragm thickness have a limited influence on the crashworthiness design of the anti-climb energy-absorbing device. Furthermore, a multi-objective surrogate model characterizing the specific energy absorption and maximum peak force was established for the aforementioned four influential parameters using the response surface method. The model was then optimized using a genetic algorithm, resulting in optimal parameters that increased the energy absorption and specific energy absorption by 27.3% and 13.8%, respectively, compared to the original values, leading to a significant improvement in crashworthiness. The findings provide valuable references for and insights into the crashworthiness design and optimization of subway vehicles’ anti-climb energy-absorbing devices.