An inverse dynamics method for railway vehicle systems

The wheel–rail action will obviously be increased during the vehicles in high-speed operation state. However, in many practical cases, direct measurement of the wheel–rail contact forces cannot be performed with traditional procedures and transducers. An inverse mathematical dynamic model for the estimation of wheel–rail contact forces from measured accelerations was developed. The inverse model is a non-iteration recurrence method to identify the time history of input excitation based on the dynamic programming equation. Furthermore, the method overcomes the weakness of large fluctuations which exist in current inverse techniques. Based on the inverse dynamic model, a high-speed vehicle multibody model with twenty-seven Degree of Freedoms (DOFs) is established. With the measured responses as input, the inverse vehicle model can not only identify the responses in other parts of vehicle, but also identify the vertical and lateral wheel–rail forces respectively. Results from the inverse model were compared with experiment data. In a more complex operating condition, the inverse model was also compared with results from simulations calculated by SIMPACK. First published online: 22 May 201

Special dynamic behavior of an aluminum alloy and effects on energy absorption in train collisions

Dynamic tension tests and compression tests were carried out for 5083-H111 aluminum alloy to investigate the dynamic mechanical behavior and its effect on energy absorption characteristics of an energy-absorbing device. The material constitutive relations were obtained at various levels of strain rates by means of tests. Three material models were performed on the energy-absorbing device of railway vehicles. We investigated the influence of the material dynamic behavior on the energy absorption capability. The results indicate that 5083-H111 aluminum alloy is endowed with negative strain rate sensitivity at medium–low strain rates and possesses the feature of negative and then positive strain rate sensitivity in the range of medium strain rates. The material presents obvious strain rate strengthening effect at high strain rates. Moreover, the order of magnitudes of the strain rate in the train collision is 0–2. It belongs to the medium strain rate. The practical absorbed energy of the structure made of 5083-H111 alloy is less than that of the same structure without regard to the strain rate effect in design phases

STUDY ON FATIGUE LIFE IN FREQUENCY DOMAIN FOR BOGIE FRAME

Traditional bogie frame fatigue design uses the amplitude loads,which is significantly not inconsistent with random excitation suffered on the frame in actual operation. This method often leads to excessive fatigue strength of the overall frame and the anti-fatigue design in local structure insufficient. Firstly,the inverse Fourier transform was used to transform the stochastic process between time domain and frequency domain,and the correctness and feasibility of load history which proposed is verified by comparative analysis. Then,based on the inverse Fourier transform method and cubic spline differential method,rail vertical irregularity and longitudinal irregularity in displacement,velocity and acceleration power spectrum were given,respectively. Finally,the multi-point and multi-axis random vibration analysis of the bogie frame was processed,the real operating conditions of the structure were simulated,and the weak fatigue position of the structure was predicted. The results shows that the fatigue life calculation of the frequency-domain can be good used to predict the vibration fatigue,and provide an effective method for anti-fatigue design of bogie frame

Study on Fatigue Crack Growth in Rail Steel at Numerical and Experimental Approaches

Affected by the service environment, the actual service conditions of rail steel are complex, and the safety evaluation methods are limited. In this study, the fatigue crack propagation in the U71MnG rail steel crack tip was analysed by means of the DIC method, focusing on the shielding effect of the plastic zone at the crack tip. The crack propagation in the steel was analysed based on a microstructural approach. The results show that the maximum value of stress of the wheel–rail static contact and rolling contact is in the subsurface of the rail. The test grain size of the material selected along the L–T direction is smaller than that in the L–S one. Within a unit distance, if the grain size is smaller, the number of grains or grain boundaries will be greater so that the driving force required for a crack to pass through the grain boundary barriers will be larger. The Christopher–James–Patterson (CJP) model can well describe the contour of the plastic zone and can well characterize the influence of crack tip compatible stress and the crack closure effect on crack propagation under different stress ratios. The crack growth rate curve at the high-stress ratio is shifted to the left relative to the low-stress ratio, and the crack growth rate curves obtained under different sampling methods have good normalization

Tool Failure Analysis and Multi-Objective Optimization of a Cutting-Type Energy-Absorbing Structure for Subway Vehicles

This paper aims to provide essential guidance for the crashworthiness design of cutting energy-absorbing structures for subway vehicles. By investigating tool failure with experiment and numerical approaches, a new energy-absorbing tube structure was proposed and optimized to improve the crashworthiness and reliability of the cutting energy-absorption structure. The impact test results revealed that multiple failure modes occurred in the tool. Mechanical wear occurs mainly in the middle of the cutting edge, while the tool’s tip failure is primarily due to thermal wear. Impact forces were no longer stable due to tool failure. The simulation results of the established tool-tube thermal–structural coupling finite element model were consistent with the tests. The temperature distribution indirectly validated the failure modes in different tool areas. By eliminating the tearing-type fracture mode, the proposed new structure effectively reduced the high temperature of the tool’s tip, better maintained the uniform temperature of the cutting edge, and smoothed changing of the cutting force. Finally, the Kriging surrogate model and NSGA-II algorithm were utilized to obtain the tool’s minimum steady-state temperature (STT) and maximum mean average cutting force (MCF). The optimal solution determined by the minimum distance method is STT = 514 K, MCF = 131 kN

Nonlinear Dynamic Mechanical Characteristics of Air Springs Based on a Fluid–Solid Coupling Simulation Method

The use of air springs has become widespread in various industries due to their exceptional superelastic properties; however, their strong nonlinear characteristics have become a hindrance to numerical simulations of air springs and have garnered increasing attention. This paper examined the nonlinear dynamic mechanical characteristics of air springs from a fluid–structure interaction perspective and verified the accuracy of the simulation analysis model through quasistatic tension and compression experiments. The average relative errors for air spring load and gas pressure were found to be 8.1% and 7.7%, respectively, which supports the validity of the model. The impact of frequency and amplitude excitations on the axial load characteristics of air springs was investigated through tension and torsion testing. The results showed that increasing the excitation frequency improves the stability of the axial load, while increasing the excitation amplitude enhances the axial load value. The change in axial compression was found to be more significant than that in axial tension, as it was affected not only by the axial load but also by the radial load, which is a key factor affecting the dynamic characteristics of air springs. A radial load analysis model was established to study the influence of frequency and amplitude excitations on the axial load characteristics of air springs. The simulation results indicated that under different amplitudes, the radial load of air springs goes through four stages: a steady period, rising period, steady period, and falling period. Additionally, under the same amplitude, the radial load value increases with an increase in frequency. This research on the dynamic load characteristics of air springs under amplitude and frequency excitations is important for their application in low-frequency and low-amplitude vibration environments, and its findings can be utilized to improve the technical parameters of air springs for suspension damping

Method for Evaluating Bolt Competitive Failure Life Under Composite Excitation

Abstract In this study, the competitive failure mechanism of bolt loosening and fatigue is elucidated via competitive failure tests on bolts under composite excitation. Based on the competitive failure mechanism, the mode prediction model and “load ratio—life prediction curve” (ξ–N curve) of the bolt competitive failure are established. Given the poor correlation of the ξ–N curve, an evaluation model of the bolt competitive failure life is proposed based on Miner’s linear damage accumulation theory. Based on the force analysis of the thread surface and simulation of the bolt connection under composite excitation, a theoretical equation of the bolt competitive failure life is established to validate the model for evaluating the bolt competitive failure life. The results reveal that the proposed model can accurately predict the competitive failure life of bolts under composite excitation, and thereby, it can provide guidance to engineering applications