Effect Of Viscoelastic Dynamic Properties Of Rail Pads On Vehicle-track Coupled Vibration Of Metro Curved Tracks

With the rapid development of urban rail transit in recent years,small-radius curved railway have been widely used to meet the requirements of metro line design.Curved sections,as the weak part in railway lines,are more likely to produce and develop serious damage problems,e.g.rail corrugation and fatigue fracture of rail fastener.Some studies have shown that the occurrence and development of numerous rail diseases are closely related to the dynamic characteristics of rail track.In order to accurately predict,analyze the ambient vibration and noise caused by the vehicles running in curves,as well as many rail vibrationrelated problems,a great deal of research has been carried out on the dynamic characteristics of the curved rail track and its dynamic wheel-rail interaction.However,few studies have involved the effect of viscoelastic-plastic mechanical properties of rail pads,making the prediction accuracy of the curved track vibration characteristics still unsatisfactory.Accordingly,it is significant to establish a more reasonable,accurate and efficient dynamic model of the curved rack and to improve the theoretical prediction ability of the random vibration response of the vehicle-track coupling system in curves.The main research contents are as follows:1.The experimental and theoretical characterization models of viscoelastic-plastic mechanical properties of rail pads,the vehicle-track coupling frequency-domain dynamics model and the dynamic characteristics of the curved rail track were discussed in detail,which clarified the research direction and content of this thesis.2.The dynamic viscoelastic mechanical properties of rail pads were tested and theoretically characterized.Specifically,the dynamic viscoelastic mechanical properties of DZrail fastener pad,which is commonly used in China’ metros,were tested under different temperature and preloads.The test results included the dynamic stiffness and loss factors of rail pads,followed by theoretical representation of the results with wide temperature and frequency range by the Fractional Derivative Zener(FDZ)model(established based on the time-temperature superposition principle and Williams-Landel-Ferry(WLF)formula).It was found that the viscoelastic dynamic properties of rail pads is independent of the loading amplitude;but is influenced by the preload dependence and becomes more significant as the temperature decreases.3.The dynamic characteristics of straight/curved rails were investigated by numerical calculations and hammer tests.Firstly,the frequency-domain spatial dynamic models of rail-fastener subsystem for straight/curved track were developed by combining the modified spectral element method(SEM)and symplectic method(SM),the necessity of considering the dynamic viscoelastic mechanical properties of the rail pad under actual loading conditions is clarified by comparing the simulation results considering the viscoelastic mechanical properties of the rail pad and the experimental data acquired by hammer test in laboratory.Subsequently,the effect of viscoelastic dynamic properties of rail pads on rail dynamic characteristics and and vibration transmission(especially for curved track)was investigated.4.The establishment of curved vehicle-track coupling frequency-domain dynamic model based on the SEM-SM hybrid method and the influence of viscoelastic dynamic properties of rail pads on random vibration response of metro curved tracks was investigated.To be specific,the effect of the frequency and preload dependence of rail pads on the safety and running stability of vehicles and the dynamic wheel-rail interaction in a curved track was analyzed,and its influence on the frequency-domain vibration response of the vehicle-track coupling system in a curved track was analysed in.Finally,the influence law of the curve superelevation and curve radius variation on the above analysis factors under large preloading was revealed,and the unfavorable situations of the metro trains running on a curved track is given under the condition of considering the viscoelastic mechanical properties of rail pads.