| With the rapid growth of the railway operation speed and mileage,many dynamics and fatigue strength problems in different level have been reported in the actual operation of high-speed trains.The most typical problem is the wheel polygonalization,which occurred in many different types of trains and different operation lines.The wheel polygonalization can significantly deteriorate the vibration level of the vehicle system,especially the high-order polygonalization,which can easily lead to fatigue failure by inducing the resonance of bogie components.This problem seriously affects the safety and serv ice life of the train.Wheel polygonalization will aggravate the wheel-rail dynamic force,accelerate the wheel wear and cause deterioration of the vibration of the track structure.This paper combined line text,bench test and dynamics simulation to syste matically study the influence of wheel polygonalization on the EMU wheelset.The main works are shown as follows:(1)A study was conducted on the shedding of the axle box grounding end cover.Firstly,the intrinsic mode of the axle box grounding end cover was analyzed through experiments and simulations,and the main modal frequencies were determined.A small roller high-frequency excitation test bench was built,and the measured field test data and the test bench data were compared.It was found that the test bench can restore the typical polygonalization on the vehicle operation line.The vibration characteristics of the axle box were studied by frequency-sweep method.Then the influence of preload force on the vibration of axle box was studied by the force measuring bolt.A vehicle-track system coupling dynamics model was established to simulate the experiment system.Compare with the field test data and the test bench data,the reason for the falling off of the axle box end cover was obtained.(2)Systematic comparison of the instrumented wheelset technology and the wheel-rail force indirect measurement method.The wheel-rail force data measured by the two methods were compared.And then the inadequacies of the two methods were pointed out,it is not suit able for measuring the high-frequency components of the wheel-rail force.So,a finite element model of the wheelset-axle box system was established,and the transfer function of wheel-rail force to axle box acceleration was obtained.According to the tran sfer function,a solution method for multi-load input was proposed.The input load of the wheel-rail force can be obtained by the acceleration response of the axle boxes on both sides,and compared with the wheel-rail force obtained by the dynamic simulati on calculation,it is found that the two methods can get similar results both in the amplitude domain and frequency domain.In this way,th e feasibility of this method on measuring the high-frequency wheel-rail force was validated.(3)The evaluation process of the axle strength in the axle design standard of EN13103 and EN13104 was introduced in detail.The fatigue strength test process of the axle was introduced in detail based on the wheel axle bending fatigue test bench in the laboratory.Applying the a dvanced wireless transmission data acquisition system on the small roller high-frequency excitation test bench,the dynamic stress data of the key parts of the axle under high-speed operation and wheel polygonalization were collected for the first time.An d this data was used to modify the dynamics simulation model.Then the model was applied to study the influence of wheel polygonalization with different orders,different wave depths and different speeds,so that the safety limits of wheel polygonalization of different orders were proposed according to the stress of the axle. |
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