Dynamic Stress Analysis And Structural Optimization Of Braking Pipeline Of Metro Vehicle

The vibration of metro vehicle system is caused by wheel-rail irregularity excitation.With the deterioration of wheel-rail wear conditions and the intensification of vibration,fatigue fracture of vehicle and track components occurs.Vibration fatigue fracture of the components is directly related to their stresses.Therefore,the study of stress response characteristics of metro vehicle components under vaious load excitations has engineering application value and design reference significance.This dissertation focuses on the fracture of the braking pipeline on the bogie frame of metro vehicle.The dynamic stress analysis and structural optimization of the braking pipeline is carried out by means of field test and numerical simulation.The main work and conclusions of this dissertation are as follows:(1)The wheel out-of-roundness wear survey,braking pipeline modal test,metro vehicle vibration test and braking pipeline dynamic stress test are carried out on a metro vehicle in China,and the causes of braking pipeline fracture are analyzed.It is found that the wheel out-of-roundness wear is serious before the wheel re-profiling,and surface condition of the wheel restore well after the re-profiling.The main modes of parking braking pipeline on the side beam of the bogie are obtained through modal test,parking brake,which can keep vehicles in ideal parking condition on slope of the track.The first-order lateral bending mode frequency of the pipeline is 74 Hz.The main modes of the bogie frame are obtained through the test carried out in a metro train operation,and it is found that the lateral bending vibration frequency of the frame side beam is 73 Hz.The amplitude and frequency spectrum characteristic of the stresses in the pipeline are obtained from the measurement conducted in the braking pipeline in service.The dynamical stress amplitude of the pipeline before wheel re-profiling is higher than that after the re-profiling,and greatly decreases after the wheel re-profiling.The dominant(at highest peak)frequency of dynamical stress is 72 Hz.It is determined that the pipeline fracture reason should be attributed to wheel out-of-roundness wear and the frame resonating with the pipeline together.(2)The dynamic stress finite element model of the braking pipeline of a B-type metro vehicle is established.A dynamic stress analysis considers frequency domain vibration analysis and time domain rainflow method.The PSD spectrum,before the wheel re-profiling,of the frame acceleration above the axle-box is used as an excitation input in the numerical simulation.The different pipelines dynamic stress cases are analyzed and find that the dynamic stress amplitude of the parking braking pipeline on side beam is higher than other braking pipelines.The reason for excessive dynamic stress amplitude of the pipeline is the lateral bending resonance of the frame side beam occurs with the first-order lateral bending vibration of the parking braking pipeline on the side beam.(3)The effects of improved measures,including increasing the braking pipeline wall thickness,changing the stiffness of pipe clamp and changing the numbers of the pipe clamps,are analyzed by using simulation model.Comparing with increasing pipeline wall thickness and reducing pipe clamp stiffness,adding an extra pipe clamp in middle position of the exsiting two pipe clamps on the side beam parking braking pipeline has the most significant effect on reducing pipeline dynamic stress amplitude.It’s suggested that the side beam parking braking pipeline should be optimized by adding one more pipe clamp to the original pipeline structure.