Research On Fatigue Crack Growth And Life Evaluation Of Metro Obstacle Detector

With the acceleration of the urbanization process,the passenger capacity and operating speed of metro vehicles have greatly increased,resulting in the actual working environment of the vehicles becoming more and more extreme.During the running of metro vehicles,the multi-axis random vibration fatigue failure of the obstacle detector has become a serious hidden danger that endangers the safety of metro operation,which has attracted widespread attention.In this thesis,the simulated long-life vibration testing was carried out on a shaking table to verify that the structure of the obstacle detector meets the service life requirement of30 years.Then,four simulation analysis methods were used to predict the fatigue life of the structure,and combined with the evaluation method of fracture mechanics,the remaining life of the metro obstacle detector was studied.According to the rail transit standard,a comprehensive analysis of obstacle detector combined with fatigue and fracture methods is of great significance for guiding the structural design and maintenance of similar suspension parts of rail vehicles,and it also has a certain theoretical value.Firstly,according to the rail transit standard IEC 61373,the standard spectrums of the metro obstacle detector for the simulated long-life testing were obtained.The acceleration power spectrum density curves of the structure were subjected to inverse Fourier transform,and the time-domain random fatigue excitation spectrums required for the calculation in Chapter 4 were obtained.After that,through reasonable selection of methods such as load cycle counting,load correction,and load spectrum classification,the fifth chapter fatigue crack propagation load spectrum was compiled.Secondly,the vertical,transverse,and longitudinal simulated long-life vibration testing was carried out on the shaking table for 5 hours in sequence to verify the rationality of the structure design of the obstacle detector.Then,four simulation analysis methods including single-axis frequency domain method,multi-axis frequency domain method,single-axis time domain method and multi-axis time domain method were used to predict the fatigue life of the obstacle detector.The results show that the simulated long-life vibration testing and uniaxial simulation results carried out in this thesis are accurate,and the structure design is reasonable and effective.In the actual operation of the structure,the damage caused by the multi-axial load and the sequential uniaxial load cannot be simply equivalent.Finally,two different types of fillet welded and butt welded aluminum beams of the obstacle detector at the initial design stage were selected as the research objects.After the compiled load spectrum was applied to the global model,the sub-models were divided.The remaining life was predicted for the key fatigue positions of the sub-models,and the key factors affecting the fatigue crack growth life of the structure were analyzed and discussed.Comparing the calculation results,it is found that the fatigue resistance of the fillet welded aluminum beam designed in this thesis is significantly better than that of the butt welded aluminum beam.The increase of the initial crack size of the semi-ellipse will seriously reduce the remaining life of the structure.The center crack of the welded structure is more dangerous than the edge cracks,and the ratio of major axis to minor axis of semi-ellipse has less influence on the remaining life.