| With the increasing speed of metro vehicles in China,the operating environment of vehicle becomes worse,which leads to the cracks of bogie.To analyze the causes of the cracks,taking metro vehicles as the research object,from the perspective of fatigue simulation calculation in the early stage design of bogie,how to rapidly calculate the vibration response of bogie frame excited by track irregularity and accurately evaluate the random vibration fatigue of weld on bogie frame were studied in this thesis.Firstly,the motion differential equation of metro vehicle excited by track irregularity and its solution according to big mass-method were derived,based on the methodology of structural dynamics under multi-point base motion excitation and pseudo excitation algorithm.Secondly,the simplified finite element model of metro vehicle was established.Thirdly,the large mass numbers were placed at wheel rail contact points,and the track irregularity excitation was transformed into the form of pseudo harmonic force applied to the large mass numbers in accordance with the form of motion differential equation.Then,the power spectrum density(PSD)of bogie frame excited by track irregularity was calculated using the finite element software,and the PSD of equivalent structure stress of weld on the bogie frame was solved through stress extension.Finally,the fatigue life of weld on the bogie frame was predicted based on the nominal stress method and equivalent structure stress method in the frequency domain respectively,and the calculation process,results and characteristics of both methods are compared.The following conclusions are as below:(1)Based on the pseudo excitation algorithm,the absolute displacement PSD of vehicle can be solved rapidly and directly by placing the large mass numbers at the wheel rail contact points and applying the excitation of the track irregularity in the form of pseudo harmonic force to the large mass numbers,Avoiding the complexity of the relative motion method to solve the quasi-static moment matrix,so the method is convenient for the realization of pseudo excitation method in the finite element software.(2)The main frequency of stress(the first principal stress or the equivalent structure stress)PSD of weld at mounting seat of motor is torsional mode(46.6 Hz),the main frequency of stress PSD of weld at mounting seat of rotating-arm is transverse mode(14.4 Hz),The peak frequencies of stress PSD of other base metals or weld are partial rigid modes and elastic modes of torsion deformation,transverse shear deformation of side beam.In addition,the stiffness of mounting seat at brake is insufficient,which shows that the partial vibration energy is concentrated in the local mode of bogie frame(37.9 Hz)based on stress PSD.(3)Under the excitation of track irregularity,the weakest position of base metal predicted by the nominal stress method in frequency domain is located at the mounting seat of brake,and its fatigue life is 2.38 million km,which is related to the insufficient rigidity of the brake seat structure.The weakest position of weld on bogie frame predicted by nominal stress method in frequency domain is same as that predicted by the equivalent structural stress method in frequency domain,which located at mounting seat of rotating-arm(node 3485649),with the fatigue life of 6.49 million km and 5.56 million km respectively,while the fatigue life predicted by the equivalent structural stress method in frequency domain is more safety.Meanwhile,the fatigue life of weld on bogie frame is higher accuracy based on the mechanical properties of the equivalent structure stress method,and the results of the equivalent structural stress method in frequency domain are consistent,Compared with the discrete results of the nominal stress method in frequency domain. |
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