| High speed train adopts lightweight design and dynamic dispersion technology,and its structure and load are different from traditional railway vehicles.The train carbody is made up of aluminum alloy extrusion profiles by welding and assembling,and the middle beam and the crossbeam structure are canceled in the carbody.With the rapid development of high speed train technology,the increasing speed of high-speed train makes the load of carbody has the characteristics of high frequency and small value.Moreover,the welding process of aluminum alloy profile is difficult to control and easy to lead to fatigue failure,so it is a challenge to the reliability of the structural strength.Therefore,this paper takes the carbody of a certain type of high speed train as the research object,it provides the reference for the design and maintenance cycle determination for high-speed train carbody,and it is of great significance to ensure the safety and reliability of train operation.The fatigue life analysis method for welding joint in IIW standard is introduced,and the calculation steps and application of nominal stress,hot spot stress and notch stress method are analyzed.Then,the principle of the structural stress method and the equivalent structural stress method in the ASME standard which have the characteristics of mesh-insensitivity are studied.A welded hollow pipe model is established,and its fatigue life is carried out by the equivalent structural stress method and compared with the experimental data.The results show that the life evaluation results obtained by the analysis using the master S-N curve are in agreement with the experimental results,which verifies the correctness of the calculation program developed in this paper.By establishing a finite element model of the carbody,the mesh sensitivity were analyzed,the results show that the structural stress is uniform in the case of mesh size 15mm,30mm,50mm.The dynamic model of multi-rigid body system is established,and the load spectrum of the air spring position is calculated with the measured track spectrum.The Box-Behnken matrix design method and polynomial fitting method are used to establish the model of the vehicle body,and the load spectrum of the carbody is transformed into the structure dynamic stress history and compared with the direct finite element method.The result shows that the maximum error of the calculated stress range is 3.68%,which meets the requirement of engineering calculation.Because of the difference between the welded joint on shell carbody and the actual welded joint,the stress concentration of the joint should be modified.The modification factor of the butt joint is 1.35,and the modification factor of the lap joint is 3.65.On the basis of the calculation of the dynamic stress of the carbody,the membrane stress and the bending stress range component matrix of the structural stress are obtained by the rain flow counting method,then equivalent structure stress spectrum on concerned position is transformed.According to the master S-N curve method,the fatigue damage results and predicted operating mileage at the welding concerned points are carried out,and the weak points of fatigue appear at the corner of the two sides of the side wall.Based on the Paris formula,the crack propagation life of concerned positions on high-speed train carbody is analyzed,the curves of the crack depth against kilometers are obtained,and the comparison with the standard maintenance and repair mileage request in our country is analyzed,this paper provides a reference for the determination of maintenance cycle for aluminum alloy carbody.According to the EN12663 standard,the fatigue dynamic stress of aluminum alloy carbody was tested,the influence of loads in three different directions on the stress of each part of the carbody is analyzed,and the results show that the fatigue weak position is consistent with the above fatigue analysis. |
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