| A large number of experimental studies have shown that fatigue failure of the structure usually occurs at the weld joint.During the welding process,defects such as blowholes,undercuts,impurities and cracks are likely to occur.These defects lead to stress concentration problems in the weld and directly affect the service life of the weld.Weld fatigue research has always been a concern in the academic community.Especially in the complicated welding structure under the random load,establishing the correct finite element model is one of the key steps in fatigue analysis.The current research on the fatigue life of welding mainly focuses on single welded joint specimens,but there are few studies on random vibration fatigue of complex welded structures.In this paper,MSC.Fatigue software is used to study the fatigue damage of water tank and welds under random vibration loads.Based on modal analysis,using three methods of nominal stress,frequency domain and time domain to estimate the fatigue life of the water tank,and compares it with the bench test results to verify the correctness of the numerical simulation method used in this paper.The main research contents are as follows:(1)In order to analyze the modal characteristics of water-bearing complex structures,the water tank of EMU is taken as the research object,Formations and frequencies were calculated for dry and wet modes based on the fluid-structure interaction and virtual mass method.The simulation results were compared with the hammer test results.It is shown that the simulation frequencies of both wet modes and dry modes are similar to experimental frequencies and the correctness of the two modal analysis methods is verified.And the dry mode finite element model can be directly used for the dynamic analysis of similar water-containing structures.(2)Based on the dry mode finite element model,the finite element model of the water tank including the weld seam was established.According to BS7608 standard,different weld grade S-N curves are selected,prediction of fatigue life of water tank is based on nominal stress approach under test conditions.The simulation results show that fatigue failure site and fatigue life of weld in tank is similar to those that in the experimental tests of random vibration.This research proves the correctness of the fatigue life prediction method of weld,and will provide a theoretical reference for the fatigue design of the welded structures for EMU tank.(3)In order to simulate the random vibration experiment of the water tank,the modal superposition method was used to calculate the random vibration response of the tank in the frequency domain load.The MSC.Fatigue software was used to combine the stress response power spectrum and transfer function of the tank node to obtain the random vibration fatigue life of the tank weld directly and compare it with the test results.It is shown that the frequency domain vibration fatigue calculation method and results are reasonable and effective,and provide a theoretical basis for the calculation of the fatigue life of random vibration structures.(4)Through the modal transient response analysis of the water tank,the curves of the stress and acceleration of the tank at various nodes over time are obtained,that is,the probability density function.On this basis,MSC.Fatigue software S-N module is used to calculate the transient vibration damage life of the water tank,and the fatigue life results are basically consistent with the test results,and the correctness of the calculation method is verified. |
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