| With the continuous improvement of the speed of high-speed train,the multi axis random load environment of vehicle body and its suspension parts is becoming worse and worse.The previous method of predicting the fatigue life of structure by successively accumulating the damage of single axis and using the excitation spectrum of the old standard is not reliable enough.Therefore,if the fatigue life of vehicle body and its suspension can be predicted accurately and efficiently,it will have great engineering significance.In this thesis,taking the underframe of EMU train and the external structure of air conditioner as an example,the fatigue life prediction under multi axis random vibration is carried out by combining simulation and test.Firstly,according to the multi axis random vibration environment,the aluminum alloy specimen is designed and subjected to frequency sweep and multi axis random vibration tests.The finite element software is used for simulation,and the simulation data are compared with the test data to verify the accuracy of the finite element model and stress response;The algorithm of determining the critical interface by damage accumulation method and maximum variance method is compiled by programming software.The simulation data are input into the critical interface algorithm to obtain the fatigue life.Compared with the test results,the error is less than twice.Therefore,the reliability of multi axis critical interface method is verified by small specimen.Secondly,after processing the measured data of the line,the road spectrum simulation test is carried out on the vibration test-bed,so as to obtain the data required for load spectrum editing.In the time domain,the original road spectrum of 1200 seconds is shortened to 874 seconds by using the method of multi-channel damage correlation editing.The time compression rate is 27% and the retention degree of pseudo damage is 96%;In the frequency domain,the 15 million km damage of the road spectrum is equivalent to the 5-hour acceleration spectrum damage through the damage equivalence principle.Comparing the RMS value of acceleration spectrum with EN61373 long-life test,there is little difference between the data.It theoretically reflects the reliability of accelerated editing.Then,on the vibration test-bed,the multi axis synchronous and single axis sequential frequency sweep test,road reduction spectrum test,road acceleration spectrum test and road standard acceleration spectrum test are carried out on the local train underframe and its suspended external air conditioning structure.The swept multi-axis synchronous test is consistent with the fifth-order natural frequency obtained in the first 200 Hz frequency range from the uniaxial sequential test;The equivalent damage of 15 million km at each measuring point in the road spectrum reduction test is slightly less than that in the road spectrum simulation test,and the damage retention varies from 89% to 98%,which is not far from the theoretical retention of 96%;In the frequency domain acceleration test,the damage of the two types of acceleration spectrum test results is greater than that of the road spectrum simulation test,but both meet the damage requirements of 15 million km.The damage of multi axis synchronous test is greater than that of the single axis cumulative test.Therefore,the reliability of accelerated editing is reflected from the test.Finally,the standard 5-hour spectrum compiled by frequency domain acceleration is used for the finite element simulation analysis of the local train underframe and the external unit structure of the suspended air conditioner.The test data and multi axis synchronous simulation data are input into the critical surface method program to obtain the damage per second of the critical interface determined based on the maximum variance method,with a total of four types of damage comparison,It is concluded that the damage errors are within 2 times.Therefore,the reliability of multiaxial critical interface method is verified from the local actual structure.Then it is extended to the whole vehicle underframe structure that cannot be tested on the bench,and the fatigue life under multi axis random vibration is obtained by using the critical surface method. |
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