Fatigue Prediction And Accelerated Fatigue Test Of Multiaxial Random Vibration

In recent years,the rail transit industry has developed rapidly,the railway operating environment is complex and variable,and the train running speed is increasing,which makes the multi-axle random vibration loads on vehicle suspension equipment and possibility of fatigue failure increase sharply,which seriously endangers passengers and traffic safety.Therefore,the accurate and efficient prediction methods of random vibration fatigue life have important practical significance in engineering.At present,two commonly used methods for predicting fatigue life are fatigue test and simulation analysis.This paper takes the structure of metro vehicle antenna bracket as an example to predict the random vibration fatigue life from two aspects of test and simulation.Firstly,according to the actual operation of metro vehicles,two test schemes of metro vehicles with different antenna bracket structure are designed.The acceleration and dynamic stress data of the two installation structures are measured respectively,and the fatigue damage of the dangerous measuring points is calculated.It is found that the original structure has a low life and cannot meet the operation requirements.The improved structure meets the design requirements.Secondly,in order to verify the fatigue reliability of the improved structure of the antenna bracket,the line test data are processed and the bench tests are designed.According to the measured acceleration data,the road simulation test spectrum suitable for bench test is obtained by using the multi-channel correlation damage method in time domain,and the acceleration efficiency reaches 46.38%.Based on the principle of fatigue damage equivalence,the fatigue damage spectrum under various working conditions is calculated in frequency domain,and the cumulative fatigue damage spectrum in service life is obtained,which is equivalent accelerated to the acceleration test spectrum for 5 hours.Then,the axial sweep test,road simulation test,standard spectrum test and accelerated spectrum test are carried out on the vibration table in turn.The resonance frequency and modal damping ratio of the structure are obtained by sweeping frequency test,which verifies the accuracy of the finite element model and provides real damping parameters for simulation analysis.By comparing the road simulation test with the line test results,it is found that the reduced load spectrum in time domain does not change the stress distribution characteristics in the frequency domain,and the RMS value of the stress time history increases which meets the acceleration requirement.The improved structure is verified to meet the 30-year operation requirement by the 5-hour test of the standard spectrum in three axes.The comparison between the standard spectrum and the accelerated spectrum test results shows that the magnitude of the vibration excitation has a greater influence on the fatigue life of the structure than the frequency range,and the fatigue life predicted by standard spectrum is more conservative.Finally,the antenna bracket structure is simulated and analyzed.Random vibration spectrum analysis and harmonic response analysis,as well as critical surface method based on maximum principal stress and shear stress criteria,are used to predict uniaxial and multiaxial fatigue life.The results show that the simulation results are larger than the test results,which are conservative,and the single-axis random vibration spectrum analysis is closer to the test results.The equivalent stress power spectrum calculated by the multi-axis maximum absolute principal stress criterion is basically consistent with the equivalent stress power spectrum calculated by the critical plane method,but the fatigue damage calculated by the fatigue life formula is too conservative due to the material parameters being too single.