| The characteristics of subway vehicles,such as large passenger flow,complex working conditions and frequent use of vehicles,put forward high requirements for the reliability and safety of key structures of vehicles.Bogie plays a role of bearing,guiding and damping in the process of vehicle operation.Whether the fatigue strength of the frame meets the requirements is directly related to the safety of vehicle operation.Based on the measured dynamic stress data under operation conditions,the following work is carried out for the fatigue reliability of the bogie frame of metro vehicles:(1)Based on the dynamic stress data measured in long period,the stress spectrum of fatigue control part is compiled.According to the principle of damage equivalence,the equivalent stress amplitude of 3.6 million km is calculated,and the nuclear density fitting analysis is carried out for all the calculated equivalent stress amplitude.According to 97.5%reliability recommended by FKM standard,the equivalent stress value under high reliability is selected,which can cover the cumulative damage equivalent stress under the actual operation,and the high reliability life prediction is carried out based on this.(2)The sample size for high reliability life assessment is studied.With the passage of test time,the sample size increases,and the mean value of equivalent stress and the change range of equivalent stress is instable with the accumulation of samples.The fitting value of equivalent stress of 97.5% nuclear density is linearly related to the number of sub samples.(3)The strain fatigue parameters of welded joints are studied.The local stress-strain method is used to predict the crack initiation life of the frame.The crack initiation life corresponding to different fatigue notch factors is studied.The results show that the increase of the fatigue notch coefficient will lead to the decrease of the crack initiation life.(4)The fracture mechanics method is used to calculate the crack growth life of the frame.The results show that the crack growth rate of the frame increases with the increase of operating mileage.When the average welding level is taken as 1.6,the ratio of the initiation life to the total life is more than 90%,which is consistent with the rule that the crack forming life accounts for the main part of the total life in high cycle fatigue.(5)The reliability analysis model of crack growth life is established,and Monte Carlo simulation is used to study the cumulative failure probability of the frame under different running mileage.The results show that the probability of fatigue failure increases with the increase of running kilometers,and the reliability of the frame decreases to less than 90% after 1 million kilometers.Based on the dynamic stress data under the application conditions,this paper studies the fatigue reliability and life prediction of the framework,which provides a theoretical basis for maintaining the operation safety of metro vehicles and establishing a scientific and reasonable maintenance cycle,and is of great significance to ensure the safe and reliable operation of metro vehicles.58 figures,17 tables,113 references. |
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