| As the key load-bearing component of the vehicle,the axle is very important for the operation safety of the train,especially in the current trend of increasing speed of the EMU.However,in the actual application of the axle,surface damage or other forms of defects occur many times.When the defect occurs,whether the structural strength of the defect part and the key part of the axle still meet the reliability requirements needs to be researched.Based on the practical application of CRH3 and CRH5 high-speed EMU axles,this paper summarizes the various defect forms of axles in actual operation and mainly focuses on two typical defects.Through the eombination of finite element simulation and theoretical calculation,the stress distribution and fatigue performance of the defective axle are evaluated based on the axle stress spectrum obtained by the actual measurement.In addition,through the field test,the influence of the extreme condition of the flat on the axle stress and life i5 studied.Through the life evaluation of the defective axle under the above various working conditions,the reference and basis for determining the defect size and maintenance period allowed by the axle are provided.The specific research contents are as follows:(1)Combining the on-site investigation and the damage report of the EMU manufacturer,the paper summarizes the various defect fonns that occur during the operation of the axle.Focusing on the typical defects of axle impact and groove type scratches,the characteristics are derived from the causes,location and shape size.The models of axles containing two kinds of defects are established through FRANC 3D and finite element software.(2)Based on the European axle design standards,the strength check of the axles of CRH3 and CRH5 EMU is completed in turn.In order to study the influence of the gap,multiple sets of parameters such as the shape or depth are set to obtain the specific influence of the notch form and size on the axle stress distribution.In addition,by comparing with the allowable stress values specified by the standard,it provides a reference for determining the axle defect limits in different forms.(3)The gap mainly leads to the decrease of fatigue.Based on the relevant theory of stress fatigue life,the stress concentration factor and the fatigue gap coefficient of different size gaps are determined by finite element simulation and theoretical calculation method.The smooth axle fatigue life curve is corrected to obtain the axle fatigue life cvirve vrnder the influence of the gap.Based on the axle stress spectrum data obtained from the actual measurement of the axle,the equivalent stress under different notches is calculated,and the crack initiation life of the defective axle is estimated from the angle of damage,which provides a reference for the development of the defective axle maintenance cycle.(4)Through the field test,the influence of the extreme situation of the flat on the axle stress distribution is studied.Set multiple sets of flat and different operating conditions and summarize the influence of the impact of the flat on the wheel-rail load and axle stress by processing the measured data.Based on the test results,the measured stress spectrum of the axle line is corrected and obtains the axle stress spectrum under the impact of the wheel flat.Then evaluate the influence of the wheel flat on the fatigue life of the axle.Considering the more dangerous situation of wheel flat and axle notch at the same time,the crack initiation life of the defective axle is estimated.Then the life evaluation of the defective axle is improved based on multiple working conditions. |
