Analysis On Fatigue Strength And Dynamic Characteristics For Welded Frame Of CRH3 EMU

With the rapid development of high speed railway in China,the running speed of trains has been continuously improved,which puts higher requirements on safety and reliability of vehicles.The vibration characteristics and service status of the key components of the bogie have changed under the orbit excitation,due to the improved speed and the application of lightweight technology of the EMU.The welding frame that supports body and connects all parts is a key structure of bogie,the safety and reliability of which will directly affect the safety of train operation.Therefore,the welding frame of CRH3 bogie is taken as the research object,the related research has been carried out from two aspects: fatigue strength and dynamic characteristics.First,the safety assessment methods of two kinds of welding structures,extrapolated hot stress stress method and equivalent structural stress method,are compared and analyzed.The equivalent structural stress method based on fracture mechanics and mesh insensitivity is used to conduct the safety assessment of welds of the CRH3 EMU frame.The mesh insensitivity of the equivalent structure stress method is verified through the T type corner joint.Secondly,the loading conditions of CRH3 EMU welding frame in actual service are analyzed.According to the UIC615-4 standard,the finite element method is used to carry out the static strength simulation analysis of the welding frame under the abnormal load conditions and the simulated operating conditions,the static strength evaluation of which is performed by the von Mises stress yield criterion.The maximum stress of the frame is 250.5MPa under abnormal conditions,the maximum stress of the frame is 185.3MPa under simulated operation condition,and the frame meets the requirement of static strength.On the basis of the static strength calculation results,the fatigue strength of the frame is analyzed through the Goodman-Smith fatigue limit diagram.The analysis results show that the frame meets the requirement of fatigue strength.Thirdly,in order to improve the accuracy and efficiency of the finite element calculation,submodel technology is used to establish the submodel of the weld weak zone — the positioning of arm locator seat,where the average stress and the stress amplitude are larger.The fatigue life of the key welds is analyzed by the equivalent structural stress method,and the minimum life of the welds of key positions is 1.172×107,which is greater than 1×107 specified in the UIC615-4 standard.So,the fatigue life of the welds of the frame meets the design requirements.Finally,the vibration characteristics of the welding frame are compared and analyzed from two aspects: the free modal and the constrained modal.The natural frequencies and corresponding modes of each order of the frame are determined by the reduction method.The influence of the track excitation on the vibration characteristics of the frame is studied through the harmonic response analysis.The amplitude frequency curves of the key points are obtained.On this account the resonance frequency of the weak parts of the CRH3 EMU welding frame is determined to be 34 Hz,43Hz,63 Hz,79Hz and 93 Hz.