Study On Casting Defects And Fracture Mechanism Of High-speed Train Gear Box Materials During Dynamic Loading

The high-speed train is the important means of delivery in high-speed railway There are many issues needing to be considered in the vehicle design,such as the safety,stability,reliability and so on.As one of the key components of the running gear in high-speed train,the service environment of gearbox is relatively bad,Fatigue crack initiation occurs in the domestic service,which seriously threatens people’s life and property safety.The fatigue crack the initiation of in the gearbox of high-speed train during operation is analyzed in this thesis,To describe the coupling behavior between aperture and hole position,the coupling coefficient of effective radius divided by offset length is puts forward.The coupling coefficient can comprehensively considers the influence of the size and pore locations on the fatigue properties of materials,which can be used to predict the failure position of gearbox materials of high-speed railway.Both the inductively coupled plasma emission spectrometry（ICP-OES）,electron backscatter diffraction（EBSD）and X-ray diffraction（XRD）were used to determine the composition,secondary phase particle composition,aspect ratio and size distribution of cast aluminum gearbox.At the same time,typical in-situ fatigue samples were tested by synchrotron radiation X-ray micro tomography（CT）,The effects of the location,size,roundness and aspect ratio of shrinkage cavity on fatigue crack growth are analyzed.The main research contents of this thesis include:（1）The gearbox material is cut from a high-speed railway gearbox that has operated about 1.2 million kilometers.Through the analysis of characterization methods such as inductively coupled plasma emission spectrometry（ICP-OES）,electron backscatter diffraction（EBSD）and X-ray diffraction（XRD）,it is found that the microstructure of gearbox materials is composed of Al matrix,eutectic Si,Mg₂Si and Fe rich particles,And the secondary phase particles are mainly composed of 1-4μm（2）Three sets of samples were collected by synchrotron radiation X-ray tomography.By observing and analyzing the reconstructed slice diagram,three-dimensional rendering diagram and statistical data,it can be seen that the geometric characteristics of pores and the orientations of ellipsoidal pores have less impact on fatigue crack growth compared with the pore size and pore position,Mean while the fatigue crack growth rate has a linear relationship with the coupling coefficient.By calculating the coupling factor of pores,the pore induces final fatigue failure can be predicted.（3）Based on the in-situ fatigue test,the material parameters needed in the simulation are determined.Through the finite element modeling and simulation,the relationship between the maximum radius of pores and the deviation depth of pores is analyzed when the same stress concentration factor is generated.