| With the continuous improvement of the speed of high-speed trains in China and the more complex operating environment,the probability of dama ge to the axle surface is also increasing.More than a half of the axle damage is caused by the impact of foreign materials,which cause defects or crack initiation on the axle surface.Therefore,it is necessary to study the fatigue strength of axles with defec ts and the service life.This article takes high-speed rail axles made of two homogeneous steels,30 NiCrMoV12 and EA4 T,as the research objects.The mechanical and fatigue p roperties of axle materials are experimentally compared,and fatigue tests are conducte d on defective axles.The influence of foreign object impact defects on the fatigue performance of axles made of different materials is studied.The crack propagation behav ior of axles containing surface cracks is studied through a combination of crack propagatio n tests and finite element simulation,And predict the crack propagation life of the full size axle.The main job responsibilities are as follows:(1)The chemical composition and mechanical properties of 30 NiCrMoV12 and EA4 T axle steel were tested.The stress-strain curve was obtained through tensile testing,and axle specimens were prepared in the surface area of the exposed part of the axle body.The fatigue limit and fracture morphology of smooth s pecimens were obtained through four point bending tests using the small sample lifting method.Comparative analysis was conducted,and it was found that the mechanical properties of30 NiCrMoV12 axle steel were better than those of EA4 T axle steel.(2)A study was conducted on the fatigue characteristics of axle steel containing defects and full size axles.Defective axle specimens were prepared using the solid indenter impact method.Fatigue tests were conducted on the defective axle specimens,and the fracture morphology of the defective specimens was scanned to obtain the predicted results.It was found that under the same load conditions,the fatigue limit of the EA4 T full size axle decreased slightly compared to the 30 NiCrMoV12 axle.Revise the Kitagawa Takahashi diagram to obtain the impact of diff erent types of impact defects on the safe loading area of axle steel.For edge defects,compared to 30 NiCrMoV12 axle steel,EA4 T axle steel has a larger critical crack size and is less prone to crack propagation after being impacted by foreign objects.(3)From an experimental perspective,the crack propagation characteristics o f EA4 T axle steel material and full size axle surface were studied.The compact tensile(CT)specimens of EA4 T axle steel material and full size axle were subjected to crack propagation experiments.After the experiment,the test data was fitted to obtain the Paris formula,and the transferability of fatigue crack propagation parameters from axle specimens to full size axles was studied.It was found that after considering the size effect of the axle specimen,the crack propagation curve of the axle materia l can be used to predict the crack propagation behavior of the full size axle.(4)Chapter 5 uses a combination of analytical method and finite element simulation to study the variation pattern of stress intensity factors for sur face cracks on EA4 T axles.Correction factors are introduced to establish an analytica l model of stress intensity factors for surface cracks on axles.Analytical solutions are calculated to establish a finite element model for axles with cracks.Initial cracks of different shapes and depths are introduced in the transition zone of the inner arc of t he wheel seat,By calculating the stress intensity factor through finite element simulation a nd verifying it,the critical crack size of the axle was calculated,and the crack propag ation life was predicted to obtain the crack propagation life of different shapes of cr acks,thus providing a theoretical basis for the formulation of the high-speed rail axle inspection cycle. |
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