Influence Of Foreign Object Damage On Fatigue Performance Of High-Speed Train Hollow Axle

The axle is an important load-bearing component in the running part of a high-speed train,and the problem of foreign body impact defects will seriously affect the fatigue performance of the axle,thereby posing a threat to the safe operation of the train.In order to carry out a detailed analysis of "the influence of foreign body impact defects on the fatigue performance of high-speed train hollow axles",this paper takes the full-size hollow axles of high-speed trains made of 30 NiCrMoV12 and EA4 T as the research object,combined with a variety of research methods,and analyzes the surface defects of axles.Angle analysis,and a comprehensive assessment of the safety and reliability of defective axles.The main work of this paper is as follows:(1)Summarize on-site feedback and literature review results,and analyze the characteristics and distribution rules of axle surface defects.Prefabrication of defects on the axle samples and scanning and measuring with optical profiler,multi-dimensional analysis of key data of various types of defects.It was found that,except for the arc defects,which were relatively smooth,the other types of defects had obvious plastic deformation and material accumulation,and there were big differences in shape and size.(2)According to the European standard EN13103,the finite element loading analysis of the axles of CRH5 and CRH3 was carried out,and it was found that the highest axial tensile stress occurred in the exposed area of the axle body,and there may be a coupling effect of foreign body impact and axial tensile stress.Analyzing the superimposed stress fields of different types of impact defects,the results show that although there are higher tensile stresses at the corners of cone defects,higher residual compressive stresses accumulate at the bottom of the defects,which effectively slows down the development of fatigue damage;quadrangular pyramids The defect not only has a high tensile stress,but the area of the high tensile stress area is also relatively large.Compared with EA4 T axle steel,30 NiCrMoV12 material will produce higher residual tensile stress after being subjected to the same impact.(3)Using the improved small sample lifting method,conduct a rotating fatigue test to simulate the operating stress state of the axle for each sample group,and use the P-S-N curve to fit the test data and calculate the fatigue limit value of each sample group.According to the results,under the same impact load,the impact defects of the quadrangular pyramid and the axial scratches will have a greater adverse effect on the fatigue limit of the axle steel specimens,but the arc defects and cone defects have little effect.Compared with30 NiCrMoV12 axle steel,the fatigue limit of EA4 T material has a relatively small reduction in the four-sided pyramid defect with the same impact load of 980 N.(4)Extend the fatigue limit of the defective axle specimens to full-size axles,make safety judgments and establish prediction models according to the iron standard TB/T2705-2010.According to the prediction results,it can be known that the quadrangular pyramid defects and axial scratches have a greater impact on the fatigue performance of axle materials,while other types of defects are relatively safe.At the same time,calculations show that the safety tolerance depths of 30 NiCrMoV12 and EA4 T full-size axles with four-sided pyramid impact defects are 93.7μm and 90.2μm,respectively.(5)Use the El-Haddad formula to modify the Kitagawa-Takahashi diagram to view the safe loading area of short cracks for different types of defects.Under the equivalent stress of the axle stress spectrum,using the revised Paris formula,the short crack propagation life of the 30 NiCrMoV12 axle is 4606.14 km,while the EA4 T axle is 5690.2km;although the former has excellent fatigue limit,yield limit and other related parameters In the latter case,the30 NiCrMoV12 material is more prone to damage during the short crack propagation stage.(6)Using the Miner formula and combining the stress spectrum of the axles during train operation,the ultra-high cycle life prediction analysis was carried out on the axles of two materials with quadrangular pyramid defects,and it was found that both met the design requirements of 25-35 years of life.It can be seen that the allowable stress of the axle body given in the iron standard is relatively conservative,and it is believed that more relevant influencing factors in train operation have been considered before the standard formulation.