Damage Mechanism of Worn and Fatigue Heavy Haul Railway Wheels
The increase in train speed and axle loads leads to increasingly significant wheel-rail rolling contact fatigue and wear.Wheels play a role in load-bearing,guiding,and transmitting traction/braking force during operation,and are the core components that ensure the safety of railway trains.Damage forms of train wheels can be divided into several major types,including wheel tread wear,wheel flange wear,rolling contact fatigue,tread spalling and dents.If wheel damage is not timely controlled,it will accelerate wheel-rail vibration,affect service comfort and even induce damage to other parts of the wheel axle.Therefore,the analysis of failure mechanism of in-situ failed wheel materials can provide theoretical support for wheel maintenance.Two typical in-situ failed wheels analyzed in this study,including worn wheel and spalled wheel.A Vickers hardness tester was used to measure the surface hardness distribution of the wheel flange,nominal rolling circle,and outer wheel rim on the cross section of the wheel.The measurement points were evenly distributed along the wheel surface to the depth direction with an interval of 5 μm.A wire cutting machine was used to cut the wheel along the longitudinal section and cross section at the wheel rim,nominal rolling circle,and outer wheel rim.Wheel samples were then embedded in resin and ground to 2 000 mesh and polished to 0.5 μm,and 4％nital was used for sample corrosion.Surface and sub-surface fatigue damage of wheel material were analyzed by the Optical Microscopy and the Scanning Electron Microscopy.The depth of the hardening layer at the nominal rolling circle and outer rim of the spalled wheel was about twice that of the worn wheel.The nominal rolling circle of the wheel displayed the severest fatigue damage compared with the wheel flange and the outer wheel rim.Fatigue cracks of the worn wheel were relatively small and shallow,and evenly distributed in the longitudinal section of the wheel.While fatigue cracks of the spalled wheel almost spread throughout the entire wheel section,and multiple cracks interweaved to form a network crack.The depth of the work hardening layer,the maximum crack angle,the maximum crack length and the maximum crack depth of the spalled wheel at the nominal rolling circle reached 6 mm,90°,2.5 mm,and 1 mm,respectively,which were approximately 2,2.5,2,and 1.5 times that of the worn wheel.The failure mechanism of worn wheel is that during train operation,the wheel is subject to significant and frequent strong stresses.The wear rate of the wheel tread is relatively high,forming a"concave"shaped wear tread in a short period,which leads to the change of wheel-rail contact state,and finally causes an increase in wheel tread wear and even material failure.The failure mechanism of the spalled wheel is complex,but it is fundamentally the result of the initiation and continuous propagation of rolling contact fatigue cracks,mainly including branched cracks bending towards the material surface,two or more intersected cracks,and material fragmentation.The wear of the worn wheel analyzed in this work is greater than that of the spalled wheel,and its rolling contact fatigue damage is smaller than that of the spalled wheel.Thus,there is a mutually restrictive relationship between material wear and rolling contact fatigue during in-situ service of wheels.
train wheelnominal rolling circlewheel flangeouter wheel rimwornspallingrolling contact fatigue
万方数据
维普
