高速铁路轮轨磨损特征、机理、影响和对策——车轮踏面横向磨耗

系统分析总结我国高速铁路轮轨断面横向磨耗情况、特征、形成机理、对车辆动态行为的影响以及对策研究。高速车轮踏面横向磨耗以在名义滚动圆处形成凹坑磨耗和轮缘磨耗为主,主要发生在相对高的等效锥度和具有较厚轮缘的轮对上。车轮踏面横向凹坑磨耗与高速轨道高平直度和高速列车高运行平稳性密切相关。轮轨平稳地高速滚动接触,导致轮轨接触光带狭窄平直,且主要集中在名义滚动圆附近,此处车轮踏面材料磨耗累积迅速形成凹坑,轮对的等效锥度迅速增大。凹坑磨耗在一定深度范围内,将会引起轮对横向晃动,影响车辆的舒适性。提出7个方面的措施,来抑制或减缓车轮踏面凹坑磨耗。最后讨论了钢轨断面横向磨耗情况,主要反映在小半径曲线处外轨内侧磨耗,原因类似普通线路小半径曲线钢轨侧磨情况,也是车轮轮缘磨耗的主要原因,简单讨论减缓措施。所做的工作将对我国高速铁路轮轨型面和硬度匹配深入研究提供重要的参考依据。     

地铁车轮踏面异常磨耗原因分析

介绍车轮磨耗的预测方法.考虑轮轨动态接触状态,采用数值分析方法分析异常磨耗的地铁车轮和新钢轨作用情况,且对导致地铁车轮踏面异常磨耗的原因作了简单分析.分析结果表明, 地铁车轮踏面经闸瓦磨耗后在凸起处的接触频率较高,磨耗率大,因而车轮磨耗后踏面凸起不是轮轨接触作用引起的;闸瓦压力过大、压力不均匀、闸瓦晃动量大、频繁制动等因素容易导致滚动圆内侧和踏面外侧的双凹槽磨耗,双凹槽处磨耗速度远远大于轮缘处的磨耗速度;轮缘磨耗主要是轮轨相互作用的结果,而踏面上的凹槽磨耗可能主要由闸瓦制动引起.     

列车紧急制动过程中踏面温度分布及磨耗预测

列车紧急制动过程中踏面温度急剧升高导致车轮踏面的摩擦磨损机理与稳态运行时有显著差异.为了准确预测列车紧急制动过程中踏面磨耗,同时考虑踏面制动过程中车轮踏面与钢轨及闸瓦接触,基于有限元软件ABAQUS建立了踏面制动过程热机械耦合有限元模型,综合考虑制动温升对车轮踏面力学性能、硬度及摩擦因数的影响,仿真得到了紧急制动过程中...     

踏面制动单元手动缓解装置的失效分析及改进

踏面制动单元是配置于轨道交通车辆的一种常用制动装置,通过压力空气驱动闸瓦产生制动、缓解作用。踏面制动单元分为停放制动和常用制动两种机制,手动缓解装置即用来实现踏面制动单元停放制动的保持和缓解。现主要针对踏面制动单元手动缓解装置在运用过程中出现的多起失效故障进行分析,并提出优化改进措施。     

制动过程踏面剥离热应力耦合仿真分析

踏面剥离的研究一直是许多的专家从事的工作,研究的轨道和车轮踏面的损伤等一系列的问题。踏面涉及的是重载、振动等一系列的问题。车轮制动产生的摩擦热应力会对于车轮踏面有着一定损伤,本文通过Solidworks建立车轮踏面模型与钢轨,利用ANSYS有限元分析进行模拟制动实验,分别通过纯机械载荷和热应力耦合仿真分析,我们通过研究得出的是在滚动的过程中,高温短时间产生,与周围的空气热交换量小,热量累积,而车轮正在高速的向前移动,导致最高的温度点向后移了一点,比较符合实体实验。     

城市轨道交通车辆踏面制动热应力仿真分析

分析了城轨列车在踏面制动方式下车轮踏面热疲劳裂纹产生的机理,并建立了车轮制动过程瞬态温度场三维有限元模型,采用整体输入热流和对流换热的简化模式为基础的传统理论的热应力计算方法,计算车轮在连续两次紧急制动工况下的热温度场及热应力场,为确定城轨列车制动方式及列车制动距离等技术规范提供计算依据。     

[轮轨磨耗及预测]列车紧急制动过程中踏面温度分布及磨耗预测

列车紧急制动过程中踏面温度急剧升高导致车轮踏面的摩擦磨损机理与稳态运行时有显著差异。为了准确预测列车紧急制动过程中踏面磨耗,同时考虑踏面制动过程中车轮踏面与钢轨及闸瓦接触,基于有限元软件ABAQUS建立了踏面制动过程热机械耦合有限元模型,综合考虑制动温升对车轮踏面力学性能、硬度及摩擦因数的影响,仿真得到了紧急制动过程中车轮踏面上温度分布、硬度分布以及接触应力分布,并利用轮轨动力学软件UM得到了紧急制动过程中轮轨接触斑形状以及轮轨蠕滑区相对滑移分布,在此基础上结合Archard磨耗模型对单次紧急制动结束后的踏面磨损深度进行了定量预测。结果表明：对于制动初速度为130 km/h、160 km/h两种工况,踏面最高温度分别达到了397.0 ℃和485.9 ℃,踏面最大累积磨损深度分别为5.90 μm和7.43 μm,与踏面制动实验对比发现,预测结果与实验结果磨损位置及形貌分布趋势一致。     

基于疲劳应力的HX_D1C机车踏面剥离的研究

介绍了机车车轮踏面剥离的现状,通过对HXD1C型机车在不同运行情况条件下的车轮剥离现象的调查后,对滚动接触疲劳应力下的机车的运行情况进行受力分析。用SolidWorks直接画图,根据受力情况运用ANSYS进行受力计算,生成温度场图,笔者将计算结果与现场剥离情况对照,从而说明分析的正确性和产生剥离的可能性,提出了减少机车车轮踏面剥离情况的可能的有效措施。     

车轮踏面制动的热-机耦合数值模拟

重载列车车轮踏面制动是一个复杂的动态接触热-机耦合问题,介绍了热-机耦合问题的求解方法,并利用有限元分析软件ANSYS对提速货车的单闸瓦踏面制动过程进行了紧急制动工况的数值仿真,定量地给出了车轮踏面温度和应力随时间的变化规律,为研究车轮踏面热疲劳提供了理论依据.     

增黏砂对机车车轮踏面剥离影响的试验研究

随着国内铁路运输需求的增加,轮轨间相互作用导致机车车轮踏面出现不同程度的剥离损伤,严重威胁了列车的安全运行。为研究增黏砂对机车车轮踏面剥离问题的影响,对机务段使用的石英砂及不同类型的河砂进行采样,搭建轮轨接触模拟试验台进行轮轨与石英砂及轮轨与河砂的碾压试验,并对车轮踏面鱼鳞状剥离部位进行金相分析。综合对比分析现场情况、碾压试验结果以及金相分析结果后,得出结论:由于河砂的存在,机车车轮踏面在运用初期形成麻点状损伤;由于河砂的存在,触发了轮轨间滚动接触疲劳的发生,继而在后期导致了机车车轮踏面出现鱼鳞状剥离损伤;不同类型的河砂会在车轮表面造成不同程度的坑状损伤,且破碎均匀性越差的砂粒所导致的车轮剥离损伤越严重;建议使用破碎均匀性较好的石英砂作为增黏介质。     

基于摩擦温升效应的地铁车轮磨耗特性研究

踏面制动引起车轮温度急剧上升,影响车轮材料性能和轮轨接触状态,加剧车轮磨耗。基于Archard磨耗模型,建立一个考虑摩擦温升效应的地铁车轮磨耗预测模型。模型中根据车轮材料属性与温度之间的关系,考虑摩擦温升对接触斑大小、黏滑区划分和磨耗深度的影响,可实现对高温下的车轮磨耗特性的研究。相对以往的车轮磨耗预测模型,该模型能反映温度对磨耗影响的物理本质,适合研究轮轨接触界面有较大温度(如踏面制动)时的车轮磨耗演化机理。用所建立的车轮磨耗数值预测模型,计算对比不同温度下的轮轨接触状态和车轮磨耗深度。结果表明,轮轨接触斑和滑动区面积随温度的升高而增加;温度升高使接触斑单元磨耗深度增加,当踏面温度从常温25℃增加到最高温度300℃时,最大磨耗深度0.4 nm,增幅为28.4%;车轮转动一圈后,其径向磨耗深度也随温度的升高而明显增加,最大径向磨耗深度15 nm,增幅为28.2%,同时,车轮横向位置的磨耗范围增加5.8%,为踏面制动形式的地铁车轮磨耗预测研究提供更加准确的理论模型。     

Numerical modeling of sub-surface initiated spalling in rolling contacts

A 3D finite element model was developed to investigate the influence of microstructure topology on the stochastic nature of rolling contact fatigue. Grains of the material microstructure are modeled with random Voronoi tessellations. Continuum damage mechanics and mesh partitioning are implemented to capture the initiation and propagation phases of fatigue damage that lead to spalling. Simulated fatigue spalling is shown to progress similarly to experimental observations of rolling contact fatigue. The fatigue lives obtained with the model exhibit scatter on par with empirical measures and are fit well by 2 and 3-parameter Weibull distributions.     

VOLUME DEFECT FATIGUE FAILURE OF CERAMIC BALLS UNDER ROLLING CONDITION

A newly developed pure rolling fatigue test rig with three contact points is used to test the rolling contact fatigue properties of silicon nitride ceramic balls. Ball surfaces are examined after failure with optical microscopy and scanning electron microscopy. The failure cause,fatigue phenomenon and mechanics are analyzed. The research shows that subsurface cracks play a dominant role in the formation of spalling failure. These cracks originated from volume defects of the material and propagate,to form elliptical fatigue spalls under the action of principal tensile stresses. The principal tensile stress increases with increasing contact load,causing spall formation and reduction of rolling contact life. The greater the principal tensile stress is,the more severe the peeling of near surface is. Under the same condition,the closer volume defects are to the surface,the more likely failure occurs,the shorter the rolling contact life is.     

Surface fatigue failure of nitride-hardened aluminium-chromium-molybdenum steel rollers under pure rolling and sliding-rolling contacts

To study surface failures of nitride-hardened gears, rolling fatigue tests were performed using nitride-hardened steel rollers as gear-tooth surface models. Surface failure of nitride-hardened rollers was by subsurface-initiated spalling under all contact conditions, nitriding depths and Hertzian stresses used. Cracks leading to spalling initiated at the case/core boundaries. White etching areas (WEA) were observed along spalling cracks. Electron probe microanalysis revealed that the WEA material was carbide. It is considered that there is a relation between the initiation of spalling cracks and the formation of WEA.     

Durability of plasma-sprayed Cr3C2-NiCr coatings under rolling contact conditions

The aim of this paper was to address the rolling contact fatigue (RCF) failure mechanisms of plasma-sprayed Cr3C2-NiCr coatings under different tribological conditions of contact stress. Weibull distribution plots of fatigue lives of the coated specimens at different contact stresses were obtained. The failure modes of coatings were identified on the basis of wore surface observations of the failed coatings. Results showed that the RCF failure modes can be classified into four main categories, i.e., surface abrasion, spalling, cohesive delamination, and interfacial delamination. The probabilities of the surface abrasion and spalling type failures were relatively high at low contact stress. When the coatings were subjected to abrasion and spalling type failures, the failure of the coating was depended on the microstrcture of the coating. The stress concentration near the micro-defects in the coating may be the may reason for the formation of spall. The coatings were prone to fail in delamination under higher contact stresses. However, the delamination of coating may be related to distribution of shear stress amplitude within coating. The location of maximum shear stress amplitude can be used as a key parameter to predict the initiation of subsurface cracks within coating in rolling contact.     

Wear of steel in rolling contact with silicon nitride

Wear of steel (AISI M-50 and AISI 52100) bearing balls in lubricated rolling contact with ground and ground-and-lapped silicon nitride rods was studied using a ball-on-rod rolling-contact-fatigue (RCF) tester. The steel balls suffered significant wear in rolling contact with the as-ground (R_a = 0.18 μm) silicon nitride rods. The wear volume loss was approximately linear with the rolling distance. The wear rate increased linearly with the initial Hertzian contact stress in the range, 3–6.5 GPa. Examination of the wear tracks in a scanning electron microscope revealed surface features that suggested a wear mechanism that involved plastic deformation of the steel surface, squeezing of the metal symmetrically outward and rupture of the metal layers at the edges. The steel balls suffered negligible wear but failed by spalling in rolling contact with the ground-and-lapped silicon nitride rods (R_a = 0.08 μm) at an initial contact stress of 5.5 GPa. The as-ground silicon nitride rods exhibited neither wear nor spalling in the RCF tests, while the ground-and-lapped silicon nitride rods showed no wear but occasional spalling failure.     

Influence of coating thickness on rolling contact fatigue of alumina ceramics thermally sprayed on steel roller

The influence of the sprayed layer thickness on rolling contact fatigue of a thermally sprayed alumina ceramics with a nominal composition of Al₂O₃–2.3 mass% TiO₂ was investigated using a two-roller test machine under pure rolling contact condition with oil lubricant. The influence of undercoating of sprayed nickel-based alloy on rolling contact fatigue was also investigated. Thicknesses of the ceramics-sprayed layer of tested rollers were 0.2, 0.5 and 1.0 mm. The failure mode of sprayed rollers was spalling caused by subsurface cracking. In the case of sprayed rollers without undercoating, rolling contact fatigue strength of rollers with 0.2 mm thickness sprayed layer was the smallest. Rolling contact fatigue strength of sprayed roller with 0.2 mm thickness sprayed layer was improved by undercoating. In case the failure depth was small as compared with the thickness of sprayed layer, effect of undercoating on the rolling contact fatigue strength was little. The depths where the maximum values of subsurface shear stresses occurred, almost corresponded to the observed depth of spalling cracks.