Investigation of the Relation between Rolling Contact Fatigue Property and Microstructure on the Surface Layer of D2 Wheel Steel

Through the rolling contact fatigue experiment under the condition of the lubricating oil, this article investigated the relation between contact fatigue property and microstructure on the surface layer of D2 wheel steel. The results showed that although the roughness of the original specimen induced by mechanical processing would diminish to some extent in the experiment, the 0.5 - 1.5 μm thick layer of ultrafine microstructure on the original mechanically-processed specimen surface would still become micro-cracks and small spalling pits due to spalling, and would further evolve into fatigue crack source. Additionally, even under the impact of the load that was not adequate to make the material reach fatigue limit, the ferrite in the microstructure underwent plastic deformation, which led the refinement of proeutectoid ferrite grains. During the experiment, the hardening and the refinement caused by plastic deformation consisted with the theory that dislocation gave rise to plastic deformation and grain refinement. The distribution laws of hardness and ferrite grain sizes measured could be explained by the distribution law of the shearing stress in the subsurface.

Effects of Lateral Motion on the Creep Forces in Wheel/Rail Rolling Contact

The influences of the lateral motion of a single wheelset running on a tangent railway on the creepages and creep forces between wheel and rail are investigated with numerical methods. The effect of the yaw motion of wheelset is neglected in the analysis, and Kalker’s theory of three dimensional elastic bodies in rolling contact is employed to analyze the creep forces in the wheel/rail rolling contact with Non Hertzian form.

State-of-Arts of Mechanics of Rolling Contact and Its Application to Analysis of the Interactions between Wheel and Rail

A few typical models of theory on rolling contact of bodies are reviewed, and the advantages and disadvantages in the applications to the dynamics of railway vehicles and the wheel/rail rolling contact are discussed in detail in the present paper.

Influence of railway wheel tread damage on wheel-rail impact loads and the durability of wheelsets

Dynamic wheel-rail contact forces induced by a severe form of wheel tread damage have been measured by a wheel impact load detector during full-scale field tests at different vehicle speeds.Based on laser scanning,the measured three-dimensional damage geometry is employed in simulations of dynamic vehicle-track interaction to calibrate and verify a simulation model.The relation between the magnitude of the impact load and various operational parameters,such as vehicle speed,lateral position of wheel-rail contact,track stiffness and position of impact within a sleeper bay,is investigated.The calibrated model is later employed in simulations featuring other forms of tread damage;their effects on impact load and subsequent fatigue impact on bearings,wheel webs and subsurface initiated rolling contact fatigue of the wheel tread are assessed.The results quantify the effects of wheel tread defects and are valuable in a shift towards condition-based maintenance of running gear,and for general assessment of the severity of different types of railway wheel tread damage.

Numerical Analysis of Rolling-sliding Contact with the Frictional Heat in Rail

Thermal damage caused by frictional heat of rolling-sliding contact is one of the most important failure forms of wheel and rail. Many studies of wheel-rail frictional heating have been devoted to the temperature field, but few literatures focus on wheel-rail thermal stress caused by frictional heating. However, the wheel-rail creepage is one of important influencing factors of the thermal stress In this paper, a thermo-mechanical coupling model of wheel-rail rolling-sliding contact is developed using thermo-elasto-plastic finite element method. The effect of the wheel-rail elastic creepage on the distribution of heat flux is investigated using the numerical model in which the temperature-dependent material properties are taken into consideration. The moving wheel-rail contact force and the frictional heating are used to simulate the wheel rolling on the rail. The effect of the creepage on the temperature rise, thermal strain, residual stress and residual strain under wheel-rail sliding-rolling contact are investigated. The investigation results show that the thermally affected zone exists mainly in a very thin layer of material near the rail contact surface during the rolling-sliding contact. Both the temperature and thermal strain of rail increase with increasing creepage. The residual stresses induced by the frictional heat in the surface layer of rail appear to be tensile. When the creepage is large, the frictional heat has a significant influence on the residual stresses and residual strains of rail. This paper develops a thermo-meehanical coupling model of wheel-rail rolling-sliding contact, and the obtained results can help to understand the mechanism of wheel/rail frictional thermal fatigue.

A numerical study on tread wear and fatigue damage of railway wheels subjected to anti-slip control

Tread wear and rolling contact fatigue (RCF) damage propagated on railway wheels are the two extremely important focal points as they can tremendously deteriorate wheel/rail interactions and hunting stability and destroy wheel surface materials, and subsequently, cut down the lifetime of the wheels. The on-board anti-slip controllers are of essence aiming to hold back the striking slipping of the powered wheelsets under low-adhesion wheel/rail conditions. This paper intends to investigate the impact of anti-slip control on wheel tread wear and fatigue damage under diverse wheel/rail friction conditions. To this end, a prediction model for wheel wear and fatigue damage evolution on account of a comprehensive vehicle–track interaction model is extended, where the wheel/rail non-Hertzian contact algorithm is used. Furthermore, the effect of frictional wear on the fatigue damage at wheel surface is considered. The simulation results indicate that the wheel/rail contact is full-slip under the low-adhesion conditions with braking effort. The wear amount under the low-adhesion conditions is observably higher than that under the dry condition. It is further suggested that the wheel tread is prone to suffering more serious wear and fatigue damage issues with a higher anti-slip control threshold compared to that with a lower one.

Study on Match Relationship between Rail and Wheel

The match relationship between rail and wheel was studied by investigating the behavior of the contact fatigue wear in rail/wheel systems.The hardnesses of samples were close or equal to that of the real rail and wheel.Meanwhile the probe of study went further into the condition match and the material match based on the hardness match.The experimental results show that the wear rate depends on the hardness ratio(H/H)between rail and wheel,and the safe value of H/Hequals 1.00-11.20.The fatigue life of materials relies on the operating conditions except hardness.The selected experimental conditions satisfy the condition match except Rheat-treated out-line.The factor H/Sis the main element effecting wears in rail steel and wheel steel.The nature of the hardness match is the microstructure match under specified operating conditions.

钢轨材料局部激光熔覆自熔性合金涂层的磨损与滚动接触疲劳行为

激光熔覆技术可用于钢轨局部损伤表面的局部修复,但局部修复钢轨材料的磨损与滚动接触疲劳损伤规律尚不清楚。通过在钢轨试样表面切除凹槽来模拟局部损伤,在凹槽处激光熔覆Ni基、Fe基和Co基自熔性合金粉末,分析修复钢轨微观组织与硬度,然后利用双轮对滚试验研究局部修复钢轨试样的磨损与滚动接触疲劳行为。结果表明,激光熔覆涂层形成了共晶与枝晶组织,Ni基涂层组织粗大、硬度较小,Fe基与Co基涂层组织尺寸较小,Fe基涂层硬度最大,Co基涂层硬度居中。相比未熔覆区域,激光熔覆区(涂层)塑性变形层厚度较小,且涂层原始硬度越高,硬化后硬度越大,但硬化率和硬化层厚度更小。未熔覆区滚动接触疲劳裂纹较长,但裂纹角度较小;熔覆区裂纹长度均有所降低,但裂纹扩展角度明显增大;熔覆区与未熔覆区结合处疲劳损伤最为严重,疲劳裂纹角度和深度均比熔覆区和未熔覆区更大。对比分析发现,Stellite21(Co基)熔覆试样摩擦因数较低,熔覆区与未熔覆区磨损深度差较小,抗滚动接触疲劳性能较好,较为适合钢轨局部损伤的激光修复。研究结果可为激光熔覆技术在钢轨局部修复上的应用与优化提供理论与技术指导。

变摩擦条件下高速钢轨焊缝处轮轨滚动接触-冲击行为研究

采用变摩擦系数能够较为准确地刻画轮轨滚动接触行为。为研究变摩擦系数对钢轨焊缝处轮轨滚动接触行为的影响,建立三种不同钢轨焊缝工况的三维轮轨瞬态滚动接触有限元模型,通过对比库伦型摩擦系数的结果,计算分析变摩擦系数对轮轨力、接触斑内的微滑以及黏滑分布等接触行为的影响。结果表明:变摩擦系数接触斑内的滑动区域占比会更大且在滑动区域会引起黏滑振荡现象,当轮轨界面滑动现象越明显时,黏滑振荡越剧烈;变摩擦系数对法向接触解的影响不大,切向接触解会因接触状态的改变显著受到影响,造成凸形1焊缝的不均匀磨耗;变摩擦系数会影响von Mises应力分布,其最大von Mises应力发生的位置会向轨底移动,对伤损出现的位置产生影响。

钢弹簧浮置板轨道垂向动态特性及对轮轨力的影响研究

钢弹簧浮置板(steel spring floating slab, SSFS)作为一种高等减振轨道广泛铺设于我国地铁线路中,在服役过程中,该轨道在部分线路中出现了钢轨波磨问题,而轮轨动态行为对波磨形成具有较大的影响。为研究该轨道垂向动态特性及其对轮轨瞬态力的影响,建立SSFS轨道的三维轮轨瞬态滚动接触有限元模型,分析在有、无车辆加载下轨道垂向位移导纳特性,模拟钢轨宽频不平顺激扰下轮轨垂向瞬态接触力的响应。结果表明:(1)无车辆加载作用下,SSFS轨道在100 Hz以下(22 Hz、43 Hz、68 Hz等)振动模态表现为钢轨和浮置板共同垂向弯曲,在100~1 400 Hz中高频段表现为钢轨相对浮置板弯曲;(2)车辆加载后,轨道导纳出现59 Hz的P2共振,及64 Hz和72 Hz的轨道整体弯曲振动峰值;(3)柔性轮轨耦合后轨道导纳受到轮对作用影响在364 Hz、489 Hz、623 Hz处出现新峰值,其中,364 Hz、489 Hz为车轮振动模态引起,623 Hz为双轮对干涉引起的钢轨弯曲模态;(4)车辆瞬态通过含60~220 mm波长钢轨不平顺的轨道时,轮轨瞬态垂向接触力在约70 Hz响应最显著,这是由轨道的整体弯曲振动模态被激发引起,该振动是SSFS轨道出现160~200 mm波长波磨的原因。

重载铁路小半径曲线内轨滚动接触疲劳机理研究

国内某重载铁路小半径曲线内轨发生严重的滚动接触疲劳及其所致剥离损伤,主要集中在内侧轨肩处。为揭示其萌生机理,在轮轨现场观测和列车参数调研的基础上,建立典型重载列车的动力学模型,并利用损伤函数与表面滚动接触疲劳指数,数值分析内轨滚动接触疲劳的主要影响因素。所预测的疲劳区位置、严重程度及裂纹扩展方向等均与现场观测吻合,并发现钢轨磨耗失形是滚动接触疲劳在内轨两侧轨肩处发生的根本原因。内轨内侧轨肩处疲劳由机车曲线通过行为主导,“Co-Co”式转向架中间轮对的贡献最显著,机车导向轮对与货车共同决定了内轨外侧轨肩疲劳。随着曲线半径R增大,轮轨间作用强度减弱,使得内轨疲劳的严重程度逐渐降低,两轨肩疲劳区向轨顶中心靠拢,并最终在R为1000 m左右时合为1个疲劳区,轨面剥离现象也趋于消失。

重载曲线钢轨滚动接触疲劳时变规律及治理优化

为探明某重载铁路小半径曲线钢轨因滚动接触疲劳提前失效机理及优化现有打磨策略,针对该重载线曲线段发生的U75V热处理钢轨滚动接触疲劳损伤,开展不同半径、运量曲线钢轨的现场试验、室内试验、数值仿真,揭示现场不同圆曲线段钢轨疲劳随服役时间的演化规律。研究结果表明:钢轨疲劳随服役时间的演化大致分为裂纹萌生与快速扩展和裂纹-磨耗共生2个阶段。在进入裂纹-磨耗共生阶段后,R600 m、R800 m重载圆曲线段随着服役时间累计会因钢轨显著失形导致轮轨匹配恶化,虽对轨距角裂纹产生了一定抑制作用,但轨面部分区域产生了严重剥离掉块,可能会威胁到安全行车,究其根本原因是钢轨失形到一定程度后轮轨接触点向轨肩集中所致;所跟踪的其余曲线因钢轨磨耗较小未明显失形,故不会出现严重剥离掉块。在实验室内通过对下道钢轨失效分析后发现,涡流探伤仪测量到的最大深度与真实最大深度间存在误差;测量深度一般大于真实深度,真实深度在变大的同时测量深度与真实深度间的误差会越来越大。基于钢轨滚动接触疲劳时变规律,为进一步延长R600 m、R800 m重载钢轨的使用寿命,建议加大打磨频率(特别是在新轨上道6个月内),优先将廓形打磨为标准廓形,兼顾磨去疲劳裂纹;对于更大半径曲线考虑到经济性等,保持当前的打磨策略即可。

缩尺车轮-环轨滚动接触与磨耗特性仿真分析

为了研究缩尺车轮-环轨滚动接触与磨耗特性,基于轮轨滚动行为(WRRB)模拟试验台参数,利用ANSYS/LS-DYNA建立瞬态滚动接触有限元模型,集成弹性蠕滑率求解程序和Tγ磨耗模型,通过试验验证模型的正确性.重点分析轮轨力、蠕滑率、接触应力和钢轨磨耗深度,并考虑车轮驱动扭矩和速度的影响规律.结果表明:缩尺车轮-环轨结构的高频弹性振动造成轮轨垂向力波动;在比例载荷作用下,纵向动力学行为和钢轨磨耗深度变化趋势与服役轮轨一致;由于环轨的极小曲线半径,自由滚动工况下的横向蠕滑力/率、自旋蠕滑率、钢轨磨耗深度偏大,切向接触应力峰值出现在接触斑后沿两侧;车轮驱动扭矩和速度的影响规律可拟合为一组经验公式.研究可以为此类试验台的设计与应用工作提供理论依据.

CL65车轮钢滚动疲劳磨损研究

利用双盘滚动磨损实验机对CL65车轮钢与U75V钢轨钢进行滚动磨损实验,研究CL65车轮钢表面出现的疲劳磨损现象。实验表明:CL65车轮钢的磨损情况由黏着磨损不断向疲劳磨损过渡。机加工表面细晶层主要出现在磨损的初始阶段,疲劳磨损裂纹的形成和扩展出现在细晶层内或细晶层与基体的界面,导致了细晶层的早期疲劳剥离。随着磨损周次的不断增加,原始片状珠光体和先共析铁素体,基体区域表层的塑性变形不断加剧,当塑性应变过大时,疲劳裂纹开始萌生,并逐渐开始向先共析铁素体区域、渗碳体与共析铁素体界面扩展。

嵌入式轨道三维滚动接触模型冲击特性研究

嵌入式轨道在城市轨道交通领域得到广泛运用,在高速铁路方面,国内外也有少量的相关报道和理论研究。嵌入式轨道对减缓轮轨冲击有显著效果,其中焊接接头是引起轮轨冲击的重要原因之一,对于时速400公里以及更高运行速度的列车,焊接接头冲击激励引起的轮轨力变化十分显著,目前对于高速工况下嵌入式轨道的研究尚不充分。基于显式动力学有限元方法,采用三维高速轮轨瞬态滚动接触模型对轮轨冲击过程进行数值模拟,并探究时速400公里速度下的嵌入式轨道的冲击特性。得出以下结论:嵌入式轨道与扣件式轨道在受到不同波长冲击时均能够减小垂向轮轨力变化幅值,焊接接头波长越长,垂向轮轨冲击力越能快速趋于平缓;车轮在受到焊接接头长波冲击时,嵌入式轨道能明显降低纵向轮轨力。研究结果可为嵌入式轨道在高速铁路的运用提供参考。

重载铁路钢轨抗疲劳型面的设计与应用

为了改善轮轨接触关系,基于三次插值样条曲线方法,通过降低钢轨轨肩-轨距边廓形,设计了重载铁路小半径曲线钢轨抗疲劳型面。结合重载运输条件下的车辆-轨道动力学模型,根据接触点位置、轮轨接触斑面积、横向力、脱轨系数、轮重减载率、磨耗指数等参数,确定了重载铁路钢轨打磨铣磨基准型面并进行现场应用。基准型面为:钢轨轨肩-轨距边廓形降低的起点在由轨顶中心向近轨距边方向移动5 mm的位置,廓形改变范围覆盖起点至轨距边侧磨点,改变范围内最大廓形弧面下降量出现在轨顶中心向轨距边26 mm处,且最大弧面下降量为0.6、0.7 mm。现场试验结果表明:该基准型面使得轮轨垂向、横向力均有所降低,轮轨接触关系改善,接触点位置稳定;预测的裂纹萌生寿命延长了16.3%~47.2%,满足改善车辆运行状态、延长重载铁路钢轨使用寿命等需求。

基于交流电磁场的高铁钢轨表面裂纹无损检测研究及展望

针对高铁钢轨表面产生滚动接触疲劳(RCF)裂纹导致对钢轨带来危害的问题,本文分析了钢轨表面滚动接触疲劳裂纹的形成机理及扩展规律,系统归纳了高铁裂纹的无损检测与表征方法。聚焦于交流电磁场检测(ACFM)技术,重点研究了ACFM技术发展及研究现状、理论研究成果以及存在的问题,综述了ACFM技术的特点及应用,通过与其他无损检测方法进行分析比较,阐述了ACFM测量法对钢轨表面裂纹的精准量化表征的优势。结果表明:ACFM探针传感器沿45°方向扫描,通过结合ACFM信号补偿量算法可将非均匀裂纹口袋深度误差降到5.5%,垂直深度误差降到7.1%,裂纹簇误差减小到7.1%;经过人工神经网络训练对钢轨RCF裂纹尺寸进行精准表征,最终计算的误差在10%以内。进一步讨论了融合人工智能技术的钢轨表面裂纹无损检测技术的发展趋势,为后续ACFM技术对钢轨表面RCF裂纹的检测和表征研究提出相关建议和展望。

小曲线钢轨滚动接触疲劳及车轴疲劳寿命分析

为探究小半径曲线上钢轨滚动接触疲劳伤损规律及车轴寿命,文章基于车辆系统动力学模型,对小半径曲线钢轨磨耗计算分析得到钢轨疲劳数据模型。针对小半径曲线的钢轨整个损伤过程进行滚动接触疲劳分析,同时也基于有限元分析简单预测CRH3型动车组在疲劳伤损的钢轨上运行时车轴的疲劳寿命。研究结果显示:(1)在小半径曲线曲中点处外轨主要体现轨距角处的侧磨,内轨主要体现轨顶处的垂磨,且外轨的滚动接触应力和损伤与内轨有显著差异;(2)轮对进行静强度分析得到车轴上轮座压装处应力最大;(3)结合车轴应力和载荷谱对车轴疲劳寿命进行预测,计算发现预测寿命约为11.8 a,车轴在已经产生疲劳磨损的线路上运行时寿命会大大缩减。

内部含裂纹车轮疲劳寿命分析

针对国内普遍采用的LM A磨耗型踏面车轮出现内部裂纹问题,通过有限元软件ABAQUS结合疲劳寿命分析软件nCode DesignLife探究了不同工况对疲劳寿命的影响。结果表明:不同长度的裂纹在裂纹尖端存在明显的应力集中现象,将对车轮损伤和疲劳寿命产生影响,虽有波动,但总体上是先快后慢的趋势;车轮的损伤系数和疲劳寿命在裂纹角0~45°变化较小,但危害较大;轴重是影响车轮疲劳性能的重要因素,避免过载可延长车轮使用寿命;裂纹深度对含裂纹车轮的损伤系数和疲劳寿命影响较大,其中10 mm以内数值变化较大,即疲劳失效更容易发生在接触斑中心位置。

某型高铁踏面廓形轮轨接触特性的对比分析

针对我国某型高铁踏面存在的疲劳裂纹出现频繁、部分轮对镟修量大等问题进行了研究,通过计算其与现行高速钢轨的接触特性,发现存在轮轨接触应力较大、接触点应力集中的现象。为了解决这一问题,文章介绍了一种可供替代的W01GT3型踏面。通过对比2种踏面在不同轮对横移量下的几何接触特性、轮轨接触应力以及直线运行工况下的疲劳裂纹萌生寿命,结果表明,W01GT3型踏面与钢轨接触范围更宽,轮轨接触应力更小,在直线运行工况下的疲劳裂纹萌生寿命更长。因此,在镟修维护时,建议采用与该型踏面相近的模板,有助于缓解某型高铁踏面的滚动接触疲劳相关问题。