Effect of wheelset flexibility on wheel–rail contact behavior and a specific coupling of wheel–rail contact to flexible wheelset

The fexibility of a train＇s wheelset can have a large effect on vehicle–track dynamic responses in the medium to high frequency range.To investigate the effects of wheelset bending and axial deformation of the wheel web,a specifi coupling of wheel–rail contact with a fexible wheelset is presented and integrated into a conventional vehicle–track dynamic system model.Both conventional and the proposed dynamic system models are used to carry out numerical analyses on the effects of wheelset bending and axial deformation of the wheel web on wheel–rail rolling contact behaviors.Excitations with various irregularities and speeds were considered.The irregularities included measured track irregularity and harmonic irregularities with two different wavelengths.The speeds ranged from 200 to400km/h.The results show that the proposed model can characterize the effects of fexible wheelset deformation on the wheel–rail rolling contact behavior very well.

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.

NUMERICAL SIMULATION OF TWO-POINT CONTACT BETWEEN WHEEL AND RAIL

The elastic-plastic contact problem with rolling friction of wheel-rail is solved using the FE parametric quadratic programming method. Thus, the complex elastic-plastic contact problem can be calculated with high accuracy and efficiency, while the Hertz＇s hypothesis and the elastic semi-space assumption are avoided. Based on the ‘one-point＇ contact calculation of wheel-rail, the computational model of ‘two-point＇ contact are established and calculated when the wheel flange is close to the rail. In the case of ‘two-point＇ contact, the changing laws of wheelrail contact are introduced and contact forces in various load cases are carefully analyzed. The main reason of wheel flange wear and rail side wear is found. Lubrication computational model of the wheel flange is constructed. Comparing with the result without lubrication, the contact force between wheel flange and rail decreases, which is beneficial for reducing the wear of wheel-rail.

ELASTIC-PLASTIC FINITE ELEMENT ANALYSIS OF THREE-DIMENSIONAL CONTACT-IMPACT AT RAIL JOINT

Using the finite element code ANSYS/LS-DYNA, a dynamic finite element modelwith an elastic-linear-kinematic-hardening plastic material is established to analyzeelastic-plastic stresses in the railhead in the impact process of wheel and rail occurring at thegap of rail joint. The model is based on the discrete elastic support condition of the rails, whichis suitable for the actual situation of wheel/track rolling contact. In the analysis the influencesof axle load, yield stress and tangent modulus of rail material on the stresses and strains areinvestigated in detail. The distribution of stresses and strains in the jointed railhead are given.It is found that the axle load, yield stress and tangent modulus of rail material greatly affect thestresses and strains in the railhead during impacting. The study provides a reliable method anduseful datum for the further research on fatigue and wear of railhead and improving the rail jointmode.

An integrated approach for the optimization of wheel-rail contact force measurement systems

A comprehension of railway dynamic behavior implies the measure of wheel-rail contact forces which are affected by disturbances and errors that are often difficult to be quantified. In this study, a benchmark test case is proposed, and a bogie with a layout used on some European locomotives such as SIEMENS El90 is studied. In this layout, an additional shaft on which brake disks are installed is used to transmit the braking torque to the wheelset through a single-stage gearbox. Using a mixed approach based on finite element techniques and statistical considerations, it is possible to evaluate an optimal layout for strain gauge positioning and to optimize the measurement system to diminish the effects of noise and disturbance. We also conducted preliminary evaluations on the precision and frequency response of the proposed system.

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.

Simulation on derailment base on a new wheel-rail contact method

The simulation package for special research on derailment of high speed vehicle is established.The process of derailment is different from other behaviors of vehicle dynamics because of large lateral displacement of wheelsets.To get correct results,a new fast algorithm to computing contact force is adopted and the exact geometry analysis is necessary to judge derailment happened.Variation of contact condition and coefficient of friction with speeds are also considered into vehicle-track coupled model.The structure of the package is presented in detail.The results are particular emphasis on investigation influence of maximum track defect,critical vehicle speed and various contact condition on derailment.The simulation can also be used to define the most risk factor leading to derailment.

Influence of Rare Earths on Contact Fatigue of Rail Steels

Rail/wheel contact fatigue of NbRE rail, Nb rail and U74 rail was investigated using contact fatigue tester. Microstructure and morphology as well as microhardness in the fatigue profiles were analyzed by scanning electron microscope and Vickers hardness respectively. The experimental results show that rare earths are able to delay the initiation and the propagation of fatigue cracks and postpone the surface shelling or spalling, even more, to reduce the crack propagation angle and the crack propagation depth in steady stab as well as the plastic deformation area, and to improve work-hardening of the rail steel.

Modeling of Energy Processes in Wheel-Rail Contacts Operating under Influence of Periodic Discontinuous Forces

In this paper we present new numerical simulation approaches for determining the energy processes under periodic conditions caused by time-discontinuous forces in the wheel-rail contacts. The main advantage of the presented method is the total elimination of frequency analysis, which in effect introduces important simplifications in the identification of the effects in the contact. The second important feature is the fact that the method is based on the analysis of appropriate loops on the energy phase plane leading to an easy estimation of the rail strength through the evaluation of the loop’s area. That model based simulation in the applied dynamics relies on advanced methods for model setup, robust and efficient numerical solution techniques and powerful simulation tools for practical applications. Fundamental properties of contact displacements of the rail surface have been considered on the basis of the newly established method. The contact zone between railway wheels and the rail surfaces made of bulk materials is perceived as strong enough to resist the normal (vertical) forces introduced by heavy loads and the dynamic response induced by track and wheel irregularities. The analysis is carried out for a wheel running on an elastic rail rested on sleepers arranged on completely rigid foundation. The equations of displacement motion are established through the application of the Lagrange equations approach. The established model of the wheel-rail contact dynamics has been applied to that same roll plane but with taking into account a nonlinear characteristic of the sleeper with respect to the ground. Attention then is focused completely on the modeling of the energy absorbed by the rail. The applied method employs the energy state variables as time functions leading to determine the susceptibility of a given contact on the strength induced by the rail roll.

Analysis of Dual-Core Type City and Its Hinterland Contact Pattern under the Background of High-Speed Rail Networking—Urban Agglomeration in Zhejiang Province as an Example

Under the background of high-speed rail networking, this paper uses the passenger trains, the type and direction of the railway via Hang Yong and its extension road line, to construct adsorption and dependency index among cities, depict the contact pattern between the Hang Yong dual-core and its hinterland, measure the “net effect” that two center cities (Hangzhou, Ningbo) have on their hinterland, and estimate population agglomeration potential and future possible population flows of Zhejiang Province and the main sample cities. The result shows that, compared with Ningbo, Hangzhou has stronger radiation force to the vast majority of sample cities, and the sample cities affected more by Ningbo mainly concentrates in Ningbo-Taizhou-Wenzhou along;in addition, the sample cities such as Hangzhou, Ningbo and so on show better population agglomeration, then the population “scramble” phenomenon between cities has begun to appear.

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.

扣件刚度非线性对波磨区轮轨瞬态滚动接触行为的影响

WJ-8型扣件橡胶垫板刚度在长期服役过程中表现出非线性特征,静刚度随荷载增加而降低,为提高三维瞬态滚动接触有限元模型计算精确性,本文以LMA踏面车轮及CHN60型钢轨为基础,基于显式积分算法,将以往研究中线弹性扣件转化为非线性扣件,建立考虑扣件刚度非线性特征的三维轮轨瞬态滚动接触有限元模型,研究刚度非线性对车轮与钢轨波磨间高频动态响应及瞬态接触行为的影响,并重点分析了波磨工况下时频域内轮轨接触力、轴箱加速度的变化信息.结果表明:扣件非线性对轮轨接触力变化影响明显,主要表现为车轮行驶至扣件前端时强振动导致橡胶垫板表现为柔软特性使轮轨接触力减小,车轮行驶至扣件上方时在轴重作用下振动减弱表现为刚硬特性使轮轨接触力增大,轮轨力变化差异最大达到13.1%.

考虑材料温变特性的三维轮轨接触热分析

为研究材料温变特性对轮轨接触行为和摩擦温升的影响,提出了一种考虑材料温变特性的三维轮轨热力耦合模型,能够考虑纵、横向蠕滑率和自旋的影响,更为真实地模拟轮轨系统的服役状态.首先,研究了热力耦合建模方式对轮轨界面摩擦温升及接触应力的影响;随后,将该模型应用于地铁小半径曲线处车辆-轨道相互作用模拟.结果表明:当轮轨界面温度达到450℃时,轮轨接触应力显著降低,降幅可达20%;考虑热力耦合建模后,轮轨界面的预测温升明显低于不考虑热力耦合建模时的结果,在蠕滑率为0.16时,两者的差异可达51%;地铁车辆在小半径曲线线路上运行时轮轨摩擦温升因过大的蠕滑率与自旋会急剧增大到750℃,应考虑轮轨热力耦合建模以避免过高估计轮轨摩擦温升以及轮轨接触应力.

考虑摇头角的非赫兹滚动接触算法对比研究

为研究轮对摇头角对轮轨接触行为的影响以及评估简化非赫兹轮轨接触算法的精度,选取EKP、MKP与MSHM共3种考虑摇头角的轮轨非赫兹简化算法分析轮轨法向与切向接触行为。以S1002CN车轮踏面和CHN60钢轨为研究对象,以精确理论CONTACT算法的结果为参考,对比各简化接触算法得到的接触斑形状、接触应力、切应力等微观接触结果的准确性。利用UM软件建立车辆-轨道耦合动力学模型进行仿真分析得到轮轨运动参数,然后输入到接触算法计算轮轨接触解,基于统计学累积误差方法评估不同接触算法在实际车辆运行工况下的计算精度与稳定性。计算结果表明:摇头角使轮轨接触斑与接触应力呈三维非对称分布;对于法向接触,在大部分工况下,MKP算法相比EKP、MSHM算法精度较高,但接触斑内轮轨曲率变化较大时,如横移量为6 mm,MKP算法所得到的最大接触应力误差为47.2%,此时更适合采用MSHM算法,其误差为27%;对于切向问题,采用EKP+FaStrip、MKP+FaStrip算法比MSHM+FASTSIM算法得到的结果更准确;对于动力学结果,MKP+FaStrip算法比EKP+FaStrip、MSHM+FASTSIM算法得到的接触结果更加精确和稳定。

炮膛间距对枢轨初始接触状态的影响分析

电磁轨道炮炮膛间距直接影响到发射过程中枢轨滑动电接触状态,尤其是起始段炮膛间距变化对电枢烧蚀具有较大影响,将炮膛等效成呈一定角度张开的两条直线,利用角平分线相关特性开展炮膛间距测量,根据炮膛间距实测数据,结合工程实际分析起始段炮膛变化形态并建立对应形态下的枢轨初始接触模型,分析了炮膛装配精度对枢轨初始接触性能的影响,分析结果表明起始段炮膛间距是造成电枢静态受力不均、枢轨接触面积及接触力非对称分布的主要原因,通过不同炮膛变化形态的静态接触试验,进一步验证了理论分析结果。通过分析炮膛间距对枢轨初始接触的影响作用,为枢轨匹配性设计提供理论依据。

轨底坡耦合轮径差对地铁车辆动力学性能及轮轨接触特性的影响

为了研究轨底坡耦合轮径差对于地铁车辆动力学性能及轮轨接触特性的影响规律,设置了3种轨底坡工况(1/20、1/30和1/40)和5种轮径差工况,通过建立地铁车辆动力学仿真模型和轮轨接触三维弹性有限元模型,分析轨底坡耦合轮径差对地铁车辆直线平稳性和曲线通过性能的影响。结果表明:直线路段车辆平稳性指标受到轮径差变化的影响大于轨底坡变化的影响,轮轨等效应力和接触应力会随着轮径差的增加而增大;曲线路段的各个动力学指标会随着轮径差的增加而增大;综合考虑动力学指标和轮轨接触特性,直线路段下尽量减少使用1/20轨底坡;曲线路段下,可以选择1/30轨底坡,减少轮径差对车辆的影响。

埋头弹步枪导轨曲线槽的设计分析

为研究不同导轨曲线槽形状对埋头弹步枪导轨-弹膛机构运动特性以及弹膛突耳与导轨曲线槽接触力的影响,以某中口径埋头弹步枪为对象,基于一次函数、二次函数、三次函数和五次多项式函数设计了4种导轨曲线槽,建立了相应的导轨-弹膛机构的三维模型,采用Adams建立了导轨-弹膛机构的虚拟样机模型,利用Abaqus建立了导轨-弹膛机构有限元模型,并进行了仿真研究与分析。仿真结果表明:选用不同导轨曲线槽时,活动弹膛升降速度、导轨曲线槽与突耳间的接触力、以及导轨曲线槽的接触应力明显不同,最大接触应力主要分布在导轨曲线槽起始位置和终止位置;选择五次多项式函数作为导轨轮廓曲线时,导轨曲线槽起始位置和终止位置的接触应力较其他导轨曲线槽的接触应力小。

基于动态阈值分割法的接触轨图像关键特征点提取方法研究

在地铁系统中,接触轨的状态对于牵引供电系统的安全性至关重要,一旦接触轨几何参数超出正常范围,不仅会导致集电靴无法正常取流,进而影响运营车辆的顺畅运行,而且在极端情况下,还可能引发严重的安全事故。传统的接触轨几何参数测量方法在采集图像时通常面临背景复杂、干扰图像多等问题,以致检测数据量少、检测密度低,从而难以精确提取接触轨的关键特征信息。针对这一问题,文章提出一种新的方法,即结合动态阈值分割法、直线拟合以及投影计算的方式,有效解决接触轨特征点提取的难点,实现几何参数的精确测量。该方法不仅能够准确捕捉到接触轨的细微变化,还能够确保测量结果的可靠性和准确性。为进一步提高测量的便捷性和实用性,研究过程中同步研制出一套接触轨几何参数的便携式测量装置,并在地铁线路上进行现场应用示范,为实际运营中的接触轨状态监测提供有力的技术支持。

基于销盘载流摩擦平台的电磁发射轨道表面防护

为避免电磁发射轨道表面转捩烧蚀损伤,对轨道表面防护工作进行了研究。首先,采用实验室自研的销盘试验机开展了极端工况载流摩擦实验;然后,利用COMSOL软件分析了实验过程瞬态温度场的特征;最后,考虑在盘试样表面采用耐高温的钼涂层,仿真对比了处理前后的温度场分布情况。研究表明:因失接触产生的高能电弧是影响滑动电接触瞬态温度场的主要因素之一,会对无处理的盘试样表面造成可达20μm深的烧蚀坑;进行钼涂层处理后的表面温度更高,处理前后的表面温差最高可达数百摄氏度,主要因为钼的热导率较低;在轨道表面处理选材时,要统筹考虑耐高温性能和导热性能。该研究成果对于延长轨道使用寿命具有重要意义。

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。