ANALYSIS OF THERMAL-ELASTIC STRESS OF WHEEL-RAIL IN ROLLING-SLIDING CONTACT

A coupling thermo-mechanical model of wheel/rail in rolling-sliding contact is put forward using finite element method. The normal contact pressure is idealized as the Hertzian distribution, and the tangential force presented by Carter is used. In order to obtain thermal-elastic stress, the ther-mal-elastic plane stress problem is transformed to an elastic plane stress problem with equivalent fictitious thermal body force and fictitious boundary distributed force. The temperature rise and ther-mal-elastic stress of wheel and rail in rolling-sliding are analyzed. The non-steady state heat transfer between the contact surfaces of wheel and rail, heat-convection and radiation between the wheel/rail and the ambient are taken into consideration. The influences of the wheel rolling speed and wear rate on friction temperature and thermal-elastic stress are investigated. The results show the following： ① For rolling-sliding case, the thermal stress in the thin layer near the contact patch due to the friction temperature rise is severe. The higher rolling speed leads to the lower friction temperature rise and thermal stress in the wheel; ② For sliding case, the friction temperature and thermal stress of the wheel rise quickly in the initial sliding stage, and then get into a steady state gradually. The expansion of the contact patch, due to material wear, can affect the friction temperature rise and the thermal stress during wear process. The higher wear rate generates lower stress. The results can help under-stand the influence of friction temperature and thermal-elastic stress on wheel and rail damage.

Contact Mechanism of Rail Grinding with Open-Structured Abrasive Belt Based on Pressure Grinding Plate

The current research of abrasive belt grinding rail mainly focuses on the contact mechanism and structural design.Compared with the closed structure abrasive belt grinding,open-structured abrasive belt grinding has excellent performance in dynamic stability,consistency of grinding quality,extension of grinding mileage and improvement of working efficiency.However,in the contact structure design,the open-structured abrasive belt grinding rail using a profiling pressure grinding plate and the closed structure abrasive belt using the contact wheel are different,and the contact mechanisms of the two are different.In this paper,based on the conformal contact and Hertz theory,the contact mechanism of the pressure grinding plate,abrasive belt and rail is analyzed.Through finite element simulation and static pressure experiment,the contact behavior of pressure grinding plate,abrasive belt and rail under single concentrated force,uniform force and multiple concentrated force was studied,and the distribution characteristics of contact stress on rail surface were observed.The results show that under the same external load,there are three contact areas under the three loading modes.The outer contour of the middle contact area is rectangular,and the inner contour is elliptical.In the contact area at both ends,the stress is extremely small under a single concentrated force,the internal stress is drop-shaped under a uniform force,and the internal stress under multiple concentration forces is elliptical.Compared with the three,the maximum stress is the smallest and the stress distribution is more uniform under multiple concentrated forces.Therefore,the multiple concentrated forces is the best grinding pressure loading mode.The research provides support for the application of rail grinding with open-structured abrasive belt based on pressure grinding plate,such as contact mechanism and grinding pressure mode selection.

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.

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.

Running safety assessment method of trains under seismic conditions based on the derailment risk domain

The accurate assessment of running safety during earthquakes is of significant importance for ensuring the safety of railway lines.Currently,assessment methods based on a single index suffer from issues such as misjudgment of operational safety and difficulty in evaluating operational margin,making them unsuitable for assessing train safety during earthquakes.Therefore,in order to propose an effective evaluation method for the running safety of trains during earthquakes,this study employs three indexes,namely lateral displacement of the wheel–rail contact point,wheel unloading rate,and wheel lift,to describe the lateral and vertical contact states between the wheel and rail.The corresponding evolution characteristics of the wheel–rail contact states are determined,and the derailment forms under different frequency components of seismic motion are identified through dynamic numerical simulations of the train–track coupled system under sine excitation.The variations in the wheel–rail contact states during the transition from a safe state to the critical state of derailment are analyzed,thereby constructing the evolutionary path of train derailment and seismic derailment risk domain.Lastly,the wheel–rail contact and derailment states under seismic conditions are analyzed,thus verifying the effectiveness of the evaluation method for assessing running safety under earthquakes proposed in this study.The results indicate that the assessment method based on the derailment risk domain accurately and comprehensively reflects the wheel–rail contact states under seismic conditions.It successfully determines the forms of train derailment,the risk levels of derailment,and the evolutionary paths of derailment risk.

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.

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.

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.

The Influence of the Supporting Wheel Deflection of Large-scale Rotary Kiln on Maximum Contact Stress

The relation between the maximum contact stress ratio and deflection angle is derived from Hertz contact theory when the deflection of rotary kiln supporting wheel happens. According to the analysis of practical example, the maximum contact stress ratio within the deflection range of rotary kiln supporting wheel is listed. The contact stress will increase largely when rotary kiln supporting wheel deflects with little angle, which probably will result in accidents correlating to safety. This will provide theory conference for the design, the operating condition analysis and adjusting of the rotary kiln.

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.

Simulation of wheel and rail profile wear:a review of numerical models

The development of numerical models able to compute the wheel and rail profile wear is essential to improve the scheduling of maintenance operations required to restore the original profile shapes.This work surveys the main numerical models in the literature for the evaluation of the uniform wear of wheel and rail profiles.The standard structure of these tools includes a multibody simulation of the wheel-track coupled dynamics and a wear module implementing an experimental wear law.Therefore,the models are classified according to the strategy adopted for the worn profile update,ranging from models performing a single computation to models based on an online communication between the dynamic and wear modules.Nevertheless,the most common strategy nowadays relies on an iteration of dynamic simulations in which the profiles are left unchanged,with co-simulation techniques often adopted to increase the computational performances.Work is still needed to improve the accuracy of the current models.New experimental campaigns should be carried out to obtain refined wear coefficients and models,while strategies for the evaluation of both longitudinal and transversal wear,also considering the effects of tread braking,should be implemented to obtain accurate damage models.

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.

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.

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。

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。

更高速下轮轨瞬态“滚-滑-跳”接触行为及中/短波不平顺临界限值研究

简述轮轨滚动接触行为预测方法现状的基础上,选择最适于400 km/h及以上更高速和中/短波不平顺激励下轮轨“滚-滑-跳”接触行为分析的瞬态滚动接触显式有限元建模方法,建立更高速轮轨三维瞬态滚动接触时域分析模型,数值模拟了轮对在典型曲线轨道上的瞬态曲线通过行为。根据现营高速轮轨的中/短波不平顺调研,以波长30~210 mm钢轨波磨为典型不平顺,考虑波磨激励下左右两侧轮轨动力作用相互影响,分析波磨几何等因素对速度500 km/h及以下轮轨瞬态“滚-滑-跳”接触行为的影响。考虑低、中频动力减载等因素的前提下,仅从轮轨接触脱离角度,提出轮轨中/短波不平顺的临界管理限值建议,讨论其重要性、合理性和应用局限,并与《高速铁路钢轨打磨管理办法》规定的波磨整治限度进行对比。

基于交叉迭代法的车辆-轨道非线性空间耦合振动模型及算法改进

针对车辆-轨道非线性空间耦合系统动力学分析计算量大、计算耗时长及计算精度难以保证的问题,对车辆-轨道非线性空间耦合振动模型和交叉迭代法进行改进。运用有限元法分别建立车辆和轨道空间子系统动力学模型,在基于“迹线法”构建轮轨接触几何关系的基础上,提出“投影对点作差法”搜索轮轨空间接触点位置,并引入轮轨准弹性接触对其进行修正,精细化轮轨接触关系;结合车辆-轨道非线性空间耦合系统特点,改进基于Newmark数值积分的交叉迭代求解系统动力学方程的算法,并给出完整的数值计算步骤。通过与相关文献进行对比,验证改进模型和算法的有效性。结果表明:改进模型的分析精度更高,搜索轮轨空间接触点位置的速度更快;改进算法的计算过程更完善,步骤更清晰;改进的模型和算法在提高计算精度的同时,仍然具有较快的计算效率,且使数值编程更易实现,方便工程应用。