高速列车车轮踏面磨耗预测方法的研究

高速铁路的发展满足日益增长的运输需求,同时带来了轮轨型面磨损问题.通过磨耗预测模型对车轮踏面磨耗量进行预测,及时对磨损的车轮踏面进行镟修,对于列车安全运行具有重要意义.通过建立轮对-钢轨三维有限元模型进行接触计算,提出一种基于有限元算法的摩擦功计算方法,即接触节点的摩擦功等于接触摩擦力与节点相对位移的乘积,实现车轮踏面磨耗预测.通过接触计算,发现接触斑中心处的接触摩擦力较大,相对位移量较小,摩擦功较小;将接触斑摩擦功叠加得到车轮踏面摩擦功,数值曲线呈中部大边缘小,且随牵引力的增大而增大;通过动力学计算,发现列车在直线钢轨运行初期的车轮横移量近似呈正态分布;对列车在直线钢轨上运行不同里程的车轮踏面进行磨耗预测,发现预测型面与实测型面具有相同的磨耗趋势,即车轮名义滚动圆处磨耗最严重,且磨耗宽度随列车运行里程增加而逐渐增大;应用有限元法计算磨耗功并预测车轮踏面磨耗,具有一定的研究意义和实用价值.     

基于恒等映射多层极限学习机的高速列车踏面磨耗预测模型

针对高速列车车轮踏面磨耗单一模型无法对各种复杂工况下列车车轮踏面磨耗进行定量计算的问题, 提出一种基于恒等映射多层极限学习机的高速列车车轮踏面磨耗测量方法. 首先将恒等映射引入到多层极限学习机中, 提出一种基于恒等映射的多层极限学习机模型(identity multilayer extreme learning machine, I-ML-ELM), 采用机器学习公共数据集对该模型进行性能验证, 数值结果表明I-ML-ELM模型具有较好的准确性与泛化性; 然后基于车辆-轨道耦合动力学理论建立高速列车的车辆-轨道耦合动力学模型, 模拟列车运行的不同工况, 观测和分析高速列车的车轮踏面磨耗情况, 并通过I-ML-ELM预测模型对高速列车车轮踏面磨耗量进行学习及预测; 最后应用高速列车车轮踏面磨耗的实际测量值对I-ML-ELM预测模型进行进一步的验证, 结果表明: I-ML-ELM预测模型的各项性能参数指标在整体上优于以下五种网络: ELM, FLN, ML-ELM, ML-KELM和DLSFLN, 通过高速列车线路实测数据的进一步验证表明, 本文提出的基于I-ML-ELM的高速列车车轮踏面磨耗预测模型能较好地反映不同参数对高速列车车轮踏面磨耗值的影响规律.      

列车车轮滚动接触疲劳裂纹评价研究

列车车轮踏面表层金属滚动接触疲劳是影响列车运行安全性和舒适性的核心科学问题.借助金相显微镜、扫描电镜、透射电镜和显微硬度计,通过开展列车车轮材料的标准滚动接触疲劳试验,将标准接触疲劳样品的损伤行为与实际服役车轮的损伤行为对比分析,研究了列车车轮的滚动接触疲劳裂纹评价方法.结果表明:车轮表层金属接触疲劳开裂是表层金属累积塑性变形损伤的结果;标准滚动接触疲劳样品剥离坑的深度恰好等于硬化层的深度,实际服役车轮剥离坑的深度小于硬化层的深度;将车轮表面的滚动接触疲劳裂纹命名为"三角形指向性裂纹";初步建立了车轮表面滚动接触疲劳损伤程度的定量评价方法.     

基于有限元的高速列车车轮多边形磨耗成因分析

研究了中国高速列车车轮多边形磨耗的形成原因,考虑轮对的旋转惯量,建立了高速列车轮对-轨道-盘式制动系统有限元模型. 基于轮轨系统摩擦自激振动的理论,采用有限元复特征值分析法研究了高速列车制动时轮对-轨道-盘式制动系统的稳定性. 研究了饱和的轮轨蠕滑力和盘式制动系统摩擦力耦合作用对车轮多边形磨耗的影响,并调查了轮轨-轨道-盘式制动系统的参数敏感性. 数值模拟结果表明:在饱和的轮轨蠕滑力和盘式制动器摩擦力耦合作用下,轮轨系统的摩擦自激振动导致高速列车车轮多边形磨耗的产生,其导致的21~22阶和23~24阶车轮多边形磨耗占主导地位,这与中国高速列车高阶车轮多边形磨耗最为符合. 饱和的轮轨蠕滑力主要影响较低阶车轮多边形磨耗,盘式制动器摩擦力主要影响较高阶车轮多边形磨耗. 制动压力为13 kN时,车轮多边形磨耗形成的几率最小,发展速度最慢. 过高或者过低的垂向悬挂力均不利于抑制车轮多边形磨耗. 垂向悬挂力为75 kN时,车轮多边形磨耗形成的可能性最小,发展速度最慢.      

合金含量对高速车轮材料滚动接触磨损性能的影响

将2种含碳量相同合金含量不同的高速车轮材料分别与钢轨材料匹配,利用滚动接触摩擦磨损试验机测试了各摩擦副的摩擦系数和磨损率,比较研究了组织、硬度和加工硬化等因素对车轮材料滚动接触磨损性能的影响.结果表明：在传统的高速车轮材料中适当地增加Si、Mn的含量,降低Cr的含量可以提高车轮材料的抗磨损性能;硬度高的车轮材料未必耐磨,组织差异对车轮材料的抗磨损性能影响显著;表面裂纹易萌生于高度变形的先共析铁素体组织;加工硬化引起的硬度增加对材料的抗磨损性能影响不大.     

基于观点法的谱随机有限元分析——随机响应面法

提出了一种基于配点法的谱随机有限元分析方法-随机响应面法(SRSM),这种方法与已有的谱随机有限元方法(SSFEM)类似,都用Karhunen-Loeve级数扩展式表示输入随机场而计算结果的输出用多项式混沌展式表达。然而这两种方法采用了不同的方法确定多项式混沌展式中的系数:SRSM利用概率最小二乘配点法而SSFEM利用概率Galerkin法。与解析的SSFEM相比,SRSM的优势在于有限元计算和随机分析计算不耦合,即可把通用有限元程序作为黑箱进行求解。与黑箱版的SSFEM相比,SRSM需要的样本计算更少。SRSM中的各配点来自高概率的区域并使均方差最小化,从而可用少量的样本计算获得较高的计算精度。算例突出了本文提出的方法的特点并显示此方法是有效的且有较高的计算精度。     

Discrete element method simulations of Mars Exploration Rover wheel performance

Mars Exploration Rovers (MERs) experienced mobility problems during traverses. Three-dimensional discrete element method (DEM) simulations of MER wheel mobility tests for wheel slips of i = 0, 0.1, 0.3, 0.5, 0.7, 0.9, and 0.99 were done to examine high wheel slip mobility to improve the ARTEMIS MER traverse planning tool. Simulations of wheel drawbar pull and sinkage MIT data for i ⩽ 0.5 were used to determine DEM particle packing density (0.62) and contact friction (0.8) to represent the simulant used in mobility tests. The DEM simulations are in good agreement with MIT data for i = 0.5 and 0.7, with reasonable but less agreement at lower wheel slip. Three mobility stages include low slip (i < 0.3) controlled by soil strength, intermediate slip (i ∼ 0.3–0.6) controlled by residual soil strength, and high slip (i > 0.6) controlled by residual soil strength and wheel sinkage depth. Equilibrium sinkage occurred for i < 0.9, but continuously increased for i = 0.99. Improved DEM simulation accuracy of low-slip mobility can be achieved using polyhedral particles, rather than tri-sphere particles, to represent soil. The DEM simulations of MER wheel mobility can improve ARTEMIS accuracy.     

高速冲击问题的离散元法数值模拟

以能量等效为原则,构建了新的求解弹塑性轴对称问题的离散元模型。通过引入断裂准则,使模型不仅可以应用于连续介质问题,还可以应用于从连续介质向非连续介质的动态转化过程。最后,通过模拟钢板受冲击载荷产生层裂的过程,说明模型在高速冲击问题中的适用性及其有效性。     

Finite element simulations on the mechanical properties of MHS materials

Finite element simulations are carried out to examine the mechanical behavior of the metallic hollow sphere (MHS) material during their large plastic deformation and to estimate the energy absorbing capacity of these materials under uniaxial compression. A simplified model is proposed from experimental observations to describe the connection between the neighboring spheres, which greatly improves the computation efficiency. The effects of the governing physical and geometrical parameters are evaluated; whilst a special attention is paid to the plateau stress, which is directly related to the energy absorbing capacity. Finally, the empirical functions of the relative material density are proposed for the elastic modulus, yield strength and plateau stress for FCC packing arrangement of hollow spheres, showing a good agreement with the experimental results obtained in our previous study. The project supported by the Hong Kong Research Grant Council (RGC) (HKUST 6079/00E) and the National Natural Science Foundation of China (10532020).     

Dynamic analysis of axle box bearings on the high-speed train caused by wheel-rail excitation

To explore the impact of wheel-rail excitation on the dynamic performance of axle box bearings, a dynamic model of the high-speed train including axle box bearings is developed. Subsequently, the dynamic response characteristics of the axle box bearing are examined. The investigation focuses on the acceleration characteristics of bearing vibration under excitation of track irregularities and wheel flats. In addition, experiments on both normal and faulty bearings are conducted separately, and th...     

On aerodynamic noises radiated by the pantograph system of high-speed trains

Pantograph system of high-speed trains become significant source of aerodynamic noise when travelling speed exceeds 300 km/h. In this paper, a hybrid method of non-linear acoustic solver （NLAS） and Ffowcs Williams-Hawkings （FW-H） acoustic analogy is used to predict the aerodynamic noise of pantograph system in this speed range. When the simulation method is validated by a benchmark problem of flows around a cylinder of finite span, we calculate the near flow field and far acoustic field surrounding the pantograph system. And then, the frequency spectra and acoustic attenuation with distance are analyzed, showing that the pantograph system noise is a typical broadband one with most acoustic power restricted in the medium-high frequency range from 200 Hz to 5 kHz. The aerodynamic noise of pantograph systems radiates outwards in the form of spherical waves in the far field. Analysis of the overall sound pressure level （OASPL） at different speeds exhibits that the acoustic power grows approximately as the 4th power of train speed. The comparison of noise reduction effects for four types of pantograph covers demonstrates that only case 1 can lessen the total noise by about 3 dB as baffles on both sides can shield sound wave in the spanwise direction. The covers produce additional aerodynamic noise themselves in the other three cases and lead to the rise of OASPLs.     

Finite element modeling of plastic anisotropy induced by texture and strain-path change

Consideration of plastic anisotropy is essential in accurate simulations of metal forming processes. In this study, finite element (FE) simulations have been performed to predict the plastic anisotropy of sheet metals using a texture- and microstructure-based constitutive model. The effect of crystallographic texture is incorporated through the use of an anisotropic plastic potential in strain-rate space, which gives the shape of the yield locus. The effect of dislocation is captured by use of a hardening model with four internal variables, which characterize the position and the size of the yield locus. Two applications are presented to evaluate the accuracy and the efficiency of the model: a cup drawing test and a two-stage pseudo-orthogonal sequential test (biaxial stretching in hydraulic bulging followed by uniaxial tension), using an interstitial-free steel sheet. The experimental results of earing behavior in the cup drawing test, maximum pressure and strain distribution in bulging, and transient hardening in the sequential test are compared against the FE predictions. It is shown that the current model is capable of predicting the plastic anisotropy induced by both the texture and the strain-path change. The relative significance of texture and strain-path change in the predictions is discussed.     

Micromechanics of particle-reinforced elasto-viscoplastic composites: Finite element simulations versus affine homogenization

The micromechanics of elasto-viscoplastic composites made up of a random and homogeneous dispersion of spherical inclusions in a continuous matrix was studied with two methods. The first one is an affine homogenization approach, which transforms the local constitutive laws into fictitious linear thermo-elastic relations in the Laplace–Carson domain so that corresponding homogenization schemes can apply, and the temporal response is computed after a numerical inversion of Laplace transform. The second method is the direct numerical simulation by finite elements of a three-dimensional representative volume element of the composite microstructure. The numerical simulations carried out over different realizations of the composite microstructure showed very little scatter and thus provided – for the first time – “exact” results in the elasto-viscoplastic regime that can be used as benchmarks to check the accuracy of other models. Overall, the predictions of the affine homogenization model were excellent, regardless of the volume fraction of spheres, of the loading paths (shear, uniaxial tension and biaxial tension as well as monotonic and cyclic deformation), particularly at low strain rates. It was found, however, that the accuracy decreased systematically as the strain rate increased. The detailed information of the stress and strain microfields given by the finite element simulations was used to analyze the source of this difference, so that better homogenization methods can be developed.     

Finite element simulations of incompressible flow past a heated/cooled sphere

This paper reports numerical simulation of the flow past a heated/cooled sphere. A Galerkin finite element method is used to solve the 3D incompressible Boussinesq equations in primitive variable form. Numerical simulations of flow around the sphere for a range of Grashof numbers and moderate Reynolds numbers, were conducted. The drag coefficient for adiabatic flow shows good agreement with standard correlations over the range of the Reynolds numbers investigated. It is shown that the drag can vary considerably with heating of the sphere and that computational fluid dynamics methods can be used to derive constitutive laws for macroscopic momentum and heat exchange in multiphase flow. © 1998 John Wiley & Sons, Ltd.     

Finite element micromechanics model of impact compression of closed-cell polymer foams

Finite element analysis, of regular Kelvin foam models with all the material in uniform-thickness faces, was used to predict the compressive impact response of low-density closed-cell polyethylene and polystyrene foams. Cell air compression was analysed, treating cells as surface-based fluid cavities. For a typical 1 mm cell size and 50 s^?1 impact strain rate, the elastic buckling of cell faces, and pop-in shape inversion of some buckled square faces, caused a non-linear stress strain response before yield. Pairs of plastic hinges formed across hexagonal faces, then yield occurred when trios of faces concertinaed. The predicted compressive yield stresses were close to experimental data, for a range of foam densities. Air compression was the hardening mechanism for engineering strains <0.6, with face-to-face contact also contributing for strains >0.7. Predictions of lateral expansion and residual strains after impact were reasonable. There were no significant changes in the predicted behavior at a compressive strain rate of 500 s^?1.