【作者】 王喆；

【导师】 王衡禹；

【作者基本信息】 西南交通大学 ， 载运工具运用工程， 2019， 硕士

【摘要】 自2008年我国第1条高速铁路“京津城际铁路”通车运营以来,中国高铁在拉动经济增长、推动社会进步等方面发挥着越来越重要的作用。与此同时,国内高铁线路里程的持续增长、载客量的不断增大以及列车运营速度的稳步提升,也对车辆运行安全提出了越来越高的要求。轮轨滚动接触疲劳(RCF),作为一种高速铁路运营安全隐患,已然成为当下急需解决的工程实际问题。深入研究轮轨RCF裂纹的萌生和扩展机理并提出合理化的防治措施,对指导工程实践有着重要意义。轮轨系统中,车轮与钢轨处于动态滚动接触状态,施于轮和轨表面的接触力是作用力和反作用力,大小相等,方向相反,故RCF既可能发生在钢轨上,也会在车轮上。本论文专注于高铁线路中发现的“钢轨表面RCF”及“车轮局部滚动接触疲劳(LRCF)”两种典型损伤形式,研究方法包括基于断裂力学的仿真计算分析和基于实验室比例试验的双盘对滚疲劳试验,第一章详细综述了近年来该领域取得的研究进展及存在的不足。目前,国内外针对轮轨疲劳裂纹扩展的分析模型中,大多依然采用移动载荷法来模拟滚动接触边界,即将移动的Hertz接触载荷边界施加于轮轨接触表面上。该方法的缺点是,不能将滚动过程中由裂纹处材料不连续所导致的瞬态接触载荷变化考虑在内。第二章以钢轨疲劳裂纹在滚动接触载荷下的瞬态扩展模拟为研究目标,采用ANSYS/LS-DYNA建立了钢轨斜裂纹扩展分析模型,其中裂纹载荷边界通过三维轮轨滚动接触算法施加,突破了以往研究中由稳态、简化接触载荷边界带来的局限性。第三、四章利用上述模型,模拟了车轮以300 km/h速度滚滑通过多斜裂纹时的裂纹瞬态扩展行为。在此,假设各裂纹呈等间距、平行分布,且每条裂纹的裂纹面完全相同。鉴于现场观测,斜裂纹在接触表面的扩展角度取典型值30°,长深比固定为常见值5,接触面内的裂纹长度和裂纹间距分别在10~20 mm和5~20 mm间变化。得出的主要结论如下:(1)裂纹的存在会降低轮轨间法、切向接触刚度,且其降低量随裂纹数量的增多而增大;(2)本文未考虑现场中液体的不可压缩性对裂纹张开型扩展的影响,加载过程中,裂纹始终处于闭合状态,这意味着本文模拟的RCF裂纹主要以滑开型(II型)模式进行扩展;(3)多条相同斜裂纹共存时,其裂尖节点的节点力低于相同网格的单裂纹工况,同时,裂纹尖端附近节点的相对位移因接触区域整体刚度的降低而增加,最终使得裂尖应力场强度因子(SIF)随裂纹数量的增多而增大;(4)对于特征尺寸(长度)15 mm的多裂纹,当裂纹间距大于5 mm时,3裂纹模型足以将裂纹间的相互影响精确考虑在内;(5)当裂纹间距大于裂纹特征尺寸时,多裂纹模型的SIF计算结果与单裂纹模型的差异在7%以内,即可采用简化的单裂纹模型进行计算。近年来引起业界广泛关注的车轮LRCF,其萌生主因在各方面努力下得以初步确定为车轮硌伤,但限于定性描述,尚未在试验内得以重现。第五章采用GPM-30滚动接触疲劳试验台,开展了双盘对滚疲劳试验,采取不同的加工方式对车轮试验盘接触表面施加了3类初始人造损伤,在由真实轮轨切割出来的试样上再现了由接触面硌伤萌生LRCF的过程。试验结果表明,采用维氏硬度计及电火花加工的初始损伤因塑性变形太小和缺失而不会萌生LRCF,而由丝锥在机床上塑性加工的方式所施加的深硌伤可能会导致LRCF萌生,其临界深度约为0.2 mm。综合来看,LRCF的萌生由硌伤产生过程中的材料塑性变形和硌伤几何的尖锐程度共同决定。最后,对论文的主要工作进行总结并作出展望。更多还原

【Abstract】 High-speed railway has played a significant important role for improving the economic growth and promoting social progress in China,after the first high-speed railway,named "Beijing-Tianjin Inter-city Railway",begun to operate in 2008.Meanwhile,the operational safety of vehicles is increasingly valued due to the growth of high-speed railway mileage,passenger capacity and operational speed.However,rolling contact fatigue(RCF)occurred on the wheel-rail,always as a potential danger for the running safety,has become an urgent problem to be solved.So,the deeply research for the initiation and propagation mechanisms of wheel-rail RCF cracks and the rational preventive measures are proposed is the great significance for guiding engineering practices.In the wheel-rail system,the wheel and the rail are in dynamic rolling contact,and the amplitudes and directions of the contact force are equal and opposite,respectively,i.e.,the force and the reaction force,resulting in the wheel-rail RCF can often occur on either the rails or the wheels.This thesis focuses on two typical damage patterns,RCF occurred on the rail surfaces and local rolling contact fatigue(LRCF)occurred on the wheels,were observed in high-speed railway.The research methods include the simulated calculation based on fracture mechanics and twin-disc rolling fatigue test based on the proportional test in laboratory.The research progresses and limits about the related field in recent years are reviewed in the first chapter.At present,the moving load method is still used by most of the crack propagation analysis models at home and abroad,i.e.,the moving Hertz contact patch,as the crack load boundary,is applied between wheel-rail contact surfaces,its defect is that the transient contact load changes caused by material discontinuities are not considered during wheel rolling over cracks.A multi-oblique crack propagation analysis model is established using ANSYS/LS-DYNA in the second chapter,and the crack load boundary is applied by the 3-D wheel-rail rolling contact algorithm broken through the limitations of steady-state contact load boundaries used in previous models.For chapters 3 and 4,the above model is used to simulate the transient process when the wheel with 300 km/h operated on multiple oblique identical cracks,based on the assumptions that the cracks are equally spaced and parallel,and the crack faces are completely the same.According to the field observations,the crack propagation angle is 30° typically,its length-to-depth ratio is fixed at 5,and the crack length and crack spacing are 10~20 mm and 5~20 mm,respectively.The main conclusions are as follows:(1)The cracks can reduce the tangential and normal contact stiffness between the wheel and rail,and the decreased amount will increase with the growth of the number of cracks;(2)The effect of the incompressibility of the liquid on the crack opening propagation is not considered,i.e.,the cracks have not been opened during the loading process,leading to the simulated RCF cracks are mainly propagated in the sliding type(type II)mode;(3)The nodal force of the crack tips for the multiple cracks is lower than a single crack under the same element size,and the relative displacement between the crack faces near the tips is larger due to the reduction of the contact stiffness,which resulting in stress intensity factors(SIF)of the crack tips increase with the increasing number of cracks;(4)For multi-cracks with a feature size(length)of 15 mm,the 3-crack model is sufficient to accurately simulate the interaction between the cracks when the crack spacing is greater than 5 mm;(5)When the crack spacing is larger than the crack feature size,the SIF results between the multi-crack model and the single crack model is less than 7%,i.e.,the multi-crack model can be simplified to the single crack model.In recent years,the wheel LRCF has attracted widespread attention,and their initiation causes have been identified as wheel indentation,but it is limited to qualitative description and has not been reproduced in the test.In the fifth chapter,the GPM-30 rolling contact fatigue test bench was used to carry out the twin-disc rolling fatigue test.Different types of initial artificial damage were applied to the contact surface of the wheel disc by different processing methods.The process of initiating LRCF from indentation is reproduced on the specimen cut from the real wheel.The test results show that the initial damage using Vickers hardness tester and EDM will not initiate LRCF due to their small and missing plastic deformation,the deep indentation applied by the plastic working of the tap on the machine tool may result in the initiation of LRCF with a critical depth of approximately 0.2 mm.In summary,the initiation of LRCF is determined by the plastic deformation and the sharp geometry in indentation which introduced during the indenting.Finally,the main work of the thesis is summarized and a prospect is made.更多还原