【作者】 肖广文；

【导师】 金学松；

【作者基本信息】 西南交通大学 ， 载运工具运用工程， 2009， 硕士

【摘要】 当今世界铁路,以无缝线路代替鱼尾板钢轨接头来连接轨道上相邻两根钢轨是一种首选的方法。无缝线路的应用在很大程度上降低轮轨冲击载荷和提高钢轨的使用寿命,但随着铁路运行速度的提高和轴重的加大,钢轨焊接接头伤损问题变得越来越严重,从而导致较高的铁路运营成本,直接影响铁路运输安全。因此,开展钢轨焊接接头伤损研究具有很强的理论意义和工程应用背景。本文以车辆-轨道耦合动力学理论、轮轨滚动接触理论、弹塑性力学和有限元方法为基础,应用数值仿真方法对不同形式的焊接接头伤损问题进行研究。(1)为了能全面反映高速铁路钢轨焊接接头处轮轨作用力学行为,建立了较为完善的车辆-轨道耦合动力学模型。模型中,采用Timoshenko梁模型模拟钢轨;考虑了轨枕的离散支撑作用对车辆/轨道耦合动态行为的影响。另外,采用赫兹非线性弹性接触理论确定轮轨法向力时用到的轮轨接触常数由轮轨表面瞬态接触条件决定;采用沈氏理论计算轮轨蠕滑力,其中基于轮轨接触面法向速度差为零原则推导轮轨蠕滑率。焊接接头不平顺以余弦函数形式加入到轮轨接触几何算法。利用该模型分析了复合不平顺和单波不平顺引起的轮轨冲击载荷;长短波长焊接接头所引起的轮轨法向冲击载荷、钢轨/轨枕支承反力、车轮和轨道各部件的加速度;行车速度、轴重、波长、波深及焊接接头所在位置对轮轨法向冲击载荷的影响。结果表明,焊接接头短波波长不平顺容易激起轮轨系统的高频振动和导致车轮和轨道系统的冲击破坏。因此在焊接接头的现场施工和检修过程中,应尽可能的避免出现短波不平顺的现象。此外以焊接接头不平顺的波深与波长之比来控制焊接接头不平顺更为合理,并制定了焊接接头不平顺的控制数表。(2)建立了基于车辆-轨道耦合动力学和三维弹塑性有限元模型的钢轨焊接接头应力分析模型。模型中考虑了钢轨母材和焊接接头材料及热影响区域具有不同的材料属性。首先由车辆—轨道耦合动力学仿真程序计算轮轨接触力、接触斑大小及位置。然后通过FASTSIM计算接触斑内切向力分布,最后输入到三维弹塑性有限元模型。应用该模型分析了不同工况下直线、曲线焊接接头区域附近的接触应力、弹塑性变形以及残余应力分布。结果表明,钢轨焊接接头不平顺将引起较大轮轨冲击载荷,导致较大的钢轨局部塑性变形。在铁路现场应尽量保证钢轨焊接接头材料和钢轨母材的材料一致,消除钢轨接头和母材间材料变形的非连续性而引起接头处高的轮轨冲击载荷。更多还原

【Abstract】 Continuously-welded rail (CWR) has replaced bolted rail joints as the preferred method of joining rails in track all over the world. The CWR efficiently reduces the level of impact forces between wheel and rail at rail joints and extends the service life of the wheel and rail with respect to bolted rail. However, with the increment of train speed and axle load, the phenomenon of rail weld defect (RWD) shows a tendency to be severe. The RWD leads to the higher operating costs and represents one of the main risks for safety of railway operation. Therefore, from the practical and cognitive points of view, studies on RWD are very important. In this thesis, based on the vehicle-track coupling dynamics theory, wheel-rail rolling contact theory, elastic-plastic mechanics and finite element method, the defects of rail weld with different type are investigated through the numerical simulation.(1) In order to better characterize the wheel-rail interaction at high speed rail weld, a vehicle-track coupling dynamics model is developed. In the model, a Timoshenko beam is used to model the rails which are discretely supported by sleepers. The sleepers are assumed to move backward at a constant speed to simulate the vehicle running along the track at the same speed, and therefore such a track model can consider the effect of the discrete support by sleepers on the coupling dynamic behaviour of the vehicle and track in the simulation. The normal contact forces between wheels and rails are decided by nonlinear Hertzian elastic contact theory. The coefficient of the normal contact stiffness is decided by the instant contact condition of the wheel and rail surfaces. The tangential wheel-rail contact forces are calculated by Shen-Hedrick-Elkins’ model. The wheel-rail creepages are deduced on the basis of the normal velocity difference of the contact planes of the wheel and rail is always equal to zero. The rail weld irregularities are modeled as the local track vertical deviation described with some ideal cosine functions. The dynamics model is used to analyze wheel-rail impact loading caused by compound irregularity, single irregularity, the long and short wavelength rail weld irregularity. The loading between the rail and sleeper and the accelerations of the wheel and the track components are also investigated. The effects of the train speed, the axle load, the wavelength and depth of the irregularities, and the weld center position in a sleeper span on the wheel-rail impact loading are analyzed. The results show that the short-wavelength irregularities of rail weld easily excite the higher resonant frequencies of the track and can lead to a severe damage of the wheel and track components. Hence, the phenomenon of short-wavelength irregularities of rail weld should be avoided in the on-site construction and maintenance. Moreover, the ratio of the depth to wavelength is more reasonable to control the rail weld irregularities. An irregularities-controling table is developed, which provides a reference when the rail weld is ground.(2) Based on the above vehicle-track coupling dynamics model and three dimensional elastic-plastic finite element model, a stress analysis model of rail weld is set up. In the model, the rail base metal, weld metal and heat affected zone have different properties of materials. The vehicle-track coupling dynamics model is applied to calculate the dynamic wheel-rail contact force and the size and location of the contact area. The contact force, the size and location of contact area obtained by the vehicle-track dynamics simulation are utilized as the inputs to FASTSIM program to obtain the normal and tangential force distributions. Then the sizes and locations of contact areas and normal and tangential force distribution are used as the inputs to finite element model. The Mises equivalent stress, residual equivalent plastic strain and residual displacement near the rail weld at the tangent and curve tracks are investigated. Results show that the rail weld irregularities lead to high wheel-rail impact loading and high localized plastic deformation. The mechanical properties of the weld metal should be equal to those of the rail base metal in the on-site construction to decrease the impact loading caused by the non-continuity deformation and rail weld irregularities.更多还原