Mechanical deformation properties of Continuous Welded Rail on kilometer-span suspension bridge for high-speed railway

The complex bridge-track interaction between kilometer-span bridges and continuous Welded Rail(CWR)brings great challenges to CWR designing.Taking a suspension bridge with laying CWR as a case,the mechanical properties of CWR on the bridge are analyzed to reveal the sensitive areas of the track,and the design method of CWR and track structures on the beam ends are proposed.The results show that the unidirectional Rail Expansion Joints(REJ)need to be installed on the beam end of the kilometer-span bridge to reduce rail longitudinal force.Due to the bridge characteristics,there is no CWR fixed area on the kilometer-span bridge,and rail longitudinal force on the main span caused by bending loads needs to be concerned.The deformation of track on the beam end is complex,which is the weak area on the kilometer bridge,the large relative displacement between the stock rail of REJ and the main beam can cause poor stability of ballast bed on beam end,small resistance fasteners need to be laid on the sides of stock rail on the main beam to increase the stability of ballast and fasteners on the beam end.To improve the driving safety and comfort of beam end,the Sleeper-Supporting Apparatus(SSA)should be specially designed to ensure the uniform transition of track on beam ends.Temperature and wind loads have a significant impact on track regularity on the kilometer span bridge,the dynamic response of trains and bridges under those loads needs to be attended to.

Study on deformation and microstructure characterizations of mild steel joints by continuous drive friction welding

Macro-deformation characteristics of continuous drive friction welded mild steel joints were examined by using one deformable workpiece （objective） and the other undeformable one （rigid）. The microstructure evolution and hardness change across the joint were studied. The results show that the axial shortening and radial increment of joints increase with increasing the frictiou time at l 200 rpm. The cementite particles of pearlites in the weld center are uniformly distributed on the ferrite matrix, while the cementites of the pearlite in the thermal-mechanically affected zone are broken and discontinuously dispersed in the pearlite. The hardness decreases rapidly from the weld center to the parent metal under the coupled effects of heat and deformation during the rapid heating and cooling processes.

Evolution of microstructural and mechanical properties of AISI 316 during continuous drive friction welding process

The aim of present study is introducing a method by subdividing friction welding phases into three steps according to the temperature change during continuous drive friction welding operation. Thermal curve allowable subdividing of the friction welding phase's time into three distinct periods, while the microstructure evolution during friction welding goes through three different situations. The effects of three distinct periods were achieved by macro-microscopy, microhardness HV_(0.1), tensile tests and scanning electronic microscopy(SEM).The results clearly show that the microstructure during the friction phase goes through three completely different situations which mechanically influenced on microstructure, tensile strength and ductility of the welded joint.

Effect of temperature field on flashes formation of continuous drive friction welding

On basis of the finite element software DEFORM, the 2D coupled thermo-mechanical model of continuous drive friction welding of ring parts is established. The temperature and the flashes during the welding process are investigated. The results of numerical simulation show that the temperature of friction surface is higher than that of other region and the peak temperature increases with the increase of welding time. During the process of friction stage, no flash appears because of the low temperature and the small axial friction pressure. At the forging stage, the flashes appear, whose dimensions and bending degree increase with the increase of welding temperature. Moreover, with the increase of rotational velocity and axial forging pressure, the dimensions and the bending degree of flashes of continuous drive friction welding increase.

Controlling the output power of soft switching arc welding inverter by two-stage continuous PWM method

The full bridge zero voltage zero current switching （ FB-ZVZCS ） , which could adjust the output power by keeping the duty ratio of lagging leg constant and changing the duty ratio of leading leg, was a common circuit of soft switching arc welding inverter power source. However, when the duty ratio of leading leg was reduced to zero, the output power stayed the constant value instead of becoming zero. The working status and waveforms of some major parameters were studied in this paper while the duty ratio of leading leg was zero. It was concluded that the minimum output power of soft switching inverter was related to the charging voltage of paraUel capacitors, and the output power also could be reduced by reducing the duty ratio of lagging leg. A novel two-stage continuous PWM control method that could switch working-mode between full bridge and half bridge was put forward in this paper. This kind of control method could further reduce the output power of soft switching inverter in order to meet the requirement of low heat input of sheet metal welding.

Longitudinal force in continuously welded rail on long-span tied arch continuous bridge carrying multiple tracks

Considering arch rib, lateral brace, suspender, girder, pier and track position, the model for the interaction between long-span tied arch continuous bridge and multiple tracks was established by using steel-concrete composite section beam element to simulate concrete-filled steel tube(CFST) arch rib, using the beam element with rigid arm to simulate the prestressed concrete girder and using nonlinear bar element to simulate longitudinal constraint between track and bridge. Taking a(77+3×156.8+77) m tied arch continuous bridge with four tracks on the Harbin-Qiqihar Passenger Dedicated Line as an example, the arrangement of continuously welded rail(CWR) was explored. The longitudinal force in CWR on the tied arch continuous bridge, the pier top horizontal force and torque due to the unbalance load case, were analyzed under the action of temperature, vertical live load, train braking and wind load.Studies show that, it can significantly reduce track displacement to set the track expansion devices at main span arch springing on both sides; the track stress due to arch temperature variation can reach 40.8 MPa; the track stress, pier top horizontal force and torque are related to the number of loaded tracks and train running direction, and the bending force applied to unloaded track is close to the loaded track, while the braking force applied to unloaded track is 1/4 to 1/2 of the loaded track; the longitudinal force of track due to the wind load is up to 12.4 MPa, which should be considered.

Longitudinal forces of continuously welded track on high-speed railway cable-stayed bridge considering impact of adjacent bridges

A proven beam-track contact model was used to analyze the track-structure interaction of CWR (continuously welded track) on bridge. Considering the impact of adjacent bridges, the tower-cable-track-beam-pier-pile finite element model of the cable-stayed bridge was established. Taking a bridge group including 40-32m simply-supported beam and (32+80+112)m single-tower cable-stayed bridge and 17-32m simply-supported beam on the Kunming-Shanghai high-speed railway as an example, the characteristics of CWR longitudinal force on the cable-stayed bridge were studied. It is shown that adjacent bridges must be considered in the calculation of the track expansion force and bending force on cable-stayed bridge. When the span amount of adjacent bridges is too numerous, it can be simplified as six spans; the fixed bearing of adjacent simply-supported beams should be placed on the side near the cable-stayed bridge; the track expansion device should be set at the bridge tower to reduce the track force near the bridge abutment.

Mechanics model of additional longitudinal force transmission between bridges and continuously welded rails with small resistance fasteners

A new mechanics model, which reveals additional longitudinal force transmission between the continuously welded rails and the bridges, is established on the fact that the influence of the mutual relative displacement (among) the rail, the sleeper and the beam is taken into account. An example is presented and numerical results are compared. The results show that the additional longitudinal forces calculated with the new model are less than those of the previous, especially in the case of the flexible pier bridges. The new model is also suitable for the analysis of the additional longitudinal force transmission between rails and bridges of ballastless track with small resistance fasteners without taking the sleeper displacement into account, and compared with the ballast bridges, the ballastless bridges have a much stronger additional longitudinal force transmission between the continuously welded rails and the bridges.

Stability issues of the continuous welded rail track on the concrete sleepers on the curves with radius R ≤ 300 m

This paper describes the economic and technological benefits of installing continuous welded rail （CWR） track on sharp （radius≤300 m） railway curves. A new form of prestressed concrete sleepers developed by the V. Lazaryan Dniprope- trovsk National University of Railway Transport is shown to improve the lateral shift resistance of CWR track in sharp curves and the use of anchor sleepers on tangents is shown to make it possible to lower the fastening temperature of the CWR track in order to increase the rail lifespan.

Influence of welding speed on microstructure formation in friction-stir-welded 304 austenitic stainless steels

The influence of welding speed on the joint microstructures of an austenitic stainless steel(ASS)produced by friction stir welding(FSW)was investigated.The FSW process was conducted using a rotational speed of 400 r/min and welding speeds of 50 and 150 mm/min.The study was carried out using electron backscattered diffraction(EBSD)technique in different regions of the resultant stir zones(SZs).The results show that the texture of the advancing side(AS)was mainly composed of C{001}〈110〉and cube{001}〈100〉texture components along with partial B/B{112}〈110〉component.Moving from the AS toward the center and the retreating side(RS),the cube texture component disappeared and the A;/A*{111}(112)component developed and predominated the other components.Higher welding speed greatly affected and decreased the intensity of the textures in the resultant SZs.Moreover,higher welding speed(lower heat input)resulted in lower frequency of cube texture in the AS.

公铁两用大跨度斜拉桥-无砟轨道体系变形适应性研究

高速铁路大跨度斜拉桥结构变形受其复杂服役环境影响显著,而无砟轨道对工后变形的调整能力有限,因此大跨度斜拉桥的复杂变形条件将直接影响其上无砟轨道结构的适应性。以沪渝蓉高铁长江北支公铁两用大跨度斜拉桥应用无砟轨道为工程背景,建立无砟轨道-大跨度斜拉桥一体化精细空间有限元模型,分析铁路、公路以及温度等多种荷载联合作用下大跨度斜拉桥-无砟轨道体系平顺性、无缝线路稳定性和无砟轨道层间变形协调性,从而对大跨度公铁两用钢桁梁斜拉桥-无砟轨道体系变形适应性开展深入研究。结果表明:在运营荷载及温度荷载最不利组合作用下,大跨度斜拉桥主梁线形平顺,变形平缓,桥梁整体刚度较好,桥上无砟轨道几何形位可以满足静态验收标准;大跨度斜拉桥上无缝线路的强度和稳定性满足要求,扣件工作性能良好,钢轨伸缩调节器的设置可有效释放梁端钢轨的纵向应力;无砟轨道层间设置橡胶隔离层且不跨主梁桁架节间的布置方式可提高大跨度斜拉桥上无砟轨道的变形协调性能,使得桥上无砟轨道层间始终处于受压状态,达到“隔而不离”的桥上轨道层间理想服役状态;大跨度公铁两用钢桁梁斜拉桥-无砟轨道体系变形适应性良好。本文研究成果可为公铁两用大跨度钢桁梁斜拉桥上无砟轨道的应用提供技术参考。

考虑加载历史的小半径曲线桥梁梁轨相互作用分析

目前,大部分考虑加载历史的梁轨相互作用研究都集中在直线桥梁上,针对曲线桥梁,尤其是小半径曲线桥梁,梁轨相互作用的研究相对较少。采用理想弹塑性滞回阻力模型模拟扣件纵向阻力,运用有限元软件,建立以城东特大桥为研究对象的钢轨-桥梁-墩台三维有限元空间力学计算模型,研究曲线半径对于梁轨相互作用的影响,探究了多荷载耦合作用、往复荷载作用以及循环荷载作用下考虑加载历史效应的曲线桥梁梁轨相互作用情况,并提出“拉力百分比”以及“压力百分比”的概念以便分析曲线半径对传统线性叠加法误差的影响。结果表明,曲线桥梁中梁轨纵、横向相互作用分别与曲线半径成正、反比,相关数据改变幅度与曲线半径成反比且当曲线半径超过800 m时基本收敛,此时可采用“以直代曲”的简化算法;曲线半径对于横向梁轨相互作用影响程度大于纵向,相较于挠曲、制动工况,伸缩工况受曲线半径影响更加显著;多荷载耦合作用下,采用传统线性叠加法相较于考虑加载历史更为保守且温度荷载起主要贡献;考虑加载历史时钢轨在往复荷载作用下会产生不可忽视的残余内力,且在循环荷载作用下将会产生收敛于第1次往复荷载下的残余内力,这是扣件纵向阻力的弹塑性滞回特性决定的;线性叠加法误差与曲线半径具有相关性,相较于挠曲、制动工况,伸缩工况下对其更为敏感。研究结果可为考虑加载历史下曲线桥梁结构设计提供参考。

地铁连续刚构桥上无砟轨道无缝线路纵向力分析

【目的】为研究地铁连续刚构桥上无砟轨道无缝线路纵向受力与变形规律,对地铁连续刚构桥上无砟轨道无缝线路设计改进、运营养护维修提供理论指导。【方法】根据梁-板-轨相互作用原理,建立地铁连续刚构桥上整体道床式无砟轨道无缝线路空间耦合模型,计算伸缩、挠曲、制动、断轨工况下轨道结构和桥梁纵向力及位移,并对轨道结构静力特性进行对比分析,为地铁连续刚构桥上无缝线路轨道结构设计提供参考。【结果】结果表明:双线列车荷载中点与中部梁端处重合时为列车垂向荷载最不利工况,此时钢轨纵向力与钢轨、桥梁纵向位移均为最大,均出现在中部梁端附近,数值分别为70.3 kN与0.6,0.8 mm;双线制动荷载列车尾部位于两侧梁端时为列车制动荷载最不利工况,此时钢轨纵向力与钢轨、桥梁纵向位移均为最大,数值分别为107.8 kN与1.6,1.7 mm。【结论】伸缩力作用下各个端部桥缝处为薄弱部位,在平时养护中应特别注意梁端部桥缝处轨道结构,防止因伸缩力过大而产生断轨;钢轨发生断轨时,在断缝处纵向力、纵向位移均发生突变,严重影响线路行车安全。

市域(郊)铁路桥上无缝道岔至梁缝距离研究

市域(郊)铁路桥梁占比高,结合车站配线设计,道岔不可避免需要设置在高架站前后的道岔连续梁上。考虑市域(郊)铁路采用的道岔型号、桥梁结构及设计荷载与高速铁路明显不同,桥上无缝道岔至梁缝距离研究相对缺乏。由于市域(郊)铁路设计速度比地铁高,轮轨作用力大,轮轨之间的振动和冲击对周围环境影响大,因此,桥上道岔采用跨区间无缝线路技术。基于“道岔-桥梁”相互作用原理,建立“岔-板-梁-墩”一体化12号无砟轨道、无缝道岔有限元模型,对常用的单开道岔、4.3 m线间距渡线道岔至梁缝距离开展计算分析并研究其影响规律,以道岔钢轨强度、尖轨尖端位移值、心轨尖端位移值、转辙机处基本轨与桥梁相对位移值及断缝值为限值条件,提出市域(郊)铁路桥上无缝道岔至梁缝合理距离限值。研究结果表明:桥上无缝道岔始终端距梁缝距离越大,尖轨尖端位移、心轨尖端位移和转辙机处基本轨与桥梁相对位移明显减小,道岔钢轨伸缩力和制动力计算结果差异不大;温暖地区道岔始端、终端至梁缝距离不小于10 m,寒冷地区道岔始端、终端至梁缝距离不小于18 m,相关研究成果纳入《市域(郊)铁路设计规范》。

热循环下铝/钢连续驱动摩擦焊接接头应力应变分析

利用ABAQUS有限元软件,建立了一个新的连续驱动摩擦焊接头热-力耦合过程的数值模型,分析了试验过程接头温度场、应力应变分布规律,通过与实际试验结果的对比,验证模型的准确性。得出如下结论:热循环过程中,冷却及低温保温过程是热应力最大的阶段;接头颈缩形貌和产生位置与试验结果吻合较好,颈缩位置与实际试验相对误差为6%,颈缩现象的本质是铝在自由膨胀收缩时应力超过强度极限产生的塑性变形。在拉伸断口观察到解理断裂圆环,其位置、宽度与模拟结果的应变集中区域吻合度高。该模型较准确的模拟了连续驱动摩擦焊接头的热-力耦合过程,为实际生产和工艺优化提供了有力支持。

全自动激光打标焊牌机器人在方坯连铸机上的应用

智能制造以及无人化现场是钢铁行业产业智能升级的发展方向,某特钢公司新建大方坯连铸机为实现产品质量异常可溯源,实现了高温热铸坯入缓冷坑、热送进加热炉等全流程物流信息跟踪。应用全自动二维码激光打标焊牌机器人,采用激光雕刻金属标识牌,将生产系统铸坯信息打印成二维码标签,工业机器人在高温连铸坯端部焊接标牌,代替人工写号,可靠性高,动作周期短,是国内该类型激光打标焊牌机器人在方坯连铸机上的首次应用,实现了热铸坯标识的物流信息化、自动化、无人化操作。

AZ31B镁合金连续铸轧板材搅拌摩擦搭焊接头组织研究

对AZ31B镁合金连续铸轧板材进行搅拌头逆时针与顺时针相结合的二道搅拌摩擦搭接焊。经对其搭接接头横截面的焊缝宏观及不同部位微观组织对比来分析二道搅拌摩擦焊对焊接接头塑性组织及成形的影响。结果表明:焊核区等轴晶粒组织特别细小、均匀;过渡区晶粒组织大小起伏较大,略大于焊核,较小于母材组织;前进侧界面迁移呈现大弧度卷起,比较突兀与焊核隔断,形成钩状缺陷,而后退侧界面迁移线缓缓渗入中部焊核区,渐渐消失于焊核组织内;前进侧迁移线的成形特点相比于孔洞隧道缺陷,成为整个焊接接头最薄弱部分;前进侧界面迁移线边的组织融合影响了对焊接头的成形;二道搅拌摩擦搭接两次搅拌头旋转方向同为逆时针时,能得到表面良好、组织熔合紧密、强度较高接头;当搭接接头上板为后退侧时,与上板为前进侧相比,搭接接头能够承受更大剪切力。

小半径曲线梁桥的无缝线路有限元模型简化研究

为更简便地建立小半径曲线梁桥的无缝线路有限元模型,降低计算成本并保证计算精度的可靠性,本文比较分析不同简化程度的模型。首先,依据已有桥上无缝线路模型的形式,通过不同程度简化桥梁上部结构,由简到繁确立了单刚臂模型、多刚臂模型、准梁格模型、平面壳模型、空间壳模型、实体模型共6种模型,并通过扣件横向和纵向阻力试验取得了模型的关键参数;其次,以曲线半径为200 m的(40+50+50+40) m连续梁桥为实例,计算了桥上无缝线路在伸缩、挠曲、制动和断轨等其他组合工况下的结果;最后,以实体模型的计算结果为基准,将前5种模型的计算结果与实体模型的进行对比,通过欧几里得距离量化分析了各模型的计算精度。研究结果表明:综合考虑模型复杂程度和计算精度,多刚臂模型和准梁格模型相比于空间壳模型性价比更高,梁格法在桥梁工程中被大量用于异形桥梁计算,且支座分布以及边界条件更符合实际情况。因此,推荐在进行小半径曲线梁桥的无缝线路计算时采用准梁格模型。

基于轨道不平顺的无缝线路稳定性统计分析

为弥补现有无缝线路稳定性设计未区分轨道平顺性等级的不足,基于轨道不平顺数值模拟方法和无缝线路稳定性有限元分析方法,提出考虑轨道不平顺和道床横向阻力随机性的无缝线路稳定性概率统计分析方法。针对不同半径的铁路线路,研究轨道不平顺、道床横向阻力大小及位置分布随机性对钢轨允许温升分布规律的影响,并与现有无缝线路稳定性分析方法计算结果进行对比。研究结果表明:当道床横向阻力服从正态分布时,单独考虑道床横向阻力大小随机性时,钢轨允许温升近似服从极值I型分布;单独考虑轨道不平顺随机性、同时考虑道床横向阻力大小及位置分布随机性或综合考虑上述3个因素随机性时,钢轨允许温升均服从正态分布;以不少于95%保证率定义的钢轨允许温升标准值及均值随着线路平顺性的改善而增加;不同曲线半径条件下,现有“等波长-有限元”确定的钢轨允许温升与美国五级谱对应钢轨允许温升标准值相近,与其他轨道谱对应结果则存在较大差异;在综合考虑轨道不平顺、道床横向阻力大小及位置分布三因素随机性条件下,建立表征钢轨允许温升分布的均值、标准差及标准值与曲线半径间的显式映射关系,使无缝线路稳定性分析中考虑线路平顺性等级成为了可能。研究结果为进一步优化铁路无缝线路极限状态法设计提供了参考。

基于机器视觉的大跨长联桥上无缝线路小阻力扣件纵向服役状态监测研究

以福厦高铁渔溪特大桥为例,提出一种基于机器视觉的小阻力扣件纵向服役状态监测方案,以获取大跨长联桥上无缝线路钢轨纵向变形与复合垫板窜出的时变特征;同时,结合梁轨温度与梁端位移测试结果,分析梁体温度、钢轨温度、梁端累积位移、梁轨相对位移与垫板窜出量之间的相关性。研究结果表明:根据图像识别结果,钢轨在监测阶段将随温度变化产生不同方向的伸缩,且钢轨位移略大于垫板窜出量。钢轨昼夜温差要显著大于桥面气温以及连续梁梁内气温、顶板温度、腹板温度,且梁体温度变化幅度显著比钢轨的小,其原因在于钢轨的比热容较小,在同等热量输入输出时产生的温度变化幅度较大。梁端纵向位移随温度变化幅度较小,最大日位移为0.15 mm;在监测周期内,梁端累积位移呈波动减小趋势,即梁体发生了缓慢收缩,其原因在于夏季到秋季时气温逐渐降低,且最大平均位移变化速率为0.09 mm/d。梁体温度、钢轨温度、梁端累积位移、梁轨累积相对位移和垫板窜出量之间的相关系数均大于0.8,说明其相关性较大,且均呈较好的正相关关系。通过基于机器视觉的小阻力扣件状态监测方法,可见小阻力扣件在福厦高铁渔溪特大桥区段具有较好的纵向服役状态,且监测周期内线路状态均正常,验证了此类方案在小阻力扣件现场监测中的适用性。