现代轨道交通刹车材料的发展与应用

分析了轨道交通车辆用盘形制动装置中闸片/制动盘组成的摩擦副的工作条件及其对材料的要求,介绍了铸铁闸片、树脂基闸片、铁基和铜基粉末冶金闸片的性能特点及适用领域,重点分析了粉末冶金闸片各组元的功能及摩擦磨损性能调控机制.基于制动盘热斑形成机理,阐明了闸片形状与排布对制动盘热源分布的影响规律.阐述了铸铁、铸钢、锻钢、金属基复合材料和C/C复合材料制动盘的研究进展,并指出了现代轨道交通刹车材料设计与制造的研究热点及研究方向.     

制动盘对盘形制动摩擦性能的影响

在l：l惯性力矩制动试验台上研究了蠕墨铸铁制动盘和灰铸铁制动盘与所研制的合成材料闸片配副时的摩擦磨损性能。结果表明制动盘材质对摩擦性能有很大的影响：所研制的合成材料闸片与灰铸铁盘配副的摩擦副具有较小的速度、压力敏感性，较高的摩擦系数，较低的制动盘表面温度，但闸片的磨损量较大。     

卫星贮箱安装板复合材料蒙皮热应力工艺设计优化

基于有限元分析方法,对热压罐成型卫星贮箱安装板复合材料蒙皮热应力工艺设计方案进行仿真分析,研究了预浸料铺层区域、均压板结构、固化温度等工艺参数对蒙皮热应力的影响。结果表明,在均压板开孔结构不变,当预浸料铺层方法从整体铺层转变为开孔铺层,最大压缩热应力为-393.7MPa,增加了3.8%;最大拉伸热应力为87.9MPa,降低了62.9%。保持均压板开孔结构-预浸料开孔铺层不变,当固化最高温度从180℃降低到120℃,最大压缩热应力为-250.5MPa,最大拉伸热应力为55.9MPa,最大压缩应力和拉伸应力均降低了36.3%。降低固化温度显著降低热应力,并通过实验验证了分析结果。     

一种车辆制动力实时检测方法研究

为实现汽车在制动过程中制动力准确地实时检测,该文提出一种变温度变摩擦系数的制动力实时监测方法——温差算法。此算法以摩擦系数与温度的关系为依据,基于制动盘内侧温度和摩擦面温度差值变化规律,通过循环迭代计算出制动过程中的实时摩擦系数,完成对制动器处制动力实时检测,使用Ansys Workbench对制动盘进行热力耦合有限元分析,模拟摩擦制动过程中温度变化情况,并基于温度数据对温差算法系数进行拟合。最后使用Matlab Simulink对温差算法进行仿真,结果表明:当输入动态的温度参数时,可以输出实时制动力数据,并且数据满足制动力变化规律。     

低温流量计标定平台冷箱内管道热应力分析

针对冷箱内管道在低温状态下受到的压力、重力以及因降温收缩而产生的应力,根据有限元理论,考虑静压和温度的热固耦合作用,建立以稳态热传导为基础的低温管道热应力模型。对其进行网格无关性验证,并以低温管道的整体结构为研究对象进行数值模拟,得到不同管道在施加温度载荷前后的应力应变情况以及管道在预冷时应力变化规律。结果表明,低温下管道的最大等效应力为135.74 MPa,最大位移量为3.42 mm,管道在预冷过程中最大等效应力为127.3 MPa,满足管道结构的设计要求。     

铝硅合金热疲劳过程的应力应变分析

对铝硅合金进行了热疲劳模拟实验和应力、应变分析。铝硅合金的导热系数高,高温弹性模量低,温度涨落过程产生的宏观热应力低于同一温度下合金的屈服应力和疲劳极限;而铝、硅热膨胀系数的差异将在铝硅相界等局部区域产生远大于宏观热应力的微观热应力,并因此萌生热疲劳裂纹。通过变质工艺改变硅相形态,可改善合金的抗热疲劳性能。     

稀土镁合金热压缩流变应力修正及热变形行为

在Gleeble-1500D热模拟机上采用等温压缩实验研究了Mg-7Gd-5Y-1Nd-0.5Zr合金的高温压缩变形行为,获得合金在温度为350 ～530℃、应变速率为0.005～5 s-1条件下的流变应力曲线.对流变应力曲线进行了摩擦和变形热修正.通过摩擦与温升修正后的应力值,计算出了平均热激活能和应力指数,Q=262.608 kJ/mol,n=3.745,分析得出了变形激活能随温度的变化规律.结合显微组织演变,合金的热锻初始温度应在500～530℃为宜.     

混杂纤维盘式制动闸片材料的装车实验研究

采用混杂纤维作增强材料生产列车客车车辆闸片,依据TB/T3118-2005进行了"现车运用试验".实际测量了闸片的磨耗和表面状况,在线测量了制动盘厚度变化并对制动盘表面进行了观测.实验结果表明,闸片线磨损率低,表面平整无龟裂、塌边和掉渣等,制动盘面光洁,无集中产生热斑和微裂纹等异常状况.摩擦学机理分析指出,混杂纤维闸片...     

薄壁低温容器加注过程降温及热应力特性研究

通过FLUENT软件计算一定加注流量下液氮容器加注过程内部流场与温度场变化情况;采用单向流固耦合方法基于ANSYS软件平台构建热-结构模型进行壁面热应力分析。研究表明:数值计算结果与实验数据吻合良好,模型能够有效预测低温加注过程中容器壁面的降温特性和热应力变化与分布规律;底部加注时液体累积过程相对稳定,随液位增长对应不同高度处壁面温度相继降低至接近液体温度后趋于稳定;目标容器最大热变形出现在排气口与上封头区域,最大变形量达3 mm左右;容器壁面外侧一般经历先拉伸后压缩的热应力变化过程,热应力集中区域与加注液面位置保持一致,最高达到近30 MPa,出现在底部封头区域。     

基于代理模型的通风盘式制动器制动盘结构优化设计

该文提出一种基于代理模型的复杂结构优化设计方法,并用于通风盘式制动器制动盘结构优化设计。提出的优化设计方法集成了CAE分析、实验设计、代理模型构造及非线性优化几部分,实验设计采用拉丁超立方抽样策略,代理模型选用改进的响应面模型,非线性优化算法采用序列二次规划算法。为了解决传统的响应面模型部分预测值与实验值误差较大问题,改进方法认为只有能够确保在每一个抽样点处的预测值与试验值的相对误差均在一定范围内的响应面模型才是一个可行的模型。在保证制动盘质量不变情况下,以寿命最大化为目标,应用设计的集成优化方法对制动盘进行优化设计,优化设计结果较好,其中制动盘疲劳寿命根据Coffin-Manson方法预测,制动过程中制动盘表面最大热应力及最高温度通过热机耦合的有限元模拟紧急制动过程获得。优化结果表明该文提出的方法是一种有效的复杂结构的优化设计方法。     

Analyzing the mechanisms of fatigue crack initiation and propagation in CRH EMU brake discs

A significant number of high-speed electric multiple units’ (EMU) brake discs, manufactured from forged steel, showed thermal cracks during work and NDT. There exist three kinds of cracks on the friction surface; namely, the crackle, radial crack and circumferential crack. Macro-morphologies of the friction surface indicate that the cracks appeared in the interior and edges of the hotspots. Crack growth methods include the single crack propagation and multiple crack connectivity. A finite element analysis (FEA) was performed to determine temperature and stress distribution in the brake disc as well as to estimate stress distribution during braking. Simulation results indicate more significant residual, circumferential tensile stress on the external friction surface after emergency braking. The maximum residual circumferential tensile stress is 200 MPa after 300 km/h emergency braking. In addition, there is only the circumferential compressive stress on a section which is a certain distance from the exterior of the friction surface, and the distance depends on braking conditions. Therefore, not taking into account thickness reduction of the friction surface due to wear, it can be concluded that when the cracks run along the thickness direction to the specified distance, they will cease to run along this direction and begin propagating mainly in the direction of the radius. In addition, based on the simulation results, a measure was presented to prevent and inhibit the crack propagation.     

Analyzing the mechanisms of thermal fatigue and phase change of steel used in brake discs

Thermal cracks on the friction surface of railway brake discs can develop during their lifespan. Cracks often initiate after severe braking conditions along with the occurrence of hot spots. The cyclic thermal and mechanical loads causes high temperature, plastic strain and even phase change of the brake disc steel. In this paper, full scale emergency braking tests were conducted and the peak temperature of localized area was found exceeding the austenitizing temperature of the steel. Thermal cyclic tests was performed to simulate the temperature variation during braking. Volume change of the steel caused by microstructure transformation was taken into consideration in numerical simulation. Combining with the fracture behavior of brake disc steel in low cycle fatigue (LCF) tests in different temperature level, the simulation results show a good consistency with the results of microstructure observation and crack initiation. The occurrence of embedded crack could be well explained according to the simulation results and low cycle fatigue test results.     

鼓式制动器制动不稳定时变特性分析

由于工作环境复杂多变,制动器工作不稳定而导致振动和噪声,鼓式制动器制动时的温度变化对制动不稳定性影响较大,研究制动不稳定性影响因素及其制动不稳定时变特性具有实际工程意义。基于鼓式制动器四自由度接触模型,分别在Hypermesh和ABAQUS中建立鼓式制动器制动鼓和制动蹄总成模型与摩擦制动接触模型并进行试验验证;通过热机耦合动态分析,研究制动鼓温度对制动应力的影响;分析弹性模量和热膨胀系数对鼓式制动器制动不稳定时变特性的影响。分析表明：制动不稳定性是摩擦力耦合所致;制动过程中制动鼓温度与应力相互作用且均先快速上升后缓慢下降;鼓式制动器制动不稳定时变特性主要体现在不稳定模态个数及不稳定倾向系数（tendency of instability, TOI）值的变化,制动温度变化导致弹性模量变化,引起不稳定模态个数和TOI值略有变化,弹性模量对鼓式制动器制动不稳定时变特性影响较小;制动温度变化导致热膨胀系数变化,引起不稳定模态个数和TOI值先大幅降低后略有升高,热膨胀系数对鼓式制动器制动不稳定时变特性影响较大。研究结果对改善汽车制动声品质具有一定指导意义。     

制动工况参数对制动盘摩擦温度场分布的影响

车用盘式制动器是车辆中的重要零件。在紧急制动过程中,制动压力、整车参数以及轮胎与路面间附着系数之间的关系对制动器摩擦温度场分布有重要的影响。通过有限元仿真,探讨不同制动工况参数对瞬时温度场分布的影响。结果表明：如果忽略制动过程中摩擦热流强度的变化,会给温度场模拟带来较大的偏差。制动初始动能和摩擦力增长过程是影响盘表面温度场的关键因素。     

Thermomechanical Behavior of Brake Drums Under Extreme Braking Conditions

Braking efficiency is characterized by reduced braking time and distance, and therefore passenger safety depends on the design of the braking system. During the braking of a vehicle, the braking system must dissipate the kinetic energy by transforming it into heat energy. A too high temperature can lead to an almost total loss of braking efficiency. An excessive rise in brake temperature can also cause surface cracks extending to the outside edge of the drum friction surface. Heat transfer and temperature gradient, not to forget the vehicle's travel environment (high speed, heavy load, and steeply sloping road conditions), must thus be the essential criteria for any brake system design. The aim of the present investigation is to analyze the thermal behavior of different brake drum designs during the single emergency braking of a heavy-duty vehicle on a steeply sloping road. The calculation of the temperature field is performed in transient mode using a three-dimensional finite element model assuming a constant coefficient of friction. In this study, the influence of geometrical brake drum configurations on the thermal behavior of brake drums with two different materials in grey cast iron FG200 and aluminum alloy 356.0 reinforced with silicon carbide (SiC) particles is analyzed under extreme vehicle braking conditions. The numerical simulation results obtained using FE software ANSYS are qualitatively compared with the results already published in the literature.     

飞机刹车用长寿命高摩擦特性炭/炭复合材料制备技术(英文)

以针刺炭纤维准三向结构整体毡为预制体,经丙烯气体狭缝定向流的"外热内冷"、"内热外冷"径向热梯度CVI工艺致密技术,优化组合的热解炭/树脂炭双元炭基体技术,通过调控高温处理技术等三大关键技术制备了A320系列飞机炭刹车盘材料。与现用的A320系列飞机进口炭刹车盘进行了地面台架对比试验和装机应用。结果表明:自主开发的炭刹车盘其设计着陆能量和超载着陆能量的摩擦特性与国外相当,但在高能载(RTO)刹车时,其摩擦系数提高了21%～48%,静摩擦系数提高了28%;装机应用寿命平均达到2700次以上,比国外产品寿命提高了23%,凸现出长使用寿命和高摩擦特性的特色。     

Performance evaluation of brake pads developed using two different manufacturing methods

The aim is to study the effect of several distinct manufacturing processes, parameters and ingredients on the physical, mechanical and frictional characteristics of brake pad developed using hand lay method (sample 1), brake pad developed using hot compression method (sample 2) and commercial brake pad (sample 3). The non asbestos brake pad samples were compared with the selected commercial brake pad sample using pin on disc test set up. Results showed that friction performances of all three samples were insensitive to water and oil absorption test. Sample 2 had better mechanical properties and greater wear resistance than other two samples which are attributed to use of hot press method of manufacturing the composite and selecting the carbon-based ingredients. Sample 1 maintained high coefficient of friction even though manufactured with the help of hand lay method. Both fabricated brake pads are stable upto the temperature 220 °C without any weight loss and degradation. Brake pad surfaces showed different shape wear debris and plateaus significantly affecting the friction characteristics. Finally, the test results indicated that both fabricated brake pad samples have potential braking characteristics to be used as a brake pad material.     

Thermomechanical Coupling Analysis of a Disc Brake Rotor

The main purpose of this study is to analyze the thermomechanical behavior of the dry contact between the brake disc and pads during the braking phase. The simulation strategy is based on computer code ANSYS11. The modeling of transient temperature in the disc is actually used to identify the factor of geometric design of the disc to install the ventilation system in vehicles. The thermal-structural analysis is then used to determine the deformation established, the von Mises stresses in the disc, and the contact pressure distribution in pads. The results are satisfactorily compared with those found in the literature.     

SiC颗粒增强铝基复合材料制动盘的研究

采用半固态搅拌熔炼-液态模锻工艺制备了与Santana轿车前制动器相匹配的SiC颗粒增强铝基复合材料制动盘,对该制动盘进行了材料拉伸性能和微观结构分析,并在SCHENCK制动试验台上进行了制动性能和制动磨损试验。结果表明,复合材料的拉伸性能优于传统制动盘材料HT250铸铁;在各种制动工况条件下,复合材料制动盘对制动衬片的摩擦系数均在大众公司企业标准规定的范围之内,且较稳定;此外,复合材料制动盘质轻、耐磨,制动噪音小、温升低,运转平稳;因此,可望以其替代传统的铸铁制动盘,提高制动器的安全可靠性和服役寿命,减轻轿车悬挂系统的重量,降低油耗。