Thermal fatigue and wear of compacted graphite iron brake discs with various thermomechanical properties

The increase in payload capacity of trucks has heightened the demand for cost-effective yet high performance brake discs.In this work,the thermal fatigue and wear of compacted graphite iron brake discs were investigated,aiming to provide an experimental foundation for achieving a balance between their thermal and mechanical properties.Compacted graphite iron brake discs with different tensile strengths,macrohardnesses,specific heat capacities and thermal diffusion coefficients were produced by changing the proportion and strength of ferrite.The peak temperature,pressure load and friction coefficient of compacted graphite iron brake discs were analyzed through inertia friction tests.The morphology of thermal cracks and 3D profiles of the worn surfaces were also discussed.It is found that the thermal fatigue of compacted graphite iron discs is determined by their thermal properties.A compacted graphite iron with the highest specific heat capacity and thermal diffusion coefficient exhibits optimal thermal fatigue resistance.Oxidization of the matrix at low temperatures significantly weakens the function of alloy strengthening in hindering the propagation of thermal cracks.Despite the reduced hardness,increasing the ferrite proportion can mitigate wear loss resulting from low disc temperatures and the absence of abrasive wear.

Numerical and Experimental Analysis of the Aerodynamic Torque for Axle-Mounted Train Brake Discs

As the velocity of a train increases,the corresponding air pumping power consumption of the brake discs increases proportionally.In the present experimental study,a standard axle-mounted brake disc with circumferential pillars was analyzed using a 1:1 scale model and a test rig in a wind tunnel.In particular,three upstream velocities were selected on the basis of earlier investigations of trains operating at 160,250,and 400 km/h,respectively.Moreover,3D steady computational fluid dynamics(CFD)simulations of the flow field were conducted to compare with the wind tunnel test outcomes.The results for a 3-car train at 180 km/h demonstrated:(1)good agreement between the air resistance torques obtained from the wind tunnel tests and the related numerical results,with differences ranging from 0.95%to 5.88%;(2)discrepancies ranging from 3.2 to 3.8 N·m;(3)cooling ribs contributing more than 60%of the air resistance torque;(4)the fast rotation of brake discs causing a significantly different flow field near the bogie area,resulting in 25 times more air pumping power loss than that obtained in the stationary brake-disc case.

Simulation Analysis and Verifcation of Temperature and Stress of Wheel-Mounted Brake Disc of a High-Speed Train

During the braking process,a large amount of heat energy is generated at the friction surfaces between the brake disc and pads and rapidly dissipates into the disc volume.In this paper,a three-dimensional thermo-mechanical coupling model of high-speed wheel-mounted brake discs containing bolted joints and contact relationships is established.The direct coupling method is used to analyze the temperature and stress of the brake discs during an emergency braking event with an initial speed of 300 km/h.A full-scale bench test is also conducted to monitor the temperatures of the friction ring and bolted joints.The simulation result shows that the surface temperature of the friction ring reaches its peak value of 414°C after 102 s of braking,which agrees well with the bench test result.The maximum alternating thermal stress occurs in the bolt hole where the maximum circumferential compressive stress is−658 MPa and the maximum circumferential tensile stress is 134 MPa.During the braking process,the out-of-plane deformation of the middle part of the friction ring is larger than that of the edge,which increases the axial tensile load of the connecting bolt.This work provides support for the design of brake discs and connecting bolts.

Preparation and characteristics of C/C composite brake disc by multi-cylindrical chemical vapor deposition processes

The C/C composite brake discs were prepared by tri-cylindrical chemical vapor deposition （CVD） process. The optimum processing parameters were as follows： deposition temperature was 830 - 930 ℃, the gas- flow rates of N2 and propylene were 4.8 - 5.2 m^3/h and 5.8 - 6.2 m^3/h, respectively, the furnace pressure was 4.5 - 5.5 kPa and the deposition time was 200 h. The effects of processing parameters on the densified rates, thermal-physical property and mechanical performance of C/C composite brake discs were studied. The results show that density, heat conductivity, bend strength and abrasion ratio of the multi-cylindrica brake discs are 1. 02 - 1. 78 g/cm^3 , 31 W/（m·K）, 114 MPa and 7μm/s, respectively, which are approximately similar to those of the singlecylindrical ones. The gas tlow rate has no relation to the number of the cylinder and furnace loading. The utilization ratio of carbon can be improved by multi-cylinder CVD process without changing the characteristics of brake disc.

Investigation into precision engineering design and development of the next-generation brake discs using Al/SiC metal matrix composites

Substantially lightweight brake discs with high wear resistance are highly desirable in the automotive industry.This paper presents an investigation of the precision-engineering design and development of automotive brake discs using nonhomogeneous Al/SiC metal-matrixcomposite materials.The design and development are based on modeling and analysis following stringent precision-engineering principles,i.e.,brake-disc systems that operate repeatably and stably over time as enabled by precision-engineering design.The design and development are further supported by tribological experimental testing and finite-element simulations.The results show the industrial feasibility of the innovative design approach and the application merits of using advanced metal-matrix-composite materials for next-generation automotive and electric vehicles.

Effect of Nb and V on the continuous cooling transformation of undercooled austenite in Cr–Mo–V steel for brake discs

The increasing speed of trains necessitates the development of brake-disc materials that meet more stringent requirements.Therefore,Nb and V have been added to Cr–Mo–V steel to improve its thermal fatigue performance when used in brake discs.In this paper,the influences of Nb and V on the static continuous cooling transformation(CCT)behaviors of undercooled austenite were studied.The microstructures,hardness,and dislocation densities at different cooling rates and with the addition of different alloying elements were also investigated.The results show that the transformation products of ferrite,granular bainite,lower bainite,and martensite form under different cooling conditions.With increasing Nb and V contents,the CCT curves are shifted to the left,ferrite and bainite transformations are promoted,and the critical cooling rate of total martensite formation is increased.The added V mainly forms V-rich M_8C_7 precipitates and reduces the dissolved C content;therefore,the A_(c1),A_(c3),and M_s-point temperatures increase.Moreover,the stability of retained austenite is also reduced;its content therefore decreases.Compared with V,the effect of added Nb is weaker because of its smaller content.However,the addition of Nb improves the hardness at lower cooling rates because of the precipitation of fine Nb C particles and refining of the microstructure.

Numerical optimisation and experimental validation of divided rail freight brake disc crown

In this study, numerical optimisation and experimental validation of a divided rail freight brake disc crown made of grey cast iron EN-GJL-250 is presented.The analysed brake disc is used in rail freight wagons and possesses a load capacity of 22.5 tons per axle. Two of the divided rail freight brake discs are mounted on each axle.With the aid of numerical analysis, the thermal dissipation properties of the brake disc were optimised and ventilation losses were reduced, and the numerical results were compared with experimental results. A one-way fluid–structure interaction analysis was performed. A computational fluid dynamic model of a divided rail freight brake disc, used to predict air flow properties and heat convection, was incorporated into a finite element model of the disc and used to evaluate the temperature of the disc. A numerical parametrical optimisation of cooling ribs of the brake disc was also performed, and novel optimised cooling ribs were developed. A transient thermal numerical analysis of the brake disc was validated using temperature measurements obtained during a braking test on a test bench. The ventilation losses of the brake disc were measured on a test bench specifically designed for the task, and the losses were compared to the simulation results. The experimentally obtained ventilation losses and temperature measurements compared favourably with the simulation results, confirming that this type of simulation process may be confidently applied in the future. Through systematic optimisation of the divided rail freight brake disc, ventilation losses were reduced by 37% and the mass was reduced by 21%, resulting in better thermal performance that will bring with it substantial energy savings.

Experimental study on the temperature evolution in the railway brake disc

Increasing operating speed of modern passenger railway vehicles leads to higher thermal load onthe braking system. Organic composite brake pads are poor thermal conductors, hence frictionalheat is absorbed mainly by the disc. In this study three brake pad types were tested on thedynamometer. Metallic fibres, steel and copper, were introduced to the formulation of twomaterials. The third was a non-metallic material - a reference case. Dynamometer test comprisedemergency brake applications to determine the frictional characteristics of the materials andconstant-power drag braking to analyse the effect of metal fibres on temperature evolution,measured by six thermocouples embedded in the brake disc. Mean friction coefficient is analysedand discussed. It is concluded that conductive fibre in the friction material formulation mayinfluence its tribological characteristics. Despite high thermal conductivity, metal fibres in theconcentration tested in this study, did not reduce temperature of the brake disc.

Characterization of Automotive Brake Discs with Laser-Machined Surfaces

In the automotive and transport industry,braking noise and vibrations are persisting issues and difficult to control.Automo-tive engineers and researchers are putting considerable effort into overcoming these problems,and significant breakthroughs have been made in this area.In this study,M-shaped grooves were bionically designed and manufactured on the frictional surfaces of four automotive brake discs using a laser machine.Various tests were conducted to characterize the physical and mechanical performance of the modified discs along with their noise and vibration responses.The experimental results demonstrate that discs with laser-machined grooved surfaces have better surface hardness and residual stress reduction than discs with un-grooved surfaces.Significant improvement in the braking performance was observed in terms of disc thickness variation,friction and wear,noise,and vibration reduction.It is concluded that the reduction in braking noise and vibrations is mainly caused by the reduction in the coefficient of friction and wear,increase in damping ratio,and improvement of disc thickness variation of the brake disc by laser surface grooving.

Numerical Analysis of Railway Brake Disc

A certain number of railway brake discs made of gray cast iron,showed the presence of small cracks only after a few thousand kilometers.To investigate main causes of a brake disc failure,numerical analysis was done by using ABAQUS software.Numerical analysis resulted from a physical model of heat flux in dependence of braking time.Physical model was applied considering all demands and presumptions given by industry representatives.

A Review of a Study on Disc Brake Noise

With the development of the automotive industry, disc brake noise has become an issue of growing concern to the automotive industry and customers. In this paper, the types of disc brake noise have been discussed. After that, the theories and models that have been proposed as an explanation of brake squeal are reviewed. On the basis of these theories and models, some example simulations of disc brake squeal which use the Finite Element method and mathematical model have been introduced.

列车制动盘散热特性分析及拓扑优化

针对紧急制动工况下制动盘散热问题,采用计算流体力学分析方法对某型通风式制动盘进行了散热特性研究。对制动盘内部流道速度场和对流换热等进行评估,在此基础上,采用由N-S方程与达西定律耦合成的Brinkman方程拓扑优化,实现制动盘散热能力提升的优化目标。结果表明:优化后的模型在整个制动工况中散热量提高了13.46%。

Gear walk instability caused by brake-disc friction characteristics

A multi-body dynamic rigid-flexible coupling model of landing gear is established to study the gear walk instability caused by the friction characteristics of the brake disc.After validating the model with the experimental results,the influence of the landing gear structure and braking system parameters on gear walk is further investigated.Among the above factors,the slope of the graph for the friction coefficient of the brake disc and the relative velocity of brake stators and rotors is the most influential factor on gear walk instability.Phase trajectory analysis verifies that gear walk occurs when the coupling of multiple factors causes the system to exhibit an equivalent negative damping trend.To consider a more realistic braking case,a back propagation neural network method is employed to describe the nonlinear behavior of the friction coefficient of the brake disc.With the realistic nonlinear model of the friction coefficient,the maximum error in predicting the braking torque is less than 10%and the effect of the brake disc temperature on gear walk is performed.The results reveal that a more negative friction slope may contribute to a more severe unstable gear walk,and reducing the braking pressure is an effective approach to avoid gear walk,which provides help for future braking system design.

服役损伤对制动盘疲劳裂纹扩展行为的影响

制动盘是高速列车制动系统的重要元件,其复杂的服役工况会使制动盘出现多种形式的服役损伤,影响制动盘后续的可维修性和服役安全性。选取未服役制动盘和产生翘曲变形且摩擦面出现疲劳裂纹的服役后制动盘为研究对象,通过测试服役前后制动盘材料在不同温度下的拉伸力学性能,构建了受摩擦面深度和温度双参数影响的力学性能衰退模型来表征制动盘的材料损伤。通过构建不同制动工况下制动盘三维瞬态仿真模型,得到了服役后制动盘的结构变形和残余应力状态来表征制动盘的结构损伤。基于Paris理论进行制动盘疲劳裂纹扩展寿命分析,评估了服役损伤对制动盘疲劳裂纹扩展能力的影响。结果表明:长期服役后制动盘本体材料力学性能会发生衰退,从摩擦面表层至心部呈现梯度分布,近表层材料强度下降约20%,制动盘残余应力释放后会使盘体产生碟形翘曲变形。服役后制动盘的力学性能衰退使裂纹前缘的应力强度因子水平显著高于服役前制动盘,摩擦面中部裂纹沿制动盘径向的扩展速率大于沿深度方向,使裂纹深长比不断减小。与服役前制动盘相比,服役后制动盘摩擦面中部裂纹从0.5 mm扩展至70 mm的扩展寿命降低了48%。螺栓孔处疲劳裂纹扩展初期主要沿深度方向扩展,随着裂纹尺寸增加沿制动盘径向与深度扩展速率逐渐一致,服役后制动盘螺栓孔裂纹从0.5 mm扩展至50 mm的扩展寿命与服役前相比降低了29%。本文的研究方法可用于不同损伤程度的制动盘本体性能表征与失效分析,对服役后制动盘的检修维护、保障制动盘的安全运用具有工程参考价值。

踏面与盘式两种制动模式温度分布特征的模拟分析

探究1∶1踏面制动与缩比盘式制动得到的温度场存在偏差的原因,有利于提高利用缩比制动模式评价制动摩擦副热负荷能力的精度。基于TM-I型缩比车辆制动试验台和1∶1制动试验台,采用ADINA有限元软件,在制动压力10、15、20 kN和初速度60、80、105 km/h条件下,模拟计算2种制动模式的温度场,并分析影响2种制动模式温度偏差的因素。结果表明:1∶1踏面制动模式和缩比盘式制动模式得到的温度存在明显差别,踏面制动的温度均高于缩比盘式制动的温度;2种制动模式的温度差别随压力的变化不明显,但随制动初速度增加而明显加大;踏面制动由于摩擦面积集中,散热程度不良,随初速度从60 km/h增加到105 km/h,制动温度增加幅度为56%~77%,盘式制动由于摩擦弧长沿盘半径方向的不均匀,散热面积大,制动温度随初速度增加幅度为32%~44%。

轻量化高速列车制动盘材料-结构研究进展

400 km/h高速列车紧急制动的强热负荷,导致制动盘温升高、温度分布梯度大和热衰减强,已超出钢质制动盘能载极限,开发耐高温强耐磨的制动盘材料,同时提升制动盘通风散热能力成为制动技术发展瓶颈。综述高速制动盘材料从高强度铸钢和锻钢、轻量化铝基复合材料至耐高温耐磨碳陶复合材料和表面改性技术发展历程,随着碳陶复合材料的台架试验和表面改性技术的摩擦磨损试验研究的深化,表面改性轻质复合材料是制动盘材料未来发展方向。概述通风制动盘内部散热层散热筋结构形貌优化、摩擦层表面耐磨性能改善的发展现状,内部散热筋由直通道设计逐渐演化为弯曲、支柱以及分形通道,镂空结构能更好地加速空气流动提高散热;表面摩擦层引入打孔或划线,更易于摩擦粉尘的抛离从而稳定摩擦因数,保持制动效果;但复杂通风导流结构和打孔划线增加了制备工艺的难度,提出高速制动盘结构构型设计需要综合材料热力学性能、制备工艺及耐热耐磨需求,形成材料-结构-功能—体化设计理念,为实现更高速的制动盘优化设计提供参考。

摩擦-消音片结构对盘式制动器尖叫噪声的影响研究

针对某汽车盘式制动器存在制动尖叫噪声问题,研究了不同倒角结构的摩擦片、不同阻尼层厚度的消音片,以及两者匹配对制动尖叫噪声的影响,并通过台架试验分别对研究得到的最佳匹配方案和原方案进行噪声测试。研究结果表明,5种不同倒角结构摩擦片中,对称结构的倒角优于不对称结构,不对称结构的倒角解决频率较为集中的单处噪声效果较好,其中,对称直倒角结构降噪效果最好,但易诱发新的噪声;消音片阻尼层厚度逐渐增大时尖叫噪声发生的倾向性呈现先减小后增大的趋势;摩擦片与消音片的合理匹配能有效改善尖叫噪声,对称倒角和不对称倒角结构的摩擦片分别匹配消音片时的降噪趋势相反,其中对称斜倒角结构的摩擦片与阻尼层厚度为0.28 mm的消音片匹配时降噪效果最好,噪声发生度比原方案降低了97.98%。

盘式制动器温度场的分析研究

针对制动器温度场的研究分析,建立额定起重量32 T的钳盘式制动器三维模型,同时在Workbench中添加制动器材料的各个参数,设置摩擦副间的接触关系,施加制动盘和制动衬片载荷、约束,对制动器制动过程产生的温度场进行仿真。使用LM算法建立包括时间、摩擦因数、制动压力、初始转速的多元非线性数学模型,通过Matlab进行回归分析。最终拟合结果和有限元仿真结果吻合,验证了起重机制动器温度模型的正确性。

试验环境的盘式制动器NVH特性研究

文中采用多体动力学和声学边界元等数值方法,研究某盘式制动器试验条件下的NVH(Noise,Vibration,Harshness)特性。首先,建立试验环境的制动器刚柔耦合模型,从结构、激励源和传递路径3个方面分析制动NVH特性影响因素;然后,运用声学边界元法仿真得到制动振动辐射的噪声,并与台架试验结果进行比较。结果表明:制动盘第2~5阶轴向模态,支架第2~3阶轴向模态,以及制动钳和连接板第1阶轴向模态等模态固有频率与台架试验噪声频率较接近,可能引起共振而产生制动噪声;在不影响制动性能的前提下,改变制动盘与摩擦衬片阻尼系数能改善制动NVH特性;悬架螺旋弹簧下端振动大,减振器与衬套对振动具有显著衰减作用;由仿真声压级云图发现,制动盘与摩擦片接触部位声压级最大,且随频率增加呈先增后减趋势,与台架试验对应测点的噪声结果进行直接比较,两者趋势一致。

高支柱起落架走步振动与稳定性分析

为改善装备碳陶刹车盘的高支柱起落架走步振动问题,对走步规律进行了深入分析。阐述走步机理,碳陶刹车盘摩擦特性引起的负斜率刹车力矩会向起落架航向系统引入负阻尼,引起走步振动的发散。基于3自由度走步动力学方程,开展了刹车力矩参数、起落架结构参数以及机身初始速度对走步振动的影响研究,定义了走步振动发散的临界状态,并提出刹车压力随刹车动静盘相对转速减小的走步控制策略。仿真结果表明:刹车盘摩擦系数负斜率绝对值的减小,刹车压力的降低,支柱刚度和阻尼的增大都可增加走步系统的稳定性,刹车盘摩擦的最小值提高至0.186可确保飞机以任意速度刹车走步稳定;刹车压力下降的斜率随刹车速度的不同而改变,飞机从144 km/h开始刹车,刹车压力降低24.7%可使走步振动收敛,轮轴航向加速度峰值降低77.23%。