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.

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.

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.

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 830930℃, the gas-flow rates of N2 and propylene were 4.85.2m3/h and 5.86.2m3/h, respectively, the furnace pressure was 4.55.5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 1.021.78 g/cm3, 31W/（m·K）, 114MPa and 7μm/s, respectively, which are approximately similar to those of the single-cylindrical ones. The gas flow 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.

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.

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%。

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.

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。

多功能全液压动力头式履带钻机的研发

目前,市场上全液压动力头式履带钻机虽生产厂家较多,但产品功能都比较单一,只能适应常规水井钻井施工、工程钻孔施工或常规勘查钻井施工不能满足用户对于可施工多种钻孔的多功能全液压动力头式履带钻机的需求。我中心根据水井钻井施工、工程钻孔施工和勘查钻井施工特点,研发了带动力头变速箱的多功能全液压动力头式履带钻机,实现了一台钻机满足多种钻孔施工的需求。本文介绍了多功能全液压动力头式履带钻机ST400B的总体结构和主要优点,尤其是动力头旋转水封可调偏心轮结构、以及动力头刹车盘和浮动轴所采用的特有技术。

基于PID的液压盘式刹车系统的优化与仿真

以提高液压盘式刹车系统的稳定为目标,提出一种具有PID反馈环节的自适应控制系统。阐述液压盘式刹车系统的基本结构与参数;构建液压盘式刹车系统的数学模型,以单神经网络算法为基础,完成PID控制环节的优化设计;利用AMESim软件,以传感器、电磁比例换向阀、PID控制环节为核心构建自适应控制系统的仿真模型并进行仿真分析。结果证明:PID控制系统提高了液压盘式刹车系统的响应速度与稳定性。

极端状态下周盘式制动器热应力耦合特性

鼓式制动器在制动过程中,由于其密封的结构,制动鼓温度过高,热应力变大,散热较难。这些因素会对制动器的制动性能产生较大影响,从而影响汽车的安全行驶。针对一种新型的周盘式制动结构,分析其在极端状态下的热应力耦合特性。以外径193 mm周制动盘为例,采用有限元仿真与实验,得出温度场、应力场、最大位移量等参数对制动性能影响的一般规律。结果显示:周盘式制动器制动过程中最大温度为153.65℃,最大应力为92.644 MPa,最大变形量为4.5562 mm,相比同类尺寸的鼓式制动器的最高温度可以降低6%,最大应力可以降低23%和最大变形量可以减小8%,其综合性能指标明显优于鼓式制动器,具有较高的工程应用价值。

高速铁路列车制动盘散热筋布置间距研究

[目的]当列车设计速度达到400 km/h等级后,车下流场环境会更加复杂,使得制动盘阻力、功率消耗加剧问题更加凸显,需要对该速度等级下列车制动盘散热筋的最优布置间距进行深入研究。[方法]基于圆柱型散热筋结构,通过有限元仿真手段建立模型,并输入了相关参数值。针对相邻两周散热筋的圆心距d周向设置了四个计算工况,针对相邻两周间的距离d径向设置了五个计算工况,分别计算不同d周向、d径向对制动盘温升、阻力及散热功率的影响,进而得到d周向及d径向的建议取值。[结果及结论]d径向=40 mm(即散热筋与制动盘边缘的距离同制动盘直径之比为0.75)时,制动盘温升达到最低值,制动盘的性能较优;散热筋直径为d周向的一半时,制动盘综合性能最优。

Comprehensive modeling strategy for thermomechanical tribological behavior analysis of railway vehicle disc brake system

A comprehensive modeling strategy for studying the thermomechanical tribological behaviors is proposed in this work.The wear degradation considering the influence of temperature(T)is predicted by Archard wear model with the help of the UMESHMOTION subroutine and arbitrary Lagrangian–Eulerian(ALE)remeshing technique.Adopting the proposed method,the thermomechanical tribological behaviors of railway vehicle disc brake system composed of forged steel brake disc and Cu-based powder metallurgy(PM)friction block are studied systematically.The effectiveness of the proposed methodology is validated by experimental test on a self-designed scaled brake test bench from the perspectives of interface temperature,wear degradation,friction noise and vibration,and contact status evolution.This work can provide an effective way for the investigation of thermomechanical tribological behaviors in the engineering field.