Generalized braking characteristics of friction pad synthetic graphite composites

Present paper discusses frictional sliding response and stability of graphite-based composite brake pad material under ranges of pressures (P), sliding velocities (V) and material properties (graphite particle size, hardness, ultimate tensile and flexural strengths) of (2-4 MPa), (11.4-15 m/s), (20-470 μm), (70-90 HRL), (6-16 MPa) and (5-37 MPa), respectively. One generalized equation is derived to express this response. Optimum μ of 0.485 is attained at values of P, V and material properties of 2 MPa, 15 m/s, 21 μm, 90 HRL, 15.84 and 6.85 MPa, respectively.     

Optimal location of brake pad for reduction of temperature deviation on brake disc during high-energy braking

Journal of Mechanical Science and Technology - During the braking process, frictional heat generated between a disc and a pad can lead to high temperatures. The location of friction blocks on the...     

Instabilities generated by friction in a pad–disc system during the braking process

This paper presents a numerical and experimental study of a pad–disc tribometer. The explicit dynamic finite element software PLAST 3 in 3-D is used to simulate the behaviour of the two bodies involved. Coulomb's friction law is used at the contact surface with a constant coefficient. For this application, temporal simulations show that separation occurs between surfaces, proof of instabilities. This unstable state is characterized by a stick–slip–separation wave. We show that instabilities describe a periodic shock phenomenon at the contact interface. Consequently, the acceleration spectrum recorded on the surface of the pad reveals periodicity in the frequency domain. It shows also that, in this case, the vibrations responsible for the instability are localized in the pad. The mode responsible for squealing can be obtained by a modal analysis of the pad–disc system by assuming that the interface is stuck. We highlight the importance of the pad Poisson's ratio in the occurrence of this unstable state. A numerical/experimental comparison has been performed and the fundamental frequency of squeal obtained experimentally and its magnitude agree with those calculated numerically with PLAST 3.     

Non-uniform contact characteristics of the friction disc during the initial period of a braking process

Journal of Mechanical Science and Technology - To reveal the contact characteristics of the hydraulic brake friction pair during the initial period of braking process and improve its working...     

盘式制动器的制动效能和接触应力分析

研究汽车制动性能的影响因素,分析盘式制动器的制动效能。计算摩擦衬块产生的最大制动力矩、制动效能因素及摩擦衬块对制动盘的压紧力等。以摩擦衬块、制动盘为研究对象,研究轿车在低速、中速、高速和最高时速制动时,制动盘和摩擦衬块上的应力分布规律,给出速度对应力分布的影响规律。应力分布影响制动器的制动转矩容量、热容、磨损等,摩擦衬块与制动盘之间既不是完全接触更不是均匀分布的接触压力,接触表面的应力分布一直是工程界和学术界关注的热点之一。     

盘式制动器辅助电磁制动装置的结构优化设计

将盘式摩擦制动器与电涡流缓速器集成,在车轮制动盘内侧挡尘板上安装若干电涡流缓速器线圈,设计了一种可应用于乘用车的电磁辅助制动装置,实现摩擦制动器与电涡流缓速器联合制动.针对所设计的电涡流缓速器分析了制动原理,建立数学模型,确定了辅助制动装置的制动力矩和制动功率的计算方法为使该型电涡流缓速器获得最大缓速效果,采用优化设计方法,以提高汽车制动力矩为目标,对电涡流缓速器的结构参数进行了优化设计,从优化结果看该设计获得了一定的辅助制动效果.     

Analysis of tribological behaviour of pad–disc contact in railway braking: Part 1. Laboratory test development,compromises between actual and simulated tribological triplets

In the field of railway braking, improving the performances of friction brake systems requires better knowledge of the local tribological behaviour of pad–disc contact under braking conditions. After analysing the tribological triplet involved in railway braking, this paper focuses on the development of laboratory tests for studying local physical phenomena caused by friction in braking. The aim is to generate at reduced scale similar contact conditions to those at full-scale. An original braking tribometer is presented whose design is based on similitude rules between reduced-scale and full-scale. As it is difficult to reproduce representative full-scale thermal loading generated by friction at reduced-scale, compromises are needed and the choice of experimental parameters, based on a non-dimensional conversion rule, is discussed. The results obtained at reduced-scale are presented and comparison with results available at full-scale shows that the reduced-scale tests are very representative.     

自行车碟刹制动距离测试系统的设计与实现

随着碟刹的使用越来越普及,刹车的可靠性测试显得尤为重要,而国内市场上尚没有针对碟刹的测试系统.针对这一问题,设计了一套自行车碟刹制动距离测试系统.首先建立了自行车的刹车模拟装置,然后在模拟装置上安装了拉力传感器和速度传感器对其进行实时监测,传感器信号由数据采集卡采集并上传至上位机,上位机软件分析数据后下发命令控制模拟装置的刹车过程,并实时显示拉力值、速度值和制动距离等.通过多次制动距离测试,求平均值,确定了碟刹的制动距离,最后进行了试验验证.研究结果表明,该测试系统能够较准确地测量出自行车的制动距离,并且性能稳定,简单易操作,实用性强,具有良好的实际应用价值.     

电机车制动类型及摩擦制动材料

我国煤炭资源丰富,目前铁路运输仍是我国煤炭运输的主要方式,而电机车的制动方式已经成了限制铁路运输能力进一步提高的急待解决的问题。本文介绍了电机车的制动类型,对摩擦制动机理及摩擦材料进行了较为详细的介绍和比较。     

Pad surface and coefficient of friction correlation analysis during friction between felt pad and single-crystal silicon

In wafer polishing pad surface plays a crucial role in the polishing process. With the increase of friction time between pad and wafer, the pad becomes flattened or glazed with particles clogging the pores of the pad and forming a layer of slurry residue and wafer particles, leading to changes of COF, material removal rates and higher defects on the wafer surface. Thus, this study aims to determine the correlation between pad surface deformation, slurry adhesive rate and Coefficient of friction (COF) during friction between felt pad and single -crystal silicon, to analyze the relationship between pad condition and COF. The real-time COF between felt pad and single-crystal silicon wafer are tested which are sorted in groups depending on various loads and oscillation frequencies and surfaces of felt pads measuring by Scanning electron microscope (SEM) are compared. The correlation between pad surface deformation and abrasive adhesion and COF is evaluated through analyzing the experiment results.

     

Determination of gear tooth friction by disc machine

The friction between the teeth of a pair of hardened and ground spur gears has been measured in a back-to-back test rig. The results are compared with friction measurements using a disc machine under comparable conditions of load, speed and temperature. Close agreement was found with discs which had been transversely ground (like the gear teeth); circumferentially ground discs to the same finish gave an average 23% higher friction.     

温度变化下的伺服系统非线性摩擦建模

针对机械伺服系统因温度变化产生的非线性摩擦变化,提出了一种反映温度因素的摩擦建模方法来实现对伺服系统的摩擦补偿。首先,分析了温度和摩擦的关系,并结合修正黏性摩擦的LuGre模型,讨论了该模型各参数与温度之间的关系。利用单隐层BP神经网络描述了随温度变化的各个参数,并确定了神经网络的输入、输出以及传递函数。然后,通过神经网络训练获得神经网络参数,从而得到与温度相关的摩擦模型。最后,改变运行条件,验证了提出的模型对摩擦的估计能力。建立的摩擦模型在不同运行条件、不同温度状态下的最大相对估计偏差小于2.5%,表明其能很好地估计系统摩擦力矩,满足高精度摩擦补偿。     

Experimental and analytical studies of dynamic friction at the head/disk interface

Friction is an important parameter that critically impacts the tribological performance of a head/disk interface. The head/disk interface with laser zone texture affords a model system for the study of dynamic friction by virtue of its precisely-controlled contact geometry. By using two types of head sliders, i.e. the conventional slider and the padded slider, and a matrix of hard disks with a wide range of laser zone texture parameters, head/disk contacts involving a small number as well as a large number of bumps are realized. A rich variety of dynamic friction behaviors are observed with respect to bump height and bump density variations. To shed new light on the nature of HDI dynamic friction, an analytical model that treats both the deformational and the adhesive friction components on equal footings is formulated. It is shown that, based on the model analysis, the friction is deformation-dominated for HDIs involving a small number of contacting bumps and adhesion-dominated for HDIs involving a large number of contacting bumps. In the former case the friction decreases with bump density, whereas in the latter the friction increases with bump density.     

风电制动片材料冲击性能及摩擦性能分析

基于对风力发电机制动片现用摩擦材料的分析,研制了纤维增强复合材料,并利用分离式霍普金森压杆试验装置和MM-1000磨粒磨损试验机,研究制动片摩擦材料的冲击性能和耐磨性能.通过对铜基粉末冶金、颗粒增强复合材料、纤维增强复合材料的应力-应变和摩擦性能比较和分析,得出纤维增强复合材料具有较好的耐冲击性能和良好的塑性性能,并且其摩擦性能高于其他两种材料,故可以取代其他两种材料成为风电制动片材料.     

Influence of pad–pivot friction on tilting pad journal bearing

Some experimental studies reported that the performance of tilting pad journal bearing is related with the pad–pivot friction. Only a few researches, however, consider the friction as a factor even though many ones have theoretically analyzed the performance of bearing. Also, there is no mathematical model for the friction to explain the effect of friction on the performance of bearing. Therefore, this study proposes a mathematical model for the pad–pivot friction and analyzes the effect of friction on the tilting pad journal bearing.The results of this analysis show that the friction has a large influence on the attitude angle of the journal. It is found that the eccentricity direction of the journal does not coincide with the load direction when the friction is not zero. According to working conditions, the attitude angle can be up to 25° when friction coefficient is equal to 0.5. It is also found that the tilt angle of the pad is not determined as a fixed value in case of the bearing with non-zero friction, even though working conditions is given for the static analysis. This study represents four different tilt angles under same working conditions.     

An investigation into friction behaviour of dispersion-strengthened copper under severe railway braking conditions

A dispersion-strengthened copper (DSC) has been studied as an alternative material for railway brake discs, to be used in severe railway braking applications. Compared to standard steel, the DSC shows a more homogeneous thermal field at the friction surface. This also applies in depth, both avoiding hot spots. This thermal behaviour implies a lower wear and a very interesting friction coefficient evolution without any “anti-fade” phenomenon.     

飞机刹车副的三维瞬态温度场和热应力仿真分析

飞机的刹车装置是利用摩擦产生制动将高速运动的动能转换成热能,产生的高温使摩擦材料的物理、化学性质发生变化,由于较大的温度梯度的出现使刹车盘上存在非常大的热应力,使刹车系统的安全性能受到威胁,所以对刹车盘瞬态温度场和由此产生的热应力进行计算就显得非常必要。针对飞机刹车盘瞬态温度场和热应力仿真建立了有限元模型,有限元网格划分采用六面体结构。对刹车过程进行了理论分析与计算,并运用MSC PATRAN/MARC软件对其进行了仿真计算。刹车副的最高温度为1 020℃,与刹车副温度场的经验值基本吻合,在以温度场和刹车副的位移约束为边界条件计算得到刹车副的热应力。热应力的分布特点和温度梯度是一致的,所以热应力的计算结果是合理可行的,可以应用于飞机刹车盘设计过程中。     

盘式制动器摩擦磨损热动力学研究进展

摩擦磨损热动力学是制动器失效分析和设计的重要理论依据,对选择摩擦副材料也有指导作用．因此从分析摩擦热对制动器摩擦副的影响着手,总结了盘式制动器摩擦磨损热动力学的数学、物理模型,并对制动摩擦表面温度场和应力场的计算方法进行分析比较,评述了盘式制动器摩擦磨损热动力学的研究进展,并对今后主要研究工作进行了展望．     

Investigation of friction in dual leaf spring

The paper presents the study of the operation of the prototype of the dual leaf spring that consists of a four-leaf main spring and a two-leaf auxiliary spring under the action of a cyclic load close to the actual operating conditions of a car suspension. The importance of friction in an operation of this type of structure has been mentioned; numerical methods and an experimental facility for studying the effect of friction on the spring operation have been considered. The investigation results have been presented in the form of summary tables, color-coded images, and diagrams of the temperature distribution for measuring points located on single leaves of the double spring. The methodology of experimental studies and the used equipment made it possible to evaluate the effect of friction and accompanying thermal stresses during the operation of the dual leaf spring.     

Electronic and phononic friction of solids at low temperatures

It has recently been shown both experimentally and theoretically that there is no static friction in a contact of atomically flat crystalline solids provided the periods of their lattices are incommensurate and their interaction does not exceed some critical value. The only mechanisms of friction in this case are phonon generation and excitation of conducting electrons. It is shown that, at low temperatures, the phonon contribution to the coefficient of friction can be very small by virtue of the quantum mechanical nature of the elementary excitations in a solid. Incommensurate dielectric crystals could therefore slip at low temperatures practically without friction. In metals, on the contrary, the excitation of electrons leads to a finite dynamic friction force at any temperature. Presently, both phonon and electron contributions to the friction force are estimated (the latter both in the normal and the superconducting state of metal).