Dynamic interaction of friction and surface topography in brake systems

In brake systems the surface topography of the brake pad is characterized by an equilibrium of flow of hard patches, which are built up and destroyed, depending on the load history. Since these patches carry the main friction power, the friction coefficient itself depends on the load history, too. So the friction coefficient has to be described by differential equations instead of algebraic equations, connecting intimately the friction- and wear process. With these dynamic dependencies we are able to build up a new model, using the technique of Cellular Automata, which gives a dynamic and detailed insight into the brake pad's surface topography during the friction process.     

基于制动器摩擦副销-盘试验的第三体摩擦磨损特性研究

风电制动器因其制动工况多变,摩擦副表面的第三体成分复杂且大小各异,在第三体影响下摩擦副的摩擦磨损特性仍有待研究。以服役期内风电制动器摩擦副为研究对象,对附着在风电制动器摩擦副表面的第三体成分及尺度进行检测。检测结果表明,风电制动器摩擦副表面第三体的主要成分为铁铜磨屑及沙石颗粒,且其尺度均在百微米级。利用销-盘摩擦磨损试验机研究具有上述成分及尺度第三体对摩擦副摩擦磨损特性的影响。试验结果表明：摩擦初期第三体在摩擦副间产生滚动起减摩作用,摩擦因数大幅减小;随着磨损程度的加剧,摩擦因数大幅上升,摩擦副提前进入剧烈磨损阶段;铁颗粒会加剧摩擦副磨损缩短其使用寿命,沙颗粒会导致制动过程摩擦力矩大幅波动,铜颗粒会导致制动力的不足。     

Influence of Thermal Fatigue on the Wear Behavior of Brake Discs Sliding against Organic and Semimetallic Friction Materials

ABSTRACT

In this article, brake discs are exposed to high thermal stress, causing thermal fatigue damage. The aim of this work is to study the evolution of the wear behavior of brake disc materials, such as cast iron, chromium steel, and metal matrix composites, under the influence of thermal fatigue. The brake disc specimens are heated and then cooled rapidly. Then, wear tests are carried out using a pin-on-disc-type tribometer. Organic and semimetallic friction materials are used for all wear tests. The results show that thermal fatigue affects the structure of the contact surfaces of all of the disc specimens by increasing their roughness. Furthermore, the wear rate of the friction materials increased, except a reduction of the wear rate is noted for the semimetallic friction material rubbing against cast iron. Moreover, thermal fatigue has no significant influence on the coefficient of friction. The worn surface of the metal matrix composite sliding against semimetallic friction material is characterized by abrasive and adhesive wear mechanisms.     

重型车辆织构化刹车系统热力学行为与摩擦学性能研究

重型车辆刹车系统受瞬态高温和雨水异常侵入的影响,易引起热力学行为与摩擦性能退化。为研究表面织构对刹车系统热力学行为和摩擦学特性的影响,基于有限元法开展刹车系统热力学分析,考虑大量雨水侵入的液体润滑极端情况,提出一种动压润滑与织构集成模型的摩擦学性能分析方法。结果表明：水平凹槽织构可使制动盘温度场及应力场分布较均匀,进而避免接触区域局部瞬态高温引起的车辆制动失效;随着凹槽织构倾斜角度增大,承载力增大,摩擦因数减小;不同组合型织构中,圆柱与椭球组合型织构表面承载力最大、摩擦因数最小,圆锥与椭球组合型织构表面承载力最小、摩擦因数最大。研究发现重型车辆刹车系统表面构筑合适倾斜角度凹槽织构和组合型织构有助于提升其工作性能。     

Simulation of Temperature Distribution in Disk Brake Considering a Real Brake Pad Wear

This paper presents a methodology for the modeling of the transient thermal behavior of the disk brake of the vehicles using finite element methods. The influence of the wear properties of friction materials on thermoelastic behaviors is investigated to facilitate the conceptual design of the model. The coupled characteristics of the friction heat flow between the disk and pad as well as the effects of the brake disk thermal stress because of the variable applied pressure was considered. At the same time, the model was optimized by the experiment. Repeated brake processes with varying load, sliding speeds and temperature are applied in the simulation of the disk brakes. Experimental dependencies of the coefficient of friction and wear rate on the temperature of brake pad were approximated and applied to the model. The temperature and pressure on the contact surface of the pad/disk brake system obtained for constant and speed/pressure sensitivity applications were confronted and compared. The thermo-distribution is operated to visualize the disk temperature.     

惯性制动条件对铜-石墨材料摩擦性能及第三体的影响

采用粉末冶金技术制备铜-10%石墨烧结材料,通过GF150D型摩擦试验机,在干摩擦状态及制动压力为0.51 MPa的条件下,研究不同制动方式对材料摩擦磨损性能的影响。结果表明,采用从高速到低速分段制动方式(摩擦方式A)时,随着制动速度降低,摩擦表面形成的致密第三体破碎、剥落,机械啮合力增加,摩擦因数提高;同时,摩擦表面温度下降,基体强度提高,磨损率降低。采用从高速到低速连续制动方式(摩擦方式B)的摩擦因数和磨损量均大于摩擦方式A。     

脂润滑条件下闸门底枢摩擦副磨损失效评价

采用摩擦磨损试验机,获得了QAL9-4/40Cr和ZCuAl8Mn13Fe3/40Cr两种闸门底枢摩擦副在不同接触应力的脂润滑条件下的摩擦学特性,并运用灰色系统理论GM（1,1）模型对其达到许用磨损量的磨损失效进行了评价。低速重载条件下,两种摩擦副的实际接触应力在许用应力之下时,其磨损形式均以犁切为主,且磨损量随接触应力的增大而增大,摩擦因数随着接触应力的增大而减小;反之,其磨损形式均以黏着为主,且磨损速度、摩擦因数均会急剧增加。受同一接触应力作用时,QAL9-4/40Cr具有更好的耐磨性。理论模型对磨损失效的预测结果与实测值吻合度达到95%。     

Development of a high-quality rare earth oxide modified resin-based brake material

A high-quality brake material was developed by using different rare earth oxide modified resin-based brake materials and designing the composite material through an orthogonal optimization test. The effect of rare earth oxide on the properties of the resin-based brake material, such as the friction and wear, thermal decay resistance, and recovery, was explored using the constant-speed friction test, Chase friction test and worn surface morphological observation. The results show that rare earth lanthanum oxide can be added to improve the friction and wear properties of the brake material compared to cerium oxide and yttrium oxide. At 100–350°C, the friction coefficient of the developed brake material fluctuates in the range of 0.40–0.50, and the material has high friction coefficient, good thermal decay resistance and favourable wear resistance. The friction coefficient of the optimal formulation can reach the GF level, so its tribological properties are very good and better than the brake pads of automobiles at home and abroad.     

带式输送机树脂基摩擦片干式制动条件下摩擦学行为

采用热压烧结技术制备桐油改性酚醛树脂和腰果壳油改性酚醛树脂基摩擦片,通过CFT环块摩擦磨损试验机研究其在不同的制动速度、制动正压力下以及在瞬时制动时的摩擦因数以及磨损率的变化规律,采用扫描电镜(SEM)对试样摩擦后的表面形貌进行观察分析。结果表明,2种树脂基摩擦片摩擦因数以及磨损率变化规律具有一致性:摩擦因数均随着制动正压力与制动速度的增加而减小;磨损率随着制动速度的增加而减小,随着制动正压力的增加而增加。以桐油改性酚醛树脂为基体,碳纤维为增强纤维的摩擦片在瞬时制动时具有较稳定的摩擦因数,而且在不同制动正压力与制动速度下磨损率较低。     

On the dry and wet sliding performance of potentially new frictional brake pad materials for automotive industry

In this work, dry and wet continuous sliding performances of newly developed four different non-commercial frictional brake pad materials (NF1, NF2, NF4, and NF5) were evaluated and compared with other two chosen commercial brake pad materials (CMA and CMB) using a small-scale tribo-tester of pad-on-disc type.Results showed that under dry continuous braking, friction coefficients for all non-commercial brake pad materials including the CMB were insensitive to the type of brake pad materials. In addition, all brake pad materials showed a slight increase in the friction coefficients (5–19%) with increasing pressure or speed. Meanwhile, the wear rates were substantially dependent on the type or ingredient of brake pad materials and the pressure. Conversely, under wet sliding condition, the friction coefficients were decreased by a factor of 2. Moreover, no evidence of HD water film could be evidenced as the measured friction coefficient values were in the order of dry friction. Thus, the wet results suggested that the friction behaviour was influenced by factors other than HD film, and the values of friction coefficient were in the range of dry friction, mixed and boundary lubrication friction. Qualitative assessment of the SEM morphologies of brake pad surfaces showed that tribofilms were easily formed in dry braking and hardly formed in wet braking. Besides, all brake pad rubbing surfaces showed contact plateaus “patches” and disintegrations of various sizes and locations depending on the braking condition. Furthermore, the removal of material was associated with either mechanical crushing action performed by entrapped wear debris or due to disintegration of plateaus which were accelerated by spraying the water.     

制动摩擦副材质对其摩擦性能影响的研究

对有机石棉和半金属衬片材料与不同化学组分的灰铸铁制动盘（鼓）进行摩擦性能试验。分析了对偶材质对衬片磨损及摩擦系数的影响及衬片材质对制动盘（鼓）磨损的影响。提出了评定衬片材料的耐磨性必须标明对制动盘（鼓）的损伤及制动副材料的最佳选配问题。     

Friction and wear during twin-disc experiments under ambient and cryogenic conditions

We present a classical rolling contact apparatus where two discs roll and slide under a constant normal loading. Experimental results concerning bearing steel used in ambient air or under severe temperature conditions (liquid nitrogen) are presented. A simplified model proposed by Kalker (Fastsim) is used to identify the dynamic friction coefficient between these discs and to study the apparatus parameters’ influence on dissipated energy. Wear evolution is simulated using classical Archard's law and compared to measured profiles. Influence of ambient conditions is highlighted by comparing friction and wear coefficients.     

石油钻机盘式刹车副材料的摩擦磨损性能研究

为提高深井石油钻机盘式刹车副的摩擦学性能和使用寿命,研制开发了新型刹车盘表面堆焊材料和无石棉刹车块摩擦材料,并通过变温摩擦磨损性能实验,研究了刹车副的摩擦学性能。研究表明,刹车副具有良好的变温摩擦特性和高温抗热衰退性能,高温下的摩擦因数比较稳定;刹车块和刹车盘的磨损率均随温度的升高而增大,但刹车盘表现出相对稳定的耐磨性能。载荷对刹车副的摩擦因数影响不大,变化比较平稳;刹车块和刹车盘的磨损率均随载荷的增大而增大,但刹车块表现出相对稳定的耐磨性。刹车副的摩擦因数随滑动速度的增加而增大,并趋向平稳;但速度对刹车块和刹车盘的磨损率影响不大,变化相对稳定。研制的刹车副材料能够满足石油矿场钻机作业的要求。     

约束对盘形制动摩擦噪声影响的有限元研究

建立了铁路车辆盘形制动装置的三维实体有限元模型,分别为该模型中的制动盘、闸片和夹钳等部件设置了不同的材料特性。利用线性弹簧力模拟制动摩擦面间的法向力,摩擦力取为线性弹簧力与摩擦因数的乘积。通过对系统有限元运动方程进行复特征值分析,根据复特征根实部为正值判断系统发生失稳的模态,这也是可能产生摩擦噪声的模态。仿真结果显示,系统的约束条件对摩擦噪声的形成有显著的影响。改变模型的约束条件,可以抑制制动系统的摩擦噪声发生趋势,说明通过优化设置约束条件来提高摩擦系统的运动稳定性从而抑制摩擦噪声的发生是可行的。     

A reduced-scale brake dynamometer for friction characterization

Friction behavior is a critical factor in brake system design and performance. For up-front design and system modeling it is desirable to describe the frictional behavior of a brake lining as a function of the local conditions such as contact pressure, temperature, and sliding speed. Typically, frictional performance is assessed using brake dynamometer testing of full-scale hardware, and the average friction value is then used for the remaining brake system development. This traditional approach yields a hardware-dependent, average friction coefficient that is unavailable in advance of component testing, ruling out true up-front design and leading to redundant lining screening tests. To address this problem, a reduced-scale inertial brake dynamometer was developed to determine the frictional characteristics of lining materials. Design of a reduced-scale dynamometer began with the choice of a scaling relation. In this case, the energy input per unit contact area was held constant between full-scale and reduced-scale hardware. All linear variables were thereby scaled by the square root of the scaling factor, while the pressure, temperature, sliding velocity, and deceleration were kept constant. Experimental validation of the scaling relations and the reduced-scale dynamometer focused on comparisons with full-scale dynamometer data, particularly the friction coefficient. If similar trends are observed between reduced-scale and full-scale testing, the reduced-scale dynamometer will become an important tool in the up-front design and modeling of brake systems.     

基于马尔可夫链的飞机刹车片检查时间确定

为结合飞机实际运行工况,科学合理地制定刹车片检查时间,笔者提出一种基于马尔可夫链理论的预测模型。以某一机群刹车片检查时间确定为实例,分别论述了刹车片磨损状态的划分,转移概率矩阵的构造与估计,并对该机群刹车片磨损状态进行了预测,其预测结果与实际检查情况较吻合。根据刹车片磨损状况的预测结果,制定了该机群在实际运行工况下的刹车片检查时间。实际运行情况表明,所制定的刹车片查检时间可行、有效。     

铜基粉末冶金/Q235B摩擦副载流摩擦磨损性能*

磁浮列车中部分制动闸片在服役时一直处于受流状态,导致材料磨损加剧,影响闸片的服役寿命。为研究中低速磁悬浮列车制动闸片在受流工况下的摩擦磨损性能,以制动闸片使用的铜基粉末冶金材料和刹车盘使用的Q235B材料为摩擦副,研究不同制动速度下铜基粉末冶金/Q235B摩擦副的载流摩擦磨损行为。结果表明：无电流时随着滑动速度的增大,摩擦因数及磨损率整体呈现下降的趋势,载流时随着滑动速度的增大,摩擦因数整体呈现下降的趋势,而磨损率则整体呈现上升的趋势;无电流时磨损后的铜基粉末冶金材料表面覆盖着一层靛色的第三体层,该第三体层低速时主要以颗粒状为主,随着速度的增加逐渐被压实成连续致密状,高速时因黏着磨损加剧使得连续致密状第三体被破环,导致材料的摩擦因数和磨损率呈现反向增长的趋势;载流下磨损后的铜基粉末冶金材料表面出现了以机械磨损为主和以电弧烧蚀为主的2个区域,其中以机械磨损为主的区域依然是由靛色的第三体层组成,而以电弧烧蚀为主的区域表面则覆盖了一层金色熔融状物质,并且随着速度的增大,烧蚀区面积也逐渐增大。     

Comparative Study on the Complex Eigenvalue Prediction of Brake Squeal by Two Infinite Element Modeling Approaches

The complex eigenvalue analysis is currently a common approach to predict squealing vibration and noise. There are two methods for modeling friction contact in the complex eigenvalue analysis of friction systems. In one method, contact springs are used to simulate friction contact. In another method, no contact spring is used. However, it has been uncertain whether these two modeling methods can predict approximately identical results. In order to clarify the uncertainty, two finite element models of the same brake system for the brake squeal prediction are established and simulated by using ABAQUS and NASTRAN software tools, respectively. In the ABAQUS model, friction coupling is applied to determine normal contact force and no contact spring is assumed. Whilst in the NASTRAN model, the contact spring is assumed by the penalty method to simulate contact connection. Through the numerical simulations, it is recognized that even if the same mesh geometry is applied, generally, these two finite element approaches are not capable of predicting approximately identical unstable frequencies. The ABAQUS approach can predict instabilities of high frequency up to 20 kHz or more, while the NASTRAN approach can only predict some instabilities of high frequency, not all. Moreover, the simulation results also show that both the contact spring stiffness and mesh size have influences to some extent on the prediction results of squeal. The present comparative work illuminates that the modeling method without contact springs is more suitable to predict squealing vibration and noise, comparing to the modeling method with contact springs. It is proposed that one should prefer using the modeling method without contact springs to predict squealing vibration and noise. The proposed study provides the reference for predicting squealing vibration and noise.     

Advanced Friction–Wear Behavior of Organic Brake Pads Using a Newly Developed System

The objective of this study was to investigate the influence of an advanced performance system on the tribological behavior of brake pad material using a specially designed brake pad tester system following standard SAE J-661. The tribological behavior and friction and wear characteristics of the organic brake pad samples were evaluated. During braking tests, the samples, in contact with a cast iron disk, were studied at different disc speeds, temperatures, and braking cycles under a constant pressure. In order to understand the friction and wear behavior, the unworn surfaces, worn surfaces, and wear debris were characterized by means of scanning electron microscopy (SEM) and energy-dispersive X-ray (EDX). Furthermore, the surface characteristics and differences in the wear modes of the brake pad samples were examined. Wear debris was permitted to deform the brake pad surfaces, leading to friction layers and enabling the estimation of the friction behavior of the brake pads. The results showed that the best friction–wear behavior was obtained with lower braking cycles at low speeds and temperature. Thus, the newly developed brake pad tester system proved very effective in evaluating the performance of the brake pad samples.     

高速列车制动片摩擦块尺寸对制动噪声特性的影响

同一工况下,在制动摩擦噪声试验机上使用3种不同尺寸的圆形摩擦块进行制动摩擦噪声对比试验,通过对不同摩擦块尺寸状态下的界面噪声信号进行等效声压级分析和频谱分析,研究摩擦块尺寸对制动噪声特性的影响;对界面磨损形貌采用光学显微镜和二维轮廓仪进行分析,并计算出摩擦界面上的摩擦弧长,以揭示摩擦块尺寸对制动噪声行为的影响机制。结果表明:在试验条件下,摩擦面积相同时,大圆形摩擦块能有效地抑制制动噪声,而中圆形和小圆形摩擦块的制动噪声强度较大;相较于大圆形摩擦块,中圆形和小圆形摩擦块表面出现明显犁沟和剥落等"不平顺"磨损因素会造成高强度的尖叫噪声;大圆形摩擦块相比于中圆形和小圆形摩擦块的摩擦弧长较短,这也是造成大圆形摩擦块状态下制动噪声强度减弱的一个重要因素。