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。     

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。     

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.     

Development and Characterization of C/C-SiC Brake Disc

A new process was developed to produce full-size carbon/carbon-SiC brake discs consisting of two friction layers and a structural layer. Different lengths of chopped carbon fibers were used for the friction layers and structural layer. A preform of each layer was produced by hot-pressing a mixture of resin and carbon fibers. After pyrolyzing the preforms, the layers were joined by hot-pressing. Finally, liquid Si infiltration was performed to obtain a C/C-SiC brake disc. The tensile strength, compressive strength, and bending strength were 40, 46, and 61 MPa, respectively. The density of the disc was 2.1 g/Cm³. The heat transfer coefficient in the vertical direction was 16.5 W/m-°C, and it was 45.9 in the horizontal direction. The friction coefficients obtained under various braking conditions showed stable and suitable values, 0.2–0.6.     

The effect of braking energy on the fatigue crack propagation in railway brake discs

Thermal fatigue cracks can often be found on the friction surface of brake discs used in railway vehicles after a period of usage and include crackle, radial and circumferential patterns. These cracks typically exhibit different initiation and propagation behavior under different braking conditions. In this paper, the effect of braking energy on fatigue crack evolution is analyzed by using experimental testing and numerical simulations. Macro observations show that a significant number of radial cracks appear on the surface of brake discs which operate at 300 km/h, while crackles typically appear after repeated emergency braking (EB) at 200 km/h. No crack growth was observed on disc surfaces after routine braking. The cyclic load that leads to the fatigue crack propagation consists of compressive stress during braking and residual tensile stress after cooling. Simulation results show that the depth of cracks correlates well with the residual tensile stress distribution in brake discs. Breaking tests exposed that the fracture surface of fatigue cracks which were covered by oxides shows nearly elliptic-type. Higher braking energy leads to a hardened layer on the friction surface and oxide generation near the crack edges, which are also important factors that contribute to accelerating 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.     

Gravity casting processing of brake discs: use of partially recycled (Al–Si–Mg)/SiCp composite

Abstract

Brake discs of (Al–Si–Mg)/SiC composite were produced by gravity casting. To this purpose ingots, containing 50 vol.-%of SiC particles, produced by pressureless metal infiltration at Lanxide Corp., were melted, diluted with an unreinforced alloy (thus achieving a SiC content of 30 vol.-%), and cast in permanents moulds. The possibility of repeating the casting process using recycled material was investigated. Brake discs were fabricated by using 50 or 100% of recycled composite. The influence of material recycling on both microstructure and mechanical strength of composite items was studied by X-ray diffractometry, optical and scanning electron microscopy, and X-ray energy dispersive analysis. Tensile tests were carried out on round bars obtained contemporaneously to the discs by casting. Only a small decrease in strength and an increase in inclusion concentration resulted from material recycling. As brake discs have frequently to experience temperature changes, due to the friction occurring during braking, their sensitivity to thermal fatigue was investigated. Thermal cycling tests were carried out in the temperature range 25–220°C. In these conditions, only negligible material weakening was observed after 2000 cycles.     

An experimental study on the energy absorption capacity of thin-walled castings

The energy absorption potential of high-pressure die cast (HPDC) components made of magnesium alloys AM20, AM50, AM60, AZ91 and the aluminium alloy A356 is investigated using a shear–bolt principle. Both quasi-static and dynamic tests have been performed. In addition, single cast plates of AM60 and A356 alloy with different thickness have been tested in order to investigate the effect of plate thickness on the shear–bolt mechanism. It is found that this deformation principle gives an approximately constant average force during the deformation process. Therefore, thin-walled HPDC components can be suitable as energy absorbing components when using the shear–bolt principle. A simple empirical model for prediction of the average shearing force as a function of plate thickness and bolt diameter is proposed.     

Failure analysis as a tool to optimize the design of a ring on disc tribotest investigating the role of surface roughness

The influence of the surface roughness of pearlitic grey cast iron discs on the formation of tribofilms and the evolution of the friction coefficient during a ring on disc tribotest with the addition of magnetite and magnetite–graphite nanopowders as interfacial media was investigated. The roughness parameters of the cast iron discs were varied by electro discharge machining (EDM) and grinding processes, producing four distinct surface roughness conditions. The evolution of the friction coefficient, however, did not reach the steady state for most of the samples and the role of the surface roughness on the friction coefficient could not be identified. Focused ion beam (FIB) microscopy on the cast iron discs was carried out to investigate the microstructure of the discs near the tribosurface. These results showed that the EDM process not only varied the surface roughness, but also changed the microstructure of the cast iron discs, promoting the incipient fusion of the cast iron surface, with the formation of ridges and casting defects (pores). As a result, a layer of rapidly solidified metal with a dendritic microstructure was formed near to the surface of the EDMed discs.     

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。      

Linear eigenvalue analysis of the disc‐brake squeal problem

This paper presents a numerical method to calculate the unstable frequencies of a car disc brake and suggests a suitable analysis procedure. The stationary components of the disc brake are modelled using finite elements and the disc as a thin plate. The separate treatments of the stationary components and the rotating disc facilitate the modelling of the disc brake squeal as a moving load problem. Some uncertain system parameters of the stationary components and the disc are tuned to fit experimental results. A linear, complex‐valued, asymmetric eigenvalue formulation is derived for the friction‐induced vibration of the disc brake. Predicted unstable frequencies are compared with experimentally established squeal frequencies of a real car disc brake. Copyright © 2004 John Wiley & Sons, Ltd.     

Geometry,mechanical properties and mounting of perforated plates for ballistic application

In this paper, the ballistic resistance of perforated plates made of different types of steel, mounting and geometry was investigated. Different types of steel in various heat treatment conditions were tested. Target mounting was also varied: rigid, oblique and hanging. Furthermore, four different perforated plate geometries were tested: two plate thicknesses and two hole diameters. Their behaviour was tested using impact from firing 12.7 mm M-8 API ammunition at eleven perforated plate samples. These samples were placed by means of a steel frame over a 13 mm RHA plate, at two distances. Damaged area on targets was correlated to ballistic resistance of the whole armour to find the optimal perforated plate. It was found that perforated plates, in optimized case offer a frequent fracture of the penetrating core in up to five parts. This debris is unable to penetrate the basic plate, offering mass effectiveness of the whole armour model of 1.76 and the mass effectiveness of the perforated plate of 5.91.     

Properties of reactively cast aluminium–TiB2 alloys

Abstract

A salt base reactive casting process has been employed to produce A356 aluminium casting alloys containing fine dispersions of TiB₂. These have been compared with commercially available Duralcan A356 material with SiC particles which have also been incorporated by a casting technique. Structural, mechanical, and wear properties have been measured. These show that TiB₂ is extremely effective in enhancing modulus in addition to significantly reducing the coefficient of friction when used against an alloy steel plate. The wear rate of the alloy is found to be independent of particle type but is governed mainly by volume fraction, as is the load transition from mild to severe wear. However, the wear mechanisms for TiB₂ and SiC composites are different when the steel disc is taken into account and the wear debris examined. The plate is effectively machined by SiC, resulting in extensive damage of the mating plate. Alloy A356 with TiB₂ additions is made by reactive casting a simple alloy to process and is thereby a viable alternative to low cost Al–SiC cast composites.

MST/1854     

基于摩擦磨损实验的双盘直槽研磨方法的研具选材研究

双盘直槽（double-disc and linear-groove, DDLG）研磨方法是以1个平端面研磨盘和1个具有多条直沟槽的研磨盘为对磨研具,对圆柱滚子的滚动面进行精密加工的新方法。在加工过程中,圆柱滚子沿直沟槽连续供料,在2个研磨盘的摩擦力矩驱动下连续自转。研磨盘材料的选择是搭建双盘直槽研磨设备的基础。为了确定适用于双盘直槽研磨方法的研磨盘材料组合,基于摩擦磨损实验展开相关研究。首先,基于摩擦原理,分析了圆柱滚子的运动状态和研磨盘材料的摩擦特性对研磨效果的影响,并确定了研磨盘材料摩擦系数的筛选条件。然后,通过销-盘摩擦磨损实验测试了铸铁、45钢、黄铜、聚四氟乙烯（polytetrafluoroethylene, PTFE）、有机玻璃（polymethyl methacrylate, PMMA）、125%铸铁基固结磨料和125%树脂基固结磨料等多种备选材料在研磨条件下的摩擦系数、耐磨性和排屑性能。最后,搭建了双盘直槽研磨试验台,通过观察圆柱滚子的自转情况来验证基于摩擦磨损实验的研具选材方法的合理性。通过摩擦磨损实验测得,铸铁和45钢的滑动摩擦系数大,磨削效率高,但耐磨性差,适合用作大去除量场合的上研磨盘材料;有机玻璃的滑动摩擦系数大,耐磨性好,磨削效率高,适合用作小去除量场合的上研磨盘材料;聚四氟乙烯的滑动摩擦系数小,耐磨性好,可用作下研磨盘直沟槽材料;固结磨料的滑动摩擦系数变化大且易堵塞,不适合用作研磨盘材料。研究结果可为双盘直槽研磨设备的设计提供可行的研具选材依据。     

Simulated three-dimensional transient temperature field during aircraft braking for C/SiC composite brake disc

In the present work, a theoretical model of three-dimensional transient temperature field for C/SiC composite brake discs was established by adopting a finite element method according to the theory of energy transformation and transportation. The variation regularities of transient temperature field and internal temperature gradient of the brake discs were obtained. The effects of initial velocity, deceleration and friction coefficient on the highest temperature of the brake discs were also discussed. The heat energy was mainly concentrated on the layer of friction surfaces. The highest temperature of the brake discs under normal landing, overload landing, and rejected take-off landing condition were 869.7 K, 1037.4 K and 1440.3 K, respectively. Furthermore, the highest temperature of the brake discs increased with the increase of the initial velocity and friction coefficient, but decreased with the increase of deceleration. Comparing simulation predictions with experimental results, it is found that the three-dimensional transient temperature field model was valid and reasonable.     

Experimental and numerical analysis of thermal striping in automotive brake discs

In the present study, thermal striping development on friction bands of brake discs is investigated through an experimental and numerical analysis. A test consisting of a series of several hundred severe brakings was carried out on a specific bench at PSA Peugeot Citroën. The experimental observations of the crack network evolution and a numerical analysis of a brake disc with a single crack helped to propose a macroscopic criterion capable of predicting the criticality of the network, namely its ability to lead to the complete failure of the structure. In addition, a numerical analysis of the crack shielding process is developed, whose results are compared with experimental findings.     

超深矿井提升机制动盘热性能分析与优化

超深矿井提升机制动盘在紧急制动过程中由于受到摩擦循环热载荷的作用，内部产生较大的热应力，同时高温会导致制动盘和闸片摩擦制动性能下降甚至失效。针对制动盘制动热性能问题，根据热传导理论和有限元分析方法，建立了制动盘组件三维有限元模型，采取直接耦合方法对制动盘制动过程中的热应力场进行模拟研究，并通过实验验证了仿真参数设置的正确性。分析了闸片数量和排布方式对制动工况下制动盘温度和应力分布的影响。结果表明，在制动阶段，制动盘摩擦面温度先急剧上升，后缓慢下降，摩擦面温度呈现锯齿状波动性变化，制动过程中应力变化规律与温度变化规律相同。原制动盘在制动过程中的最高温度为134.8℃，最大应力为230.2 MPa，高温和大应力区域集中于摩擦面附近；增加闸片数量的制动盘最高温度为142.4℃，最大应力为251.1 MPa，高温和大应力区域同样集中于摩擦面附近；改变闸片排布方式的制动盘最高温度为86.5℃，最大应力为119.1 MPa，高温区域和大应力区域范围较小。由此可知，改变闸片排布方式更能显著降低制动盘温度和应力，并且温度场和应力场分布更均匀。研究结果可为制动盘热性能优化设计提供理论参考。     

Thermal cycles and their effects during friction stir welding of AA7075 thicker plates with and without in-process cooling

Friction stir welding of AA 7075 plates in three different thicknesses such as 10, 16 and 25 mm at natural convection condition was carried out successfully without defects. Water cooled friction stir welds were also produced on 16 mm thick plates. The thermal cycles at different locations of the plate, during the friction stir welding process, were predicted using a three-dimensional thermal model. Mechanical properties of the welds were evaluated using tensile and hardness tests. Weld microstructures were also examined with optical and transmission electron microscopes. The weld hardness values and tensile properties were found to decrease with increase in plate thickness. The use of water cooling was found to improve the weld properties to some extent, although not to the level of base metal. The reasons for this behavior are discussed, correlating thermal cycles, mechanical properties, fracture locations and precipitate morphology.     

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.     

Study of the interaction between microstructure,mechanical and tribo-performance of a commercial brake lining material

The interaction between microstructure, mechanical, and frictional properties of a commercial brake lining material (BLM) was investigated in order to correlate them to braking performance. For this purpose, a Scanning Electron Microscope (SEM) with energy dispersive X-ray (EDX) mapping and spectrum were used to identify and analyze different constituents. The mechanical properties were determined using compression test. Relevant physical properties (density and porosity) were determined using standard test methods. The friction coefficient and wear behavior of the friction material on contact with the grey cast iron disc were established using a pad-on disc tribometer. The results have shown that the brake lining material contains phenol resin such as the matrix and other various ingredients, including silica, rock and mineral filler reinforcement, barium sulfate and carbon-rich particles as filler and brass particles as friction modifier. It had a varied amount and size up to 1 mm for brass particles. The density and porosity were 1.8 g cm⁻³ and 7%, respectively. The investigated material exhibited excellent mechanical properties in the normal solicitation direction. The average friction coefficient was about 0.65, whereas the friction coefficient was stable. The different actions of various ingredients in terms of their effects on the friction and wear behavior of the BLM could be related to their different bonding strengths with the resin matrix and their different abilities to form friction films (third-body layer) on the surfaces of the material and transfer films on the counterpart cast iron surface in relation to the surface temperature evolution and mechanical properties.