High temperature wear of semimetallic disc brake pads

The wear of friction materials as measured by isothermal techniques remains insensitive to temperature to about 230°C (drum) and increases exponentially at higher temperatures. The high temperature wear of organic friction materials was found to be related to the thermal decomposition of the organic ingredients with an activation energy of 4–10 kcal mol^?1. The results indicate that high temperature wear of semimetallic friction materials is controlled by thermal degradation of organic ingredients as it is for organic friction materials.     

The chrysotile content of the wear debris of brake linings

Electron microscopy of the wear debris from brake linings has indicated that the particle size is about 10 nm, the characteristic chrysotile asbestos fibre being almost absent. No evidence of the chrysotile structure was found by either X-ray diffraction or thermal analysis and it is suggested that the structure has been reduced to an amorphous state or to forsterite.     

Neural network prediction of brake friction materials wear

Wear of brake friction materials depends on many factors such as temperature, applied load, sliding velocity, properties of mating materials, and durability of the transfer layer. Prediction of friction materials wear versus their formulation and manufacturing conditions in synergy with brakes operating conditions can be considered as a crucial issue for further friction materials development. In this paper, the artificial neural network abilities have been used for predicting wear of the friction materials versus influence of all relevant factors. The neural model of friction materials wear has been developed taking into account: (i) complete formulation of the friction material (18 ingredients), (ii) the most important manufacturing conditions of the friction material (5 parameters), (iii) applied load and sliding velocity of the friction material both represented by work done by brake application, and (iv) brake interface temperature.     

Wear mechanisms for asbestos-reinforced automotive friction materials

An asbestos-reinforced automotive friction material was evaluated by dynamometer testing for its wear characteristics at elevated temperatures. Wear rate constants were obtained for different temperatures, and an activation energy was obtained for the high-temperature wear process. It is concluded that the wear is controlled by a pyrolysis mechanism at elevated temperatures (above 450°F drum temperature) and by adhesive and abrasive mechanisms at low temperatures.     

Effects of potassium titanate fiber on the wear of automotive brake linings

Asbestos reinforcing fiber in an automotive friction material was replaced by an experimental ingredient having better thermal stability and the effects on wear and friction were studied. A friction materials test machine (SAE J661a) was used to determine friction and wear, under constant energy output conditions, as a function of temperature between 121 and 343°C (250 and 650°F). When potassium titanate fiber replaced one-half of the asbestos in a standard commercial lining, with a 40% upward adjustment of phenolic resin content, wear above 204°C (400°F) was improved by 40% and friction by 30%. Tests on a full scale inertial dynamometer supported the findings of the sample dynamometer tests. It was demonstrated that the potassium titanate fiber contributes directly to the improvement in wear and friction.     

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.     

Wear mechanisms of the C/SiC brake materials

The C/SiC brake materials were fabricated by chemical vapor infiltration combined with liquid melt infiltration. The wear mechanisms of C/SiC brake materials were investigated. The main wear mechanisms were grain-abrasion, oxidation-abrasion, fatigue wear, and adhesive wear. These wear mechanisms always occurred simultaneously , and showed mutual enhancing effects between them. Grain-abrasion mainly was the result of hard SiC grain action. Adhesive wear could cause high wear rates and a large unstable friction coefficient. Si was the significant factor on the adhesive wear, so Si in the C/SiC brake materials must be removed.     

Comparison of Chase and inertial brake Dynamometer testing of automotive friction materials

For effective and safe automotive brake system applications, friction materials must meet certain minimum requirements for performance, noise and durability. To ensure this, friction materials are subjected to a series of vehicle tests on a test track or on the road before they are released as commercial products.While vehicle tests are expensive, time consuming and subject to road conditions and weather variability, brake dynamometer testing in the laboratory is faster and less costly to screen or verify friction material characteristics. Furthermore, because of the capability to control test conditions precisely, a brake dynamometer serves as an excellent tool for the research and development of friction materials.In the U.S.A. two major types of brake dynamometers are commonly used: the inertial dynamometer which evaluates a full size brake or a brake system and simulates vehicle braking well, but is time consuming and expensive, or a smaller Chase dynamometer that features low capital expenditure and shorter test time using a small friction material sample against a large drum. The Chase dynamometer does not simulate brake conditions as well as the inertial dynamometer, and therefore is used primarily for rapid screening and/or for quality control only.The correlation, or the lack of it, between these two brake dynamometers is discussed in this paper. Friction and wear data from both test systems on several friction pairs under various temperature, sliding speed and load conditions are compared and discussed. The materials used were (a) non-asbestos organic disc pads against cast iron rotors, (b) semimetallic disc pads against cast iron rotors and (c) non-asbestos organic disc pads against copper rotors.     

Some relations for determining the wear of composite brake materials

Investigation of several types of composite brake materials showed that both the mean temperature of the friction surface and the wear rate of the materials vary non-linearly as a function of load and speed. The presence of some metal inclusions leads to a less complex non-linear relationship of the wear rate.     

Effects of moisture adsorption on laboratory wear measurements of brake friction materials

As is the case for tribological systems in general, the wear of brake friction materials, sliding against brake discs or drums, is influenced by many factors. This dependency requires very complicated test matrices in order to characterize the range of lining wear properties. Furthermore, the wear rate is very low under normal operating conditions, and thus a substantial amount of test time is needed before the wear progresses to reach a measurable amount. One way to reduce the test time is to use small brake material samples and to measure their weight change with an accurate electronic balance. A laboratory-scale, block-on-disc brake testing machine was used to measure the wear rate of two brake friction materials against cast iron. While conducting these tests, the lining specimen weight changes caused by moisture adsorption were found to be similar in magnitude to the weight change caused by wear. These effects were studied using weight change experiments with both desiccants and heating. Gravimetric methods for wear measurement in porous materials like brake linings are problematic. Several alternatives are offered for mitigating this problem.     

汽车制动器摩擦材料的研究现状和发展

介绍汽车制动器摩擦材料的研究现状。探讨半金属基摩擦材料、非石棉有机摩擦材料和粉末冶金摩擦材料的优缺点。提出汽车制动摩擦材料研究的发展趋势。     

The effect of Al2O3 on the friction performance of automotive brake friction materials

This study consists of two stages. In the first stage, bronze-based break linings were produced and friction-wear properties of them were investigated. In the second stage, 0.5%, 1%, 2% and 4% alumina (Al₂O₃) powders were added to the bronze-based powders and Al₂O₃ reinforced bronze-based break linings were produced. Friction–wear properties of the Al₂O₃ reinforced samples were aslo investigated and compared to those of plain bronze-based ones. For this purpose, friction coefficient and wear behaviour of the samples were tested on the grey cast iron disc. The hardness and density of the samples were also determined. Microstructures of the samples before and after the sintering and the worn surfaces of the wear specimens were examined using a scanning electron microscope (SEM). The sample compacted at 350 MPa and sintered at 820 °C exhibited the optimum friction–wear behaviour. With increase in friction surface temperature, a reduction in the friction coefficient of the samples was observed. The lowest reduction in the friction coefficient with increasing temperature was for the 2% and 4% Al₂O₃ reinforced samples. The SEM images of the sample indicated that increase in Al₂O₃ content resulted in adhesive wear. With increase in Al₂O₃ content, a reduction in mass loss of the samples was also observed. Overall, the samples reinforced with 2% and 4% Al₂O₃ exhibited the best results.     

Development of fly ash-based automotive brake lining

Coal-fired power plants all over the world generate huge amounts of fly ash each year, 70 million tons of which are produced in the United States alone. Only 40% of all fly ashes generated in the USA find beneficial applications and rest have to be disposed off, which is burden for the generation industry. Fly ash particles possess certain characteristics that make them suitable for use in friction composites as a filler material. An attempt has been made through this research to incorporate more than 50 wt% of fly ash particles in automotive brake lining friction composites. This paper presents the research carried out on development of friction composites, using fly ash obtained from a specific power plant in Illinois. Ingredients such as phenolic resin, aramid pulp, glass fiber, potassium titanate, graphite, aluminum fiber and copper powder were used in the composite development phase, in addition to the fly ash. The developed brake lining composites have exhibited consistent coefficients of friction in the range of 0.35–0.4, and wear rates lower than 12 wt%.     

电感式磨粒传感器中铁磁质磨粒特性仿真研究

针对机械装置的在线监测传感器,模拟了铁磁质磨粒通过传感器过程中传感器线圈的磁场和感应线圈的感应电压瞬态变化特性.考虑了线圈与铁磨粒的材料、线圈匝数和激励线圈的输入电压等因素,应用Jmag Designer I0.4软件建立了传感器的二维有限元模型.仿真结果揭示了磨粒运动过程中线圈磁场与感应线圈中感应电压的变化规律,获得了感应电压与球形磨粒的直径大小的立方成正比,与磨粒运行速度成正比.研究结果对于电感式磨粒传感器的开发具有重要的指导价值.     

Effect of rubber component on the performance of brake friction materials

Various composite friction materials containing 40 vol.% organic binder (phenolic resin plus styrene–butadiene–rubber (SBR)) with varying phenolic-resin/SBR ratio were prepared. The content of phenolic resin in each composite was indicated by the resin value (RV) index ranging between 0 and 100%. The composites with RVs greater than 50% form resin-based friction materials in which the primary binder is the phenolic resin. For RVs less than 50%, the composites become the rubber-based materials where the primary binder is the SBR. The analysis of mechanical properties exhibited that the conformability of the composites increases upon incorporation of SBR. The frictional analysis revealed that type of polymeric binder, i.e. resin or rubber, dominates greatly the frictional behavior of the composites. The increment of friction force and higher improvement in the frictional fade and recovery with sliding velocities are the general features of rubber-based friction materials. It was attributed to the inherent properties of rubber on the viscoelastic response at higher sliding velocities and entropic contribution on the mechanical properties at higher temperatures. The wear rate of resin-based materials and its drum temperature is lower than those of rubber-based materials. It was attributed to the strongly adhered multilayer secondary plateaus formed on the surface of resin-based materials.     

Prediction of brake friction materials recovery performance using artificial neural networks

The brake friction materials in an automotive brake system are considered as one of the key components for overall braking performance of a vehicle. The sensitivity of friction material performance and accordingly brake performance, versus different operating regimes, has always been an important aspect of its functioning. In this paper, the influences not only on the brake operation conditions but also on the formulation and manufacturing conditions of friction materials have been investigated regarding friction materials recovery performance by means of artificial neural networks. A new neural network model of friction material recovery performance, trained by the Bayesian Regulation algorithm, has been developed.     

Effect of wear debris on wear in rolling-sliding motion

The effect of wear particles on wear was investigated using a four-ball extreme pressure lubricant test apparatus. The wear particles present in both filtered and unfiltered oil samples were examined using a duplex Ferrograph analyser and a bichromatic microscope. The wear track widths were measured for various wear modes and were found to increase if the wear debris was recirculated. The size of the wear particles increased with test duration.     

A pin-on-disc investigation of novel nanoporous composite-based and conventional brake pad materials focussing on airborne wear particles

Wear particles originating from disc brakes contribute to particulate concentration in the urban atmosphere. In this work novel nanoporous composite-based and conventional brake materials were tested against cast-iron discs in a modified pin-on-disc machine. During testing airborne wear particles were measured online and collected on filters, which were analysed using SEM and EDX. The morphology of airborne wear particles containing elements such as iron, oxygen, and copper is presented. These results show that two of the nanoporous materials generated 3-7 times less airborne wear particles than the conventional materials. Both the conventional and nanoporous materials displayed a bimodal number distribution.     

A pin-on-disc investigation of novel nanoporous composite-based and conventional brake pad materials focussing on airborne wear particles

Wear particles originating from disc brakes contribute to particulate concentration in the urban atmosphere. In this work novel nanoporous composite-based and conventional brake materials were tested against cast-iron discs in a modified pin-on-disc machine. During testing airborne wear particles were measured online and collected on filters, which were analysed using SEM and EDX. The morphology of airborne wear particles containing elements such as iron, oxygen, and copper is presented. These results show that two of the nanoporous materials generated 3–7 times less airborne wear particles than the conventional materials. Both the conventional and nanoporous materials displayed a bimodal number distribution.     

Acoustic radiation from modal vibration of automotive brake drum

The vibro-acoustic characteristics of an automotive brake drum is studied by applying a hybrid approach, which combines a numerical vibration analysis with an analytical acoustic solution. Specifically, structural vibration of a drum is investigated with the numerical finite element analysis, and vibratory displacements of the outer surface of the drum is approximated by simple mathematical expressions. Then, radiation of sound from the drum vibration is calculated using well-known theoretical solutions based on the simplified modal displacements. Finally, the calculation results are compared with those obtained by full numerical analyses. The results show that the numerical-analytical hybrid method allows relatively accurate calculation of vibro-acoustic properties of a brake drum under realistic boundary conditions.