Effect of carbon fiber content on the friction and wear performance of paper-based friction materials

In order to get homogeneous pores distribution of friction materials, four kinds of micron-level carbon fibers reinforced paper-based friction materials were prepared. Experimental results showed that the porosity of samples decreased with the increase of carbon fiber content. Pores formed in micrometer-level fibers reinforced friction materials were more regular than friction materials reinforced by millimeter-level fibers. The tensile strength of samples decreased with the increase of carbon fiber content. The wear rate of samples increased with the increase of carbon fiber content. The sample with 55% carbon fibers exhibited the best friction stability and anti-shudder performance under oil lubricated conditions.     

Distinguishing the effects of adhesive wear and thermal degradation on the tribological characteristics of paper-based friction materials under dry environment: A theoretical study

Adhesive wear and thermal degradation are the main aging mechanisms of paper-based friction materials. However, how these aging mechanisms affect the tribological characteristics of such materials is not fully understood. In this paper, the respective influences of the two aging mechanisms on the tribological characteristics of the friction materials are investigated through simulation. It is assumed that adhesive wear pre-dominantly affects the surface topography, while thermal degradation significantly affects the mechanical properties of the friction material. The simulation results show that the static friction coefficient and both normal and tangential contact stiffnesses increase due to adhesive wear, but decrease due to thermal degradation. These trends are qualitatively in agreement with experimental observations reported in the literature and our previous work.     

Performance and evaluation of eco-friendly brake friction materials

Eco-friendly brake friction materials were formulated without copper, lead, tin, antimony trisulfide, and whisker materials, to minimize their potential negative environmental impacts. A combination of scanning electron microscopy with energy dispersive microanalysis, profilometry, and thermogravimetry allows successful analysis of friction surface and thermal stability of friction materials. Extension evaluation method was applied to rank the friction materials using multi-parameter criteria, including friction, wear, thermal stability, cost of raw materials, and parameters from the brake effectiveness evaluation procedure (BEEP) assessment. The eco-pad (sample E) exhibited the best overall quality, expressed as the weighted average dependent degree in extension evaluation.     

Effects of ZrSiO4 in non-metallic brake friction materials on friction performance

The effects of ZrSiO₄ (zirconium silicate or zircon) as an abrasive on brake friction performance and friction layers of non-metallic brake friction materials were evaluated. The experimental results indicated that ZrSiO₄ enhances friction coefficient, but depresses wear rate. However, ZrSiO₄ can improve the negative wear rate of the friction materials. The formation and development of friction layers are complex so that the friction layers formed during friction process were carefully characterized using scanning electron microscopy (SEM), light microscopy (LM), and X-ray diffraction (XRD) methods. Following characteristics of friction layers were identified—(1) dynamic behavior: the structure of friction layers changes at the different surfacial positions and across sample's thickness; (2) friction condition dependence: formation of friction layers depends upon temperatures, time, and thermal history such as fade and recovery; and (3) compositional dependence: the compositions of friction surface and bulk differ, nevertheless the bulk's composition determine the friction layers. The phenomena as baryte films, altered layers, iron patches, and zircon loose areas formed on the friction surfaces were observed. Baryte films were detected on the friction surfaces of Zr-0 (sample without zircon). Baryte films have positive effect on wear property, but the films disappear in the presence of ZrSiO₄. The amount of carbonaceous materials decreases with the increase in ZrSiO₄. Only negligible thickness of altered layers was found on the friction surfaces of Zr-0 sample, while samples containing zircon show out relatively thick altered layers. Both iron-patches and zircon loose areas increase with the ZrSiO₄ contents. The relationships among formulation, friction performance, and friction surfaces were summarized.     

纳米SiC对半金属摩擦材料性能的影响

通过对比试验,研究纳米SiC对半金属摩擦材料性能的影响。试验表明,在半金属材料中,用纳米SiC代替普通的SiC粉体,摩阻材料的摩擦系数并没有明显的改善,而磨损率却大大地增加。借助扫描电镜(SEM)对混合粉体和摩擦表面的观察以及试验数据的分析,找到引起磨损增大的原因。     

On the friction and wear behavior of PTFE composite filled with rare earths treated carbon fibers under oil-lubricated condition

Carbon fibers (CF) were surface treated with air-oxidation, air-oxidation followed by rare earths (RE) treatment and RE treatment, respectively. The friction and wear properties of the polytetrafluoroethylene (PTFE) composites filled with differently surface treated carbon fibers, sliding against GCr15 steel under oil lubrication, were investigated on a reciprocating ball-on-disk UMT-2MT tribometer. The worn surfaces of the PTFE composites were examined using a scanning electron microscopy (SEM). Experimental results revealed that surface treatment of carbon fibers reduced the wear of CF-reinforced PTFE composites. Among all the treatments to carbon fibers, RE treatment was the most effective and lowest friction and wear rate of CF-reinforced PTFE composite was exhibited, owing to the effective improvement of the interfacial adhesion between the carbon fibers and PTFE matrix.     

纳米颗粒增强铜基摩擦材料的摩擦学性能

基于粉末冶金法分别制备了纳米氮化铝和纳米石墨增强铜基摩擦材料,研究了纳米颗粒对铜基摩擦材料的摩擦磨损和耐热性能的影响规律.采用扫描电子显微镜(SEM)分析了材料的微观结构和磨损形貌,并利用惯性摩擦磨损试验机考核其摩擦学性能.实验结果表明:与未添加纳米颗粒的摩擦材料相比,添加纳米氮化铝和纳米石墨的摩擦材料的摩擦因数高而稳定,且随接合次数增加无明显衰退现象;耐磨性能分别提高了25％和11％;耐热性能分别提高了18％和25％.未添加纳米颗粒的摩擦材料的磨损机制主要为犁沟式磨料磨损,纳米氮化铝和纳米石墨能减少摩擦材料的磨料磨损,从而增强了摩擦材料的耐磨性.实验结果显示,纳米氮化铝和纳米石墨可显著提高铜基摩擦材料的摩擦学性能.     

Comparison of tribological properties of various carbon plastics under water-lubricated sliding friction

Carbon plastics based on polyphenylene sulfide matrix and carbon fabric have been synthesized using various technological procedures. Comparative triboengineering test results are cited for pure polyphenylene sulfide, carbon plastics on its base, and carbon plastics of grade FUT and UGET. Carbon plastics based on polyphenylene sulfide show higher wear resistance as compared to FUT and UGET. Carbon plastics based on polyphenylene sulfide with slight addition of C₆₀ fullerene show even higher wear resistance.     

Effects of filler crystal structure and shape on the tribological properties of PTFE composites

In this paper, effects of filler crystal structure and shape on the friction and wear properties of potassium titanate whisker (K₂Ti₄O₉ whisker, K₂Ti₆O₁₃ whisker), TiO₂ whisker and TiO₂ particle filled polytetrafluoroethylene (PTFE) composites under dry friction conditions were studied. Meanwhile the influence of filler content, sliding duration, test speed and load were also investigated. Experimental results show that the friction coefficients of various PTFE-based composites are weakly dependent on filler shape but they are more strongly dependent on filler crystal structure. However, for improving the anti-wear property of PTFE, filler crystal structure has less importance than filler shape in the wear-reducing action of PTFE-based composites, and whisker-like filler is better than particle-like filler.     

Calculation of tribological characteristics of composite materials

We present the formulas for calculating the friction coefficient when fibrous composite material is rubbed against the homogeneous rigid material. The wear of the composite is taken into consideration in the calculation.     

Effect of pin specimen contact length in the sliding direction on tribological results of pin-on-disc tests

Tribological properties of a material depend on a wide range of parameters/conditions. While some of them are obvious, some are quite subtle. One of these subtle parameters has been identified and reported here. Under sliding conditions, whenever surface layers are formed due to the interaction at the sliding interface (e.g., tribochemical interaction), the resultant tribological response has been conjectured to depend upon the relative length of the pin, parallel to the sliding direction, with respect to the corresponding length of the disc track. The results obtained from the experiments reported in this paper as well as those reported by different researchers in the past, furnish evidence to support this conjecture. It can be considered as a general parameter because of this wide spectrum of applications. It is shown in this paper that this parameter helps in selecting the optimum contact geometry of the pin under various experimental conditions. This might reduce the observed scatter in tribological test results. Such a study leads to the conclusion that, for tribological testing, a square/rectangular contact configuration of pin is preferable to a circular one. This revised version was published online in June 2006 with corrections to the Cover Date.     

Investigation of mechanical and tribological properties of amorphous diamond-like carbon coatings

We investigated the mechanical and tribological properties of amorphous diamond-like carbon (DLC) coatings deposited on Si(100) by a pulsed bias deposition technique. Tribological studies were performed using a pin-on-disc (POD) apparatus under a normal load of 6.25 N and at 10% relative humidity, with a ruby pin as a slider. Hardness measurements were performed using a nanoindenter and apparent fracture toughness using indentation techniques. We studied the influence of residual stresses on apparent fracture toughness. The data revealed that the thickness, hardness and compressive stress of the coating play different roles in the apparent fracture toughness. Crack initiation is influenced by the thickness and hardness of the coating, whereas crack propagation is influenced by the compressive stress in the film. The apparent fracture toughness of DLC coatings increased with coating hardness.     

A new tribometer for friction and wear studies of dental materials and hard tooth tissues

This paper presents a new tribometer developed for a study of the tribological behaviours of dental materials and hard tooth tissues. The device simulates oral kinematic conditions and the loading produced during masticatory process. The tribometer is similar to the existing devices regarding the kinematic features, i.e. it produces an adjustable oscillating movement. However, the device machine is equipped with a unique pneumatic system of loading controlled via computer by special software called TOOTHY. The programmable system allows easy adjusting of the loading parameters such as the magnitude of normal force and its amplitude or pattern of cyclic loading. In this way different combinations of loads can be applied thus making the investigation of different wear situations possible. The device has two full bridge strain gauges for the measurement of loading and friction forces, by which the coefficient of friction is determined.The use of the tribometer is illustrated by a comparative study of tribological behaviour of human enamel subjected to two- and three-body friction, and to two different loading patterns as well. The obtained results are discussed.     

The influence of added carbon nanotubes on the properties of the carbon‐fiber‐reinforced paper‐based wet clutch friction materials

Different carbon nanotubes (CNT) content was used to investigate the influence on physical properties, microstructure, tribological behaviour and thermal endurance properties of the materials. Experimental results show that the bulk density of the specimens increase with the increase of the CNT content, and the open porosity of the samples gradually reduced, whereas the CNT content increases. When comparing the tribological properties of the specimens with different CNT content, specimens that contain 4 wt.% carbon nanotubes show the highest dynamic friction coefficient and the lowest variation coefficient of the dynamic friction coefficient. Moreover, the specimens exhibit more thermal stability and lower weight loss after adding the CNT. Copyright © 2015 John Wiley & Sons, Ltd.     

Coefficient of friction for aluminum in contact with a carbon fiber epoxy composite

In bolted joints, a large part of the load is transferred by friction. The objective of this investigation is to measure the coefficient of friction for carbon fiber epoxy matrix composite, HTA-6376, in contact with aluminum, 3637-77, in reciprocal sliding. During testing, the coefficient of friction increased initially with number of cycles and after reaching a maximum, slowly decreased. The initial coefficient of friction is approximately 0.23 and the peak coefficient of friction after wear in is approximately 0.68. The coefficient of friction is independent of normal load. During wear, cracks are formed at the fiber–matrix interface, which causes the matrix layer on the original composite surface to break off in pieces. It also causes single fibers or groups of fibers to be broken off and removed from the surface. Pieces of carbon fiber caused depressions in the aluminum surface. The wear debris is reattached to the composite surface but not to the aluminum surface.     

Interaction between friction surfaces and lubricating materials of the 2H-MoS2 type

The paper presents an analysis of investigations concerning the concept of the molecular-mechanical origin of the friction and fatigue mechanism as applied to solid lubricants having a structure of the 2H-MoS₂ type.     

无石棉制动带摩擦磨损性能预测系统的研究

以实验为基础,利用Matlab软件平台上的BP神经网络工具箱,建立并训练了无石棉制动带复合纤维优化设计中所需的各纤维组分体积百分含量与制动带摩擦磨损性能指标之间的人工神经网络映射模型。研究结果表明,该BP网络映射模型的网络误差小,映射结果与实际实验结果的吻合度高,能较为准确地预测复合纤维组成对应制动带的摩擦磨损性能指标,解决了二者关系无法用显函数表征的问题,为制动带无石棉复合纤维组成的优化设计奠定了基础。     

Preparation and properties of Fe3Al-based friction materials

A promising friction material, Fe₃Al intermetallics-based friction material, was prepared by powder metallurgy (PM). The preparation technology and properties were discussed in this paper. The results show that the novel Fe₃Al intermetallics-based friction material possesses low density, high strength and smooth friction coefficient, as well as excellent wear and oxidation resistance at high temperatures. The wear mechanisms of this material are different at different friction stages, mainly including: particles abrasion, plastic deformation, crack nucleation and propagation, brittle split and oxidation wear.     

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。     

A test method to investigate the tribological behaviour of friction materials under ultrasonic fretting conditions

To investigate and understand the tribological behaviour of high-frequency tribosystems such as ultrasonic motors, a specific test method is necessary. This work reports on the construction of a test machine to evaluate the friction and wear behaviour of friction materials under ultrasonic fretting conditions, as well as giving some representative experimental results. Hard/soft (steel/polymer) and hard/hard (steel/alumina, alumina/alumina) couples were studied with respect to their application as contact materials in ultrasonic motors. Investigation of friction behaviour at high frequencies showed that friction-induced vibrations lead to friction forces of much lower magnitude than predicted by quasistationary friction coefficients obtained for sliding friction. The wear behaviour is characterised by abrasive, adhesive, fatigue and oxidative mechanisms, depending on the mating materials. For polymeric friction materials, the influence of fibre reinforcement and the incorporation of PTFE as a solid lubricant were evaluated. The presence of PTFE resulted in a strong improvement of both friction and wear behaviour.