The effect of fibre reinforcement on the friction and wear of polyamide 66 under dry rolling–sliding contact

An investigation into the effect of fibre reinforcement on the friction and wear of PA66 in rolling–sliding contact is reported. Three types of short fibre—aramid, carbon and glass—were examined with the composites running against identical materials in a twin disc machine. It was found that the aramid-fibre reinforcement did not significantly alter the friction of the matrix material. However, both the carbon-fibre and glass-fibre reinforcement reduced the coefficient of friction substantially. Wear of the aramid- and carbon-fibre composites was essentially linear with time and generally around ten times greater than that of the unreinforced material. The wear of the glass-fibre composite was complex with an initial period where the wear rate was similar to that of the unreinforced material. After a significant depth of wear had occurred the wear rate changed to a value similar to, but slightly higher than, that of the other reinforced materials.It appears that one of the major benefits of introducing fibre reinforcement, particularly glass, is that it reduces the coefficient of friction and hence allows the material to be used for higher duties without exceeding the softening point of the matrix. This increase in duty is, however, at the expense of an increased wear rate and shorter component life.     

A testing device for rolling–sliding behavior in harsh environments: the twin-disk cryotribometer

Understanding the mechanical behavior of angular contact ball bearing contacts in extremely harsh environments has led to the development of specialized apparatus. This device simulates the rolling–sliding behavior of elliptical contacts where the dynamic and kinematic conditions are perfectly controlled. Such a device facilitates several types of analyses: that of mechanically induced surface damage, that of transfer film, that of characterizing surface treatments and surface coatings, and that of thermal phenomena at the contact. Moreover the testing device allows the experimental confirmation of theoretical models developed for determining bearing lifetimes. First we shall describe the testing device end afterwards we shall present results for each type of analysis mentioned above.     

Calculation of sliding power loss in spur gear contacts

An engineering-level calculation model for sliding power loss in spur gear contacts is presented. Teeth contact through the line of action is modelled as a constantly changing roller contact whose radius, speed, and load can be calculated from the gear geometry under the given operating conditions. The gear mesh cycle is approximated by a large number of elastohydrodynamic contacts. A constant film thickness and a Hertzian pressure distribution are assumed in each contact. The model includes non-Newtonian lubricant behaviour together with temperature and mixed lubrication effects in contact. The numerical solver is reasonably fast in evaluating effectively the sliding power loss dependence on the essential gear and lubricant parameters. The features and behaviour trends of the calculated sliding power losses have a close similarity with published results obtained from measurements and experiment-based power loss models with mineral oil. The limiting shear stress of the lubricant is observed to have an essential role in the power loss behaviour especially at high loads.     

The role of surface roughness in the friction of sliding contacts

Results are presented of studies to assess the role of surface roughness in the friction of sliding contacts. A model of the surface roughness uses conical steel needles. A theoretical model based on the mechanics of interaction is included. Experimental and calculated results are discussed in relation to real engineering surfaces and the models compared     

Viscosity–pressure–temperature behaviour of mineral and synthetic oils

A new high‐pressure viscometer that can measure viscosity at pressures up to 0.8 GPa has been developed in the authors' laboratory. The ‘modulus equation’ has been used to compare the behaviour of mineral and synthetic lubricants. Among the oils investigated there was one ester that biodegraded rapidly both before and after ageing in a long‐term test‐rig operation. To facilitate a comparison or application of the results to other oils, an analysis of the correlation between the viscosity—pressure coefficient and the kinematic viscosity measured at atmospheric pressure has been provided. A prediction of lubricant film thickness based on high‐pressure viscosity data is compared with film thickness measurements in a roller bearing.     

Traction and wear of an elastomer in combined rolling and sliding

Under combined rolling and sliding materials can experience millions of cycles as well as complex loading and slip conditions, which can dramatically affect their friction and wear behaviour. It was shown that for a carbon black‐filled natural rubber compound in combined rolling and sliding contact with a smooth alumina coated disk, the traction coefficient, as a function of slip percent, was dependent upon the normal load and independent of rolling velocity. The wear rate of this material pair was found to be independent of slip percentage as well as rolling velocity but dependent upon sliding distance. The wear rate was found to be approximately the same for all tested cases (K ~ 1 × 10⁻⁴ mm³·Nm⁻¹). The worn profiles of the ball specimens showed that this wear occurred preferentially on the left side (inner radius) of the contacting area. Copyright © 2015 John Wiley & Sons, Ltd.     

The effect of gear oil viscosity and friction reducer type on transmission efficiency

The effects of gear oil viscosity and friction reducer type on transmission efficiency have been investigated using the manual transmission and hypoid rear axle of a typical Japanese car. A reduction in the viscosity of the oil improved the efficiency of the manual transmission but led to positive and negative effects in the rear axle, depending upon operating conditions. The effect of the friction reducer varied according to the type of EP additive used, indicating the necessity of preliminary investigations of compatibility with EP additives before adding friction reducers to gear oils.     

On the influence of test parameters on friction and wear of ceramics in oscillating sliding contacts

The tribological behaviour of different ceramics in contact with steel was studied for the case of oscillating sliding motion with a ball-on-disc apparatus. The influence of several test condition parameters was investigated by a systematic variation of the stroke, frequency, and normal load at room temperature in laboratory air at different levels of relative humidity. Each of the four parameters was varied in three stages. While the coefficient of friction was only mildly influenced by the operational variables, the coefficient of wear showed great variations and depended strongly on the humidity of the surrounding air. The effect of the operational variables and of the humidity on friction and wear varied for the different materials under investigation.     

Influence of sliding velocity on friction force in rubber seal rings under reciprocal motion

The influence of sliding velocity on the value of maximum and steady friction force in rubber seal rings under reciprocal motion is studied. It is established that the nature of the change in a static friction force and a steady-state friction force as a function of the sliding velocity is the same all other conditions being equal. The greater the sliding velocity, the faster the decrease and stabilization of a friction force after endurance of rubber seal rings in fixed contact with a cylinder. The maximum of the friction force dependence on the velocity in an investigated pair decreases with increasing temperature of a sealed medium.     

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.     

Contact and thermal analysis of an alumina—steel dry sliding friction pair considering the surface roughness

In the present study, finite element transient contact and thermal sliding simulation and temperature measurement of dry sliding friction were performed in order to analyse the real contact area and temperature developed in the contact region. Real 3D surface worn topographies were taken into consideration, at macro and intermediate stages. The calculated real contact area has been changing in time and space in the course of sliding. The sliding components were high purity alumina ceramic palettes and 100Cr6 steel with constant accelerated motion. The calculated temperature results are in good agreement with the temperature data measured. Heat partition was changing in time during sliding. The developed algorithm based on incremental FE technique can characterize real processes.     

Impact of Cr3C2/VC addition on the dry sliding friction and wear response of WC–Co cemented carbides

Two grades of WC–10 wt.%Co cemented carbide with or without addition of Cr₃C₂/VC grain growth inhibitor during liquid phase sintering were produced with the goal to investigate their reciprocating sliding friction and wear behaviour against WC–6 wt.%Co cemented carbide under unlubricated conditions. The tribological characteristics were obtained on a Plint TE77 tribometer using distinctive normal contact loads. The generated wear tracks were analyzed by scanning electron microscopy and quantified topographically using surface scanning equipment. The post-mortem obtained wear volumes were compared to the online assessed wear. Correlations between wear volume, wear rate and coefficient of friction on the one hand and sliding distance and microstructural properties on the other hand were determined, revealing a significant influence of Cr₃C₂/VC on the friction characteristics and wear performance.     

Effect of temperature on friction and oscillating sliding wear of dense and porous 3Y-TZP zirconia ceramics

Microstructures of 3 mol% Y₂O₃-ZrO₂ (3Y-TZP) with systematically varying porosity up to about 15% were produced by sintering. Hardness and fracture toughness of the ceramics as well as the amount of tetragonal, cubic and monoclinic phase were measured. Wear tests were carried out on the different self-mated microstructures under dry reciprocating sliding contact using ring-on-block geometries in air at five different contact temperatures up to 500°C. The microstructures and worn surfaces were extensively analysed using scanning electron microscopy (SEM) and X-ray diffraction techniques. The experimental results revealed a reduction of the amount of wear (independent of porosity) by more than one order of magnitude compared with room temperature if the test temperature was increased to 250°C. Between room temperature and 250°C, wear increased with increasing porosity while at 500°C the highest wear was measured on the dense structure. Microscopic observations showed that plastic deformation, surface layers consisting of compacted wear debris and also intercrystalline, transcrystalline or delamination type fracture influenced friction and wear.     

The effect of lateral vibrations on transport and friction in nanoscale contacts

We demonstrate that lateral vibrations of a substrate can dramatically increase surface diffusivity and mobility and reduce friction at the nanoscale. In contrast to the enhancement of diffusion and mobility that has a resonance nature, the reduction of friction does not exhibit pronounce resonance features. We find an abrupt dilatancy transition from the state with a small tip–surface separation to the state with a large separation as the vibration frequency increases. Dilatancy is shown to play an essential role in dynamics of a nanometer-size tip which interacts with a vibrating surface. Atomic force microscopy (AFM) experiments are suggested which can test the predicted effects.     

The influence of surface roughness and the contact pressure distribution on friction in rolling/sliding contacts

A numerical contact model is used to study the influence of surface roughness and the pressure distribution on the frictional behaviour in rolling/sliding contacts. Double-crowned roller surfaces are measured and used as input for the contact analysis. The contact pressure distribution is calculated for dry static contacts and the results are compared with friction measurements in a lubricated rolling/sliding contact made with a rough friction test rig. The mean pressure is suggested as a parameter that can be used to predict the influence of surface roughness on the friction coefficient in such contacts. The results show two important properties of the friction coefficient for the friction regime studied in this paper: (1) there is a linear decrease in friction coefficient as a function of the slide-to-roll ratio, and (2) the friction coefficient increases linearly with increasing mean contact pressure up to a maximum limit above which the friction coefficient is constant. The absolute deviation of experimental results from the derived theory is for most cases within 0.005.     

二维粗糙面间滑动摩擦过程中平稳性研究

基于现有的分形模型,考虑到黏着现象的普遍性,通过在界面引入黏着剪切强度并考虑材料断裂,建立了考虑黏着、弹塑性变形影响的二维分形金属粗糙面间的滑动摩擦模型,并运用有限元软件进行数值求解.通过设置不同界面剪切强度及滑动速度参数,研究了两粗糙面间滑动过程中的平稳性.对建立的二维双粗糙弹塑性分形模型的实例进行分析,结果表明:当界面剪切强度较小时,法向速度波动幅值增大;当界面剪切强度增大到一定值后,法向速度波动幅值迅速的减小,使滑动较为平稳.滑动速度对平稳性的影响较大,滑动速度越大,滑动过程中振动越剧烈.     

Dry sliding wear of Cu–15Ni–8Sn alloy

Using a pin-on-disc apparatus, the wear behavior of Cu–15Ni–8Sn alloy aged for different periods of time at 400 °C was investigated under dry condition. The results showed the wear rate was inversely proportional to the hardness of the alloy, but the maximum wear resistance was not consistent with maximum hardness. The alloy contained about 10% (volume) cells precipitated along grain boundaries had the lowest wear rate. The friction coefficient was constant for different hardness. SEM micrographs of the debris and pin revealed that the removal process of surface material involved subsurface deformation, crack nucleation, crack propagation and delamination of the material.     

Theoretical investigation on the dimple occurrence in the thermal EHL of simple sliding steel–glass circular contacts

The conical depression (surface dimple) phenomena observed by Kaneta et al. (Kaneta M, Nishikawa H, Kameishi K, Sakai T. Effects of elastic moduli of contact surfaces in elastohydrodynamic lubrication. ASME J. Tribol. 1992;114:75–80; Kaneta M, Nishikawa H, Kanada T, Matsuda K. Abnormal phenomena appearing in EHL contacts. ASME J. Tribol. 1996;118:886–892.) in optical interferometry experiments are simulated numerically by a complete solution to the simple sliding circular contact thermal elastohydrodynamic lubrication (TEHL) problem. Good agreement is displayed between the theoretical and experimental results. This agreement is explained by the “temperature–viscosity wedge” mechanism, which was first proposed by Cameron (Cameron A. Hydrodynamic lubrication of rotating discs in pure sliding, a new type of oil film formation. J. Inst. Petrol 1951;37:471.). Effects of the viscosity–pressure coefficient, the ambient viscosity, and the entrainment velocity on the behavior of the surface dimples are discussed.     

齿面摩擦和啮合刚度对双渐开线齿轮传动动态特性的影响研究

针对双渐开线齿轮传动动态特性问题,通过建立双渐开线齿轮的有限元模型,综合考虑齿面摩擦与齿轮啮合刚度二因素,对双渐开线齿轮传动系统进行了有限元模态分析,运用响应曲面法研究了齿面摩擦与齿轮啮合刚度对双渐开线齿轮振动变形和模态频率的影响;选取不同模态阶数对双渐开线齿轮传动系统进行了动态特性研究,分析了不同模态阶数下双渐开线齿轮的振动变形与模态频率变化状况。研究结果表明,随着齿面摩擦因数与齿轮啮合刚度的增加,不同模态阶数下双渐开线齿轮传动系统各阶振动变形与模态频率均显著增加,齿面摩擦与齿轮啮合刚度对双渐开线齿轮传动动态特性有一定影响,在对齿轮传动系统进行动态特性研究时,必须对齿面摩擦与齿轮啮合刚度进行充分考虑。     

Some comments on micro‐abrasion interactions of pure metals in bio‐oils

An attempt has been made to study the effect of bio‐oils on the two‐ and three‐body abrasion process of pure metals and steel. The equipment used was a micro‐abrasion tester (TE‐66, Phoenix Tribology (Plint)). The materials considered were mild steel, copper, and aluminium, being the most usable and basic materials for industrial applications such as bearings and gear assemblies. The results were used to identify transitions between wear regimes as a function of sliding speed and load. The effect on the abrasion process in the presence of various lubricant oils was also assessed. The mechanisms of abrasion with and without particles were characterised.