A phenomenological friction model of tripod constant velocity (CV) joints

Constant velocity (CV) joints have been favored for automotive applications, compared to universal joints, due to their superiority of constant velocity torque transfer and plunging capability. High speed and sport utility vehicles with large joint articulation angles, demand lower plunging friction inside their CV joints to meet noise and vibration requirements, thus requiring a more thorough understanding of their internal friction characteristics. In this paper, a phenomenological CV joint friction model was developed to model the friction behavior of tripod CV joints by using an instrumented CV joint friction apparatus with tripod-type joint assemblies. Experiments were conduced under different operating conditions of oscillatory speeds, CV joint articulation angles, lubrication, and torque. The experimental data and physical parameters were used to develop a physics-based phenomenological CV joint dynamic friction model. It was found that the proposed friction model captures the experimental data well, and the model was used to predict the external generated axial force, which is the main source of force that causes vehicle vibration problems.     

Grease Degradation in Constant Velocity (CV) Joints

Constant velocity (CV) joints have been widely used for modern vehicles. The sealed grease of CV joints must provide low friction and wear protection for the lifetime use of the vehicle. Grease performance affects the vibration and noise level in the vehicle. Vehicles that have traveled long distances may suffer mechanical and thermal overloads, thus causing the grease to degrade due to changes in its physical and chemical properties. In this article, the grease degradation phenomenon in CV joints is investigated by collecting grease samples from both tripod joints and Birfield joints in actual vehicles that traveled various ranges of distance. In order to analyze the property changes of grease, grease penetration and oxidation induced time are measured using a penetration meter and infrared (IR) spectrometer, respectively. Where oxygen induced time (OIT) is the point that the oxidation occurs in grease. The performance variations of grease are investigated by measuring the friction and wear using linear-oscillation (SRV, Schwingung (oscillation) Reibung (friction) Verschleiss (wear)) test machine as well as the four-ball wear tester. Degradation of properties as well as performance in CV joint grease due to physical and/or chemical changes is identified.     

Fretting-induced friction and wear in large flat-on-flat contact with quenched and tempered steel

Fretting may cause severe surface damage and lead to unexpected fatigue failure. Our test apparatus was designed based on reciprocating, large, annular flat-on-flat contact without any edge effects in the direction of the fretting movement. Fretting wear tests were run with quenched and tempered steel with different normal pressures and sliding amplitudes under gross sliding conditions. The development of the friction coefficient and total wear mass depended mostly on the accumulated sliding distance. Initially, friction and wear were highly adhesive but gradually changed to abrasive due to third body accumulation in the interface.     

Friction and wear behavior of human teeth under various wear conditions

Previous reports have described the differences in the friction and wear behavior between different zones of human teeth. The objective of this research was to study the friction and wear behavior of human teeth under different wear conditions to extend the understanding of the tooth wear process, as well as to provide a more rational explanation for wear mechanism of teeth. Two typical wear tests, namely two- and three-body wear, were conducted on human tooth enamel using a reciprocating apparatus. The effect of food particles was of particular interest. Three loads, 10, 20 and 40 N, were used. Wear was assessed by sample wear volume. The results show that human tooth enamel exhibits lower friction and smaller wear volume under three-body wear conditions than under two-body wear conditions. Under three-body wear conditions, although increasing normal load results in a progressive increase in the wear volume of enamel, the increasing rate is lower at high load than that under two-body wear conditions. Further analysis of wear surfaces indicates that human tooth enamel experiences different wear mechanisms under different wear conditions.     

Tribological investigation of low friction duplex surface treatment based on modified molybdenum disulphide coating

Abstract

One of the numerous possibilities to decrease friction and wear of sliding surfaces consists of the application of two-step (so called duplex) technologies. A novel duplex technology of gas sulphonitriding of a 41CrAlMo7 steel with subsequent deposition of a low friction MoS₂(Ti,W) coating by means of non-reactive magnetron deposition is described in the present paper. A pin and vee block geometry and a relevant Falex apparatus were chosen for implementation of a linear friction contact under heavy loadings. For comparison, five other treatments of machine parts applied in the industry were used in the paper as well. As a result of the tests, only the specimens after the proposed novel duplex treatment based on sulphonitriding and a low friction MoS₂(Ti,W) coating deposition outlasted the full load of 3500 N during 6 min without any failure from all the six different treatments investigated in the work.     

Design of generated axial force measurement tester for tripod constant velocity joints under shudder condition

Generated axial force (GAF) induced by internal friction in a tripod constant velocity (CV) joint causes shudder, which is related to lateral vibration in a vehicle. GAF is produced by tripod dynamics in the CV joint, and its magnitude is related to an applied torque and articulation angle. GAF provides periodic frictional force, owing to its kinematics, and causes take-off shudder that occurs when a vehicle abruptly accelerates from a stop position. Therefore, accurately estimating the GAF in a CV joint is necessary. A non-rotating type GAF measurement tester is developed to measure GAF more accurately, considering the shudder condition. Results of GAF measurements are compared with those obtained using an existing rotating-type tester. The developed tester provides linear results regardless of test conditions; thus, it can be used to estimate the magnitude of GAF and evaluate the friction performance of grease.     

交联超高分子量聚乙烯人工髋关节磨损仿真模拟

人工髋关节超高分子量聚乙烯（UHMWPE）关节面磨损仍是影响置换关节远期寿命的主要因素,其仿真建模是对关节模拟机磨损测试手段的重要补充,也是实现置换关节临床前性能评估的有效方法。由多向运动产生的交叉剪切效应是影响UHMWPE磨损的主要原因之一,也是仿真建模的关键。现有理论方法将磨损深度确定为滑动距离的函数,并将90°交叉剪切运动条件下的磨损作为度量基准计算不同角度下的交叉剪切效应,但尚未考虑接触应力变量对磨损深度的影响。针对以上问题,提出了在垂直交叉剪切运动条件下将磨损深度表示为摩擦功函数的方法。该方法利用UHMWPE摩擦因数与接触压力的定量关系计算摩擦因数并确定摩擦功,解决了UHMWPE磨损交叉剪切效应中滑动距离与接触应力的耦合问题。基于磨损仿真新模型研究了36 mm直径的交联UHMWPE髋关节,并与已有ProSim模拟机试验结果进行了验证。结果显示该仿真模型可准确计算体积磨损和线性磨损等磨损量以及髋关节载荷方向改变对磨损的影响。磨损新模型为进一步仿真模拟奠定了有效基础。     

Effect of temperature on friction and wear of prehardened tool steel during sliding against 22MnB5 steel

Abstract

Mechanical components in tribological systems exposed to elevated temperatures are gaining increased attention since more and more systems are designed to operate under extreme conditions. In hot metal forming, the effect of temperature on friction and wear is especially important since it is directly related to process economy (tool wear) and quality of the produced parts (friction between tool and workpiece). This study is therefore focused on fundamental understanding pertaining to the tribological characteristics of prehardened hot work tool steel during sliding against 22MnB5 boron steel. The tribological tests were carried out using a high temperature reciprocating sliding friction and wear tester under a normal load of 31 N (corresponding to a contact pressure of 10 MPa), a sliding speed of 0·2 m s^?1 and temperatures ranging from 40°C to 800°C. It was found that friction coefficient and specific wear rate decreased at elevated temperature because of formation of compacted wear debris layers on the surfaces.     

Estimation of Generated Axial Force Considering Rolling–Sliding Friction in Tripod-Type Constant Velocity Joint

ABSTRACT

This study proposes a new generated axial force (GAF) estimation model of tripod-type constant velocity (CV) joints. For development of the model, kinematic analysis was performed to derive the relative coordinates of components and contact points. Through the analysis, the normal load that acts on contact points was also obtained. This study employs two friction models—pure sliding and rolling–sliding—to obtain the friction coefficients on the contact points. Particularly for the rolling–sliding model, this study used the experimental analysis on rolling–sliding ratio and friction coefficients were studied using a tribometer. By introducing two models, this study considers not only the pure sliding friction but also the rolling–sliding friction that occurs between spherical rollers and tracks.

This study verifies the GAF estimation model by comparing the simulation results with the experimental results. A tripod-type CV joint was set as a target and its GAF was derived by the model. Then, its actual GAF was measured and the results were compared with each other. A GAF measurement system was set up for the measurement in this study. The estimated results show similar trends with the measured results under low-resistance torque condition and the GAF model provides very accurate estimation under high-resistance torque conditions.     

A Model for Wear and Friction in Cylinder Liners and Piston Rings

Abstract

A one-dimensional elstohydrodynamic mixed lubrication wear and friction model is developed. The model can predict the effects of surface roughness, asperity contact, temperature-pressure-viscosity on wear, lubrication, and friction of the piston rings and cylinder liner. Wear is predicted based on the surface asperity contact pressure. The cylinder bore wear and the ring pack friction during an engine break-in are simulated and compared with the experimental results. The influence of cylinder wall temperature and surface roughness on friction and wear is investigated. The ring pack friction due to oil viscous shearing and asperity contact is found to reach its minimum at a certain oil temperature.     

车轮滚动接触疲劳与磨耗耦合关系数值模拟

滚动接触疲劳和磨耗是车轮失效的主要方式。通过三维弹性体非赫兹滚动接触理论得到接触斑内的法向、切向应力和材料上不同深度处的最大切应力分布,以CL60钢和贝氏体车轮钢为例,基于"layer"滚动接触疲劳失效模型和Zobory车轮磨耗模型,分析LM型车轮踏面和75 kg.m–1钢轨型面匹配时轮轨接触条件和车轮材质对车轮滚动接触疲劳和磨耗竞争关系的影响。计算结果表明,摩擦因数为0.3时,CL60钢在小蠕滑条件下会发生滚动接触疲劳损伤,在大蠕滑条件下只有轴重大于30 t时才会出现滚动接触疲劳损伤,而贝氏体车轮钢只有在大蠕滑条件且轴重为30 t时,载荷循环次数小于1×105的情况下才会出现滚动接触疲劳损伤;摩擦因数为0.6时,CL60钢和贝氏体车轮钢在各种工况下的滚动接触疲劳损伤速度都小于相同条件下的磨耗速度。     

A two phase circular regression algorithm for quantifying wear in CV joint ball race tracks

In this paper, a two-phase circular regression algorithm is presented for extracting wear profiles from Rzeppa-type constant velocity (CV) joints and for quantifying race track wear. In ball races operating under harsh cyclic loading conditions the predominant brinelling and “false brinelling” wear mechanism result in small indentations or grooves in the race track. These are particularly difficult to measure as the reference or nominal surface is curved in two planes in three-dimensional space. The presented algorithm achieves absolute measures of ball race track wear by a two-phase surface fitting regression methodology. The wear grooves are identified in the first phase and extracted to obtain sections of “unworn” surface; in the second regression phase, these sections are used to construct the datum surface and to establish absolute measures of wear groove depth. An important property of this algorithm is that it does not require the user to input parameters specific to the particular type or size of joint. This is particularly important in automotive aftermarket applications such as in drive-line servicing and in CV joint rebuilding/recycling. Results presented for a range of different CV joints demonstrate that race profiles can be obtained quickly and efficiently and that wear groove depth can be measured accurately to a ±3σ repeatability of 2.4 μm (±0.000 093 in).     

Friction and wear properties of UHMWPE/Al2O3 ceramic under different lubricating conditions

Friction and wear behavior of ultra-high molecular weight polyethylene (UHMWPE) sliding against Al₂O₃ ceramic under dry sliding, and lubrication of fresh plasma, distilled water and physiological saline were investigated with a self-made pin-on-disk apparatus at 37±1°C. The worn surfaces were examined with a scanning electron microscope (SEM). The results show that the friction behavior of UHMWPE is very sensitive to its water absorption state. The wear rate of UHMWPE under dry sliding is the highest and under plasma lubrication is the lowest. The wear mechanisms are different under dry friction and various lubricating conditions.     

A rational human joint friction test using a human cartilage-on-cartilage arrangement

Efficient lubrication is essential for synovial joint mobility in both health and disease. It is well known that extremely low friction is required for proper functioning of synovial joints. In several medical treatments, bio-lubricants are injected into human joints to maintain their proper functioning. In the course of developing and screening such bio-lubricants, it is important to measure their effect under conditions similar to the ones in vivo. To this end, a first attempt was made to test the friction of two slices of human articular cartilage sliding over each other under various working conditions in the presence of different lubricating fluids. The results can be used for future research in the field of joint lubrication.     

Friction models for sliding dry, boundary and mixed lubricated contacts

Friction, lubrication, and wear have a strong influence on the performance and behavior of mechanical systems. This paper deals with different friction models for sliding contacts running under different conditions. The models presented are suited to different situations, depending on the type of contact, running conditions, and the behavior of interest. The models will be discussed from simulation and tribological points of view. The different types of friction models considered are:

• friction models for transient sliding under dry, boundary and mixed lubrication conditions,

• friction models for micro-displacements of engineering surfaces subjected to transient sliding,

• friction models often used in the simulation and control of technical systems,

• combined friction models that represent physical behaviors fairly well but are also suitable for use in simulating systems,

• friction models that take into account the stochastic nature of interacting surface asperities.

基于动力学特性的挖掘机工作装置端面摩擦副间隙磨损机理研究

机械动力装备中常因为作业工况恶劣导致关节端面摩擦副间隙处磨损严重,为了探讨关节端面摩擦副间隙处作业过程中磨损变化行为及作用机理,以某型号挖掘机为例,基于动力学模拟分析两种典型工况下得到动臂关节处动态载荷数据基础上,利用有限元数值模拟技术并修正Archard磨损模型计算得出端面摩擦副间隙处磨损深度与磨损次数的关系,在端面磨损试验机上验证两种工况下关节间隙处耐磨垫片磨损变化过程,在扫描电镜下观察磨损后的表面形貌分析磨损作用机理。结果表明：两种工况下,磨损区域均为环形区域;偏载工况磨损主要与接触应力值大小和偏载角度有关,磨损过程中表面产生锥刺凹坑和交叉犁沟等,磨损机制由疲劳磨损向黏着磨损转化,同时伴随有少量的磨粒磨损;满载启动回转工况磨损主要与接触碰撞程度有关,磨损形式主要为黏着磨损与磨粒磨损。此分析方法对工程机械行业分析其它动力装备关节摩擦副和工程应用具有较好的参考价值。     

Wear Performance of Phenolic Composites: A Comparison of Experimental and Theoretical Data

ABSTRACT

This study investigated the wear performance of phenolic composites under various conditions. Samples of brake pad material (UCV018) were subjected to friction and wear tests against grey cast iron (HT250) under dry sliding conditions. The friction coefficient and wear rate as well as material properties, such as density, elastic modulus, and Poisson ratio, were measured at six temperatures. The wear behavior of the friction material was analytically and numerically simulated using experimental data. Numerical calculations were performed on the basis of Archard's linear wear model. Through further experimental verifications, the friction and wear behavior were analyzed under conditions of static loading, quasistatic rotation, and wear. The friction and wear test results verified the accuracy of the simulation model and revealed the distribution of wear depth and contact pressure. Furthermore, the effects of contact pressure variation on wear performance were studied numerically. The results of the experimental and numerical investigations were compared.     

Frictional characteristics of the beetle head-joint material

Frictional properties of the head part in the beetle head–thorax articulation were studied in two beetle species, Pachnoda marginata and Geotrupes stercorarius (Coleoptera, Scarabaeoidea). Using the microtribometer, the head part of the joint was brought into contact with the flat glass and slid along a distance of 120 μm. The friction experiment was carried out with two conditions of the head material: fresh and air-dried. The tribosystem, consisting of the sapphire sphere in contact with flat glass, was used for comparison. Frictional coefficient of the joint material on glass was significantly lower than that of the sapphire sphere on glass. The material of the joint cuticle is rather stiff and the surface is hydrophobic (the contact angle of distilled water was 88.3°). It is suggested here that the high stiffness of the joint material and hydrophobicity of the joint surface are parts of the mechanism minimizing friction in insect joints.     

LUBRICATION MECHANISMS OF LN2 IN ECOLOGICAL CRYOGENIC MACHINING

ABSTRACT

Cryogenic machining is considered an environmentally safe alternative to conventional machining where cutting fluid is used. In cryogenic machining, liquid nitrogen (LN2) is well recognized as an effective coolant due to its low temperature, however, its lubrication effect is less well known. Our previous studies of the change in cutting forces, tool wear, chip microstructure, and friction coefficient indicate a possible lubrication effect of LN2. This paper proposes two mechanisms on how LN2 can provide lubrication in the cutting process. To verify these proposed LN2 mechanisms and distinguish them, idealized disk-flat contact tests were performed. A low temperature can alter the material properties and change the friction coefficient between the specimens. However, from the test results, this lubrication mechanism was dependent on the material pairs. An uncoated carbide insert with a low carbon steel or titanium alloy disk test showed reduction of friction under LN2 cooling, but a coated insert increased the friction force. LN2 injection to form a physical barrier or hydrodynamic effect between two bodies is always effective in reducing the friction force.     

含间隙的变拓扑多体系统动力学建模分析

分析了含间隙多体系统的变拓扑结构特性,引入了基本约束变结构约束概念。在动力学建模中将系统拓扑结构的变化表示为含间隙处约束关系的变化,即变结构约束的增加与删除,给出了拓扑结构切换点的识别方程,建立了含间隙多体系统动力学的广义模型,对典型含间隙系统进行了仿真研究,验证了本理论模型的正确性。