The critical condition for intrusion of a steel ball into sliding contact space

The intrusion tests of a ball into sliding contact space were carried out. A stainless steel ball with 3.175 mm radius was used as a sphere particle to study the critical intrusion condition of the ball into the contact space between the organic glass and the polyurethane rubber. The effect of intrusion angle of the contact space and the friction coefficients among the ball, the organic glass and the polyurethane rubber on the critical condition were studied experimentally. Then, the intrusion conditions for the ball into the contact space were analysed theoretically. The results showed that the calculated critical intrusion angles agreed well with the experimental ones. Finally, the intrusion diagram as a function of critical intrusion angle, friction coefficient µ₁ and µ₂ (here, µ₁ is the friction coefficient between the ball and the polyurethane rubber, µ₂ is the friction coefficient between the ball and the organic glass) was introduced to evaluate the intrusion performance of a ball into the sliding contact space. Copyright © 2010 John Wiley & Sons, Ltd.     

Tribological and vibroacoustic behavior of a contact between rubber and glass (application to wiper blade)

The wiping of the windshield of a car is carried out with the reciprocating motion of a rubber blade on glass that removes the water from glass. This function is realized by a contact dimension between the rubber and glass of a few tens of micrometers. A good wiping is characterized by a homogeneous disposal of the water, without noise generation and by limiting as much as possible the phenomenon of wear (loss of wiping or noise presence). This wiping is only possible by a good understanding of the tribological, mechanical and vibroacoustic parameters that control completely the contact. Our article proposes to approach four typical phenomena occurring on rubber wiper blades. Also, we will describe the evolution of dry friction coefficient with temperature. Later, we will approach the influence of velocity on the friction coefficient of a wiper rubber blade by water. Then we will talk about a phenomenon called tacky friction where the friction coefficient reaches a very important value. And in conclusion, we try to give a relationship between the stick–slip and the squeal noise.     

Consequence of contact local kinematics of sliding bodies on the surface temperatures generated

When studying contact with friction between two bodies, it is not possible to obtain data on real contact conditions on the basis of steady-state situations. Indeed, contacts with friction usually lead to dynamic instabilities generated at the contact interface. It is therefore necessary to take into account contact dynamics in order to better understand the phenomena involved during sliding with friction. The explicit dynamic finite element code PlastD in 2D is used to simulate the contact between two bodies. A constant Coulomb friction coefficient is imposed at the interface. The simulations carried out permitted identifying local contact conditions (kinematics, tribological state, stresses, etc.). They revealed that different instability regimes can be generated (stick–slip, slip–separation, stick–slip–separation, etc.). Local contact stresses and the sliding velocity oscillate through time when instabilities are generated and their maximum values can be much higher than those expected for steady-state conditions. The aim of this paper is to analyse the frictional instabilities and their consequences on the heat generated in the contact. First, the influence of the different instability regimes is studied on a simple contact. Then, an industrial mechanism is studied (wheel–rail contact) to investigate the influence of local contact conditions on the temperature of the rail surface.     

Estimation of rubber sliding friction from asperity interaction modeling

Interaction between a soft rubber asperity and its hard counterpart is traced with the help of a finite element computation. The analysis is aimed to estimate the influence of adhesion between rubber and rigid surfaces and the energy losses arising from the deformation of rubber bulk to the sliding resistance. At the contact zone, interfacial bonds are formed due to adhesion and their resistance to sliding is represented by the shear strength of the contact interface. In the rubber bulk, the hysteresis loss is calculated using an appropriate model of the viscoelastic mechanical behavior of rubber for large strains. Dependence of friction on sliding speeds and temperature is hence detected. Influence of surface roughness and contact pressure on friction is also examined.     

Rubber friction and the rheology of viscoelastic contact

The phenomena accompanying friction at low speeds (1–1500 μm/s) of a clean glass hemisphere (R = 2 mm) on a plate of soft, transparent, natural vulcanized rubber (E' = 1.6 × 10⁷dynes/cm²) were studied using an optical microscope equipped with Nomarski interference contrast (× 150) and with a device to form Newton's rings around the area of contact. The friction force under loads of zero, 1 and 2 × 10³ dynes was recorded, and its variation on the appearance of Schallamach waves was assessed. The elastic adhesion between both surfaces was specially studied, and Johnson's theory verified. The profile of the deformed rubber surface was determined, in static as well as in dynamic conditions, and the geometric process of the formation of detachment waves was demonstrated. The contact angle between rubber and glass was measured in the case of zero load.Relaxation phenomena were observed for the free surface and the bound surface (interfacial relaxation), and the corresponding characteristic relaxation times roughly estimated.Some conditions for the appearance of Schallamach waves were established and hypotheses made concerning their eventual role in the problems of tyre and seal friction. The need for a new theoretical approach to these questions is briefly discussed.     

Friction of rubber on ice: A new machine,influence of rubber properties and sliding parameters

Friction of rubber on ice and snow is important for performance of vehicle tyres in winter. We introduce a new linear tribometer that was designed for measuring the friction of rubber on ice. We present a systematic study of rubber sliding on ice, investigating speed, load, temperature and rubber properties. The friction was linked to behaviour at the interface, particularly melt–water formation and real area of contact. Friction tends to decrease with conditions that promote melt–water formation, and tends to increase as real area of contact increases. We observe stick-slip behaviour with high real area of contact and high load.     

On the Friction of Carbon Black- and Silica-Reinforced BR and S-SBR Elastomers

Friction of carbon black- and silica-reinforced elastomers is studied experimentally and theoretically, using Persson’s model. The effect of reinforcement fillers on elasticity was determined by dynamical mechanical analysis. Carbon black-filled samples have a higher Young’s modulus than the silica-filled compounds. Silica-filled rubbers have a higher tan (δ) at lower temperatures and a lower loss tangent at higher temperatures, which is a rough indication for higher wet grip and lower rolling resistance, respectively. Friction tests on a ball-on-disk test rig were performed to study the effect of the reinforcement fillers and their amount on the friction between rubber samples (disks) and relatively smooth or rough granite surfaces (balls). The results were discussed and compared with the friction model presented by Persson. It was shown theoretically and experimentally that hysteresis does not play a significant role in the friction of rubber samples in contact with smooth granite and that it plays a minor role in contact with a rough granite sphere. Therefore, the hysteresis contribution of friction can be neglected in the contact of rubbers with just smooth spheres. Moreover, a higher friction coefficient is seen in samples with a higher content of fillers. Silica-filled compounds show a slightly higher coefficient of friction compared with the carbon black-filled compounds. The effect of attached wear debris to the granite surfaces on the friction level has been studied. The results are supported by SEM and confocal microscopic images of the wear debris itself and wear debris attached to the granite spheres, respectively.     

Evaluation of tribological properties of pick up roller measured using a laser microscope with a wide field of view

Analysis of contact conditions between rubber rollers and printing paper is important for stable paper feeding operation. Direct observation of apparent contact area is necessary to understand contact conditions, such as distributions of real contact area and micro-slips. However, conventional optical microscopy takes too long to observe the whole apparent contact area because the field-of-view is too narrow. We developed a wide field-of-view laser microscope, and applied it to determine the distributions of real contact area of rubber rollers against glass plates. Critical torques at which micro-slips of the rubber rollers occurred were proportional to total real contact area.     

湿滑状态下轮胎路面摩擦特性的数值分析方法

为研究湿滑状态下轮胎路面的摩擦特性,以胎面橡胶和沥青路面作为研究对象,利用谐波叠加法建立三维粗糙路面模型,采用“伪”流体动力轴承作用等效反映路面水膜“密封”作用,综合使用有限元软件ABAQUS和计算流体动力学软件Fluent得到湿滑状态下橡胶与路面滑动接触时的橡胶接触压力、滞后摩擦力及路面水膜承载力,由此形成了综合兼顾橡胶材料、接触压力、滑动速度、路面形貌和路面水膜等多因素的轮胎与湿路面摩擦特性的仿真方法。通过橡胶与干-湿路面摩擦特性的变化与公开的试验对比,证明本方法的合理性和可行性,并进一步分析滑动速度、接触压力和路面特征对湿滑状态下轮胎路面摩擦特性的影响规律。研究结果为轮胎和路面的抗湿滑性设计及优化提供理论依据。     

Role of Frictional Heating in Rubber Friction

The energy dissipation in the contact regions between solids in sliding contact can result in high local temperatures which may strongly affect the friction. This is the case for rubber sliding on road surfaces at speeds above 1 mm/s. I derive equations which describe the frictional heating for arbitrary (non-uniform) motion, taking into account that some of the frictional energy is produced inside the rubber due to the internal friction in rubber. Numerical results are presented for one limiting case for steady sliding.     

非线性弹性材料在多层圆柱结构中接触预紧作用的模拟

利用非线性弹性材料对多层圆柱结构进行接触预紧，涉及到几何非线性和材料非线性以及接触面上摩擦力的影响。当材料间刚度差别较大时，刚度低的材料呈现大变形特征，加大了几何非线性的程度。结构内部预紧力的大小和分布与结构的整体刚度、结合部位的局部刚度、过盈配合程度、接触面积等因素有关。本文对以橡胶作为预紧垫层的双层金属柱体的预紧过程进行了力学实验和数值模拟。预紧后的模型受中心集中力的作用，以得到橡胶垫层在复杂载荷作用下的状况。在数值模拟模型中，接触面采用直接约束模型，摩擦力的模拟选用库仑摩擦模型，预紧力的施加与力学实验模型相同，利用两个金属半圆环逐步压紧橡胶材料。数值模拟结果和实验数据吻合较好，表明结构非线性大变形接触预紧模拟的数值模型是合理的。     

Friction Force Measurement at Windscreen Wiper/Glass Contact

In the present study, a novel windscreen wiper-on-cylinder machine has been used to investigate the influence of sliding speed and normal force on the coefficient of friction. Using this machine it is possible to measure the friction force not only on specimen level, as in former studies to be available in the literature, but also on structural level by considering the whole windscreen wiper. As measurement results are strongly influenced by both the real, non-circular cross-section, and the eccentricity of the rotating glass cylinder an analytical model has been developed to explain the measurement results. The good agreement to be found between theory and experiment confirms the validity of the model. Majority of the results belongs to partial contact where the wiper blade is not in contact with the glass countersurface along its total length. After the discussion of experimental results, as a last step, authors made an attempt to compare quantitatively the predictive capability of two different contact models widely used in mixed friction model of sliding rubber components. The results show that the difference in film thickness due to solid–solid contact can be larger than three orders of magnitude in case of a typical windscreen wiper.     

The Antiwear Action of Zinc Di-n-Butyl Phosphate

The dynamics of MoS₂ particles in a mineral oil dispersion are studied in the same manner as reported in Part I for graphite dispersions. A Hertzian contact consisting of a steel ball in contact with a glass disk is lubricated with MoS² dispersions and observed by optical microscopy at various. slide/roll conditions. In general, the behavior of MoS₂ and graphite are similar. That is, the solids lend to enter the contact and form a film on the contacting surfaces whenever a rolling component of motion is used, but solid particles seldom enter the contact during pure sliding. MoS₂ has more pronounced plastic flow behavior than graphite. However, the polished steel ball is more readily scratched by MoS₂ than by graphite. Under the conditions of these studies, lower friction and wear are observed with pure oil rather than with the dispersions. However, under other conditions (such as different contact geometry or rougher surfaces), the solid-lubricant dispersions might be beneficial.     

封隔器胶筒大变形摩擦接触的有限元分析

关于封隔器胶筒接触压力的求解，目前文献所给出的计算公式均没有考虑摩擦因数对封隔器胶筒接触压力的影响，而摩擦因数对接触压力有较明显的影响。针对胶筒与套管之间的粘-滑摩擦接触问题，采用罚函数技术，结合橡胶大变形问题的增量分析过程，给出解决封隔器胶筒摩擦接触问题的数值方法，并在此基础上对胶筒与套管之间的摩擦接触进行有限元分析。计算结果表明，采用大变形非线性粘弹性理论和接触摩擦描述的有限元模拟技术，可以比较准确地模拟摩擦因数对封隔器胶筒接触压力的影响，所得的结果比经典理论公式的分析结果的精度更高，具有理论价值和工程应用价值，可为胶筒的优化设计提供一定的依据。     

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.     

The dissipation of energy in the friction of rubber

The sliding of rubber over glass when waves of detachment are responsible for the relative motion at the interface has been studied. The frictional force and the velocity and frequency of the waves were recorded for various sliding conditions. In a separate experiment, the work required to peel apart and then re-adhere unit area of rubber-glass interface was measured as a function of peeling velocity. Assuming that the passing of a wave corresponds to a peeling and re-adhering of the contact area, the work of adhesion is calculated from the friction observations and compared with the values measured directly. The good correlation which is found indicates that in these circumstances the frictional energy dissipation may be accounted for in terms of the net work of adhesion.     

水平井裸眼封隔器密封结构优化研究

针对水平井压缩式裸眼封隔器存在的密封性差、坐封力低、胶筒与井壁间存在间隙等问题,对其密封结构进行改进与优化,设计出一种凸球形隔环和凹球形胶筒组相结合的新型密封结构。运用 ABAQUS 软件模拟密封结构封隔器胶筒的坐封情况,获得胶筒组轴向接触压力的分布规律,并分析胶筒硬度和摩擦因数对接触压力的影响。结果表明：新型密封结构凸球形隔环在轴向压缩胶筒的同时也起径向压缩作用,提高了胶筒与井壁和中心管间的接触压力,增强了封隔器的密封性能;胶筒与井壁间的接触压力随着胶筒硬度和摩擦因数的增大而增大,但过大的摩擦因数会导致下胶筒接触压力明显减小,应选择硬度和摩擦因数合适的胶筒,从而保证封隔器的密封可靠性。     

Experimental investigation of transient and thermal effects on lubricated non‐conformal contacts

In this work, thermal and transient effects on non‐conformal lubricated contacts are investigated through experimental analyses. Experiments between a ball and a plane surface of a disc are described. Friction coefficients and film thicknesses are measured (the film thickness only for the glass‐on‐steel contact). A paraffin base mineral oil is used as a lubricant. First experiments are carried out under steady‐state conditions. To include effects due to different thermal properties of contacting materials, a steel‐on‐steel and a glass‐on‐steel contact with different slide‐to‐roll ratios are tested. If the contacting materials have different thermal properties, as in the case of a glass‐on‐steel contact, thermal effects like the temperature–viscosity wedge action could clearly be shown. It is found that the friction coefficients are influenced by the slide‐to‐roll ratio and the thermal properties of the contacting materials. Under transient conditions, the entraining velocity is varied with a sinusoidal law. Squeeze effects explain ‘loops’ of friction and film thickness found also in previous works. The formation of friction loops is related to the measured film thickness differences. However, also under non‐steady‐state conditions, thermal effects, like the temperature–viscosity wedge action, influence the friction coefficients. Copyright © 2007 John Wiley & Sons, Ltd.     

Friction on a Microstructured Elastomer Surface

The friction of microstructured polydimethylsiloxane samples against a glass surface is studied through force measurements and simultaneous optical microscopy. Both average friction forces and the amplitude of stick-slip oscillations are greatly reduced by the structuring. Optical microscopy reveals waves propagating through the contact in connection which stick-slip events. The experimental observations are interpreted with the help of simulations of a spring-block model for which parameters are directly derived from the experiment. Stress gradients across the contact area are found to play an important role for the frictional behavior.     

On the dynamics of the friction coefficient

The paper deals with the principal wear mechanism in brake systems and introduces a new dynamical model of the friction coefficient, where necessarily both friction and wear are taken into account. This model explains many open questions on the principal functionality of brake systems.In brake systems, characteristic structures are formed in the contact area by the flow of wear particles. Modulated by the friction power the wear particles are used by the system to build up hard contact patches on the brake pad. Nearly all energetic dissipation of the system is concentrated on these patches. By wear, these contact patches are destroyed after some time.So the friction coefficient is given by the equilibrium of flow of birth and death of contact patches. The resulting dynamical model describes the dynamical behaviour of the friction coefficient and the dependence of the temperature in the friction layer.This theory explains the fading effect of brake systems as well as complex hysteretic effects in the diagram of the friction coefficient versus the velocity, known from instationary measurement procedures.The structure of this theory seems to be quite general to describe other frictional systems too.