橡胶线接触摩擦规律的研究

由于橡胶磨损机理与摩擦机理之间密切相关,因此,对橡胶摩擦机理及其规律的了解将有助于深入了解橡胶磨损机理.本文通过对橡胶在线接触下摩擦机理和规律的研究发现:橡胶线接触的主要摩擦机理是粘附,橡胶线接触的摩擦系数随时间周期性变化,并随法向载荷增大而略有下降,且基本不随滑动速度而变化.     

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.     

冰面上橡胶滑动摩擦特性的数值分析

基于摩擦熔化理论,考虑流体动力润滑和热传导的耦合作用,采用打靶法和线性插值法获得了冰面上滑动橡胶块摩擦界面上的压力、流体膜厚及温度的无量纲分布规律,研究了胶块的摩擦特性。结果表明,摩擦界面上的压力峰值随载荷的减小向界面中部移动,摩擦因数与滑动速度的平方根成正比,而与载荷和试样长度的平方根成反比。所用方法可应用于其它材料在冰面上的摩擦及其它情况下的摩擦熔化问题。     

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.     

Thermal and thermomechanical effects in dry sliding

Whenever friction occurs in dry sliding of mechanical components, mechanical energy is transformed into heat through surface and volumetric processes in and around the real area of contact. This frictional heating, and the thermal and thermomechanical phenomena associated with it, can have a very important influence on the tribological behavior of the sliding components, especially at high sliding velocities. Significant developments in the study of these phenomena are reviewed in this paper. Among the topics reviewed are mechanisms of frictional heating and the distribution of heat during sliding friction, the measurement and analysis of surface and nearsurface temperatures resulting from frictional heating, thermal deformation around sliding contacts and the changes in contact geometry caused by thermal deformation and thermoelastic instability, and the thermomechanical stress distribution around the frictionally heated and thermally deformed contact spots. The paper concludes with a discussion of the influence of the thermal and thermomechanical contact phenomena on wear, thermocracking and other modes of failure of sliding mechanical components.     

Model and computer simulation of friction

A model, consisting of the stochastic formulae which describe the relationship between the friction coefficient and the parameters known to be significant in dry friction, is proposed for dry sliding friction between two randomly rough surfaces. The model considers the frictional phenomena which dominate in energy dissipation and which may occur simultaneously between contacting elements. The kind of interaction in a given spot of asperity contact depends on the local energy flux density. The effect of several parameters on the friction coefficient, the real area of contact, and the number of contact spots can be calculated with the FRI-SIM program. A comparison of the simulation and experimental data shows a convergence of results.     

A new theory of hysteretic sliding friction

This paper supports the concept that the damping properties of rubber contribute the greater proportion of frictional resistance when rubber slides on an irregular lubricated surface. The author presents and largely validates his rigorous mathematical mechano-lattice analogy analysis for calculating the hysteretic sliding friction of, and stresses in rubber sliding on, variously shaped asperities. The analysis allows large deformations and any Poisson's ratio, rigidity or damping factor of the rubber. A method of applying the results of this analysis to the problem of predicting the coefficient of lubricated friction of rubber sliding on roadstones is shown to be reasonably accurate.     

Correlation between the frictional behaviour and the physical properties of metals

The surface topography of mating surfaces is characterized by plastically deformed asperities which form real areas of contact. As sliding leads to the shearing of junctions, it is feasible that physical properties will affect adhesion and shear strength and influence frictional behaviour.The sliding friction of similar metals and of metals sliding against a steel specimen was investigated for most commonly used metals in terms of their fundamental physical properties including atomic volume, surface energy and thermal properties.     

The influence of thin hard coatings on frictional behaviour in the orthogonal cutting process

New knowledge about the tribological response deriving from the interaction of the substrate/coating-chip system, with special attention to the orthogonal cutting process when chatter-free end turning using natural contact tools, is developed. In order to evaluate the frictional behaviour of this process under modified contact conditions, experimental investigations including the contact temperature, the contact loads, friction and the frictional heat flux per unit area were carried out. In contrast to the most obvious approach, the coefficient of sliding friction versus the cutting speed, the contact temperature, the normal pressure and the interface control factor is considered. A number of different coating structures, starting from single up to three and four layer films, in combination with medium carbon and austenitic stainless steels, were tested. It is pointed out that the results obtained provide a modified approach to the frictional behaviour of the cutting process and its controllability. Among various responses, specific for such tribo-contact pairs, of particular interest is the self-adaptation resulting in controlled generation of friction energy and conduction of the frictional heat flux.     

A reduced-scale brake dynamometer for friction characterization

Friction behavior is a critical factor in brake system design and performance. For up-front design and system modeling it is desirable to describe the frictional behavior of a brake lining as a function of the local conditions such as contact pressure, temperature, and sliding speed. Typically, frictional performance is assessed using brake dynamometer testing of full-scale hardware, and the average friction value is then used for the remaining brake system development. This traditional approach yields a hardware-dependent, average friction coefficient that is unavailable in advance of component testing, ruling out true up-front design and leading to redundant lining screening tests. To address this problem, a reduced-scale inertial brake dynamometer was developed to determine the frictional characteristics of lining materials. Design of a reduced-scale dynamometer began with the choice of a scaling relation. In this case, the energy input per unit contact area was held constant between full-scale and reduced-scale hardware. All linear variables were thereby scaled by the square root of the scaling factor, while the pressure, temperature, sliding velocity, and deceleration were kept constant. Experimental validation of the scaling relations and the reduced-scale dynamometer focused on comparisons with full-scale dynamometer data, particularly the friction coefficient. If similar trends are observed between reduced-scale and full-scale testing, the reduced-scale dynamometer will become an important tool in the up-front design and modeling of brake systems.     

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。     

The formation of schallamach waves

Schallamach's premise that surface instability causes the wrinkles or waves observed on the surface of soft rubber which undergoes frictional sliding is substantiated in this paper. An analysis of the problem of homogeneous compression of a semi-infinite Mooney-Rivlin solid shows that surface instability occurs at a certain critical extension ratio. The critical value of this ratio is 0.54 in the case of sliding without prestraining. The instability manifests itself as surface waves of arbitrary wavelength. The evaluation of the analytical results in the light of experimental findings reported in the literature lends support to this theory. The analysis has been extended to study the effect of prestraining rubber prior to sliding on the initiation of these waves. It is shown that when rubber is prestrained prior to sliding the critical extension ratio λ_cr is equal to or less than 0.54 depending on the direction of prestraining. Again there is good qualitative agreement with the results of recent experiments. The explanation of the origin of Schallamach waves appears to be justified. The condition for the appearance of Schallamach waves is established: the rubber should be sufficiently soft and the frictional force sufficiently large for the extension ratio in a region near the leading edge of the contact area to attain its critical value.     

Role of Rubber Stiffness and Surface Roughness in the Tribological Performance on Ice

The aim of this work is to investigate the effect of slider surface roughness and stiffness on the friction between rubber compounds and ice surfaces in order to provide insight into rubber–ice friction generation mechanisms. For this purpose, rubber compounds were designed to have different levels of macroscopic roughness and cured stiffness by modifying the filler system and plasticizer loading. In order to accurately evaluate the effects of surface and bulk rubber property on ice friction, linear friction tests were performed on laboratory ice with varied frictional heat buildup by modifying the friction test protocol. The results showed that the friction force was in general increased through the ploughing effect of a rough rubber block sliding on smooth ice. The increase in friction by ploughing was more pronounced when the contacting rubber block had sufficiently low stiffness and when the accumulation of frictional heat on ice was sufficiently high. It was also evidenced that a sufficiently hard rubber with test conditions leading to low heat buildup on ice could nevertheless lead to an opposite influence of roughness on rubber–ice friction; that is, lower friction force with a slider with a higher roughness.     

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.     

表面微凹坑和纹理方向对界面摩擦的耦合影响

选取三种不同纹理的铝合金试样,并在试样上加工不同面积占有率的规则圆形微凹坑,利用自制的摩擦试验装置,在油润滑条件下以不同接触压力进行摩擦试验,试验过程中滑动方向与表面纹理方向的夹角分别为0°、45°、90°。利用非接触式三维轮廓仪测量试验前后试样的三维表面形貌,并选取Sa、Str、Vvv、Vvc等表面表征参数来分析滑动接触界面表面形貌的变化。结果表明：表面纹理方向的差异导致铝合金表面在滑动接触摩擦过程中表现出各向异性,而在其表面加工不同面积占有率的微凹坑,减弱了铝合金表面纹理方向性对界面摩擦的影响,反映出表面微凹坑和纹理对界面摩擦的耦合作用。同时界面摩擦对试件的表面形貌也有明显的影响,Str、Vvv、Vvc在试验后发生了规律性的变化。     

Friction and Thermal Effects of Engineering Plastics Sliding Against Steel and DLN-Coated Counterfaces

Polymers are increasingly used in tribological applications, because of their self-lubricating ability, corrosion resistance and chemical compatibility. However, their performance depends strongly on the parameters of the total tribological system. Not only polymer characteristics, but also counterface properties become important because of their influence on friction and wear, on surface energy and on the thermal conductivity of the total system. Applying a Diamond-Like Nanocomposite (DLN) coating on a steel counterface can improve the tribological behaviour of the sliding couple under certain conditions. In the case of metal sliding against DLN, the high hardness and the wear resistance of the coating is advantageous for better tribological properties. However, for polymers sliding against DLN, the lower thermal conductivity of the DLN coating compared with a steel mating surface dominates friction and wear. In case of polyamides this results in worse tribological performance in contact with the DLN coating, because of polymer melting. In the case of more rigid polymers, such as, e.g., POM-H and PETP, lower coefficients of friction lead to lower frictional heat generation. In these cases, the thermal characteristics of the counterface are less important and the lower surface energy of the DLN coating is favourable for decreased adhesion between the polymer and the coating and consequently better tribological properties.     

热力耦合下微接触点塑性应变沿深度变化分析

在考虑粗糙实体弹塑性变形、热力耦合、微凸体间相互作用和摩擦热流耦合等影响下,运用有限元法数值模拟具有三维分形特性的粗糙面与刚性平面间滑动摩擦过程,分析了粗糙实体接触凸点塑性变形随深度变化情况。发现：在速度的突变和闪点温度形成时,摩擦接触表层等效塑性应变增大明显;在这一摩擦表层,过不同接触点的纵向剖面塑性应变沿深度分布不同：有的是接触表面塑性变形最大,有的是在接触微凸体表面下某一深度塑性变形最严重,而接触凸点表面的塑性应变稍小些。这与相关文献用SEM研究干摩擦后金属摩擦表层变形照片后发现的结果一致。滑动摩擦过程中,金属粗糙摩擦接触表层塑性变形的不断累积,将会导致材料表层中的夹杂或微观缺陷周围萌生微孔和裂纹源。     

磨粒微观滑动接触过程热效应的有限元分析

利用ANSYS有限元软件分析了磨粒与被磨损材料表面滑动接触过程中,在摩擦热和力场的耦合作用下,接触区表现出的局部温度变化、应力变化等特性。结果表明,在磨粒滑移过程中,磨粒相当于接受固定热源作用,接触区温度逐渐上升,温度存在起伏波动现象,瞬现温升最高点在磨粒接触区两侧,反映出接触状态的不连续性,接触区状态的非稳定性;被磨材料表面的各点在进入接触前、经历接触时、脱离接触时,接触区温度存在先升高再下降的变化过程,同时,接触区的应力、剪应力、接触压力也发生变化。磨粒滑动过程的热效应问题研究将有助于揭示接触过程中材料表面损伤机制。     

Evaluation of Tribological Behaviour of Polymeric Materials for Hip Prostheses Application

The tribological (friction and wear) behaviour of different polymeric materials was evaluated for hip prostheses applications. First, three polymeric materials were tested with fixed conditions of contact stress and sliding velocity. In a second phase, the material which presented the best results was selected. Its frictional behaviour under dynamic conditions of contact stress and sliding velocity was evaluated.     

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.