Sliding friction at elastomer/glass contact: Influence of the wetting conditions and instability analysis

The aim of this paper is to simulate and give a better understanding of the behavior of rubber blade/windscreen contact: the friction behavior of the rubber/glass contact, the wiping quality and the characterization of friction instabilities are investigated. Therefore, the tribological prospect of a rough natural compound rubber sliding over a smooth glass in various wetting conditions is analyzed. This study is carried out using a modified elastohydrodynamic tribometer that allows us to investigate the rubber dynamical behavior under controlled conditions, thanks to the coupling of dedicated dynamical sensors and the contact visualization. Wetting conditions are varied as the impact of velocity and normal load is studied and a specific interest has been given to the transition between wet and dry regimes. Frictional instabilities are observed and correlated to the contact vibrations.     

Dependence of polymer sliding friction on normal load and contact pressure

The sliding friction of bulk polymers was studied varying the normal load, contact pressure and sliding velocity. The variation of the area of apparent contact A with normal load W was also measured both under the sliding and unloaded conditions. For the sliding condition A ∝ W, while for the unloaded condition A ∝ Wⁿ where n is less than unity. The friction measurements were performed on a tribometer in the low load range and on a lathe using a strain gage dynamometer in the high load range. It was found that the coefficient of friction depends upon the velocity and pressure and the variation can be explained by the adhesion theory of friction in the light of the conditions at the interface. The measurement of sliding friction in an extrusion process shows that the coefficient of friction decreases with contact pressure and the interface friction shear stress is almost equal to the bulk shear strength of the material. All of these findings support the adhesion theory of friction for polymeric materials.     

用不同方法测定材料的玻璃化转变温度

玻璃化转变温度是材料的重要特性参数 ,对材料的研究有着重要意义。测定材料玻璃化转变温度的方法很多 ,各种方法由于其测试条件和测试内容不同 ,结果也各不相同。为更好的了解各种测试方法 ,本文用不同方法对同种样品的玻璃化转变温度进行测定 ,并对其结果进行讨论。     

The contact pressure distribution in the friction region of miniature journal bearings

The contact pressure distribution in miniature journal bearings is theoretically studied taking into consideration the friction between the contacting surfaces of the journal and the bearing bush. The experimentally confirmed formulae for the contact pressure distribution, the angle of contact and the ratio of the maximum contact pressure to the bearing contact pressure are derived. The contact pressure distribution may be described with a parabolic function.     

Effect of high hydrostatic pressure on the external friction coefficient

Experiments are carried out to determine the molecular and mechanical components of the specific friction force under the effect of hydrostatic pressure of up to 140 MPa. The molecular component of the friction coefficient declines by up to two times under the effect of the hydrostatic pressure in various fluids. It is found that the combined influence of the temperature and hydrostatic pressure on the mechanical properties and the contact pressure leads to considerable variations in the deformation component of the static friction coefficient in plastic contact at temperatures of up to 200°C and under pressures of up to 140 MPa. The dependence of the hardness of structural materials on the hydrostatic pressure is analyzed to predict the effect of the latter on the deformation component of friction. It is shown that with increasing pressure within the above range the hardness grows in proportion to the square of the pressure and is inversely proportional to the initial hardness. The formula for calculating the dependence of the indentation depth of a spherical indenter in elastic contact on the hydrostatic pressure is derived.     

Effect of resin modification on friction and wear of glass phenolic composites

The effect of resin modification on the friction and wear of glass woven roving phenolic composites has been studied. The friction and wear tests were carried out on a purpose built pin-on-disc apparatus. Straight (unmodified) phenolic resin, when chemically modified with poly (vinyl butyral) (PVB) containing 10 wt.% of butyraldehyde, results in improved ductility of the resin and increases the tensile modulus and impact energy of the composite. Modification of the matrix resin with PVB reduces the coefficient of friction and improves the wear resistance of the composite.     

Effect of temperature on the friction and wear of heat-resistant polymer-based composites

The friction and wear of polyether sulphone (PES: ‘Victrex’-ICI), polyether etherketone (PEEK: ICI), polyamide-imide (PAI: Torlon'-Amoco) and Polytetrafluoroethylene (PTFE) composites were measured at a constant sliding speed and under a constant load at various temperatures up to 300 °C by rubbing against a steel disc. The frictions of the composites, except for some PAI composites, were generally little dependent upon temperature over a wide range of temperature. PTFE filler was effective in reducing the wear of composites at high temperatures. However, the addition of various fibres to the composites was not effective at high temperatures. The wear of PAI composites increased rapidly with increasing temperature and thus their temperature variations were considerably greater than those of the other composites. The wear of PTFE containing ‘Econol’ E–1 OI, a polyoxybenzylene nomo-polymer (Sumitomo Chemical Co.) and graphite was similar to that of the PEEK composite containing PTFE, and their wear rates were remarkably low over a wide range of temperature. The wear-reducing mechanisms of PTFE and ‘Econol’ fillers are discussed on the basis of microscopic examinations of the frictional surfaces.     

测量玻璃化转变温度的几种热分析技术

高分子材料玻璃化转变的表征可提供丰富的信息,例如固化程度、热历史、材料的最高服役温度,共聚、共混物组分的相容性和相分离、组分的定性和定量等等,因此长期以来它都是高分子物理研究的主要内容[1-3]玻璃化转变有多种测试手段,本文讨论了热分析技术测量玻璃化转变的四类实验方法,比较了它们的特点和主要影响因素。     

Velocity and size dependences of the erosion rate in silicon

The results obtained in this investigation for the velocity and size dependences of the steady state erosion rate in silicon single crystals are consistent with the predicted power law relation only if certain modifications are made. The velocity exponent n must depend on the particle size in such a way that n decreases as D increases, and allowance should be made for the onset of an apparent size threshold effect at small particle sizes. Further theoretical work is needed to extend the existing models, taking into account a number of new physical features. Possible mechanism changes and thresholds seem most important in this context. Further systematic experiments are also needed to establish the important parameters and to extract reliably their phenomenological relations. It is pointed out that a cursory analysis of erosion rate data according to simple power law velocity and size dependence is likely to be inconsistent and a suitable range of D and υ values must be systematically analyzed.     

Effect of shoulder size on the temperature rise and the material deformation in friction stir welding

A fully coupled thermo-mechanical model is adopted to study the effect of shoulder size on the temperature distributions and the material deformations in friction stir welding. Numerical results indicate that the maximum temperature can be increased with the increase of the shoulder diameter. The stirring zone can be enlarged by the increase of the shoulder size. With consideration of the recrystallization formula, it is found that the temperature variation is the main factor for controlling the grain growth near the welding line. But, when the strain and the strain rate become smaller near the border of the stirring zone, the recrystallization process is dominated by the material deformations instead of the temperature rise.     

Effect of thermal sensitivity of materials of tribojoint on friction temperature

An analytical solution of a friction-heat problem for two semi-infinite solids taking into account the temperature dependence of their thermal characteristics has been obtained. It is assumed that the specific power of friction is constant and the thermal contact of the solids is imperfect. Because of the latter assumption, the linearization of the corresponding boundary heat conduction problem carried out using the Kirchhoff transform has turned out to be incomplete. Two methods for the final linearization of this problem have been proposed, i.e., the expansion of the nonlinear function in a power series, followed by the retention of only two first terms in it, and the use of linearizing multipliers. A numerical analysis for the materials with linear dependences of the thermal conductivity and the specific heat on the temperature is carried out.     

差示扫描量热法测定橡胶玻璃化温度

阐述了应用差示扫描量热法测定橡胶玻璃化转变温度的方法原理和分析步骤,通过具体研究实验条件(升温速率、试样用量、试样的预处理、二次升温及气氛等)对测定结果的影响,寻找测定的最佳实验条件以及对玻璃化转变温度测试结果的影响程度,对于橡胶玻璃化温度测试具有很大意义。     

Effect of atmospheric pressure on friction and wear of 0.45% C steel in fretting

Oxidative wear is significant in fretting wear when sufficient oxygen is supplied. In vacuum, however, oxide does not form readily. In this paper friction and wear behaviours were studied at various atmospheric pressures in order to clarify the effect of ambient pressure on them.Experiments were conducted with 0.45% C steel at ambient pressures from 1.0 × 10⁵ to 1.3 × 10^?3 Pa. The load was 14 N, the peak-to-peak slip amplitudes were 35 and 110 μm and the frequency was usually 8.3 Hz.Friction behaviours are characterized into three types according to the ambient pressure: 1.0 × 10⁵ ? 10 Pa, 10 ? 10^?1 Pa and below 10^?1 Pa. The coefficient of friction increases with a decrease in ambient pressure below 1 Pa. The critical pressure in fretting is found to be 10 Pa, above which the oxidation rate is independent of the ambient pressure and α-Fe₂O₃ is formed. Wear decreases with ambient pressure below the critical pressure where Fe₃O₄ is formed. Adhesive transfer of metallic debris occurs below 10^?1 Pa.The relationship between the coefficient of friction and oxide thickness is obtained analytically, and the effect of frequency on the oxidation rate is considered.     

Studying the temperature dependences of the parameters of laser-generated lamb waves

The process of laser generation of pulses of symmetrical and antisymmetrical Lamb waves in a ferromagnetic plate due to the thermoelastic effect was experimentally studied. The temperature dependences of the shape, amplitude, duration, and vibration frequency of acoustic pulses and the velocities of their propagation in the plate were investigated.     

进气畸变对发动机压缩系统稳定性影响的数值模拟

介绍了一种在发动机环境下评定航空燃气涡轮发动机压缩系统稳定工作边界的数学物理模型。研究了进气畸变对航空燃气涡轮发动机压缩系统稳定工作边界的影响。对总压畸变进气条件下压气机稳定工作边界的变化进行了计算分析,结果表明进气总压畸变对发动机稳定性有很大的影响,使得压气机稳定工作边界在压气机的特性图中向右下方移动,降低了发动机的喘振裕度。主要数学物理模型可以正确地反映发动机压缩系统的工作状况,用它判断发动机不稳定工作点的重复性和灵敏度都比较好。     

Effect of contact pressure on wear and friction of ultra-high molecular weight polyethylene in multidirectional sliding

Computational wear models need input data from valid tribological tests. For the wear model of a total hip prosthesis, the contact pressure dependence of wear and friction of ultra-high molecular weight polyethylene (UHMWPE) against polished CoCr in diluted calf serum lubricant was studied, and useful input data produced. Two test devices were designed and built: a heavy load circularly translating pin-on-disc (HL-CTPOD) wear test device and an HL-CTPOD friction measurement device. Both can be used with a wide range of loads. The wear surface diameter of the test pin was kept constant at 9 mm, whereas the load was varied so that the nominal contact pressure ranged from 0.1 to 20 MPa. The wear factor decreased with increasing contact pressure, whereas the coefficient of friction first increased with increasing contact pressure with low pressure values and then decreased. Up to the pressure of 2.0 MPa, the wear mechanisms and wear factors were in good agreement with clinical findings. In the critical range of 2.0-3.5 MPa, the wear mechanisms and wear factors started to differ from clinical ones, and the decrease of the wear factor steepened. The discrepancy became more and more evident as the pressure was gradually increased beyond 3.5 MPa. It appears that the pressure value of 2.0 MPa should not be exceeded in pin-on-disc wear tests that are to reproduce the clinical wear of UHMWPE acetabular cups.     

Effect of cyclic internal pressure on the temperature distribution in a viscoelastic cylinder

A modified numerical method is introduced to study the interaction between the heat and dynamic response of viscoelastic bodies with temperature-dependent properties. The method is applied to calculate the stress and temperature distributions in a viscoelastic cylinder subjected to cyclic internal pressures. It is found that a large temperature rise may occur due to the interaction, where the value depends upon the thermal and mechanical properties of the material, cylinder size and the frequency of the applied pressure.     

喷雾干燥过程中的产品玻璃化转变初探

喷雾干燥是一种把固液体转变为干粉的常用手段，已在许多工业中运用了很多年，处理过的物料成千上万…。过去，人们的研究主要集中在料液的雾化、热空气的均匀分布、喷雾干燥的设计。喷雾干燥的数学模型和针对某一种物料的成功喷雾干燥等方面，关于物料在整个喷雾干燥过程中的状态变化，对于产品的质量影响几乎未见报道。从喷雾干燥料液的干燥阶段着手，通过分析物料在整个喷雾干燥阶段中的状态变化，研究了物料的玻璃化转变特性和产品质量与干燥工艺参数的关系，得出了相应的结论，使得喷雾干燥工艺用于制粉更加合理。     

Wet sliding friction of elastomer compounds on a rough surface under varied lubrication conditions

‘Green’ tire bearing tread rubber reinforced with precipitated silica can exhibit improved wet traction performance. The underlying mechanism is currently not well understood. To improve our capability of rational material design for enhanced driving safety, wet sliding friction for various rubber compounds is tested on a Portland cement concrete surface under varied lubrication conditions. The wetting liquid is either ethanol or water, and the initial amount of liquid on the concrete surface is adjusted. Sliding friction is detected to alter with lubrication condition. Under ethanol lubrication, the sliding friction is markedly lower than that under water lubrication. Additionally the benefit in wet traction from silica is significantly diminished or eliminated in ethanol. Such observations cannot be rationalized with simple considerations of rubber bulk viscoelasticity, liquid viscosity, cavitation, or capillary effect. We believe that these observations strongly indicate the significance of interfacial interactions in determining the wet sliding friction of elastomer compounds. The potential relevance of capillary porosity in concrete and Marangoni drying effect to wet traction is also introduced.     

摩擦火花瞬时高温对中高碳钢中碳的影响

选取42CrMo、60Si2Mn、GCr153种常见的中高碳钢理论分析和检测验证两方面对高速打磨过程中摩擦火花瞬时高温是否会对中高碳钢表面形成脱碳层,从而影响中高碳钢中碳含量的检测进行探讨、验证。结果表明高速打磨过程中摩擦火花瞬时高温无法达到中高碳钢表面脱碳所需的温度,并且在实际检测中标准物质11次测试结果的RSD在0.499%~0.698%,测试结果的平均值和认定值的差值均在标准样品证书的不确定度范围内。因此高速打磨过程中摩擦火花瞬时高温不会影响中高碳钢中碳含量的检测。