粗糙表面弹流润滑的摩擦系数的分析计算

本文在弹性流体动力润滑情况下对摩擦系数的计算方法进行了分析,考虑了流体的非牛顿流变特性和微凸体接触压力的影响。以平均型条纹粗糙表面为计算模型,在各种工况下对摩擦系数进行了计算对比。     

Observations on the effectiveness of some surface treatments of mineral particles and inorganic compounds from Armenia as the fillers in polyphenylene sulfide for tribological performance

This is a general study in which a number of minerals and inorganic compounds from Armenia were investigated for their effectiveness as the fillers in polyphenylene sulfide (PPS) for tribological performance. The minerals studied were tuff, bentonite, and travertine, and inorganic compounds MoO₃ and MoO₂. The filled polymer specimens were prepared by compression molding and tested for tribological behavior in the pin-on-disk sliding configuration. The particulate fillers included many variations in terms of the size (micro and nano) and surface treatment. Friction and wear test results revealed that MoO₂ and nano size bentonite particles were effective in improving the wear resistance. The lowest steady state wear rate in this study was observed for PPS+7% MoO₂ (50 nm)+5% PTFE composite, and MoO₂-filled composites had generally lower coefficients of friction than that of the unfilled PPS. From the wear plots, filler abrasiveness, and transfer film studies, it was concluded that the abrasion by filler was mostly responsible for the detrimental wear behavior. The wear behavior has been discussed in terms of the abrasion by filler and transfer film uniformity, texture, thickness, and coverage. The effects of particulate size and surface treatment are also included in the discussion. In view of the results reported for these fillers in formaldehyde and dioxolane copolymer (CFD) and the observations in this study, it is felt that the fillers from Armenia with the exception of tuff and MoO₃ have considerable appeal for further investigation using other innovative surface treatments for fillers.     

钢铜摩擦副摩擦磨损特性的试验研究

本文试验分析了ＺＱＡ１９－４和ＺＱＺｎ６－６－３两种铜合金材料在不同的表面粗糙度下对摩擦系数和出口区油温的影响，以及改变载荷和相对滑动速度时，摩擦系数的变化状况。结果表明；铜合金成分不同时具有不同的硬度。     

Effects of filler crystal structure and shape on the tribological properties of PTFE composites

In this paper, effects of filler crystal structure and shape on the friction and wear properties of potassium titanate whisker (K₂Ti₄O₉ whisker, K₂Ti₆O₁₃ whisker), TiO₂ whisker and TiO₂ particle filled polytetrafluoroethylene (PTFE) composites under dry friction conditions were studied. Meanwhile the influence of filler content, sliding duration, test speed and load were also investigated. Experimental results show that the friction coefficients of various PTFE-based composites are weakly dependent on filler shape but they are more strongly dependent on filler crystal structure. However, for improving the anti-wear property of PTFE, filler crystal structure has less importance than filler shape in the wear-reducing action of PTFE-based composites, and whisker-like filler is better than particle-like filler.     

Tribochemical Processes and Wear Resistance of Polymeric Materials

Tribochemical transformations of polyphenylquinoxaline (PPQ) and a composite material on its basis containing graphite are investigated. A mass-spectrometric analysis shows that in the polymer surface layers the destructive-structurizing processes occur on friction that changes the structure and properties of the surface layer. It is shown that, in the presence of a graphite filler, the tribochemical transformation character also changes. Based on the investigation data, a general scheme of tribochemical changes of PPQ is proposed and their relation to wear is suggested.     

Comparative study of the tribological properties of various modified mild steels under boundary lubrication condition

AISI1045 steel was modified by laser heat-treatment and conventional heat treatment. The friction and wear behaviors of the steel specimens after various surface modifications sliding against SAE52100 steel under the lubrication of liquid paraffin containing sulphurized olefin were comparatively investigated on an Optimol SRV oscillating friction and wear tester. The worn surface morphologies of the modified steel specimens were analyzed using a scanning electron microscope. The elemental compositions and chemical states of some typical elements on the worn surfaces of the modified steel specimens were analyzed with an energy dispersive X-ray analyzer and X-ray photoelectron spectroscope, respectively. It was found that the laser heat-treated specimen showed the highest hardness and best wear-resistance. The laser heat-treated and conventionally heat treated AISI1045 steel specimens sliding against SAE52100 steel under the lubrication of liquid paraffin containing sulphurized olefin registered smaller friction coefficients than under the lubrication of liquid paraffin alone. This was partly attributed to the increased hardness of the modified specimens. The tribochemical reaction between the steel and the active elements in the additive was involved in the sliding of the modified steel specimens against SAE52100 steel ball under the boundary lubricating condition, with the formation of a surface protective film composed of various tribochemical products. This also contributed to improve the friction and wear behavior of the modified steel specimens. The steel specimens subject to different surface modifications showed differences in the wear mechanisms under the boundary lubricating condition as well. Namely, the tempered steel specimen was mainly characterized by plastic deformation and pitting, the quenched specimen by grooves and delaminating, and the laser heat-treated one by polishing and mild adhesion.     

在乳化液润滑条件下几种常见材料的摩擦磨损特性研究

本文研究了在乳化液润滑条件下，四种常见材料（尼龙、铸铝、40Cr、45^#钢）的摩擦磨损特性。利用M－200摩擦磨损实验机，对这四种材料进行了在不同载荷、转速条件下的摩擦磨损性能对比实验。结果表明尼龙适合在较低载荷与转速下工作，异种材料之间配合的摩擦特性要优于同种材料间的摩擦特性。     

Experimental Study on the Friction Characteristics of Lasertex Steel Sheets During Metal Forming Process

The surface of steel sheets used in the metal-forming process discussed in this article was textured by a laser-ablation technique. Differently shaped craters are formed in a patterned structure on the steel surface by controlling the pulsed-laser power density, pulse-repetition rate, and pulse duration. Lasertex sheets formed by this process have unique friction characteristics because of the uniform surface roughness and valley-biased topography. The friction of lasertex sheets was studied using a metal-forming bench test rig. Influencing factors, including surface roughness and sliding velocity, were studied under lubricated conditions. The friction of lasertex sheets was compared with that of shot-blasted sheets. The results showed that the coefficient of friction of the lasertex sheet under dry friction decreases with an increase in surface roughness and changes little with varying sliding velocity. With lubrication, the coefficient of friction of the lasertex sheet rises with an increase in surface roughness and decreases with an increase in sliding velocity. Lasertex sheets were found to have lower friction coefficients than shot-blasted sheets over the rage of surface roughness and sliding velocity investigated.     

Mechanical and tribological properties of short-fiber-reinforced SiC composites

The short-carbon-fiber-reinforced SiC (C_sf/SiC) composites were prepared by hot-pressing sintering with Si, Al and B as sintering additives. The effects of fiber volume fraction on the mechanical and tribological properties of the C_sf/SiC composites were investigated. The results show that the bending strength values of the composites containing a certain content of the short carbon fibers are higher than that of the monolithic SiC. The friction coefficients of the composites decrease with increasing short carbon fibers content. Except of the composite containing 53 vol% short carbon fibers, the wear rates of the composites decrease with increasing short carbon fibers content, and are lower than that of the monolithic SiC drastically.     

The Effect of Temperature on the Tribological Behavior of RBD Palm Stearin

The wide use of petroleum-based oils raises concerns with regard to pollution, and the rising of awareness of greenhouse gases has created a demand for the use of environmentally friendly and biodegradable lubricants for industrial applications. Vegetable oils are one of the bio-oils that have been promoted as a replacement for petroleum products, in part due to their environmentally friendly characteristics; they are nontoxic, biodegradable, and easy to dispose of. Many researchers have performed studies on sunflower oil, corn oil, and soy oil, but few have studied palm oil as a lubricant. Palm oil produced in a high-throughput manner could fulfill the demand for bio-based lubricants. In this study, the influence of temperature on friction and wear performance for refined, bleached, and deodorized (RBD) palm stearin and additive-free paraffinic mineral oil is presented. The experiments were conducted using a four-ball tribotester. Test temperatures of 55, 65, 75, and 85°C were used. The sliding speeds were set to 1,200 rpm. Experiments were run for 1 h under a 392.4 N load. The results of RBD palm stearin were compared with those of paraffinic mineral oil. The experimental results showed that the RBD palm stearin had better performance compared to paraffinic mineral oil in terms of reducing frictional constraints.     

Design of experiments approach to the study of tribological performance of Cu-concentrate-filled PPS composites

The tribological performance of copper-concentrate (CC) mineral deposit as the filler in polyphenylene sulfide (PPS) was studied as a function of the filler proportions and sliding test variables. CC is a complex mixture of CuS, Fe_xO_y, SiO₂, Al₂O₃, and other trace materials. The design of experiments based upon L₉ (3⁴) orthogonal arrays by Taguchi was used. Sliding tests were performed in the pin-on-disk configuration against a hardened tool steel (55-60 HRC) disk. The improvement in wear resistance of PPS was considerable with the use of fillers. The lowest steady state wear rate of 0.0030 mm³/km was obtained for PPS+20%CC+15%PTFE composition. It was two orders of magnitude lower than that of unfilled PPS. The variations in steady state coefficient of friction with the changes in filler proportions and sliding test variables were small. The transfer film was studied by atomic force microscopy (AFM) and scanning electron microscopy (SEM). X-ray photoelectron microscopy (XPS) was used to detect chemical reactive species developed during sliding, especially in the interface between transfer film and its counterface. Wear particles and the polymer worn surfaces were analyzed by energy dispersive spectroscopy (EDS) for elemental distribution.     

The Effect of Laser Texturing of Steel Surfaces and Speed-Load Parameters on the Transition of Lubrication Regime from Boundary to Hydrodynamic

Laser surface texturing (LST) is an emerging, effective method for improving the tribological performance of friction units lubricated with oil. In LST technology, a pulsating laser beam is used to create thousands of arranged microdimples on a surface by a material ablation process. These dimples generate hydrodynamic pressure between oil-lubricated parallel sliding surfaces. The impact of LST on lubricating-regime transitions was investigated in this study. Tribological experiments were carried out on pin-on-disk test apparatus at sliding speeds that ranged from 0.15 to 0.75 m/s and nominal contact pressures that ranged from 0.16 to 1.6 MPa. Two types of oil with different viscosities (54.8 cSt and 124.7 cSt at 40°C) were evaluated as lubricants. Electrical resistance between flat-pin and laser-textured disks was used to determine the operating lubrication regime. The test results showed that laser texturing expanded the range of speed-load parameters for hydrodynamic lubrication. LST also reduced the measured friction coefficients of contacts that operated under the hydrodynamic regime. The beneficial effects of laser surface texturing are more pronounced at higher speeds and loads and with higher viscosity oil.     

Experimental Investigation of Partial Laser Surface Texturing for Piston-Ring Friction Reduction

An experimental study is presented to evaluate the effect of partial laser surface texturing (LST) on friction reduction in piston rings. In a previous study, 30% friction reduction was obtained with full LST where the full width of the piston ring is textured with a very large number of microdimples that act individually as microhydrodynamic bearings. In partial LST, only a portion of the piston-ring width is textured with high dimple density, producing a “collective” effect of the dimples that provides an equivalent converging clearance even with nominally parallel mating surfaces. Experimental results obtained with flat and parallel test specimens with partial LST are presented, confirming a previously published theoretical model and the advantage of partial over full LST. Friction reduction by LST with actual production-crowned piston rings and cylinder liner segments is not straightforward and needs further investigation.     

Tribological properties of some phenolic composites suggested for automotive brakes

Brake linings used in automotive disk brakes are usually made of various components such as phenolic resin, Cu powder, BaSO₄, Al₂O₃, etc. In this study, 20 specimens with different compositions of the components were manufactured and a pad-on-disc-type wear tester was used. Friction and wear characteristics of the specimens next to a disk made of cast iron were studied. In addition, micro-structural characterisation of braking pads was carried out using SEM and also the effect of temperature on behaviour of the pads was investigated at the temperatures of 50–400 °C and pressure of 1050 and 3000 kPa. Finally, the effect of environment on the pads was investigated in water, salty water, oil and braking liquid media.     

Investigation of the surface structure and elastic properties of calcium silicate hydrates at the nanoscale

This work is the first step towards the understanding of the structure of calcium silicate hydrate (C–S–H), the main constituent of cement paste, at the nanoscale. The first demonstration of atomic-resolution imaging of the (C–S–H) surface with an atomic force microscope (AFM) was performed.

C–S–H nanoparticles (60×30×5 nm³) were partially recrystallized by Ostwald ripening after long-term equilibrium in saturated calcium hydroxide solution of different concentration, leading to C–S–H of different calcium/silicon ratio (Ca/Si). The results of atomic resolution made possible the investigation of the C–S–H cell surface parameters. The surface layer structure depended on the calcium hydroxide concentration with which it equilibrated.

The change in structural properties perpendicular to the C–S–H layer was probed by modifying AFM for nanoindentation hardness measurements with a depth of indentation as low as 1 nm. The change in elastic modulus depending on the calcium/silicon ratio was evaluated and correlated in the change in structural parameters in this direction as estimated by X-ray diffraction.     

Artificial neural networks for predicting sliding friction and wear properties of polyphenylene sulfide composites

In this paper the potential of using artificial neural networks (ANNs) for the prediction of sliding friction and wear properties of polymer composites was explored using a newly measured dataset of 124 independent pin-on-disk sliding wear tests of polyphenylene sulfide (PPS) matrix composites. The ANN prediction profiles for the characteristic tribological properties exhibited very good agreement with the measured results demonstrating that a well trained network had been created. The data from an independent validation test series indicated that the trained neural network possessed enough generalization capability to predict input data that were different from the original training dataset.     

Effect of surface coating and tin plating on friction characteristics of P-110 tubing for different thread compounds

Design factor problems related to galling failure have become an increasing concern for deepwater offshore wells. This paper presents the results of an experimental study conducted to determine friction characteristics of P-110 tubing coated with manganese phosphate and plated with tin. Six repeated tests were run to investigate the effect of lubrication type on friction characteristics of P-110 tubing by using thread compounds of API modified Threadkote-706, Shell Type-3 and Graphite/PTFE at a rotational speed of 5 rpm. In each test the bearing load was increased monotonically to a maximum value of 625 kN. The results of this study clearly indicate the importance of tin-plating in reducing the coefficient of friction.     

缸套—活塞环材料在往复滑动中摩擦系数的试验研究

为了研究机车柴油机缸套活塞环材料的摩擦学性能,我们设计并制造了一台往复式摩擦磨损试验机。该试验机可在一定范围内实行载荷、速度、润滑量的单因素控制,并可同时定性和定量的显示运动中的摩擦力大小。我们利用该试验机对美国GE公司采用的软氮化铸铁缸套—表面镀铬铸铁活塞环材料进行了摩擦学性能的试验研究,得出了该配对副在往复滑动中摩擦系数随载荷和速度变化的关系曲线。     

Investigation of the tribochemical and physico-mechanical processes in sliding of mineral-filled formaldehyde copolymer composites against steel

The effect of the treatment of the mineral fillers travertine, bentonite and tuff by organic lubricating materials on the structure and tribological properties of polymer composites was studied. The composites were made with these fillers and the formaldehyde based copolymer. They exhibited higher wear-resistance, improved strength properties and decreased coefficient of friction. The thermo-gravimetric, thermo-mechanical and sol-gel analyses indicated higher thermostability and improved elastic-viscous properties of the composites. The electron paramagnetic resonance spectroscopy confirmed the formation of intermolecular chemical bonds between polymer chains, which contributed to the increase in stiffness of the filled composite as a consequence of the formation of reticular structure. The analysis of transfer films formed on steel counterfaces by secondary-ion mass-spectrometry indicated thermo- and tribocracking of composites because of the depolymerization of polymer chain and the formation of low-molecular fractions. The modified mineral fillers contributed to the decrease in the rate of tribodestruction of basic copolymer chain by retarding the active oxidation of friction surfaces. Because of these processes, the increase in wear-resistance and the decrease in the coefficient of friction were obtained.     

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.