Formation and frictional properties of boundary lubricating and surface‐modified layers at elevated temperatures

The influence of heating on the properties of lubricating layers formed on steel by inactive and chemically active lubricant components has been studied by electrical probe methods. Model experiments combining X‐ray photoelectron spectroscopy analysis and measurements of friction and electrical characteristics in static and dynamic point contact have shown the approach to be promising in separate studies of the properties of the physically adsorbed layer (A‐layer) and chemisorbed layer (D‐layer) of deposits. It has been confirmed that D‐layers can be formed on metal surfaces at moderate temperatures (T ∼ 200°C) by both active additives and inactive components of mineral oil. Zinc dialkyldithiophosphate additives provide higher load‐bearing capacity of the A‐layer compared to pure mineral oil and can form D‐layers on steel at relatively low temperatures (of about 100°C). Lubricating layers with different physicomechanical and frictional properties can be formed depending on the chemical origin of the lubricating medium and the temperature regime.     

Effect of high-pressure rheology of lubricating oils on boundary lubrication

High-pressure rheology of lubricating oil was determined using different experiments, and the phase diagram was drawn. The four-ball wear tests were used to evaluate anti-wear characteristics of oils in boundary lubrication condition. The bridged ring compound oils showed the minimum wear scar in the four-ball wear tests. The diameter of wear scar decreases with increasing the elastohydrodynamic film-forming capability. Next, we considered the molecular packing parameter T_VE−T at the four-ball wear test. The T_VE−T values of bridged ring compound oils were in the range 250-360 and oils were elastic-plastic solid. It is concluded that the solidified oil film under boundary lubrication conditions has the anti-wear action.     

纳米结构双层类脂膜的发展及应用

双层类脂膜(Bilayer Lipid Membrane,BLM)作为生物膜的基本结构模型已被广泛的接受,双分子层结构使双层类脂膜的厚度不到10 nm.介绍了纳米结构双层类脂膜的实验进展及电学特性,阐述了双层类脂膜在生物化学传感器中的应用,并展望了发展前景.     

Kinetics of formation of adsorption boundary lubricating film under lubricant starvation

The kinetics of the formation of the boundary lubricating film at severe sliding friction is described. A new probabilistic model of the adsorption process running within the interfacial capillary net is used to determine the characteristic time of the formation of a polymolecular lubricating film. It considers the supramolecular ordering of the film by introducing the ordering factor.     

Hydrogen's interaction with hardened surface layers in lubricated frictional couples

The obtained results confirmed the influence of surface layer structure on the boundary layer durability of oil in concentrated contact. The advantageous effect of increased concentration of hydrogen in surface layer on the quality of lubrication as well as its significant contribution to tribological process was validated. The results of boundary friction for different structures of surface layer will be presented taking into consideration or not the influence of hydrogen on their durability. The experimental methods were based on the measurements of relative time when the short circuit was present in lubricated frictional nodes, chromatography and low-temperature diffraction measurements. The physico-chemical model of interaction between lubricant (oil base and motor oil) and hardened elements varied from chemical and structural point of view has been proposed. The model is based on the specific interactions of protons with aliphatic chains of lubricant.     

Orientation ordering of boundary layers and lubricity of oils

A computer model of the adsorption process of lube oil molecules on friction surfaces reveals that carbon monocrystalline coatings with a strongly orientating effect promote the level of molecular orientation in boundary layers contrary to the amorphous ones because there is no essential orientating effect on these layers. The results of lab tribological tests of carbon coatings deposited on steel surfaces in some model oils corroborate that the coatings with a higher level of orientation ability yield better lube properties.     

The friction of sliding surfaces carrying boundary layers

Conventional boundary films are thought of as ``solid' layers in which shear strength is directly proportional to local contact pressure. However, recent studies suggest both that the properties of adsorbed or deposited surface films may be much more com- plex than this and that the details of surface topography cannot be ignored in determining the overall coefficient of friction of real engineering contacts. In this contribution we examine both these effects.     

Correlation between performance and boundary layers in high speed bearings lubricated with polymer-enhanced greases

In this paper the effect of greases enhanced with polymer additives on the tribological behavior of high speed angular contact bearings is investigated. Bearing test results indicate lower operating temperatures for grease enhanced with dispersing polyalkylmethacrylate in relation to plain reference grease. The effect of the additives on the boundary layers was investigated by means of nano indentations on the raceways. It could be shown that the loading–unloading curves differ significantly, depending on the nature of the reaction/boundary layers on the raceways. Additionally, ToF-SIMS with depth profiling (time of flight secondary ion mass spectroscopy) helped to analyze the composition of the boundary layers. The profiling showed significantly different reaction layers with beneficial layers resulting from grease enhanced with dispersing PAMA.     

Characterization of the near-surface layers of carbon steels modified by interaction with intense pulsed plasma beams: scanning electron microscopy investigations

Modification of materials is a wide area in materials science, especially surface modification. To investigate the results of the modification process, treated and nontreated samples were compared. Intense plasma pulses of argon or nitrogen were used to irradiate the carbon steels. In all samples, the near‐surface layer was melted. Results of scanning electron microscopy investigations of the surface morphology and cross‐sections, as well as the results of tribological tests, are presented. The obtained results allowed us to draw conclusions about changes in material properties and to propose subsequent studies using other investigation techniques.     

Interrelation between dynamic processes in boundary lubricating films and physicomechanical characteristics of radial sliding bearing

The mechanism of the appearance of reverse secondary flows in boundary lubricating films in a radial sliding bearing has been proposed. It has been found that the axial load and the velocity of sliding determine the sign and magnitude of the pressure gradient in the lubricating films astride the contact. The inter-relation between the aggregate state of the lubricant, as well as the local pressure in it and the force of friction, has been established.     

Sliding mode control with varying boundary layers for an electro-hydraulic position servo system

In this study, a new sliding mode control with varying boundary layers is proposed to improve the tracking performance of a nonlinear electro-hydraulic position servo system, which can be found in many manufacturing devices. The key feature of the proposed control scheme is the use of varying boundary layers instead of fixed boundary layers, which are usually employed in conventional sliding mode control. The validity of the proposed control scheme is verified through practical testing on an experimental electro-hydraulic positioning device. In the cases of step and sinusoidal command inputs, the experimental results strongly suggest that the proposed control scheme is capable of improving the tracking precision without causing any chattering. In addition, the new control scheme seems to be very robust against various set point conditions .     

Direct Numerical simulation of 3-Dimensional axial turbulent boundary layers with spanwise curvature

Direct numerical simulation has been used to study turbulent boundary layers with convex curvature. A direct numerical simulation program has been developed to solve incompressible Navier-Stokes equations in generalized coordinates with the finite volume method. We considered two boundary layer thicknesses. When the curvature effect is small, mean velocity statistics show little difference with those of a plane channel flow. Turbulent intensity decreases as curvature increases. Contours suggest that streamwise vorticities are strong where large pressure fluctuations exist.     

Pressure distribution and flow development in unsteady incompressible laminar boundary layers

It is shown that in an unsteady flow the friction drag is always accompanied by the form drag whose magnitude is comparable to that of the former and that the pressure around the unsteady boundary layer can be far from that of the inviscid irrotational flow. The unsteady boundarylayer equations and boundary conditions for the external potential flow are modified accordingly and the flow around a circular cylinder which is set impulsively to move in a constant velocity is analysed using these modified boundary-layer equations. The solutions are in power series of \(\sqrt \tau \) rather than τ where τ is the dimensionless time elapsed since the onset of motion, and the form drag, like the friction drag, decreases from infinity in inverse proportion to \(\sqrt \tau \) , when τ is small.     

A method for the evaluation of the boundary lubricating properties of aviation turbine fuels

Using the principle of the Amsler machine, a method has been developed for evaluating the boundary lubricating properties (lubricity) of aviation turbine fuels over a temperature range from ambient to 150°C in a controlled atmosphere. The method of fuel supply was found to be a critical factor, a single-pass flooded system being superior to both trickle feed and static flooded arrangements. Equally important were the hardness and surface finish of the test specimens. Fuel lubricity properties were quantified using a derived failure load based on coefficient of friction, a parameter which, for aviation turbine fuels, accurately reflected the lubrication conditions at the rubbing contact. Failure loads based on wear and gross seizure were less satisfactory. The correlation of friction failure loads with practical experience in the field was excellent for a wide selection of Jet A-1 type fuels including low lubricity fuel with added lubricity-improving boundary lubricating additive. The method is recommended for measuring the lubricity performance of candidate lubricity-improving additives, for monitoring low lubricity fluids used in hardware development and for investigating lubricity problems as they occur in practice.     

Demonstration of a laser vorticity probe in turbulent boundary layers

A laser-based probe for the nonintrusive measurement of velocity gradient and vorticity was demonstrated in turbulent boundary layers. Unlike most other optical methods, the current technique provides an estimate of the velocity gradient, without having to first measure velocity at multiple points. The measurement principle is based on the heterodyne of coherent light scattered from two adjacent particles. The beat frequency of the heterodyne is directly proportional to the velocity gradient. The probe is assembled from commercially available, inexpensive optical components. A laser Doppler velocimeter (LDV) processor is used to analyze the heterodyne signal. A component of vorticity is obtained by using two appropriately aligned velocity gradient probes. The optical probes developed were used in turbulent boundary layers to measure local, time-frozen velocity gradients partial differential u / partial differential y, partial differential v / partial differential x, and partial differential v / partial differential y, as well as the spanwise vorticity. The measurements were compared to those inferred from LDV measurements in the same facility and to data available in the literature.     

The mechanism of electrical charge transfer in lubricant boundary layers

The electrical properties of lubricant boundary layers have been studied by establishing the current-voltage characteristics of some lubricating materials. The justification of a boundary layer concept is confirmed and the properties of the boundary layer are due to its defect structure and the higher energy of the defective areas.     

Determination of ganciclovir as an antiviral drug and its interaction with DNA at Fe3O4/carboxylated multi-walled carbon nanotubes modified glassy carbon electrode

The electrochemical oxidation of an antiviral drug, ganciclovir (GCV) at Fe₃O₄/carboxylated multi-walled carbon nanotubes modified glassy carbon electrode (Fe₃O₄/cMWCNTs/GCE) was studied by voltammetric techniques. The influence of the effective parameters on the electrochemical behavior of GCV was investigated. Under optimized conditions, the proposed sensor was applied for low level GCV determination. The relationship between peak current and the concentration of GCV was linear in the range of 80–53,000 nM with a detection limit of 20 nM through square wave voltammetry (SWV). The interaction of GCV with calf thymus DNA was also explored by voltammetric and spectrofluorometric methods. Based on the obtained data the mode of binding of GCV to DNA was intercalative binding. The decrease in the SWV peak current of GCV in the presence of DNA was used for the determination of DNA. The modified electrode exhibited a good sensitivity, stability and pleasant reproducibility, and it was applied for the determination of GCV in spiked serum and urine, with satisfactory results.     

轴承元件陶瓷化——简述陶瓷金属耦合材料润滑油脂在轴承上的应用

陶瓷金属耦合材料在轴承工业的应用使轴承陶瓷化,实现了陶瓷金属航天材料在轴承工业中的普及化和民用化。在不更换设备、不改变技术、工艺和材料的基础上,冲破材料本身的极限,使轴承的寿命、精度、档次产生一个质的飞跃。