Conditions Of Boundary Friction Research Articles

ON A LUBRICATION PROBLEM WITH FOURIER AND TRESCA BOUNDARY CONDITIONS

The asymptotic behavior of a Stokes flow with Fourier boundary condition on one part on the boundary and Tresca free boundary friction condition on the other, when one dimension of the fluid domain tends to zero is studied. The strong convergence of the velocity is proved, a specific Reynolds equation is obtained, and the uniqueness of the limit velocity and pressure distributions is established.

Tribochemistry of aluminium and aluminium alloy systems lubricated with liquids containing alcohol or amine additive types and some other lubricants — a review

AbstractThe ability of a lubricating oil to reduce wear and prevent damage of interacting solids is a crucial factor controlling lubricant formulation. It is well known that friction produces local high temperatures. Many chemical reactions that are initiated by the friction process itself occur at much lower temperatures than those needed to provide the activation energy. Under boundary lubrication conditions, a clean surface exposed as a result of mechanical activity of the solid surface is extremely reactive, especially in the case of metals. This review mostly relates to the tribochemistry of aluminium, and discusses the tribological characteristics of alcohol‐ and amine‐type liquids used as either additives or lubricants to lubricate aluminium and its alloys under boundary friction conditions. Although tribochemical reactions during sliding are perceived in various ways, here the emphasis is on the negative‐ion‐radical action mechanism (NIRAM) approach. This review addresses the question as to how present knowledge of tribochemistry can be applied to the elucidation of the mechanisms of action by which the boundary lubricant compounds considered reduce aluminium‐on‐aluminium, steel‐on‐aluminium, and aluminium‐on‐steel wear. Also, information and a discussion on the tribological behaviour of other additives and/or lubricants in relation to the friction and wear of aluminium and its alloys are presented. A concise review of the most recent work on the tribochemistry of selected fluorinated alcohols is also included.

The phenomenon of non-adhesion sliding friction in conditions of boundary friction

For the first time it is proved experimentally the opportunity of realization the phenomenon of nonadhesion friction in conditions of boundary greasing. For research of realization this phenomenon in technics the new probing system of friction with an original technique of tests was developed and created.

Investigation of the Wear Products of Austenitic Manganese Cast Irons

We study the wear products of austenitic manganese irons. We have shown that the mechanism of fracture of these alloys (and, correspondingly, the formation of wear products) depends on both the structural-phase composition of the alloys and the load-speed characteristics of external friction. Under conditions of boundary friction, the average size of wear particles varies from 0.1 to 3.0 μm. In the case of oxidative wear, among its products we have found (Cr, Fe)2O3 and Fe3O4 oxides, which are component parts of the secondary structures of oxide origin. We have established that the fracture of the alloys occurs also along the boundaries of graphite inclusions, and it is especially intense under conditions of the onset of seizure for specific loads exceeding 5.0 MPa and a slip velocity of 0.628 m/sec.

Formation of Friction Layers and Wear Resistance of Steels under Conditions of Boundary Friction

We studied the influence of the lubricant compositions “Grafitol” with ∼10% graphite (1), “Aerol” containing ∼17% MoS2 (2), “Limol” containing ∼60% MoS2 (3), “Limol” + 10% chlorine-paraffin (4), and “Limol” + 10% copper powder (5) on the wear rate and formation of the fine structure of surface friction layers of structural steels. We established a correlation between the tribological characteristics of steels and lubricants. The abrasive wear of 40KhFA steel was minimum if it was lubricated with “Limol” + 10% copper powder. In this case, its wear was smaller by a factor of 10, 2, 1.25, and 7.25 as compared with lubricant compositions 1–4, respectively. In the course of minimum wear of 40KhFA steel, in the surface friction layers, we observed the minimum values of second-kind distortions (Δa/a) and of the true size of domains of X-ray coherent scattering (D) as well as the minimum difference between the crystal lattice constants (a) of steel before and after friction.

Wear Resistance of Laser-Modified Arc-Sprayed Coatings Made of FMI-2 Powder Wires

A fine crystal nonporous structure of arc-sprayed coatings with uniformly distributed chemical elements can be obtained as a result of optimization of the parameters of laser treatment. The wear resistance of these coatings under the conditions of boundary friction and abrasive wear also significantly increases.

On a free boundary problem for the Reynolds equation derived from the Stokes system with Tresca boundary conditions

The asymptotic behaviour of a Stokes flow with Tresca free boundary friction conditions when one dimension of the fluid domain tends to zero is studied. A specific Reynolds equation associated with variational inequalities is obtained and uniqueness is proved.

Asymptotic analysis of solutions of a thin film lubrication problem with Coulomb fluid–solid interface law

The asymptotic behavior of a Stokes flow with Coulomb free boundary friction condition when one dimension of the fluid domain tends to zero is studied. The strong convergence of the velocity is proved, a specific Reynolds equation is obtained, and the uniqueness of the limit velocity and pressure distributions is established.

Fractal fragmentation theory for shape effects of quasi-brittle materials in compression

The influence of the slenderness (shape effects) of a specimen in compression and of the friction between it and the loading platens on the dissipated energy density and on the compressive strength (strain-softening response) is theoretically and experimentally analysed. The energy dissipated during the process is assumed to be proportional to the area of the free surface of the fragments created under compression. A very general law, describing the energy dissipation in natural as well as in man-made fragmentation phenomena, is herein presented, obtaining, as particular cases, the classical comminution laws (Surface, Volume and Third Comminution theories). As a consequence, the dissipated energy density and the strength for a structural element under compression are obtained, by varying its slenderness under different boundary friction conditions. Finally, a comparison between experimental data and theoretical predictions on shape effects is presented. The influences of the specimen slenderness and friction on dissipated energy density and compressive strength are captured by the proposed model in a satisfactory way.

Fractal fragmentation theory for shape effects of quasi-brittle materials in compression

The influence of the slenderness (shape effects) of a specimen in compression and of the friction between it and the loading platens on the dissipated energy density and on the compressive strength (strain-softening response) is theoretically and experimentally analysed. The energy dissipated during the process is assumed to be proportional to the area of the free surface of the fragments created under compression. A very general law, describing the energy dissipation in natural as well as in man-made fragmentation phenomena, is herein presented, obtaining, as particular cases, the classical comminution laws (Surface, Volume and Third Comminution theories). As a consequence, the dissipated energy density and the strength for a structural element under compression are obtained, by varying its slenderness under different boundary friction conditions. Finally, a comparison between experimental data and theoretical predictions on shape effects is presented. The influences of the specimen slenderness and friction on dissipated energy density and compressive strength are captured by the proposed model in a satisfactory way.

Triboemission as a basic part of the boundary friction regime: A review

AbstractThis paper reviews selected phenomena related to the boundary friction process. The central thrust is on triboemission, defined as emission of electrons, charged particles, photons, etc., under conditions of boundary friction and/or surface damage caused by fracture processes. Low‐energy electrons are one of the most important particle components in triboemission. Accordingly, the triboemission process is of particular significance for (i) the boundary friction process as such, and (ii) the tribochemistry of the boundary lubrication process. This review considers all the major issues of triboemission and related phenomena/processes. It is shown that, in the boundary lubrication regime with hydrocarbon lubricants, charge intensities decrease with an increase in lubricant molecular weight. The paper also includes some recent information concerning research on triboemission along with a newly developed apparatus.

Structural changes in friction surfaces of plasma-sprayed coatings

The features surface morphology are considered for plasma-sprayed coatings used with various counterbodies under conditions of boundary friction. The tribotechnical characteristics of the coatings are examined in relation to the structure. There is found to be a substantial effect from the porosity on the formation of the secondary structures, the changes in topography, and the changes in elemental composition of the friction surface.

Tribotechnical properties of coatings on titanium alloys

We compare the antifriction properties of different types of coatings on titanium alloys under conditions of boundary friction as applied to parts of the hydraulic cylinders of an aircraft. We show that gasthermal titanium carbide coatings cladded with nickel and with both copper and nickel have better antifriction characteristics than ones obtained by chrome electroplating, nickel chemoplating, thermooxidation, anodization, etc.

Rigid viscoplastic finite element analysis of the gas-pressure constrained bulging of superplastic circular sheets into cone disk shape dies

This paper describes the development of a rigid viscoplastic finite element formulation for analysing the gas-pressure constrained bulging processes of superplastic circular sheets in cone disk shape dies. In this formulation, the effects of strain hardening and strain-rate sensitivity of materials are included, and the boundary friction condition is introduced into the formulation in the form of friction functional. The finiteelement model based on the membrane theory is developed, and then applied to simulate superplastic constrained bulging processes. The solutions by the rigid viscoplastic finite element method are compared with existing experimental data. The influences of the geometrical parameters of the dies, the friction factor in the friction functional, the strain hardening and the strain-rate sensitivity on the inhomogeneity of thickness distribution are studied in detail.

Effect of porosity on the properties of a sintered powder material for piston rings of internal combustion engines

Piston rings of internal combustion engines operate under conditions of boundary and semidry friction. Comparatively high temperatures, reversible motion under variable loads and pressures, and insufficient lubrication impose stringent requirements on the properties of piston rings, namely, high wear and scoring resistance with maintenance of the requisite elasticity and strength. The possibility of fabricating piston rings from a powder alloy with a structure close to cast iron is considered.

Dynamics of a rotating cylinder-friction block contact pair

The rotating cylinder-friction block contact pair is a model of wearing joints such as drum brakes, contact seals and journal sliding bearings. In this paper the results of a theoretical and experimental study of a rotating cylinder-friction block, which is considered to be a contact pair with distributed parameters, are discussed. Differential equations which describe the dynamics of sliding, friction and wear are derived and numerical solutions are given. The friction block is assumed to be a rigid or an elastic body. Formulae for calculating the wear, friction torque and contact pressure distribution under constant load are proposed. The test apparatus and the results of the model experiments are presented. A pneumatic multichannel device for the measurement of contact pressure and its distribution in wearing joints is described. This device can be used in dry and boundary friction conditions under varying loads and velocities. The theoretical relationships are in good agreement with the experimental results.

Molybdenum complexes as synthetic additives to lubricating oils

In earlier work the authors studied in detail two types of additive-dithiocarbamates of metals and dithiophosphates of metals. In this study a number of molybdenum complexes containing dithiophosphoric and dithiophosphoric ligands are synthesized and described. It is shown that the molybdenum complexes possess the properties of anti-wear additives (they reduce friction and wear in conditions of boundary friction) and antioxidants. Complexes containing the maximum number of sulfur atoms are the most effective. The molybdenum complexes possess the ability to form molybdenum disulfide (during friction of metallic surfaces), which affects the process of friction.

Chemical composition of mineral base for lubricating-cooling fluids in relation to susceptibility to extreme-pressure and antiwear additives

1. Petroleum hydrocarbons of various classes and blends of these hydrocarbons, with and without extreme-pressure and antiwear additives, have been investigated with respect to chemical composition and extreme-pressure properties. It has been shown that, under boundary friction conditions, the extreme-pressure properties increase in the series from paraffinic to aromatic hydrocarbons. Blends of paraffinic or naphthenic hydrocarbons with aromatics behave synergistically. 2. The chemical nature of the hydrocarbon medium has a decisive influence on the lubricity of blends with sulfur-, chlorine-, and phosphorus-containing extreme-pressure and antiwear additives. 3. The paraffinic and naphthenic hydrocarbons have the greatest across-the-board susceptibility to all of the additives studied. 4. Aromatic hydrocarbons completely suppress the action of alkylphosphate additives and partially suppress the action of sulfurized aliphatic fats. 5. Aromatic hydrocarbons are satisfactory in susceptibility to chlorinated hydrocarbons and to the additive Khloref-40. 6. The synergistic effect from blending aromatic hydrocarbons with paraffins or naphthenes is quite insignificant when sulfur- or chlorine-containing additives are used in such blends.

A Review on Chemical Reactions of Solid Lubricants During Friction

A historical background on chemical reactions between solids, in which the chemical activation energy is generated by mechanical forces, is presented and a literature review on “mechano-chemical” or “tribo-chemical” reactions occurring between solid lubricants such as MoS2 and Zn2P2O7 and metal surfaces is given. According to the work reviewed, MoS2 reacts with steel surfaces under boundary friction conditions forming FeS on the surface, and Zn2P2O7 forms iron phosphides.

Antifriction properties of plasma-sprayed steel coatings

1. Spray-deposited steel coatings possess an optimum combination of strength and density, which is responsible for their excellent antifriction properties — a low coefficient of boundary friction (Μ=0.1), good running-in characteristics, low sensitivity to load variation during the friction process, and high resistance to seizure. 2. Plasma-sprayed steel coatings are superior, as regards most of the antifriction properties noted above, to both quenched Type 45 steel and electrometallized steel coatings. 3. Under boundary friction conditions, the wear resistance of plasma-sprayed steel coatings is 1.5 times that of electrometallized steel coatings and is comparable to that of quenched Type 45 steel; at the same time, plasma-sprayed coatings induce less wear in their mating parts.