Yoshitsugu Kimura

• Professor Emeritus at The University of Tokyo

The preceding paper Part 1 showed that the service life of urea grease in angular contact ball bearings, determined on FAG FE9 rolling bearing grease testers, considerably differed depending on the type of thickeners. Further, it reasoned that insufficient “Feed” of the base oil to the bearing raceway led to seizure limiting the service life on the...

The life of rolling bearings can be limited by sudden increase in friction torque due to exhaustion of lubricant after long-term operations. With the purpose of developing grease having long “service life”, research has been conducted with angular contact ball bearings lubricated with urea greases, and the present First Report describes experimenta...

An intuitive understanding of the pressure spike appearing in the elastohydrodynamic pressure distribution is presented. This comes from my personal memories of Professor Dowson from my first encounter with his book to my final conversation with him.

An unexpected behavior of grease in rolling contact has become known among tribologists that it forms thick film at low speeds, but the nature of the film has still been in dispute. The dominance of EHL effects has been demonstrated in the previous works, in which the increase in the generalized viscosity of grease has been reasoned to cause the in...

Engineering plastic materials like polyamide and polyacetal are widely used for worm wheels and other tribological elements under EHL conditions with grease; typical examples are found in electrical power steering systems and power window mechanisms. Low elastic modulus of those materials makes their contact pressure much lower than steel-To-steel...

“Tribology” celebrated its 50th anniversary last March. During the past half century, Japanese industry has shown remarkable progress. This article briefly follows in the footsteps of the progress to show how tribology has contributed to it and then to society, and discusses a future direction tribology should take.

Ultra-thin optical interferometry revealed that grease formed thick elastohydrodynamic lubrication (EHL) films at extremely low speeds, 2mm/s for example, demonstrating a V-shaped film-thickness-vs.-speed plot, as previously reported. The present work tries to confirm that this characteristic behavior occurs in ball bearings. A pair of deep-groove...

Film thickness of grease in rolling contact is determined by ultrathin-film optical interferometry, where increase in thickness is found at low speeds having the thickness depending on both base oils and thickeners. A characteristic horse shoe observed at low speeds shows the film is formed mainly by EHL effect. Analysis employing the Carreau-Yasud...

Paper-based friction materials are widely used for oil-immersed clutches in automatic transmissions for passenger cars. It is known that repetition of engagements of the clutches causes wear of the friction materials leading to running-in with an increase in contact area. Observation of the contact of a typical paper-based friction material has bee...

An ultrasonic technique is applied for detection of abnormalities in a ball bearing in its life test. Ultrasonic wave pulses are entered into a bearing housing from a piezoelectric vibrator attached to the outside of the housing. Those pulses are partially reflected from the interface between the housing and the outer ring of the bearing. Because o...

Life Cycle Assessment was conducted for two types of aluminum alloy bush bearings used for automotive transmissions. Equivalent CO2 emission was used as the index of the environmental impact for global warming, and was compared through their manufacturing processes. The effect of lubricating oils on the bearing performance and the environmental imp...

Researches on wear and fatigue in rolling contact from a tribological viewpoint are introduced. Transmission of traction and accompanying microslip in the contact region play critical roles in these phenomena. First, a quantitative analysis of wear in rolling contact with microslip is introduced, and it is shown that a simplified microslip theory c...

An analysis and assessment by using life cycle analysis were conducted on sliding bearings for automobile engines considered as tribo-components, from the acquisition of raw materials to the production aluminum alloy bearings and overlay-provided kelmet bearing. The resistance to fatigue was estimated at a sliding speed of 17.6 m/sec, bearing backs...

Effects of tempering the nitrided substrate on the life of TiN-duplex-treated tool steel are studied as a potential tool material for plasticity processes. Ring-on-block sliding tests are carried out against aluminum alloy without lubrication to evaluate the life of the TiN coating film under a high-load, low-speed condition where wear takes place...

Ring on block sliding experiments were carried out in nitrogen atmosphere in order to evaluate wear behaviors and film lives of coated tool steels prepared by CVD, aiming at improving performances of tools for aluminum plasticity processes such as extrusion dies. Coated blocks of tool steels, SKD61 and SKH51, with three layers of TiC/TiCN/TiN or si...

A brief survey is presented of the trends of reduction of lubricating film thickness in several components which has taken place in recent decades, and of the operation of certain components in the presence of extremely thin lubricating films from birth. New technologies are introduced which have been developed to ensure their successful operation.

Ring on block sliding experiments were carried out in nitrogen atmosphere in order to evaluate wear behaviors and film lives of coated tool steels prepared by CVD, aiming at improving performances of tools for aluminum plasticity processes such as extrusion dies. Coated blocks of tool steels, SKD61 and SKH51, with three layers of TiC/TiCN/TiN or si...

So-called adhesive wear is caused by microscopic fractures on sliding surfaces. An approach is described in which the wear process is broken down into several elemental processes, i.e. formation of real contact points, action of forces on real contact points, distribution of stresses and strains, accumulation of damage in the subsurface, initiation...

Following to a study on tribological properties of a duplex surface treatment of tool steel, which comprises nitriding of a substrate and coating of a titanium nitride(TiN)layer, effects of tempering of the substrate sre studied by sliding experiments against aluminum alloy without lubrication. Experiments are carried out under a high-load, low-spe...

Hexagonal boron nitride (BN) has a graphite-like lamellar structure, but has been considered less effective than other solid lubricants except for high-temperature applications. The present paper describes a series of sliding experiments which show somewhat curious behavior of BN when added to lubricating oil, and discusses their results by compari...

A duplex surface treatment of tool steel, which comprises of nitriding of a substrate and coating of a titanium nitride (TiN) layer, is studied as a potential tool material for plasticity processes of aluminum alloy without lubrication. Tribological properties are determined on a ring on-block arrangement, where the ring is made of aluminum alloy,...

Although tribology provides important tools for maintenance engineering, and maintenance forms an important area to which tribology contributes in practice. This paper reviews the economical significance of maintenance, details a strategic trend from time-based to condition-based maintenance, and gives examples of maintenance systems in plants. Som...

Emulsions, when used as the lubricant, form ehl films having a minimum thickness different from the prediction from their bulk viscosity. This behavior originates from the much larger particle diameter of the dispersed phase than the ehl film thickness they form. The present paper undertakes to present a unified view about the behavior of O/W and W...

Based on the continuum theory of nematic liquid crystals, the authors analyzed the electrorheological effect. Regarding one-dimensional shear flow between infinite parallel flat boards, based on the parallel anchoring model and uniform director model which put forth differing assumptions regarding directors, we determined an equation which describe...

This paper is a state-of-the-art report on tribology research presented or published in Japan recently, and covers a wide variety of topics that the authors consider are interesting and should be focused on. This article hopefully can give readers a general view of recent activities of Japanese tribologists and what they are now interested in.

Elastohydrodynamic analysis is conducted and a numerical solution is presented for the film thickness in grease lubrication in isothermal, fully-flooded rolling line contact with or without slip. By making use of a perturbational method, a modified Reynolds equation is established, which can be used with various constitutive equations if the equiva...

Friction and scuffing behaviour of grey cast iron as influenced by the surface roughness under sparse lubrication conditions is studied. The studies are carried out on a three-shoe-on-disc machine under the conditions of parallel sliding. The experiments were conducted at three oil supply rates of 0.10, 0.22 and 0.36 μg/cm2 per contact obtained thr...

Higher performance of recent automotive engines requires their bearings to operate under more severe conditions like higher speeds, higher loads and higher temperatures. To meet this requirement, plain bearings with circumferential microgrooves have been developed. Experimental evaluation as well as theoretical analysis has revealed that the ease o...

Although water-in-oil (W/O) emulsions have higher viscosity than the base oils, they often form thinner elastohydrodynamic films than those formed with the base oils alone. This unreasonable behavior of W/O emulsions is studied experimentally and analytically. First, atmospheric and high-pressure viscosities of W/O emulsions are measured in a rolli...

Frictional properties of typical tribomaterials are evaluated under sparse lubrication conditions where lubricating oil is supplied but its amount is far from sufficient even for boundary lubrication. These conditions are provided by employing a mist oiling system which can continuously supply oil at constant, extremely low and quantitatively contr...

Experiments are described in which friction coefficients under boundary lubrication regime are measured with a nematic liquid crystal as the lubricant. Using steel-to-steel contacts, with one of the mating surfaces coated with a thin insulating film, electric fields are applied across the liquid crystal film. A substantial decrease in the friction...

Wear of ceramics occurs in two major modes, i.e., tribochemical wear and microscopic fracture wear. The present paper discusses the possibility of a fracture-mechanics approach to the latter, which is responsible for detrimental surface damage. A longitudinal contact-point model is employed, and stress intensity at wear cracks is evaluated by three...

Results of wear simulation motoring experiments are presented for various wear-resistant materials used to make automotive engine cam followers. A multiple regression analysis is conducted to find the relation between follower wear and typical material properties. A linear regression formula is derived which provides a high multiple correlation coe...

This paper describes the eiectroviscous effect of a thermotropic liquid crystal in nematic phase. Liquid crystals are characterized by orientation of their own molecules, whose direction can be controlled by the applied electric field or magnetic field. Because of the controllability of this orientation of molecules, liquid crystals are being used...

Liquid crystals are characterized by the orientation of their molecules, the major axis of whose direction can be controlled by an applied electric or magnetic field. In the present paper the viscosity variation of three thermotropic liquid crystals in the nematic phase having different dielectric constants is studied at varying electric field stre...

Aspects of the current state of tribology in Japan are reviewed. The marked activity of the Tribology Society, international relations, tribology in industry and tribology education are described and several topical research areas are highlighted. The greatest change in the last 25 years is that individual tribologists have begun to share their own...

Wear can be considered as surface fracture and, therefore, the fracture theory of wear involves the analysis of actual forces acting on the surface, evaluation of accumulated damage in the surface and subsurface, together with material properties which represent the resistance to fracture. A preliminary approach to this procedure is outlined. (A)

Flake-like wear particles, which are most commonly observed in engineering practice, are understood to be caused by fractures of surface layers. Fracture-mechanics approaches to this problem conducted so far have predicted values of stress-intensity factors for crack growth which are too low. In order to remove this difficulty, three-dimensional an...

A longitudinal contact-point model is proposed for the evaluation of stress-intensity factors at the tips of wear cracks. The concept and the significance of the model are discussed, and the finite element method analysis is described. The model can lead to the determination of stress-intensity factors which have a sufficient order of magnitude for...

Wear experiments were conducted with used gasoline engine oils as the lubricants. Several oil samples were obtained from gasoline engines run under various conditions. Friction and wear properties of the oils were determined and are discussed in connection with some of their chemical characteristics, such as total acid number (TAN), total base numb...

An experimental study has been made of the effect of temperature rise on rheololgoical properties of some mineral and synthetic hydrocarbon base oils over a wide range of temperature. The representative stress τ0 expressing the limit of Newtonian is determined by a curve fitting method from a traction curve obtained on a four-roller machine while t...

Analysis is present of EHL traction with low-viscosity lubricating oils, which is the case encountered at higher temperatures. Extension is made of the approximate formula already derived by the authors, where it is assumed that viscosity, instead of viscoelasticity, predominates when the limiting Newtonian viscosity in an EHL film falls below a cr...

Experiments are described in which elastohydrodynamic and boundary lubrication properties of O/W emulsions of mineral oil are studied with a variety of nonionic surfactants as the emulsifying agents. The changes in the minimum elastohydrodynamic film thickness are determined with different surfactants, with changes in oil concentration, with change...

Experiments are described in which sintered silicon nitride was slid against itself in plane contact in oil and in various gaseous atmospheres. Results of observation of wearing surfaces by microscopy, profilometry etc. which show the history of surface damage are presented. First, subsurface defects seem to act as preferential sites of origin of i...

A series of sliding experiments were conducted in which sintered silicon nitride rings were slid against silicon nitride in plane contact at room temperature under various environments: in dry and humid air, in nitrogen and in white oil. Microscopy of sliding surfaces at an early stage shows that brittle fracture takes place presumably at the preex...

The atmosphere exerts significant effects on the performance of PTFE-based self-lubricating composites. Experiments are described in which the friction and wear characteristics were determined for a glass-fiber filled PTFE composite sliding against stainless steel in air of varying humidity. With increasing humidity, both the coefficient of frictio...

A 'running-in equation' is offered which describes the changes in surface microtopography due to wear. It relates the height distribution of a composite profile of wearing surfaces to the size distribution of the wear particles. Solutions of the equation are obtained by successive computation, which is conducted on a lubricated wear experiment. The...

Elastohydrodynamic film thickness is determined between steel rollers lubricated with oil-in-water emulsions of beef tallow by detecting the rate of X-ray transmission through the film. It is shown that a thick film is formed which is quantitatively explained.

The traction characteristics of nine mineral base oils were determined with a four-roller machine, and are analyzed according to a theory derived earlier. Three rheological parameters, namely, the shear modulus G, the effective viscosity-pressure coefficient alpha and the representative shear stress tau //0, are determined and are correlated with t...

It has been reported that, in concentrated conjuctions lubricated with oil in water emulsions, only the oil is entrained to form hydrodynamic films. To study this phenomenon, experiments are conducted in a four roller machine where oil in water emulsions of beef tallow are used as the lubricant. It is found that, even at oil concentrations as low a...

Application of the thermal theory derived in the preceding report to traction curves is discussed. The isothermal region of a traction curve is employed to experimentally determine the three rheological parameters characterizing the nonlinear viscoelasticity of a fluid. That is, the representative shear stress is firstly read off the slope of the t...

Localized pick-up resembling the heat streaks in cold rolling occurs at rolling/sliding contacts lubricated with oil-in-water emulsions of tallow- and mineral-oil-based lubricants. The conditions for the occurrence of this pick-up are discussed as a lubrication failure problem. First, the formation of real contacts is statistically analyzed, and th...

The lubrication characteristics of oil-in-water emulsions of tallow- and mineral-oil-based lubricants were studied in a four-roller machine, and were compared with those of the near lubricants themselves. The rollers were run under stepwise increasing loads at constant speeds with a fixed slide/roll ratio. When the contact resistance across the lub...

Heatstreak is a kind of pick-up which appears sometimes in large numbers at the roll/strip interface and impairs the efficiency of cold rolling operations. The heatstreaks were believed to occur as a result of local breakdown of the lubricating film under severe rolling conditions, but this severity was not yet sufficiently interpreted in terms of...

It is widely accepted that so-called adhesive wear occurs as a result of fracture around microscopic contact points. A basic strategy in analysing the wear is discussed such that the wear process is broken down into several elemental processes in which removal of wear particles and associated modification of the microgeometry form important parts....

Experiments on lubricated wear are conducted and profiles of the wearing surfaces are studied. Two types of cross-correlation coefficient are introduced: one compares the profiles obtained at the same position before and after sliding for a fixed duration, and the other compares the profiles at different positions on the same wear track. It is foun...

The application of a thermal theory derived in a preceding report to traction curves is discussed. The isothermal region of the traction curve is employed to experimentally determine the three rheological parameters characterizing the nonlinear viscoelasticity of a fluid. That is, the representative shear stress is firstly read off the slope of the...

Heat streaks are a kind of pick-up which sometimes appear in large numbers at the roll/strip interface and impairs the efficiency of cold rolling operations. The heat streaks were believed to occur as a result of local breakdown of the lubricating film under severe rolling conditions, but this severity has not yet been sufficiently interpreted in t...

An approximate thermal viscoelastic solution is derived for the traction in elastohydrodynamic contact, which describes traction curves with several non-dimensional parameters. A nonlinear Maxwell viscoelastic model is applied to the behavior of fluid film, in which viscosity is represented by the Eyring 'sinh law'. The thermal effect is assumed on...

The effects of atmospheric pressure on the friction and wear properties of glass-fiber-filled PTFE composites vs. 2024-T4 aluminum alloy combinations are examined. Optical microscopy of the worn surfaces of the composites has revealed that, when rubbed in dry air, the glass fibers exposed on the surfaces abraded the aluminum alloy. The abraded debr...

The friction and wear properties of two glass-fiber-filled PTFE composites and a PTFE-filled polyimide composite against AISI 304 stainless steel and 2024-T4 aluminum alloy are assessed in air and in vacuum to 10** minus **7Pa. In high vacuum all material combinations show low and stable friction, as well as low wear rates. The friction is almost u...

An approximate thermal viscoelastic solution for the traction in an elastohydrodynamic contact is derived which describes the traction curves with several nondimensional parameters. A nonlinear Maxwell viscoelastic model of the behavior of a fluid film is employed in which the viscosity is represented by the Eyring 'sinh law'. The thermal effect is...

A series of experiments describing the wear of steel rollers during lubricated pure rolling contact are presented. A four-roller machine is used for the experiment; the velocity difference between the mating rollers is maintained equal to zero, while the surface roughness and oil film thickness are varied. Even under the lubricated pure rolling con...

Measurements were made of plastic flow in cylindrical rollers caused by repeated rolling contact. Assembled test rollers were composed of twin discs joined together so that each one of their facial planes comes to contact. Radial lines had been marked on the contacting planes by scribing and subsequent plating before being assembled. The flow was d...

Traction characteristics of eight fluids of various compositions are evaluated with a four-roller machine, in which rotational speeds of mating rollers are positively controlled. The fluids tested are paraffinic and naphthenic mineral oils, liquid paraffin, polyisobutylene, and synthetic branched hydrocarbons. When the coefficient of traction is de...

Outer race deformation can have marked effects on the life of rolling element bearings. Two model housings were made which allowed appreciable deformation of the races. One consists of a U-shaped steel strip which wraps around the lower half of the outer races. The other supports a bearing by a line contact between the outer race and a concave cyli...

A study was made of the effects of an electric current on the wear of a solid lubricant compact, 33. 3 Ag-16. 7 Ni-50 MoS//2 (in wt%), which is successfully operating as motor brushes in the scientific satellite ″EXOS-A″ . It was found that the amount of wear increases progressively with increasing current. An analysis of the wear fragments shows t...

Solid lubricant compacts were developed for use as motor brushes to operate on the scientific satellite ″EXOS-A″ . Some candidate materials of varying compositions were hot-pressed from Ag, Ni and MoS//2 powder. Wear in air and in vacuum as well as friction, hardness and electric resistance were determined. It was found that two compositions, 80 Ag...

The dependence of wear on atmospheric pressure was studied in relation to the fatigue of materials. Ni, Cu and Au specimens were fatigued at various atmospheric pressures and the results were compared with their wear behaviours. Similar curves were obtained for each material when the reciprocal of the fatigue life and the number of wear fragments w...

The relations between the size of wear fragments and the sliding velocity or normal load were studied from a mechanical point of view for the unlubricated wear of nickel. It was found that the size of mean wear fragments has a definite quantitative correlation with the thickness of the plastically deformed substrate layer, irrespective of the exper...

Experiments were carried out on the wear of three f.c.c. metals, Ni, Cu and Au, under unlubricated conditions using a pin and disk machine in a vacuum chamber. Wear was determined with varying load, sliding velocity and atmospheric pressure. As no oxygen is chemisorbed on Au, the extent of the influence of the chemisorbed oxygen film was determined...

Wear of steel rollers has been investigated under unlubricated rolling contact with a small amount of sliding. A four-roller machine is used for the experiment; the velocity difference between the mating rollers is kept constant, while the slip ratio and the normal load are varied. A common feature is found in the wear characteristics when either t...

A statistical analysis is made of the geometrical nature of contacting surfaces and mathematical expressions are deduced for the number and the mean area of the real contact points. The expressions are derived, first in generally applicable forms, and numerical examples are given for the case where Gaussian distribution is assumed for the height an...

Adhesive wear has been widely accepted as the type of wear most frequently encountered in practical sliding systems. However, with developments in theoretical research and analysis of wear particles, the concept of adhesive wear has been re-examined, and the possible role of fatigue has acquired increasing importance in recent work on wear processe...

MECHANISMS OF ADHESIVE WEAR ARE DISCUSSED, WHERE THE PROCESS OF FRAGMENT REMOVAL IS REGARDED AS THE SUCCESSIVE FRACTURE OF SLIDING SURFACES CAUSED BY SUBSTRATE FATIGUE.THE PHYSICAL SIGNIFICANCE OF THIS APPROACH IS FIRST DISCUSSED, AND AN ANALYSIS IS PRESENTED IN WHICH A PROCESS IS HYPOTHESIZED THAT ACCUMULATION OF DAMAGE WITHIN THE SUBSTRATE LEADS...

rights: 本文データは社団法人日本機械学会の許諾に基づきCiNiiから複製したものである Ring on block sliding experiments were carried out in nitrogen atmosphere in order to evaluate wear behaviors and film lives of coated tool steels prepared by CVD, aiming at improving performances of tools for aluminum plasticity processes such as extrusion dies. Coated blocks of tool steels, SKD61 an...