The Japanese Society of Tribologists organizes domestic Tribology Conferences named “JAST Tribology Conference” in spring and autumn every year. The last one was held at Saga University in September 2007.

“JAST Tribology Conference, Saga, September 2007” covered a range of tribology researches with the following aspects:
Contact mechanics, Friction, Wear, Tribomaterials, Coatings, Surface modifications, Manufacturing processes, Bearings, Gears, Seals, Hydrodynamic lubrication, Elastohydrodyanamic lubrication, Boundary lubrication, Lubricating oil, Grease, Solid lubricants, Additives, Micro-, Nano- and Molecular tribology, Molecular simulations, Automobiles, Railways, Aerospace, Hard disk drives, Heavy machinery, Manufacturing equipment, Maintenance, and Biotribology.
A total of 186 presentations were made with seven parallel sessions.

At every Tribology Conference, JAST publishes a bound volume of proceedings, which includes extended abstracts of all the papers presented. However, the pages are limited to two pages for each paper and most of them are written in Japanese. In order to distribute their high-quality research works worldwide, JAST has decided to invite the authors to write their works in English to submit to Tribology Online.
The papers thus submitted to the Tribology Online have subsequently undergone the normal peer review process by multiple reviewers. In this special issue, twenty five papers selected from high-quality works in various areas are published.

On behalf of the Editorial Committee, I, Editor-in-Chief, acknowledge the authors' efforts to submit their papers to this International Journal. In addition, I would like to express my sincere thanks to the Associate Editors, the Reviewers, and the Publication Coordinators for their effort to complete the peer-review processes and the publication work under the tight schedule.

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The rheological properties of solidified traction oils used in continuously variable transmissions (CVTs) under pressure were evaluated by observing large plastic deformation of metal microspheres (φ about 0.07 mm), occurring due to non-hydrostatic pressurization in these oils using a diamond-anvil pressure cell. The solidification pressure values obtained by observing aluminum sphere deformation were almost equal to those extrapolated from high-pressure viscosity; thus, aluminum sphere deformation experiments are effective for evaluating solidification pressure. Shear stresses of the solidified oils could be estimated up to 5 GPa from the deformed Cu spheres based on several assumptions. The stresses were almost equal to the mean shear stress obtained from a traction test between 1.0 GPa and 1.7 GPa and were below it for pressures above 1.7 GPa. The stress values varied little among different oils.

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The paper describes a newly developed smart device, which can detect the dielectric breakdown of the grease elastohydrodynamic film formed between a steel ball loaded against a glass disc due to electric discharge, while observing the shape and thickness of the film. The electric discharge between contacting surfaces can be observed as a white flash signal. It is found that the dielectric breakdown voltage increases with the film thickness.

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The water contact angles of disks coated with Z-tetraol and A20H decreased gradually with time, starting from the initial value of approximately 105° and approaching a value below 100° in 20 seconds. The cause of temporal change was the interaction between the polar end groups of lubricant molecules and water molecules of the droplet. In the measurement environment, a part of the polar end groups was attracted to a polar droplet from the carbon surface. The contact angle consequently decreased. However, on the robust lubricant films prepared by using the ester lubricants with long-UV (254 nm) irradiation, the temporal changes were not observed. It attests to the formation of chemical bonds without polar end groups. It is proposed that the temporal change of the contact angles reflected dynamic behavior of the lubricant molecules on the disk surface.

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In this paper, in order to clarify the tribology between diamond-like carbon (DLC) and metals under water lubricated conditions, nano-indentation and shear strength measurements for the tribo-layers were attempted in water. Stainless steel (AISI 630) and brass (P31CHL) with the tribo-layer formed by rubbing against the DLC were cut and immersed in the water, and then, the indentation and shear strength measurements were carried out with the Berkovich type indenter and a spherical indenter. The nano-indentation measurement showed that the tribo-layer in the water is a water-absorbing, gel-like product. The shear strength measurement indicated the value between a few MPa and 10 MPa.

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The peroidicity of motor disassembly for maintenance is currently determined by the durability of the sealed grease they contain. The lifetime of this grease is the shortest of all the motor's bearing parts and materials, and therefore needs to be made longer. For this purpose, therefore, the authors discussed the shape of the grease pocket, and concluded that the efficiency of lubrication depends on the shape of the pocket and the relative position between pockets and the bearing, which should be appropriately modified. In this report, the authors performed laboratory testing with full-scale grease pocket models of refined and conventional shapes to compare the service lives and determine the effects of improvement.

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The effect of gait parameters such as step length and walking speed on the traction coefficient and the slip between a shoe sole and a walkway was clarified experimentally, and desirable gait to reduce the chance of slipping was also suggested. The maximum peak value of traction coefficient obtained at heel-strike period |F_h/F_n|_h and that at toe-off period |F_h/F_n|_t increased with an increase of step length irrespective of subjects when walking on dry walkway. Meanwhile, |F_h/F_n|_h or |F_h/F_n|_t slightly decreased or took almost constant value with respect to walking speed. Based on the results of gait experiments on glycerin-lubricated walkway, it was clarified that a walk with a shorter step length and a higher walking speed was effective for prevention of slip irrespective of subjects, and such a gait provided a shorter slip distance. The reason why the smaller maximum peak values of traction coefficient can be obtained in case of walking with a shorter step length and a higher walking speed was discussed based on the kinematic analysis using the body center of mass (COM) and center of pressure of shoe sole (COP).

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The coefficient of static friction is one of the basic factors of actuator performance; it influences the operational characteristics of actuators. In this present study we focus on the dependence of the coefficient of static friction on the time of stationary contact through experiments .We start with the development of a static friction measurement device that can control extremely short contact time durations (approximately 5 ms), using an inertia drive system.

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An ultrasonic liquid processor with the frequency of 20 kHz was used to cleave a principal chain in a polyethylene glycol molecule. The amount of the lubricant molecules cleaved by the ultrasonic disruption was evaluated by the kinematic viscosity measurement. As the kinematic viscosity in the water-glycol hydraulic fluids of the ethylene glycol solutions containing polyethylene glycols decreased monotonously under the condition that the ultrasound of 20 kHz and 40 W was irradiated for one second every five seconds at either 20 or 40 °C, the lubricant molecules could be effectively cleaved while reducing the inter-molecular polymerization. The friction coefficients, ultrasonic velocities, densities, and compressibilities in the water-glycol hydraulic fluids were not influenced by the cleavage process of the lubricant molecules. On the other hand, the kinematic viscosities in the undiluted solutions of ethylene glycol and the polyethylene glycols were proportional to their molecular weights, but the friction coefficients and compressibilities in polyethylene glycols hardly depended on their molecular weights except for those in ethylene glycol. These dependences of the frictional coefficients and compressibilities on the molecular weights resulted from a structure of the lubricant oil film formed on the metal surface.

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The property of belt friction in an over-wrapped condition was studied. A fractional expression with respect to the ratio of belt tensions was derived by this study. The Euler's belt formula was included as a special case in the equation derived. The equation is a function of the contact angle θ and two kinds of the coefficient of friction μ and μ_b, where θ is wrapping angle of a belt around a cylinder, μ is the coefficient of friction between the belt and the cylinder and μ_b is the coefficient of friction between the belt and belt respectively. As the equation signifies the possibility of self-locking, the self-locking mechanism was investigated theoretically by the equation. It occurs when the discriminant of self-locking condition became 0 or negative. The necessary conditions for self-locking are μ_b<μ and a sufficient over-wrapping angle of the belt. Providing the coefficient of friction μ and the ratio of the coefficients of friction κ=μ_b/μ, some critical over-wrapping angles for self-locking were calculated numerically. Experiments were carried out to confirm the occurrence of self-locking predicted by the equation by using a polyethylene film to reduce friction between the belt. Self-locking occurred in the experiment with the polyethylene film wrapped around the belt. But it never occurred without the polyethylene film as predicted by the equation.

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We investigated the decomposition reaction mechanism of a molybdenum dithiocarbamate (MoDTC) molecule using computational chemistry methods: density functional theory and hybrid quantum chemical/classical molecular dynamics methods. The density functional theory results showed that the linkage isomerization reaction of the MoDTC preferentially takes place than its direct decomposition reaction. During a hybrid quantum chemical/classical molecular dynamics simulation, the linkage isomer of MoDTC was observed and subsequently bond weakening of its Mo-O was also observed in the polyalphaolefine phase. From these results, we proposed a new decomposition reaction pathway of the MoDTC molecule: it first forms its linkage isomer as the intermediate in the engine oil phase then decomposes into molybdenum disulfide and monothiocarbamic acid molecules on the rubbing nascent surfaces.

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The pressure-viscosity coefficient α is one of the most important property for EHL condition, however its measurement has difficulty. Therefore authors attempt to predict α for blend oils by using the relationship between pressure-viscosity coefficient and logarithm of kinematic viscosity at atmospheric pressure, which is used for single oil as ever. The pressure-viscosity coefficient of mixtures enables to predict with base oils properties and viscosity of mixture at atmospheric pressure. Test fluids are SN-HV, PBSN, DOS, BBPH and mixtures of these oils. High-pressure viscosity measurement was done at pressure up to 0.4 GPa and temperature range at 20°C to 100°C. The authors proposed the prediction method of α for mixtures.

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This study investigates about the characteristic of the thermo-reversible gel-lubricant (TR Gel-Lube) under elastohydrodynamic lubrication (EHL) conditions. TR Gel-Lube is the lubricant, which consists of base fluid and a gel agent. TR Gel-Lube is repeatedly able to change gel-state to liquid-state at the melting point of its gel agent. Moreover, TR Gel-Lube has good tribological properties, anti-evaporability and so on. This paper describes about investigation of the EHL oil film thickness characteristic, the oil starvation at EHL inlet region and the EHL traction characteristic. It was observed that TR Gel-Lube had low EHL traction, thick EHL film thickness and good stability of EHL oil film formation compared with conventional greases.

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Surface asperities were made on the surface of UHMWPE by sandblasting with sodium hydrogen carbonate abrasive in order to enhance the adhesion of hydrogen-containing carbon (HCC) coating to substrate. Sodium hydrogen carbonate abrasive was used because it easily solutes in hot water and the blasted abrasive stuck into the surface of UHMWPE can be entirely removed by washing with hot water. The HCC coating was deposited on the polished UHMWPE substrate and blasted substrate by RF-plasma CVD method. Friction test was conducted with the ball-on-disk tribometer in the distilled water. As the results of SEM observation and Raman spectroscopy analysis of the friction track on the HCC coating, it was confirmed that a substantial quantity of HCC coating deposited on the blasted substrate was remained on the friction track as compared with the polished substrate. It is concluded that the appropriate blasting treatment of UHMWPE substrate enhances the adhesiveness of the HCC coating to the substrate and improves wear resistance of HCC coating.

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Carbon Nitride (CNx) coating was reported to show a superlow friction coefficient when it slid against a Si₃N₄ ball in nitrogen gas at atmospheric pressure. This superlow friction phenomenon occurred after a number of sliding cycles, in the so-called running-in period, due to the nitrogen atom desorption from the topmost CNx coating surface; its the surface became a graphite-like layer, and a transfer layer was formed on the counter material surface. However, a friction test and surface analysis should be conducted simultaneously, when detailed frictional phenomena including functional groups are observed on the topmost CNx surface. It was supposed that several functional groups were adsorbed on the topmost surface of the carbon system coating when the specimen was withdrawn from the synthesis chamber. In this study, we constructed a friction test apparatus in a FTIR analytic chamber to conduct friction tests and surface analysis without taking the friction test chamber out of the analytical chamber. The analysis results of 1500 cycles each indicated that the -OH or -NH functional group gradually increased with the number of sliding cycles. However, the group decreased suddenly as the friction coefficient decreased. Finally, these kinds of functional groups were not detected when the CNx coating showed superlow friction phenomena.

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The study highlighted the potentiality and effectiveness of Acoustic Emission (AE) signals monitoring along with data clustering analysis as a powerful tool applicable to the rolling elements under examination for incipient damage failure. The AE technique was applied to rollers in contact using rolling contact fatigue test-rig running under constant load and speed for detecting the incipient damage initiation and its damage location. The results demonstrated the successful use of the AE activity monitoring combination with AE source locator and AE data analyzer as a new technique for incipient damage detection. The recorded AE signals from run-to-incipient damage life testing were investigated by unsupervised clustering analysis to examine and to produce numerical validation of the results by separating AE sources data into several classes that reflected the internal structure of the data during contact. A methodology including descriptor selection, methods, procedures for numerical verification and cluster validity criteria were followed.

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In order to estimate the wear process of diamond-like carbon (DLC) films, a ball on disk test and a micro laser Raman spectroscopy are employed in this study. DLC films are deposited on high-speed tool steel (JIS-SKH51) surfaces by a plasma based ion implantation and deposition (PBII&D). After the ball on disk test with a steel ball (JIS-SUJ2) as an indenter, a mapping measurement using micro laser Raman spectroscopy has been accomplished against both the wear surface of the DLC films and the surface of the indenter. As a result, obvious changes in the structure of the DLC films originating from the contact interface between the substrate and the indenter are observed. This is like to be caused by the graphitization of the DLC films. On the other hand, except for the preceding descriptions, the Raman spectra are almost same to each other and there are no changes in the structure of the DLC films. This means that the effects of the sliding on the changes in the structure can be neglected. In addition, the carbon compounds and the solid solutions of carbon and iron included in the substrate and the indenter hardly influence the Raman spectra with or without sliding.

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The purpose of this study is to investigate the effect of cavitation peening on the rolling contact fatigue life of steel gears. The steel rollers and gears cavitation-peened under different conditions were fatigue-tested using a roller testing machine and a gear testing machine. After the cavitation peening, the surface hardness and the surface compressive residual stress of the steel rollers and gears were increased. On the other hand, the surface roughness was not increased so much. As a result, the fatigue life of most cavitation-peened rollers and gears was longer than that of the non-peened ones. In particular, the fatigue life was significantly improved by using a modified nozzle for a high-speed water jet to obtain a greater peening effect. It is suggested from these that the cavitation peening is good for the increase in fatigue life of steel gears, because the peening effect is obtained with less increase of the surface roughness.

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In order to improve the lubrication properties of silicon carbide (SiC) in water, symmetrically spiral periodic structures for bi-directional rotation were intermittently and alternately produced on the surface. These periodic structures of submicron size develope in a self-organized fashion on a surface illuminated by linearly polarized femtosecond laser pulses with a low fluence (slightly above the ablation threshold). The periodic structures formed on the sliding surface of the disk. Ring-on-disk tests were performed to investigate the influence of the periodic structures on the friction coefficient. The experiment showed that the symmetrically spiral periodic structures for bi-directional rotation accelerated the running-in process and achieved a low friction coefficient, μ<0.01, which was about the same as the uni-directional spiral periodic structures.

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The alteration of hair surface properties due to hair damage results in a coarse texture for tactile feeling. The relationship between the surface properties of hair and the recognition of hair damage was investigated using unique artificial hair surface model plates engraved with an excimer laser. Four model plates that specifically represent normal and damaged states of hair were utilized for these experiments. The relative tactile feeling for the degree of hair damage of the 4 plates was evaluated by volunteers (n=10) who touched and rubbed the plates with their fingers. Simultaneously, the coefficient of dynamic friction of their fingers against the plates was measured by recording the normal and frictional forces which indicated that the plate with a wider area of artificial cuticle structure was recognized as damaged hair. Further, an irregular pattern of height and width in the cuticle structure influenced the perception of hair damage. As the friction of the fingers against the plates increased, the tactile feeling of each plate became more coarse in texture. In contrast, not all the tests of friction measured corresponded exactly with the results mentioned above. These results show that the recognition of hair damage depends on a wider cuticle and on an irregular order of cuticle structure (both in width and in height).

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The tribological properties of a new unique thermo-reversible Gel-Lubricant (TR Gel-Lube) were investigated. TR Gel-Lube which includes 10-40% of amide type gel agent in base fluid, is repeatedly able to change from gel-state to liquid-state at the melting point of its gel agent. TR Gel-Lube can be used as an impregnant for porous-material due to its physical state change. TR Gel-Lube indicated lower frictional and better lubricating properties than that of conventional greases. In particular, when TR Gel-Lube was sintered in a copper-type sintered bearing, a lower friction coefficient compared with oils was observed. In this study, to clarify the mechanisms of TR Gel-Lube, the behavior of gel agent on the EHL region was investigated by ball-on-disk tribometer. It was found that gel agent played a key role in the lubricating properties. Some mechanisms such as adsorbed film formation, smooth surface formation and solid like film formation are proposed.

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Hard materials and WC/Co HVOF coating are used for various industrial applications which require long lifetime operation. Compared with hard materials, HVOF coating is considered to have enough merit about resource saving, however, hard materials is mainly used. The reason is mechanical properties of HVOF coatings are not investigated in detail. In addition, the HVOF coating is thought to be inferior to hard materials. The objective of this study is to investigate the mechanical properties of HVOF coating and the hard materials. About abrasive wear resistance, it is cleared that the HVOF coatings have similar performance compared with the hard materials. On the other hand, erosive wear resistance and hardness of the HVOF coatings are inferior to the hard materials. This reason is considered that the difference of crystal and micro structure between HVOF coatings and the hard materials.

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We used a transparent pin-on-disk seek wear test to evaluate the effectiveness at reducing disk drive head wear of several perfluoropolyether lubricants with different end-groups, under various heat and UV irradiation conditions. The extent of Pin wear decreased as bonding ratio increased, with a wear minimum between 30 and 40% bonding ratio on UV irradiated Fomblin Z-dol or Phospharol A20H lubricants. A further wear minimum occurred at higher bonding ratios on both lubricants. Pin wear amounts on disks with heat treated lubricants were different from those on disks with UV irradiated lubricants. Disk failure occurred on disks with UV irradiated Fombrin Z-dol lubricant of high bonding ratio. Sliding conditions during wear tests were also recorded and investigated, showing changes in the lubricant picked-up on pin surfaces - at low bonding ratio disks, this was liquid-like whereas at medium to high bonding ratio disks it became gel-like. On UV irradiated high bonding ratio disks, black powdery debris were found. The mimima in wear found on UV irradiated Z-dol and A-20H lubricated disk seemed to be affected by the amount of debris under the pins. Changes in lubricant rheological properties by UV irradiation or heat treatment should be studied further.

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In this paper, effects of tribological stimulations for tissue regeneration on the expression of tribological functions were investigated. Chondrocyte-fibroin constructs were cultured by using the stirring chamber, which can apply tribological movement to the surface of the specimens. Five culture conditions were prepared by the combination of static incubation (S) and stirring culture (D) as follows: S-, D-, SS-, DS- and DD-culture group. From the results of friction tests, it was found that the friction durability in DS-culture group was significantly improved, compared to that in the other groups. However, there was not a significant difference in glycosaminoglycan content between DS-culture and DD-culture group. These results would indicate that the evaluation of tribological performances on regenerated cartilage tissues is not always consistent with the synthesis of extracellular matrix, and that the tribological movement in the pre-conditioning period induces the functional expression and the post-conditioning static incubation can reinforce the effect. Long-term tribological movement, however, has a potential to induce detrimental effects on the surface properties of the regenerated tissues. These findings would be useful information for a clinical application of tissue-engineered cartilage and for an elucidation of the mechanism on a formation of tribological performances in cartilage.

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The relationship between dispersants (succinimide), calcium detergents and phosphorus antiwear agents, which were added to CVT fluids as additives and the metal-to-metal friction coefficients (μ) were systematically evaluated using a Block-on-Ring tribometer (LFW-1). Succinimides which contain boron, overbased calcium detergents, and phosphorus antiwear agents which contain =O and -OH groups contributed to increased μ. Removal of only one of the three above-mentioned additive components resulted in decreased μ.
The μ of sample fluids that were oxidized using ISOT were also evaluated. When the sample fluid contained no antioxidant, the μ of the fluid was greatly decreased. It was clarified that antioxidants can inhibit decreases of μ. Although it is shown that there is a proportional relationship between the ratio of antiwear agent and μ, the μ of oxidized fluids are lower than that of fresh fluids, due to the degradation of other additives.

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This study is to pilot the future possibilities of the use of the fine particle bombarding (FPB) as the final finishing of the carburized sliding-rolling contact machine elements. In order to evaluate the influence of FPB process on the surface strength of the carburized steel, four kinds of test specimens, which are as-carburized, ground and FPBed ones, were fatigue tested using a thrust rolling bearing type testing machine under a constant loading. The results of the fatigue tests were discussed using the statistic analysis and the observations on the surface properties after the fatigue tests. From the results of both the Weibull plot and the nonparametric test, there was a good possibility that the FPB process after carburizing will be available for the purpose to increase the fatigue life by the improvement of the abnormal layer. The formation of the wear trace of the FPBed disk during fatigue process was different from that of the as-carburized and ground disks, and the FPB process might control the propagation of the fatigue crack due to flaking.

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