The tribological enhancement of base lubricant under different concentration of formulated Eichhornia Crassipes carbon nanotubes (EC-CNTs) was conducted in this research. Cyclic heating approach was adopted in the formulation of EC-CNT and scientifically characterized. The characterization results confirmed the sample EC-CNTs. The effect of EC-CNT in base rapeseed oil terms of concentration, coefficient of friction (COF) and surface roughness (Ra), load carrying capacity, lubrication film stability and film mechanism were evaluated using high frequency reciprocating rig machine. The results showed that inclusion of EC-CNTs into base rapeseed oil, enhanced the tribological properties. The resultant values of COF were 0.064, 0.051 and 0.087 for rapeseed blended 1 mass%, 2.5 mass%, 4 mass% EC-CNT respectively. This is 38.5% COF reduction from 2.5 mass% EC-CNT against base oil. Under wear scar diameter, 2.5 mass% showed 47.9% reduction compared to base oil. The Ra was reduced with addition of nanoparticles, especially with 2.5 mass%. The tribological enhancement by EC-CNT is attributed from tribo-chemical reaction between the particles and the interfaces leading to formation of active protective tribo-film. The mechanism exhibited by the nanoparticles were healing and rolling from which the tribo-enhancement were achieved.

Recently, it has been reported that combinations of various types of vegetable oils containing organic acids and DLC coatings are effective for reducing friction, but there are few reports of detailed investigations into the relationship between differences in the chemical structures of vegetable oil lubricants and friction reduction. Therefore, the authors investigated the influence on friction properties of two types of DLC coatings, a-C:H and ta-C under lubrication with vegetable oils which have different degrees of unsaturation. The ta-C coating displayed markedly lower friction coefficients than the a-C:H coating and the uncoated steel with all of the vegetable oil lubricants used. It was found that the low friction properties of the ta-C coating showed even lower friction coefficients with vegetable oils containing a higher content of monounsaturated fatty acids. Additionally, the sliding surfaces of ta-C coated discs and cylinders were analyzed by XPS and ToF-SIMS analysis. The results confirmed the formation of a surface layer consisting of C-OH bonds, and a lower friction coefficient was seen as the detected intensity of these bonds increased.

A previously developed and validated rolling bearing life model that separates the surface and the subsurface survivals is now adapted to account for superior bearing steel that allows bearings to operate in the region near contact pressures of 3 GPa and speeds of nd_m = 3 × 10⁶ (n is the rotational speed in rpm and dm is the bearing mean diameter in mm), common of high-load and high-speeds applications like modern spindle bearings. The adapted model is verified with the support of endurance testing and its range of application is also verified with the support of a full non-seizure test. The adapted model can now be used in the bearing selection process for those tough application conditions.

Dry friction tests were performed using a pin-on-plate tribological tester. In this study, Al₂O₃ and Al₂O₃ with MoS₂ admixture plate with PEEK/BG pin. Plate surfaces were created using the constant current method and the non-periodic alternating current method. The dimension of Al₂O₃ fibers walls were calculate based on SEM micrographs. SGP measurements of the oxide layers were made by a Taylor Hobson Talysurf 2D pin profilometer. It was found that the gradient structure favors the reduction of the friction coefficient and weight loss of PEEK/BG in the tested friction pairs, and the method of gradually reducing non-periodic alternating current allowed to obtain a more homogeneous microstructure of aluminum oxide. The use of high current densities at the beginning of the process leads to the production of non-gradient coatings characterized by higher SGP amplitude parameters. This property translates directly into higher wear of the sliding PEEK/BG material and higher values of the friction coefficients of the tribological pairs thus obtained. The research also identified a strong correlation between the friction coefficient µ and surface topography parameters before the tribological cooperation of PEEK/BG pairs - Al₂O₃ oxide coating.

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 experimental work. The life was determined on FAG-FE9 rolling bearing grease testers, and considerable difference in the life was found among the greases with different type thickeners. Observation of bearings by interrupting the run inferred the following scenario. In a short churning period, grease was re-distributed to form a lump on the front face of the outer ring and thin layers on some other parts of the bearing. The lump served as an oil reservoir, and the oil bled from it infiltrated through the thin layer on the outer ring to lubricate the raceways. A part of the oil was then carried by the balls to lubricate the sliding interface between the cage and the balls and, when this lubrication became insufficient, seizure initiated to limit the life.

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 basis of the results obtained by tracing infiltration of the base oil through re-distributed grease in the bearing. In order to provide a logical rationale for these findings, the present paper Part 2 analyzes the “Feed” behavior. The equivalent radius characterizing the infiltration rate of the base oil through grease with different thickener concentration is determined with a newly developed methodology using filter paper as the medium. A chart is introduced to show the change in the equivalent radius of grease during an operation and the limiting condition leading to the failure is discussed. Finally, the means to make relative comparison of the service life of grease without conducting bearing tests is proposed.

In this study, nano-scratch tests were conducted using atomic force microscope (AFM) to clarify the hardness of a tribofilm derived from an additive (Fluid A or Fluid B in automatic-transmission fluid) formed on an SKS3 cold work tool steel substrate surface. Comparisons between nano-indentation hardness tests and AFM nano-scratch tests were performed for each specimen. Prior to these tests, the tribofilms on the SKS3 substrate were examined with energy-dispersive spectroscopy (EDS). In order to calculate the hardness of the tribofilm from the nano-scratch results, we assumed that the AFM diamond tip acted as an abrasive to plough the tribofilm. The phosphorous-derived tribofilm formed from Fluid A was harder than the sulfur-derived tribofilm from Fluid B, and it was calculated that the phosphorous-derived tribofilm was approximately 2.64 GPa and the sulfur-derived tribofilm was 1.89 GPa. After 10 nano-indentation hardness tests on each tribofilm, the maximum indentation depth into the tribofilm formed from Fluid A was approximately 31 nm, while it was approximately 36 nm for Fluid B. These results are qualitatively consistent with the hardness results obtained by the AFM nano-scratch test method.

In general, several mechanical parts are subjected to friction and wear. To prevent wear and high friction coefficient under lubrication, additives can work to reduce friction force, to build up thin film on surfaces which is so-called tribofilm. Recently, Diamond-Like Carbon (DLC) is focused because it has excellent low friction and high wear proof as solid lubricant. However, several researchers already reported that tetrahedral amorphous carbon (ta-C) showed abnormal wear when it rubbed with glycerol mono-oleate (GMO) that is a kind of additive, although it showed very low friction coefficient. To improve tribological properties, new additives were developed that had both phosphate-oxide structure derived from ZnDTP which had high wear resistance and hydroxy group derived from GMO in one structure. To clarify the effects of the additives, friction tests were performed fixed-roller-on-disk type rotating friction tester. In the friction tests, hydrogenated amorphous carbon (a-C:H) disks, and a-C:H coated rollers were used under boundary lubrication condition at 20-80°C. Friction tests were conducted in Poly-α-olefin (PAO) oil with each GMO and the additives. The results exhibited that a-C:H gave ultra-low friction with the additive. Elemental analysis of the surface showed that tribofilm of phosphorus and oxygen was detected on the a-C:H surface in the additive used condition.

Ball bearings on the main shaft of rocket engine turbopumps which supply cryogenic propellants to the main combustion chamber are critical elements of the entire propulsion system of a rocket. A self-lubricating ball bearing with a retainer made of glass-cloth-polytetrafluoroethylene (PTFE) laminate has been used in turbopumps developed in Japan. In the operation of the turbopump, the bearing heat generation is possible to cause sudden temperature rises of bearing elements which finally result in bearing seizure. Therefore, it is important to predict the accurate bearing heat generation under various operating conditions. In this research, the bearing heat generation operated in cryogenic hydrogen was experimentally investigated under the various operating conditions where the rotational speed and the bearing coolant condition were changed. In addition, the bearing heat generation was compared with that theoretically predicted on a numerical model of mechanical losses. It was finally clarified that the bearing heat generation is influenced dominantly by the friction loss on balls and the drag loss on an inner race.

Taking the elliptical bearing as the research object, adopting the mixture two-phase flow model and energy equation, the pressure characteristics, the cavitation distribution and the thermal effect of elliptical bearing with different ellipticities are analyzed. The results show that the maximum temperature rise of elliptical bearing is lower than cylindrical bearing. The optimal ellipticity of elliptical bearing is 0.6, the upper and lower bush of elliptical bearing can form the effective oil film, the proportion of cavitation area and volume is small, the maximum temperature rise of oil film is lowest, which is conducive to the stable operation of journal bearings.

The advent of smart materials and modern control theory has seen the rapid development of ultrasonic motors over the last decades. They have become promising precision driving components due to their unique piezoelectric transduction and friction drive mechanisms. This review summarizes the synthesis of the key technical aspects, research efforts, conclusions, and challenges that need to be highlighted concerning ultrasonic motor structural design and tribological performance. The analysis shows that the development of ultrasonic motor with new principles is in the ascendant. Simplifying the body structure, developing advanced friction contact models and life prediction models, developing new and environmentally friendly friction materials, and developing customized tribological testing devices are goals and tasks that should be considered in the future design of efficient ultrasonic motors.

In this study, we have analyzed the effect of elastic deformations on the static characteristics of finite self-lubricating journal bearings. This analysis takes into account the rheological lubricant behavior which obeys to Rabinowitsch law. The governing equations considering both the fluid flow in the porous bush and the fluid film lubricant are based on Rabinowitsch fluid model and solved numerically using the finite difference method. The static performances of the porous journal bearings have been investigated for various parameters such as the elastic deformation parameter, the nonlinear factor which characterizes the pseudo-plastic fluid, the eccentricity ratio and the bush permeability. Obtained results demonstrated that the pseudo-plastic lubricant decreases the characteristics of the porous journal bearings compared to the Newtonian fluid lubricant. This reduction is more pronounced where the effect of both elasticity and permeability of the bush have been considered.

The mechanical properties of ultra-thin films with monolayer thicknesses adsorbed onto a solid surface are of great interest when understanding tribological phenomena. In this study, we measured the Young's moduli of ultra-thin liquid perfluoropolyether (PFPE) lubricant films on diamond-like carbon (DLC) films using Ar-gas cluster ion beams (Ar-GCIBs). Two types of PFPE lubricants with different mainchain structures (D-4OH and Z-tetraol) were used in this study. The dissociated ion yields of Ar⁺₂/(Ar⁺₂ + Ar⁺₃) were measured by time-of-flight secondary ion mass spectroscopy using Ar-GCIB as the primary ions. The dissociated ion yield was calibrated based on the relationship between Young's modulus and the dissociated ion yield of seven different samples. Using this calibration, the Young's moduli of the two PFPE lubricant films on the DLC surfaces were estimated. They showed relatively good agreement when compared with those derived from the intermolecular pressure calculated via molecular dynamics simulations. It can be concluded that the Young's modulus measurement method using Ar-GCIB is an effective tool for evaluating ultra-thin adsorbed films. In the future, it will be possible to measure the Young's moduli of tribofilms and boundary lubrication films using this technique.