Palm oil shows significant potential for development as a lubricant due to its long molecular fatty acid chain, which is capable of minimizing wear and friction. However, in certain conditions, the formation of a thin layer of fluid film may no longer sustain to protect the contact surfaces. Therefore, a relevant additive is needed to address this issue. In this study, trimethylolpropane (TMP) was used as a lubricant, and Graphene Oxide (GO) was employed as the nano-based additive. A Four-ball tribotester was utilized to determine the friction coefficient, wear scar, and surface roughness of the contact surfaces under various operating conditions. The results were compared to mineral and synthetic-based oils. It was found that the combination of TMP and GO exhibited a lower friction coefficient compared to mineral and synthetic-based oils, but slightly higher compared to pure TMP. However, TMP+GO demonstrated significant improvement in terms of wear scar diameter and surface roughness. The physical appearance of the wear was also discussed in this study.

Organophosphates are well-known as the canonical additives for lubricants. Thus, understanding of the additive behaviour is a key aspect in the design of films on metal surfaces. Different types of phosphates are added to improve their antiwear properties, but the contributions of individual esters to these properties has not been studied using a combination of practical and theoretical approaches. In this study, organophosphates were isolated with high purity and their tribological characteristics were evaluated by using a Bowden-type reciprocating friction tester and a four-ball wear tester. Mono-oleylphosphate had a lower friction than di-oleylphosphate and exhibited excellent antiwear characteristics. Analysis of the sliding surfaces using desorption electrospray ionization-mass spectrometry (DESI-MS) and X-ray photoelectron spectroscopy (XPS) indicated that the film structure could predict the occurrence factor of the tribological characteristics of the oleylphosphates. Then the adsorption energies of the monoester on iron and iron oxide surfaces were higher than those of the diester, as assessed using density functional theory (DFT) calculations, owing to the difference in their chemisorption processes, as confirmed by further DFT analysis. Studies on the reactivity of additives and their interactions with surfaces are important for understanding the tribochemistry of additives.

This paper formulated a modified Reynolds equation that can calculate the lubrication characteristics of bearings with high-viscosity surface layers on both bearing surfaces expressed by arbitrary viscosity function. From comparison with the measured effective viscosity of engine oil with metallic detergent, the saturated viscosity function was determined, where the effective viscosity saturates to 500 times the bulk viscosity when the gap decreases to the saturated viscosity film thickness 2z_c of 100 nm. Then, the lubrication characteristics of micro-tapered pad bearing of 250 µm in length were analyzed. The load capacity was ~70 times the bulk viscosity case when the trailing gap h_T decreased to 2z_c. Next, the effective viscosity of engine oil with only a viscosity modifier additive can be obtained by using another viscosity function in which the increasing rate in viscosity is maximum on the bearing surface and 2z_c is ~60 nm. Using this viscosity function, the bearing characteristics of tapered pad bearing were analyzed. The load capacity was ~13 times the bulk viscosity case when h_T was z_c. For both the viscosity functions, the load capacity was almost the same if the film thickness of the one-side model is twice as large as that of the two-side model.

In elastohydrodynamic lubrication (EHL) theory published in 1962, Dowson et al. derived a density pressure relational equation. Therefore, it seemed that this equation could be utilized as an estimation equation of the density term of the viscosity pressuretemperature-density linear equation of Part 1 of the paper. However, since the temperature function is not included in the equation, the calculated value at 40°C is in good agreement with the measured value, but in the high temperature range, the calculated value found large deviation from the measured value. Therefore, introduction of temperature function into the equation was studied, and density-pressure-temperature relational equation was newly derived. In this result, it became possible to estimate the high pressure density at each temperature, and it became possible to utilize as the estimation equation of the density term of the 1st report. And it was found that the linear equation can also be applied to the ASME report data up to around 1 GPa. Incidentally, the slope a of the linear equation is a characteristic constant of the lubricant related to the high pressure density and the 1 + 1/b value obtained from the intercept b indicates the maximum density ratio.

In recent years, endovascular treatments, in which a treatment device such as a catheter is inserted into a blood vessel to directly approach a lesion, have become increasingly popular worldwide. For safer treatment and further optimization of medical devices, a deeper understanding of the vascular biotribology of the medical devices, biomodels, and blood vessels and an appropriate evaluation method are required. This review paper presents the current state of research on the evaluation of the friction between an intravascular device and a vascular biomodel. We review the experimental conditions, including the sample shape, sliding speed, contact pressure, lubricant, materials, and temperature. Standardized methods should be established for evaluating the friction between an intravascular device and a vascular biomodel.

High-strength aluminum is a good candidate for use in light-weighting applications, but forming it is difficult due to its low formability. Elevated temperatures are therefore necessary to improve formability, but this reduces lubricant performance. The use of calcium carbonate (CaCO₃) as a lubricant additive in warm- and hot-forming of high-strength aluminum is evaluated by strip-drawing tests at room temperature, 225°C and 425°C. Further, the influence of tool surface roughness on the performance of the particles in reducing friction is evaluated. Lastly, the particle-additivated oil is compared to fully formulated, commercially available warm- and hot forming oils. The results show that CaCO₃ particles are suitable for improving tribo-systems in warm- and hot-forming of aluminum, and that they can robustify processes where preparation and maintenance of tool surfaces is difficult as the tribo-system is less sensitive to the tool surface. The performance of the particle-additivated oil was similar to the commercial lubricants at room temperature and 225°C, but was worse at 425°C. However, due to the low cost and effort necessary to prepare the particle-additivated oil, it is a promising alternative to existing lubricant additives.

The durability of super-low friction of hydrogenated carbon nitride (CNx:H) coatings sliding against Si3N4 balls in high-vacuum (HV) environments and the phenomena that occur at the interface were clarified. In an HV, CNx:H achieved super-low friction (µ<0.01), which increased after a certain number of cycles even without coating delamination, indicating the existence of “the lifetime of super-low friction.” During super-low friction, a carbonaceous tribolayer with a transformed structure from the initial CNx:H was formed on Si3N4 and transformed to a similar structure to the initial CNx:H after friction increased. Scanning transmission electron microscopy and time-of-flight secondary ion mass spectroscopy (TOF-SIMS) revealed that the carbonaceous tribolayer during super-low friction had 10–15 nm thickness and chemically bonding with the Si3N4 bulk. This changed to the interface with patch-like carbon adhesions after friction increased, indicating that the carbon transfer states from CNx:H transited during the lifetime. TOF-SIMS depth analysis revealed that desorption of the hydrogen content of CNx:H occurred on the friction surface at a depth of less than 10 nm. We concluded that the lifetime of super-low friction is due to the transformation of the tribolayer formed on Si3N4 owing to the desorption of the hydrogen content of CNx:H.

This study examined the effects of polytetrafluoroethylene (PTFE) and Eichhornia crassipes carboxymethyl cellulose (EC-CMC) polymers in base jatropha lubricant and employed commercial shell lubricant as the reference. Wear reduction and coefficient of friction (COF) were measured using 1 mass% polymer concentrations. Characterization analysis showed that the formulation processes required functional groups like carbonyl, alkene, aliphatic CH₂ and CH₃ group that the Fourier Transmission Infrared (FT-IR) studies indicated were necessary for lubrication. According to the frictional analysis, the polymers’ tribological performance was influenced by changes in both load and operational speed. At 40 kg and 1200 rpm, PTFE and EC-CMC reduced COF by 53.7% and 49.8%, respectively, compared to base jatropha. However, commercial shell oil produced exceptional performance.

It is possible to calculate the oil film thickness and the pressure distribution on the Hertzian contact surface of bearings, gears, traction drives, etc. by the EHL theory by Dowson et al.. For these calculations, it is important to determine the high pressure viscosity and high pressure density of lubricant. In a previous report, I constructed a theory of the relationship between viscosity, temperature and pressure. And the van der Waals type viscosity equation was derived. Similarly, in this study, I constructed a theory of the relationship between density, temperature and pressure. As a result, it was found from the dimensional analysis that 1/3 power of density (line density) was negatively proportional to temperature. This linear equation was found to be a van der Waals type line density equation which consists of three eigen constants: absolute zero line density ρ_t=0^1/3, line density constant 1/G and pressure constant H/G. Furthermore, the pressure constant H/G of the line density equation is equivalent to the P_R of the liquid state equation and the pressure constant C/B of the van der Waals type viscosity equation. And I report the results of estimating the high pressure density of various lubricants by the line density equation.

Indentations in rolling bearings from particle contamination introduce surface damage because they disturb lubrication and produce stress concentrations. In this article, a methodology is proposed where non-failed bearings that have been running in the field are inspected, indentations are counted and their geometry is characterized. With this information and the use of a mathematical model previously developed, the inferred damage in the bearing can be estimated and with this also the actual contamination parameter, η_c as described in the ISO 281 standard. In this way giving more certainty on the real contamination conditions in the application than other indirect assessment methods.