Scuffing is becoming a common failure mode in gears and bearings. It has been shown that some polymethacrylates (PMAs) when used as additives can enhance the anti-scuffing performance of lubricants. This study has employed a step-sliding speed scuffing test to explore the ability of PMAs to prevent scuffing when a rolling/sliding contact is subjected to immediate severe conditions. It is found that the PMA concentration and properties such as sulphur content, Mw and functional group significantly affect scuffing protection. It is suggested that PMAs provide scuffing protection by forming thick and dense adsorption films that can withstand high sliding conditions.

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Seizure occurs when a sudden heat generation at the real contact surface, called the flash temperature, becomes the source point, raising the surrounding temperature and progressing plastic flow. In previous experimental studies, in-situ observations of the contact surface between metals have been conducted, but the complete seizure process has still not been fully elucidated. We propose to apply the smoothed particle hydrodynamics (SPH) method to tribology, a solid friction simulation technique. This makes it possible to express mesoscale sliding surfaces that are difficult to express in terms of spatial scale using all-atom molecular dynamics and can predict frictional heat such as heat generation and heat conduction at the real contact surface, as well as mechanical properties such as large deformation and plastic flow. In this study, we used this simulation model to reproduce the mesoscale sliding surface of aluminum (Al) and titanium (Ti) by creating models with unevenness in the center. In this study, we performed a simulation of the sliding speed, frictional heat, and plastic flow for each material alone and for solid contact models of Al and Ti. As a result, heat generation from the center of the protrusions was confirmed for both metal materials, and then heat was diffused throughout the entire sliding surface. A similar trend is seen when a solid is in contact with a Ti solid, however, whereas the temperature rises overall at the sliding surface of Al, no significant heat diffusion is observed at the sliding surface of Ti, and considerable frictional heat is generated at the contact area. The results of the flash temprature and average temperature shown in this study are considered to indicate the physical properties of each material. In addition, plastic deformation was confirmed on the Al surface, suggesting that the generation of frictional heat and plastic deformation can be analyzed by sliding simulations.

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Polyoxymethylene (POM) has excellent self-lubricating properties and is widely used in tribological applications. However, the mechanism of wear debris formation during polymer–polymer friction remains unclear. In this study, acrylic resin was employed as a transparent counter material to enable in-situ optical observations of the sliding interface formed by the surfaces of a POM ball and an acrylic resin disc. Pin-on-disk tests were conducted at different sliding speeds, and the friction coefficient and near-interface temperature were measured. In-situ optical observations and SEM analyses were also performed to evaluate wear debris flow and material transfer. At a sliding speed of 0.25 m/s, wear progressed relatively gradually, debris flow was confined to grooves and accompanied by localized stagnation, transfer to the acrylic side remained localized, and the debris mainly exhibited a flake-like morphology. In contrast, at 0.56 m/s, wear progressed more rapidly, and debris was generated over the entire POM surface, flowed continuously across the interface without significant accumulation or re-adhesion, and predominantly exhibited a roll-shaped morphology. A thick transfer layer covering the wear track was also formed on the acrylic side. These findings suggest that the sliding speed strongly influences debris flow and transfer, thereby governing the mechanism of wear debris formation in POM–acrylic resin sliding systems.

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In recent years, there has been increasing demand in the fields of industrial equipment and automobiles for lighter and more compact units to save energy. The use of low-viscosity lubricant with high fluidity is known to reduce stirring resistance and decrease energy loss, delivering notable improvements in unit efficiency. As rolling bearings provide essential support to rotating components, the use of lightweight units incorporating slim and thin-section bearings has increased due to their smaller outer ring outside diameter at the same inner ring bore diameter. However, there are concerns that the bearing outer ring (the fixed ring) in these units will rotate in the same direction as the inner ring, a harmful phenomenon known as creep. In a previous study [1], we investigated the cause of creep in the thin fixed thrust washers of thrust needle roller bearings. Experimental evaluations and FEM analysis revealed that creep occurs in fixed thrust washers when circumferential strain on their back face exceeds a certain limit. In this study, a test method was established to assess the creep speed of fixed thrust washers using three types of lubricants with different kinematic viscosities. In addition, detailed observation of the thrust washer surface after testing and X-ray analysis techniques were used to verify the contribution of creep speed to rolling contact fatigue. Results indicate that although creep speed exhibits slight variation depending on differences in lubricant viscosity, lubricant additives represent a critical factor. Furthermore, controlling creep speed could significantly enhance the bearing life of thrust needle roller bearings under conditions involving substantial inclination of the support surface, which contrasts with conventional rolling contact fatigue theory.

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The squeeze film reaction between parallel annular disks is fully theoretically treated in this research using a non-Newtonian Rabinowitsch fluid model enhanced by nanoparticle influences. The Chelyshkov Wavelet Operational Matrix Method (CWOMM) provides a quick and precise computer method for solving the governing equations. The Krieger – Dougherty model, which represents the exponential dependency of viscosity on particle volume fraction, is used to realistically account for the concentration-dependent viscosity of nanofluids. According to the results, shear-thinning (pseudoplastic) behaviour results in a decrease in performance when compared to Newtonian liquids, whereas shear-thickening behaviour introduces a larger load-carrying capacity and longer response times. Numerous parametric studies highlight how nonlinear rheological factors and geometry configurations affect film dynamics and pressure distribution. This data aids in the development of novel, cutting-edge lubrication systems based on non-Newtonian fluid enhanced by nanoparticles.

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Friction fade‑out (FFO) is a superlubricity phenomenon observed when a catalytic ZrO₂ pin slides against a hydrogenated diamond‑like carbon (a‑C:H) film in H₂ environments containing alcohol vapor. FFO achieves ultralow friction coefficients near 10⁻⁴ under high loads (63.7 N, P_max 2.6 GPa). However, the tribocatalytic mechanism and carbon‑bonding structures remain incompletely understood. This study investigated FFO in H₂ environments containing ethanol‑derived decomposition gases (C₂H₄, CH₄, C₃H₆, CO₂) and analyzed the resulting tribofilms to infer their formation pathways. Stable FFO was observed with C₂H₄ at relatively low loads (19.6 N, 1.8 GPa), whereas CO₂ addition increased the load capacity to 49.0 N (2.4 GPa). Depth‑resolved XPS suggested that ethanol‑derived tribofilms were dominated by sp¹‑hybridized carbon, with subsurface fractions reaching 70–78 at.%. These sp¹ structures are inferred to transform into softer sp²–sp³ bonds at the sliding interface through hydrogenation. TOF‑SIMS suggested that sp¹‑hybridized tribofilms likely consist of linear polyenyne polymers [– (C≡C)₄CH=C(CH₃)–]_n, while C₂H₄ is presumed to yield non‑polymerized polyyne monomers H(C≡C)₄H. CO₂ addition may promote sp² cross‑linking, thereby enhancing tribofilm stiffness and load capacity. These findings support a tribo‑induced topochemical polymerization forming sp¹‑hybridized tribofilm. The results provide new insight into the potential for sustained superlubricity under high-load, oil-free conditions.

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This study investigates the MnPh surface treatment applied to improve the tribological properties of steel and rolling fatigue life of gears, focusing on the wear behavior and tribofilm formation during the initial sliding stage. The MnPh-coated layer is almost completely worn off in a short time during sliding, exposing the roughness peaks of the base steel, at which wear mainly occurs. Since the MnPh treatment etches the base steel during the treatment process to roughen the surface, MnPh-treated and MnPh-removed disks are used to match the roughness and morphology of the steel surfaces. The wear rate of the MnPh-treated steel is higher than that of the MnPh-removed steel during the initial sliding stage, following which the wear rate of the MnPh-removed steel increases. The formation of a sulfur-based tribofilm is significant on the MnPh-treated steel, whereas the formation of a calcium-based tribofilm is significant on the MnPh-removed disk. The role of the MnPh treatment is comprehensively discussed through the relationship between the wear behavior and tribofilm formation during the initial sliding stage, which contributes to improving the fatigue life.

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