High-speed deep-groove ball bearings for the eAxle of electric vehicles must adapt to higher rotational speed conditions, because eAxle motor speed increases to downsize the unit. Therefore, it is necessary to clarify the lubrication process of ball bearings at the high rotational speeds to prevent seizure and wear. The oil-film thickness between outer-ring and ball, and the oil distribution around balls in 6008 deep-groove ball bearings incorporating experimental quartz outer rings were measured under high-speed conditions, with speeds exceeding 20,000 min⁻¹. These measurements were carried out by employing the three-wavelength flash-light optical interferometry method and the UV-LED light-induced fluorescence method. It was found that the oil-film thickness did not increase even when the rolling speeds increased, which is in contrast to the EHL theory under sufficient lubrication condition. Contrary to the EHL theory, these phenomena can be attributed to the oil starvation and lowering effective viscosity of oil containing bubbles resulting from aeration under high-speed conditions.

Polyester base oil has good lubricating properties and biodegradability, which meets the requirements of green and sustainable development. In this work, polypropylene adipate (PPA) was synthesized with spherical nano-MoS₂/sericite (SMS) as catalyst. SMS did not need to be separated from PPA after the reaction and could be retained in PPA as a lubricant additive. The SMS precipitated slowly in the SMS/PPA suspension during standing storage, and after 7 days, there was still 1236 mg/L SMS in the PPA. Compared with PPA synthesized without SMS, the friction coefficient of the SMS/PPA suspension after standing for 7 days was reduced by 13.9%. Moreover, the suspension also decreased the wear volumes of the steel ball and the steel disc by 59% and 94%, respectively. The characterization results showed that SMS participated in the formation of tribofilm, and decomposed into silicon and oxygen-rich compounds filled in the peeling caves. This study provides an alternative path for the synthesis of polyester base oil, and also expands the potential application range of MoS₂ lubricant additives.

It is well known that the friction coefficient of viscoelastic solids against the drive speed exhibits a bell shape. In previous theoretical studies on viscoelastic friction, we can find two origins for the bell shape. One is due to the material response (i.e., the bell-shaped rheology of viscoelastic solids), and the other is due to the mechanical response (i.e., the vertical lift of the counter surface with asperities). Although these two origins do not contradict each other, their relationship seems unclear. This paper theoretically examines the friction coefficient for the steady sliding contact between a rigid probe and a viscoelastic foundation exhibiting the standard linear solid viscoelasticity. Capitalizing on the strength of the simple model, we successfully find the complete set of dimensionless numbers and master curves describing the velocity dependence of the friction coefficient. Comparing them with the dimensionless numbers and master curves for the Kelvin-Voigt viscoelasticity, we clarify two origins for the bell-shaped velocity-dependent friction coefficient and their relationship.

Under low-speed or start/stop conditions, the rubbing of top foil in foil journal bearing (FJB) prompting the application of heat treatment to improve the rubbing behavior of the foil bearing. During heat treatment, various factors can influence the thermo-physical properties of foil. Therefore, the present study is carried out to analyze the impact of heat treatment variables on the rubbing behavior of FJB. To obtain it, bump-type FJBs are fabricated using SS 316 foil material with a corrugated die. Subsequently, experimental investigations of the developed bump-type FJB are conducted based on response surface methodology. The rubbing behavior of the FJB, including wear rate and surface roughness, is evaluated under various heat treatment conditions. The results indicate that both the wear rate and surface roughness of bump-type FJB decrease with increasing HT time duration. Furthermore, it is observed that the temperature distribution of the heated foil becomes more uniform with longer HT time durations. At the optimal HT variables of 500°C and 3 hours, the surface roughness and rubbing temperature of bump-type FJB are measured at 1.295 μm and 55.20°C, respectively. Additionally, the rubbing temperature of bump-type FJB is thoroughly evaluated.

The mechanisms of chemical mechanical polishing (CMP) of copper (Cu) surface using a slurry containing hydrogen peroxide (H₂O₂) and silica abrasive grains were theoretically investigated. First, molecular dynamics (MD) simulations using ReaxFF were used to analyze reactions that remove Cu atoms from the Cu(111) surface. At the Cu/H₂O₂ interface, Cu atoms were oxidized by forming Cu-O atoms were oxidized. In the second pathway, the atomic arrangement around the oxidized Cu atoms was disordered caused by surface vacancies. In relation to the first reaction pathway, activation energies were calculated to study the effects of the oxidation of Cu atoms on the Cu removal reactions. The results showed that the lowest activation energy was obtained when the structure in which neighboring Cu atoms were most oxidized, which supported the results of the MD simulations. The findings of this study indicate that the oxidation degree of adjacent Cu atoms and the atomic arrangement of the Cu surface affect the Cu removal reactions.

Machining processes hold a pivotal place in the sphere of modern manufacturing. Thus, constant advancements to enhance their efficiency and sustainability are warranted. This review paper discusses the recent advancements in machining with Minimum Quantity Lubrication and a combination of Nano-Fluids with Minimum quantity lubrication (Nano-Fluid MQL). Recent developments are assessed with particular emphasis on critical parameters such as cutting temperatures, tool wear, and surface quality. In addition, the environmental and economic aspects of using MQL in combination with nano-fluids are discussed. This combinatory approach is evaluated as a sustainable solution in machining. This paper also presents the literature survey of nano-fluids and the application of nano-fluids in MQL.