Lubrication Science最新文献

The study investigated the potential of waste plastic oil (PO) as an alternative to petroleum-based lubricants, specifically mineral oil. The rheological properties, dispersion stability, friction, and wear performance of PO were examined and compared with mineral oil. Results showed that PO demonstrated similar lubrication performance to mineral oil. To enhance the lubrication performance of PO, the study incorporated various concentrations of nano CuO solid lubricant additives, resulting in the formation of CuO nano lubricants. These lubricants showed an improvement in friction and wear by 20% and 44% compared with PO. Furthermore, the CuO solid lubricant additives were functionalized and incorporated in the same concentrations into PO, resulting in the formation of functionalized nano lubricants, which further lowered the friction and wear by 28% and 91% compared with PO. The novelty of the paper is that a simple chemical functionalization process that not only helped in improving its dispersion stability of additives in the PO, but also enhanced the wear performance. The mechanisms behind the enhancement of friction and wear performance were discussed. Based on these findings, it can be concluded that incorporating functionalized nano additives in PO improve friction and wear performance in mechanical components, promoting wider utilisation of PO.

Functionally graded coating (FGC) has played a pivotal role in numerous engineering applications owing to its exceptional properties. This work proposes a novel elastohydrodynamic lubrication (EHL) model with FGC, in which the elastic deformation and stress are computed using influence coefficients (ICs) and discrete convolution-fast Fourier transform (DC-FFT) algorithm. Comparisons are made with homogeneous EHL solutions and finite element analysis (FEA) to validate its accuracy. The study systematically explores how coating elastic modulus, coating thickness and substrate elastic modulus influence contact and lubrication behaviours. The developed model is expected to establish a theoretical framework for FGC material design, enhancing the performance of friction pairs.

In order to investigate the anti-friction and anti-wear performance of different crystal forms nano MoS₂ in paraffin oil. Freeze-drying method combined with hydrothermal was used to prepare different crystal forms nano MoS₂ and their microstructures were characterised by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The anti-friction and anti-wear performance of MoS₂ nanoparticles as lubricat additives under different working conditions was investigated by the ball-and-disk friction and wear testing machine and the mechanism of friction and wear reduction was investigated. The results showed that the thickness of the floral sheet MoS₂ flakes was about 10 nm and the particle size of the spherical MoS₂ was about 90 nm. When the addition concentration was 3 wt%, the friction coefficient of the floral sheet MoS₂ in paraffin oil was lower at 0.094, which was 29.3% lower than that of the pure paraffin oil, the width of the abrasion marks was 24.2% lower than that of the pure paraffin oil and the wear rate was 71.6% lower than that of the pure paraffin oil; The friction coefficient of the spherical MoS₂ with 2.5 wt% addition was 0.082, which was 38.3% lower than the friction coefficient of pure paraffin oil, 24.1% lower than that of paraffin oil in terms of wear scar width and 81.9% lower than that of paraffin oil in terms of wear rate.

In numerical studies of grease lubrication, thermal effect is often neglected and surface plastic deformation is almost not considered. This paper has developed a deterministic thermal plasto-elastohydrodynamic lubrication (PEHL) model for grease-lubricated rolling bearing. The influence of tangent modulus, rheological index and texture orientation on lubrication characteristics and temperature rise is analysed. The results show that increasing the rheological index of grease and decreasing the wavelength factor are obviously positive for improving lubrication behaviour. Since surface plastic deformation in the EHL state is at nanoscale, film thickness, friction coefficient and temperature rise of solid surfaces decline slightly with the decrease of tangent modulus.

The coefficient of friction of low carbon chromium alloy steel with military grade lubricant was high, resulting in increased heat generation and temperature rise of the lubricant in the aircraft power transmission units such as engine gearbox, accessory gearbox and so on. To address this, the current research proposes the addition of TiO₂ nanoparticles to MIL grade lubricant as an additive to enhance the tribological performance. In this experimental study, TiO₂ nanolubricant was prepared using various surfactants for better suspension of TiO₂ nanoparticles, and properties were evaluated for both base lubricant and nanolubricant. The tribological experiments were conducted using a four ball tester, a shear stability tester and a reichert tester. In a four ball test, TiO₂ nanolubricant resulted in a 27.3% reduction in wear scar diameter by the addition of TiO₂ nanoparticles to the base lubricant. In a shear stability test, TiO₂ nanolubricant showed 80% better shear stability than the base lubricant. In the reichert test, the coefficient of friction was reduced by 13% with the TiO₂ nanolubricant. The experimental findings demonstrated that the TiO₂ nanoparticles, as an additive to a military grade lubricant, have superior tribological properties for aerospace applications.

The accuracy and efficiency of the wheel-rail adhesion model are important to the wheel-rail rolling contact issues. The purpose of this study is to develop a simplified non-Hertzian wheel-rail adhesion model under interfacial contaminations to predict the wheel-rail adhesion coefficient. Firstly, a non-Hertzian full elasto-hydrodynamic lubrication (EHL) model was developed and applied to determine the wheel-rail contact pressure and film thickness under interfacial contaminations. Then, the empirical formula of central film thickness available to non-Hertzian wheel-rail normal contact relating to train speeds, axle loads and material parameters were proposed based on a large number of non-Hertzian full EHL simulation for smooth surface under interfacial contaminations using linear regression. The empirical non-Hertzian central film thickness formula and minimum film thickness formula for wheel-rail contact obtained in this paper show certain differences from the formulas based on Hertzian contact. Using the proposed non-Hertzian central film thickness formula, a simplified non-Hertzian wheel-rail contact adhesion model was developed, and the adhesion coefficient was obtained at different speeds and compared with the field test data. The numerical results showed good agreement with field test data.

As one of the liquid metals, Ga–In–Sn liquid metals can function as an advanced lubricant with high conductivity in a tribology system. It has already revealed advancements in several applications, such as coolants and electromechanical relays. However, Ga–In–Sn liquid metal shows poor lubrication performance on industrial metallic materials, which limits its application in engineering. In this study, the electrochemical boronising strategy was applied to improve the lubrication effect of Ga–In–Sn liquid metal on steel friction pairs. Electrochemical boronising treatment was performed to the base material AISI 52100, and a boronised layer with a thickness of around 64 μm was generated. Tribology tests were carried out on both boronised and original samples with the lubrication of Ga–In–Sn liquid metal (68.5 wt% Ga, 21.5 wt% In and 10 wt% Sn). Results show that the wear resistance of the tribo-system reveals great improvement: The coefficient of friction decreases by 59% and the wear rate drops 85% compared to the steel/steel friction pair. EDS and XPS results show that a tribofilm consisted of Fe/Ga was in situ–generated on the wear scar of the boronised sample, which results in the synergy effect between the boronised layer and the Ga–In–Sn liquid metal. Therefore, we provided a robust strategy to enhance the lubrication performance of Ga–In–Sn liquid metal on a steel friction pair by using electrochemical boronising treatment, which could broaden the application field of Ga–In–Sn liquid metals.

The scuffing load capacity of gear is closely related to the meshing temperature rise of tooth surface. The key to predict the temperature rise is to establish an accurate meshing temperature rise model. In the paper, a tribo-dynamic model of helical gear is established through coupling of tooth surface lubrication parameters, and the influence of temperature rise on ambient temperature during meshing process is considered. Then, the effects of oil supply temperature, input speed and torque on tooth surface temperature rise, film thickness, friction excitation and gear dynamic characteristics are discussed. The results show that the temperature rise of the gear is higher during the engaging-in and engaging-out regions. Meanwhile, there is local high temperature at the end of the contact line due to the end effect. The vibration of gear along the off-line-of-action direction is mainly determined by friction excitation. With the increase of oil supply temperature, input speed and torque, the risk of scuffing failure increases and the influence of oil supply temperature and input load is more significant. The conclusions of this paper may provide some valuable suggestions for the anti-gluing failure design of gear in engineering.

This study investigates the impact of oil additives on the performance of hydrodynamic journal bearings using hazelnut oil. Various additives, including titanium dioxide, hexagonal boron nitride and graphite, are mixed with hazelnut oil in specific concentrations. Experimental tests are conducted in boundary and mixed lubrication regimes using a specialised rig to simulate bearing operating conditions. The friction performance of these oil-additive combinations is evaluated in terms of bearing load, rotating speed and oil temperature. The findings contribute to understanding hazelnut oil as a potential lubricant and optimising its formulation for specific applications, promoting environmentally friendly lubricants and sustainability.

In order to investigate the impact of micro-textured surfaces with varying surface density on coating properties, the bionic leaf vein micro-texture with different surface densities were prepared on the substrate surface by laser processing. Bi₂S₃ soft coatings were deposited on the textured surfaces by electrohydrodynamic atomization. The influence of textured surface density on the adhesion and tribological properties of the coatings was analysed and discussed by scratch tests and friction wear tests. The results showed a significant increase in the friction coefficient as the surface density increased. However, after reaching a certain point, the friction coefficient tended to decrease. The coatings deposited on the lower surface density (13.9%, 14.5%) have better tribological performance compared with the higher surface density (35.6%, 36.2%). Meanwhile, the adhesion of coatings on the textured substrate enhanced compared with coatings deposited on the polished substrate. A reasonable textured surface density can effectively improve the adhesion and tribological properties of the coating.