Lubrication Science最新文献

To cope with lubrication failure of mechanical parts caused by leakage of water-based lubricants, we designed a novel and facile hydrophilic modification method for MoO₃ nanoparticles to generate oleic acid diethanolamide (ODEA)-functionalized MoO₃ nanoparticles (ODEA-MONP). The as-prepared ODEA-MONP nanohybrids were systematically characterised using technologies such as XRD, TEM, XPS, and FTIR. The tribological properties of ODEA-MONP and water-based sulfur-containing additive (W4770) were evaluated with UMT-2 and SRV5 tribometers; concurrently, the collaborative lubrication process involving ODEA-MONP and W4770 was investigated. It was found that water plays a decisive role in the initial stage by promoting the formation of a uniform and stable lubricating film structure (SEM shows homogeneous Mo/S distribution), which critically determines the lubrication performance in the subsequent water-free state. XPS analysis confirmed that after high-temperature water evaporation in the aqueous system, a composite tribofilm consisting of MoS₂, MoO₃, MoO _x , iron oxides, and organic compounds formed. The present work not only provides new insights into the in situ vulcanization of molybdenum-containing materials in water-lubricated systems but also broadens the application potential of water-based additives under water-depleted conditions.

The present study investigates the dynamic characteristics of journal bearings with rectangular macro-grooves, focusing on parameters such as stiffness, damping coefficients and stability threshold speed. Using the finite element method to solve the governing Reynolds equation for lubricant flow, the analysis explores the influence of varying macro-groove texture numbers, groove depth and area density across different bearing regions such as the full region, first half, second half and pressure-increasing region to identify the optimal performance parameters in each region. Findings reveal that both stiffness and dynamic coefficients of the journal bearing improve at higher and lower eccentricity ratios. Among the various investigated macro-grooved regions, at an eccentricity ratio of 0.2, the maximum enhancement of stability threshold speed of 84.23% is found for full grooved macro rectangular-textured surface with two macro-grooves at non-dimensional groove depth of 0.9 with an area density of 54.01%. Additionally, incorporating 0.5% weight fractions of copper oxide and cerium oxide nanoparticles into the base lubricating oil at 90°C significantly enhances stiffness, damping coefficients and stability threshold speed.

The interfacial bonding between a matrix and a lubricating phase has a considerable effect on the mechanical properties of lead-free FeS/Cu–Bi self-lubricating composites, but the effect of the load-induced interfacial bonding behaviour of heterophases on the composites' tribological properties is unclear. In this study, FeS/Cu–Bi self-lubricating composites with weak and strong FeS/Cu interface bonding were prepared, and the effects of sliding load on the precipitation characteristics of FeS particles and tribological properties of FeS/Cu–Bi composites were studied through experiments and numerical simulation. Results showed that the interfacial failure of FeS/Cu heterophases and precipitation morphology of FeS particles varied because of the varied strength of FeS/Cu bonds. In FeS/Cu–Bi composites with weak interfacial bonding between FeS and Cu, FeS is prone to detachment and expulsion from the friction interface in the form of wear debris during sliding. Under low-load conditions, the effect of FeS discharged as wear debris is weak, and the material exhibits a relatively low friction coefficient (0.31) and wear rate (5.7 × 10⁻⁵ mm³·N⁻¹·m⁻¹). The friction coefficient and wear rate of the material gradually increased with load. Strengthening the interfacial bonding between FeS and Cu impedes the detachment of FeS as wear debris during sliding, promoting its precipitation and deposition on the worn surface and thereby mitigating adhesive wear. The friction coefficient and wear rate of the material decreased initially and then increased with increasing load. The material with strong FeS/Cu interfacial bonding effectively induced the precipitation of FeS towards the worn surface under a moderate-load condition and formed a complete and continuous lubricating film. The minimum friction coefficient and wear rate were 0.22 and 1.3 × 10⁻⁵ mm³·N⁻¹·m⁻¹, respectively.

The surface of copper-based electronic devices typically exhibits nanoscale roughness rather than being an ideal smooth plane. To accurately assess the authentic tribological performance of graphene (Gr) and hexagonal boron nitride (h-BN) coated on rough substrates, a molecular dynamics model is constructed to simulate the interaction between a diamond tip and a coated copper substrate. The sliding friction simulation is accomplished on both smooth and rough substrates. The friction, wear and subsurface damage on substrates coated with Gr and h-BN are compared. The results show that the substrate coated with h-BN exhibits enhanced friction, increased wear and fewer dislocations compared to the one with Gr for the same rough topography. Furthermore, the transition of the substrate topography from smooth to rough leads to higher friction, increased wear and reduced subsurface damage within the same coating. This effect is more pronounced for h-BN than for Gr, due to the strong adhesion of h-BN and the high compressive strength of Gr, which results in distinct differences in coating buckling behaviour on the rough substrate. This study offers valuable guidance for the development of durable coatings in microelectronic devices.

Due to the incomplete understanding of the mixed lubrication mechanisms of novel multi-layered composite water-lubricated stern bearings under complex operational conditions, this paper addresses the cantilevered offset loading conditions and the multifactorial coupling characteristics that these bearings frequently encounter in such complex scenarios. Firstly, a mathematical and physical model for mixed lubrication within the multi-layered composite water-lubricated bearing-flexible rotor system was established. Secondly, numerical simulations were utilised to analyse the impact of coupled factors such as rotational speed, load, water supply pressure and radial clearance on the mixed lubrication performance of the bearings. Finally, a water-lubricated bearing test rig was constructed to conduct multi-condition and multi-section lubrication performance tests on the bearings. The research findings indicate that under single-sided loading conditions with the same velocity increment, the water film pressure decay rate accelerates from measurement points P1 to P5, with a pronounced decay observed at section P5, with a decrease of 48%. As the rotational speed increases, the squeezing effect diminishes for sections further from the cantilever end, leading to a reduction in water film pressure and alleviation of pressure concentration. Under double-sided loading conditions, the water film pressure in the cross-section at measurement point P2 decreases by 10%, and this trend moderates as the load increases. In contrast, the water film pressure in the cross-section at measurement point P5 increases to 25 kPa, and the circumferential distribution of the water film broadens. Moreover, as the rotational speed increases, the water film pressure decreases and the circumferential distribution of the water film narrows.

The contact fatigue of carbon steel gear tooth surfaces under different lubrication conditions has been investigated and a model of the effect of lubrication conditions on contact fatigue has been established. Micro damage less than Hertzian contact is more likely to expand into macro pitting. The pressure around the micro damage increases when the micro damage partially coincides with the contact width, so the tooth surface around the pit is more likely to produce new pits, and then forms the superposition and aggregation. The larger the lubricating oil supply, the larger the contact width, and the larger the width of the micro damage that can be activated, the improvement of lubrication can promote the propagation of micro damage.

In this study, a dynamic friction testing apparatus was independently developed to investigate the frictional properties of tire-asphalt pavements under varying road conditions, tailored to complex working environments. This device underwent rigorous reliability analysis to ensure compliance with the experimental standards. The calibration of asphalt pavements with varying heating durations established regions of uniform temperature. Experiments were conducted using custom-designed equipment under conditions involving changes in particle size, temperature, and surface roughness. Results showed that both the maximum static friction and average friction forces increased with increasing temperature. Smaller particle sizes intensified stick–slip behaviour but reduced frictional forces, whereas greater tire surface roughness enhanced friction and accentuated stick–slip phenomena. An improved spring-slider model was proposed to simulate the frictional behaviour of asphalt pavements, yielding results consistent with the experimental data. Adjusting the roughness parameter in the model demonstrated that friction gradually decreases with reduced roughness, while stick–slip effects diminish, aligning qualitatively with the experimental observations.

Rolling contact fatigue (RCF) is the default mode of failure observed in Hertzian rolling contact elements, such as bearings. Experimentally, the current study examines the influence of the existence of solid lubricant dispersed in liquid base lubricant on RCF life. Polytetrafluoroethylene (PTFE), a solid lubricant additive, is selected for this purpose, and the RCF performance of varying percentages of PTFE (0.1–2.5 wt%) on the base lubricant has been examined. RCF tests were carried out on a two-disc on-cylinder test rig under pure rolling conditions within the mixed lubrication regime. The RCF life was enhanced for every concentration of PTFE-added lubricant composition. The base lubricant containing 2 wt% PTFE concentration exhibits the highest improvement in mean and L₁₀ RCF life, yielding a 2.3-fold increase in improvement over the base lubricant. The excellent RCF performance is attributed to the decreased wear rate, PTFE particle adsorption and tribo-chemical film formation, and there is a decreased likelihood of metal-to-metal contact and a delayed onset of micropitting.

In this study, lithium stearate and fumed silica co-thickened grease with po-ly(sodium-4-styrenesulfonate) (PSSNa) additive was synthesised and characterised for application as an automotive lubricant, including for the potential use in an electric vehicle (EV). Oscillatory shear and steady shear rheological tests confirmed that the sample exhibited appropriate shear thinning required in greases. Fumed silica was found to increase thermal stability. Additionally, the conductivity of the synthesised grease was higher than the threshold conductivity required to avoid electrical arcing and static charge buildup (4 × 10⁻¹² S/cm). The tribo-pair lubricated with LSFSPNa grease demonstrated a significant improvement in tribological performance, with the coefficient of friction reduced by approximately 65% compared to commercial grease, decreasing from 0.31 to 0.11. The wear volume showed a tenfold reduction, accompanied by a substantial decrease in surface roughness (Ra), which dropped from 0.81 μm with commercial grease to 0.17 μm with LSFSPNa grease. At the same time, the synthesised grease exhibited better copper corrosion resistance. Overall, the synthesised grease was found to be compatible for EV applications in terms of rheology, friction reduction, copper corrosion resistance, conductivity, and thermal stability.

Friction and wear are major challenges in automotive engines, and they can lead to significant operating issues such as increased fuel consumption, component damage, heat generation, loss of performance, etc. Friction and wear between piston rings and cylinder liner are significant issues in automotive engines, and researchers continually focus on reducing them to improve engine performance and efficiency. Numerous studies have been carried out to minimise friction and wear losses. However, coating is one of the promising techniques used in the automotive industry. PVD-deposited, CrN-coated piston rings demonstrated excellent tribological properties. However, CrN coatings become less effective under conditions of lubrication starvation, exhibiting a high coefficient of friction. In the present study, PVD-based magnetron sputtered CrN and carbon-doped CrCN coatings were applied to the surface of the piston rings. The structure, elemental composition, surface morphology, thickness, and hardness of the coatings were characterised systematically. The coated samples underwent tribological testing under loads of 50, 80, and 110 N to assess the coefficient of friction at the piston ring-cylinder liner interface under the boundary lubrication condition and evaluate the wear behaviour of the coated ring samples. The carbon-doped CrCN coating exhibits a low coefficient of friction at each load and exhibits a 16.59% reduction in the coefficient of friction compared to the CrN coating. This could be ascribed to the graphitisation effect of the CrCN coating. However, both coatings showed almost equal and minimal wear loss. Finally, the possible worn morphology of coated samples was proposed based on their microstructure, film deposition, and Raman's spectroscopy results.