Lubrication Behavior Research Articles

Mechanisms of MoS 2 dry film lubricant behavior at low temperatures

Mechanisms of MoS ₂ dry film lubricant behavior at low temperatures

Numerical Simulation and Experimental Investigation on Friction and Lubrication Behaviors of Chevron Micro-Textured Valve Plate/Cylinder Block Interface With Various Area Densities

Abstract As the critical friction pairs of swashplate-type axial piston pumps, the cylinder block/valve plate lubricating interface is the primary source of friction, wear, and leakage in axial piston pumps. Surface micro-texturing has been widely employed in cylinder block/valve plate conjunctions to ameliorate tribological performance. However, little research has been conducted to investigate the influence of chevron micro-texture area density on the tribological behaviors and lubricating properties of cylinder block/valve plate interface both experimentally and numerically. In this article, the chevron micro-textures with various area densities were manufactured on H62 brass by micro-milling and subsequently characterized with a laser scanning confocal microscope (LSCM). The friction and wear performance of H62 brass/38CrMoAl conjunctions were obtained via disc-on-disc tribological tests to simulate the cylinder block/valve plate lubricating interface. Moreover, the load-carrying capacity of untextured and chevron micro-textured samples was numerically investigated under hydrodynamic lubrication. It was found that the chevron micro-textured surface with an area density of 30.1% displayed the lowest friction coefficient and the shallowest wear depth. Although the load-carrying capacity of chevron micro-textured samples with a high dimple area density was larger, the severe stress concentration induced by the reduced micro-texture spacing caused the increment and large fluctuations of friction coefficient.

Lubrication Prediction of Sphere‐Gradient Coated Half Space Interfaces

ABSTRACTFunctionally 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.

Numerical Thermal Analysis of Greased Rolling Bearing Considering Surface Topography and Plastic Deformation

ABSTRACTIn 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.

Modelling and theoretical research on transient lubrication and wear coupling behavior of main bearing during start-up of low-speed diesel engine

This study endeavors to establish a transient mixed lubrication model for time-varying wear of main bearings under dynamic loading conditions during the startup process. This model accounts for variations in oil film thickness attributable to deformation, wear profiles, and journal misalignment throughout the operational cycle. The evolution of main bearing lubrication characteristics during the startup process was analyzed, as well as the evolution of wear profiles and their effects on lubricating properties under different numbers of startups. The results indicate that as the number of startup cycles increases, the wear rate gradually levels off. With increasing startup times, there is a decrease in contact pressure and a slight reduction in oil film pressure, resulting in enhanced lubricating performance. Furthermore, the influence of startup duration on wear is significantly greater than that of radial clearance.

Combining in-situ quadrupole mass spectrometer analyses: Study on the structure–activity relationship and lubrication mechanisms of ammonium phosphate ionic liquids

Since the lubrication performances of ionic liquids are closely linked to their unique structures, four protic ionic liquids (PILs), [N44HH][DEHP], [N444H][DEHP], [N448H][DEHP] and [N4412H][DEHP], are designed to investigate the effect of cationic structures on the lubrication behaviors and lubrication mechanisms. Vacuum tribological tests were carried out to minimize the impact of the atmospheric environment. The structure–activity relationships and lubrication mechanisms of PILs were emphatically examined by in-situ quadrupole mass spectrometer (Q-MS) and XPS analyses. Results demonstrated that all four PILs exhibited outstanding lubrication performance under a vacuum condition. Unusually, extended alkyl chain cationic structures resulted in a changed lubrication mechanism, leading to a slight decrease in performance. In-situ Q-MS analyses and XPS further revealed that the length of the alkyl chain in cations influenced the strength of intermolecular forces in PILs, leading to changes in their lubrication performance and mechanisms.

The effect of Ag electroplated layer on temperature-adaptive lubrication behavior of the CoCrMo coating with a texture interface

The effect of Ag electroplated layer on temperature-adaptive lubrication behavior of the CoCrMo coating with a texture interface

Solid/liquid hybrid lubrication behaviors of amorphous carbon film coupling with nonpolar and polar base oils

The amorphous carbon film (a-C) has aroused intensive interest in solid-oil hybrid lubrication design due to its low friction, high wear resistance, and good chemical inertness. However, the solid/liquid hybrid lubrication behaviors and mechanisms of a-C films when coupled with nonpolar and polar oils of similar viscosity are still insufficiently understood and ambiguous to date. In this study, we compared the lubrication properties of nonpolar paraffin oil and polar polyether oils with different molecular structures when combined with a-C film. The results demonstrated that the lubrication performance of polyether oils coupled with a-C film surpassed that of paraffin oil across various lubrication regimes. Notably, the stable superlubricity (friction coefficient<0.01) was achieved under mixed lubrication regime on the a-C film when coupled with polyethylene glycol (PEG) oil after a prolonged sliding duration. The tribo-induced formation of carbon quantum dots (CQDs) at the steel/a-C friction interface lubricated by PEG oils was firstly observed. The hydroxylation of the counter ball surface and the fabrication of CQDs might jointly contribute to the achievement of the robust superlubricity of the PEG oil/a-C film hybrid lubrication system.

Solvent‐Induced Dynamic Bond Regulation for Constructing Adaptive Lubricating Hydrogels with Switchable Tribological Performance and Environmental Adaptability

AbstractAdaptive lubricating hydrogels (ALH) show promise for reducing friction and energy consumption in various industrial applications. However, retarded switchable tribological performance and poor environmental adaptability limit their integration into application devices. Herein, a dynamic bond regulating strategy based on solvent conversion for producing an ALH with highly switchable tribological performance and decent environmental tolerance is proposed. By incorporating dynamic B─O bonds into the sodium alginate (SA) framework, these bonds transition between associative and dissociative states, facilitated by solvent conversion between glycerol and ethanol. This process modulates the mechanical modulus of the SA network, allowing for achieving highly switchable tribological performance. Furthermore, the inclusion of glycerol not only as a modulus regulator but also serves as an antifreeze component to impart the ALH with superior antifreeze and heat resistance properties, thus allowing the ALH to demonstrate excellent environmental adaptability. As a result, the resulting ALH exhibits highly switchable lubrication behavior, with a dynamically adjustable coefficient of friction (COF) between 0.022 and 0.157, and maintains consistent lubrication performance under a harsh environment (−40–60 °C), representing the state‐of‐the‐art in reported ALHs. This advancement allows for the development of intelligent brake devices (IBD), demonstrating potential applications in controlling drone speed.

A general strategy for developing eco-friendly, harsh condition adaptive, and friction tunable supramolecular gel lubricants via hydrogen bonding interaction

As green tribology and controllable lubrication technology progress, traditional lubricants fail to meet the evolving requirements of environmental sustainability, adaptability to extreme conditions, and precise friction coefficient control. In this work, a general strategy is proposed to obtain eco-friendly, harsh condition adaptive, and friction tunable polyol supramolecular gel lubricants. Molecular dynamics simulations reveal that the formation of supramolecular gels is induced by the hydrogen bond interaction between PVA, MXene, and polyols. Rheological tests demonstrate the excellent shear thinning and creep recovery properties of the prepared supramolecular gel at both room and low temperatures, positioning it as a promising new lubricant. Tribological tests further show that the supramolecular gel achieved a low friction coefficient of 0.056 and a wear rate as low as 1.88 × 10−9 mm3 N−1 m−1. Moreover, the tribological properties of various polyol supramolecular gels were compared and the viscosity-controlled friction lubrication behavior was observed. This research not only presents a novel strategy for developing environmentally friendly supramolecular gel lubricants that are adaptable to harsh conditions and tunable in friction, but also offers practical solutions to address challenges such as environmental pollution, lubrication failures in extreme environments, and precise friction control.

Investigating lubricant behavior in a partially flooded tapered roller bearing: Validation of a multiphase CFD solver for aerated oil sump via particle image velocimetry studies and high-speed camera acquisitions

In the recent years, the efficacy of utilizing sapphire outer rings as a viable tool for experimentally observing oil flows within rolling bearings has been demonstrated. However, in previous studies, such approach was applied under fully-flooded lubrication conditions exclusively. This paper presents the outcomes of observations and measurements conducted under oil-bath lubrication conditions of a vertical-axis Tapered Roller Bearing (TRB). The experimental work encompasses four operational speeds ranging from 1000 min−1 to 2500 min−1, and two oil levels, i.e. 10% and 100% of the bearing width. Pictures were captured using an High-Speed Camera (HSC) for a qualitative inspection. Particle Image Velocimetry (PIV) measurements were conducted for a quantitative assessment of the oil velocity fields. The findings reveal specific lubricant flows, highlight aeration, and show particular vorticity patterns that intensify with increasing speed. These experimentally obtained results align with Computational Fluid Dynamics (CFD) simulations conducted using a specially developed model in OpenFOAM®, leveraging a solver that accounts for aeration.

Full-size experimental investigations on planetary gear journal bearings in high-power wind turbines

Abstract To satisfy the large-scale and high-power demands of wind turbines, planetary gear journal bearings (PGJBs) have been applied in large wind turbine gearboxes (WTGs), as an alternative to traditional rolling bearings, due to their higher reliability and smaller size. To simulate the actual lubrication behaviors of PGJBs and investigate their hydrodynamic performance, a full-size test rig for PGJBs was built in this paper. A multi-parameter detection system coupled with the ultrasonic testing method was developed. Four ultrasonic piezoelectric elements, eight thermistors, two pressure transducers, and one torque sensor were used to obtain the film thickness, oil temperature, oil pressure, and friction torque data of the test PGJB. The rated condition experiment was conducted to investigate the variation of measured lubrication performance with the operating time. Three-dimensional predictions of oil film pressure, temperature, and thickness were presented to analyze the steady-state lubrication characteristic at the rated condition. Moreover, a series of steady-state experiments were also carried out to simulate the normal operations of the test PGJB at different conditions. And the measured results were verified by the numerical predictions. The influence of rotational speed, input load, oil supply temperature, and oil supply flow on the hydrodynamic performance of the test PGJB were explored.

Tribological properties of the P and S-free protic ionic liquids as water-based lubricants

Three kinds of P and S-free 1,8-Diazabicyclo[5.4.0] undec-7-ene water-soluble protic ionic liquids (PILs) were successfully synthesized and applied as additives in water-1,2-Propylene glycol (PG). The physicochemical properties of PILs and the anti-friction, anti-wear and anti-corrosion properties were investigated. Research results demonstrated that the addition PILs lubricant additive could greatly improve the tribological properties of water-1,2-PG. The addition of 5 wt% PILs with long alkyl chain will result in the reduction of friction coefficient and wear volume by about 45 % and 95 %, respectively. Meanwhile, the PILs with long-chain show more effect lubrication behavior than the short one. In addition, the obtained PILs also possess excellent anti-corrosion properties as water-based lubrication additives. The elemental analysis of the contact area showed that the PILs would generate a chemical reaction film during the friction process, and the carboxylate anion could form a chemical and physical adsorption film on the surface of contact area, which would provide better anti-friction and anti-wear properties.

Adsorption-enhanced friction reduction in TiN-Ag/polyalphaolefin (PAO) solid-liquid systems: Catalytic induction of amorphous carbon formation

The construction of green and friendly solid-liquid lubrication system, especially the composite system without harmful elements such as phosphorus and sulfur, has been a hot research topic in tribology. In this paper, through the friction and wear performance of the prepared TiN-Ag/polyalphaolefin (PAO) composite system, various factors affecting the lubrication behavior of the solid-liquid composite system were deeply explored, including the surface energy of the film, the lubrication state of the composite system, the adsorption energy of the TiN-Ag/PAO system, tribochemical products, etc. The friction reduction mechanism of TiN-Ag/PAO solid-liquid composite system was revealed. In particular, through the characterization of tribochemical products accumulated at the contacting interface, the internal mechanism of PAO degradation to form amorphous carbon was revealed, and the catalytic induction mechanism of Ag and AgO2 in the process of PAO degradation was clarified.

Tangential contact modeling to seal considering elastic-plastic for lubrication transition mechanism

Researches on the reciprocating seals lubrication under elastic-hydrodynamic lubrication (EHL) are mature, and leakage of failure criterion has been described with Couette flow for more than 30 years, which could not reflect to leakage mechanism in multiscale. Thus, it is necessary to explore seal leakage failure to focus on micro convex bodies of asperities model under contact pressure and cycle tangential friction stress in mixed lubrication. This is because convex bodies behaviors determine sealing effect and lubrication behaviors in microscale with subjecting to the dominant pressure. Interaction between convex bodies fatigue hysteresis curve and elastic-plastic strain are also calculated to explore sealing effect with leakage rate mechanism. We then design water seal at high pressure of 100 MPa with the speed of 0.1–1 m/s and medium temperature from 5 ℃ to 40 ℃. IWAN model of the convex bodies are calculated. Probability density function and Jenkin’s elements critical slip displacement are obtained. Convex bodies of radial and tangential deformation are also calculated through loading of contact pressure and friction stress with cycle strength coefficient to obtain seal fatigue lifespan. Ratio to seal stick and slip friction is calculated for evaluating the loading boundary. Seal leakage failure mechanism with fatigue characteristics is illustrated with macro lubrication parameters and micro convex bodies mechanics performance.

Enhancing protein content and lubrication behavior of plant-based milk with microparticulated wheat gluten protein via SS-SH interchange

The protein fortification and mouthfeel improvement (achieving dairy-like lubrication properties) in plant-based dairy alternatives have consistently been challenging tasks. To achieve this task, we developed a fully plant-based milk product by enhancing lubrication through microparticulated wheat gluten particles. By utilizing a combination of pH shifting, disulfide bond reductants, and high-pressure microfluidization, SH-SS exchange reactions were successfully induced, leading to the preparation of microparticulated wheat gluten particles with a particle size ranging from 1 to 2 μm and excellent dispersion properties. Introduction of a thiol-blocking agent confirmed the dominance of disulfide bonds in particle formation. The findings demonstrated that even at a high protein concentration of 15%, microparticulated wheat gluten sample maintained good flowability. Friction analysis revealed that the micro-particulated gluten protein treated with a disulfide bond reducing agent (GRM) exhibited a lower friction coefficient compared to other samples. Upon the addition of oat milk, GRM effectively reduced the coefficient of friction while increasing the protein content (5 wt%), achieving a lubrication effect similar to that of microparticulated whey protein. This study provides a novel solution for the preparation of microparticulate wheat gluten and enhances its incorporation into plant-based dairy products, offering a new approach to developing high-protein plant-based dairy products with improved mouthfeel and texture.

Digitally enhanced development of customised lubricant: Experimental and modelling studies of lubricant performance for hot stamping

Digitally enhanced technologies are transforming every aspect of the manufacturing sector towards the era of digital manufacturing. Traditional lubricant development methods involving systematic but time-consuming iterative processes is still extensively used in the metal forming industry. In the present study, a novel digitally enhanced lubricant development scheme was proposed by leveraging a mechanism-based interactive friction modelling framework and quantitative and comprehensive evaluation of lubricant performance via the data-centric lubricant limit diagrams. By predicting transient lubricant behaviour following the complex contact condition evolution experienced in actual forming operations, a close association and quantified relation between the lubricant performance and its properties such as viscosity, evaporation rate and fraction of dry matter was established. This can facilitate the optimisation efficiency of lubricant parameters and minimise the experimental cost for iterative lubricant trials. A case study was conducted in this work to develop a customised lubricant using this digitally enhance scheme for the target hot stamping process based on a benchmark lubricant as a reference. Further industrial forming tests of an automotive component were conducted to validate the ideal performance of the customised lubricant.

Effect of phosphide additives on the tribological properties of polyethylsiloxane (PES) in Si3N4 and M50 system

PurposeThe incorporation of phosphide additives is regarded as a highly effective strategy for enhancing the lubricative qualities of base oils. This study aims to assess the lubrication behavior and efficacy of various phosphide additives in polyethylsiloxane (PES) through the employment of the Schwingum Reibung Verschleiss test methodology, across a temperature range from ambient to 300°C.Design/methodology/approachPES demonstrated commendable lubrication capabilities within the Si3N4/M50 system, primarily attributable to the Si-O frictional reaction film at the interface. This film undergoes disintegration as the temperature escalates, leading to heightened wear. Moreover, the phosphide additives were found to ameliorate the issues encountered by PES in the Si3N4/M50 system, characterized by numerous boundary lubrication failure instances. A chemical film comprising P-Fe-O was observed to form at the interface; however, at elevated temperatures, disintegration of some phosphide films precipitated lubrication failures, as evidenced by a precipitous rise in the coefficient of friction.FindingsThe results show that a phosphide reactive film can be formed and a reduction in wear rate is achieved, which is reduced by 64.7% from 2.98 (for pure PES at 300°C) to 1.05 × 10–9 μm3/N m (for triphenyl phosphite at 300°C).Originality/valueThe data derived from this investigation offer critical insights for the selection and deployment of phosphide additives within high-temperature lubrication environments pertinent to PES.Peer reviewThe peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-04-2024-0139/

Tribocorrosion of couplings in seawater environment: An investigation on the positive-negative role of synergy

Tribocorrosion is a recent paradigm of tribology defined as the combination of simultaneous mechanical and chemical wear of couplings. To date, this phenomenon is common in several engineering fields, such as the naval sector where marine equipment, offshore platforms and so on are clear examples. In this regard, the synergy between the mechanical and the chemical effects has a notable effect on the behavior of couplings in seawater environment. Nevertheless, the latter can act also as antagonistic factor. Hence, in this manuscript, an investigation was conducted on a tribosystem composed of an alumina sphere and a stainless-steel AISI 316 L flat, immersed in an artificial seawater solution of 3.8 % NaCl and a pH of 8.2. The analysis, carried out by a reciprocating tribometer equipped with a two/three-electrode potentiostat, was performed for different loads and frequency values, and their correlation with synergistic effects was investigated. The open-circuit potential, friction coefficient, tribocorrosive current and total wear were evaluated for different tribological conditions. It was found that the force and sliding velocity had a significant position in the synergistic response, passing from positive to negative mainly due to the protective action of oxide layer and lubrication behavior of corrosion products formed during the motion. Moreover, the current was modeled via two analytical laws discussed in literature, providing a good agreement with experimental data. Lastly, was provided the oxide thickness evolution formed on the samples surface and its relationship with total wear.

Achieving excellent mechanical and robust lubrication behavior in the CoCrNi medium-entropy alloy via in-situ graphite

The unsatisfactory wear resistance and lubrication performance of CoCrNi multi-principal elements alloys (MPEAs) have emerged as critical challenges, impeding their extensive utilization as advanced engineering materials, despite their desirable mechanical and physical properties. Incorporating graphite to obtain MPEAs-based self-lubricating composites is believed to improve the wear resistance. However, it is challenging to prepare composites with high strength, large plasticity, and excellent anti-friction performance simultaneously. The present study reports the fabrication of novel CoCrNi MPEA-based self-lubricating composites, consisting of in-situ graphite and high-hardness silicides/carbides as reinforcement, prepared by powder metallurgy and reactive sintering. The 20.6 vol% Gr@CoCrNi–SiC composite exhibits an optimal trade-off between strength and ductility, along with anti-friction and wear resistance which is superior to the reported composites with different solid lubricants. The wear mechanism is attributed to the coordinated deformation mechanism between the CoCrNi FCC matrix and silicides/carbides, and the stabile lubrication effect supported by the structural transformation from the original polycrystalline lattice structure to core-shell nanocomposite structure (similar to diamond-like carbon) of the in-situ graphite. This simple, economical and practical strategy contributes to the development of MPEA self-lubricating composites with excellent comprehensive properties.