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The main idea of this study was to utilize the pressure and heat produced in the friction process to make Mo nanoparticles mixed in lubrication oil into the multi-layered tribo-film. An in-house developed reciprocating wear rig was used for the tribo-film deposition and associated tribological tests. By design of experiment, the optimal deposition parameter was obtained. Results indicate that the multi-layered film consists of a Mo-based concrete structure layer and a carbon-based film. The carbon-based film was produced by the dehydrogenation and carbonization of the lubricating oil catalyzed with Mo nanoparticles. The consumption and deposition of the carbon-based film was dynamically balanced during the wear process, resulting in the outstanding tribological performance. [Display omitted] • A great amount of Mo nanoparticles were ultrasonically mixed in the base oil. • Film fabricated by utilizing the heat and pressure produced in friction process. • The film consists of Mo-based film mixed with amorphous carbide. • Realize carbon film formation and restoration in lubrication. [ABSTRACT FROM AUTHOR]

Protecting bearings from electrical environments is crucial as modern industry evolves. With increasing exposure to electrical conditions, the risk of bearing failure due to electric erosion becomes a significant concern. To better understand how lubrication interacts with electric discharge in rolling bearings, an optical ball-on-disc tribometer was modified to measure film thickness under elastohydrodynamic lubrication (EHL) with electric discharge. The results of the study revealed that an electrical potential difference between the surfaces separated by the lubrication film leads to a reduction in film thickness, which can be attributed to the generation of Joule heating. As the electrical potential difference increases, the film thickness decreases even further, ultimately resulting in destructive electric discharge. Interestingly, sporadic discharge was observed in the region of minimum film thickness as the entrainment velocities increased prior to the occurrence of destructive discharge. In addition, the study also investigated the use of grease with a conductive additive, a double trifluoro-sulfonate ionic liquid. It was found that incorporating this ionic liquid into the grease can decrease the energy during discharge, thereby mitigating bearing electric erosion. [Display omitted] • An optical ball-on-disc tribometer was revised to measure film thickness under an applied electric field. • The electric potential difference across oil film reduced film thickness, lessened friction due to Joule heating by current. • Two forms of electric discharge were identified in the contact area: sporadic discharge and destructive discharge. • With double trifluoro-sulfonate ionic liquid added as the additive it was shown that the electric discharge becomes weak. [ABSTRACT FROM AUTHOR]

This study explores the influence of fluid viscoelasticity in soft lubrication, in which elastohydrodynamic lubrication (EHL) plays an important role. Our findings reveal that introducing polymers can significantly reduce the friction coefficient, particularly for high Deborah numbers, i.e., the ratio between the polymer relaxation time and the flow residence time, due mainly to an increased minimum film height. This augmented film thickness reduces the Newtonian pressure contributions, lowering friction. The study highlights the non-linear relationship between Deborah numbers, load, and viscoelasticity effects, as well as the complex interplay between these factors in the Pipkin space analysis. These insights provide a comprehensive understanding of the fluid viscoelasticity in soft lubricated contacts. [ABSTRACT FROM AUTHOR]

Genetic algorithms and machine learning methods can accurately anticipate hybrid nanofluids' complicated rheology. Scientists and engineers can understand hybrid materials by using genetic algorithms to optimize and machine learning to discover complicated relationships between input variables and rheological responses. As a continuation of the author's previous research on the rheological properties of a nano-lubricant based on engine oil and hybrid nanoparticles, this study uses machine learning and genetic algorithms to theoretically assess the dynamic viscosity of the MWCNT-MgO/oil SAE 50 hybrid nanofluid and identify optimal properties. MLR, D-Tree, Ridge, PLR, SVM, Lasso, ECR, GPR, and MPR are used for regression analysis. Best multi-objective issue solutions are represented by the Pareto front. The NSGA-II algorithm determines the Pareto front. The MPR and NSGA-II algorithms provide a Pareto front with the most precise optimal spot boundaries. The Weighted Sum Method (WSM) simplifies multi-objective problems into single-objective problems, making optimal solutions easier to find. The results show that the maximum margin of deviation for μ nf and τ is − 2.5615 and − 5.239, respectively. According to the Taylor chart, the best μ nf mode for R, RMSE and STD is equal to 0.9983, 7.6639, 130.0056. Also, these values for τ are equal to 0.9996, 15.4515, and 516.0219. • Rheological behavior of the MWCNT-MgO/SAE 50 hybrid nanofluid was studied. • use of meta-heuristic algorithm NSGA-Ⅱ to find the most optimal point that satisfies μ nf and τ. • Optimal solution is represented by a set of points known as the Pareto front. • The best algorithm in terms of the Taylor diagram for μ nf output is the MPR algorithm, and the worst is the Lasso algorithm. [ABSTRACT FROM AUTHOR]

Hybrid journal bearings are crucial components in many equipment, such as nuclear reactor cooling pumps and hydraulic motors. However, there exists a significant challenge to understand the lubrication behaviors of hybrid bearings with multiple thermal effects at low-speed, heavy-load conditions. Therefore, a composite thermal lubrication model is proposed, which includes four thermal effects: edge suction heat, hydrostatic pressure loss heat, oil viscous friction heat, and asperity friction heat. The lubrication and contact model are modified by actual rough surfaces to evaluate friction heat accurately. The experiments from a homemade testing rig verify the model well. Friction and temperature characteristics of the hybrid bearing are obtained, and the influence of hydraulic pressure and speed on four types of heat are analyzed. • The composite thermal oil film lubrication model is proposed to predict the overall performance of hybrid journal bearings. • The model contains edge suction heat, hydrostatic pressure loss heat, oil viscous friction heat, and asperity friction heat. • The flow factors and contact coefficients from the actual rough surfaces are used to correct the lubrication and contact model. • The four types of heat play a role in specific conditions and correspondingly cannot be ignored. [ABSTRACT FROM AUTHOR]

Laser surface texturing is an effective method to enhance gear lubrication by improving lipophilic properties, thereby increasing transmission performance and longevity. This study investigated the effects of laser parameters on lipophilicity using a grid texture and found that a scanning speed of 100 mm/s maximized diffusion and climbing. The textured specimens showed higher wetting hysteresis and adsorption, forming a thicker oil film for better lubrication. Wear tests indicated that the textured specimen had reduced friction, wear quality, and depth by 49.2% and 66.34% compared to unprocessed specimens. Gear efficiency is effectively increased, and gear oil temperature is significantly reduced. This research offers insights into lipophilic characterization and gear lubrication enhancement, potentially decreasing surface failures like pitting, adhesion, and wear. • A method for characterizing the lipophilicity of material surfaces is proposed. • Maximum wettability and adsorption force increased by 49.2% and 66.34% over US. • Minimum wear quality and depth decreased by 29.65% and 45.33% compared to US. • Textured gears increase efficiency > 3.67%, reduce oil temp > 7.45% vs. untextured. [ABSTRACT FROM AUTHOR]

Surface micro-texturing involves creating microscopic pits or textures, serving as lubricant reservoirs to enhance lubrication distribution, potentially reducing friction and wear. This study specifically delves into the influence of varied depth patterns of pits on the operational performance of textured rolling bearings under severe lubrication conditions. Five distinct patterns with a fixed pit diameter (250 µm) and different depth variations (concave, decreasing, increasing, convex, and horizontal) were introduced on the shaft rings of cylindrical roller thrust bearings using the laser marking method. Wear tests were conducted under starved lubrication condition. Wear loss and signal analysis highlight the profound effect of depth variations, whereby bearings with shallow pits near the outer side of their working surfaces exhibit longer lubrication times, improved tribological performance, and enhanced vibration characteristics. Notably, the convex pattern stands out for providing comprehensive and favorable tribological and vibration properties. This research contributes valuable insights for the optimal design of micro-textures for rolling bearings, paving the way for enhanced efficiency and reliability in mechanical systems. [ABSTRACT FROM AUTHOR]

The lubricated non-conformal contact generally works under the mixed-EHL regime. Optimizing the surface topography or selecting the right coating is an effective way to improve its performance. This paper presented an improved mixed-TEHL model for the lubricated non-conformal contacts with the effects of roughness and coating in consideration. The effect of coating was solved analytically by employing the Papkovich–Neuber potentials. It was found that the properties of coatings, especially their elastic modulus, significantly affect the pressure and stress distribution. In comparison to other roughness parameters, standard deviation and kurtosis have a significant impact. As expected, the present model can provide an efficient analysis of the tribological behavior and the stress distribution of the lubricated non-conformal contacts. [ABSTRACT FROM AUTHOR]

A sulfur-containing carbon nanosphere (SCN) with the corrosion inhibitor M16 (M16 @SCN) was successfully prepared through post-carbonization and then electrostatic adsorption. The as-prepared SCN have rich pore and high specific surface area of 578.9 m2g−1 due to high-temperature carbonization of polythiophene (PT), which as a nanocontainer could upload corrosion inhibitor M16 to obtain M16 @SCN. The M16 @SCN exhibits anti-corrosion performance via controlled release of M16 and improved tribological performance, with friction coefficient of 0.1, extreme pressure of 850 N, and reduction in wear volume of 88.6%. The M16 adsorbed on the nanosphere improves the dispersion of SCN in the lubricating oil, and the SCN acts as a nanocontainer to ensure the performance of M16 under harsh conditions. The good tribological properties are attributed to the synergistic effect between SCN and M16 in the friction process, resulting in a rigid protective oil film was produced on friction pair via tribochemical reactions and physical adsorption. [Display omitted] • Sulfur-containing carbon nanosphere with corrosion inhibitor (M16 @SCN) was prepared by electrostatic adsorption. • The as-prepared M16 @SCNs exhibit excellent tribological performance when used as oil additive. • The superior lubrication performance was attributed the oil film formed by the synergistic interaction during friction. [ABSTRACT FROM AUTHOR]

A fully coupled FE model for mixed EHL of finite line contacts is proposed, integrating all of the governing equations into a monolithic system. The solution reveals the fully coupled model achieves 5% higher accuracy and 50% greater efficiency compared to the weakly coupled one. Additionally, there is evidence to support the assertion that profiling contributes to the mitigation of surface roughness contact. Logarithmic profiling can increase the minimum film thickness by a factor of 30, resulting in a reduction of up to 64.6% in the maximum asperity contact pressure, and thus, the boundary friction force is decreased by more than 19%, under heavy-load low-velocity condition. This contributes to the reduction of abrasive wear. • A fully coupled FE model for the mixed EHL analysis of finite line contacts is developed. • Lubrication of mixed EHL film with straight, dub-off, and log profiles under different loads and velocities is analysed. • Influences of profiling on asperity contact and friction force are discussed and revealed. • A logarithmic profile has the potential to enhance the boundary lubrication condition at the free-end. [ABSTRACT FROM AUTHOR]

The journal-thrust coupled bearing (abbreviated as JTC bearing) works at the end of the crankshaft in diesel engine, with the function of carrying radial load and prevent axial movement of the crankshaft. The journal part and the thrust part of this special bearing both form the oil film lubrication when subjected to the time-varying loads in axial and radial directions during the working condition. In this work, the JTC bearing in marine diesel engines was analyzed using a transient thermal elastohydrodynamic (TEHD) lubrication model. The thermal and pressure (thermal-pressure) coupled effects were taken into consideration based on the flow, pressure, and thermal continuity conditions between the journal and thrust parts. Moreover, the transient time-varying load was considered in the lubrication analysis to explore the coupled effect under the actual operating conditions. A test rig was built to validate the established transient TEHD lubrication model for the JTC bearing. The thermal-pressure coupled effect between the journal and thrust parts was found to significantly affect the transient lubrication behaviors of the JTC bearing, which cannot be ignored. Also, different boundary conditions were investigated for the influence of the coupled effect on transient lubrication characteristics, including axial clearances, radial clearances, waveforms of radial load, incline angles and inlet oil temperatures. This work could theoretically support the lubrication design of the JTC bearings used in the diesel engine crankshafts. [ABSTRACT FROM AUTHOR]

Based on the material property exhibiting a sublinear dependence of friction on load, a new mechanism of texturing for friction reduction has been identified and explored. In this, the nominal contact area is reduced by textures, the load of the non-concave area thus increases, and the friction coefficient is reduced by the sublinear dependence. Non-textured and textured samples were tested by a reciprocating tribometer to obtain the friction coefficient between polytetrafluoroethylene (PTFE) and steel. An empirical equation for the sublinear dependence was found, and used in a numerical mixed lubrication model to evaluate the mechanism. The results show that this mechanism explains well for the friction reduction of textured surface in dry conditions, and is still beneficial under mixed lubrication. • A new mechanism of texturing for friction reduction is identified, and explored under dry/mixed lubrication conditions. • In this, texturing is used to artificially control the contact pressure distribution, and achieve a lower friction. • This mechanism explains well for the friction reduction of textured surface in dry conditions. • A numerical model is established to evaluate the friction reduction from this mechanism under mixed lubrication. • This mechanism may supplement the hydrodynamic theory to design the texturing appliable in multi lubrication conditions. [ABSTRACT FROM AUTHOR]

In the framework of stochastic representation of surface roughness, a novel Reynolds-type Equation has been derived recently by the authors and utilized to calculate the average values of a bearing's operational parameters. To acquire an improved insight to the hydrodynamic lubrication phenomena in rough bearings, the stochasticity of the operational parameters should be described, by calculating their higher-order moments, such as the variation. The present work aims at deriving equations for calculation and quantification of these higher-order moments. More specifically, in the present paper equations for the variation of a slider bearing operational parameters (pressure, load carrying capacity, friction force and friction coefficient) are derived. The obtained results are validated against the deterministic Reynolds Equation solution, for a series of bearings with different random Gaussian surface roughness profiles, over a wide range of bearing design and operational parameters. • Stochastic implementation of the surface roughness profiles as Gaussian variables. • Hydrodynamically lubricated bearings with surface roughness on the bearing and slider. • Utilization of Stein's Lemma, novel stochastic calculus theorem of probability theory. • Mathematical derivation of novel equations for calculating the variance of critical bearing's operational parameters. • Validation of acquired equations via numerical simulations and with existing results found in literature. [ABSTRACT FROM AUTHOR]

This study addresses the oil starvation problem in roller bearing line contacts and proposes a novel Chevron-shaped wetting/oleophilic pattern on the bearing track to enhance oil replenishment. Validation through optical cylinder-on-disc lubrication film tests reveals the impact of the pattern on inlet oil supply and film thickness. Notably, a Chevron pattern oriented opposite to disc movement significantly increases film thickness. Wetting is more pronounced in oleophilic areas (Chevron pattern), forming an inverted V-shaped "virtual wall" that directs lubricant backflow toward the center and reduces side leakage. A pattern length equal to the bearing track width was found to be more effective compared to smaller sizes, as the oil side ridges are located on the oleophobic and oleophilic boundaries, which capitalizes the wettability step effect more effectively. This research provides a basis for designing oleophobic surfaces with improved anti-wear and anti-friction properties. [Display omitted] • Chevron wetting patterns guide oil to the central inlet, enhancing oil film thickness under LLS. • With backward movement, the wetting patterns create a "virtual wall" that suppresses reverse flow and side leakage of oil. • Chevron pattern length directly influences lubrication efficiency, optimal when track width equals pattern length. [ABSTRACT FROM AUTHOR]

A deterministic mixed lubrication model for parallel surfaces is proposed. The oil film force is solved by the Reynolds equation with a mass-conserving cavitation model. The contact force is predicted by using a neural network trained on a database, which was built by conducting finite element analysis on a single asperity. In addition, an extended Archard equation is introduced to predict the transient running-in wear. The contact model is proved to be suitable for Gaussian and non-Gaussian surfaces. The Stribeck curves calculated under the different wear coefficients and wear steps are compared with the experimental results. The influence of initial surface topography on the running-in behavior has also been studied. The contact database for GCr15 is provided. [ABSTRACT FROM AUTHOR]

Gallium-based liquid metal (GLM) has excellent extreme-pressure properties, but at low sliding speeds, it is typically in a boundary or mixed lubrication, causing poorer properties compared to traditional lubricants. In this paper, GLM/P composite lubricants composed of GLM particles and polydimethylsiloxane are prepared. Under a maximum-Hertz-stress of 0.69 GPa, GLM/P2–30% (viscosity of 1260 mPa∙s) can enter the elastohydrodynamic lubrication (EHL) regime at 0.2 m/s, has good EHL properties (friction coefficient of 0.06, wear rate in the order of 10−9 mm3/N·m). Meanwhile, it has high extreme-pressure properties (P B of 2300 N). The EHL film is formed mainly by polydimethylsiloxane, while GLM particles increase the thermal conductivity of lubricant and can be adsorbed on the frictional interfaces, thereby improving the EHL properties. [Display omitted] • GLM/P composite lubricant can enter the elastohydrodynamic lubrication regime under conventional load and low sliding speed. • Lubrication regimes and transition laws of GLM/P are determined by combining Stribeck curve with lubrication film thickness. • The lubrication mechanisms of GLM/P in elastohydrodynamic lubrication regime are revealed in detail. [ABSTRACT FROM AUTHOR]

While a rolling element bearing is operating, the lubricating film is desired to maintain a sufficient thickness to avoid asperity contact between surfaces. When using grease as lubricant, the film thickness undergoes evolution over time, due to the transient formation of the deposited thickener-rich layer and a bled oil film. Therefore, a model, which can address both type of film formation, is required. In this contribution, an experimentally validated numerical model is proposed by assuming the grease as a porous medium. This model can calculate the transient formation of thickener-rich layer and the oil bleeding process for grease-lubricated contacts. The predicted film thickness evolution, by superposing the thickener-rich layer and oil film, shows a reasonable agreement with the experimental result. • First transient grease film formation model based on the two-component hypothesis. • A new model for the formation of thickener-rich layer. • A new model for the grease bleeding. • Good agreement between measurements and simulations. [ABSTRACT FROM AUTHOR]

This paper investigates the squeeze film behavior of a rigid indenter punch with parabolodial surface profile which interacts with a thin, soft, linearly elastic layer through a thin lubricant film. The layer has infinite radial extent and is either bonded or unbonded to a rigid foundation. Slow and fast squeeze film regimes of lubrication are defined and delineated based on the dry contact radius of a spherical indenter and the radial extent of the lubricant film. Favorable agreement with relevant experimental studies supports the formulation method and regime classification. • New insights on elastohydrodynamic squeeze films with soft materials. • Novel results for a lubricated indenter punch onto unbonded and bonded elastic layers. • Novel classification of slow and fast squeeze regimes of lubrication. • Good agreement of numerical results with available experimental evidence. • Results may be useful for footwear design and biological tissue lubrication. [ABSTRACT FROM AUTHOR]

The superior tribological properties of bearings with low friction appear to be actualized by not a single lubrication, but the adaptive multi-mode co-lubrication in which the interface can adjust according to the friction conditions. This study attempts to reveal the friction adaptive mechanism of textures under grease lubrication. The single-stage linear groove surfaces (SLGSs) and the multi-stage bionic texture surfaces (MBTSs) were respectively designed, and MXenes lithium composite grease (MLCG) with MXenes as an additive was prepared. Compared with the non-textured surface, the friction coefficient of MBTS-1.5 is reduced by 67.6%, and the wear rate is reduced by 45.4%. The friction contact area presents an adaptive multi-mode lubrication trend from oil to grease-solid synergistic lubrication. [Display omitted] • MBTSs can help to improve the flow characteristics of grease. • MXenes and thickener could achieve the synergistic self-repairing effect. • MXenes can form a beneficial friction layer at the friction interface. • Multi-mode lubrication system has excellent adaptability and reliability. [ABSTRACT FROM AUTHOR]

This manuscript developed a novel DLC–supramolecular gel (HTG) composite lubrication system to achieve long-life outstanding lubrication under extreme contact stress while avoiding sealing challenges relying on the unique thixotropic properties of the gel. DLC–HTG exhibited ultra-low wear and excellent friction reduction performance under a maximum contact stress of 2.24 GPa. DLC films with designed double transition layers possess high interfacial bond strength and mechanical properties, providing the basis for high wear resistance. The establishment of a robust tribofilm and the confinment effect of HTG on wear debris dominate the achievement of ultra-low wear. This ultra-low wear sliding extends the service life of the lubrication system with the broad implications for mechanical engineering, transportation, and wind power generation. [Display omitted] [ABSTRACT FROM AUTHOR]

The lubrication characteristics of planetary roller screw mechanism (PRSM) with eccentric errors are investigated in this work. And the formulas of entrainment velocities with eccentric errors are derived. The film thickness and pressure distributions of screw-roller (SR) and nut-roller (NR) thread pairs are analyzed. It finds that the film thickness of SR thread pair is larger than that of NR thread pair. Moreover, the effects of eccentric errors on comprehensive meshing radius, entrainment velocities and lubrication characteristics of SR and NR thread pairs are discussed. The results show that the eccentric errors have significant effects on lubrication characteristics of PRSM. • The EHL characteristics in contact regions are investigated with eccentric errors. • The formulas of entrainment velocities and entrainment angles with eccentric errors are derived. • The film thickness in screw-roller contact region is larger than that in nut-roller contact region. • The eccentric errors of screw and nut have the superposition effects on the film thickness and film pressure in contact regions. [ABSTRACT FROM AUTHOR]

The present work investigates the performance of TiAlSiVN coating with 5 and 11 at% of V concentration deposited on the Al 2 O 3 /SiC cutting tools during dry turning of austenitic 316 L stainless steel. The maximum flank wear reduction compared to the uncoated tool for coated tools with 11% and 5% V concentration was 85% and 67%, respectively. The Raman analysis indicated the formation of V 2 O 5 in the cutting zone, which helps to reduce friction and machining forces for the coated tools. Overall, the presence of higher V content (11 at%) enhances the self-lubrication behaviour of the TiAlSiVN coating, accounting to lower fluctuations in cutting forces, superior surface finish, and lower flank wear when compared to the TiAlSiV5N coated and uncoated cutting tools. [ABSTRACT FROM AUTHOR]

Understanding the relevance and significance of the various replenishment mechanisms in grease-lubricated bearings is very important in choosing the appropriate lubrication strategy. This study shows that the lubricant film thickness in the ball-ring contacts of a deep groove ball bearing may increase by 10%–25% due to vibrations. The possible mechanisms behind this film thickness increase are discussed. Of the proposed contact replenishment mechanisms, the micro-lateral motion of the contact edge across the tracks caused by in-operation vibrations appears crucial. Results show that in the starved contacts, vibration plays a vital role in determining the film thickness. • Film thickness in grease-lubricated DGBB increases due to vibrations. • A model to predict the vibrations-induced film thickness increase is proposed. • Film replenishment appears to be due to a reciprocating curvilinear displacement. • Vibrations-induced film thickness increase depends on the contact size. [ABSTRACT FROM AUTHOR]

The lubrication alignment behaviors of 4-Cyano-4′-pentylbiphenyl (5CB) liquid crystal were investigated. A 60 s-long running-in pre-treatment was first performed using micro-sized diamonds. The ball was then deflected by a certain direction and an alignment agent (Sebacic Acid) was applied on the disc. Results show that the coefficients of friction for GCr15 and Si 3 N 4 self-matching pairs were reduced to 0.036 and 0.017 respectively, 45.5 % and 67.3 % lower than the ones lubricated directly with 5CB. The surface morphology after running-in-deflection was smoother and flatter, with enhanced surface texture characteristics. It is believed that increased the order parameter of 5CB, induced by the synergistic effect of the alignment agent and running-in-deflection, is the reasons for the improvement in lubricating performance. [Display omitted] • The alignment agent and running-in-deflection reduce the COF of 5CB notably. • The reduction of COF is attributed to the liquid crystal molecular orientation. • An appropriate running-in-deflection is beneficial to reduce the COF of 5CB. • The relationship between surface parameters and characteristics has been analyzed. [ABSTRACT FROM AUTHOR]

Herein, the internal lubrication of polyether ether ketone (PEEK) with added whiskered carbon nanotubes (Wh-CNTs) was investigated under point-contact dry sliding conditions with various loads and velocities. The wear rate of the composite was reduced by 86.99% at a maximum Hertzian contact pressure of 344.69 MPa, which was attributed to the addition of additives with excellent mechanical properties and high-temperature stability. Wh-CNTs could be uniformly distributed in the PEEK to form a three-dimensional (3D) network structure with load-bearing capacity, thus the load could be effectively borne to prevent crack propagation on the PEEK surface. Besides, the filler was induced to form a micron-sized 3D spherical structure with a ball bearing effect, which promotes lubrication more effectively than the fragment structure. [ABSTRACT FROM AUTHOR]

Most mechanical systems have mating interfaces that require effective lubrication for smooth functioning. Thus, understanding and accurately modeling lubrication regimes is an essential research task. The present work proposes a set of normalized coefficients based on homogenization and stochastic theories to model the partial and full-film lubrication regimes between a smooth and a rough surface. The modified Greenwood and Williamson theory, considering inter-asperity-interactions, was used to model the contact-zones. Subsequently, the film-thickness was evaluated and the homogenized Reynolds equations were solved to compute the normalized coefficients. The estimated coefficients were compared with Patir and Cheng's flow-factors, and the similarities and disagreements between both approaches were discussed. New sets of coefficients for running-in surfaces were proposed for modeling their lubrication regimes. • Normalized homogenization coefficients are evaluated based on stochastic analysis. • Inter-asperity interactions have been considered to model the solid contacts. • New sets of homogenization coefficients for running-in surfaces are proposed. [ABSTRACT FROM AUTHOR]

Herein, the functionalized N-doped carbon nanosheet (N@PCNs) was successfully achieved through pyrolysis of metal−organic framework (MOF) and then surface modification with anti-wear agent. Firstly, the N@PCNs was obtained via carbonization of copper pyridine coordination polymer-based MOFs. Then tannic acid (TA) cross-linked by polyethylenimine (PEI) via Michael addition was grafted on the N@PCNs surfaces. Finally, the anti-wear agent 2,5-dimercaptothiadiazole dimer (DTD) was grafted onto N@PCNs via Michael addition reaction with TA to obtain DTD-N@PCNs. The average COF of 500SN decreases to 0.110 from 0.195, accompanied by 69.3% reduction in wear volume with 1.00 wt% DTD-N@PCNs addition. The lubrication performance is ascribed to the formation of a stable protective film through DTD-N@PCNs facilitating tribochemical reactions, preventing direct contact of the ball-disc pairs. [Display omitted] • The functionalized N@PCNs was prepared through pyrolysis of copper-based MOFs and then surface modification with DTD. • The resultant DTD-N@PCNs exhibits improved anti-wear and friction reducing properties when used as a lubricant additive. • The lubrication performance was attributed to the polishing effect and mending effect of DTD-NN@PCNs, along with formation of a protective film. [ABSTRACT FROM AUTHOR]

Lubrication plays an important role in mouthfeel sensation and various tribometers have been developed for in vitro studies. This study introduces a new design to solve artefact of the surface load for a soft tribometer. Reliability of the probe was verified using glycerol as lubricant. Effects of surface load and substrate roughness on the lubrication behaviour were investigated using glass and PDMS probes. It was found that increased surface load lowered friction coefficients in both boundary and mixed lubrication, probably due to the deformation of surface asperity. Increased surface roughness decreased friction coefficient in boundary regime, but rendered a later transition from boundary to mixed lubrication. Hydrophilic contact lowered the friction in boundary and mixed lubrication by promoting full-film lubrication. • A soft tribometer with new probe design has been developed. • The new probe design eliminates surface load artefact in the original design • The new design successfully tested for its reliability with near Newtonian lubricants. • Reliability also tested for both hydrophilic and hydrophobic substrates. [ABSTRACT FROM AUTHOR]

Thrust bearing finds application as a key element for heavy duty machines such as hydro-power plants (vertical shaft), submarines, steam engines, cement plant-ball mills (horizontal shaft) etc. Bearing temperature is a primary factor that affects the performance of hydrodynamic thrust bearings. Thermal deformation, misalignment, reduction in minimum oil film thickness and subsequent drop in load carrying capacity, are some of the manifestations related to high bearing temperatures. The present study attempts to decrease the bearing temperature by utilizing novel hybrid bearing set up. It involves the integration of water-cooled pads coupled with nanoparticle-infused lubricant films. This approach represents a convergence of two key technologies aimed at addressing the thermal effects linked with elevated temperatures generated during the operation of bearings. This study utilizes computational simulations to evaluate the effect of integrated thrust pad design on performance characteristics like pressure, temperature, and thermal deformation of a thrust bearing. The simulation results of new integrated design confirm (i) enhancement in pressure values e.g. maximum pressure increases from 5.6 MPa to 6.5 MPa (ii) reduction of pad temperature values e.g. maximum pad temperature value reduces from 85 ℃ to 70 ℃ (iii) reduction of pad thermal deformation values e.g. maximum pad thermal deformation value reduces from 36.5 µm to 22.3 µm. By leveraging the direct cooling effect of embedded cooling circuitry and the enhanced thermophysical properties of nanoparticles, this novel configuration promises to unlock new levels of efficiency and reliability in thrust bearing operation. [ABSTRACT FROM AUTHOR]

Estimating the film thickness in a grease lubricated bearing in the post-churning phase is complex because of the prevalent starved lubrication conditions. In our earlier work, we showed that the relative film thickness ( h g / h f f ) in an axially loaded 6209 deep groove ball bearing (DGBB) depends on the product of viscosity, load and linear speed (η b u). In this article, we present the results of experiments performed using bearings of different sizes – 6204, 6206, 6209 – and show that the relative film thickness maintains a power-law relationship with η b u , independent of the bearing size. • Level of starvation in grease-lubricated DGBBs correlate well with η b u. • The η b u concept is independent of bearing size. • Lubricant replenishment is a local phenomenon. • Starvation reduces film thickness dependency on speed. • Starvation increases film thickness dependency on load. [ABSTRACT FROM AUTHOR]

A radial shaft seal (RSS) model is established to reveal mixed thermal lubrication (MTL) and wear performance at speeds ranging from 3000 r/min to 7000 r/min. The model takes into account the initial temperatures of the oil medium and the running time of the RSS to investigate the transition limit of lubrication. Then a thermal fluid-solid method was developed to simulate the lubrication performance of RSS, which shows lubrication transition boundaries through rough micro convex bodies for wear deformation. The RSS deforms wedge-shaped during the wear process and a localized fluid pressure is created on the convex bodies. Considering the wear deformation of the convex bodies due to the wedge effect, the micro performance of the RSS can fully describe the mechanism of the leakage rate. As the dynamic pressure decreases and the leakage rate increases with the temperature of the medium, the RSS lubrication gradually transitions from MTL to EHL. Thus, the initial medium temperature should be considered to maintain the RSS under the mixed lubrication regime with low friction. [ABSTRACT FROM AUTHOR]

A method for calculating time-varying mesh stiffness (TVMS) is proposed by developing a stiffness model for elastohydrodynamic lubrication (EHL) contact and integrating it into three-dimensional loaded tooth contact analysis (3D-LTCA). To enhance the accuracy and efficiency of the calculation, three projects have been implemented: Firstly, the contact deformation is modified, and the average slope is employed for calculating contact stiffness. Secondly, the lubricant film and EHL contact deformation are introduced into the deformation compatibility equations. Finally, the polynomial chaos expansion (PCE) surrogate model is employed to enhance computational efficiency. The proposed method is used to calculate TVMS of the planetary gear set, and the influence of speed, torque, and rough surface are analyzed. The results show that the previous method underestimating the TVMS of planet-ring gear pair in double-teeth meshing area under fluid lubrication, while the proposed method effectively addresses the issue. The different effects of the torque and speed on TVMS under mixed and fluid lubrication also have been revealed, emphasizing the significance of surface topography in gear meshing characteristics. [ABSTRACT FROM AUTHOR]

An analytical EHL model suitable for highly loaded point contacts operating in mixed and boundary regimes of lubrication is presented. The results are compared and validated with the experimental measurements of friction coefficient from an MTM tribometer. Measurements are carried out upon a PAO40 oil at medium to high temperatures. In general, a good agreement in trend and magnitude over a wide range of operating conditions is observed. Both the experimental findings and the model predictions show an inverse relationship between friction and contact load in mixed and boundary regimes of lubrication, an effect not hitherto reported in literature. [ABSTRACT FROM AUTHOR]

Accurately predicting the performance of lubricated rolling elements is critical for certain key bearing applications. A widely employed simulation technique is quasi-static models, which although computationally efficient to implement, lack accuracy in predicting the kinematics of bearing components. This problem arises from their construction under kinematic assumptions, instead of solving the kinematic based on real frictional interactions. This paper presents a quasi-static model based on the minimum energy hypothesis for lubricated contacts, which determines the kinematic of the ball considering the effects of the frictional interactions governed by the elastohydrodynamic lubrication mechanism. The influence of kinematic variables on the sliding patterns and power loss distribution of the contact are analysed. The results are compared with other published quasi-static models, revealing substantial differences. The influence of the kinematic hypotheses on power losses are also studied at a bearing component scale. Finally, the effect of the governing lubrication mechanism of the contact is discussed, concluding that the limiting shear stress of the lubricant and the centrifugal forces have a significant effect on the kinematic of the ball. • Development of a semi-analytical quasi-static model of ball-raceway contacts based on the minimum energy hypothesis. • Analysis of the influence of the pitch angle and pure rolling line locations on the contact kinematics and power losses. • Analysis of the impact of the working conditions on the pitch angle and comparison to literature models. • Study of the governing lubrication mechanism on kinematic and power loss behaviour. • Theoretical demonstration of the transition between inner and outer control raceway hypothesis. [ABSTRACT FROM AUTHOR]

Misalignment of roller bearings is a characteristic defect mode, which is accompanied by variations in thermal, mechanical, and lubrication performances. Regarding this aspect, a novel model considering the thermal-fluid-solid coupled effect is proposed to evaluate the performance evolution of lubricated cylindrical roller bearings (CRB) under misalignment states. The proposed model regards structural parameters, contact characteristics, and lubrication status as time-varying variables. By integrating the quasi-static model of CRB with a thermal network model, the influence of internal contact shape and stress on the thermal characteristics of misaligned bearings is reasonably considered. The accuracy of the proposed model is validated through the thermal performance experimental platform. In addition, the influence of thermal and misalignment on time-varying mechanical properties such as contact load, radial stiffness, and clearance loss is assessed. Eventually, the deterioration of the lubrication performance over operational time is quantitatively characterized by the time-varying film thickness at the load region. [Display omitted] • A novel model of misaligned bearings with the thermal-fluid-solid coupled effect is developed. • A transient thermal contact resistance evaluation method for spindle shape is presented. • The influence of thermal and misalignment on time-varying mechanical properties is investigated. • The degradation level of the lubricant is characterized through the time-varying film thickness. [ABSTRACT FROM AUTHOR]

Traditional methods of evaluating the performance of journal bearings, for example thermal-elastic-hydrodynamic- lubrication theory, are limited to simplified conditions that often fail to accurately model real-world components. Numerical models that include additional phenomena such as cavitation and fully coupled effects like deformation, temperature, pressure and viscosity can be more accurate but require a large amount of computational overhead, making analysis slower and more costly. To address this limitation, a novel machine learning-driven approach is developed to predict the 2D distribution of surface deformation, film thickness, temperature, and pressure across the bearing surface as a function of design variables such as load and speed. The training dataset, generated using a fully coupled Reynolds' Equation solver implemented in OpenFOAM, contains a significantly extended range of conditions than in previous studies with approximately 39 000 000 points encompassing 4925 different test cases. Modelled bearing speeds range from 2000 to 10 000 rpm, while load values are varied between 1 and 30 kN. Predicting surface deformation, film thickness, temperature and pressure across the bearing surface results in a mean absolute percentage error below 0.4 % or better. The work also demonstrates that the trained models have a strong ability to generalise the prediction beyond the original training data range with only a 1 % error at up to 200 % of the highest trained speed. This work also demonstrates that machine learning-based processes are a practical alternative to physics-based numerical modelling, especially in cases where rapid performance evaluation is desired as real-time calculation is possible with significantly reduced computational cost. This has the potential to enable development of rapid design optimisation tools and real-time performance monitoring at high resolution and with low latency. Using consumer hardware, it is found that the neural network-based approach is faster than the existing numerical modelling technique by a factor of over 10 000, enabling real-time predictions of lubrication systems. • A neural network approach is demonstrated, using independent models to predict each variable. • Neural network models trained using an OpenFOAM numerical model display a mean error of < 0.4%. • Once trained, the neural network models are ∼ 10 000 x faster than traditional numerical models. [ABSTRACT FROM AUTHOR]

The increasing application of diamond-like carbon (DLC) coatings in engine mechanical parts requires the investigation on interaction mechanism between DLC and fully formulated engine oil. This study shows that the friction can be controlled by monitoring the load for a steel/DLC contact, lubricated by a fully formulated 5W30 engine oil in boundary/mixed lubrication regime. A calcium carbonate-rich patchy tribofilm, mainly formed on steel ring, was characterized by multiple surface analyses. X-ray photoelectron spectroscopy (XPS) indicates an increase quantity of calcium carbonate (CaCO 3) with increasing contact load. Transmission Electron Microscope (TEM) showed that the original calcium carbonate in the overbased detergent additive within the lubricant itself was amorphous. However, the amorphous calcium carbonate crystallizes in vaterite (low load), aragonite (medium load) and calcite (high load) during the tribological tests. The intrinsic lubricity of each calcium carbonate polymorph was estimated by density functional theory calculations, while the tribological properties of the sliding interface composed by H-passivated diamond and CaCO 3 polymorphs were investigated by ab initio molecular dynamic simulations. The in-depth investigation presented here sheds light into the main factors leading to the unexpected pressure-induced friction reduction. [ABSTRACT FROM AUTHOR]

Various anti-wear and anti-corrosion coatings are applied on the surface of journal and bearing to maximise service life of a bearing system. These coatings influence the wettability of surfaces consequently causes velocity slip phenomena in the bearing system. This article addresses a novel investigation to examine the influences of velocity slip and PVP (Piezo-viscous-polar) lubrication on multirecessed hybrid conical journal bearing (MHCJB). For various cases of velocity slip, novel forms of Reynolds equation are derived and solved numerically by using FEM. The results reveal that velocity slip severely affects the generation of oil film pressure. Consequently, it deteriorates the bearing characteristics viz. load carrying capacity, oil flow rate and rotordynamic coefficients. Further, PVP lubricant offers substantial enhancement in bearing characteristics. • Anti-wear/anti-corrosion coatings influence the wettability of surfaces consequently causes velocity slip in the bearing system. • Novel forms of Reynolds equation for various cases of velocity slip in conical journal bearing with PVP lubrication. • Velocity slip impacts oil film pressure distribution and thereby load carrying capacity, rotordynamic coefficients. • PVP lubricant offers valuable enhancement in load carrying capacity and stability characteristics of conical bearing. [ABSTRACT FROM AUTHOR]

The aim of this work was to examine the impact of running-in with micron-sized diamonds on the lubrication performance of 4-Cyano-4′-pentylbiphenyl (5CB) liquid crystal (LC). It was observed that an appropriate running-in pretreatment resulted in a remarkable 37.9% decrease in the coefficient of friction (COF) compared to friction tests without running-in. This improvement in lubrication performance is believed to be attributed to the formation of a textured surface during the running-in process. Additionally, the study found a significant correlation between COF and various surface parameters, namely Sa, Ssk, Sku, Svk, and Spk. The wear surface exhibits characteristics such as high Sku, negative Ssk, Svk/Spk ratios, and smaller Str under the optimal running-in conditions. • An appropriate running-in with process diamonds reduces COF of 5CB LC notably. • The reduction of COF is attributed to the pretreatment of surface morphology. • The correlation between surface parameters and COF has been investigated. • The relationship between surface parameters and characteristics has been analyzed. [ABSTRACT FROM AUTHOR]

The coupled bearing (including a tilting-pad journal and a thrust bearing) is mainly used in a nuclear power circulating pump to simultaneously support the high axial loads and radial loads of a vertical rotary system with minimum power loss, low vibration, and high load capacity. Its lubrication and vibration characteristics have significant effects on the operation reliability of the nuclear power circulating pump. In this paper, an original mixed-lubrication dynamic model for the coupled bearing-rotor system is proposed to study the dynamic characteristics of the system considering the effects of the pivot clearance, asperity contact, and elastic deformation. The innovation of the proposed model is that it integrates the horizontal-rocking vibrations of the rotor and pads with the mixed lubrication of the coupled bearing and the wear of journal pads and thrust pads. The effects of different external loads and pad wear levels on the dynamic characteristics of the coupled bearing-rotor system are revealed. Additionally, a series of experiments are performed to measure the vibration responses of the system, which are directly compared to the simulated responses of the proposed model for validation purposes. It is expected that the proposed mixed-lubrication dynamic model can provide practical engineering guidance for the condition monitoring and fault identification of coupled bearing-rotor systems. [ABSTRACT FROM AUTHOR]

Insufficient load capacity and stiffness of aerostatic bearings with traditional inherent orifices is limiting their applications. Recently, the aerostatic bearing with close-spaced micro holes (ABMH) shows the potential of performance improvement. However, its lubrication mechanism is still not clear and the static characteristics have not been comprehensively investigated. This paper applies numerical method and extends the pneumatic resistance theory from single orifice bearing to ABMH to reveal its lubrication mechanism. The results indicate that ABMH reduces the gas flow towards the high-pressure region of bearing center and impedes the pressure decrement in this area, thus resulting in the higher load capacity and stiffness. Additionally, bearing load capacity has positive relationships with total mass flow rate and exhibits similar varying trends. • Lubrication mechanism of aerostatic bearings with close-spaced micro holes (ABMH) is revealed. • ABMH improves over 22% load capacity and over 32% maximum stiffness compared to aerostatic bearings with inherent orifices. • The lubrication characteristics of ABMH with different configurations are concluded. • The shunt pneumatic resistance is employed to elucidate the mechanism of pressure formation at the hole outlet of ABMH. [ABSTRACT FROM AUTHOR]

This work investigates the friction and wear reduction effects of adding functionalized graphene nanoplatelets (GNPs) to a fully formulated engine oil. Friction tests using a continuous sliding/rolling ball-on-disk tribometer showed that 0.2 wt% GNP oil reduced friction by up to 28% and 11% in the boundary and elastohydrodynamic lubrication regimes, respectively. The disk tested with GNP oil also exhibited lower wear and evidence of carbon tribofilm formation. Raman spectroscopy indicated that the mechanical stresses in the tribological tests altered the graphene morphology. Furthermore, the study evaluated the literature mechanisms for graphene-induced friction and wear reduction, and concluded that the interplay between interlaminar shearing and protective film formation mechanisms was the most plausible explanation for the obtained results. [ABSTRACT FROM AUTHOR]

The effect of surface texture on the efficiency of friction energy dissipation in a nonlinear energy sink (NES) was investigated. Analysis of variance (ANOVA) was employed to develop a quadratic regression model explicating the relationship between control factors (groove width, depth, and density) and responses (shear stress and friction coefficient) associated with rectangular groove surface texture. Response surface methodology (RSM) was utilized to optimize the control variables for increasing shear stress and friction coefficient between magnetic fluids (MFs) and groove texture. Prototype testing revealed that groove texture significantly enhanced friction energy dissipation efficiency, confirming the effectiveness of optimized texture for MF-NES. [Display omitted] • Surface wettability significantly influences MF tribological properties. • The quadratic regression model of texture parameter optimization is established. • Surface texture can effectively enhance the friction damping force of MF. • Surface texture can significantly improve the energy dissipation efficiency of MF-NES. [ABSTRACT FROM AUTHOR]

The wealth of soft contact tribological (SCT) investigations utilising ball-on-disc tribometers assume Hertzian contact model to describe substrate deformation. We hypothesise this is invalid for soft-adhesive viscoelastic discs with a finite thickness. Here, we uniquely use the wear transducer in the mini-traction machine to indirectly measure the load-dependent deformation and fluid film thickness of rigid-soft, soft-rigid, and soft-soft contacts across a range of loads, speeds and viscosities. Macroscopic deformation within these configurations and compliance of the respective tribopairs vary considerably, which is not predicted by the Hertzian model. We consider how to account for these deformation effects in SCT. [Display omitted] • MTM wear transducer measures film thickness in EHL regime for soft contacts (ball-disc). • MTM wear transducer measures substrate deformation in BL-ML regime. • Hertzian contact mechanics is invalid for viscoelastic substrates with finite thickness. • A large effective gap arises in BL-ML regime due to the deformation of VE substrates (disc). [ABSTRACT FROM AUTHOR]

Maintaining the condition of the friction pair is an important measure to reduce mechanical failure. This paper integrates a vacuum elastohydrodynamic oil film measurement device and a current amplifier to simultaneously observe the optical interference image, friction coefficient and triboelectric signal during the friction process. In a high vacuum environment, the discharge phenomenon of steel balls corresponds to the time when the friction pair wears. Changes in the friction state in high vacuum environments have a significant impact on triboelectricity. Based on the relationship between the two, a sensor for real-time monitoring of the friction and wear status of the friction pair is designed, which provides a reliable real-time monitoring method for friction pair monitoring in vacuum machinery. [Display omitted] [ABSTRACT FROM AUTHOR]

A major factor affecting the life of an axial piston pump is the tribological behaviour of the slipper/swash plate friction pair. To disclose the slipper pair's time-varying lubrication process, a unique thermal-fluid-structure dynamic coupling model based on cumulative damage is developed. Viscosity-temperature-pressure effects, damage deformation, kinetic behaviour, and hydrodynamic lubrication are all thoroughly accounted for in this model. A broader time range of dynamic slipper lubrication state recognition allows for an effective evaluation of wear characteristics. The outcome shows that the classic lifespan under the rated pressure consists of three stages: Infant mortality stage, life cycle stage and the wear-out stage. Otherwise, only one stage with a high wear rate is shown. [Display omitted] [ABSTRACT FROM AUTHOR]

Stiffness is the key dynamic parameter of the angular contact ball bearing. This work established a dynamic bearing model based on Hertz theory and thermo-elastohydrodynamic lubrication (TEHL) and compared the contact angle, inner race position, and stiffness. In most cases, the stiffness calculated via Hertz was higher than when using TEHL. The axial stiffness values determined via the two theories were close, while the radial stiffness calculated via the Hertz theory was smaller than that determined by TEHL under light load and high speed. Considering the elastic deformation of the races and the initial contact angle, the results obtained by TEHL displayed a lower error rate in the experiment than Hertz. [ABSTRACT FROM AUTHOR]

This study investigates lubricating performances of oils through altering the working conditions in accelerated aging tests, observing the degradations on the lubricants' performances and incorporating in-time detections for verification. To meet the aims, a new measuring system has been developed to observe alterations of the recorded viscosity index, color difference, thermal coefficient and torque transmission in the oil film under electrical discharges. To resolve the quality of lubricating oil in real time, the discharging waveforms and the acoustic indexes were applied to the marginal Hilbert spectrum for characterizing the time-frequency domain features. The Fisher score of the selected features successfully differentiated the new and used lubricants. The physical effects in association with the degradations of oil films are reported in detail. [ABSTRACT FROM AUTHOR]

Cavitation in hydrodynamic bearings is a fundamental factor in the behavior of the fluid film and in the equilibrium position the journal will have after the application of external loads. The calculation of these parameters by robust tools is an active research topic even though accuracy, stability and conservativeness are not so often discussed. This work shows the results obtained through the implementation of a novel model developed from first principles that allows characterizing the pressure field of a liquid–gas lubricant mixture avoiding the reported instabilities with the time derivative of the mixture density. The formulation also relies on a coupled transport equation describing the evolution of the liquid fraction, ensuring mass conservation. This model is applied to study cases with gaseous, vaporous or pseudo-cavitation through the use of the Rayleigh–Plesset equation to characterize the physical behavior of the bubbles formed taking into account the characteristic time of each phenomenon. High resolution schemes are used for the spatial treatment of the advection and a temporal discretization based on the Strang splitting method which allows for a second order convergence in space and time. The numerical results obtained are contrasted and discussed with experimental data found for static and dynamic bearings for the three types of cavitation mentioned, obtaining a very good agreement. • A two-phase model for cavitation in journal bearings is developed. • The physical behavior of each cavitation phenomenon can be modeled correctly. • High resolution schemes are used to obtain a higher convergence order. • Cavitated region depends on saturation pressure, not bubble advection. • Cavitation model impacts vapor region, pressures, shaft stability and final position. [ABSTRACT FROM AUTHOR]

Understanding the behaviour of engine and gear oils, especially the viscosity, under temperature and shear is important to improve machine operation. A novel viscometer using ultrasound is presented and used under a range of temperatures. A single cross-temperature (between 20 ° C and 60 ° C) ultrasonic calibration is shown to be sufficient. Next, the ultrasonic viscometer is compared to a conventional viscosity measurement technique for Newtonian and non-Newtonian lubricants. Newtonian viscosity standard fluids and shear-thinning engine oils are studied. Both viscosity measurement techniques match for Newtonian fluids but ultrasonic measurements are consistently lower for shear-thinning fluids. It suggests that the ultrasonic viscometer is similar to a high-shear viscometer with a shear rate of about 1 0 6 s − 1 . [ABSTRACT FROM AUTHOR]