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Moving contact line dynamics calculations include two models: precursor film models and slip models. The lubrication approximation method is used to establish a three-dimensional mathematical model to analyze the droplet thermocapillary migration behavior on a non-uniformly heated solid substrate with a wettability track. The contact line dynamics in the slip model and the disjoining pressure effect in the precursor model are proposed to regulate the substrate wettability. Both models are numerically implemented to investigate droplet spreading for three cases: free spreading on an isothermal substrate, thermocapillary migration on a uniform wettability substrate, and thermocapillary migration on a wettability-confined track. For the case of free spreading on an isothermal substrate, the three-dimensional results of the slip and precursor contact line models are essentially consistent with two-dimensional slip model results. For the case of thermocapillary migration on a uniform wettability substrate, the results of the two models essentially agree with the experimental results. Decreasing the thermal gradient reduces the discrepancies between the two models that result from the coordinate transformation method used in the slip model, which reduces the contact angles measured in the y-direction and enlarges the advancing contact angle in the migration direction. For the case of thermocapillary migration on a wettability-confined track, the slip model gradually shows a "dynamic-pinning" behavior with increasing equilibrium contact angle in the hydrophobic region. By contrast, the precursor film model maintains a stationary pinning behavior but separates a residual liquid outside the track. The precursor film model is preferred over the slip model in lubrication approximations for three-dimensional fluids when calculating complex moving contact dynamics caused by wettability differences. However, the precursor film model must be further optimized to prevent numerical instability. [ABSTRACT FROM AUTHOR]

Predictions of film thickness in elastohydrodynamic lubricated (EHL) contacts generally rely on the assumption of a semi-infinite equivalent solid to calculate elastic deformations. However, this assumption often fails when the contact is near an edge of one of the solids. This paper explores the impact of a solid edge being close to or within a theoretical EHL contact area on film thickness. We specifically highlight the advantages of a sharp edge over a chamfer, and the non-monotonous effect of the fillet radius on the minimum film thickness. Semi-analytical equations are developed to determine the maximum and minimum lubricant film thickness in a truncated contact and compare numerical results with experimental data in cases involving a chamfer. [ABSTRACT FROM AUTHOR]

The fixed-setting face-milled curvilinear cylindrical gear features teeth that are arc-shaped along the longitudinal direction. Some researchers hypothesize that this arc-tooth may enhance the lubrication conditions of the gear. This study focuses on this type of gear, employing both finite element analysis (FEA) and analytical methods to determine the input parameters required for elastohydrodynamic lubrication (EHL) analysis. The effects of assembly errors, tooth surface modifications, load, and face-milling cutter radius on the lubrication performance of these gears are systematically investigated. The finite element model (FEM) of the gear pair is utilized to calculate the coordinates of contact points on the tooth surface and the corresponding contact pressures at the tooth surface nodes throughout a meshing cycle. Subsequently, the normal load on specific gear teeth is determined using a gradient-based approach. Entrainment speed, slip-to-roll ratio, and effective radius near the contact points on the tooth surface are derived through analytical methods. The data obtained from FEA serve as input parameters for EHL simulations. The lubrication performance of the curvilinear cylindrical gear is evaluated through example studies. The findings indicate that using FEA to provide input parameters for EHL simulations can reveal the occurrence of edge contact phenomena during gear meshing, allowing for a more accurate representation of the gear's lubrication conditions. The lubrication performance of the curvilinear cylindrical gear is shown to be independent of the face-milling cutter radius but is significantly influenced by the size of the contact pattern on the tooth surface. Curvilinear gears with larger contact patterns demonstrate superior lubrication performance. [ABSTRACT FROM AUTHOR]

Purpose: This paper aims to study the lubrication mechanism of textured journal bearings. Design/methodology/approach: CFD models for textured journal bearings are established. The effect of texture coverage on the pressure distribution is studied to find the proper texture distribution. To enhance the local load-carrying capacity at textures, the micro-hydrodynamic pressure and microflow at different texture depth ratios are captured. The interaction between the texture-induced microflow and the bearing lubrication film is analyzed from the microflow perspective. Findings: The bearing performance is on the one hand enhanced by the micro-hydrodynamic pressure generated by textures. On the other hand, the main bearing land and maximum pressure can be interfered by textures, leading to the reduction of load-carrying capacity. To minimize the interference effect, textures are suggested to distribute downstream of the minimum film thickness location. As the lubrication film thickness increases, the corresponding optimum texture depth ratio rises. The vortices influence the local flow rate through the lubrication film at textures and further affect the micro-hydrodynamic pressure and local load-carrying capacity. The texture depth ratio, at which vortices begin to occur, generates the maximum micro-hydrodynamic pressure. Originality/value: The proper texture distribution is introduced, which is capable to generate the micro-hydrodynamic pressure without interfering with the primary load-carrying capacity of the bearing. The microflow effect is found to considerably influence the local load-carrying capacity at textures. The necessity of sub-regional optimization in textured journal bearings is pointed out. This study provides the fundamental reference for the design and optimization of textured journal bearings. [ABSTRACT FROM AUTHOR]

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

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

The rotation speed directly influences the vibration and lubrication behaviors of gear pairs, but studying the effects of time-varying rotation speeds during their operation poses substantial challenges. The present work proposed an approach to analyzing the dynamic response and lubrication performance of spur gear pairs under time-varying rotation speeds. A single-degree-of-freedom torsional dynamics model was established to capture the vibration responses and meshing forces of a gear pair, with the meshing stiffness modulated by the time-varying rotation speed. Additionally, a transient elastohydrodynamic lubrication model of the gear system was proposed to obtain the pressure pro-file and film shape, incorporating the effects of time-varying rotation speeds. Three types of time-varying rotation speeds were investigated: acceleration, deceleration, and oscillation. The results reveal that the time-varying rotation speed induces chaotic motion of the gear system, resulting in significant changes in the dynamic meshing force, entrainment velocity, and curvature radius of the gear pair compared to those in constant-speed scenarios. The lubrication performance under time-varying rotation speeds also shows diverse dynamic characteristics, highlighting significant differences from that observed under a constant rotation speed. These insights contribute to a more comprehensive understanding of gear dynamics under realistic operating conditions, enhancing gears' performance and reliability in practical applications. [ABSTRACT FROM AUTHOR]

Copyright of Lubrication Engineering (0254-0150) is the property of Editorial Office of LUBRICATION ENGINEERING and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

During maritime operations, extreme events such as explosions, grounding, and seal failures can cause water ingress into lubricant compartments, forming oil-water emulsions that significantly affect the lubrication performance of ship stern bearings. Existing studies mainly focus on low water content, with limited exploration of the impact of high water content on lubrication performance. To address this gap, viscosity measurements of oil-water mixtures were conducted, and an emulsification viscosity equation applicable to varying water contents was derived. A thermal elastohydrodynamic lubrication model for stern bearings, incorporating rough surface contact and emulsification viscosity, was developed. Numerical results reveal two flow regimes of oil-water mixtures—water-in-oil (W/O) and oil-in-water (O/W)—each exhibiting distinct lubrication behaviors. In the high-viscosity W/O regime, water contamination increases lubricant viscosity, raises minimum oil film thickness, and lifts the journal, but significantly increases the friction coefficient and power consumption. The high specific heat capacity of water mitigates the temperature rise caused by increased viscosity. In the low-viscosity O/W regime, the mixture shows lower temperature rise and friction power under high-speed light-load conditions. However, under low-speed heavy-load conditions, the lubrication transitions to the boundary regime, leading to sharp increases in friction and temperature detrimental to bearing performance. This study highlights the critical influence of water content in oil-water emulsions on stern bearing lubrication, providing valuable insights for improving bearing design and operational reliability. [ABSTRACT FROM AUTHOR]

At present, in the dynamic modeling of rolling bearings with composite faults, Hertz contact theory is mostly used to describe the contact between the rolling element and the raceway, while ignoring the influence of lubricating oil film under elastohydrodynamic lubrication (EHL) on key modeling parameters, which brings errors to the accurate calculation of parameters such as stiffness and damping. On the basis of composite fault modeling, this article carefully considers the influence of EHL on the stiffness and damping of rolling bearings, establishes a five degree‐of‐freedom (DOF) composite fault model of rolling bearings, and verifies the correctness of the model through bench test data. The vibration response characteristics of rolling bearings with composite faults under different loads and fault sizes are mainly studied. The results indicate that the frequency‐domain characteristics of composite faults are the result of coupling and superimposing the frequency‐domain characteristics of single‐point fault signals. As the radial load increases, the amplitude of the vibration response also increases gradually. In the inner ring–outer ring composite fault and the outer ring–rolling element composite fault, the outer ring fault is more sensitive to change in radial load. If the radial load is appropriately increased, it is beneficial to identify the outer ring fault in both kinds of composite faults. However, excessive radial loads may inhibit the diagnosis of other fault frequencies other than the outer ring, which may affect the diagnosis of all components in the composite fault. In the inner ring–rolling element composite fault, the inner ring fault is more sensitive to change in radial load. If the radial load is appropriately increased, it is beneficial to identify the inner ring fault in the inner ring–rolling element composite fault. Similarly, in the diagnosis of such composite faults, excessive radial load may affect the detection and diagnosis of rolling element faults. [ABSTRACT FROM AUTHOR]

ABSTRACT A thermal elastohydrodynamic lubrication model is combined with a wear model under mixed lubrication to investigate the lubrication performance and wear characteristics of double‐circular‐arc spiral bevel gears for nutation drive. Moreover, the effects of operating conditions on the characteristic parameters of the film are analysed under the mixed lubrication point‐contact conditions. Furthermore, the characteristics of gears in terms of friction coefficient and wear depth are discussed. According to the results, the performance of lubrication and wear during the mutual meshing of the convex tooth surface of the external bevel gear and the concave tooth surface of the inner bevel gear is better than that during the mutual meshing of the other pair of tooth surfaces. The minimum film thickness of the whole meshing process occurs near the inner of the bevel gear due to the joint action of the load and the end edge effect. Moreover, an increase in torque at a certain rotational speed is favourable to the lubrication performance of the meshing process. The wear depth in the double‐circular‐arc spiral bevel gears' meshing process is heavily influenced by the roughness of the tooth surface. [ABSTRACT FROM AUTHOR]

To enhance the sliding tribological performance between PTFE and 40#steel (AISI 1040) under full film lubrication conditions, laser surface texturing (LST) technology was employed to prepare micro-dimples on the contact surfaces of 40# steel discs. The Box–Behnken design response surface methodology (BBD-RSM) was applied to optimize the micro-dimple parameters. Coefficients of friction (COFs), wear losses and worn contact surfaces of the PTFE–40# steel tribo-pairs were researched through repeated wear tests, as lubricated with sufficient anti-wear hydraulic oil. The influencing mechanism of micro-dimples on the tribological behavior of tribo-pairs was also discussed. The results proved that micro-dimples can significantly improve the tribological properties of PTFE–40#steel tribo-pairs. The deviation between the final obtained average COF and the prediction by the BBD-RSM regression model was only 0.0023. Following optimization, the average COF of the PTFE–40# steel tribo-pair was reduced by 39.34% compared to the smooth reference. The wear losses of the PTFE ring and 40# steel disc decreased by 91.8% and 30.3%, respectively. This study would offer a valuable reference for the optimal design of key seals used in hydraulic cylinders. [ABSTRACT FROM AUTHOR]

ABSTRACT Harmonic gears are widely used in precise space technology, robotic, medical equipment and other fields, while the magnitude of surface topography changes due to wear is usually comparable to or larger than the original surface roughness and elastic deformation, leading to severe transmission failures. This paper reports a numerical approach to simulate the lubrication status considering wear evolution based on mixed elastohydrodynamic lubrication (EHL) and Archard models, in which the Reynolds equation is solved with finite difference method and surface deformation is calculated by the discrete convolution‐fast Fourier transform (DC‐FFT) algorithm. The interfacial pressure and film thickness distributions are validated by comparison with available results from literature. The harmonic gear lubrication and wear performances are calculated, including effects of machined surface, velocity, load, wear time and material properties, and the results suggest that avoiding long‐term and high‐torque working with a large wear coefficient can effectively prevent surface wear failure, which is beneficial for increasing the harmonic gears' lifespan. [ABSTRACT FROM AUTHOR]

From the earliest theoretical studies on elastohydrodynamic lubrication, it was believed that film build-up is governed by lubricant rheology in the low-pressure contact inlet. Recently, it was discovered that this is only true for the theoretical line contact case, where lubricant out-of-contact lateral flow is absent. In actual contacts, though central film thickness is indeed governed by low-pressure lubricant rheology, minimum film thickness is additionally influenced by the high-pressure response. Thus, a proper prediction of minimum film thickness (either by analytical formulae, or machine-learning frameworks) would require input parameters that define the high-pressure viscous response of the lubricant. The current work identifies and formulates these parameters with the help of machine-learning regression tools. These are fed with minimum film thickness results from finite element simulations of smooth steady-state isothermal Newtonian circular contacts, lubricated with sets of hypothetical fluids having the same pressure-viscosity response at low pressure, but different high-pressure ones. It is found that conventional dimensionless groups are not sufficient to describe minimum film thickness formation, and that an additional pressure-viscosity coefficient—evaluated at half the Hertzian contact pressure—is required. [ABSTRACT FROM AUTHOR]

Antiwear additives permit energy-efficient lubrication of gearboxes, bearings, and other tribological interfaces. We study zirconia (ZrO2) nanocrystal additives, which readily form protective tribofilms in tribological contacts. Our prior work demonstrated cooperative antiwear performance between ZrO2 and the S- and P-based co-additives in fully formulated hydrocarbon gear oils. Here, we extend that work by examining the growth kinetics of the ZrO2 tribofilms, including the influence of the co-additives. In the boundary lubrication regime for mixed rolling-sliding contacts, the initial phase of ZrO2 tribofilm growth is soon overtaken by removal processes, phenomena whose importance has gone unnoticed in prior work. Tribofilm removal affects the steady-state thickness and morphology of the tribofilm as well as its growth kinetics. The S- and P-based co-additives are incorporated into the ZrO2 tribofilm, and alter the competition between the growth and removal processes, increasing initial net growth rates per contact cycle and contributing to a more polished final interface. This work highlights the significance of removal processes in determining tribofilm antiwear performance, and suggests several routes for improving tribofilm growth kinetics using co-additives. [ABSTRACT FROM AUTHOR]

The roller-floating bush pin is a major component in the fuel supply mechanism of a diesel engine, and its tribological performance seriously affects the reliability of the equipment. In this study, a transient thermoelastic hydrodynamic lubrication analysis model of the double-layer oil film on the roller-floating bush pin is established, which is coupled with the dynamic and kinematic analysis model of the cam-roller. The transient dynamic characteristics, such as time-varying speeds and loads of the roller during the operation of the cam, were considered. Also, the elastic deformation and the thermal effect were considered in the lubrication model. The relevant experimental platform for this double-layer oil film lubrication structure was built, and the simulation model was verified through experiments. The influence of the operating conditions, including cam speed and plunger fuel pressure, on the lubrication performance of the structure is explored, and besides, the influence of the structural parameters, including length-diameter ratios and clearance ratios, is also analyzed. It shows the lubrication condition of the inner oil film is worse compared with the outer oil film. As the explored factors change, the pressure of the inner oil film is more affected than that of the outer oil film. This work could provide useful guidance in designing the roller-floating bush pin in the fuel supply mechanism. [ABSTRACT FROM AUTHOR]

The so-called controversy in elastohydrodynamic lubrication (EHL) regarding the nature of the shear dependence of viscosity, Eyring versus Carreau, is truly a controversy regarding the pressure and temperature dependence of low-shear viscosity. Roelands removed data that contradicted his claims of accuracy for his correlation. The Roelands hoax became acceptable in EHL because ignoring the universal previtreous piezoviscous response made the traction calculated with the Eyring assumption appear to be reasonable. Traction and minimum film thickness calculations sometimes require the description of viscosity at pressures up to the glass transition pressure. There have been few measurements of viscosity at pressures up to glass pressure. Therefore, a need exists for a piezoviscous model that extrapolates accurately, and the Hybrid model fills that need. Here, an improved relation for the temperature dependence of divergence pressure is offered and extrapolation is demonstrated for a polyalphaolefin and propylene carbonate. A linear dependence of divergence pressure with temperature is more useful than previous versions. An improvement in the capability of high-pressure viscometry is suggested based upon the fractional Stokes Einstein Debye relation and the relatively simple measurements of DC conductivity. [ABSTRACT FROM AUTHOR]

The document discusses the history and development of tribology research in Germany, focusing on the German Society for Tribology (GfT) and its 65th anniversary. It highlights key figures and milestones in the field, such as Georgius Agricola, Gottfried Wilhelm Leibniz, and Prof. Dr. Richard Stribeck. The text also covers the latest research and development in tribology, including topics like rolling bearings, plain bearings, gears, lubricants, surface modifications, elastomer friction, and fundamental tribological aspects. The Special Issue contains 21 contributions from various experts in the field. [Extracted from the article]

This study presents a model of starved mixed Elastohydrodynamic Lubrication (EHL) in point and line contact to investigate the lubrication performance and material response. In formulating the governing equations for the lubrication, the dimensional Reynolds equation is discretized to involve all possible regimes from the boundary lubrication to fully hydrodynamic lubrication, and an additional algorithm is provided to determine the fractional film content based on the profiles of pressure distribution and film thickness. Solutions of the point contact from the present model are compared with those reported by the previous studies and good consistency can be found. The three-dimensional line contact is used to predict the load carrying capabilities of the film thickness at the interface of mating spur gear teeth. A return mapping method is implemented to take the plastic revolution into account. The solution at the initial stage of a startup process with the lubricant entrainment velocities of u x = u y = 0 is compared with that from a dry contact to validate the elasto-plastic solutions. Sample cases are presented to reveal the effects of inlet oil supply condition and material plasticity on lubrication starvation. [ABSTRACT FROM AUTHOR]

Electropolishing using a high-current density results in a pitting phenomenon, producing a surface texture distinguished by many pits. Apart from the change in surface topography, electropolishing forms an oxide surface layer characterized by beneficial tribological properties. This paper introduces surface texturing in worm gear pairs by electropolishing a 16MnCr5 steel worm surface. Electropolishing produces surface pits 1 μm to 5 μm deep and 20 to 100 μm in diameter. The material characterization of 16MnCr5 steel is compared against the electropolished 16MnCr5 steel based on microstructure, hardness, surface topography and chemical composition. Experimental tests with worm pairs employing electropolished worms are conducted, and the results are compared to conventional worm pairs with ground steel worms. Electropolished worms show up to 5.2% higher efficiency ratings than ground ones and contribute to better running-in of worm gear pairs. Moreover, electropolished worms can reliably support full contact patterns and prevent scuffing due to improved lubrication conditions resulting from the produced surface texture and oxide surface layer. Based on the obtained results, electropolishing presents a promising method for surface texturing and modification in machine elements characterized by highly loaded non-conformal contacts and complex geometry. [ABSTRACT FROM AUTHOR]

The accurate design of tribological contacts, such as those in bearings and gearboxes, makes them highly efficient and helps reduce emission in all driven systems. Traditionally, this process requires more lubricant data than data sheets typically provide, mainly kinematic viscosity at 40 °C and 100 °C and density, which limits the design process. This study introduces a simplified methodology for determining lubricant film thickness, one of the main design critical parameters, using minimal viscosity measurements obtained with a high-pressure viscometer. The researchers demonstrate that essential lubricant parameters can be derived effectively from a few measurements. By combining state-of-the-art models for film thickness with practical measurements from an EHL tribometer, this study confirms that reliable film thickness predictions can be made from basic viscosity data. This approach streamlines the design process, making tribological simulations more accessible and cost-effective, and enhances the design of tribological contacts under extreme conditions. [ABSTRACT FROM AUTHOR]

Copyright of Lubrication Engineering (0254-0150) is the property of Editorial Office of LUBRICATION ENGINEERING and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This paper introduces an optimized computational domain for fully flooded circular elastohydrodynamic lubrication (EHL) contacts, enhancing the accuracy of numerical calculations of pressure and oil film thickness. First, the computational domain was configured based on Kapitza's analytical solution. Then, a resolution sensitivity study for the mesh of the 2D computational domain for the Reynolds equation was conducted to investigate the effect of mesh resolution on the accuracy of the numerical solution. Subsequently, the impact of the size of the full 3D computational domain on the simulation's accuracy and computational efficiency was analyzed. The main result is the 3D computational domain, which automatically adapts to operating conditions within the piezoviscous rigid, the isoviscous rigid, the piezoviscous elastic, and the isoviscous elastic regions, as well as in the transition regions between them. This results in a model which provides accurate predictions across a wide range of operational conditions. Another outcome is a new approximate expression for the central oil film thickness, showing a maximum relative difference of less than 4.6% compared to the numerical model. [ABSTRACT FROM AUTHOR]

Numerical investigations of capped T-ring (CTR) seals performance in reciprocating motion for landing gear shock absorber applications are presented. A lubrication model using the Elastohydrodynamic lubrication theory and deformation mechanics is developed in a multi-material contact zone, and a procedure for coupling fluid and deformation mechanics is introduced. By conducting Finite Element Method (FEM) simulations, the static contact pressure is obtained, which subsequently is used within the model developed herein consisting of a modified Reynolds equation and an asperity contact model, to calculate the fluid film pressure, and the deformation of the fluid channel is determined using an elastic deformation model applied to a multi-component multi-mechanical property channel. These computational results are used for estimations of the seal leakage and friction under various conditions. In addition, the influence of asperity orientation is compared with other parameters, such as sealing pressure and piston velocity. A correlation between asperity orientation and leakage was found, and a general trend of reduced leakage with longitudinally oriented asperities was established. [ABSTRACT FROM AUTHOR]

We consider a cylinder immersed in viscous fluid moving near a flat substrate covered by an incompressible viscoelastic fluid layer, and study the effect of the fluid viscoelasticity on the lift force exerted on the cylinder. The lift force is zero when the viscoelastic layer is not deformed, but becomes non-zero when it is deformed. We calculate the lift force by considering both the tangential stress and the normal stress applied at the surface of the viscoelastic layer. Our analysis indicates that as the layer changes from the elastic limit to the viscous limit, the lift force decreases with the decrease of the Deborah number (De). For small De, the effect of the layer elasticity is taken over by the surface tension and the lift force can become negative. We also show that the tangential stress and the interface slip velocity (the surface velocity relative to the substrate), which have been ignored in the previous analysis, give important contributions to the lift force. Especially for thin elastic layers, they give dominant contributions to the lift force. [ABSTRACT FROM AUTHOR]

The authors have previously developed the electrical impedance method which simultaneously measure the thickness and breakdown ratio of oil films in EHD (elastohydrodynamic) contacts. Furthermore, using a ball-on-disc-type apparatus, the authors have also confirmed that the accuracy of oil film measurement by the developed method is comparable to that of optical interferometry (i.e., glass-steel contacts). In this study, we discussed the experimental results obtained by applying the electrical impedance method to steel-steel contacts using a steel disc instead of a glass disc. It was found that under the mixed lubrication regime where wear occurs, the oil film thickness obtained by this method is calculated to be significantly thicker than the theoretical value. This can be attributed to the increase in the apparent dielectric constant of the lubricant due to wear particles in the lubricant. [ABSTRACT FROM AUTHOR]

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

Purpose: This paper aims to study the problem of starvation lubrication of high-speed ball bearings due to temperature rise during operation and to avoid thermal failure of bearing lubrication. Design/methodology/approach: Under the quasi-statics model of grease lubrication, both the oil film dragging force and the rolling friction between the balls and raceways collectively counteract the gyroscopic torque. Initially, the static model for grease lubrication is solved, followed by calculating the generated heat using the local heat generation method and ultimately the multinodal thermal network model is solved, and the solved results of the quasi-statics are updated by the temperatures of the grease nodes based on the relationship of the grease temperature and viscosity, as well as the relationship of the viscosity and the film thickness. Findings: By comparing the numerical calculation results of bearings under different working conditions, the influence of starvation lubrication on the oil film thickness, oil film drag force and rolling friction of bearings is discussed, and it is found that the numerical calculation results of the outer ring temperature of bearings under the starvation lubrication due to the consideration of temperature rise are closer to the experimental values. Originality/value: This study reveals the dynamic characteristics of bearings under starvation lubrication, which is more practical and engineering guiding significance for the design of bearings, and introduces a new method and basis for the calculation of temperature rise of rolling bearings. Peer review: The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-06-2024-0208/ [ABSTRACT FROM AUTHOR]

Thermal elastohydrodynamic lubrication (TEHL) plays a crucial role in meshing stiffness, friction, wear, vibration, and transmission stability during the gear meshing. Based on the TEHL and Blok theories, a comprehensive meshing stiffness model of spur gear is proposed by combining thermal stiffness, oil film stiffness, and time-varying meshing stiffness, which is closer to the actual working conditions compared with conventional method. The influences of torque, rotational speed, and module on the lubrication performance and meshing characteristics are investigated, and the distributions of oil film pressure, film thickness, tooth surface temperature rise, friction coefficient, and stiffness are obtained. The results reveal that a light torque, large rotational speed, and module can improve loading capacity and lubrication performance, but excessive parameters will increase tooth surface temperature rise and thermal deformation, and reinforce meshing impact, which further increase the tooth surface wear or bonding. Therefore, it can be concluded that the reasonable parameter match is valid in improving gear lubrication characteristics, mitigating meshing impact and improving gear meshing characteristics, and further enhance system stability. [ABSTRACT FROM AUTHOR]

Considering an elastohydrodynamic lubrication line contact, this study investigates the tribo-dynamic effects introduced by surface waviness. These waviness profiles are inevitable during various machining processes, such as grinding, and are on a larger scale than roughness. The waviness feature excites vibratory motions of contact bodies, and influences the lubrication performance through dynamic contact force and periodic squeezing. In this work, a tribo-dynamic formulation is implemented to examine such impact on film thickness, contact pressure, friction, and movement of the contact components. Owing to the presence of subharmonics, waviness introduced tribo-dynamic behavior cannot be eliminated within the adopted operating speed range. However, it is shown to be feasible to implement engineered waviness profile for lubrication performance improvement, providing a new and effective technique for friction/power-loss reduction, for instance. [ABSTRACT FROM AUTHOR]

A theoretical model for the micro-texture on the inner wall of the stator rubber in screw pumps was developed. The finite element analysis method was employed. The pressure and streamline distributions for warhead-type, concentric circle-type, and multilayer rectangular-type textured surfaces were calculated. The effects of textured morphology, groove depth, groove width, and other parameters on the lubrication field were systematically investigated and analyzed. A nanosecond laser was employed to process the textured rubber surface of the stator in the screw pump. Subsequently, a micro-texture friction performance test was conducted on the rubber surface of the stator in actual complex well fluids from shale oil wells. Given the results of the simulation analysis and experimental tests, the lubrication characteristics of textured rubber surfaces with varying texture morphologies, rotational speeds, and mating loads were revealed. Furthermore, it indicated that the irregular symmetric warhead-type micro-texture exhibited excellent dynamic pressure lubrication performance compared with concentric circle-type and multilayer rectangular-type textures. The irregular symmetry enhanced the dynamic pressure lubrication effect, enhanced the additional net load-bearing capacity of the oil film surface, and reduced friction. As the groove depth increased, the volume and number of vortices within the groove also increased. The fluid kinetic energy was transformed into vortex energy, leading to a reduction in wall stress on the surface of the oil film, thereby affecting its bearing capacity. Initially, the maximum pressure on the wall surface of the oil film increased and then decreased. The optimal dynamic pressure lubrication effect was achieved with a warhead-type texture size of 3 mm, a groove width of 0.2 mm, and a groove depth of 0.1 mm. Well-designed texture morphology and depth parameters significantly enhanced the oil film-bearing capacity of the stator rubber surface, improving the dynamic pressure lubrication effect, and consequently extending the service life of the stator–rotor interface in the screw pump. [ABSTRACT FROM AUTHOR]

The EHRA (Electro-Hydraulic Rotary Actuator), using a vane rotary actuator, has the advantages of a high torque density and integration and is expected to become a joint actuator for robots. This research focuses on the sealing characteristics of various parts of a vane rotary actuator. The average Reynolds equation was used to analyze the leakage characteristics at the gap. A detailed theoretical analysis was conducted on the internal leakage mechanism of a vane rotary actuator using an X-ring as the dynamic seal for the rotor vane. According to the path of internal leakage, different sealing forms are considered as a series or parallel, and the Newton iteration method is used to obtain the total internal leakage characteristics of a vane rotary actuator. It was also considered that the deformation of the vane rotary actuator caused a thicker gap, leading to an increase in internal leakage. The calculation results are consistent with the experimental data. The analysis results indicate that when estimating the internal leakage of a vane rotary actuator, it is necessary to take the pressure of the high-pressure chamber and output shaft position as inputs. This research provides a reference for an analysis of the method of internal leakage for vane rotary actuators. It provides theoretical support for designing a vane rotary actuator with more minor internal leakage and a higher volumetric efficiency. [ABSTRACT FROM AUTHOR]

Thermoplastics show great potential due to their lightweight design, low-noise operation, and cost-effective manufacturing. Oil lubrication allows for their usage in high-power-transmission applications, such as gears. The current design guidelines for thermoplastic gears lack reliable estimates for the coefficient of friction of oil-lubricated rolling–sliding contacts. This work characterizes the friction of elastohydrodynamic rolling–sliding contacts with technical and high-performance thermoplastics with oil lubrication. The influence of polyoxymethylene (POM), polyamide 46 (PA46), polyamide 12 (PA12), and polyetheretherketone (PEEK), as well as mineral oil (MIN), polyalphaolefin (PAO), and water-containing polyalkylene glycol (PAGW), was studied. Experiments were carried out on a ball-on-disk tribometer, considering different loads, speeds, temperatures, and surface roughness. The results show that, for fluid film lubrication, there is very low friction in the superlubricity regime, with a coefficient of friction lower than 0.01. Both sliding and rolling friction account for a significant portion of the total friction, depending on the contact configuration and operating conditions. In the mixed to boundary lubrication regime, the sliding friction depends on the thermoplastic and rises sharply, thus increasing the total friction. [ABSTRACT FROM AUTHOR]

Gaining insight into tribological systems is crucial for optimizing efficiency and prolonging operational lifespans in technical systems. Experimental investigations are time-consuming and costly, especially for reciprocating seals in fluid power systems. Elastohydrodynamic lubrication (EHL) simulations offer an alternative but demand significant computational resources. Physics-informed neural networks (PINNs) provide a promising solution using physics-based approaches to solve partial differential equations. While PINNs have successfully modeled hydrodynamics with stationary cavitation, they have yet to address transient cavitation with dynamic geometry changes. This contribution applies a PINN framework to predict pressure build-up and transient cavitation in sealing contacts with dynamic geometry changes. The results demonstrate the potential of PINNs for modeling tribological systems and highlight their significance in enhancing computational efficiency. [ABSTRACT FROM AUTHOR]

In this work, electrostatic minimum quantity lubrication (EMQL) has been applied in grinding. When the droplets were charged, it could promote penetrability in the processing area. The electric field formed between the charged droplets and the surface of Cr12 die steel could affect the hardness of the workpiece surface. The grinding mechanism of EMQL has been revealed under different charging voltage by analyzing the wetting angle of droplets and the hardness of Cr12 surface. The reduction of grinding force (11.5% to 49%), surface roughness (10% to 22.1%), and the increase in grinding ratio (1.9% to 27.3%) and surface quality of EMQL under various charging voltages were studied. The results showed that the wetting angle decreased when the droplets were charged. Compared to MQL, the charged lubricant droplets with better penetrability are easier to penetrate and spread on the contact surface between the grinding wheel and the workpiece, thereby improving the lubrication of the friction interface and obtaining better grinding performance. Moreover, we also found that the positively charged EMQL not only effectively improves the penetrability of droplets but reduces the hardness of the Cr12 surface. Thus, the grinding performances under positively charged EMQL are always better than these under negatively charged when grinding Cr12. [ABSTRACT FROM AUTHOR]

The objectives of this investigation were to experimentally characterize the effect of hydrogen on the tribological performance of heavily loaded lubricated contacts. In order to achieve these objectives, a ball-on-disk film thickness and traction measurement test rig and a four-ball wear tester were modified to introduce gaseous hydrogen into the lubricated contact. Using the ball-on-disk test rig, lubricant film thickness, and traction were measured operating in air, nitrogen, and hydrogen environments. The results indicate that hydrogen environment has no effect on the lubricant film thickness and traction coefficient. The wear performance of the lubricant was evaluated in air, nitrogen, and hydrogen environments using the four-ball tester according to ASTM D4172 standard. Wear scar dimensions were determined through optical profilometry and compared for each condition. The results demonstrated that the wear scar diameter is slightly higher in a hydrogen environment. Additionally, the effects of hydrogen embrittlement on the wear performance were investigated using the four-ball tester. The balls used in the four-ball tester were precharged with hydrogen in Ammonium Thiocyanate. Wear scar profilometry results showed significantly larger wear scars and excessive pitting on the worn surface of precharged specimens. Results from this investigation shows that a gaseous hydrogen environment has a negligible effect on friction and wear as compared to diffused hydrogen in the material. [ABSTRACT FROM AUTHOR]

The article "Fluid-mediated impact of soft solids" in the Journal of Fluid Mechanics explores the impact of soft solids with a thin film of fluid between the solid and a rigid surface. The study develops a scaling for the viscous approach stage of fluid-mediated normal impact, revealing the transition between elasticity and inertia regimes. By comparing solid impactors with highly viscous droplets, the research provides insights into the dynamics of fluid-mediated contact in biological and physical processes. The study by Bouwhuis et al. (2012) investigates the impact dynamics of soft solids approaching a smooth surface, uncovering mechanisms through numerical simulations and scaling analysis. The research emphasizes the role of relative time scales in governing contact processes and understanding nonlinear dynamics in suspensions and dense particle collections. [Extracted from the article]

For investigating the rail corrugation characteristics of metro small curve track under the combined effect of rail side lubrication and slip rate dependence, by developing a three-dimensional vehicle-track coupling numerical model, the wheel-rail (WR) contact stick-slip (SS) characteristics under different transition areas of rail side lubrication in the presence of corrugation were analyzed. Meantime, on the basis of considering the friction slip rate dependence, the SS vibration characteristics under different rail side lubrication conditions were further analyzed to understand the effect mechanism of rail surface friction characteristics on corrugation. The results show that, when there is rail side lubrication, both inner and outer WR systems have the possibility for SS vibration, and the longitudinal SS vibration intensity is greater than the transverse SS vibration intensity; the SS vibration intensity of the inner WR system is greater than that of the outer WR system, indicating that the inner rail is more susceptible to corrugation and the corrugation is more acute. With the expansion of the rail side lubrication range, the standard deviations of longitudinal and transverse adhesion coefficients decrease, illustrating that the expansion of the lubrication range can reduce the SS vibration intensity of WR system. When the co-effects of rail side lubrication and slip rate dependence are considered, the increase of the rail side lubrication range leads to the increase of standard deviations of adhesion coefficients, which may be related to the enhancement of slip effect induced by the increase of the lubrication range. The introduction of slip rate dependent effect can reduce the standard deviation of the WR adhesion coefficient, which demonstrates that the slip rate dependent effect can ease the degree of SS vibration of WR system, thus reducing the probability of corrugation occurrence caused by the SS vibration. [ABSTRACT FROM AUTHOR]

In many engineering applications, including coating and lubrication operations, analyzing the temperature behavior of thin film flows on a vertically upward-moving tube is crucial to improving predictive models. This paper examines a steady third-grade fluid film flow with a surface tension gradient on a vertical tube. The mechanisms responsible for the fluid motion are upward tube motion, gravity, and surface tension gradient. This analysis focuses on heat transfer and stagnant ring dynamics. The formulated highly nonlinear ordinary differential equations are solved using the Adomian decomposition method. The conditions for stagnant rings and uniform film thickness are attained and discussed. The inverse capillary number C, Stokes number S t , Deborah number De, and Brinkman number Br emerged as flow control parameters. The temperature of the fluid film rises with an increase in the C, S t , De, and Br, whereas it decreases with an increase in thermal diffusion rate. The radius of stagnant rings tends to shrink by the increase in C, S t , and De. When the value of De is high, third-grade fluid behaves like solids; only free drainage happens with smaller radius stagnant rings and high temperatures. A comparison between Newtonian and third-grade fluids regarding surface tension, velocity, temperature, stationary rings, and fluid film thickness is also provided. [ABSTRACT FROM AUTHOR]

A theoretical model for the calculation of thermal elastohydrodynamic lubrication performance of the flow distribution pair of piston pumps is established, which is composed of the oil film pressure governing equation and energy equation, and solved by means of numerical solution and simulation. We carry out quantitative analysis of the influence of various parameters on the thermal elastohydrodynamic lubrication characteristics of the flow distribution pair. The results indicate that both the oil film thickness and the cylinder tilt angle of the flow distribution pair vary in a periodic manner. The increase in the rotational speed of the cylinder block will increase the film thickness of the oil film and reduce the fluctuation, and the inclination angle of the cylinder block and its fluctuation amplitude will decrease. An increase in working pressure will lead to a decrease in the average oil film thickness, an increase in fluctuations, and an elevation in both the tilt angle of the cylinder block and its fluctuation amplitude. The increase in the rotational speed of the cylinder block and the increase in the working pressure will lead to the increase in the viscous friction dissipation of the flow distribution pair, the increase in the oil film temperature and the increase in the leakage. The reduction in the sealing belt will lead to the reduction in oil film friction torque and leakage. [ABSTRACT FROM AUTHOR]

Engineering practice has demonstrated that seal failure can result in severe leakage and wear, reducing the efficiency of hydraulic systems and even leading to major safety risks. Currently, analyses of the thermal aspect of seal interfaces are relatively limited, with most studies focusing on mechanical analysis. However, in actual applications, temperature has a significant impact on sealing performance. In this paper, nonlinear elastomechanics, viscous fluid mechanics, micro-contact mechanics, micro-deformation theory, and thermodynamics are coupled to establish a mixed lubrication model considering the thermal effect. The reliability of the mixed lubrication model is verified through experiments, and the temperature distribution of the oil film in the sealing area and the temperature distribution of the seal ring are simulated. Finally, the effects of the reciprocating speed, root mean square roughness, fluid medium pressure, and seal pre-compression on seal friction force and leakage are investigated. The results show that the heat generated in the sealing area accumulates at the bottom of the V-ring. Under the same conditions, compared with the instroke, the temperature-rise area of the outstroke is biased to the left and the increase in temperature is greater. In addition, the piston rod speed and the preliminary compression of the seal ring have a greater impact on the overall seal friction force and leakage. Under a lower seal pre-compression, the RMS roughness has a great influence on the leakage and friction in the outstroke, while the impact of the internal stroke is limited. [ABSTRACT FROM AUTHOR]

The reduction of frictional power losses in power transmitting gears takes a crucial role in the design of energy- and resource-efficient drivetrains. Water-containing lubricants like glycerol and polyalkylene glycols have shown great potential in achieving friction within the superlubricity regime with coefficients of friction lower than 0.01 under elastohydrodynamic lubrication. Additionally, a bio-based production of the base stocks can lead to the development of green lubricants. However, one challenge associated with the application of water-containing lubricants to gearboxes is the evaporation of water and its impact on the lubricant properties. In this study, the influence of water evaporation on elastohydrodynamic friction and film thickness was investigated for three water-containing polyalkylene glycols. Two nominal water contents of 20 wt% and 40 wt% and two viscosities were considered. The results show that the friction increases continuously with higher evaporated water content, while the overall friction level remains low in nearly water-free states. A similar trend is observed for film thickness, where the strong increase in viscosity results in a notable increase in film thickness. Nevertheless, the sensitivity of friction and film thickness to water evaporation is low for small amounts of evaporated water. This allows generous thresholds for permissible variations in water content. [ABSTRACT FROM AUTHOR]

The benefits of surface textures on rolling and sliding tribological contacts have been an exciting field of study over the last three decades. Laser surface texturing (LST) is a comparatively newer texturing methodology that yields repeatable precise microtextures. A detailed overview of the available literature on the various works in this field is consolidated in this review. The main focus is on the effect of surface textures (with focus on laser ablation) for nonconformal contacts with elastohydrodynamic lubrication (EHL), as in rolling element bearings. A review of literature on textured contacts for the EHL regime, emphasizing its effect on friction, wear, rolling contact fatigue, vibration, texture geometry, and numerical simulation studies, is carried out with possibilities of future works. Basic details on LST processes and various parameters of the laser beam that determine the texture geometry are discussed. Being a field of continuing research, the review paper will aid in understanding the present developments and future directions in laser‐based surface texturing for nonconformal tribological contacts. [ABSTRACT FROM AUTHOR]

Stick–slip is a standard friction-induced self-excited vibration that usually occurs in the boundary or mixed lubrication regimes. Broadening of the hydrodynamic lubrication regime is conducive to suppressing stick–slip motion. In this paper, the load carrying capacity of a magnetic fluid (MF) film in the presence of a magnetic field is derived based on the modified Reynolds equation. An additional lifting force produced by MF under the magnet was applied between the tribopairs to achieve the full fluid lubrication. Thus, the stick–slip is expected to be inhibited in a lower speed scope. The effect of magnet thickness on the lifting force is investigated experimentally and theoretically. Special attention is given to the influence of the lifting force on the friction and the critical transition speed of the hydrodynamic lubrication regime. Results demonstrate that the lifting force increases with the increment of the magnet thickness. The presence of the additional lifting force expands the hydrodynamic lubrication and makes the critical transition speed move left, as shown by the friction transitions on the Stribeck curve. Therefore, stick–slip motion can be suppressed at a lower sliding speed. Such beneficial effects are more pronounced in thicker magnets. It can be confirmed that, so long as the lifting force is higher than the normal load, the friction will invariably operate in the full film lubrication and the stick-slip motion may be eliminated theoretically. [ABSTRACT FROM AUTHOR]

Aiming at the key problems such as serious friction and wear and large leakage of aviation piston pumps operating under high-speed and high-pressure harsh conditions, the lubrication characteristics of aviation plunger pumps are studied in this paper. In order to improve the lubrication performance of the plunger pump, as well as its working efficiency and service life, the equations of pressure, the thickness, and the leakage of the plunger pair oil film under the combined actions of viscosity temperature and pressure under pressure flow, shear flow, and cylinder elastic deformation are established. The finite difference method is used to analyze the lubrication characteristics and the leakage of the plunger pair under these four different conditions: considering, respectively, the effect of viscosity temperature and pressure, only considering the effect of viscosity temperature or viscosity pressure, without considering the effect of viscosity temperature and viscosity pressure. As a result, coupled by the effects of viscosity temperature and viscosity pressure, when the temperature increases from 20 to 60 °C, the oil film pressure increases, and the thickness decreases faster. When the temperature increases from 60 to 120 °C, the oil film pressure increases and the thickness decreases slower When the contact length of the plunger pair increases from 17 to 37 mm, the leakage ratio decreases more rapidly, and when it is greater than 37 mm, it decreases more slowly. The following conclusions were obtained: the viscosity of lubricating fluid is greatly affected by temperature and pressure. The viscosity decreases and increases hyperbolically with the increase in temperature and pressure, the maximum oil film pressure when considering the effect of viscosity temperature and pressure was significantly greater than that without considering the viscosity temperature and pressure, and the minimum oil film thickness was much smaller than that without considering the viscosity temperature and pressure. The leakage curve when considering the viscosity temperature and pressure effect was obviously different from when only considering a single factor or not considering the viscosity temperature and pressure effect. The magnitude of leakage in the four cases is: considering the viscosity temperature effect, considering the viscosity temperature and pressure effect, not considering the viscosity temperature and pressure effect, and considering the viscosity pressure effect. This study can provide a reference for the accurate theoretical design and safe and stable operation of the plunger pair in the plunger pump. [ABSTRACT FROM AUTHOR]

In the modeling of elastohydrodynamic lubrication problems considering mixed friction, strongly coupled dependencies occur due to piezo-viscous effects and asperities, which can make a numerical solution exceptionally difficult. A fully implicit coupled scheme for solving mixed elastohydrodynamic lubrication problems is presented. Our scheme uses finite-volume discretization and co-allocated grids for hydrodynamic pressure and elastic deformation. To provide strong coupling between pressure and deformation even in the highly loaded zone, a correction term that adds numerical diffusion is used. The resulting linear equation system of this scheme can be efficiently solved by Krylov subspace methods. This results in an improved accuracy and computational efficiency compared to the existing methods. This approach was validated and has been shown to be accurate. [ABSTRACT FROM AUTHOR]