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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]

The dynamic behavior of the pump-turbine thrust bearing is important to the safety operation of the unit. This paper analyzed the lubrication and energy dissipation mechanism of pump-turbine thrust bearing during load-rejection based on the thermo-hydrodynamic model. The results show that the variation of the axial force and the maximum pad surface pressure is basically consistent with that of the inclination of the pad surface. The change of the friction loss is consistent with the change of rotational speed, while the change of pad surface temperature is affected by the combination of pad inclination and rotational speed. The chaotic flow in the oil tank is accompanied by different forms of vortices, such as Taylor vortices, vortex pairs, and Karman vortices, and results in a significant asymmetry in the pressure distribution. The flow in the bearing pad groove has an effect on the energy dissipation in the oil film. This paper provides a theoretical basis for the design and optimization of thrust bearings, and provides a reference for solving the problems of wear, oil mist, and other related problems of thrust bearings in engineering. [ABSTRACT FROM AUTHOR]

Purpose: The purpose of this study is to design and process the optimal V-shaped microstructure for 7075 aluminum alloy and reveal its wear resistance mechanism and performance. Design/methodology/approach: The hydrodynamic pressure lubrication models of the nontextured, V-shaped, circular and square microtextures are established. The corresponding oil film pressure distributions are explored. The friction and wear experiments are conducted on a rotating device. The effects of the microstructure shapes and sizes on the wear mechanisms are investigated via the friction coefficients and surface morphologies. Findings: In comparison, the V-shaped microtexture has the largest oil film carrying capacity and the lowest friction coefficient. The wear mechanism of the V-shaped microtexture is dominated by abrasive and adhesive wear. The V-shaped microtexture has excellent wear resistance under a side length of 300 µm, an interval of 300 µm and a depth of 20 µm. Originality/value: This study is conductive to the design of wear-resistant surfaces for friction components. [ABSTRACT FROM AUTHOR]

Purpose: This paper aims to focus on the high-speed rotary lip seal in aircraft engines, combining its service parameters, its own structure and application conditions, to study the influence of different eccentric forms, eccentricity, rotational speed and other factors on the performance of the rotary lip seal. Design/methodology/approach: A numerical simulation model for high-speed eccentric rotary lip seals has been developed based on the theory of elastic hydrodynamic lubrication. This model comprehensively considers the coupling of multiple physical fields, including interface hydrodynamics, macroscopic solid mechanics and surface microscopic contact mechanics, under the operating conditions of rotary lip seals. The model takes into account eccentricity and uses the hazardous cross-sectional method to quantitatively predict sealing performance parameters, such as leakage rate and friction force. Findings: Eccentricity has a large impact on lip seal performance; lips are more susceptible to wear failure under static eccentricity and to leakage failure under dynamic eccentricity. Originality/value: This study provides a new idea for the design of rotary lip seal considering eccentricity, which is of guiding significance for the engineering application of rotary lip seal. [ABSTRACT FROM AUTHOR]

A steady plane hydrodynamic problem of lubrication of a lightly loaded contact of two parallel cylinders lubricated by a non-Newtonian fluid with Giesekus rheology is considered. The advantage of this non-Newtonian rheology is its ability to properly describe the real behavior of formulated lubricants at high and low shear stresses. The problem is solved by using a modification of the regular perturbation method with respect to the small parameter α , characterizing the degree to which the polymeric molecules of the additive to the lubricant follow the streamlines of the lubricant flow. It is assumed that the lubricant relaxation time and the value of α are of the order of the magnitude of the ratio of the characteristic gap between the contact surfaces and the contact length. The obtained analytical solution of the problem is analyzed numerically for the dependencies of the problem characteristics such as contact pressure, fluid flux, lubrication film thickness, friction force, energy loss in the lubricated contact, etc., on the problem input parameters. [ABSTRACT FROM AUTHOR]

Solid additives can effectively overcome/alleviate the deficiencies of pure liquid lubricants themselves. However, the additive morphology involved in most of the reported solid additive/liquid lubricant systems is mostly irregular. They take more into account species differences and ignore the potential advantages of the sizes of unequal particles for the purpose of superlubricity. Herein, a mixed unequal-diameter sphere additive/ionic liquid analogue (Uneq-SA/ILA) model system is designed from the perspective of asymmetric contact between unequal-diameter spheres. It can easily enter a stable macroscopic superlubricated state (coefficient of friction as low as 0.0046) with negligible wear relative to an equal-diameter sphere additive/ILA system. Such excellent lubrication performance is attributed to the synergy of asymmetric contact between unequal-diameter spheres and low-shear-viscosity ILA; the ILA adsorbed on the sphere additive makes asymmetric slip interface between the spheres mainly concentrated inside the ILA, avoiding direct point-to-surface contact between the spheres. The film thickness of 948 μm implies that unequal-diameter spheres in the ILA have a normal accumulation space during contact, and the lubrication mechanism is dominated by hydrodynamic lubrication. This study deepens the understanding of asymmetric contact function of solid additives and provides new insights for the design of next-generation solid additive/liquid superlubrication systems. [Display omitted] [ABSTRACT FROM AUTHOR]

A model hydrodynamic lubrication tribometer consisting of two hydrodynamic journal bearings working under thin film conditions was developed to investigate the mechanisms of hydrodynamic friction with low-viscosity fluids and the role of surface effects. A small nominal radial clearance of about 5 µm was considered between the two surfaces. This fully instrumented setup provides in situ information on the sheared fluid film in terms of simultaneous measurements of film thickness; localization and extension of the cavitation zone, with a resolution of 30°; nominal friction torques up to 0.5 N m, with an accuracy of 0.05 mN m; temperature; and the position of the shaft for velocities up to 12 000 rpm. To illustrate the capability of the Osiris tribometer, thin hydrodynamic film measurements were performed on smooth surfaces. The results are presented here, and the thermal effects, acceleration, and inertia contributions are discussed. Finally, the influence of the surface topography using textured surfaces was demonstrated and the role of adsorbed layers on the surface due to fluid formulation was highlighted. [ABSTRACT FROM AUTHOR]

The purpose of this paper was to understand how axial cylinder distortions influence the tribological performance of piston ring. The current model contains the effects of axial distortions and ring conformability under mixed to hydrodynamic regimes of lubrication through computational fluid dynamics predictions. The axial cylinder profiles were modelled using series of sinusoidal waves. The effect of axial distortions on ring wear rate was determined using the Archard's model. The ring friction and minimum lubricant film were predicted for low and high combustion pressures near to top dead centre. The study shows that, when the maximum combustion pressure rises, the different wear identities affect the operation of the ring friction much more limited, while the number of sine waves are more pronounced. Finally, it is proved that, even the increase of oil film thickness, it does not presuppose the reduction of friction when it comes to shaping the surface of the cylinder liner. [ABSTRACT FROM AUTHOR]

Due to the relatively low load-carrying capacity, low-viscosity lubricated bearings can easily operate in a mixed-lubrication regime. Furthermore, low lubricant viscosity may cause local turbulence in the area with relatively thick film. To analyze the influence of local turbulence on the transient characteristics of mixed-lubrication bearings, a simulation approach for unsteady mixed-lubrication bearings considering local turbulence effects is proposed. Transient journal center locations are solved via journal dynamic equations and numerical integration. The ratio of the film thickness to the roughness determines whether each node of the bearing is in the mixed-lubrication area or the pure hydrodynamic lubrication area. The liquid film in the mixed-lubrication area is analyzed by a transient average Reynolds equation to account for the surface roughness effect. A liquid film in the hydrodynamic lubrication area is analyzed by a transient generalized Reynolds equation to consider local turbulence. The transient average Reynolds equation and transient generalized Reynolds equation are derived in a form convenient for coupling with the governing equations of the journal center. The proposed model is experimentally validated. The influence of local turbulence on unsteady mixed-lubrication bearings is analyzed. The results show that local turbulence and asperity contact can coexist in low-viscosity lubricated bearings, even if the journal speed is relatively low. In the mixed-lubrication regime, local turbulence increases the minimum film thickness and decreases the friction coefficient as well as the journal speed at which the mixed-lubrication transitions to hydrodynamic lubrication. [ABSTRACT FROM AUTHOR]

Modelling hydrodynamic lubrication helps engineers and material scientists designing lubricants that minimize viscous energy losses without compromising the durability of engine components. This type of modelling requires selecting lubricant rheological constitutive equations that provide realistic information on fluid behaviour within tribological contact zones. Due to complexity of differential constitutive equations the modelling effort was limited to generalized Newtonian or Oldroyd-B fluids. In this paper, we present more realistic description of hydrodynamic lubrication using the Giesekus fluid capturing both viscous shear thinning and the development of elastic stresses at high Weissenberg numbers. The problem analysis is done using a modified regular perturbation method with respect to the small mobility parameter |$\alpha $|⁠. The perturbation analysis modification is caused by the fact that the problem contains several a priori unknown boundaries. The actual perturbation solutions for functions of pressure and gap, as well as the coordinate of exit from the contact and the exit film thickness, are obtained as linear functions of |$\alpha $|⁠. The effects of the model parameters such as the mobility factor, relaxation time and the polymer contribution to viscosity on pressure, shear and extensional viscosities within the contact zone are analysed. It is shown that the presence of polymers helps to increase the gap and reduce the viscous losses associated with hydrodynamic friction. This result is consistent with empirical observations of fuel economy enhancement for polymer-containing lubricants. [ABSTRACT FROM AUTHOR]

Purpose: The purpose of this paper is to compare the spherical protruded and dimple textured journal bearings performance characteristics with the untextured bearing. Design/methodology/approach: The governing Reynolds equation considering the mass conserving (JFO) boundary conditions is solved using the computationally efficient progressive mesh densification (PMD) method. The central difference scheme is used for the discretization of the governing Reynolds equation. The numerical code developed is validated with the experimental results available in the literature. Findings: From this numerical study, it has been observed that the protruded textured journal bearing gives better performance compared to the dimple textured and untextured journal bearing for friction variable, whereas dimple textured journal bearing provides better performance compared to the protruded textured and untextured journal bearing for load carrying capacity and flow coefficient. For better performance, dimple and protruded textured bearings must be textured in second-half textured region configuration. Practical implications: The results shown here would be quite useful for the researchers generally and the bearing designers particularly. Originality/value: The load carrying capacity should be maximum whereas, the friction coefficient should be minimum and also the adequate flow of lubricant is necessary to maintain hydrodynamic lubrication and to remove the heat generated within the bearing due to friction, which impacts the bearing performance and life. Thus, this study would be significant in effective bearing design aspect. [ABSTRACT FROM AUTHOR]

Friction has been a significant research concern for decades. Most of the energy input into an internal combustion (IC) engine is wasted because it is used to overcome friction. Scientific developments have been made to reduce friction, including surface coatings and surface textures, which have emerged as potential solutions to reducing friction throughout the lubricating regimes. This study combines surface texturing with the coating approach to investigate the frictional response. Realistic tribo-dynamics (secondary motion of the piston skirt) are considered during actual engine-like conditions to explore the effects of pattern-based coating on friction in hydrodynamic lubrication. Results show a remarkable reduction in friction and encourage the pattern-based development of surface coatings to extend the benefit across lubricating regimes. Consequently, the surface coated with optimized patterns had 7.98 ± 0.34 % reduced energy loss per engine cycle as compared with the surface coated without a pattern. [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]

• A novel simulation method is proposed to identify the causes of lubrication failure in high-speed coolant pumps for electric vehicles. • Experimental validation confirms the accuracy of simulations for both the pump and bearing. • The steady radial forces of the pump rotor are effectively balanced by the bearing load capacity. • The rotor–stator interaction results in unsteady radial forces, inducing substantial whirl in the bearing. • The bearing whirl reduces lubricant film pressure gradient and load capacity, ultimately leading to lubrication failure. The high-speed coolant pump is essential for electric vehicle thermal management, ensuring optimal module temperatures. The pump impeller and bearing are combined into a rotor and then fit on a fixed shaft with a clearance, aiming to generate a complete lubricant film between the stationary journal and rotating bearing during pump operations. However, during the pump durability test under off-design conditions, severe wear occurred on both the journal and bearing. A novel simulation method based on computational fluid dynamics and dynamic mesh is developed to investigate the lubrication failure. User-defined functions are programmed to articulate the simultaneous rotation and whirl of the bearing, and the effects of temperature and cavitation are considered. Both the pump and bearing simulations closely align with experimental results. When the radial force of the pump rotor is steady, the bearing only rotates without whirling, and the bearing load capacity can counteract the maximum radial force of the rotor. However, the rotor experiences fluctuating radial forces over time, primarily attributed to elevated pressure levels at the volute tongue caused by the rotor–stator interaction. This phenomenon results in the bearing to rotate and whirl simultaneously. The load capacity generated by the backward whirl of the bearing is greater than that of the forward whirl. Nevertheless, the bearing whirl initiates a decline in the extremum values of lubricant film pressure. Subsequently, both load capacity and minimum film thickness exhibit a continuous decrease, eventually culminating in the breakdown of the complete lubricant film and resulting in contact wear failure. These new findings contribute to proposing measures to reduce wear under unsteady excitations. [ABSTRACT FROM AUTHOR]

A comprehensive numerical model was proposed to investigate the disengaging process of a wet multi-disc clutch, which included the hydrodynamic lubrication, the micro elastic-plastic contact, the spline resistance, and the impact between the piston and clutch hub. The clutch disengaging process was divided into the boundary, mixed, and hydrodynamic lubrication stages to discuss the variations in friction pair gaps and friction torque. Moreover, the nonuniformity coefficient was employed to characterize the disengaging uniformity of friction pair gaps. During the disengaging process, the friction pair gaps increased slowly, increased rapidly, and stabilized after fluctuating. The increase in spline friction coefficient and the decline in pressure decrease rate dramatically deteriorated the disengaging uniformity; the decline in pressure decrease rate also significantly prolonged the disengaging time. This research demonstrated for the first time evidence for the dynamic characteristics of the clutch disengaging process. [ABSTRACT FROM AUTHOR]

Water-lubricated stern bearing (WSB) is a vital part of the ship propulsion-shaft system, and it is of great significance to monitor and analyze its lubrication status through film thickness data to improve the equipment operational reliability. In this paper, a full-size, large length-to-diameter ratio WSB experiment is carried out, and multi-sectional journal displacement data are collected under offset load. Accordingly, a bearing film-thickness identification model is established, which can identify the dynamic film thickness data in the circumferential direction of bearing section by limited measurement points. On this basis, the film thickness distribution of the full bearing is obtained by combining finite element (FE) simulation and particle swarm optimization (PSO) algorithm. The effect of different speeds on the distributed lubrication characteristics of WSB under offset load was systematically analyzed based on film thickness data. Results show that the maximum identification error of the bearing film-thickness identification model is less than 7%. The bearing lubrication state changes dynamically as the speed increases, and the hydrodynamic lubrication effect in the middle of the bearing is enhanced. The area of each lubrication sub-region varies nonlinearly. Research results are instructive for further determine the service life of the shaft system. [ABSTRACT FROM AUTHOR]

In this paper, External Gear Machine (EGM) torque losses arising from friction at lubricating interfaces are modeled by considering mixed lubrication conditions. A novel contribution of this paper is to consider mixed elastohydrodynamic lubrication contact conditions along with the effect of gear flank surface roughness to determine the meshing losses, which are also the major contributors towards the EGM torque loss. These hydromechanical loss models are integrated in a multibody, multi-physics simulation tool Multics-HYGESim developed at the authors' research center. Experimental activity is performed on two EGM units using different surface finish for gears. Simulated hydromechanical efficiencies match the experimental trends with average deviation of 2.5%. Most importantly, the results capture effects of different gear flank roughness on the torque efficiency. An average increase of 0.9% in the efficiency value is predicted by the simulation model for the EGM with lower teeth roughness, as compared to 1.1% rise obtained via experiments. The proposed torque loss evaluation methodology shows high potential in assisting designers and manufacturers of EGMs to choose the suitable surface finishing for achieving desired hydromechanical performance. • Torque efficiency of external gear machines has been determined via simulation. • Mixed Elasto hydrodynamic lubrication model is used to evaluate meshing frictional loss. • Experimental tests show rise in torque efficiency for lower gear surface roughness. • Computational analysis of lubricating interfaces predicts leakage and friction loss. • Proposed model exhibits potential for virtual prototyping of new gear pump designs. [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]

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]

Investigation of Oil Film Thickness (OFT) in balanced vane pumps is particularly relevant as they could experiment both loss of contact and elasto-hydrodynamic lubrication condition of the vane tip, detrimental to Noise-Vibration-Harshness behaviour and durability, respectively. Accordingly, this paper proposes an experimental method for measuring the OFT between the vane tip and stator by means of capacitive sensors. The transducer is housed in the cam ring of a prototypical pump for automatic transmissions and the OFT is acquired in different positions of the pump cycle at different operating conditions. The steps followed to modify the pump parts to house the sensor are reported. Moreover, the dedicated test bench and experimental procedure are described. An original post-processing procedure is proposed to obtain the OFT quantity. Finally, attention is devoted to the influence of the lubricant dielectric constant variation, due to the wear of components, showing its great influence on the results. • Oil Film Thickness (OFT) measurement by means of capacitive sensors. • The capacitive sensor has been housed in different positions of the pump stator. • Description of the steps followed to modify the components for the sensors housing. • Definition of an ad-hoc post-processing procedure to obtain the OFT quantity. • Study of the influence of the dielectric constant of the lubricant on the results. [ABSTRACT FROM AUTHOR]

The current research examines how a long cylinder, and an infinitely flat surface are affected by surface roughness, MHD, couple stress, and slip velocity using the stochastic theory of hydrodynamic lubrication of rough surfaces as developed by Christensen. Squeeze film time, load carrying capacity, and pressure are calculated using a derived mathematical form of Reynolds' modified equation that accounts for surface roughness and coupling stress. The amount of time needed to squeeze a film under a specific pressure and load can be determined using an analytical method called Reynolds' equation. The lubrication characteristics are graphically represented for various parameters. When a magnetic field occurs and the slip velocity increases, the pressure of the squeeze film, its capacity to carry loads, and the time it takes are all significantly increased. The lubricating properties caused a decrease or increase in the values of the longitudinal (transverse) roughness parameter. [ABSTRACT FROM AUTHOR]

The contact properties of gear rough surfaces during meshing are influenced by various factors. The analysis of rough surface thermoelastoplastic hydrodynamic lubrication (TPEHL) considering micro-scale effect and thermal effect has not been addressed in the literature. This study establishes a new TEPHL model with multi-factor coupling of thermal field, fluid lubrication, stress-strain, and geometric profile. Based on strain gradient theory (SG), a new thermoelastoplastic material constitutive considering micro-scale effect is developed. Subsequently, the three-dimensional rough surface TPEHL-SG analysis of gear is conducted. The paper investigates the impact of thermal and micro-scale effects on various parameters during the meshing of gear in the full oil film lubrication condition, including surface pressure, oil film thickness, surface temperature, surface deformation, and friction coefficient. [ABSTRACT FROM AUTHOR]

Bio-inspired surface microtexture has been adopted in mechanical systems for its advanced lubrication performance. In this study, we discerned the aerodynamic characteristics of different parts of the peregrine falcon's wing, summarized the influence of its distinctive shape on the fluid flow, and, based on simplified geometries and the bionic concept, designed a novel wing-shaped microtexture to enhance lubrication performance in friction pairs. Its shape was simplified by the following parameters: area ratio S p , dimensionless depth h *, and orientation angle α. Using a multiphase flow model, we investigated the effect of the above geometrical parameters on the lubrication performance of the wing-shaped microtexture by numerical simulation. The corresponding geometrical parameters of the wing-shaped microtexture to achieve optimum lubrication performance were: S p = 30%/ h *=1.75/ α = 0°. The wing-shaped microtexture's friction coefficient(COF) corresponded to a reduction of 18.8% and 20.7%, respectively, compared to the triangle and rectangular microtexture, which had the best lubrication performance for existing applications. The results showed that the wing-shaped microtexture enhanced the lubrication performance for three reasons: 1. The biomimetic leading edge created more negative pressure and cavitation zones; 2. The interference between positive and negative pressure zones was effectively mitigated; 3. The sharp design of the biomimetic trailing edge and tail wing concentrated the positive pressure zone while increasing its area. Two double-layer composite wing-shaped microtextures were further introduced to maximize friction reduction. The impact of inner-outer layer area ratio S p * and inner-outer depth ratio h * on the lubrication performance was investigated. Their simulation results revealed that the optimal geometric parameters for the composite microtextures were S p *=6.3%/ hp *=3.0 and S p *=12.7%/ hp *=2.0, respectively. The configurations led to additional COF reductions of 7.6% and 10.56% compared to the single-layer wing-shaped microtexture. These insights offer valuable guidance for reducing friction and wear in mechanical systems. • A novel bio-inspired peregrine falcon wing-shaped microtexture was designed, reaching an effective friction reduction. • Compared to the triangular and rectangular microtextures, the COF decreased by 18.8% and 20.7%, respectively. • The lubrication performance of the double-layer composite microtextures were further promoted compared to the single-layer. [ABSTRACT FROM AUTHOR]

A ship's propulsion system has a significant impact on the ship's energy efficiency, environmental friendliness, reliability and safety. An indispensable part of a propulsion system with mechanical power transmission is a stern tube with bearings. During operation, the sliding bearings material is subjected to stresses caused by a force proportional to the total mass of the shaft and propeller. The reliability of stern tube bearings is particulary important for safety, and their durability has a significant impact on maintenance costs. Depending on the lubricant, there are bearings that are lubricated with oil or water. The permissible bearing load with hydrodynamic lubrication depends primarily on the material, the viscosity of the lubricant used and the shaft speed. Metals and their alloys with a low coefficient of friction are used for oil-lubricated bearings. Bearings lubricated with water are made of a special type of hardwood ("tree of life", lat. lignum vitae), rubber or various synthetic materials. The main advantages of oil-lubricated bearings are higher allowable load and durability than water-lubricated bearings. This paper analyses the technical and environmental aspects of the application of waterlubricated bearings whose main advantages are simplicity, better cooling and environmental protection. [ABSTRACT FROM AUTHOR]

Lubricated contact performance can be improved by using a textured surface as well as a hydrophobic surface. A procedure to obtain the optimal partially textured journal bearing combined with the hydrophobic coating is presented through the computational fluid dynamics (CFD) codes. In this study, lubricated hydrophobic textured contacts with and without cavitation modeling are discussed. The cavitation phenomena in the lubricant is modeled using a multiphase model of “mixture” to obtain a realistic condition. The effect of dimple depth, as well as the eccentricity ratio, on the tribological performance, is of particular interest. It is found that the tribological performance is greatly influenced by the multiphase flow cavitation scheme. When cavitation modeling is taken into account, higher load support is noted. Furthermore, the simulation results show that a hydrophobic textured surface with a shallow depth (d/hmin<1) seems to be better for enhancing the tribological performance. Meanwhile, for the case of the low eccentricity ratio, there is an optimal dimple depth giving the highest load support. The findings explored in this work can be considered as a theoretical basis to increase the performance of hydrophobic textured journal bearing. [ABSTRACT FROM AUTHOR]

There exists a huge volume of studies of hydrodynamic and elastohydrodynamic lubrication problems for lubricants with Newtonian rheology. Lubricants with Newtonian rheology do not exhibit the usually observed experimentally behavior of having relatively high viscosity for low stresses and relatively low viscosity for high stresses. In this paper we extend the earlier conducted analysis of lubricants with a non-Newtonian Giesekus behavior for the case of thrust bearing modeling. The main goal of the paper is to obtain an analytical solution for a hydrodynamically thrust bearing lubricated by a fluid with the Giesekus rheology. This goal is achieved by careful application of perturbation methods. A three-term approximate analytical solution is obtained and its dependence on the problem input parameters is analyzed. [ABSTRACT FROM AUTHOR]

Journal and thrust bearings utilise hydrodynamic lubrication to reduce friction and wear between the shaft and the bearing. The process to determine the lubricant film thickness or the actual applied load is vital to ensure proper and trouble-free operation. However, taking accurate measurements of the oil film thickness or load in bearings of operating engines is very difficult and requires specialised equipment and extensive experience. In the present work, the performance parameters of journal bearings of the same principal dimensions are measured experimentally, aiming at training a Machine Learning (ML) algorithm capable of predicting the loading condition of any similar bearing. To this end, an experimental procedure using the Bently Nevada Rotor Kit 4 is set up, combined with sound and vibration measurements in the vicinity of the journal bearing structure. First, sound and acceleration measurements for different values of bearing load and rotational speed are collected and post-processed utilising 1/3 octave band analysis techniques, for parametrisation of the input datasets of the ML algorithms. Next, several ML algorithms are trained and tested. Comparison of the results produced by each algorithm determines the fittest one for each application. The results of this work demonstrate that, in a laboratory environment, the operational parameters of journal bearings can be efficiently identified utilising non-intrusive sound and vibration measurements. The presented approach may substantially improve bearing condition identification and monitoring, which is an imperative step to prevent journal bearing failures and conduct condition-based maintenance. [ABSTRACT FROM AUTHOR]

The cylinder liner-piston ring is one of the most significant friction pairs in diesel engines. This study aims to explore the effects of fuel diluting low-viscosity oil on the lubrication property. Taking a farm diesel engine as the research object, the typical wall wetting was utilized to clarify the variation in the lubricant viscosity of diluting oil. The results indicated that the lubricant viscosity first dropped rapidly, and then remained stable, as the diluting ratio increased. Specifically, the lubricant viscosity dramatically declined by 44.9%, when the diluting ratio of oil rose from 0 to 10%, whereas, the dynamic viscosity decreased by 38.8% when the diluting ratio of oil was continuously elevated from 10% to 30%. It infers that there was a great effect of a little fuel diluting in the lubricating oil on the lubricant viscosity, while this effect became weaker than before when the diluting ratio reached a critical value. A mixed lubrication model was then built to investigate the tribological properties of the cylinder liner-piston ring, where the percentage of fuel diluting lubricant was changing. The simulated data showed that the minimum thickness ratio of fuel film decreased significantly, as the diluting ratio rose, indicating that the specific thickness of fuel film decreased between the cylinder liner-piston rings in a diesel engine. The area of hydrodynamic lubrication also decreased on the friction pair of the cylinder liner-piston rings, while the mixed lubrication area expanded with the increase of the fuel dilution ratio. Furthermore, the thickness of the oil film was too thin between the friction pair of cylinder liner and piston rings, especially at the diluting ratio of 30%. It was found that the whole process was in a mixed lubrication state, where the fuel lubrication was not enough. The hydrodynamic lubrication was therefore dominated by the mixed lubrication between cylinder liner and piston ring when the external load of the piston ring was relatively small. Even if the viscosity of lubricant was very low, a certain thickness of the oil film was also enough to bear the external load. Correspondingly, the external load of the piston ring was extremely large, while the oil film thickness was very thin in the compression stroke and expansion stroke. The mixed lubrication between cylinder liner and piston ring was dominant in the whole process, where the pressure of the oil film cannot fully bear the external load eventually. Additionally, the area of mixed lubrication was extended to the threshold, as the region of hydrodynamic lubrication shrank constantly, where the film pressure declined, while the asperity friction force increased significantly. Therefore, the average asperity pressure increased in turn to nearly double times at a 30% diluting ratio, compared with that without dilution. As such, the probability and pressure of direct contact surface were higher between the cylinder liner-piston rings near the top dead center of reciprocating stroke, when much more diesel fuel was mixed in the lubricating oil. In this case, there was a negative impact on the surface wear of friction pair with the growing diluting ratio. The asperity friction force increased in turn to a large friction, as the dilution ratio increased from 0 to 30%, indicating there was a significant effect on the total friction of cylinder liner and piston ring. The viscosity decreased gradually with the increase of diluting ratio, which made the fluid friction decrease. The asperity pressure also contributed to the asperity friction, thereby to the total friction. In addition, the cycle friction loss on the ring/liner pair decreased at first and then increased, finally reached the lowest point at a 10% diluting ratio. An engine test bench was built to carry out the motored friction test. The testing data verified that the variations of motored torque were consistent with the simulated ones under different diluting ratios. Consequently, potential guidance was that the diluting ratio should be controlled under 20% to keep the lubrication effects in the application of low-viscosity lubricating oil. [ABSTRACT FROM AUTHOR]

Purpose: The purpose of this study is to investigate the influence of dimple radius, depth and density on the lubrication performance of the plunger. Design/methodology/approach: A lubrication model was adopted to consider eccentricity and deformation during the working process of the plunger, and a rig test was performed to confirm the simulation results. The texture was fabricated using laser surface texturing. Findings: The simulation results suggested that when dimple radius or depth increases, oil film thickness of the plunger increases before decreasing, and asperity friction displays an opposite trend. Therefore, appropriate microdimple texture could facilitate lubrication performance improvement and reduce the wear. Microdimples were then lased on the plunger surface, and a basic tribological test was conducted to validate the simulation results. The experimental results suggested that the average friction coefficient decreased from 0.18 to 0.13, a reduction of 27.8%. Social implications: The introduction of microdimple on a plunger couple to reduce friction and improve lubrication is expected to provide a new approach to developing high-performance plunger couple and improve the performance of the internal combustion engine. If applied, the surface texture could help reduce friction by around 27% and cap the cost relative to the plugger friction. Originality/value: The microdimple texture was introduced into the plunger couple of a vehicle to reduce the friction and improve the performance. Findings suggested that surface texture could be used in the automotive industry to improve oil efficiency and lubrication performance. Peer review: The peer review history for this article is available at: http://dx.doi.org/10.1108/ILT-07-2020-0259. [ABSTRACT FROM AUTHOR]

Elliptical bearing is characterized by low induced temperature and high stability at higher speed in comparison with the cylindrical journal bearing. The performance of such bearings can be affected by the type of oil used and its surface properties. The main goal of this work is to study the surface micro protrusion effect on the steady state operation of elliptical journal bearing lubricated with couple stress lubricant. The modified Reynolds' equation to take into account the effects of couple stress lubricant and micro protrusions of the bearing surfaces is solved using finite difference method. The governing equations were solved using a prepared FORTRAN computer program. Pressure distribution, load carrying capacity and coefficient of friction have been studied for a bearing in laminar flow regime. The mathematical model was validated by comparing pressure results for the elliptical bearing of the present work with that obtained by Hussain et al.(1996). The obtained results demonstrate that the lubricant pressure and the load carried by the bearing decrease for the bearing with higher ellipticity factor while the load carried by the bearing increases for the bearing with higher protrusions or when using a couple stress fluid with higher couple stress variable. [ABSTRACT FROM AUTHOR]

A type of compound texture combining micro‐dimple and variable‐depth groove was designed to improve sealing performance and reduce wear of the plunger couple in diesel engine. The simulation results indicate that moderate oil film thickness can be produced by compound texture to settle the lack of lubrication of groove mode. Meanwhile, higher hydrodynamic pressure is produced to improve sealing performance of a plunger couple, tackling the problem of relatively high leakage of micro‐dimple mode. The compound texture was fabricated on the plunger surface by laser surface texturing (LST) and the test results confirmed the improvement of lubrication and sealing performance. The basic tribological test result shows that that the deepest wear depth and average roughness were reduced by 72.4% and 22.6%, respectively. Meanwhile, the engine bench test result shows that the amount of fuel leakage was reduced by 73.1% as well. [ABSTRACT FROM AUTHOR]

In this research, a three-dimensional model is proposed to simulate the behavior of particle-covered droplets that contain soluble surfactant. The model includes a full two-way coupling between surfactant transport and particle motion, with surfactant concentrations at the interface and in the bulk linked to the flow and motion of the interface by a convection-diffusion equation. A front-tracking method is used to track the interfacial flow, while a semi-resolved particle method is used to model the particles, accounting for various forces acting on them, such as the excluded volume force, the direct contact force and the hydrodynamic lubrication force. The model also includes a surfactant-dependent surface tension that can affect the particle-interface interactions. The model is validated against previous numerical data and a parametric study is performed to examine the delicate interplay between flow fields and interfaces associated with surfactant concentration and particle motion. The study then investigates the role of surfactants in the dynamics of a particle-covered droplet, focusing on their coupled influence on droplet deformation. In addition, it is observed that particles bridge colliding droplet interfaces and suppress fluid drainage from the gap, preventing droplet coalescence along with the interparticle repulsion force. • A front-tracking/semi-resolved Lagrangian particle method is developed. • Particle and surfactant are bidirectionally coupled to two-phase flows solver. • Convergence and performance of method is validated with benchmarks. • Particle-surfactant interactions on interfacial deformation is presented. • Interparticle interactions delay coalescence of two particle-covered droplets. [ABSTRACT FROM AUTHOR]

To reveal the thermal-fluid-structure interaction characteristics of water-lubricated slipper/swash plate interface, a transient mixed thermoelstohydrodynamic (MTEHD) lubrication model incorporating asperity contact, elastic deformation, heat transfer and viscosity temperature effect is originally presented. The change in fluid properties caused by cavitation is considered for solution the piston chamber pressure. Distributions of pressure, temperature, deformation and tilting state of slipper simulated by MTEHD show strong reasonableness. Effect of operating and structural parameters on energy consumption characteristics calculated by MTEHD and hydrodynamic lubrication is contrastively analyzed. The results show that energy consumption is different in delivery and suction stroke due to different degrees of MTEHD effects and transient contact. Besides, the optimal dimension for the width of studied sealing surface is determined. [Display omitted] • A TFSI model for water hydraulic slipper/swash plate interface is originally presented. • Lumped parameter method for flow properties is coupled with MTEHD lubrication model. • Transient MTEHD lubrication behavior is obtained. • Effects of working and structural parameters on energy loss characteristics are investigated. [ABSTRACT FROM AUTHOR]

This study experimentally investigates the influence of cavitation effect caused by surface texture on the lubrication performance of friction pairs. In order to verify and research the cavitation phenomenon induced by surface texture, cavitation images are collected by visual experimental apparatus. The results show that the surface texture will induce the cavitation of the lubricating oil under certain speed and load conditions, gas bubbles will be generated at the outlet of the dimples, and the cavitation will affect the lubrication performance of the friction pair. When the texture depth is close to the oil film thickness, it has the best effect in terms of inducing cavitation and promoting lubrication. And it is found in the experiments when area density of texture is 8% and the square dimples are arranged at inlet area of the sample, the best effect of the surface texture can be obtained. [ABSTRACT FROM AUTHOR]

Purpose: After more than a century of agreement with the postulate of non-slip condition (adhesion to the wall), the study of fluid-solid boundary conditions has shown renewed interest over the past two decades. Although numerous studies have not yet been arrived to a complete description of slip phenomena, however, it appears that the influence of wetting and/or surface roughness results in a weak interaction between fluid and solid; thus, the presence of the slip phenomenon is observed at the fluid-solid interface. The purpose of this paper is to highlight the presence of the slip phenomenon at the lubricated piston skirt-cylinder contact. Design/methodology/approach: For this proposal, a modified Reynolds equation and operating characteristics are determined by taking into account the slip conditions at the interface between oil-film and entire cylinder surface. Findings: The findings indicate that the operating characteristics are strongly influenced when the slip conditions are taken into account at the interface between oil-film and cylinder surface. The friction force and dissipated power might be reduced to improve diesel engine performances. Originality/value: Various research studies have been conducted to model the slip phenomenon in different lubricated contacts over the past two decades. However, there are no studies available concerning the piston-cylinder system. Peer review: The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-11-2019-0483/ [ABSTRACT FROM AUTHOR]

The oil consumption in an internal combustion engine is an important source of pollution and particulate emissions, main efforts are done by the manufacturers to reduce to the maximum the impact of the oil consumption on the emissions of the engine, and to satisfy the increasingly rigorous standards of pollution. The losses by friction due to piston ring friction explain 20% of the total mechanical losses in internal combustion engines. A reduction in piston ring friction would therefore result in higher efficiency, lower fuel consumption and reduced emissions. The goal of this study is to develop a numerical method by using of GT-Suite software to analyze the influence of engine speed and engine load during the working cycle on oil film thickness, frictional force, power losses. Our predicted results were validated with the experimental data of a previous study, and they have shown a good agreement. The results in the current analysis demonstrated that the engine speed and load have a remarkable effect on oil film thickness, friction force and friction power losses between the top ring and cylinder liner. So, it would help in reducing friction as well as making a contribution towards the improvement of engine performance such as torque, efficiency and fuel consumption. [ABSTRACT FROM AUTHOR]

Purpose: This study aims to uncover the influencing mechanism of the tilt angles of the cage pocket walls of the high-speed cylindrical roller bearing on the bearing skidding. Design/methodology/approach: A novel cylindrical roller bearing with the beveled cage pockets was proposed. Using the Hertz contact theory and the elastohydrodynamic and hydrodynamic lubrication formulas, the contact models of the bearing were built. Using the multibody kinematics and the Newton–Euler dynamics theory, a dynamics model of the bearing was established. Using the Runge–Kutta integration method, the dynamics simulations and analysis of the bearing were performed. Findings: The simulation results show that the effects of the tilt angles of the front and rear walls of the pocket on the bearing skidding are remarkable. Under a 5° tilt angle of the front wall of the pocket and a 10° tilt angle of the rear wall, the bearing skidding can be effectively decreased in the rotational speed range of 10,000-70,000 r/min. Originality/value: In this paper, a novel cylindrical roller bearing with the beveled cage pockets was proposed; a dynamics model of the bearing was established; the influence mechanism of the tilt angles of the front and rear walls of the pocket on the bearing skidding was investigated, which can provide fundamental theory basis for optimizing the pocket. Peer review: The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-01-2020-0035/ [ABSTRACT FROM AUTHOR]

To make a deep investigation into the lubrication characteristics of the liquid metal film (LMF), the existing 2-D hydrodynamic lubrication models cannot meet the requirement as it fails to describe the flow of the liquid film at the transverse direction. This article makes the first step toward a 3-D model of the LMF at the armature/rail (A/R) interface. A 2-D Reynolds equation is derived considering the self-acceleration of the film and the Lorentz force acting on it. By coupling the electromagnetic fields, stress, and fluid fields, a magneto-elastohydrodynamic model is established completely. Based on this, the distribution characteristics of the LMF are explored which includes the distribution of the film thickness, hydrodynamic pressure, and fluid velocity. Besides, the dynamic characteristics of the LMF in the launch process are analyzed. The results show that: 1) the LMF is trapped in an arching gap in the transverse direction. The liquid pressure is symmetrically distributed along the centerline. In addition, the positive transverse fluid velocity indicates the jetting of the molten metal which may do damage to the bore. 2) At the current down-slope, the film thickness and liquid pressure both decrease rapidly which may put the film at risk of break. This article can provide a reference to the modeling of LMF hydrodynamic lubrication and help to understand the flow behavior of the liquid film. [ABSTRACT FROM AUTHOR]

The dynamic rolling force model in the coexistence regime of boundary lubrication friction and hydrodynamic lubrication friction was established in this paper, mainly aiming at the common mixed lubrication friction state in the actual rolling process, while the research of rolling mixed lubrication is relatively few. Combining Karman differential equation of unit pressure with Celikoff equation, a linearized differential equation of unit pressure was obtained. The expression of total friction stress under mixed lubrication state was given according to the oil film thickness at any position in the working area and the surface real contact area ratio. It is characterized by the consideration of the mixed lubrication friction state of the coexistence of boundary lubrication and hydrodynamic lubrication, which is applicable to the whole deformation zone and the general rolling mixed lubrication friction regime. The expressions of the unit normal pressure in the front-slip zone and the backward slip zone were obtained by considering the boundary conditions at the entry and exit cross sections. The dynamic rolling force model of cold rolling strip was established by numerical integral calculation. It is based on the above expression of total friction stress; therefore, this dynamic rolling force model is more universal, the prediction accuracy is higher, and it is closer to the actual industrial production. Based on the dynamic rolling force model, the effects of friction coefficient, reduction ratio, shear strength, and roll flattening on the unit normal pressure along the contact arc and the rolling force was also analyzed in this paper. Verification with actual industrial production data showed that the prediction model of rolling force had high precision, and it could provide guidance for calibration of rolling mill equipment and parameter optimization of production technology. [ABSTRACT FROM AUTHOR]

Purpose: This paper aims to study the frictional performance of reciprocating pair with high velocity by using hydrodynamic lubrication principle and fish scale textured piston model. Design/methodology/approach: Based on the idea of function characteristic approximation and coordinate change, a mathematical representation model of imitating fish scale texture pit section is established. According to the principle of dynamic pressure lubrication of the textured fluid, a three-dimensional numerical model of flow field for fish scale texture is established without considering cavitation. Numerical analysis of the model carp scale texture unit by orthogonal experimental design and FLUENT software is carried out. Findings: Effects of fish scale pit texture on friction properties for a reciprocating pair piston surface with high velocity (impact piston) are acquired. Effects of texture characterization parameters and flow rate on the surface friction performance for impact piston are found. Effects of different characteristic parameters combination of imitating fish scale texture on friction performance for impact piston surface are obtained. Originality/value: The model is an effective tool to study the friction and wear of reciprocating pair with high velocity. The effects of fish scale textured piston pair supply a theory lead to design the reciprocating pair with better friction performance. Peer review: The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-09-2019-0398 [ABSTRACT FROM AUTHOR]

Purpose: The purpose of this paper was to study the hydrodynamic lubrication of rough bilayer porous bearing to reveal the effect of percolation. Design/methodology/approach: The seepage lubrication model of the circular bilayer porous bearing was established in polar coordinates. The digital filtering technique and Darcy's law were used to simulate the rough surface and the percolation characteristic of the oil bearing, respectively. The influence of the structural parameters on the lubrication performance was analyzed. Findings: Compared with the ordinary monolayer oil bearing with high porosity, the bilayer bearing can reduce the whole porosity, prevent oil infiltrating into the porous medium and have better lubrication performance. The lubrication performance of bilayer oil bearing is better than that of the single-layer oil bearing which has a higher porosity. With increasing root-mean-square roughness or decreasing surface porosity, the lubrication performance of the bilayer bearing improves. The lower the porosity of the surface layer, the better the lubrication performance. Originality/value: This research provides a theoretical basis for clarifying the lubrication mechanism and influence the mechanism of the bilayer oil bearing. [ABSTRACT FROM AUTHOR]

Journal bearings are the most commonly used load elements in rotating systems and have a long history in tribology research. However, the relatively new surface modification technique of femtosecond laser texturing has rarely been used to increase the efficiency of journal bearings. We used a 300-fs laser to create chevron-shaped microstructures in different circumferential texture locations on half-bearing shells to investigate the effect of partial texturing on the tribological performance of journal bearings. With a customized shaft-bearing shell setup, the coefficient of friction and lubrication film thickness was tracked in two load scenarios at varying rotational speeds. In fully film conditions, the findings demonstrate that textures in the high-load region of journal bearings provide the highest lubricant film thickness and lowest friction compared to textures in the pressure build-up, divergent zone, and unstructured reference. Moreover, surface textures in the high-load area also perform better in boundary and mixed lubrication. Experimental data have also shown that asymmetric texture designs have a detrimental effect on lubrication performance. In contrast to symmetric designs, the lubrication film build-up is hindered. The research results represent a step toward transferring laboratory findings on laser surface texturing for tribological optimization in real applications. [Display omitted] • Textures in the high-load region provide the highest lubricant film thickness and lowest friction in hydrodynamic lubrication. • Textures in the high-load area also perform better in boundary and mixed lubrication. • Asymmetric texture designs can be detrimental for the lubrication performance of journal bearings. [ABSTRACT FROM AUTHOR]

Modifying the surface of materials through texturing and coating can have a significant impact on their tribological properties. In the present study, a hybrid surface modification process, texturing combined with coating, has been applied to a steel surface and the tribological behavior in lubricated conditions was studied. The surface of the steel was textured using micro-electric discharge machining (micro-EDM) to create two distinct patterns (rectangular and circular). Following this, transition metal dichalcogenides (TMD); tungsten-sulphur‑carbon (WSC) coating was applied to the surface using magnetron sputtering. To evaluate the specimens, they were subjected to tribological testing in various lubrication conditions using a block-on-ring configuration. The results were corroborated using a reciprocating sliding test and compared to those of a smooth uncoated specimen. The findings revealed that the tribological properties of the textured and coated specimens were enhanced, particularly in specimens with circular dimple patterns. The WSC coated circular dimple specimens showed a reduction of the COF by 7–12 %, in the boundary lubrication regime and by 9–25 %, in the mixed and hydrodynamic lubrication regimes as compared to the untreated specimen. • M2 substrate was modified by EDM texturing and WSC coating originating a hybrid surface. • Two hybrid surfaces were produced, one with rectangles and another with circles. • Two different contact conditions: block-on-ring and pin-on-disc showed the same trend in friction. • Synergic effect of texturing plus coating compared with smooth and uncoated specimens was obtained. [ABSTRACT FROM AUTHOR]

Abstract We present an experimental study into the impact of surface texturing on crank shaft bearing friction. This was achieved by applying a series of laser-etched patterns to the surface of shell components and comparing friction measurements - obtained using a journal bearing test rig - to those of a non-texture reference. Tests were performed under a range of applied loads, speeds and lubricant viscosities in order to simulate the operating conditions encountered in an engine. Three texture configurations were assessed with varying dimple density and area coverage. The lubricant film temperature was also measured in order to remove shear heating effects and deduce accurate friction values. The bearing shell with a texture pattern applied to the whole of its circumference showed substantial reduction in friction (approximately 18%) when compared with the non-textured reference. This reduction in friction increases as the film thickness increases (i.e.: moving right on the Stribeck curve) and is most pronounced under full film hydrodynamic conditions. Friction reductions of up to 13% were observed using bearing shells that were only textured outside the loaded region. This is attributed to a reduction in shear rate due to an increased gap without alteration of the pressure generation and is important since this texture configuration maintains its effectiveness, even after the heavily loaded region becomes worn. These reported hydrodynamic friction reductions have practical implications for automotive bearings. Highlights • Friction was measured on a Journal Bearing Machine over a range of speeds and temperatures for a set of textured shells. • Substantial reduction in friction (c. 18%) can be achieved by texturing the entire shell circumference. • The importance of continuously accounting for thermal response in journal bearings was greatly emphasized. • All texture patterns reduce friction in the hydrodynamic regime – the regime where journal bearings typically operate. • Results contrast research on piston-liner contacts which show texture reduces friction only under mixed/boundary conditions. [ABSTRACT FROM AUTHOR]