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ABSTRACT 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]

A simple numerical approach is developed to predict the wear and friction of piston ring pack and cylinder liner during the break-in period and under transient speed conditions. In the model, a solution of mixed lubrications using the load-shearing concept is presented based on the selected elastic-plastic equations of asperity contacts in conjunction with well-established elastohydrodynamic equations. The model takes shear-thinning, thermal effects in elastohydrodynamic lubrication (EHL) and lubricant starvation effects into account. Modified Archard's wear coefficient to describe the piston ring against cylinder liner wear is introduced. The approach is valid for the calculations of the asperity pressure at low values of the ratio of oil film thickness to combined roughness of the interacting surfaces, that is, less than 0.5. Applications are discussed, including association of piston side thrust force on wear and friction characteristics of piston ring/cylinder bore, gas blowby through the ring pack on the cylinder liner wear, a strong coating dependence for the piston ring wear, and wear distribution across the stroke under engine operating conditions. A good agreement between the experimental and analytical data indicates that the proposed model can be used to predict the wear and friction of the piston ring pack sliding against cylinder liner. [ABSTRACT FROM AUTHOR]

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Friction and wear are the main failure sources of face seals. When the surfaces of sealing rings exhibit greater roughness, the level of friction might increase and lead to sealing failure. Therefore, in this paper, based on the elastic contact hypothesis of rough and wavy surfaces and the influence of temperature on the elastic modulus of materials, a thermoelastic contact lubrication model of a gas-lubricated end seal is established. The novelty and advantage of this study is that it takes the effect of surface roughness into consideration during thermoelastic analysis of gas-lubricated seals. The film pressure, temperature, contact force and deformation of a gas spiral groove-faced seal are numerically determined. The influence of surface roughness on the contact distribution, deformation and temperature of the end-face seal at different speeds and pressures is analyzed. The film thickness increases as the rotational speed increases from 1 rpm to 2000 rpm, while the contact pressure sharply decreases from 0.25 kPa to 0. The analysis shows that the roughness contact mainly happens on the inner side of the rings due to convergent distortion of the seal faces, which easily causes partial wear of the seal faces. Moreover, it can also be found that the spiral grooves on the sealing surface can produce obvious hydrodynamic pressure effect due to the function of shear speed when the speed increases to 2000 rpm, while the film temperature increases from 293.3 K to about 306 K. The greater surface roughness results in a larger temperature rise under low-rotational-speed and lower-seal-pressure conditions, which further increases the risk of severe wear or even failure of the seal faces. [ABSTRACT FROM AUTHOR]

The tribological behavior of an addendum modified altered tooth sum optimized spur gear set were experimentally compared with that of the standard spur gear under several loading conditions including the wear morphology study and wear debris analysis. The temperature, viscosity, elastohydrodynamic oil film thickness, specific film thickness, and combined surface roughness variation under increasing operating load were analyzed experimentally. Finally, the performance impact of addendum shifted altered tooth sum optimized gear was examined. Results show that the tribological improvement strongly depends on the addendum alteration and modified tooth sum condition. The modification of the addendum in gears with a negatively altered tooth sum facilitates the transition from single-tooth contact to two-tooth contact, broadening the lubrication range while preserving optimal film thickness and improving wear resistance. However, it is reverse to decrease the film thickness and increase wear for standard and profile-modified positively altered tooth sum gear. The gear tribological performance can be significantly improved by profile modification and negatively altered tooth sum approach with a lower rate of degradation of oil and damage on the tooth contacting surface. [ABSTRACT FROM AUTHOR]

The locally oriented roughness is a common feature of surface finished by a machining process, such as the surface of the cylinder liner, and may significantly influence lubrication characteristic. A homogenised transient Reynolds equation for the locally oriented roughness is derived. The Jacobsson–Floberg–Olsson (JFO) boundary conditions was implicitly incorporated into the transient Reynolds equation to ensure the mass flow conservation. On this foundation, a model for the transient lubrication in the cylinder liner‐piston ring considering the effects of the surface roughness and cavitation is established. Then, the results of model developed here are compared with those from the stochastic model by Patir and Cheng. and the effect of the direction of roughness on the lubrication properties is analysed. The homogenised transient Reynolds equation and the lubrication model developed here have great potential for understanding and optimising the transient lubrication considering the surface local roughness orientation, cavitation and starved lubrication. [ABSTRACT FROM AUTHOR]

The generation of third particles and change in viscosity lead to the gradual degradation of the performance of the machine interface. The generation of third particles may come from wear debris or environmental particles, which form a three-body contact system at the contact interface. The viscosity of the lubricant will also change with the long-term operation of the components. This paper uses a three-body lubrication model to study the influence and interaction of lubricant viscosity change and the presence of third particles on the contact characteristics, including the real contact area, the particle contact area ratio, the solid load percentage, the film thickness, and the evolution of the lubrication regime. The results show that when the interface is in a three-body mixed lubrication regime, the dimensionless total real contact area increases with the increase in particle size and density at the same lubricant viscosity, while the trend is the opposite in dry contact and boundary lubrication interfaces. When viscosity decreases, a three-body contact interface is more prone to entering boundary lubrication than a two-body contact interface, resulting in surface damage. Regardless of surface roughness, particle size, and dry or lubricated contact conditions, the turning point of the contact area (TPCA) phenomenon is usually when the ratio of particle size to surface roughness is 0.8-1.3. Under the same ratio of particle size to surface roughness, the critical load of the TPCA phenomenon increases with the increase in third-particle size and surface roughness, but decreases with the increase in lubricant viscosity and particle density. [ABSTRACT FROM AUTHOR]

In this work, a modified numerical algorithm that couples the quasi-static theory with the mixed thermal elastohydrodynamic lubrication (mixed-TEHL) model is proposed to examine the mechanical properties and lubrication performance of the spindle bearing that is used in a high-speed machine tool with spinning. The non-Newtonian fluid characteristics of the lubricant and the non-Gaussian surface roughness are also considered. Moreover, the mechanical properties and lubrication state of the bearing are examined in various service environments. The results indicate that the temperature reduces the lubrication efficiency, which in turn exerts a significant impact on the mechanical properties. The lubrication that either behaves in the manner of Newtonian or non-Newtonian fluid has a relatively negligible influence on the bearing working state, while the non-Gaussian surface roughness significantly alters the oil film thickness and temperature. Calculations with different operating conditions demonstrate that the operating parameters (i.e., axial load, rotation speed) will directly affect the performance of the bearings via the changes in the oil film thickness and the temperature. [ABSTRACT FROM AUTHOR]

The transient mixed lubrication behaviors in thermal elastohydrodynamic lubrication (TEHL) contacts during startup and stop are investigated. A transient mixed TEHL model for point contacts under time-varying speed conditions is proposed with comprehensive consideration of surface roughness, thermal effect, and transient behavior. The model is validated by the comparison to available published data. Based on the developed model, significant differences have been found compared with transient EHL and steady TEHL models. In addition, the transient mixed TEHL performance during start–stop with different acceleration rates and surface roughness is investigated. It shows that the lubrication behaviors during start–stop have an irreversible process. The roughness can significantly enhance the transient behavior. The roughness effect has a remarkable impact on lubrication performance in mixed lubrication. The evolution of lubrication behaviors during start–stop is highly related to the acceleration rate and surface topography. [ABSTRACT FROM AUTHOR]

Porous materials impregnated with lubricants can be used in conditions where limited lubricant is desirable. In this work, three porous polyimides (PPI) with different densities were prepared. Polyalphaolefin (PAO) impregnated PPI (iPPI) discs were rubbed against steel and sapphire balls. In operando observations of the iPPI–sapphire contacts show that oil is released under an applied load, forming a meniscus around contacts. Cavitation at the outlet is created at high sliding speeds. The amount of released oil increases with increasing PPI porosity. Contact moduli, E*, estimated based on the actual contact size show that trapped oil in iPPIs contributes to load support. At higher speeds, tribological rehydration of the contact occurs in low density iPPI, with that E* rises with speed. For high density PPIs, high speeds give a constantly high E* which is limited by the viscoelastic properties of the PPI network and possibly the rate of oil exudation. Friction of iPPI–steel contacts is governed by the mechanical properties of the PPI, the flow of the lubricant, and the roughness of the PPI surfaces. For low- and medium- density (highly porous, high roughness) PPIs, large amount of oil is released, and lubrication is mainly via lubricant restricted in the contact in the pores and possibly tribological rehydration. For high density (low porosity) PPI, with lower roughness, hydrodynamic lubrication is achieved which gives the lowest friction. Our results show that polymeric porous materials for effective lubrication require the optimization of its surface roughness, stiffness, oil flow, and oil retentions. [ABSTRACT FROM AUTHOR]

Wheel‐rail adhesion is important to the traction and braking of railway vehicles. This paper develops a three‐dimensional numerical model considering surface roughness and temperature to investigate water‐contaminated adhesion characteristics. A simplified elastohydrodynamic lubrication model considering the thermal effect is developed to obtain the normal load carried by liquid film and asperities. Meanwhile, a third body layer (3BL) model, which considers the effects of pressure and temperature on 3BL, is used to calculate the tangential stress and friction coefficient of asperity contact. To verify the numerical model, firstly, the results are compared with the existing experimental results at low and high speeds. In addition, the effects of surface roughness and temperature on adhesion coefficient are investigated. Furthermore, the elastoplastic behaviour of the tangential stress and the adhesion characteristics for large creepages are studied. The obtained adhesion‐creepage curve can represent the decreasing trend after reaching saturation because of temperature. [ABSTRACT FROM AUTHOR]

Purpose: This study aims to enhance the lubrication performance of thrust bearings. The influence of columnar convex–concave compound microtexture on bearing performance is investigated Design/methodology/approach: Based on the compound microtexture model of thrust bearings, considering surface roughness and turbulent effect, the variation of lubrication characteristics with the change in the compound microtexture parameters is studied. Findings: The results indicate that, compared with circular microtexture, the maximum pressure of compound microtexture of thrust bearings increases by 7.42%. Optimal bearing performance is achieved when the internal microtexture depth is 0.02 mm. Turbulent flow states and surface roughness lead to a reduction in the optimal depth. The maximum pressure and load-carrying capacity of the bearing decrease as the initial angle increases, whereas the friction coefficient increases with the increase in the initial angle. The lubrication performance is best for bearings with a circumferential parallel arrangement of microtexture. Originality/value: The novel composite microtexture with columnar convex-concave is proposed, and the computational model of thrust bearings is set. The influence of surface roughness and turbulent flow on the bearing performance should be considered for better conforming with engineering practice. The effect of microtexture depth, arrangement method and distribution position on the lubrication performance of the compound microtexture thrust bearing is investigated, which is of great significance for improving tribology, thrust bearings and surface microtexture theory. [ABSTRACT FROM AUTHOR]

The impact of non-Gaussian height distribution and spectral properties on the lubrication performance of counterformal (point) contacts is quantitatively studied (film parameter, Λ, and asperity load ratio, La) by developing a mixed lubrication model. The Weibull height distribution function and power spectral density (PSD) are used to generate artificial surface topographies (non-Gaussian and Gaussian, isotropic), as these surface topographies are found in many tribological components. The set of variables needed to parametrize and their effect on mixed lubrication is discussed, including the shape parameter, the autocorrelation length, the wavelength ratio, and the Hurst coefficient. It is revealed that a rough surface with a lower shape parameter exhibits higher hydrodynamic lift. The spectral properties (the autocorrelation length and the wavelength ratio) of rough surfaces significantly affect the film parameter and the hydrodynamic and asperity pressures. The film parameter is slightly influenced by the Hurst coefficient. [ABSTRACT FROM AUTHOR]

This article presents the results of an analysis of the influence of friction process parameters on the coefficient of friction of steel sheets 1.0347 (DC03), 1.0338 (DC04) and 1.0312 (DC05). A special tribometer was designed and manufactured in order to simulate the friction phenomenon occurring in the blankholder area in deep drawing operations. Lubricant was supplied to the contact zone under pressure. The value of the coefficient of friction was determined under various contact pressures and lubrication conditions. Multi-layer artificial neural networks (ANNs) were used to predict the value of the coefficient of friction. The input parameters considered were the kinematic viscosity of lubricants, contact pressure, lubricant pressure, selected mechanical properties and basic surface roughness parameters of sheet metals. The value of the coefficient of friction of 1.0312 steel sheets was predicted based on the results of friction tests on 1.0347 and 1.0338 steel sheets. Many ANN models were built to find a neural network that will provide the best prediction performance. It was found that to ensure a high performance of ANN prediction, it is necessary to simultaneously take into account all the considered roughness parameters (Sa, Ssk and Sku). The predictive performance of the 'best' network was greater than R2 = 0.98. The lubricant pressure had the greatest impact on the coefficient of friction. Increasing the value of this parameter reduces the value of the coefficient of friction. However, the greater the contact pressure, the smaller the beneficial effect of pressure-assisted lubrication. The third parameter of the friction process, the kinematic viscosity of the oil, exhibited the smallest impact on the coefficient of friction. [ABSTRACT FROM AUTHOR]

A simplified mathematical model has been developed for understanding combined effects of surface roughness, viscosity variation and couple stresses on the squeeze film behaviour of a flat and a curved circular plate in the presence of transverse magnetic field. The Stokes (1966) couple stress fluid model is included to account for the couple stresses arising due to the presence of microstructure additives in the lubricant. In the context of Christensen's (1969) stochastic theory for the lubrication of rough surfaces, two types of one-dimensional roughness patterns (radial and azimuthal) are considered. The governing modified stochastic Reynolds type equations are derived for these roughness patterns. Expressions for the mean squeeze film characteristics are obtained. Numerical computations of the results show that the azimuthal roughness pattern on the curved circular and flat plate results in more pressure buildup whereas performance of the squeeze film suffers due to the radial roughness pattern. Further the Lorentz force characterized by the Hartmann number, couple stress parameter and viscosity variation parameter improve the performance of the squeeze film lubrication as compared to the classical case (Non-magnetic, Newtonian case and non-viscous case). [ABSTRACT FROM AUTHOR]

Purpose: Harmonic gears always work under different operating conditions and may usually break down due to lubrication failures, while its lubrication mechanism is still not clearly understood. This paper aims to present a lubrication model comprehensively considering the influence of contact geometry, lubrication properties and three-dimensional (3D) real surface roughness to analyze the lubrication performance under different conditions. Design/methodology/approach: Based on the discrete convolution-fast Fourier transformation with duplicated padding and quasi-system numerical methods, the lubrication model for harmonic gears is developed, which is verified by comparing results with available lubrication data. Findings: The effects of meshing process, working conditions and 3D roughness on the lubrication characteristics are discussed. From the calculated cases, the increase in rotational speed and decrease of applied torque may increase the film thickness, enhancing the lubrication performance of harmonic gears. It is also observed that proper surface roughness can be used for lubrication design. Originality/value: The research results can provide theoretical guidance for improving lubrication performance and reducing friction/wear of the harmonic gear interfaces. This study can be promoted to various engineering scenarios of harmonic gears, such as industrial robots, space-driven agencies and precision measuring instruments. [ABSTRACT FROM AUTHOR]

Carbon films have been considered suitable to be applied in water lubrication since they exhibit excellent friction-reducing and wear resistance, chemical inertness, etc. However, the basic understanding of tribological behaviors of carbon-based films under water lubrication still needs to be explored. In the present work, carbon films with different nanostructures were prepared by the electron cyclotron resonance (ECR) plasma nano-surface manufacturing system, and micro-textures with different sizes were prepared on the surface of carbon films by plasma etching. The influence of nanostructure and surface texture on the tribological properties of carbon films was investigated. The results show that different nanostructured carbon films can obtain lower friction coefficients and longer wear life under water lubrication than under dry condition. Due to low surface roughness, high hardness, and compact structure, the tribological properties of amorphous carbon (a-C) films under water lubrication are much better than those of graphene sheet-embedded carbon (GSEC) films. The prepared surface texture has a negative effect on the hard a-C film, but it can make the soft GSEC film generate soft wear debris at the initial stage. With the action of water, the soft wear debris is bonded on the surface of the contacting ball to form a silt-like transfer film, which increases the wear life by nearly three orders of magnitude. These results extend the basic understanding of the tribological behavior of carbon film under water lubrication, which is crucial in both fundamental and applied science. [ABSTRACT FROM AUTHOR]

The formation of lubrication films is described using the hydrodynamic lubrication theory, which is based on the Reynolds equation that includes shear thinning behaviors of lubricant. Contacting surfaces are considered to undergo elastic deformation owing to concentrated contact pressures that exceed 1.0 GPa in most engineering applications. Under the contact condition of a high load on a relatively small contact area, elastic deformation of contacting bodies directly influences the formation of the lubricated film. Elastohydrodynamic lubrication (EHL) analysis is applied to correctly analyze the lubricated contact. Under an EHL contact, the scale of the lubrication film thickness is frequently less than that of the surface roughness that results from either the manufacturing or running-in processes. In this work, surface roughness is considered in detail, and two-dimensional surface roughness is measured as that characterizing general engineering surface roughness. The deterministic method regarding the surface roughness is considered for computing EHL film formation under several contact conditions such as load, contact velocity, and elasticity of contacting materials. [ABSTRACT FROM AUTHOR]

In order to analyze the bearing wear in the spindle system considering different speed and load conditions, a four-bearing spindle system was investigated. Two different working conditions, Case I and Case II, are considered. Case I condition has lower spindle speed and higher external loads and preload than Case II condition. Based on Archard model, a new wear depth model of angular contact ball bearing is presented which takes into account the influence of lubrication on bearing wear. The wear depths of inner and outer raceways for angular contact ball bearings are calculated based on the motion parameters and contact parameters of ball elements which are obtained by spindle system model. The effects of spindle speed, angular misalignment, external load and surface roughness on the wear depths of bearings are comparatively studied. Increasing spindle speed at Case I condition can significantly increase bearing wear. Angular misalignment may be beneficial to individual bearing, but overall, no angular misalignment is the most beneficial to spindle system. The change rate of wear depth of bearing raceway with external loads at Case I condition is much greater than that at Case II condition. The surface roughness can significantly affect the bearing wear in the spindle system, especially at Case I condition. [ABSTRACT FROM AUTHOR]

This article, published in Acta Polytecnica: Journal of Advanced Engineering, examines the effects of porosity and surface roughness on annular discs under squeeze film lubrication. The study uses a semi-analytical approach and the Rabinowitsch fluid model to analyze the characteristics of the discs. The findings show that the performance of annular discs is significantly influenced by porous material and radial roughness patterns. The research aims to optimize the design of these discs for specific applications, such as heat exchangers and filtration systems. The text also provides equations and mathematical formulations to understand the behavior of fluid flow within these discs. The study concludes that further research should focus on advanced materials, optimization of porous structures, and numerical modeling. The provided list of references includes research papers that cover various aspects of lubrication in different systems and materials, providing valuable insights for researchers studying tribology and engineering. [Extracted from the article]

In order to reveal the effect of surface roughness on the lubrication performance of marine water lubricated polymer bearings, theoretical research on elastohydrodynamic lubrication of water lubricated bearings was conducted. A hybrid lubrication model of water lubricated bearing considering the roughness and elastic deformation of lining material was established and verified by simulation. The influence of inner liner roughness peak on water film thickness, water film pressure distribution and bearing capacity was analyzed. The results show that the increase of liner roughness will slow down the increase ratio of water film thickness during the increase of rotating speed, so that the bearing needs higher rotating speed to enter the hydrodynamic lubrication state. Reducing the roughness of the bearing lining can effectively reduce the take-off speed of the bearing, accelerate the process of the bearing from mixed lubrication to hydrodynamic lubrication, reduce the local contact between the bearing and the journal, and reduce the possibility of abnormal vibration and noise of the bearing. This research reveals the mechanism of the influence of the change of the inner liner roughness on the lubrication characteristics of the bearing, and provides a theoretical reference for the optimal design of the water lubricated bearing. [ABSTRACT FROM AUTHOR]

Utilizing the average Reynolds equation, lubrication friction theory, metal rolling deformation theory, and temperature energy theory, a multi-parameter-coupling mixed lubrication model considering the influence of surface roughness with Gaussian distribution characteristics under rolling conditions was established. The results show that the stress distribution of the lubricating oil at the rolling interface conforms to the typical characteristics of line contact stress distribution. The oil film pressure does not increase significantly with the increase in the reduction ratio. A second peak pressure appears before the outlet. The second peak pressure reaches its maximum when ε = 0.2. The rolling speed has little effect on oil film pressure, but greatly affects oil film thickness. The influence of rolling speed mainly occurs in the outlet zone and at the second peak pressure location. The oil film thickness increases with rolling speed. During rolling, the temperature rise in the rolls exhibits two peak values. The first peak appears near the neutral point, and the second peak appears near the outlet, which is also where the second peak pressure is located. The influence of temperature will reduce the peak stress on the rolls. The overall stress on the rolls will also decrease. [ABSTRACT FROM AUTHOR]

An endeavor has been made to study the performance of a ferrofluid based squeeze film in circular cylinder near a plane resorting to Shliomis model, considering slip velocity. The stochastic model of Christenson and Tonder has been brought in here to evaluate the effect of surface roughness. The associated stochastically averaged Reynolds type equation is solved to obtain the pressure distribution. Then load bearing capacity has been calculated. The results show that Shliomis model based ferrofluid lubrication is relatively better as compared to the Neuringer-Rosensweig model for magnetic fluid lubrication of this type of bearing system, even if the slip is higher. The adverse effect of roughness can be reduced considerably at least in the case of negatively skewed roughness with a suitable choice of curvature parameters. It is observed that this type of bearing system supports some amount of load even when there is no flow, unlike the case of conventional lubricants. Some of the results presented here establish that the adverse effect of slip velocity can be minimized with suitable magnetic strength, irrespective of the fact that the roughness induces adverse effect. [ABSTRACT FROM AUTHOR]

Predicting changes in the surface roughness caused by friction allows the quality of the product and the suitability of the surface for final treatments of varnishing or painting to be assessed. The results of changes in the surface roughness of DC03 steel sheets after friction testing are presented in this paper. Strip drawing tests with a flat die and forced oil pressure lubrication were carried out. The experiments were conducted under various contact pressures and lubricant pressures, and lubrication was carried out using various oils intended for deep-drawing operations. Multilayer perceptrons (MLPs) were used to find relationships between friction process parameters and other parameters (Sa, Ssk and Sku). The following statistical measures of contact force were used as inputs in MLPs: the average value of contact force, standard deviation, kurtosis and skewness. Many analyses were carried out in order to find the best network. It was found that the lubricant pressure and lubricant viscosity most significantly affected the value of the roughness parameter, Sa, of the sheet metal after the friction process. Increasing the lubricant pressure reduced the average roughness parameter (Sa). In contrast, skewness (Ssk) increased with increasing lubrication pressure. The kurtosis (Sku) of the sheet surface after the friction process was the most affected by the value of contact force and lubricant pressure. [ABSTRACT FROM AUTHOR]

To reveal the influence of surface morphology characteristics in mixed lubrication on the contact characteristics of the rolling interface, a random three-dimensional rough surface model based on Gaussian distribution theory was established. The model utilizes the finite element method (FEM) to simulate the regular contact and tangential sliding behavior of micro-asperities at the rolling interface in mixed lubrication conditions. The connection bearing capacity of models with varied roughness in mixed lubrication was studied. Furthermore, the effect of various sliding and normal indentation amounts on the normal and friction stress was investigated. The simulation result reveals that the roughness of the surface influences the distribution of the lubricating oil film. The lubricating oil layer between the interfaces with a lower roughness has a higher bearing capacity due to its more uniform distribution of peaks and valleys. An increase in the normal indentation amount raises the friction stress and normal stress. In contrast, an increase in sliding lowers the normal pressure, substantially impacting the fluctuation of the friction coefficient dramatically. Finally, the random three-dimensional rough surface model is verified by comparing it with the experimental data in the related literature. [ABSTRACT FROM AUTHOR]

Purpose: This study aims to present a numerical solution for the analysis of the influence of surface roughness as presented by a sinusoidal ripple of different amplitude and wavelength on the performance of transient elastohydrodynamic lubrication at motion start-up under different operational parameters of entraining speed and load as well as different acceleration rates. Design/methodology/approach: A statistical asperity micro-contact model represented by a sinusoidal ripple expressed by two parameters (wavelength and undeformed amplitude) is considered. The ball equation of motion is used to calculate the force on the ball as it starts to move. The time-dependent Reynolds equation is solved together with surface deformation and statistical asperity models using the Newton–Raphson technique with the Gauss–Seidel iteration method. Findings: The behaviour of the film thickness was found to be strongly influenced by the acceleration rate for different ripple amplitude and wavelength parameters. The effect of increasing the final entraining speed will eventually lead to rapid film thickness build-up and increase the film thickness jump at the moment of motion start-up. The effect of increasing applied load is to reduce the deviation of the minimum film thickness jump at the start-up of motion, making its value approximately equal to the steady-state value over the entire run-time period. Originality/value: Influence of surface roughness for various wavelength and undeformed amplitude on the performance of transient elastohydrodynamic lubrication at motion start-up is presented at different acceleration rates as well as for different operating parameters of entraining speed and load. Ball equation of motion is used to calculate the force on the ball as it starts to move. [ABSTRACT FROM AUTHOR]

In this work, a numerical model simulating friction hysteresis for lubricated rough and textured surfaces in contact is presented. Friction hysteresis occurs in sliding contacts that are subjected to a non-constant (e.g., sinusoidal) motion. It refers to the phenomenon where the observed friction force during acceleration differs from that during deceleration. Besides the dynamics of the sliding system, a classic mixed friction model is adopted, in which the transient Reynolds equation for the description of the thin lubricant film is combined with a statistical Greenwood–Williamson model for the description of rough surface asperity contacts. The model enables the prediction of the friction hysteresis for predefined contact descriptions (i.e., surface profile and roughness, lubricant, etc.) and allows the study of the physics and parametric influences of dynamically sliding contacts. In this paper, it is shown that (i) friction hysteresis is captured by classic transient models for mixed lubrication; (ii) system parameters, such as roughness, applied load, viscosity and velocity, including the offset, amplitude and motion reversal, influence the shape and area of friction hysteresis; and (iii) the selection of the aforementioned parameters may minimize friction hysteresis. [ABSTRACT FROM AUTHOR]

To research the dynamic response characteristics of the multi-link complex mechanism with lubricated clearance joint, an improved transitional lubrication model considering the roughness of the contact surface is established based on the fuzzy set model of the lubrication state. The dynamic model of a six-bar rocking feeding mechanism with lubricated clearance joint is established, and the influence of dry friction clearance and lubricated clearance on the dynamic response of the mechanism are analyzed. By comparing with the simulation results of ADAMS and Flores lubrication model, the correctness and effectiveness of the established dynamic model and the improved transition lubrication model are verified. The influence of driving speed, clearance size and number of clearances on the dynamic response of the mechanism with lubricated clearance joint is mainly studied. The simulation results show that the driving speed, clearance size and number of clearances have an impact on the dynamic characteristics of the mechanism. With the increase of driving speed and clearance value, the greater the impact on the mechanism, the increase in the number of clearances, which reduces the stability of the mechanism, and there is interaction between different clearance joints. [ABSTRACT FROM AUTHOR]

Over last couple of decades, various regimes of lubrication attracted lots of attention. Among these regimes of lubrication, the least understood and studied are the regimes or boundary lubrication and lubricity. Better understanding these regimes of lubrication is necessary due to the fact that many moving joints such as, for example, bearings and gears at least part of their operating time work in these regimes. It may occur due to slow motion of counter parts or their relative overload. This paper proposes a model for analysis of these regimes of lubrication. Specifically, the model takes into account roughness of one of the contact surfaces. It is shown that for sufficiently high applied load it can be expected that contact surfaces are completely separated by a lubricant layer in spite of the presence of surface asperities. The definitions of boundary lubrication regimes and super lubricity are proposed. A method based on the method of matched asymptotic expansions is applied for analyzing such cases and an approximate analytical solution of the problem away from the contact region boundary is found. In the narrow inlet and exit zones adjacent to contact boundaries equations describing the main solution terms are derived. For the case of super lubricity, a resemblance of a superposition between the lubrication and surface roughness effects is determined and the effect of surface roughness on the lubrication film thickness is considered. Specifically, certain roughness conditions are identified for which the lubrication film thickness can be higher than for smooth surfaces while in other cases it can be lower. For the super lubricity regimes, the equations for the main pressure asymptotic terms in the inlet and exit zones are reduced to the corresponding equations for the smooth (not rough) surfaces for which a series of numerical solutions is obtained earlier. A general analysis of the effect of texturing on lubrication conditions in case of super lubricity is conducted based on a simple geometric criterion. Several models of textured surfaces and their influence on the lubrication film thickness in case of super lubricity regimes are considered. [ABSTRACT FROM AUTHOR]

Elastomers are the class of materials that are widely used in a variety of industrial, commercial, and consumer applications due to their unique mechanical properties, including high elasticity, high flexibility, and high resilience. However, there are many challenges in machining of elastomers such as poor surface finish, build up of heat, degradation of elastomers, etc. To overcome these challenges, cryogenic cooling assistance has been introduced as a means of improving the machinability of elastomers. This paper presents a soft computing approach for optimizing the surface roughness and cutting force during turning of elastomers under different lubrication conditions. Three types of elastomers, namely Nitrile Rubber (NBR), Polyurethane Rubber (PU), and Neoprene Rubber (CR), are studied, and a cryogenic fluid delivery system is employed to improve the machining process. Taguchi's L27 array is used to vary the input parameters, and a Back-Propagation Artificial Neural Network (BPANN) model is developed to predict the cutting force and surface roughness. The cutting force and surface roughness are analyzed under different cooling conditions, cutting speeds, feeds, and depths of cut for various elastomers. The results show that changes in cutting conditions significantly affect the cutting force and that the type of lubrication used affects the cutting force by altering the material's physical properties. Cutting force is significantly influenced by cutting conditions, and NBR requires the highest cutting force compared to PU and CR. Further, at a cutting speed of 55 m/min, a feed of 0.11 mm/rev, and a depth of cut of 0.25 mm, the cutting force for NBR (85.1 N), while for PU (75.1 N) and CR (80.3 N), respectively. Finally, with LN2 lubrication conditions, the Cutting Force decreased by 45% and Surface Roughness decreased by 16.9%. This study provides insights into the factors affecting the elastomer machining process, which can be useful for optimizing the machining process parameters and improving machining efficiency. [ABSTRACT FROM AUTHOR]

The fuel injection system heavily relies on the high-pressure fuel pump, which plays a critical role in its overall performance. The fuel pump plunger is subjected to high levels of stress and experiences irregular lubrication during dynamic loads, causing premature wear. In the industrial sector, laser surface micro-texturing has been utilized to reduce friction and enhance anti-wear properties, and its positive impact has been supported by both theoretical and experimental evidence. This article presents a method for determining the hydromechanical characteristics of plunger pairs under conditions of hydrodynamic friction. The microgeometry of friction surfaces was taken into account through the cavitation effect of the lubricating fluid, described by the modified Reynolds equation. Software was developed according to the proposed method. The developed software can be used to analyze the contacting surfaces of plunger pairs and evaluate their tribotechnical characteristics based on the microgeometry parameters of the friction surfaces. The article also discusses the impact of the microgeometry parameters on the quality criteria of the hydromechanical characteristics of the plunger pairs. Computational examples are given for the analysis of contacting surfaces of plunger pairs separated by a lubrication layer. The technical characteristics are evaluated depending on the parameters of the microgeometry of the roughness of the friction surfaces. The influence of the microgeometry parameters on the quality criteria of the hydromechanical characteristics of the plunger pairs is presented. [ABSTRACT FROM AUTHOR]

The influence of various process parameters on the deep drawing process is a current research topic in sheet metal forming technology. Starting from the application of the previously constructed original testing device, an original tribological model was developed based on the process of sheet metal strip sliding between flat contact surfaces under variable pressures. A complex experiment was executed using an Al alloy sheet, tool contact surfaces of different roughness, two types of lubricants and variable contact pressures. The procedure included analytically pre-defined contact pressure functions based on which, for each of the mentioned conditions, the dependencies of the drawing forces and friction coefficients were obtained. The pressure in function P1 constantly decreased from a high initial value until the minimum, while in function P3 the pressure increased until the minimum value at the halfway point of the stroke, after which it increased up to the initial value. On the other hand, the pressure in function P2 constantly increased from the initial minimum value until the maximum value, while in function P4 the pressure increased until reaching the maximum value at the halfway point of the stroke, after which it decreased to the minimum value. This enabled the determination of the influence of tribological factors on the process parameters of intensity of traction (deformation force) and coefficient of friction. The pressure functions starting with decreasing trends produced higher values for the traction forces and the friction coefficient. In addition, it was established that the roughness of the contact surfaces of the tool, especially those with titanium nitride coating, has a significant influence on the process parameters. For surfaces of lower roughness (polished), a tendency of the Al thin sheet to form a glued-on layer was noticed. This was especially prominent for lubrication with MoS2-based grease under conditions of high contact pressure (functions P1 and P4 at the beginning of the contact). [ABSTRACT FROM AUTHOR]

Purpose: The purpose of this study is to develop a 3D wheel-rail adhesion model under wet condition, which considers the generated surface roughness topography and the traditional braking procedure for high-speed trains. Design/methodology/approach: Wheel-rail adhesion has an important effect on the braking ability of railway vehicle. Based on the deterministic mixed lubrication approach, the model was solved to get the adhesion characteristics of the train during braking. The elastic deformation was calculated with the discrete convolution and fast Fourier transform method. The simulation results of adhesion coefficient were compared with the experimental values. The wheel-rail adhesion characteristics of train braking at several different initial speeds were investigated. The effects of the time-step length and roughness orientation on the contact load ratio were also discussed. Findings: The results show that the adhesion coefficient of the numerical model is in good agreement with the experimental results. At the instant of braking, the adhesion coefficient drops to a lower adhesion level, the value of adhesion coefficient is lower than 0.06, especially at a higher speed (200, 300 and 400 km/h). Originality/value: It can provide a better understanding of the low adhesion phenomenon of train braking under wet condition. Peer review: The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-02-2023-0040/ [ABSTRACT FROM AUTHOR]

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In this article, a finite line contact tribo-dynamics model of helical gears is established by coupling the tooth surface friction, friction moment, and vibration velocity. To obtain convergent results, a cycle iteration strategy is adopted to solve the two submodels, the dynamic model and the thermal elastohydrodynamic lubrication model. The parameters obtained from the dynamic model such as the dynamic load, dynamic transmission error, and instantaneous speed of the teeth surfaces are used as the boundary conditions for solving the lubrication model. Meanwhile, the friction force and friction moment obtained by the lubrication model are used as parametric excitations of the dynamic model. Based on the proposed model, the influence of dynamic effect, thermal effect, rotational speed, and tooth surface roughness on the tribological and dynamic properties of helical gears are discussed. The results show that the tribological and dynamic parameters deviate significantly from the quasistatic values, especially at the characteristic speed. The vibration along the off-line-of-action direction is obviously affected by the friction excitation. As the rotational speed increases, the friction coefficient and friction force decrease as well as the vibration of the gear pair along the off-line-of-action direction weakens. In addition, the surface roughness has the greatest influence on the vibration of the off-line-of-action direction in all directions of gear vibrations. [ABSTRACT FROM AUTHOR]

Increasing the performance of gear drives of machines is an urgent task, so to estimate the total losses in engagement, it is worth considering all components of losses. To solve this problem, the article proposes a method for determining the sliding friction losses in a gear pair. At present, the effect of sliding in the tooth's direction contact line on the friction coefficient and lubrication conditions has not been studied sufficiently. There are two groups of semi-analytical models in the published works. The first group of authors studied the efficiency of spur gears, assuming that the friction coefficient is constant along the entire contact surface of the friction surfaces in any position of the gears during their rotation. The second group of semi-analytical models can be considered as an improvement of the models of the first group with a constant friction coefficient. The accuracy of the empirical formulas used in them limited the accuracy of the description using these models. These empirical formulas are not general and are often a function of certain types of lubricant, available temperatures, speed and load limits, and surface fineness of the test specimens. The coefficient of sliding friction depends on the speed of the mating teeth and the properties of the lubricant; it can also consider such factors as the values of the normal load, the roughness of the tooth surfaces, and the radii of curvature of the tooth profiles. The dependencies have been got to determine the work consumed by friction along the entire meshing line, considering the friction coefficients in the tooth pair for single and double meshing. In this case, the friction coefficient in the gear transmission can be variable by the speed of the mating surfaces, but is the same for two-pair and single-pair meshing. Analytical dependencies have been obtained that make it possible to calculate power losses because of sliding friction depending on kinematic, force, and strength factors, properties of lubricants and gear materials. [ABSTRACT FROM AUTHOR]

Functionally graded materials (FGMs) are a promising engineering material, which is highly desirable in extreme environments of aerospace, nuclear, and bio-implants. Although the surface accuracy and quality of 3D-printed Ni–Fe FGMs can meet most application scenarios, it still requires post-cutting treatment especially in nuclear industry. The FGMs, with the gradient of mechanical property, are a new type of difficult-to-cut material. However, no ready-made post milling process can be referred. The poor-machined surface quality induced by excessive tool wear still cannot be handled even with textured tool under minimum quantity lubrication (MQL). In this paper, the mechanical properties and machinability of the Ni–Fe FGMs as well as its 5 isotropic component 304LxIN625y were firstly studied and correlated. Then, two milling parameter selection strategies were proposed by minimum milling force and by minimum surface roughness, corresponding to strategy I and strategy II. The results show that tool breakage occurs in bottom cutting edge when strategy I is adopted. On the contrary, strategy II can reduce tool major flank wear 40.1% by forming an elastohydrodynamic lubrication between bottom cutting edge and the machined surface, which is a prospective method to solve the tool failure during milling of 3D-printed Ni–Fe FGMs. [ABSTRACT FROM AUTHOR]

Small end bearings are a critical component of reciprocating engines, and the performance of their lubrication performance directly affects engines' reliability and mechanical efficiency. There are many factors that influence their lubrication. A new type of small-end bearing test rig was developed to reveal key influencing factors and their influence on lubrication characteristics, and a multi-body dynamic model coupled with elastohydrodynamic (EHD) characteristics was built. The model was verified through experiments. In accordance with the orthogonal experimental requirements, the impact of various factors on small-end bearing lubrication characteristics was analyzed, and the results showed that: (1) minimal oil film thickness (MOFT), friction power, and maximum oil film pressure (MOFP) are the major evaluation indicators of small-end bearing lubrication, and the most significant influencing factors are the pin bushings' clearance, engine speed, and bushing surface roughness; (2) increasing the clearance of the pin bushings can increase the hydrodynamic lubrication percentage and the average thickness of the oil film, but it also reduces the local minimum thickness of the oil film; (3) an increase in roughness can improve the MOFT and enhance its carrying capacity, but may also increase friction power; and (4) high speeds can increase the thickness of the oil film between the piston pin and bushing and improve lubrication status, but it also increases friction power on the asperity contact region, reducing mechanical efficiency. The research results can be used for the design of connecting rod small-end bearings to improve their mechanical efficiency and reliability. [ABSTRACT FROM AUTHOR]

The proposed lubrication theory of textured journal bearing is a major innovation in the study of the tribological properties of surface morphology. When it comes to the study of surface topography, it is essential to consider the effect of surface roughness when analyzing the characteristics of journal bearing. In this paper, a Reynolds equation containing longitudinal roughness is established for journal bearing and solved by the finite difference principle to obtain the bearing load and friction characteristics. Subsequently, a combination of laser etching and ultrasonic vibration milling processes was used to prepare 5 µm, 20 µm, and 40 µm bearing friction subsets with square micro-texture surfaces. The analysis of the results shows that the surface roughness distributed in the non-texture region can substantially increase the oil film pressure. When the roughness profile and the surface weave work together, the presence of a surface texture with an optimum depth of 5 µm within a roughness range of less than 1.6 µm can improve the load-bearing characteristics by a maximum of 43%. In the study of the preparation of textured bearing friction substrate, it was found that laser etching can ablate the surface of the friction substrate to a depth greater than 20 µm with the ideal effect, while the surface texturing to a depth of 5 µm is more suitable using an ultrasonic vibration processing process. In the simplified journal bearing operating condition, the frictional wear test shows that if the effect of roughness is considered, the frictional force of the depth of 20 µm and 40 µm is significantly reduced and changes less with increasing load, while the frictional force of the textured frictional pair with a depth of 5 µm is improved but significantly affected by the load carrying capacity. Therefore, when the difference between the roughness profile and the depth of the texture is of a small order of magnitude, it indicates that the effect caused by the roughness factor is not negligible. [ABSTRACT FROM AUTHOR]

The cylinder gas film seal between dual-rotor reverse shafts is a new method for sealing aircraft engines that has excellent developmental prospects. We propose a novel method for determining if the sealing ring is fully fluid-lubricated using the average Reynolds equation. Considering surface roughness and centrifugal expansion, we calculated the dynamic pressure, gas film force and friction power consumption with and without inlet pressure differences for each of the four rotation modes. The gas film's dynamic pressure effects were weakest when the dual rotors rotated in a reverse direction (Mode 3), with or without differences in inlet pressure, since solid contact is most likely to occur under counter-rotation. When the dual rotors were in counter-rotation with an inlet differential pressure of 80 kPa and fixed inner and outer rotor speeds (e.g., 3000 rpm), we calculated the minimum sealing ring film thickness, leakage rate, friction power consumption and gas film force. Changes in outer rotor speed greatly influenced the minimum film thickness and the sealing ring's performance. Meanwhile, changes in the inner rotor speed had little influence on the minimum film thickness and sealing ring's lubrication performance. When the speed difference was fixed and the sealing ring was fully fluid-lubricated, lubrication performance changes were mainly affected by changes in centrifugal expansion caused by the outer rotor speed. Given a fixed rotor speed and under dual-rotor counter-rotation, we calculated the effects of inlet differential pressure changes on minimum gas film thickness, leakage rate, friction power consumption, gas film force and other sealing performance variables. Leakage rate and the friction power consumption increase as inlet differential pressure increases. Our results provide a theoretical reference for avoiding solid contact of the cylinder seal between dual-rotor reverse shafts. [ABSTRACT FROM AUTHOR]

The numerous prepreg characteristics benefit industries like the aerospace and automotive ones, producing a wide range of high-performance components for primary or secondary applications. Parts production is usually assisted by a thermoforming process in which the prepreg is heated and reshaped employing a moulding system. The ply-ply and ply-tool sliding behaviours in the Thermoforming govern the defects generation, such as wrinkles, making its study a crucial step. This work analyses ply-ply and ply-tool friction coefficients for UD AS4/8552 Carbon/Epoxy prepreg. A pull-out test method was employed to determine the friction coefficients at different velocities, pressures, and temperatures related to the thermoforming process conditions, supplying a detalied report of friction parameters and mechanisms. The measurements of the interlaminar resin layer thickness and the surface roughness geometry resulted respectively in a range of 11–14 μm and 3–4 μm were taken into account in the Lubrication Theory approach to developing an analytical model. Based on the Stribeck curve and Reynolds equation for a viscous fluid, the developed model accurately predicts friction coefficients for prepreg composite materials in the process and contact conditions mentioned below. [ABSTRACT FROM AUTHOR]

Purpose: This study aims to investigate the combined effects of roughness and ferrofluid lubricant on finite journal bearing load capacity and squeeze time. Design/methodology/approach: The stochastic theory of Christensen is applied to study the surface roughness effect. The Shliomis model is used to take into account the effects of the rotational viscosity of ferromagnetic particles and their magnetic moment. A finite wire located in the center of the shaft produces the applied magnetic field. A developed computing code allows predicting the effect of the surface roughness on the performance of the considered journal bearing. The good agreement with the results of the literature validates the used approach. Findings: This study shows that unlike longitudinal roughness, the presence of transverse roughness makes the use of ferrofluid more beneficial in terms of increasing the performance of finite journal bearings. This increase is more significant for large relative eccentricities, which present an ideal confinement. Originality/value: This study shows the effect of two surface roughness patterns on the squeezing performance of a finite journal bearing lubricated by a ferrofluid. [ABSTRACT FROM AUTHOR]

In this study, the effects of surface roughness and thermal on slider bearings with turbulent fluid film were examined using the Streamline Upwind Petrov–Galerkin (SUPG)-Finite Element Method. Using the assumption that roughness is stochastic and has a Gaussian random distribution, one-dimensional transverse and longitudinal surface roughness models were taken into consideration. The texture of the surface's irregularity is changed into a regular domain for computational efficiency. To derive the modified Reynolds equation for turbulent lubrication, the Ng-Pan turbulent model is used. For all local Reynolds values, the pressure distribution of the combined effect is less than the thermal and surface roughness influences of the one-dimensional longitudinal surface roughness, which is a reduction of 16% in load-carrying capacity performance and 3% decrease in friction force, for non-parallel (w = 0.4) between the surface roughness effect and the combined effect condition, respectively. However, the pressure distribution of the thermal effect is smaller than the combined and surface roughness effects in the transverse, one-dimensional roughness model for all local Reynolds values, which is a reduction of 33% in load–carrying capacity performance and 13% decrease in friction force, for non-parallel (w = 0.4) between the surface roughness effect and the thermal effect condition, respectively. Moreover, the combined effects at various temperatures are examined. As a result, the load-carrying capacity performance is better in the case where the pad temperature is lower than the slider in both longitudinal and transverse models. The performance of a slider bearing will generally be improved by taking surface roughness and the coefficients of turbulent lubrication equations into account. Tables and figures were used to present the results. [ABSTRACT FROM AUTHOR]

This study investigates how operating conditions such as ambient temperature and sealing pressure affect sealing performance for a typical U-cup seal. The developed analysis method combines inverse fluid lubrication (IHL) theory and the Greenwood–Williamson contact model (G–W model), and the effect of increasing surface temperature due to frictional heat generated between two surfaces is considered. Commercial FE software (ABAQUS) was used to simulate the interference fit analysis of rubber seals and the pressurized process. Through this model, the film distribution, working fluid leakage, and friction force in the sealing area were discussed according to the operating parameters, such as sealed pressure, rod velocity, and ambient temperature. The simulation results demonstrate the effect of fluid viscosity on oil film formation (which varies with ambient temperature), the effect of increasing the surface temperature, and the effect of surface roughness at a very small film thickness. [ABSTRACT FROM AUTHOR]

Based on mixed thermal-elastohydrodynamic lubrication, the dynamic contact of ball bearings with worn band is investigated, and the film thickness, pressure, profile and interfacial temperature are analyzed. The temperature-pressure-viscoelastic equation of lubricant is constructed. The surface roughness, the elastic deformation and the worn band are included in the film thickness. The discretization method and compound iteration method are combined to solve the problem. Through numerical examples, the distribution and contour of film thickness, pressure and temperature with consideration of surface roughness and worn band are discussed, and the point contact with lower entrainment speed is found. [ABSTRACT FROM AUTHOR]

For high-speed, heavy-load gear units, the meshing tooth surfaces are generally under the mixed lubrication state, which is crucial for gear pitting or micro pitting damage. To clarify the effects of lubrication state on tooth pitting damage, carrying out both numerical and experimental studies on the contact severity of gears under different lubrication states is necessary. In this paper, a 3D line-contact elasto hydrodynamic lubrication model considering fractal surface roughness was developed and used to investigate the lubrication characteristics of involute gears. Both the distributions of pressure and film thickness fluctuated under the rolling contact of rough surfaces. The fluctuations became more substantial with the increase of load and roughness. Furthermore, from the calculated film thickness ratio λ, the contact of gear tooth surfaces with a fractal roughness of Ra = 0.8 µm was always under full lubrication state (λ > 1). When the roughness was increased to Ra = 3.2 µm, the contact was first transmitted into the mixed lubrication state (0.2 < λ < 1) under the load of 1000 N*m and finally deteriorated to boundary lubrication state (λ < 0.2) under the load of 2000 N*m. The boundary lubrication state that occurred under the contact of highly rough surfaces could induce the formation of gear pitting damage. The contact fatigue test showed the gear tooth surface roughness increased from 0.7 µm to around 2.7 µm after 8 million running cycles and then suffered pitting failure after another 2 million cycles, which was consistent with the simulation analysis prediction. [ABSTRACT FROM AUTHOR]