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The oil film lubrication performance of a large hydrostatic turntable operating at the model of constant surface cutting speed is studied. Firstly, the rotary speed equation which is bound by the constant surface cutting speed is established. According to the fluid lubrication theory, the gap flow equation, the oil film temperature rise equation and the double‐rectangular‐cavity oil pad bearing capacity equation are derived. Further, a prediction model of oil film lubrication performance in the operating mode is established. The change rules of temperature, pressure and other performance indexes of the film with time are obtained by numerical simulation. And, the above laws are verified by design experiments. It is found that the cutting speed, feed rate leaves a significant impact on the law of variations of oil film performance with time. According to the conclusions, it will be beneficial to improve the bearing capacity of the hydrostatic turntable and further improve the machining accuracy by using cutting parameters reasonably to control the speed within a certain range. [ABSTRACT FROM AUTHOR]

In order to predict the spiral bevel gear churning power loss, based on the Computational Fluid Dynamics (CFD) method, the computational model for the splash lubrication of the spiral bevel gear pair is established and validated by experiments. The churning power loss of spiral bevel gears is obtained and the corresponding flow field distribution in the gearbox with a pair of spiral bevel gears is analysed under a standard operating condition. For the churning power loss of spiral bevel gears, the loss of teeth surface is mainly caused by pressure while the loss of gear side is mainly generated by the viscous force. The effects of the gear rotational speed, oil level, oil temperature and oil shroud on the churning loss are also investigated and analysed. Ultimately, an optimisation method is proposed for the original spiral bevel geared transmission. [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]

In this research, an angular contact ball bearing with two‐half inner rings is used as a carrier. Considering the two‐phase flow characteristics of oil and air in the bearing, the flow characteristics of lubricating oil inside the bearing with under‐race lubrication are studied. Based on the volume of fluid (VOF) method and the standard k–ε turbulent flow model, the characteristics of oil and air two‐phase flow inside the ball bearing are analysed. The bearing internal pressure field distribution, streamline distribution, and other flow properties for the different radial working clearances, pocket clearances and guide clearances are determined. The distribution of the lubricating oil in key areas is observed. The oil phase volume fraction of the key lubrication areas, such as the cage pocket surface and the inner and outer ring surfaces is used to evaluate the influence of different structural parameters on the bearing lubrication performance. The lubrication influences of the inner and outer guides of the cage are evaluated, and the internal flow characteristics of the bearing are analysed with different guide clearances. The results show that with the radial working clearance range from 0.100 to 0.145 mm, the pressure in the working contact area of the bearing decreases 26%. The pocket clearance ranges from 0.48 to 0.28 mm, and the pressure in the working contact area of the bearing significant increases from 0.642 to 1.165 MPa. From this perspective, the larger the radial working clearance and pocket clearance are, the more favourable it is for bearing lubrication. For bearings with under‐ring lubrication, when the bearing adopts outer guidance, the distribution of lubricating oil in the key areas of the bearing is worse than that for internal guidance. However, the pressure in the working contact area of the bearing slightly increases from 0.642 to 0.759 MPa with the inner guide clearance increasing from 0.4 to 0.8 mm. [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]

A numerical method is proposed to evaluate the effect of non‐Gaussian roughness on point contact elastohydrodynamic lubrication (EHL). A mixed EHL model of point contact, considering non‐Gaussian roughness, is developed. The oil film pressure in the model was controlled by the Reynolds equation of average flow, and the contact pressure of asperity was obtained by the rough surface micro‐contact model. The influence of non‐Gaussian roughness parameters on contact pressure distribution, film thickness profile and the ratio of asperity pressure to contact load (asperity load ratio) are investigated based on the mixed EHL model. The results show that the asperity pressure increases as root mean square (RMS) roughness increases, skewness and kurtosis. The film thickness also increases with RMS roughness and skewness, but is not sensitive to kurtosis. [ABSTRACT FROM AUTHOR]

The elastohydrodynamic lubrication (EHL) model of angular contact ball bearings (ACBB) with local defects under spin condition is established. The local defect surface profile is characterised. On this basis, the modified quasi‐static model of ACBB with local defects is proposed. Then, the comprehensive stiffness model of ACBB with local defect under EHL is built, and the influence of different factors on the mechanical characteristics of ACBB with local defect is investigated. The results show that with the increase of the local defect size, the equivalent contact stiffness of the defect area decreases, and the contact load in non‐defect area increases. Considering EHL, the contact deformation of bearing decreases, the contact load and equivalent comprehensive stiffness increases obviously. The axial contact angle of the defect area largely determines the equivalent comprehensive stiffness of the roller at the defect. [ABSTRACT FROM AUTHOR]

The distribution of lubricant flow field inside the two‐stage transmission reducer is very complicated during splash lubrication, which is difficult to be visually simulated and analysed using traditional finite element methods (FEM). There are many problems in model processing, algorithm selection, mesh division, and computational workload. Through sufficient investigation and experimental validation based on literature, the moving particle semi‐implicit (MPS) method is proposed to study the splash lubrication characteristics of a rail vehicle reducer. Through this method, the visual simulation calculation of multiple working conditions of reducer with complex structure is realised, and the unreasonable structure of the gearbox body is optimised. The model of oil supply demand in the Hertz contact zone of gear transmission is established, and the time‐domain variation law of oil particles number in the contact zone and oil supply state are analysed. It is found that the optimised reducer model can meet the demand of oil supply under the four typical working conditions of the rail vehicle. The higher the initial oil volume is, the more sufficient the oil supply is. Compared with the working temperature conditions of 20 and 80 °C, the lubrication effect is better at 40 and 60 °C. By analysing the power loss proportion of each gear, it is found that the sum of power loss of gear 1 and gear 2 is dominant under different working conditions, reaching 76%–99.5% of the total churning power losses. [ABSTRACT FROM AUTHOR]

In this paper, a tribo‐dynamic model of a helical gear is established. For the lubrication sub‐model, a finite line thermal elastohydrodynamic lubrication model of helical gear is adopted. The lateral vibration, axial vibration of gear and torsional vibration of the gear shaft are considered in the dynamic sub‐model. Results show that the tribological parameters of helical gear under the tribo‐dynamic model deviate significantly from that of the quasi‐static model, especially in the engaging‐in region of tooth pair. The friction excitation mainly affects the vibration along the off‐line‐of‐action direction of the gears. The influence of operating conditions on the tribological and dynamic properties of a helical gear pair is significant, especially in the case related to the characteristic frequency of gears. [ABSTRACT FROM AUTHOR]

Porous materials are widely used in friction pairs. The transient squeezing flow of the lubricant significantly affects the lubrication quality. The study found that the lubricant penetrates into the porous matrix in the contact area and exudes upward to the entrance of the contact area. The maximum stress occurs at the subsurface of the contact zone, and the maximum pressure occurs at the contact centre. In the early loading stage, the lubricant exudates, resulting in a higher liquid‐phase load. With the prolongation of the time, the average stress decreases and then increases gradually, whilst the average pressure has the opposite change. In the late loading stage, the load is completely borne by the solid phase. Increasing the load will increases the seepage velocity of the lubricant, which enhance the pumping effect of the friction interface. The findings can help for better understanding of the self‐lubrication mechanism of the porous materials. [ABSTRACT FROM AUTHOR]

In this paper, a simulation model of reciprocating rod seal systems when there is axial texture on the rod surface due to wear is studied. The model includes macroscopic solid mechanics analysis, microscopic contact mechanics analysis and fluid mechanics analysis, and on this basis, the change of surface pressure when the sealing ring fall into a texture is calculated by the micro‐deformation mechanics analysis of the seal surface. Then, the stiffness matrix method is used to find the film thickness when the three pressures in the sealing area are in equilibrium, completing the fluid–solid coupling calculation. Combined with the above simulation process, the performance parameters of the sealing system such as leakage and friction can be obtained. Results show that axial texture will degrade sealing performance, which increases leakage and friction. The simulation results can quantitative characterise the influence of rod wear on sealing performance and provide some theoretical basis for the study of seal failure mechanism and prediction of seal life. [ABSTRACT FROM AUTHOR]

In the actual working condition, due to the manufacturing errors, improper installation, load, thermal deformation or other factors can cause the journal surface to produce the form and position errors. The mathematical models are developed that takes into account the form and position errors, the lubrication performance of four‐recess capillary restrictor hybrid journal bearings with different journal tilt angles and cylindricities is studied, and the effect of eccentricity on the oil film lubrication performance is analysed. The results show that the dimensionless oil film pressure and loading capacity increase as the journal tilt angle and eccentricity increase considering journal tilt, and the friction coefficient tends to increase and then decrease. Compared with journal alignment, the oil film thickness distorts, the oil film pressure peak shifts to the edge of bearing, and the horizontal tilt has a greater impact on bearing when the journal is tilted. The oil film pressure distribution has no significant change considering cylindricity errors, while the oil film pressure value increases, the loading capacity increases and the coefficient of friction decreases as the cylindricity and eccentricity increase. The research shows that the presence of a certain cylindricity error contributes to the lubrication performance of four‐recess capillary restrictor hybrid journal bearings. [ABSTRACT FROM AUTHOR]

Based on the lubrication angle field and the locus of lubricating weak point, the lubricating characteristic of the toroidal surface enveloping cylindrical worm drive is globally investigated. The nonlinear equation system to determine the lubricating weak point is established by utilising the lubrication angle. Generally speaking, the weak locus always exists roughly in the middle of the tooth surface of cylindrical wormgear and a zone with worse lubricating behaviour is around the locus. By increasing the number of worm thread, the locus of lubricating weak point can be completely removed from the wormgear tooth surface, and the locus approximately is in the shape of the inverse capital letter L. On this occasion, the entire wormgear tooth surface is half surrounded by the locus, and the overall lubrication performance of the worm drive is improved. The current research is an application of elastohydrodynamic lubrication (EHL) on worm drive. [ABSTRACT FROM AUTHOR]

To improve the tribological characteristics of the face seal, the squamous groove micro textures with different area proportion and the circular dimple micro texture were designed and manufactured. The disc‐disc friction and wear experiments and numerical simulation were carried out in oil lubrication. The pressure distribution, friction coefficient, fluid temperature and wear morphology are investigated. The study show that the friction coefficients of the micro textured and untextured samples decline with the increase of load, but first increase and then decrease with the rise of rotational speed. Micro textured samples could decline the friction coefficient effectively, and the asymmetric structure in the lubricant inflow and outflow region of the squamous groove micro texture makes it have better tribological performance. In addition, the micro texture can increase heat dissipation area, reduce heat production and collect wear debris, which could modify the lubricant temperature and wear morphology effectively. [ABSTRACT FROM AUTHOR]

The oil storage effect of textures is beneficial for lubrication performance under starved lubrication. When the larger of the two surfaces in friction pairs is textured, the moving textures should be considered because the boundary conditions are transiently changed at each moment. This is especially for the cross‐hatched textures, which are manufactured on the cylinder liner while not on the piston ring. However, it means that the calculation cost will be very expensive for engineering friction pairs because the required calculation scale is very large and the required time step is very small. So the dynamic characteristics of moving textures on engineering surfaces are normally neglected in the existing researches. In this study, a starved lubrication model of the piston ring‐cylinder liner (PRCL) system is established considering the oil storage effect, local hydrodynamic effect and dynamic characteristics of the moving cross‐hatched textures. To speed up the calculation, an efficient parallel algorithm is developed. The results show that there is a significant difference in minimum oil film thickness (MOFT), wear load and oil film boundaries between stationary textures and moving textures, so the moving textures should not be simplified. This is helpful to find a better design of textures for engineering friction pairs. [ABSTRACT FROM AUTHOR]

Reciprocating spur gear rack is prone to lubrication failure near the reversing dead center position. Ree‐Eyring lubrication fluid, multigrid method and multigrid integral method were used to calculate the pressure profile, film thickness and oil temperature rise. Compared with linear motion, the process of reciprocating commutative movement is more complicated and the lubrication state are more unstable. The effects of different reversing duration time and commutation meshing state on lubricant film were analysed. The results show that, the oil thickness during the gear reversing process is significantly reduced. While shortening the reversing time can improve the lubricating film thickness, it causes the instantaneous oil temperature to rise. Therefore, the gear tooth damage caused by high temperature can be avoided by prolonging the reversing duration time properly. The longer the reversing duration time, the minimum value of central film thickness and central pressure is closer to the meshing outlet area. No matter what the reversing time change, the minimum lubrication film thickness is in the reversing dead center position. So the reversing dead center is still the dangerous point for the lubrication failure of the spur gear rack mechanism. When the reversing dead center is in the leading tooth of double‐tooth meshing, the gear has the largest film thickness and the largest contact area. In addition, the synthetic radius of curvature and entrainment velocity become larger so the lubrication conditions have been improved. The results provide the theoretical basis and guidance for the reasonable design of the spur gear rack and the improvement of its lubricating performance. [ABSTRACT FROM AUTHOR]

In this study, an interfacial slip model including the limiting shear stress is proposed and applied to the thermal elastohydrodynamic lubrication (EHL) analysis of a helical gear pair. The main difference between the proposed model and the classical EHL model is that, the term of entrainment velocity in Reynolds equation is modified. The influences of interfacial slip, thermal effect, initial limiting shear stress and operating conditions on the tribological properties are evaluated. Due to the interfacial slip, the pressure distribution moves towards the inlet region, and the fluctuation distributions of entrainment velocity and film thickness are similar to the trigonometric function. The influence of thermal effect on interfacial slip cannot be ignored, especially in the case of high speed and heavy load. As the input torque and input rotational speed increase, the interfacial slip gradually extends to the whole meshing process. [ABSTRACT FROM AUTHOR]

In mixed lubrication, material wear is inevitably caused due to solid contact. Simultaneously, the surface morphology after wear will affects the lubrication performance. To understand this coupling process, virtual surface reconstruction technology and mixed lubrication sliding wear model were applied to predict the evolution of wear characteristics and lubrication characteristics during wear in this study. The effects of the roughness root mean square (RMS), roughness direction and wavelength ratio on the contact area ratio, the contact load ratio, accumulated wear, film thickness and the friction coefficient were analysed. The results indicated that the contact area ratio and the contact load ratio and the friction coefficient decreased and average film thickness increased with the increase in the number of the wear cycles. In addition, a surface with low‐roughness RMS, longitudinal roughness texture and high‐wavelength ratio is suitable for improving lubrication performance and reducing wear. [ABSTRACT FROM AUTHOR]

Calculating the flow of a film of lubricant between rough surfaces by solving the Reynolds equation requires a very fine mesh to capture the details of the topography and is thus very time consuming. In the present paper, a multiscale method is proposed. The domain is divided into an appropriate number of subdomains on which deterministic simulations are performed. The results of this microscale solution are coupled at the macroscale by employing a macromesh on which a mass flow balance is implemented. This method has already been successfully applied to liquid lubrication and is extended to gas lubrication. A significant reduction in computation time is obtained compared to a fully deterministic solution. The calculation of the load is also accurate. [ABSTRACT FROM AUTHOR]

Free surface lubrication of rotating cylinders by Newtonian liquid jets was investigated at different impingement positions, jet‐ and circumferential velocities. The interaction between impinging round laminar jet and rotating surface was characterised by high‐speed imaging. Compared to flat surface impingement, the liquid deposition mechanism is more complex and often accompanied by phenomena such as splashing, jet deflection and formation of radial surface stripes. Liquid splashing initially develops in direct deposition regime due to hydraulic jump‐induced droplet shedding, transitioning to lamella instability splash at higher Reynolds numbers. The critical Reynolds number for splash onset is of same order of magnitude as for flat surface impingement and fairly constant at low relative jet impingement angles, but increases exponentially when angle approaches 90°. Liquid film width and thickness were both determined proportional to the square root of the jet/surface velocity ratio, with respective power law models in good agreement with measured values. [ABSTRACT FROM AUTHOR]

This study proposes a tribo‐dynamic model for point contacts under lubrication, focusing on the excitations caused by surface movement, defect and load impact. Surface movement and load impact can cause changes in contact force, resulting in acceleration and dynamic displacement, which may affect the flow of the lubricant. The traditional lubrication model is usually steady or transient, and load balance is used to correct the normal height, ignoring a series of influences such as the mass, stiffness and damping. It requires repeated corrections to obtain a balanced position, which is very time‐consuming. By combining tribology and dynamics, dynamic excitation is introduced in the contact process in this study. After determining the initial value, the normal height can be directly obtained from the dynamic equation. Besides, a comparison between the tribo‐dynamic model and the steady‐state model is presented. It is found that the film thickness and pressure distribution calculated by the two models are almost the same at medium and low speeds, while the calculation results of the two models are different at high speed or under load impact, which emphasises the importance of considering the dynamic behaviour in the study of contacts. [ABSTRACT FROM AUTHOR]

Many contributions have focused on the pitting analysis in gear transmissions. However, studies on pitting fatigue in spiral bevel gears are limited due to the complexity of tooth contact and lubrication analysis. This paper is to present a reasonable methodology to simulate the pitting crack nucleation of spiral bevel gears considering the real three‐dimensional (3D) rough surface contact where the intermittent asperity stress concentrations is prominent. The proposed model includes a loaded tooth contact analysis model, a mixed elastohydrodynamic lubrication model proposed previously, 3D stress filed formulation, and multi‐axial fatigue criterions. In order to determine an appropriate multi‐axial fatigue criterion for spiral bevel gear, a characteristic plane approach and a conventional critical plane approach are employed in this study. The predicted micro‐pitting lives are compared to published micro‐pitting investigations to assess the reliability of two fatigue criterions in simulation of the micro‐pitting failure. It is observed that the characteristic plane approach is better to reveal the failure mechanism in spiral bevel gears. [ABSTRACT FROM AUTHOR]

Thrust bearings are widely used in many rotary industrial applications. In this work, a thrust bearing surface under the mixed lubrication regime is analysed and then optimised with aim for use in an injection moulded polymer bearing. A model which couples the mechanical deformation, boundary lubrication and solid contact is developed to investigate the behaviour of the thrust bearing under the load balance condition. This model provides the predictions of important quantities such as load carrying capacity from fluid and solid contact, minimum film thickness and contact pressure. More important, the large‐scale surface geometry is optimised using a quadratic geometry and this large‐scale surface is superimposed with the small‐scale roughness from measured surface to form an optimised surface. This large‐scale geometry might be controlled in the injection moulding process of polymer thrust bearings, whereas it is more difficult to control the roughness. The fluid load carrying capacity for the optimised surface has more than doubled compared to the fluid load carrying capacity for the measured surface. [ABSTRACT FROM AUTHOR]

The study presents a profile design method to improve the wear performance of misaligned water‐lubricated bearing based on the modified Archard model. This method takes into account the variation of the film thickness under the mixed elastohydrodynamic lubrication (mixed‐EHL). A transient hydrodynamic Reynolds equation model with the Patir–Cheng flow factors is used to predict the evolution of the mixed‐EHL performance over time. The Archard model is extended to predict the time‐varying wear based on the fatigue concept. To verify the effectiveness of the proposed profile design method; the simulation results, including the transient contact pressure, wear depth and wear volume, between the considering and not considering the profile design are compared. To gain insight, several illustrative examples are presented to show the amelioration of the profile design. Parametric studies are reported to show the applicability of the profile design and emphasise the profile height selection. Therefore, the profile design is an extraordinary method to reduce the edge wear. [ABSTRACT FROM AUTHOR]

The plasto‐elastohydrodynamic lubrication (PEHL) model of the greased ellipsoid contact is established and solved numerically. In doing so, the increment theory of the plastic surface is adopted to solve the residual deformation, and the fast Fourier transform (FFT) method is employed to accelerate the deformation and stress calculations. Meanwhile, the effeteness of the PEHL model is verified through the residual stress experiment and finite element method. It is found that the plastic behaviour results in a reduction in the maximum grease film pressure. Under heavy load conditions, the grease with large rheology index, large tangential modulus or high entrainment speed of the lubricant is helpful to reducing the maximum residual deformation and maximum residual stress of the greased ellipsoid contact. [ABSTRACT FROM AUTHOR]

A mixed elastohydrodynamic lubrication (EHL) model for a coated angular contact ball bearing is developed by coupling the influence coefficients with the unified deterministic mixed EHL model. Based on the bearing quasi‐dynamics analysis, the influences of the surface roughness, coating thickness, and boundary friction coefficient on the mixed EHL performance of the coated bearing are discussed. The results reveal that high surface root‐mean‐square roughness can be detrimental to bearing lubrication performance and increase the risk of coating failures. Coating thicknesses on the order of a few microns have a limited effect on the contact load ratio, film thickness ratio, and friction coefficient while having a significant effect on the maximum surface tensile stress and interfacial shear stress, especially for high‐friction low‐speed conditions. A low‐friction self‐lubricating coating can effectively improve the tribological performance and prolong the service life of the bearing, especially in the bad lubrication state with severe asperity contacts. [ABSTRACT FROM AUTHOR]

Citric acid‐synthesised Eu‐doped WO3 (WO3:Eu3+) and Mn3B7O13Cl nanoparticles were characterised by X‐ray diffraction and transmission electron microscopy. The tribological properties of the Eu doped WO3 and Mn3B7O13Cl prepared as anti‐wear additives for enhanced lubrication were studied using a four‐ball tester. The experiment results indicated that Eu doped WO3 nanoparticle reinforce Mn3B7O13Cl has excellent load‐carrying capacity, wear‐resistance and friction‐reducing properties in water‐based lubricant, optimum concentration of WO3:Eu3+‐Mn3B7O13Cl was 0.5 wt%. The wear scar diameter decreased from 0.62 to 0.37 mm and the coefficient of friction was reduced from 0.083 to 0.065, which reductions are attributed to the nanotribofilms composed of B2O3, WO3, Fe2O3 and Eu2O, which prevented direct contact between metals. Hot rolling experiments of laminated Cu‐Fe composite sheet were carried out to study the effect of nano‐WO3:Eu3+‐Mn3B7O13Cl on surface qualities including topography of rolled strips. Results show that the surface topography becomes smooth with the addition of nanoparticles into water‐based lubricant, which is mainly attributed to the nanoparticles increase the viscosity of water‐based lubricant and the oil film to avoid the direct contact tribopair during hot rolling, thus reducing the friction coefficient and roll wear. [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]

This paper investigated the effect of oil‐air lubrication on contact temperature and sliding tribological properties. On the basis of heat transfer theory, a numerical simulation model of forced convection was established. Experiments were conducted using the tribology machine. Results show that in oil‐air lubrication, forced convection can significantly reduce the temperature at the contact position. Nonlinear decline and decrease in the descent rate of contact temperature were observed with the increase in convective heat transfer coefficient. The convective heat transfer between friction pairs increased with air supply velocity, whereas the sliding friction coefficient initially decreased and then increased. The friction flash temperature reached its lowest value with proper heat dissipation capacity. With the increase in ambient temperatures of the friction pairs, the sliding friction coefficient decreased, whereas the friction flash temperature increased. Influenced by the oil‐air lubrication heat dissipation in the test, the wear mechanism of point contact sliding friction was abrasive wear. [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]

In order to investigate the dynamic characteristics of an oil film under vibration, the dynamic model of an involute gear system was established based on the dynamics theory. The vibration and lubrication characteristics of the gear system were analysed in detail. Furthermore, based on the numerical solution of lubrication, a model of oil film stiffness was established. The dynamic characteristics of the oil film were verified by calculating the oil film stiffness. It was found that both oil film pressure and thickness manifested certain dynamic characteristics under vibration. Moreover, the intensities of oscillation amplitude and frequency were different under different loads and rotating speeds. The oil film stiffness gradually decreased and increased, respectively, with the increasing rotating speed and load. Therefore, for a heavy‐duty high‐speed gear system, the coupling effect of vibration and lubrication should be considered. [ABSTRACT FROM AUTHOR]

Real‐time measurement of the lubrication state is one of the critical problems in studying the lubrication state and its transformation characteristics. Based on the experimental results, shrinkage resistance principle and Greenwood's contact theory, a mathematical model for cylinder liner‐piston ring that can be used to measure the resistance of film thickness ratio is established. On this foundation, the correspondence between the film thickness ratio and the contact resistance for cylinder liner‐piston ring was presented and the technical possibility to characterise the real‐time lubrication state was provided. An experimental study for determining the lubrication state of cylinder liner‐piston ring based on resistance measurement method was conducted on a reciprocating friction and wear tester to verify the applicability of resistance measurement method in cylinder liner‐piston ring friction pair. Results show that the contact resistance method is reliable and practicable to determine the lubrication state of cylinder liner‐piston ring friction pair. [ABSTRACT FROM AUTHOR]

In current researches on the lubrication of engine piston ring, some were based on a hypothesis that the piston ring is on a flooded lubrication status. Although some others belong to the starved lubrication analysis, the one‐dimensional model, a certain form of starved lubrication status or simplified manner were used. In this paper, on the basis of the equations about the lubricating oil flow‐rate and control volume, a flow model of lubricating oil in the piston ring‐cylinder liner conjunction is established, and the influence of the situation of supplied lubricating oil film at the piston ring inlet on the two‐dimensional starved lubrication characteristics of piston ring for a four‐stroke engine is studied. The results indicate that the lubrication condition at the piston ring inlet has significant impact on the lubrication characteristics of piston ring. When the supplied lubricating oil at the piston ring inlet increases, the minimum film thickness of piston ring will increase, meanwhile the maximum film pressure, asperity contact force, friction force and power loss will decrease. If the film thickness at the piston ring inlet is smaller, the increase of the supplied film thickness can improve obviously the lubrication characteristics of piston ring. [ABSTRACT FROM AUTHOR]

Thickener as an important ingredient affects the performance characteristics of lubricating grease. Here, seven lithium complex greases (LCGs) were prepared by saponification of 12‐OH stearic acid and low molecular weight dibasic acids (including adipic acid, sebacic acid, phthalic acid, dodecanedioic acid, and the combination of sebacic acid and phthalic acid in different molar ratios) with LiOH, using polyalphaolefin (PAO 40) as base oil. Physical properties and lubrication function of as‐prepared LCGs were evaluated in detail, and the friction mechanism was explored via analysis on the morphologies and composition of worn surfaces. Results illustrate that the saponification of mixed 12‐OH stearic acid and sebacic acid with LiOH provides good thickener for improving the physico‐chemical performance of LCG, while the thickener prepared by 12‐OH stearic acid and adipic acid with LiOH enhances lubrication function of LCG, mainly depending on synergy of grease film and tribo‐chemical reaction film. [ABSTRACT FROM AUTHOR]

In this paper, an elastohydrodynamic impact model is proposed, and the prediction of lubricating film performance considering squeeze effect and thermal effect is presented. Effects of sinusoidal impulse load, sinusoidal impulse entrainment velocity, multi‐frequency vibration, and acoustic noise on thermo‐mechanical characteristics of gear lube are numerically investigated. Results show that both sinusoidal impulse load and sinusoidal impulse entrainment velocity can cause remarkable increases in central film thickness and minimum film thickness and induce small reduction in friction coefficient. The sinusoidal impulse load causes considerable increase in central film pressure; however, the sinusoidal impulse entrainment velocity induces significant decrease in central film pressure. The multiple high constant frequency vibration causes considerable increment in film pressure, but maintains small fluctuation in film thickness. Additionally, the consequence of multiple high constant frequency vibration induces evident reduction in friction coefficient. [ABSTRACT FROM AUTHOR]

The connecting rod big end bearings are under dynamic lubrication during working cycle, and in most of the time, the con rod is subjected to compressive stress. The conventional method of performing an EHL analysis on a bearing involves development of complex mathematical equations and simplification of actual physical model. This paper presents a methodology to model and simulate the elastohydrodynamic lubrication and wear study of connecting rod big end bearings of off‐highway application engine using the application of computational fluid dynamics (CFD) and computational structural dynamics (CSD) approaches. The pressure field for a full journal bearing operating under laminar flow regime with various eccentricities was obtained by CFD, and fluid pressure distribution and deformation in the bearing liner due to pressure were evaluated using FSI approach. Relevant parameters of lubrication characteristics were analyzed to optimize the eccentricity value. The maximum bearing load value of 21 kN was noticed at TDC position for the optimum eccentricity. The load distribution indicated critical points in the bearing, and the data obtained from bearing load and sliding velocity of journal were used in Archard's wear relation to determine the wear depth along the bearing width. The simulated wear results were compared with three‐cylinder off‐highway application engine con rod big end bearings, which ran for 1000 hours at full load condition, and satisfactory agreement was observed between experiment and simulation values. [ABSTRACT FROM AUTHOR]

Internal gears with small tooth number difference are widely used as core component in robotics, medical, and other fields. The clearance between the entire meshing teeth is much smaller compared with other gear transmissions, indicating that the entire tooth profile can significantly affect the mixed elastohydrodynamic lubrication (EHL) state of a certain meshing point. Thereby, available lubrication analysis is limited with the assumption of effective radius at each meshing point. In the present study, the entire tooth profile with gear flank modification is studied to improve lubricating characteristics. A mixed EHL model for predicting the film, pressure, power loss, and subsurface stress is presented with consideration of the entire tooth geometry. We find that the tooth geometry away from the meshing location shows a remarkable influence on the film and pressure distribution as well as power loss of tooth rubbing interface, which is commonly unrecognised in previous study. Optimization of modification parameters is observed under different operating conditions, highlighting the critical role of entire tooth geometry in mixed EHL behaviour for internal gears with small tooth number difference. [ABSTRACT FROM AUTHOR]

In this paper, the angular contact ball bearings under low‐speed and heavy‐load conditions is studied with a coupled numerical method of mixed elastohydrodynamic lubrication (EHL) and quasi‐dynamic analysis. Compared with the quasi‐dynamic analysis without consideration of the mixed lubrication characteristics, the present coupled method reveals a smaller minimum film thickness and a larger frictional coefficient in ball‐race contact interface, leading to increases in the normal contact load, slide‐to‐roll ratio, and relative sliding velocity. Effects of operation condition (eg, rotational speed) and structural parameter (eg, inner raceway curvature coefficient and initial contact angle) on the contact and lubrication performances are discussed. The results show that a larger inner raceway curvature coefficient results in a smaller average film thickness and film thickness ratio, a larger frictional coefficient, and maximum contact pressure, while the increase in the initial contact angle has an opposite effect on these parameters. [ABSTRACT FROM AUTHOR]

This paper presents a new numerical model of wheel/rail in rolling contact to study the adhesion mechanism under the starved interfacial contaminations at high speed considering surface roughness. A thermal starved mixed elastohydrodynamic lubrication (EHL) theory is hired in the model. The empirical equations for analysing the contact force of rough surfaces that are based on amount of accurate finite element analysis (FEA) of an elastic‐plastic single‐asperity contact over a rigid flat are proposed. Multilevel method is used to solve the modified Reynolds equations, and sweeping column method is used to solve energy and heat conduction equations. The pressure field, the fractional film content, and the temperature field are obtained through the present model. In addition, the influences of train speed, surface roughness amplitudes, and inlet film thickness on the adhesion coefficient are investigated. The results from the present model have been compared with those from flooded analyses for water and oil‐contamination cases. The numerical results show that the inlet film thickness and the train speed had a significant effect on the wheel/rail adhesion ability. [ABSTRACT FROM AUTHOR]

An elastohydrodynamic model of ferrofluid‐lubricated involute spur gears was established, and transient thermal elastohydrodynamic lubrication (EHL) analysis was conducted using multigrid method and multigrid integral method. The transient lubricant film thickness, pressure, and friction coefficient characteristics of the spur gears were compared under different carrier fluid ferrofluids. Ester‐based H01 ferrofluid was selected to further examine the lubricant film elastohydrodynamic characteristics of the involute spur gears under different loads and speeds. The results indicated that the film thickness and the inlet area pressure were the largest when hydrocarbon‐based E02 ferrofluid was used for lubrication and were the smallest when ester‐based ferrofluid H01 was used for lubrication. When ester‐based H01 ferrofluid was used, the film thickness, the inlet area pressure, and the second pressure peak increased with the increase of speed, and the second pressure peak shifted toward the inlet area. The friction coefficient and the maximum temperature gradually decreased with the increase of speed, and the second pressure peak, the friction coefficient, and the maximum temperature gradually increased with the increase of load, while the film thickness gradually decreased. [ABSTRACT FROM AUTHOR]

In the present study, thermal starved elastohydrodynamic lubrication (EHL) model is developed for a helical gear pair. The influences of inlet oil‐supply layer, input speed, lubricant viscosity, and surface roughness on the lubrication behaviour are investigated. The minimum film thickness, temperature rise of teeth surfaces and oil film, and the friction coefficient are predicted along the line of action (LOA). Results show that the effects of inlet oil‐supply layer, input speed, and lubrication viscosity on the tribological performance are remarkable. Under the starved lubrication, the influence of inlet oil supply on the temperature rise is insignificant. Meanwhile, the effect of surface roughness has been discussed. It reveals that the roughness texture along the entrainment velocity direction has significant influence on the lubrication characteristics. The results provide the tribological guidance for design of a helical gear pair in engineering. [ABSTRACT FROM AUTHOR]

The rapidly growing demand for wet‐mate electrical connectors in underwater projects has attracted the attention of researchers in the field. Sealing is the key to underwater connectors. In this paper, the reciprocating O‐ring seal during underwater operations of the pressure‐balanced connectors was studied. A numerical model containing the Reynolds equation, hyperelastic deformation, and asperity contact was used to describe mixed elastohydrodynamic lubrication (EHL) in the O‐ring seal. Results indicate that the friction force of the seal in the connector decreases directly with the increased sealed pressure, and its friction force is smaller than that in the conventionally hydraulic structure. As the sealed pressure increases, the minimum film thickness in the connector increases, which means a better lubrication in the deeper sea. The oil leakage in the connector increases with the sealed pressure, but the increase rate is smaller than that in the hydraulic structure. It proves that the design of pressure‐balanced structure can not only achieve wet‐mate operation at any depth but also facilitate its dynamic sealing performance. [ABSTRACT FROM AUTHOR]

An oil‐air lubrication system is driven by high‐speed air. Oil is transported to the contact portion in the form of fine oil droplets to form a lubrication film, thereby improving lubrication performance among matching pairs. A test for point contact sliding friction and wear was conducted under oil‐air lubrication conditions. Oil‐phase and pressure distributions near the contact zone were investigated through numerical simulation. This study aims to explore the effect of air velocity on sliding wear characteristics of a point contact. Results show that point contact sliding wear is considerably affected by air supply speed. The lubrication performance between friction pairs is optimal under appropriate air supply speed, which can enable the oil‐air pressure and oil‐phase volume fraction near the point contact area to obtain appropriate values that are useful to the spread of fine oil droplets. This process ensures that the sliding friction coefficient and specific wear rate can be reduced. The friction coefficient decreases to approximately 0.027, and the specific wear rate is 1.06 × 10−5 mm3/N·m. Under oil‐air lubrication, microfurrows appear on the worn surfaces of materials with the change in air supply speed. The shape of debris is mainly a flake or block with a few long strip abrasives. The wear mechanism is abrasive. [ABSTRACT FROM AUTHOR]

The entire load in human body is supported by the hip joint bearing. In the present work, elastohydrodynamic lubrication analysis of metal and metal hip implant is performed by using Newtonian lubricant. The Reynolds equation coupled with stress equilibrium equation has been used to get the pressure and performance characteristics of hip joint bearing. The governing Reynolds equation is nonlinear and cannot be solved by using close form solution methods. The finite element method and Newton‐Raphson method are used to obtain solution of the present equation. It has been observed that numerical convergence is much faster with NR method. From the results, it is observed that FEM with modified Newton‐Raphson method has the capability to compute accurate results for realistic modelling. [ABSTRACT FROM AUTHOR]

Surface topography parameters significantly control physical processes which have asperity‐to‐asperity contacts in tribological components undergoing friction and wear. In this study, the effect of correlation length, maximum contact load, and surface roughness on friction coefficient and load distribution is studied. The load‐sharing concept is employed to determine friction coefficient and load distribution in the mixed‐lubrication regime. Results clearly demonstrate the effect of correlation length on friction coefficient and load distribution. It is found that the lower value of the coefficient of friction may be achieved even at low velocity for the smooth surface as compared with rough surfaces having higher surface roughness. For a particular value of velocity, the coefficient of friction decreases with an increase in maximum contact load. This work will help in predicting the coefficient of friction in the mixed‐lubrication regime for the engineering surfaces produced by processes like grinding, which is the result of an abrasive action. [ABSTRACT FROM AUTHOR]

In tribo‐system, thermal gradients will drive the liquid lubricant to migrate from warm to cold regions, resulting in starved lubrication. This study reports an experimental investigation on the influence of surface topography on the migration behavior of paraffin oil lubricants. Experimental results are provided for specimens treated by polishing, shot‐blasting, and sandpaper grinding techniques. 3D surface parameters of average surface roughness Sa and developed interfacial area ratio Sdr are measured via a 3D optical microscope, and the influences on migration behavior are discussed. Experimental results demonstrate that shot‐blasting process is an effective approach to impede the thermocapillary migration, and that decreasing surface roughness will contribute to the obstruction effect. A particular attention is paid to the inherent correlation of the migration capacity with the contact angle and surface free energy. [ABSTRACT FROM AUTHOR]

Abstract: Considering the tribology design theory of arbitrary intersecting line gear (AILG) is still a blank, the equivalent ellipsoid model of contact area of the AILG pair was built and then improved by 3 modification methods of line teeth profile. Based on the improved model, semiquantitative analyses of the relationship between the parameters of the AILG and the ratio of principal curvature radii of equivalent ellipsoid Rx/ Ry were presented, and design criteria for the parameters of AILG based on elastohydrodynamic (EHL) point contact model were proposed. The results of the theoretical calculation and the optical EHL experiment proved that the modifications of teeth profile and the parameters design criteria for the AILG are conducive to improving its EHL performance. [ABSTRACT FROM AUTHOR]

Abstract: Planetary drives with small teeth number difference are key components widely used for transmitting significant power. In general, these components are designed with short tooth depth to avoid the interference of addendum, which may have significant effect on contact conditions and lubrication characteristics. In the present study, a modified mixed elastohydrodynamic lubrication model is employed to analyse the lubrication performance in tooth pairs with consideration of real geometry profile (short tooth depth) and 3D machined roughness. Numerous sets of cases from meshing in to meshing out have been analysed under a wide range of operating conditions to study the tribological behaviour. Obtained results suggest that the lubrication and friction behaviours are much worse especially at meshing out points than those ignoring the influence of real tooth geometry. The modified elastohydrodynamic lubrication model is compared with finite element analysis results which indicate that it is able to handle practical cases in which the real contact width is much shorter than Hertzian contact width and can be employed for the analysis and design of planetary drives with small teeth number difference. [ABSTRACT FROM AUTHOR]

Numerical calculations have been conducted to study elastohydrodynamic lubrication (EHL) with lubricant in the form of droplet groups, which was aimed to simulate air-oil lubrication. Two types of lubricant droplet distributions, ie, 1 row of droplets along the centreline of the contact or 2 rows of droplets on each side of the centreline, were adopted. The results showed that continuous EHL film could be obtained in spite that discontinuous lubricant droplets were supplied, which is attributed to the squeeze spread and rejoining of the droplets at the inlet. The total effective lubrication time for full film lubrication has a linear correlation with the number of the droplets, and there exists an optimum droplet spacing distance for continuous full film lubrication. For a constant volume of lubricant, calculations indicated that for most efficient lubrication, there is a trade-off between the droplet size and the number of droplets divided. [ABSTRACT FROM AUTHOR]

Abstract: The object of this paper is to develop a 3‐dimensional numerical model to estimate the wheel and rail adhesion coefficient considering surface roughness under wet condition. The water film thickness formed between wheel and rail plays an important role on the adhesion coefficient. Firstly, the full isothermal elasto‐hydrodynamic lubrication (EHL) theory of elliptical contact is used to obtain more than 20 different film thickness cases using Bett and Cappi's viscosity equation of water. Based on the numerical solutions, empirical formulas for the central and minimum film thickness are obtained relating to rolling speed, wheel and rail contact force, and material parameters and compared with results obtained by previous studies. Secondly, taking the surface roughness into consideration, the EHL theory is used to obtain the load carried by water, and the statistical elastic‐plastic mico‐contact model presented by Lee et al. was applied to calculate the load carried by asperities. Meanwhile, the thermal influencing reduction factor is used to consider the inlet heating effects on the film thickness, and the change of water viscosity is also taken into consideration due to the flash temperature generated between the moving rough surfaces. Furthermore, the present work investigates the dependence of the wheel/rail adhesion coefficient on train speed and surface roughness amplitude under wet condition. [ABSTRACT FROM AUTHOR]