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Surface texture is a valid way of improving hydrodynamic lubrication performance and reducing friction. In this work, a novel micro-additive manufacturing technique, selective laser melting ink-pri...

The purpose of this study is to explore the transient hydrodynamic coupling mechanism for misaligned journal–thrust microgrooved coupled bearings (referred to as coupled bearings) considering the a...

The primary objective of this research is to study the bearing performance characteristics having different operating conditions. Experimental investigations are carried out on phosphorous bronze h...

When a hydrodynamic journal bearing works under an excessively heavy load, there occurs the very small bearing clearance where physical adsorbed layer boundary lubrication is present. For evaluatin...

This work improves the tribological behavior via innovative surface designs for slipper pairs in seawater axial piston pumps. 316L stainless steel and carbon fiber/polyether ether ketone (CF/PEEK) ...

An analysis is presented for the performance of a hydrodynamic journal bearing where the interfacial slippage occurs, respectively, in two different areas with different sleeve surface properties o...

Lubrication of a wrist pin journal can become a limiting factor in the performance of internal combustion engines. A wrist pin journal is a hydrodynamic bearing with a radial clearance of only a fe...

In recent years, extensive use of smart lubricants has been made in order to control the tribological performance of fluid film bearings. The grooved surfaces of the journal bearing greatly influen...

One of the tribological requirements on engine bearing material is its ability to safely embed contaminant particles onto its surface and minimise damage to both the bearing and crankshaft surfaces. In this work, a journal bearing test rig that operates under constant load has been employed to investigate the embeddability behaviour of selected multi-layered Pb-free engine bearing materials at three different rotational speeds using engine oil contaminated with SiC particles. Experimental results have shown that third-body abrasive wear is influenced by the lubricant film thickness. There was also difference in embeddability of the different materials. Bismuth-based overlay and MoS2 containing polyamide-imide-based overlay-coated materials show higher wear compared to tin-based overlay and a polyamide-imide-based composite overlay-coated material. Steel counter surfaces sliding against bismuth-based overlay and MoS2 containing polyamide-imide-based overlay exhibited higher wear than those sliding against tin-based overlay and polyamide-imide-based composite overlay. Validerad;2019;Nivå 2;2019-04-12 (oliekm)

A second mode of abnormal hydrodynamic step bearing formed by boundary slippage is proposed. In this bearing, the lubricating film thickness in the inlet zone is lower than that in the outlet zone....

The present investigation was carried out to predict the oil-film pressure of a chemically modified rapeseed oil (CMRO) containing nano CuO/WS2/TiO2 using Response Surface Methodology (RSM) based D...

A new clearance design method is proposed for a reciprocating fuel pump. Structural and hydrodynamic lubrication analyses were conducted to design the clearance of the pump, and the former was used to evaluate the clearance reduction due to the deformation that results from applying maximum supply pressure. The reduction in the maximum clearance was used as the limit of the design, and the two-dimensional Reynolds equation is used to evaluate the lubrication characteristics of the pump with variations in the viscosity and clearance. The optimal clearance in the pump must be separately designed in both the stem and the head because the lubrication characteristics and the deformation patterns of the two parts are different. The validity of the numerical model was then verified by determining that the position of the wear was also similar to that of the minimum film thickness. Moreover, a rig test system was also used to verify the clearance of the proposed design method.

The lubrication characteristics of fuel pumps with spiral grooves are investigated by numerical analysis. The two-dimensional Reynolds equation is used to evaluate lubrication characteristics with variations in grooves and viscosity. Moreover, the equilibrium equation of moment and forces in the horizontal and vertical directions is used to determine the motion of the plunger. The lubrication characteristics of the fuel pump with spiral grooves are compared to those without spiral grooves. The lubrication characteristics of the pump are investigated by comparing the film parameters. The fuel pump with spiral grooves is effective for relieving any uneven pressure distribution surrounding the plunger and can improve the lubrication characteristics. The application of spiral grooves is shown to be more effective in a low-viscosity condition compared to in a high-viscosity condition.

This paper presents a friction model describing the tyre rubber/road interaction that takes into account the viscoelasticity of the tyre rubber, the texture of the road surface and a water layer between the tyre/road interface by introducing explicitly a computation of the water layer effect in the calculation process of the hysteretic friction. The geometry of the wetted portion of the interface model is simplified by transforming it into an equivalent hydrodynamic bearing. Utilising the Reynolds equation, the bearing load capacity is calculated and the resulting forces are subtracted from the contact load when calculating the forces of the hysteretic friction. The mechanical behaviour of the rubber is represented in the model by Kelvin–Voigt model. The frictional forces due to hysteresis are calculated at any given operating conditions (load, slip speed, etc.) from the contact geometry of rough surfaces caused by the viscoelastic behaviour of rubber. To validate the model, a set of surfaces incl...

The aim of this article is to propose a model capable of estimating the friction along a heavily loaded journal bearing under mixed and hydrodynamic lubrication. The finite element analysis–computa...

The present article describes a low-cost active aerostatic thrust bearing controlled via an Arduino card and with feedback transducers and valves embedded in it. Efforts were made to design a compact thrust bearing with small overall dimensions, robust behavior, and reduced costs. Two embedded electropneumatic digital valves are controlled with pulse width modulation (PWM) logic and used to modify the thrust bearing supply pressure. The feedback signal for the control comes from two embedded backpressure sensors designed and characterized for this purpose. The test benches required for static and dynamic thrust bearing characterization are described; preliminary experimental tests were carried out in open and closed loop configurations. The closed loop configuration of the system, with a proportional integral (PI) control, shows good behavior and the time needed for the thrust bearing to return to the reference gap value after a force perturbation of 40 N is about 0.1 s.

Adequate high-temperature lubrication between loaded surfaces in sliding contact can be one of the most challenging tribological problems confronting today's designers. In an attempt to provide a possible solution a test program was initiated to evaluate PS400, a recently patented, high-temperature solid lubricant coating. Made from nickel–molybdenum–aluminum, chrome oxide, silver, and barium fluoride–calcium fluoride, PS400 is a variant of the earlier coating, PS304, but is formulated for higher density, smoother surface texture, and greater dimensional stability. It was initially developed to minimize the start–stop wear in foil air bearings but is expected to perform well in other high-temperature applications where sliding friction and wear are a concern, such as variable inlet guide vanes and process control valve stems. To better define its operational capabilities, a series of tests was conducted to study the behavior of PS400 under reciprocating sliding contact at temperatures from 260 to ...

This research work explores the effects of thermal and inertia on hydrodynamic lubrication of asymmetric rigid rollers by incompressible non-Newtonian power law fluids and assesses the contribution of inertia to the system under consideration. The consistency of the power law lubricants is assumed to vary with the pressure and mean film temperature. The governing equations are solved first analytically and then numerically by the Runge-Kutta-Fehlberg method together with some reasonable tolerance. The results obtained confirm that there is significant increase in load and traction due to inertia. In addition, the effect of inertia shifts the pressure peak and the cavitation points toward the left.

The present study was conducted to examine the effect of laser surface texturing combined with couple stress fluids on the hydrodynamic lubrication of finite journal bearing in this work. The Jakobsson-Floberg-Olsson (JFO) boundary conditions were engaged instead of Reynolds boundary conditions to achieve realistic results. Moreover, the results were computed and authenticated with the previous published work. It was observed that the load-carrying capacity is increased with couple stresses for smooth journal bearings at different eccentricity ratios. However, the increment in load-carrying capacity with texture affects only at low eccentricity ratios. The combined effects of texturing with couple stress fluids lower the performance of journal bearings at different eccentricity ratios.

Hydrodynamic effects are responsible for a dimensionless load increase ΔW (relative to the load WHertz calculated in a dry contact) calculated primarily as a function of the dimensionless rolling element–race geometrical interference Δ/Rx, dimensionless speed, and radii ratio. The final load (W = WHertz + ΔW) is therefore never nil, even in cases when the geometrical interference is negative or nil, which corresponds to a Hertzian load nil.The final load is calculated by solving the following dimensionless algebraic relationship: , where δ is the elastic deformation (function of the load and radii ratio) calculated using a Hertzian relationship and H is the dimensionless film thickness, again a function of the load and radii ratio but also dimensionless speed and material parameters, the latter being included in piezoviscous-rigid (PVR) and piezoviscous-elastic (PVE, also called elastohydrodynamic or EHD) film thickness relationships. Advanced new curve-fitted relationships are also suggested in t...

A numerical analysis of the thermohydrodynamic lubrication of a rolling piston and two misaligned journal bearings in a rotary compressor has been carried out. The temperature rise of the oil film was calculated according to the transient energy equation of viscous fluid, and coupled analysis with the hydrodynamic lubrication of the rolling piston and journal bearings was conducted by using the finite element method and finite difference method. The distributions of the pressure and temperature rise of the oil film for several cycles were calculated. The analysis results show that for the journal bearings, the temperature of the oil film rises with the increase in pressure, the highest temperature appears around the region of the maximum pressure, whereas for the rolling piston bearing, there is a sharp peak in the temperature distribution. The maximum temperature in the oil film varies periodically with the rotation of the crankshaft, and after several cycles the balance between viscous heating a...

The scope of this article is to examine the effects of thermal expansion (up to seizure) on the clearance of a hydrodynamic bearing under prescribed operating conditions. This parametric study uses angular speed, eccentricity, and the journal/bushing material pairings as varying parameters. The study focuses on how the size of the clearance varies with temperature and pressure (elastic deformation) and whether it is possible for a complete thermal lockup (seizure) to occur when certain material pairings are used. The effects of the thermal expansion on the load-carrying capacity, torque, and total deformation of the clearance are presented. Thermal versus mechanical effects domination are also analyzed in order to establish the conditions under which one, or the other become dominant. The present model uses the three-dimensional Navier-Stokes equations and a fully termed energy equation for the fluid coupled in a two-way feedback mode with the 3D energy and the elasticity equations for the bushing and jou...

High aspect ratio microtools find numerous applications in the production of miniaturized components and structures, e.g., drilling of microholes in ink jet nozzles, air bearings, and biomedical devices. The present study aims to machine microrods using reverse microelectrical discharge machining (R-μEDM) process. These microrods can be used as microtools for drilling microholes. A detailed experimental investigation has been carried out with the help of Taguchi's orthogonal array for understanding the mechanism of the process. The process parameters such as voltage, feed rate, and capacitance are considered to perceive their effect on response measures such as machining time, deviation in length, deviation in average diameter, standard deviation (SD) in diameter, and surface roughness. The optimal process parametric condition of R-μEDM has been determined for desired performance, i.e., obtaining the target length and average diameter of the microrod and ensuring its straightness with minimum time duratio...

For multileaf foil bearings, the interactions between adjacent foils, foils, and gas film are key to predicting the bearing performance. However, most of the analytical models were based on line contact rather than area contact between adjacent foils and the latter may occur and play an important role in load capacity. In this study, the curved beam model is adopted to build an elastohydrodynamic model considering the area contact between adjacent foils, which is solved iteratively coupling the Reynolds equation with the finite element method. An algorithm is developed to judge and determine the contact condition of adjacent foils. The simulation results show that the area contact between adjacent foils does occur and the contact area expands with increasing eccentricity ratios and rotational speeds, which make the film thickness distribution smooth and are beneficial to the increase in load capacity. The area contact occurs near the trailing end of the foils first and then gradually expands. The later fo...

In this article, an investigation on viscoseal behavior is presented. In a laminar flow and a hydrodynamic regime, the finite element model is chosen, associated with lubrication hypotheses. The mathematical model corresponds to the classical Reynolds equation. However, this equation is modified, introducing a mass conservative algorithm assuming the film breakdown and re-formation. A different approach for sealing analysis is proposed based on the sealing length factor that characterizes the liquid-filled area in the seal.First, an adequate geometry, enabling optimal operation, is set. The proposed parametrical study refers to the groove angle, width, and depth calibration. Second, the influence of the journal speed and the groove number on the sealing length is discussed.

A linear stability analysis of hydrodynamic journal bearings is presented, including the effects of elastic distortion of the liner and micropolar lubrication. Hydrodynamic equations of the lubricant and equations of motion of the journal are solved simultaneously with the deformation equations for the bearing surface to predict the fluid film pressure distributions theoretically. The components of stiffness and damping coefficients, critical mass parameter, and whirl ratio, which reflect the dynamic characteristic of the journal bearing, are calculated for varying eccentricity ratio taking into account the flexibility of the liner and the micropolar properties of the lubricant. The results presented show that stability decreases with an increase in the value of the elasticity parameter of the bearing liner and micropolar fluids exhibit better stability in comparison to Newtonian fluids.

This article presents an experimental and numerical investigation of temperature distribution in a pocketed thrust washer. An experimental test rig was designed and developed to measure the temperature in the thrust washer contact under various operating conditions. To measure the temperature in the contact, a thin layer of thermochromic material was placed beneath the pocketed surface. The thermochromic material allowed temperature measurements across the contact through color contours displayed on the sheet. Video recording during operation showed the thermochromic sheet dynamically adapting to the rising temperature in the bearing. For the numerical investigation, the thermal Reynolds and energy equations were simultaneously solved subject to boundary condition to determine the pressure and temperature within the thrust washer. The thermal Reynolds equation was augmented with the Jacobsson-Floberg-Olsson (JFO) boundary condition to model cavitation and the energy equation was used to determine temperat...

In this article, numerical analyses of hydrodynamic lubrication and dynamics of the crank, rolling piston, and vane were carried out to study the tribological performance of a rotary compressor. Dimensionless Reynolds equations of journal and thrust bearings in dynamic load condition were derived and solved numerically. To deal with the lubrication of the rolling piston, the effect of the nonuniformity of tangential velocity over the bearing surface on the Reynolds equation was taken into account. In addition, combined with the analyses of dynamics and kinematics of the crank, piston, and vane, the angular velocities of the crank and piston as well as the motion mode between the piston and vane were studied. Analysis results illustrate characteristic oil film pressure distributions of the crank and piston bearings, which are different from that of common journal bearings. Under the influences of dynamic load and eccentricity of the cam, the wedge effect as well as the stretch and squeeze effect contribute...

Thermo-hydrodynamic lubrication of a polymeric liquid composed of short chains between parallel plates is analysed by a multi-scale simulation, i.e. the synchronised molecular dynamics simulation v...

A comprehensive model of the system piston–ring–cylinder (PRC) of a marine two-stroke engine is presented. Among submodels developed by the author concerning gas flow through the labyrinth seal of piston rings, oil flow, ring twist, and axial ring motion in piston grooves, the model includes submodels of mixed lubrication formulated by Patir, Cheng and Greenwood, Tripp. The main parts of the developed model and software have been experimentally verified by the author during a research period at a marine engine design center. A relatively good qualitative and quantitative compatibility between the experimental measurements and calculated results has been achieved.

In the paper production, doctor (scraping) blades are placed in contact with press rolls during wet pressing so as to purge the surface of the rolls from processing water, contamination and stickies. The contact is achieved by mounting the blade on a holder, which is tilted around a rotation axis until the blade tip contacts with the roll. The contact force is determined by the supply pressure of the air forced through the tube that is placed at the bottom of the holder. Owing to contact, the blade wears off and needs to be replaced periodically. Our aim is to optimise the cleaning performance of the system by modelling the tribological contact between the doctor blade and press roll in order to achieve an optimum cleaning performance, thus increasing the blade lifetime and reducing energy consumption. The model is susceptible to an inextensive numerical evaluation as compared to that of a more advanced modelling approach, e.g. in terms of a full finite element analysis of the beam deflection. A first comparison with experimental findings is encouraging.

A hydrodynamic rolling hybrid bearing (HRHB) composed of a rolling bearing with a fixed clearance and a hydrodynamic bearing is developed to solve the wear problem in hydrodynamic bearings. In this study, the maximum eccentricity ratio is developed to assess the protection of the rolling bearing offers to the hydrodynamic bearing. An analytic model for the maximum eccentricity ratio is presented. The effects of the size of the ball bearing and cylindrical roller bearing on the maximum eccentricity ratio are investigated. The results show that the maximum eccentricity ratio is affected by the clearance constraint and contact deformation of the rolling bearing. The maximum eccentricity ratio presents itself at zero speed, at which the rolling bearing reaction is equal to the external load. The results also show that the type of rolling bearing has significant effects on the maximum eccentricity ratio. The increment of the maximum eccentricity ratio due to elastic deformation of ball bearings is about 8.6 ti...

To improve the tribological performance of mating surfaces such as journal bearings, dimples with different shapes were introduced through laser surface texturing. In laser surface texturing processes, bulges are always induced around the dimples and may influence the tribological performance of the surface. In this article, the influence of the bulges on the tribological performance of a journal bearing is numerically investigated. Variations in both the friction coefficient and the eccentricity ratio of a journal bearing with the width and height of the bulges are studied. The influence of the radius of the dimples on the tribological performance of a journal bearing is also investigated. Results show that the friction coefficient increases with both the width and the height of bulges in the case of journal bearing under light and moderate loading conditions, which is in accord with the experimental results in previous works. The linear variation in the friction coefficient with the height of the bulges...

Because a perfectly smooth surface does not actually exist, the classical principles of fluid mechanics dictate that the flow between two surfaces that are in relative motion is fundamentally unsteady. Therefore, the fluid film profile can be submitted to rapid oscillations in both space and time. This article shows how these oscillations become dependent on the surface geometry. By employing a transient mass-conserving cavitation model, we study several cases in which surface roughness and surface texturing are considered on both surfaces of a parallel bearing. For an applied load, the model shows the impact of surface geometry on the hydrodynamic performance of the bearing in terms of nominal film thickness, friction force, and volumetric flow rate. In addition, the results illustrate how different operating parameters such as the applied load and the speed of the moving surface affect the presence of cavitation within the bearing.

The objective of this study was to experimentally investigate hydrodynamic pressure generation in surface-pocketed thrust washers. A novel method of pressure mapping was developed to allow for in situ measurement of the pressure generated by surface modifications. Thin-film pressure transducers, located just below the thrust washer surface, were used to measure pressure variations as a function of the operating conditions. Contour maps showing the cavitation region and the location of peak pressure were clearly displayed. The experimental work presented maps the pressure profiles with real-time, high-resolution sensors. The thin-film pressure transducers were used to investigate the pressure interactions between surface features. In addition to the experimental setup, a model of the contact was developed using ANSYS FLUENT. Cavitation, friction, film thickness, and load support were all compared with experimental results and the two were shown to be in good agreement. The model demonstrated an accurate pr...

It has been proven experimentally that surface texturing represents a viable solution for increasing the load-carrying capacity of parallel fluid bearings. Along with several load-supporting mechanisms that have been identified in the literature, the texture geometry remains an important feature. With the main objective of evaluating the effects of the texture geometry, a mass-conserving model is employed. While avoiding the use of the bulk modulus β, the algorithm also deals with the cavitation phenomenon and provides rapid and accurate results. For given operating conditions (supply pressure, surface speed, or lubricant viscosity), essential geometrical features such as size, density, and shape are analyzed in detail. In terms of load support and friction, the results reveal a strong dependence between certain parameters such as the texture cell number and dimple depth, and an increase in the texture density has beneficial effects in most cases. With regard to shape, the influence of this feature proves...

International audience; Multistage abrasive finishing processes (grinding, polishing, honing, etc.) are commonly used to produce the geometrical properties of a surface to meet its technical functionalities in the operating characteristics of contacting parts in friction, relating to their durability and reliability (running-in performance, wear resistance, load-carrying capacity, etc.). Coarse abrasive grits followed progressively finer ones are used, which leads to a multiscale stratified surface texture. In this article, a numerical model of elastohydrodynamic (EHD) contact coupled to a multiscale surface texture model was developed that allows tracking the scale effect of surface features and their interactions on friction performance and lubricant flow under hydrodynamic lubrication conditions. Because the simulation model has as an input the surface topography and to overcome the variability in surface finish formation, textured surfaces at different stages of the finishing process were simulated (virtual texturing method). Surface topography can be decomposed into two principal components: superficial roughness and valleys. Superficial roughness was modeled using a fractal model and a scaling factor was introduced to model valley patterns. The results show the relationship between friction and surface scales.

The objectives of this study were to experimentally and numerically investigate oil flow in surface-pocketed thrust washers. In order to achieve the experimental aspects of this investigation, a thrust washer test rig was designed and developed to visualize the lubricant flow at the contact interface. A novel approach for creating the pockets was developed to allow optical inspection of the lubricant during thrust washer operation. The thrust washers were fabricated using a glass disk with a thin layer of steel shim stock adhered to the surface. The micrometer-thick shim stock was machined using an Nd:YAG laser to create the circular pocket geometries and then glued to the glass disk. A mirror and camera were placed below the semitransparent washer to observe the lubricant flow in the pocket. The results obtained from this configuration illustrate a cavitation bubble forming on the leading edge of the pocket followed by a sharp transition back to liquid. The size of the cavitation area was found to be a f...

A programme of experimental work has been carried out to determine the viscosity and friction performance for a range of borosilicate based glass forging lubricants for conditions relevant to the closed die forging operations used in the manufacture of aerospace parts in titanium and nickel alloys. A simple experimental method for the measurement of glass viscosities has been described and the measured viscosities and the friction coefficients have been used to provide an interpretation of the behaviour observed. Isothermal friction tests in the temperature range from 800 to 1100°C were carried out to determine the basic performance of the glass followed by tests representative of forging operations with the workpiece at 925°C and the dies between 300 and 600°C. It has been found that both boundary layer and hydrodynamic lubrication regimes occur for the temperatures and strain rates encountered during the forging of aerospace materials coated with glass lubricants.

An inclined elliptical dimpled gas face seal was experimentally investigated in order to provide evidence for theoretical study. An experimental setup and theoretical model were developed to study ...

An analytical model is developed to investigate a partially textured slider of infinite width with orientation parabolic grooves. The generating mechanism for hydrodynamic lubrication of the partial surface texturing in the sliding surface is similar to that of a step slider. By using the multigrid method, the hydrodynamic pressure generated by the partial surface texturing is obtained. The surface texturing parameters are numerically optimized to obtain maximum hydrodynamic effect in terms of the dimensionless average pressure for a given set of operating parameters. The results indicate that parameters such as groove orientation angle, depth, area density, and textured fraction have an obvious influence on the hydrodynamic pressure for partial surface texturing. However, the groove width has little or no effect on the dimensionless average pressure. The results of the study show that the hydrodynamic lubrication performance can be ameliorated by optimizing the surface texturing according to the operatin...

A theoretical model for gas-lubricated foil journal bearings that incorporates thermal structural effects is presented. Bending and membrane effects in the top foil resulting from temperature are included along with thermal expansion of the journal, subfoil, and bearing housing. The model includes thermal transport through the journal, foils, and bearing housing. Pressure in the gas film is predicted using the Reynolds equation, and a thermal bulk flow model is used to predict temperature. The results demonstrate that models will overpredict film thickness along the side edge of a bearing if thermal strain in the top foil is not included. In addition, the results show the need for a three-dimensional thermal flow model at the trailing edge of a bearing when backflow occurs.

A thermal management technique for radial foil air bearings was experimentally evaluated. The technique is based on injecting air directly into the internal circulating fluid-film to reduce bulk temperatures and axial thermal gradients. The tests were performed on a single top foil, Generation III, radial foil bearing instrumented with three thermocouples to monitor internal temperatures. A through hole in the bearing shell coincident with the gap between the top foil's fixed and free ends provided entry for the injection air. The tests were conducted at room temperature with the bearing operating at speeds from 20 to 40 krpm while supporting 222 N. Two different mass flow rates of injection air were evaluated for this method, 0.017 and 0.051 kg/min. Test results suggest that the air injection approach is a viable thermal management technique capable of controlling bulk temperatures and axial thermal gradients in radial foil air bearings.

Surface texturing has been recognized as a feasible method of surface engineering to improve the lubrication properties of mechanical components. This work focuses on the hydrodynamic lubrication properties of the textured surface with asymmetric microdimples. The validity of the Reynolds equation in asymmetric microdimples is discussed based on theoretical analysis and numerical simulation. The effects of modified Reynolds number, motion directions, and parameters of the microdimple profile are investigated. The following results were obtained: Firstly, the Reynolds equation is invalid under almost all of the general conditions used in experiments and industries. Secondly, the ultimate load-carrying capacity can be taken as a new characteristic parameter to assess the lubrication property of a textured surface. Thirdly, the motion directions have a great effect on the lubrication properties. The positive motion can generate more stable load capacity under all of the modified Reynolds numbers employed, ev...

The combined effects of external pressurization and herringbone grooves are studied according to the incompressible Whipple analysis; results are examined in terms of nondimensional parameters that bring out the interaction between the action of herringbone groove self-pressurization and external pressurization through orifices. It is found that interaction is beneficial in a wide range of rotational speeds. An optimized interacting design can improve the bearing stiffness and load-carrying capacity. The herringbone grooves add to bearing stiffness and load-carrying capacity even in stationary state (rotation speed is zero) and in steady state the action of herringbone groove self-pressurization further promotes bearing performance with negligible effect on orifice pressure ratio. The orifice flow tends to be saturated ahead because of the spiral grooves in the stationary state and their herringbone self-pressurization has negligible effects on flow rate in the steady state. Herringbone grooving is found ...

The development and understanding of elastohydrodynamic lubrication (EHL) can be traced back to the beginning of the previous century. However, it was not until 1949 that the first real solution of the problem was published. Since then, the technology has evolved enormously. In the current article a summary of these developments is given. Smooth surface EHL has become well established. Numerical methods, analytical solutions, and experimental techniques have become mature. Focus areas of research today are thermal EHL, starved EHL, friction (non-Newtonian lubricants), roughness, and grease. The scope of EHL is so wide that the authors needed select the topics of focus in this article. Therefore, in addition to the general overview of the areas of friction, analytical methods, starved EHL, and grease EHL are highlighted in this article.

Chemical mechanical polishing (CMP) has become a primary technique for planarization of semiconductor wafers in submicro device fabrication. Increasing demands for high uniformity and dimensional precision make previously discountable levels of asperity, powder slurry, and wafer-pad contact significant. In this study, a CMP model considering both the elastic microcontact mechanism and the grain flow with roughness effects is presented. The model applies the average lubrication equation with partial hydrodynamic lubrication theory and elastic microcontact theory proposed by Greenwood and Williamson. In experiments, a test rig is used to simulate the CMP process and acquire the signals of polishing. The shear force is measured by a load transducer mounted on the lever and connected with the polishing head during CMP process. Furthermore, the theoretical results are compared with the experimental data. The theoretical and experimental results increase the understanding of CMP process.

Several load-supporting mechanisms have been studied to deal with the cavitation problem in parallel bearings. The formation of cavities and their disposition affect the pressure generated in a continuous thin film and hence the load capacity of bearings. In solving the Reynolds equation, proper cavitation boundary conditions must be applied. In this article, the mass-conserving Vijayaraghavan-Keith cavitation algorithm is utilized to analyze the hydrodynamic lubrication performance of parallel bearings with one or more grooves. Using the finite difference method, a one-dimensional Reynolds equation is discretized. Gauss-Seidel iteration is used to solve the obtained set of linear algebraic equations. For a given lubricant, sliding speed, and minimum film thickness, several comparative studies are made between the Vijayaraghavan-Keith cavitation algorithm and a published analytic solution. Several factors affecting the hydrodynamic lubrication performance are considered, such as cavitation pressure, inlet...

High value of coefficient of friction was obtained for dry friction between AISI 304 stainless steel specimen and counter body made from 100Cr6 steel. Aliphatic hydrocarbon liquid films of dodecane (C12 H26 ) and monounsaturated oleic acid (C18 H34 O2 ) were used as lubricating layers between the above two contacting pairs. This was carried out to evaluate the effect of alkane and alkene liquid lubricants on the evolution of coefficient of friction. Furthermore, the cyclic loading effect of progressive and regressive loading on coefficient of friction was also evaluated. Sliding speed of the contacting bodies also varied. The loading and sliding effects resulted in interruption of hydrodynamic lubrication, which caused breaks in the superlubricity of these hydrocarbons. Such circumstances led to manifestation of higher coefficient of friction. Frictional behaviour of these contacting bodies during cyclic loading procedure has been correlated with deformation induced morphologies of wear tracks.

An optical interferometric technique has been used to investigate fluid film thickness in sliding, isoviscous elastohydrodynamic contacts (I-EHL). Monochromatic two-beam interferometry has been employed to map lubricant film thickness across a range of applied loads and entrainment speeds. The contact was formed between an elastomer sphere and plain glass disc, illuminated under red light, λ= 630 nm. Experimental work has employed sunflower oil and glycerol/water solutions as the test lubricants, due to their similar refractive indices and varying viscosity. A black-and-white-image-intensified camera has been employed to capture interference images and a computer processing technique used to analyse these images, pixel by pixel, and create film thickness maps based on their gray-scale intensity representations. Comparison of film thickness results to theoretical models shows reasonable qualitative agreement. Experimental results show both a reduced horseshoe, which is limited to the rear of the contact, a...