Pure Squeeze Elastohydrodynamic Lubrication Research Articles

Effects of Load, Squeeze Velocity, Viscosity on Pure Squeeze EHL Motion Using Optical Interferometry

This paper presents a novel experiment method to investigate the microscopic mechanism of the oil film under the pure squeeze elastohydrodynamic lubrication (EHL) motion. An optical EHL squeeze tester is used to measure the interference fringe patterns of the contact region. In order to show the dimple thickness clearly, the grayscale interferometry method is employed to obtain the film thickness map. In addition, the effects of squeeze speed, load, and lubricant viscosity on the dimple film thickness are explored under a quasi-static condition.

Effects of elastic ball and coating on pure squeeze EHL motion for constant load with couple stresses using FDM method

In this paper, an elastic sphere approaching a lubricated elastic coating surface with couple stress lubricant is explored under constant load condition. The finite difference method (FDM), Gaussian elimination, and Gauss-Seidel iteration method are used to solve the transient modified Reynolds equation with its boundary condition, the elasticity deformation equations of ball and coating layer, load balance equation, and lubricant rheology equations simultaneously. The transient pressure profiles, film shapes, and elastic deformation during the pure squeeze process under various operating conditions in the elastohydrodynamic lubrication (EHL) regime are discussed.

EFFECTS OF SURFACE FORCES ON SQUEEZE EHL MOTION BETWEEN ELASTIC BALL AND ELASTIC COATED SURFACE

The effects of surface forces (SF) and coated layers (CL) on pure squeeze elastohydrodynamic lubrication (EHL) motion of circular contacts are explored under constant load condition by using the finite difference method (FDM) and the Gauss–Seidel iteration method. The transient pressure profiles, surface force, film shapes, and elastic deformation during the pure squeeze process under various operating conditions in the TFEHL regime are discussed. The simulation results reveal that the difference between SFEHL model and EHL model is apparent as the film thickness is thinner than 5 nm. The oscillation phenomena in pressure and film thickness come mainly from the action of solvation forces. At contact region, the greater elastic modulus and smaller coating thicknesses, the greater pressure distribution, and the smaller film thickness. The film thicknesses are found reverse at outside the contact zone. At the exit region, i.e. the minimum film thickness region, it is valid that the greater the elastic modulus and the smaller the coating thicknesses, the greater the solvation pressure distribution. The effects of surface forces become significant as the film thickness becomes thinner.

Squeeze film characteristics of circular contacts at impact and rebound motion with micropolar lubricants

In this paper, pure squeeze elastohydrodynamic lubrication (EHL) motion of circular contacts with micropolar lubricant is explored at the impact and rebound processes from a lubricated surface. On the basis of micro-continuum theory, the transient modified Reynolds equation is derived. Then it is solved simultaneously with the elasticity deformation, rheology, and ball motion equations in order to obtain the transient pressure profiles, film shapes, normal squeeze velocities, and accelerations. The simulation results reveal that the effect of the micropolar lubricant is equivalent to enhancing the lubricant viscosity, which would also enlarge the damper effect. Therefore, as the characteristic length (L) and coupling number (N) of the micropolar lubricants increase, the pressure spike and the dimple form earlier, the maximum pressure and the film thickness increase, the diameter of the dimple decreases, the rebounding velocity and the maximum acceleration decrease, and the maximum relative impact force decreases. Furthermore, the secondary peak of central pressure occurred at the rebound end is greater than the first peak of central pressure occurred at maximum impact force. As the effects of micropolar lubricants increase, the first and second peaks form earlier, the total impact time decreases, and the first and the second peaks increase.

Elastohydrodynamic lubrication of circular contacts at pure squeeze motion with micropolar lubricants

Purpose This paper aims to explore pure squeeze elastohydrodynamic lubrication (EHL) motion of circular contacts with micropolar lubricants under constant load. The proposed model can reasonably calculate the pressure distributions, film thicknesses and normal squeeze velocities during the pure squeeze process. Design/methodology/approach The transient modified Reynolds equation is derived in polar coordinates using micropolar fluids theory. The finite difference method and the Gauss–Seidel iteration method are used to solve the transient modified Reynolds equation, the elasticity deformation equation, load balance equation and lubricant rheology equations simultaneously. Findings The simulation results reveal that the effect of the micropolar lubricant is equivalent to enhancing the lubricant viscosity. As the film thickness is enlarged, the central pressure and film thickness for micropolar lubricants are larger than those of Newtonian fluids under the same load in the elastic deformation stage. The greater the coupling parameter (N), the greater the maximum central pressure. However, the smaller the characteristic length (L), the greater the maximum central pressure. The time needed to achieve maximum central pressure increases with increasing N and L. Originality/value A numerical method for general applications was developed to investigate the effects of the micropolar lubricants at pure squeeze EHL motion of circular contacts under constant load.

Effects of Surface Forces on Pure Squeeze Elastohydrodynamic Lubrication Motion of Circular Contacts with Coated Layer

The effects of surface forces (SF) on pure squeeze elastohydrodynamic lubrication (EHL) motion of circular contacts with coated layer are explored under constant load condition by using the finite element method (FEM) and the Gauss-Seidel iteration method. The difference between SFEHL model and EHL model is apparent as the film thickness is thinner than 5 nm. The oscillation phenomena in pressure and film thickness come mainly from the action of solvation forces. The effects of surface forces become significant as the film thickness becomes thinner.

Effect of surface roughness on pure squeeze EHL motion of circular contacts

PurposeThe purpose of this paper is to explore the pure squeeze elastohydrodynamic lubrication motion of circular contacts with surface roughness under constant load conditions. The proposed model can reasonably calculate the effects of surface roughness on the transient pressure profiles, film shapes, and normal squeeze velocities during the pure squeeze process.Design/methodology/approachBased on Christensen's stochastic theory, the transient modified Reynolds equation is derived in polar coordinates to consider the effects of surface roughness. The finite difference method and the Gauss‐Seidel iteration method are used to solve the transient modified Reynolds equation, the elasticity deformation equation, load balance equation, and lubricant rheology equations simultaneously.FindingsThe simulation results reveal that the circular type roughness possesses storage oil capacity. Comparatively, the radial type roughness possesses leak oil capacity. Therefore, the film thickness is found with circular type roughness, followed by smooth, and then radial type roughness. In additional, the central dimensionless pressure is found with radial type roughness, followed by smooth, and then circular type roughness.Originality/valueA numerical method for general applications with surface roughness was developed to investigate the pure squeeze action in an isothermal EHL spherical conjunction under constant load conditions, but without asperities contact.

Effects of temperature on pure squeeze EHL motion using grayscale interferometric method

Purpose – The purpose of this paper is to present a novel method to investigate the microscopic mechanism of the oil film under the pure squeeze elastohydrodynamic lubrication (EHL) motion. An optical EHL squeeze tester is used to explore the effects of squeeze velocity, load, temperature, and lubricant viscosity on the dimple film thickness that occurs when a ball approaches a flat plate covered by a thin layer of oil.Design/methodology/approach – The grayscale interferometric technique was used to study the thickness of the lubricating film in an EHL point contact. The light source was a He‐Ne laser. Through the transparent optical glass and by means of optical interference, the interference fringe patterns of the contact region were observed by a charge‐coupled device camera recording. The two elastic bodies were a sapphire disk and a steel ball. The contact was lubricated with paraffin‐based oil.Findings – Results show that increasing the squeeze speed, load, viscosity, and decreasing the temperature,...

Effects of Couple Stress on Elastohydrodynamic Lubrication at Impact Loading

Abstract In this paper, pure squeeze elastohydrodynamic lubrication motion of circular contacts with couple stress lubricant is explored at impact loading. On the basis of microcontinuum theory, the transient modified Reynolds equation is derived. Then it is solved simultaneously with the elasticity deformation equation and ball motion equation, thus obtaining the transient pressure profiles, film shapes, normal squeeze velocities, and accelerations. The simulation results reveal that the effect of the couple stress is equivalent to enhancing the lubricant viscosity, which would also enlarge the damper effect. Therefore, as the characteristic length of the couple stress fluid increases, the pressure spike and the dimple form earlier, the maximum pressure and the film thickness increase, and the diameter of the dimple, the rebounding velocity, the maximum value of the relative impact force, and the acceleration decrease. Furthermore, the fact that the contact central pressure for a ball impacting and rebounding from a lubricated surface reached two peaks during the total impact period is proved numerically in this analysis. As the effect of couple stress increases, the first and second peaks form earlier; as the total impact time decreases, the pressure of the first peak increases and that of the second peak decreases. Moreover, the phase shift between the time of the peak value of the squeeze acceleration and the zero value of the squeeze velocity increases with increasing the characteristic length of the couple stress fluid.

Elastohydrodynamic Lubrication of Circular Contacts at Impact Loading with Generalized Newtonian Lubricants

In this article, pure squeeze elastohydrodynamic lubrication (EHL) motion of circular contacts with power law model lubricant is explored at impact loading. The coupled transient modified Reynolds, the elasticity deformation, and the ball motion equations are solved simultaneously, thus obtaining the transient pressure profiles, film shapes, normal squeeze velocities, and accelerations. The simulation results reveal that the greater the flow index (n), the earlier the pressure spike and the dimple form, while the maximum pressure and the film thickness increase, and the diameter of the dimple, the maximum value of the impact force, the rebounding velocity, and the acceleration decrease. Further, this analysis numerically demonstrates that the contact central pressure for a ball impacting and rebounding from a lubricated surface reached two peaks during the total impact period. As the flow index increases, the primary and the secondary peak increase, and the first and second peaks form earlier; as the total impact time decreases. Moreover, the phase shift between the time of the peak value of the squeeze acceleration and the zero value of the squeeze velocity increase with increasing flow index.

Occurrence of a Noncentral Dimple in Squeezing EHL Contacts

Previous studies about pure squeeze elastohydrodynamic lubrication (EHL) have disclosed a film profile with a central dimple. Two problems about pure squeeze EHL are numerically solved in this paper. One is for a very small initial impact gap, and the other is the response of a squeezed EHL conjunction under stepwise loads. None of them result in the familiar film with a central dimple, which can be attributed to the local squeeze effect generated in the periphery region. In the first problem, it has been found that when there is adequate oil present on the plate, with a decrease in the initial impact gap, a shallow circumferential dimple occurs at the periphery of the conjunction instead of the primary central dimple presented in previous studies. Correspondingly the minimum film thickness occurs at the central region. The effect of the initial impact velocity on the periphery dimple is also investigated. In the second problem, the response of a conjunction subjected to a prescribed stepwise load is studied. When the first step load is applied, a central dimple film is produced. When the applied load is increased with a second step load, a periphery dimple appears, similar to that in the first problem. The local squeeze effect for the present numerical periphery dimple has been observed in previous experiments under similar conditions.

Study on pure squeeze elastohydrodynamic lubrication motion using optical interferometry and the inverse approach

This paper uses an optical elastohydrodynamic lubrication (EHL) impact tester to explore the effects of squeeze velocity, load, and lubricant viscosity on the dimple film thickness occurring when a ball impacts a flat plate covered by a thin layer of oil. Three types of motion for the ball are combined and simulated in this experiment to find important operation parameters. In the direct numerical solution, hydrodynamic lubrication is assumed at the initial impact stage and EHL is assumed at the high-pressure stage. Pressure and dimple shapes are obtained by numerical solution of the coupled transient Reynolds equation, elasticity equation, and ball motion equation. The inverse approach is proposed to estimate pressure and apparent viscosity in pure squeeze EHL motion. Results show that, with higher impact speeds and loads, more time is needed to reach stability. Also with lower viscosities, more time is needed to reach stability. Increasing the squeeze speed, load, and viscosity all make the dimple deeper. The post-impact high-pressure condition for the constant-load case is suitable for evaluating the pressure-viscosity index. The inverse approach is successfully used to estimate the pressure distribution resulting from the film thickness map obtained by interferometry. Agreement between the experimental value of the test fluid and the estimated value is quite good.