Li-Ming Chu, Jaw-Ren Lin and Cai-Wan Chang-Jian
The modified Reynolds equation for non-Newtonian lubricant is derived using the viscous adsorption theory for thin-film elastohydrodynamic lubrication (TFEHL) of circular…
Abstract
Purpose
The modified Reynolds equation for non-Newtonian lubricant is derived using the viscous adsorption theory for thin-film elastohydrodynamic lubrication (TFEHL) of circular contacts. The proposed model can reasonably calculate the phenomenon in the thin-film lubrication (TFL) unexplained by the conventional EHL model. The differences between classical EHL and TFEHL with the non-Newtonian lubricants are discussed.
Design/methodology/approach
The power-law lubricating film between the elastic surfaces is modeled in the form of three layers: two adsorption layers on each surface and one middle layer. The modified Reynolds equation with power-law fluid is derived for TFEHL of circular contacts using the viscous adsorption theory. The finite difference method and the Gauss–Seidel iteration method are used to solve the modified Reynolds equation, elasticity deformation, lubricant rheology equations and load balance equations simultaneously.
Findings
The simulation results reveal that the present model can reasonably calculate the pressure distribution, the film thickness, the velocity distribution and the average viscosity in TFL with non-Newtonian lubricants. The thickness and viscosity of the adsorption layer and the flow index significantly influence the lubrication characteristics of the contact conjunction.
Originality/value
The present model can reasonably predict the average viscosity, the turning point and the derivation (log film thickness vs log speed) phenomena in the TFEHL under constant load conditions.
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The purpose of this paper is to investigate the dynamic characteristics of exponential slider bearings lubricated with a ferrofluid. Because of the development of modern…
Abstract
Purpose
The purpose of this paper is to investigate the dynamic characteristics of exponential slider bearings lubricated with a ferrofluid. Because of the development of modern engineering, the increasing use of ferrofluids in lubrication fields has shown great importance. Understanding the dynamic characteristics of exponential film bearings is helpful for engineers in bearing selection.
Design/methodology/approach
Applying the Shliomis ferrohydrodynamic flow model and considering the squeezing action of bearing pads, a dynamic Reynolds equation is obtained for an exponential film slider bearing lubricated with a ferrofluid in the presence of a transverse magnetic field. Analytical solutions of dynamic characteristics are obtained.
Findings
According to the results, the ferrofluid-lubricated exponential film bearing provides better dynamic stiffness and damping characteristics than the non-ferrofluid ones, especially the bearing operating at higher values of the volume concentration parameter and the magnetic Langevin parameter.
Originality/value
Numerical tables of stiffness and damping coefficients for different values of the volume concentration parameter and the Langevin parameter are also included for engineering references.
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Li Ming Chu, Jaw-Ren Lin, Yuh-Ping Chang and Chung-Chun Wu
This paper aims to explore pure squeeze elastohydrodynamic lubrication (EHL) motion of circular contacts with micropolar lubricants under constant load. The proposed model can…
Abstract
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.
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The purpose of this paper is to explore the pure squeeze thin film elastohydrodynamic lubrication (TFEHL) motion of circular contacts with adsorption layers attached to each…
Abstract
Purpose
The purpose of this paper is to explore the pure squeeze thin film elastohydrodynamic lubrication (TFEHL) motion of circular contacts with adsorption layers attached to each surface under constant load condition. The proposed model can reasonably calculate the pressure distributions, film thicknesses, normal squeeze velocities, and effective viscosities during the pure squeeze process under thin film lubrication.
Design/methodology/approach
The transient modified Reynolds equation is derived in polar coordinates using viscous adsorption 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 thickness of the adsorption layer and the viscosity ratio significantly influence the lubrication characteristics of the contact conjunction in the thin film regime. In additional, the turning points in the film thickness which distinguish thin film lubrication from elastohydrodynamic lubrication curve is found. In thin film region, the effective viscosity predicted by present model is better than that predicted by traditional elastohydrodynamic theory.
Originality/value
The paper develops a numerical method for general applications with adsorption layers attached to each surface to investigate the pure squeeze action in a TFEHL spherical conjunction under constant load condition.
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Li‐Ming Chu, Hsiang‐Chen Hsu, Jaw‐Ren Lin and Yuh‐Ping Chang
The purpose of this paper is to explore the pure squeeze elastohydrodynamic lubrication motion of circular contacts with surface roughness under constant load conditions. The…
Abstract
Purpose
The 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/approach
Based 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.
Findings
The 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/value
A 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.
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Li‐Ming Chu, Hsiang‐Chen Hsu, Jaw‐Ren Lin and Yuh‐Ping Chang
The purpose of this paper is to describe an inverse approach to estimate the pressure distribution, temperature distribution, and pressure‐viscosity index (z) in a thermal…
Abstract
Purpose
The purpose of this paper is to describe an inverse approach to estimate the pressure distribution, temperature distribution, and pressure‐viscosity index (z) in a thermal elastohydrodynamic lubrication (TEHL) line contact.
Design/methodology/approach
Once the film thickness is given, the pressure distribution can be calculated using the inverse approach. Subsequently, thermal expansivity and temperature‐viscosity coefficient of lubricant are given, and then the z is guessed initially. The Gauss‐Seidel iteration is employed to calculate the temperature distribution from the rheology, energy, and surface temperature equations. In order to increase the algorithm stability, the least‐squares method must be employed to calculate the optimum value of the z in the computational domain. Furthermore, the pressure‐viscosity index must be updated by the iteration method to calculate accurate temperature distribution and apparent viscosity until convergence.
Findings
This approach presents a smooth curve of the pressure and temperature distributions with the measurement error from the resolution in the film thickness measurement and z value. Furthermore, this approach still provides a superior solution in apparent viscosity, whereas the direct method provides a much larger error in apparent viscosity.
Originality/value
The paper describes an inverse approach to estimate the pressure distribution, temperature distribution, and pressure‐viscosity index in a TEHL line contact. This approach overcomes the problems of pressure and temperature rise fluctuations and generates accurate results of pressure and temperature distribution from a small number of measured points of film thickness, which also saves computing time. Furthermore, this approach still provides a superior solution in apparent viscosity.
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Jaw‐Ren Lin, Chi‐Ren Hung, Li‐Ming Chu, Wei‐Liang Liaw and Ping‐Hui Lee
In the present paper, the authors aim to analyze the non‐Newtonian effects of Rabinowitsch fluids on the squeeze film performances between wide parallel rectangular plates.
Abstract
Purpose
In the present paper, the authors aim to analyze the non‐Newtonian effects of Rabinowitsch fluids on the squeeze film performances between wide parallel rectangular plates.
Design/methodology/approach
Based on the cubic‐stress equation model, a nonlinear squeeze‐film Reynolds‐type equation has been derived. By using a small perturbation method, a closed‐form solution of the squeeze film characteristics is derived for the parallel plates considering the non‐Newtonian effects of cubic stresses.
Findings
Comparing with the Newtonian‐lubricant parallel plates, the effects of non‐Newtonian cubic‐stress flow rheology provide significant influences upon the squeeze film characteristics.
Originality/value
It is shown that the non‐Newtonian pseudoplastic behavior reduces the load capacity and the response time; however, the effects of non‐Newtonian dilatant lubricant provide an increase in the load‐carrying capacity and therefore lengthen the response time of parallel squeeze‐film plates.
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Jaw-Ren Lin, Rong-Fang Lu, Li-Ming Chu and Chi-Ren Hung
– The purpose of this paper is to investigate the effects of non-Newtonian rheology on the dynamic characteristics of a secant-shaped couple-stress lubricated slider bearing.
Abstract
Purpose
The purpose of this paper is to investigate the effects of non-Newtonian rheology on the dynamic characteristics of a secant-shaped couple-stress lubricated slider bearing.
Design/methodology/approach
By applying the linear dynamic theory to the film force equation, a closed-form solution of the stiffness and damping coefficients is obtained for the secant-shaped bearing taking into account the non-Newtonian effects of Stokes couple stress fluids.
Findings
Comparing with the secant-shaped Newtonian-lubricant bearing, the effects of non-Newtonian couple stresses provide an apparent improvement in the dynamic stiffness and damping characteristics, especially for the secant-shaped slider bearing operating at lower squeezing-film heights and with larger non-Newtonian couple stress parameters.
Originality/value
Comparing with those of the inclined plane-shaped non-Newtonian slider bearings, better dynamic stiffness and damping performances are provided for the secant-shaped non-Newtonian slider bearing designed at larger values of the shoulder parameters. The advantages of secant-shaped slider-bearing types provide engineers useful information in bearing selection and engineering application.
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Li‐Ming Chu, Jin‐Yuan Lai, Chi‐Hui Chien and Jaw‐Ren Lin
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…
Abstract
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, make the dimple deeper, and the contact area increases. Moreover, as the squeeze speed and load decrease and temperature increases, the fluidity of the lubricant increases and less time is needed to extrude. The maximum thickness of the dimple increases with increasing squeeze speed, load, lubricant viscosity, and decreasing temperature. The greatest effect of pure squeeze EHL motion is found with squeeze velocity, followed by load, and then temperature for the same lubricant viscosity.
Originality/value
The paper usefully describes the use of a self‐development optical EHL squeeze tester to explore the effects of temperature, squeeze velocity, load, and lubricant viscosity on the dimple film thickness which occurs between two components approaching each other.
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Li‐Ming Chu, Wang‐Long Li, Yuh‐Ping Chang and Hsiang‐Chen Hsu
The purpose of this paper is to analyze and discuss the coupled effects of surface roughness and flow rheology for a homogeneous mixture of Newtonian base oil and power law fluids…
Abstract
Purpose
The purpose of this paper is to analyze and discuss the coupled effects of surface roughness and flow rheology for a homogeneous mixture of Newtonian base oil and power law fluids on the performance of elastohydrodynamic lubrication (EHL) circular contact problems.
Design/methodology/approach
The average flow model is adapted for the interaction of the flow rheology of lubricant and surface roughness. The average Reynolds type equation (ARTE) and the related flow factors (which describes the coupled effects of surface roughness and flow rheology of a mixture), the viscosity‐pressure and density‐pressure relations equations, the elastic deformation equation, and the force balance equation are then solved simultaneously. The multilevel multi‐integration algorithm and Gauss‐Seidel iteration method are utilized to calculate the film thickness and pressure distributions of the EHL circular contact problems effectively.
Findings
The effects of volume fraction, flow index of power law fluid, and surface roughness parameters (Peklenik number, standard deviation of composite surface roughness) on the film thickness and pressure distributions are discussed. The results show that the effects of surface roughness should be considered especially in EHL contact problems.
Originality/value
The EHL of circular contacts lubricating with mixture of two lubricants is first analyzed. The coupling effects of surface roughness and flow rheology of mixture (a Newtonian fluid and a power‐law fluid) on the EHL performance are first discussed in this paper.