Showing papers in "Journal of Tribology-transactions of The Asme in 1990"
786 citations
333 citations
TL;DR: In this article, a series of experiments were run to examine friction-velocity characteristics of line contacts operating under unsteady sliding velocities in the mixed, elastohydrodynamic and hydrodynamic lubrication regimes.
Abstract: Although many contacts operate under unsteady loading and sliding conditions, friction behavior under such conditions is still not well understood. In this paper we report on a series of experiments that were run to examine friction-velocity characteristics of line contacts operating under unsteady sliding velocities in the mixed, elastohydrodynamic and hydrodynamic lubrication regimes. A periodic, time-varying velocity component was superimposed on a steady sliding speed in such a way that all three lubrication regimes could be covered in a cycle. It was found that as the frequency of oscillation was increased, a multi-valued friction coefficient appeared as a loop about the average (steady state) friction-velocity relation. It is shown that this behavior can be modeled by a characteristic time lag between a changing velocity and the corresponding steady state friction. The latter is described by a single equation that was matched to measured average friction data. In the mixed lubrication regime, which is where this lag most significantly affects friction behavior, the lag time increases with normal load and lubricant viscosity. It is shown that the time shift is not associated with a fixed characteristic distance. The observed delay arises due to entrainment and normal approach, which includes squeeze-films combined with rough surface contact deformations.
324 citations
TL;DR: In this article, the use of a Poiseuille flow rate database for rapid calculation of a generalized lubrication equation for high Knudsen number gas films was proposed, based on numerical calculations based on the linearized Boltzmann equation.
Abstract: We propose the use of a Poiseuille flow rate database for rapid calculation of a generalized lubrication equation for high Knudsen number gas films. The database is created by numerical calculations based on the linearized Boltzmann equation. The proposed interpolation method is verified to reduce calculation time to several tenths of that required to perform rigorous calculations with the same accuracy
295 citations
110 citations
TL;DR: In this paper, an implicit numerical scheme, based on an approximate factorization technique, is applied to a cavitation algorithm, which automatically predicts film rupture and reformation in bearings, and provides time accurate solutions with a minimum expenditure of CPU time.
Abstract: In this paper, an implicit numerical scheme, based on an approximate factorization technique, is applied to a cavitation algorithm. The algorithm is a modified version of the Elrod cavitation algorithm, which automatically predicts film rupture and reformation in bearings. At each time step, Newton iterations are performed to achieve time accurate solutions for unsteady problems. This numerical scheme is applied in both orthogonal and nonorthogonal grid arrangements. An aligned finite grooved bearing and a flared, misaligned line grooved bearing are analyzed using this new approach. The predictions are compared with the results obtained with procedures currently being used. The new scheme is robust, quickly convergent, and provides time accurate solutions with a minimum expenditure of CPU time.
109 citations
96 citations
TL;DR: In this paper, a non-Newtonian fluid model associated with the limiting shear strength was considered and a modified Reynolds equation was developed which was almost the same as the classical Reynolds equation except for the viscosity term.
Abstract: A circular non-Newtonian fluid model associated with the limiting shear strength was considered. Using this model a modified Reynolds equation was developed which is almost the same as the classical Reynolds equation except for the viscosity term. The effects on performance of dimensionless load parameter, dimensionless speed parameter, slide/roll ratio, different oils, the limiting shear strength proportionality constant were studied
94 citations
90 citations
TL;DR: In this paper, a complete numerical solution of thermal compressible elastohydrodynamic lubrication of rolling/sliding contacts has been obtained using the Newton-Raphson technique to solve the simultaneous system of Reynolds and elasticity equations.
Abstract: A complete numerical solution of thermal compressible elastohydrodynamic lubrication of rolling/sliding contacts has been obtained. The Newton-Raphson technique is used to solve the simultaneous system of Reynolds and elasticity equations. The control volume finite element modeling was employed to solve the energy equation and its boundary conditions. The effects of various loads, speeds, and slip conditions on the lubricant temperature, film thickness, and friction force have been investigated. The results indicate that the temperature effects are significant and cannot be neglected.
85 citations
TL;DR: In this article, a thermohydrodynamic analysis of the 19 in. diameter tiltingpad journal bearing for steam turbine was performed in both laminar and turbulent flow regimes considering mixing inlet temperature.
Abstract: This paper describes a thermohydrodynamic analysis of the 19 in. diameter tiltingpad journal bearing for steam turbine in comparison with experimental data. The three-dimensional thermohydrodynamic analysis is performed in both laminar and turbulent flow regimes considering mixing inlet temperature
TL;DR: In this article, the authors used multilevel multi-integration to the calculation of the elastic deformation integrals and the use of an alternative relaxation process in the multi-level solution of the governing equations have resulted in an algorithm solving the EHL line contact problem in 0(n In n) operations.
Abstract: The application of multilevel multi-integration to the calculation of the elastic deformation integrals and the use of an alternative relaxation process in the multilevel solution of the governing equations have resulted in an algorithm solving the EHL line contact problem in 0(n In n) operations, also for highly loaded situations. The reduction in computing time thus obtained was used to solve the problem using large numbers of nodal points and to study the pressure spike. The presented algorithm will enable fast and accurate solution of surface roughness and transient problems.
TL;DR: In this paper, a new experimental technique using optical interferometry has been developed to obtain a direct indication of non-Newtonian response of an oil film under conditions of elastohydrodynamic (EHD) lubrication.
Abstract: A new experimental technique using optical interferometry has been developed to obtain a direct indication of non-Newtonian response of an oil film under conditions of elastohydrodynamic (EHD) lubrication. A glass disk or a steel ball has been driven by a stepping motor so that crescent-shaped thick oil films with undulation in thickness along the direction of motion have been generated. The experiments have been carried out under pure rolling and pure sliding conditions. It has been found that the oil in an EHD contact behaves like a solid and slips at or near the contact surfaces.
TL;DR: In this paper, the effect of journal misalignment on the predicted performance of a finite-grooved journal bearing is analyzed, and the numerical procedure used incorporates a cavitation algorithm, which automatically predicts film rupture and reformation in the bearings.
Abstract: The effect of journal misalignment on the predicted performance of a finite grooved journal bearing is analyzed in this paper. The numerical procedure used incorporates a cavitation algorithm, which automatically predicts film rupture and reformation in the bearings. The misalignment considered varies in magnitude and direction with reference to the boundaries of the bearing. In addition to the misalignment, the effect of lubricant starvation at the groove is also considered and compared with flooded inlet conditions. The effects of various degrees of starvation, or higher lubricant supply pressure, bearing length to diameter ratio and groove size are also investigated
TL;DR: In this paper, the adhesive force between magnetic-recording heads and thin film disks in a direction normal to the interface has been measured for a variety of loads, contact times, separation rates, and relative humidities with and without a layer of perfluoropolyether lubricant at the interface.
Abstract: The adhesive force between magnetic-recording heads and thin film disks in a direction normal to the interface has been measured for a variety of loads, contact times, separation rates, and relative humidities with and without a layer of perfluoropolyether lubricant at the interface. At low humidities, the adhesive force due to the lubricant film alone is small for the lubricant thickness and disk surface roughness used. We find that the major component of the adhesive force between the slider and the disk in humid environments may be attributed to an adsorbed water film which can displace the lubricant (if the disk is lubricated) at sufficiently high loads, during tangential sliding, or after extended exposure to high concentrations of water vapor and create menisci around individual asperity contacts. The adhesive force was found to increase with contact duration on the unlubricated disk, but was essentially independent of contact duration on the lubricated disk. For both lubricated and unlubricated disks, the adhesive force increased with increasing relative humidity and loading rate, but was independent of applied normal load.
TL;DR: In this article, the modal EHD analysis method was applied to an engine bearing geometry and load, and the results from the new method were compared to those from an available EHD analyzer, DEHD.
Abstract: A method for performing transient elastohydrodynamic lubrication (EHD) analysis of journal bearings using the concept of modeshapes was developed earlier. This method was referred to as the modal EHD analysis method. In the present work, the method is applied to an engine bearing geometry and load. The results from the new method are compared to those from an available EHD analysis, DEHD. Modal EHD analysis results with only 8 modeshapes compared well with those from DEHD, both for film thickness and for pressure
TL;DR: In this paper, a thermohydrodynamic analysis of finite journal bearings has been developed, which not only allows a more accurate prediction of the bearing performance characteristics, but also provides the temperature distribution in the bearing.
Abstract: A rigorous thermohydrodynamic (THD) analysis of finite journal bearings has been developed. THD analysis not only allows a more accurate prediction of the bearing performance characteristics, but it also provides the temperature distribution in the bearing. It involves the simultaneous solution of the Reynolds and energy equations and can handle a wide variety of flow situations, including reverse flow, recirculating flow and cavitation
TL;DR: In this article, an existing cavitation algorithm (a numerical procedure that automatically predicts film rupture and reformation in bearings) is modified by using second order upwinding to difference the shear induced flow terms in the cavitated region.
Abstract: An existing cavitation algorithm (a numerical procedure that automatically predicts film rupture and reformation in bearings) is modified in this paper. Second order upwinding is used to difference the shear induced flow terms in the cavitated region. A grid transformation procedure using a body fitted coordinate system and grid adaption techniques are applied to the algorithm. Four statically loaded finite journal bearing cases are analyzed. The results are compared with the results obtained using a conventional grid
TL;DR: In this article, gaseous cavitation in steady-state and transient lubrication problems is considered, both conventional numerical procedures associated with the Reynolds cavitation model and a new finite element analysis for implementation of the Jakobson-Floberg model are presented.
Abstract: In this paper gaseous cavitation in steady-state and transient lubrication problems is considered. Both conventional numerical procedures, associated with the Reynolds cavitation model, and a new finite element analysis for implementation of the Jakobson-Floberg model are presented. Applications to circumferentially supplied bearings and to seals are given.
TL;DR: In this paper, the effects of air entrainment and cavitation on the synchronous response of squeeze film supported rigid rotors were analyzed and the fluid film force coefficients were obtained from experimental measurements corresponding to a wide spectrum of operating conditions.
Abstract: This paper analyzes the effects of air entrainment and cavitation on the synchronous response of squeeze film supported rigid rotors. The fluid film force coefficients are obtained from experimental measurements corresponding to a wide spectrum of operating conditions. These conditions include regimes in which air entrainment effects are dominant. Other conditions where vapor cavitation and fluid inertial effects are dominant are included for comparison. The effects of air entrainment are shown to produce a nonlinear response representative of a softening spring effect not previously known to exist in squeeze film dampers.
TL;DR: In this article, the cavitation of liquid lubricant films in a dynamically loaded journal bearing was repeated with a quartz sleeve, which was more rigid than the Polymethylmethacrylate (PMMA) sleeve used previously.
Abstract: The earlier study made by Jacobson and Hamrock on the cavitation of liquid lubricant films in a dynamically loaded journal bearing was repeated with a quartz sleeve, which was more rigid than the Polymethylmethacrylate (PMMA) sleeve used previously. Various improvements of the test rig were made concomitantly so that the experimental errors could be better controlled and assessed. The updated speed photography experiment and its results are described.
TL;DR: In this paper, two formulas for the characteristic time of filling a void with the vapor of the surrounding liquid, and one of filling the void by diffusion of the dissolved gas in the liquid, are derived.
Abstract: Two formulas, one for the characteristic time of filling a void with the vapor of the surrounding liquid, and one of filling the void by diffusion of the dissolved gas in the liquid, are derived. By comparing these time scales with that of the dynamic operation of oil film bearings, it is concluded that the evaporation process is usually fast enough to fill the cavitation bubble with oil vapor; whereas the diffusion process is much too slow for the dissolved air to liberate itself and enter the cavitation bubble. These results imply that the formation of a two phase fluid in dynamically loaded bearings, as often reported in the literature, is caused by air entrainment. They further indicate a way to simplify the treatment of the dynamic problem of bubble evolution.
TL;DR: In this article, the interaction force between a disk medium coated with a functional liquid lubricant greater than 11.0 nm and tungsten tips with radii of 5 μm-100 μm was examined.
Abstract: Atomic force microscopy is used to investigate the interaction force between the sharp tips of various elastic solids and four different samples. The samples are: thin film disk media coated with functional liquid lubricant having diol end groups, unlubricated disk media, a single-crystal silicon wafer, and Au evaporated onto single-crystal silicon. Relationships between the interaction and static friction force of disk media and a taper flat type head slider are examined. The interaction force between a disk medium coated with a functional liquid lubricant greater than 11.0 nm thick and tungsten tips with radii of 5 μm-100 μm is caused by the functional liquid lubricant meniscus