Showing papers in "Journal of Tribology-transactions of The Asme in 2001"
TL;DR: In this paper, the preparation of Ni nanoparticles in microemulsions of sodium dodecyl sulphate (SDS)/isopentanol/cyclohexane/water and their tribological performance as additives in oils were described.
Abstract: The application of nanoparticles in tribology has received considerable attention in recent years. In this paper, we described the preparation of Ni nanoparticles in microemulsions of sodium dodecyl sulphate (SDS)/isopentanol/cyclohexane/water and their tribological performance as additives in oils. The size of these nanoparticles is about 10 nm, and their shape is spherical. The four-ball test results indicate that Ni nanoparticles are potential additives for lubricating oils, and the tribological performance of lubricating oils can be improved significantly by dispersing Ni nanoparticles in oils. The maximum non-seizure load (PB) has been increased by 67 percent as compared with background oil. The wear scar diameter has been reduced from 0.71 mm to 0.49 mm. The relative percentage in friction coefficient has decreased 26 percent. The tribological mechanism is that a deposit film in the contacting regions was formed, which prevented the direct contact of rubbing surfaces and greatly reduced the frictional force between the contact-ing surfaces.
204 citations
TL;DR: In this paper, a modified two-variable Weierstrass-Mandelbrot function with fractal parameters determined from real surface images was used to generate 3D rough surfaces.
Abstract: Three-dimensional rough surfaces were generated using a modified two-variable Weierstrass-Mandelbrot function with fractal parameters determined from real surface images. The number and size of truncated asperities were assumed to follow power-law relations. A finite element model of a rigid sphere in normal contact with a semi-infinite elastic-plastic homogeneous medium was used to obtain a constitutive relation between the mean contact pressure, real contact area, and corresponding representative strain. The contact model was extended to layered media by modifying the constitutive equation of the homogeneous medium to include the effects of the mechanical properties of the layer and substrate materials and the layer thickness. Finite element simulations of an elastic-plastic layered medium indented by a rigid sphere validated the correctness of the modified contact model. Numerical results for the contact load and real contact area are presented for real surface topographies resembling those of magnetic recording heads and smooth rigid disks. The model yields insight into the evolution of elastic, elasticplastic, and fully plastic deformation at the contact interface in terms of the maximum local surface interference. The dependence of the contact load and real contact area on the fractal parameters and the carbon overcoat thickness is interpreted in light of simulation results obtained for a tri-pad picoslider in contact with a smooth thin-film hard disk.
167 citations
TL;DR: In this paper, a micro-contact model incorporating asperity interactions in elastic-plastic contact of rough surfaces is presented, and the effect of the asperities interactions on the local deformation behavior of a given microcontact is first modeled based on the Saint-Venant's Principle and Love's Formula.
Abstract: This paper present a micro-contact model incorporating asperity interactions in elastic-plastic contact of rough surfaces. The effect of the asperity interactions on the local deformation behavior of a given micro-contact is first modeled based on the Saint-Venant's Principle and Love's Formula. The local contact interference is related in closed form to the local contact load, the global mean pressure and material parameters. This micro-contact model equation is then integrated into the elastic-plastic contact model developed in Zhao et al. (2000) to allow the asperity interactions and plastic deformation to be considered simultaneously. The effects of the asperity interactions on the mean surface separation, the real area of contact and the redistribution of the contact load among contacting asperities of different heights are studied. The results show that the asperity interactions can significantly affect the mean surface separation and microcontact load redistribution. The results also reveal that the effect of asperity interactions can be largely cancelled out by the effect of asperity plastic deformation.
133 citations
TL;DR: In this article, an axi-symmetric, hydrodynamic, mixed lubrication model was developed using the averaged Reynolds equation and asperity contact approach in order to simulate frictional performance of piston ring and cylinder liner contact.
Abstract: An axi-symmetric, hydrodynamic, mixed lubrication model has been developed using the averaged Reynolds equation and asperity contact approach in order to simulate frictional performance of piston ring and cylinder liner contact. The friction force between piston ring and cylinder bore is predicted considering rupture location, surface flow factors, surface roughness and metal-to-metal contact loading. A fully flooded inlet boundary condition and Reynolds boundary conditions for cavitation outlet zone are assumed. Reynolds boundary conditions have been modified for non-cavitation zones. The pressure distribution along the ring thickness and the lubricant film thickness are determined for each crank angle degree. Predicted friction force is presented for the first compression ring of a typical diesel engine as a function of crank angle position.
128 citations
TL;DR: In this article, the elastic modulus of each polymer was determined from the unloading material response using the compliance method, whereas the hardness was calculated as the maximum contact load divided by the corre-sponding projected area, obtained from the known tip shape function.
Abstract: The nanomechanical properties of various polymers were examined in light of nanoindentation experiments performed with a diamond tip of nominal radius of curvature of about 20 μm under conditions of maximum contact load in the range of 150-600 μN and loading/unloading rates between 7.5 and 600 μN/s. The elastic modulus of each polymer was determined from the unloading material response using the compliance method, whereas the hardness was calculated as the maximum contact load divided by the corre-sponding projected area, obtained from the known tip shape function. It is shown that while the elastic modulus decreases with increasing indentation depth, the polymer hard-ness tends to increase, especially for the polymers possessing amorphous microstructures or less crystallinity. Differences in the material properties, surface adhesion, and time-dependent deformation behavior are interpreted in terms of the microstructure, crystallinity, and surface chemical state of the polymers. Results obtained at different maximum loads and loading rates demonstrate that the nanoindentation technique is an effective method of differentiating the mechanical behavior of polymeric materials with different microstructures.
124 citations
TL;DR: An average Reynolds equation capable of predicting the effects of roughness induced inter-asperity cavitation is introduced in this article, which is based on the JFO cavitation model and the Patir and Cheng flow factor method.
Abstract: An average Reynolds equation capable of predicting the effects of roughness induced inter-asperity cavitation is introduced. The average Reynolds equation is based on the JFO cavitation model and the Patir and Cheng flow factor method. The flow factors are calculated in numerical experiments as functions of the local surface separation, surface statistics, and cavitation number. The model is extended into a universal average Reynolds equation capable of predicting the combined effects of inter-asperity cavitation and macroscopic cavitation. Both the Patir and Cheng method and the present model are verified in numerical experiments.
123 citations
TL;DR: In this paper, the reflection of ultrasound at a static interface between a rough, nominally flat aluminum plate and a rough hardened steel punch has been investigated and the effect of surface roughness on the resultant contact has also been investigated.
Abstract: The measurement of ultrasonic reflection has been used to study the contact between rough surfaces. An incomplete interface will reflect some proportion of an incident wave; this proportion is known as the reflection coefficient, If the wavelength is large compared with the width of the gaps in the plane of the interface then the reflection mechanism can be modeled by considering the interface as a spring. The proportion of the incident wave reflected (reflection coefficient) is then a function of the stiffness of the interface and the frequency of the ultrasonic wave. The sensitivity of the ultrasonic technique has been quantified using a simple model, from which the stiffness of individual gaps and contacts are calculated and their effect on the ultrasonically measured stiffness predicted. The reflection of ultrasound at a static interface between a rough, nominally flat aluminum plate and a rough, nominally flat hardened steel punch has been investigated. Plastic flow on first loading was evident, while repeated loading was largely elastic. However, subsequent cycles indicate a small amount of further plasticity and contact irreversibility. The effect of surface roughness on the resultant contact has also been investigated. A simple plastic contact model is described which allows prediction of the average size of the asperity contacts and their number. This model shows that the average size of the contacts remains constant over most of the loading whereas the number of contacts increases almost linearly. The contact stiffness has also been modeled with two well known elastic rough surface contact models. These models predicted a lower interface stiffness than was observed in the experiments. However they provide a useful way of interpreting the ultrasonically measured interface stiffness data.
122 citations
TL;DR: In this paper, a Couette approximation to the energy equation is used in conjunction with the compressible Reynolds equation to obtain a theoretical temperature distribution in the air used as a lubricant.
Abstract: The paper presents an analytical and experimental investigation aimed at eliciting the thermal characteristics of air lubricated compliant foil bearings. A Couette Approximation to the energy equation is used in conjunction with the compressible Reynolds equation to obtain a theoretical temperature distribution in the air used as a lubricant. The effect of temperature on the thermal properties of the working fluid is included. In parallel, an experimental program was run on a 100 mm diameter foil bearing operating at speeds up to 30,000 rpm employing cooling air across the bearing. The temperature rise of the cooling air provided an indication of the amount of heat energy conducted across the top foil of the bearing from the hydrodynamic film. The temperatures resulted from some tests are compared with the temperatures predicted by the analysis, and maximum over-prediction of about 19 percent was obtained. This simplified approach provides us with reasonably predicted temperatures. By comparing the theoretical heat dissipation obtained from the analytical predicted temperatures with the amount of heat carried away by the cooling air it was possible to arrive at the relative quantities of heat transferred from the bearing by convection via side leakage and by conduction via the top foil. From these comparisons it was deduced that about an average of 80 percent of the heat energy is carried away by conduction. The transient temperatures of the foil bearing in conducted tests for various speeds and loads are also presented.
103 citations
TL;DR: In this paper, the authors studied the three dimensional thermomechanical contact of non-conforming rough surfaces, the model of which includes the normal surface displacements caused by the contact pressure, frictional shear, and frictional heating.
Abstract: A necessary step in understanding failure problems of tribological elements is to investigate the contact performance of rough surfaces subjected to frictional heating. It is essential that the interfacial variables are obtained through solving the interactive thermomechanical contact problem. This paper studies the three dimensional thermomechanical contact of non-conforming rough surfaces, the model of which includes the normal surface displacements caused by the contact pressure, frictional shear, and frictional heating. Influence coefficients and frequency response functions for elastic and thermoelastic displacements, as well as those for temperature rises, are investigated for model construction. In order to develop an accurate and efficient solver, the numerical algorithms with the discrete convolution and fast Fourier transform techniques and the single-loop conjugated gradient method are used. The model modules are numerically verified and the thermomechanical performance of the rough surfaces in a point contact is studied.
102 citations
TL;DR: In this article, the steady dimples measured in elliptical glass-steel contact under pure sliding conditions are presented, where two dimples connected with a shallower furrow are generated, each near an end of the major radius of the contact ellipse.
Abstract: Experimental results of steady dimples measured in elliptical glass-steel contact under pure sliding conditions are presented. It is found that two dimples connected with a shallower furrow are generated, each near an end of the major radius of the contact ellipse. The complete solution of the corresponding thermal elastohydrodynamic lubrication (TEHL) problem is calculated numerically. Good agreement is obtained between the experimental and theoretical results. This agreement can be explained by the temperature-viscosity wedge mechanism, Correctness of this mechanism is demonstrated using additional experiments with ceramic balls in contact with glass and sapphire disks.
98 citations
TL;DR: In this article, an analytical method that evaluates the evolution of stress and surface profile in fretting under the partial slip conditions is presented, based on two scales of time: time for one cycle of the oscillating tangential force and time corresponding to the number of cycles.
Abstract: An analytical method that evaluates the evolution of stress and surface profile in fretting under the partial slip conditions is presented. The repeated slip occurring near the edges of contact generates wear that changes the contact geometry and contact stresses. The method is based on two scales of time: time for one cycle of the oscillating tangential force and time corresponding to the number of cycles. Archard's wear law is used to evaluate wear and gap variation within the slip zones during one cycle. The governing integral equations are reduced to calculate the contact pressure after each cycle. Evolution of the contact characteristics (contact pressure and shear stress, contact width, gap and slip functions) in fretting is calculated using a stepwise procedure. It is shown that the size of stick zone does not change in wear process of bodies with similar elastic properties under the constant amplitude load conditions, and that an asymptotic solution corresponding to the number of cycles approaching to infinity exists. Analytical expressions for the asymptotic contact pressure, shear and tensile stress, and the gap function are presented. It is proved that the asymptotic contact pressure and shear stress are singular at the ends of stick zone. Detailed results are given for two initial shapes of elastic indenter contacting with an elastic half-space: for the parabolic cylinder and for the indenter having a flat base with rounded edges.
TL;DR: In this article, a transient finite element simulation is developed for the two-dimensional thermoelastic contact problem of a stationary layer between two sliding layers, with frictional heat generation.
Abstract: A transient finite element simulation is developed for the two-dimensional thermoelastic contact problem of a stationary layer between two sliding layers, with frictional heat generation. The petrov-Galerkin algorithm is used to discretize the sliding layers because of the high Peclet numbers involved. The results in the linear, full contact regime were validated by comparison with the analytical predictions of Lee and Barber (1993). After separation occurs, there is a non-monotonic transition to a steady state with the contact regions separated by the same wavelength. During the transition, the migration speed exhibits values lower than those in either the linear regime or the final steady state. When several wavelengths are unstable, the final steady state is generally that corresponding to the longest unstable wavelength, even though other modes have more rapid growth rates in the linear regime.
TL;DR: In this article, a new load/deformation relationship is derived analytically and use is made of the thickness of the outer race section, where a minor effect of the section thickness is shown.
Abstract: Results given in this paper are threefold. In the case of Hertzian line contact, a new load/deformation relationship is derived analytically and use is made of the thickness of the outer race section. A minor effect of the section thickness is shown. The exponent on the deformation is 1.074 (instead of 1.1 usually accepted). Results calculated with the new relationship are successfully compared to results calculated with other published relationships and also are compared successfully to some available experimental results. For the case of point contact, useful relationships, obtained by curve-fitting, are given to calculate easily the load versus deformation, maximum Hertzian pressure and ellipse contact dimension as a function of a dimensionless load parameter and ratio k of equivalent radii (instead of sum of curvatures and elliptical integrals before). A large range of k is covered, from 0.05 (found at roller rib contact) to 13,000 to cover all bearing cases, from ball bearings to spherical and tapered roller bearings. Finally, an important analytical relationship, based on curve-fitting, also is suggested to describe a smooth transition from point contact to line contact as the load increases. It is recommended to define bearing setting and bearing preload with the suggested relationship.
TL;DR: In this article, a ball/v-ring test rig was used to initiate and progress spalls on bearing halls where spall progression was measured as a function of time, and vibrations monitored using accelerometers.
Abstract: Typically, the life of a component containing rolling contacts is defined as the time to the initiation of a fatigue spall. Initiation of a spall does not always cause the component to stop performing its designed function. Operating the component past the initiation of a spall increases the heat generation rates and vibrations, eventually leading to total failure. A ball/v-ring test rig was used to initiate and progress spalls on bearing halls where spall progression was measured as a function of time, and vibrations monitored using accelerometers. A spall progression life mathematical model for balls endurance tested in the v-ring rig was created by extending the loannides-Harris fatigue life theory. Also. excessive vibratory loading was determined to be the major cause of total component failure.
TL;DR: In this paper, a numerical model was developed to investigate the effects of groove geometry on the hydrodynamic lubrication mechanism of thrust washers, and design curves were generated for load support and other operating parameters as a function of each of the groove geometrical parameters (i.e., depth, width, number of grooves, and shape).
Abstract: A numerical model was developed to investigate the effects of groove geometry on the hydrodynamic lubrication mechanism of thrust washers. In order to achieve the objectives the isothermal, time-dependent, polar-coordinate Reynolds equation, including the cavitation and centrifugal effects, was solved numerically to determine the pressure distribution for various groove geometries and operating conditions. The polar coordinate Reynolds equation was discretized using the control volume finite difference approach. The results indicate that thrust washers are capable of supporting a significant amount of load with proper groove geometries. Design curves were generated for load support and other operating parameters as a function of each of the groove geometrical parameters (i.e., depth, width, number of grooves, and shape) as well as the operating conditions so that thrust washers performance can be predicted and optimized.
TL;DR: In this paper, a model is presented to investigate the start up condition in elastohydrodynamic lubrication and its effects on bearing performance, and the results of start up with smooth surfaces are provided for the case when speed increases from zero to desired speed in one step.
Abstract: In this paper a model is presented to investigate the start up condition in elastohydrodynamic lubrication. During start up the lubrication condition falls into the mixed lubrication regime. The transition from solid contact to lubricated contact is of importance when investigating the start up process and its effects on bearing performance. The model presented uses the multigrid multilevel method to solve the lubricated region of the contact and a minimization of complementary energy approach to solve the solid contact region. The FFT method is incorporated to speed up the film thickness calculation. An iteration scheme between the lubrication and the solid contact problems is used to achieve the solution of the mixed lubrication contact problem. The results of start up with smooth surfaces are provided for the case when speed increases from zero to desired speed in one step and the case when speed is linearly increased to desired speed. The details of the transition from full solid contact to full lubricated contact in EHL start up are presented. The change of pressure and film thickness as well as contact forces and contact areas are discussed.
TL;DR: In this article, a new numerical model for the three-dimensional contact analysis of a layered elastic-perfectly plastic half space with another rough surface is presented, based on a variational principle in which the real area of contact and contact pressure distribution are those which minimize the total complementary potential energy.
Abstract: A new numerical model for the three-dimensional contact analysis of a layered elasticperfectly plastic half space with another rough surface is presented. The model is based on a variational principle in which the real area of contact and contact pressure distribution are those which minimize the total complementary potential energy. A quasiNewton method is used to find the minimum. The influence coefficients matrix is determined using the Papkovich-Neuber potentials with fast Fourier transformation. The model is extended to elastic-perfectly plastic contacts in dry and wet conditions. Contact analyses have been performed to predict contact statistics of layered elastic/plastic solids with rough surfaces using this model. The effects of the stiffness of the layer and the substrate, layer thickness, as well as normal load are studied. Optimum layer parameters are identified to provide low friction/stiction and wear.
TL;DR: In this article, a numerical formulation for the dynamic analysis of spiral-grooved gas lubricated mechanical face seals with a flexibly mounted stator is presented, where both finite volume and finite element methods are employed for the spatial discretization of the unsteady, compressible form of the Reynolds equation.
Abstract: A numerical formulation is presented for the dynamic analysis of spiral-grooved gas lubricated mechanical face seals with a flexibly mounted stator. Axial and angular modes of motion are considered. Both finite volume and finite element methods are employed for the spatial discretization of the unsteady, compressible form of the Reynolds equation. Self-adapting unwinding schemes are employed in both methods, making them suitable for situations when the compressibility number is high. Both the lubrication analysis and the kinetic analysis are arranged into a single state space form, which makes coupling the two analyses straightforward. The resulting set of equations is solved using a linear multistep ordinary differential equation solver. Examples of the transient response to static stator misalignment and rotor runout are given. Although a properly designed spiral grooved face seal provides good dynamic performance, it is shown that unacceptably large face separation can occur when large angle spiral grooves are employed together with a sealing dam. @DOI: 10.1115/1.1308015#
TL;DR: In this article, a full numerical solution for the thermal EHL problem in circular contact formed by steel-glass conjunctions with slide-roll ratios larger than 2 has been carried out.
Abstract: A full numerical solution for the thermal EHL problem in circular contact formed by steel-glass conjunctions with slide-roll ratios larger than 2 has been carried out. An anomalous film profile, which is similar to that reported by Kaneta et al. (1996), has been obtained. The numerical results by the authors, involving three basic kinds of film profiles, the kinematic conditions for the formation of dimples, and the variations of dimples and traction behavior with operating conditions, have been carefully compared with the experiments by Kaneta et al., and provided a sound theoretical evidence of the dimple phenomena under steady-state conditions. The present study indicates that the temperature-viscosity-wedge effect seems to be an essential mechanism for the dimple phenomena.
TL;DR: In this article, complete numerical solutions for the steady-state line contact thermal elastohydrodynamic lubrication (TEHL) problems are obtained for the TEHL problem, where the contact surfaces are arranged to run in opposite directions and the slide-roll ratios are allowed to be as high as infinity.
Abstract: Complete numerical solutions are obtained for the steady-state line contact thermal elastohydrodynamic lubrication (TEHL) problems. The contact surfaces are arranged to run in opposite directions. The slide-roll ratios are allowed to be as high as infinity. The new theory reveals that the characteristics of the high slide-roll contacts are significantly different from those of the low slide-roll contacts. The unusual zero-entrainment films discovered by Dyson and Wilson and the abnormal surface-dimple phenomena observed by Kaneta et al. are explained.
TL;DR: In this paper, a modified Reynolds equation for prediction of the pressure in a homogeneous bubbly mixture flow is advanced along with an empirical formula for estimation of the amount of air entrained in an open-ended damper.
Abstract: Squeeze film dampers (SFDs) reduce vibrations and aid in suppressing instabilities in high performance rotor-bearing systems. However, air ingestion and entrapment, pervasive in open-ended dampers with low supply pressures, leads to a bubbly lubricant that severely reduces the dynamic film forces and the overall damping capability. Analyses based on conventional film rupture models, vapor or gaseous lubricant cavitation, fail to predict the actual performance of SFDs, and thus lack credibility in engineering practice. A modified Reynolds equation for prediction of the pressure in a homogeneous bubbly mixture flow is advanced along with an empirical formula for estimation of the amount of air entrained in an open-ended damper. Careful experimentation in a test SFD operating with controlled bubbly mixtures and freely entrained air evidenced similar physical behavior, guided the analytical developments, and provided the basis for validation of the model forwarded, Comparisons of predictions and test results show a fair correlation. A simple equation to predict the amount of air ingestion is also advanced in terms of the damper geometry, supplied flow and operating conditions. The criterion may lack practical implementation since the persistence of air entrainment increases with the frequency and amplitude of journal motions, unless enough lubricant is supplied at all operating conditions.
TL;DR: In this paper, the bifurcation of a rigid rotor supported by a gas film bearing is studied and the existence of a complex dynamic behavior comprising periodic and subharmonic response of the rotor center is analyzed.
Abstract: This paper studies the bifurcation of a rigid rotor supported by a gas film bearing. A time-dependent mathematical model for gas journal bearings is presented. The finite differences method and the Successive Over Relation (S.O.R) method are employed to solve the Reynolds' equation. The system state trajectory, Poincare maps, power spectra, and bifurcation diagrams are used to analyze the dynamic behavior of the rotor center in the horizontal and vertical directions under different operating conditions. The analysis shows how the existence of a complex dynamic behavior comprising periodic and subharmonic response of the rotor center. This paper shows how the dynamic behavior of this type of system varies with changes in rotor mass and rotational velocity. The results of this study contribute to a further understanding of the nonlinear dynamics of gas film rotor-bearing systems.
TL;DR: In this paper, the effects of applied load, surface roughness, welding power and welding time on bonding strength were investigated using an ultrasonic bonding machine and a pull tester.
Abstract: Wire bonding is a popular joining technique in microelectronic interconnect. In this study, the effects of applied load, surface roughness, welding power and welding time on bonding strength were investigated using an ultrasonic bonding machine and a pull tester. In order to relate bonding strength to contact phenomena, the asperity model was used to compute real contact area and flash temperature between the wire and the pad. The experimental results show that a decrease in load or ultrasonic power produces a larger weldable range in which the combination of operation parameters allow the wire and pad to be welded. Regardless of roughness and applied loads, the bond strength increases to a maximum with increases in the welding time, and then decreases to fracture between wire and pad. The theoretical results and experimental observations indicate that bond strength curves can he divided into three periods. The contact temperature plays an important role in bonding strength in the initial period, and surface roughness is the dominant factor in the final period. The maximum bonding strength point occurs in the initial period for different loads and surface roughness values. Our results show that bond strength of ultrasonic wire bonding can be explained based on the input energy per real contact area.
TL;DR: In this paper, the effects of running speed, applied normal load, contact temperature and surface roughness on friction coefficient have been investigated for conventional cast-iron cylinder bores and results correlated well with bench test results.
Abstract: A bench friction test system for piston ring and liner contact, which has high stroke length and large contact width has been used to verify the analytical mixed lubrication model presented in a companion paper (Part 1). This test system controls the speed, temperature and lubricant amount and records the friction force, loading force, crank angle signal and contact temperature data simultaneously. The effects of running speed, applied normal load, contact temperature and surface roughness on friction coefficient have been investigated for conventional cast-iron cylinder bores. Friction coefficient predictions are presented as a function of crank angle position and results are compared with bench test data. Analytical results correlated well with bench test results.
TL;DR: In this paper, a set of AISI 9310 steel gears were provided with a near-mirror finish by superfinishing, which reduced the roughness average by about a factor of 5.
Abstract: Previous research provides qualitative evidence that an improved surface finish can increase the surface fatigue lives of gears. To quantify the influence of surface roughness on life, a set of AISI 9310 steel gears was provided with a near-mirror finish by superfinishing. The effects of the superfinishing on the quality of the gear tooth surfaces were determined using data from metrology, profilometry, and interferometric microscope inspections. The superfinishing reduced the roughness average by about a factor of 5. The superfinished gears were subjected to surface fatigue testing at 1.71 GPa (248-ksi) Hertz. contact stress, and the data were compared with the NASA Glenn gear fatigue data base. The lives of gears with superfinished teeth were about four times greater compared with the lives of gears with ground teeth but with otherwise similar quality.
TL;DR: In all previous numerical simulations of the rotary lip seal, the sealing surface was modeled by regular periodic structures as mentioned in this paper, and a more realistic quasirandom surface was used.
Abstract: In all previous numerical simulations of the rotary lip seal, the sealing surface was modeled by regular periodic structures In the present study, a more realistic quasirandom surface is used A mixed elastohydrodynamic analysis is used to generate predictions of such seal operating characteristics as friction coefficient, reverse pumping rate, film thickness distribution, hydrodynamic and contact pressure distributions, contact area, and cavitation area The results are in qualitative agreement with previous experimental observations In the course of the simulations, a new physical mechanism of reverse pumping has been identified
TL;DR: In this article, the authors describe the optimum design methodology for improving operating characteristics of hydrodynamic journal bearings and its application to elliptical journal bearing design used in high-speed rotating machinery.
Abstract: This paper describes the optimum design methodology for improving operating characteristics of hydrodynamic journal bearings and its application to elliptical journal bearing design used in high-speed rotating machinery. The hybrid optimiza technique combining the direct search method and the successive quadratic programming is applied effectively to find the optimum solutions. In the optimum design of elliptical journal bearings, the design variables such as vertical and horizontal radial clearances, hearing length-to-diameter ratio and bearing orientation angle are determined to minimize the objective function defined by the weighted sum of maximum averaged oil film temperature rise, leakage flow rate, and the inversion of whirl onset speed of the journal under many constraints. The results obtained are shown in graphical form for a wide range of journal rotational speed. Comparing the optimized operating characteristics with the characteristics calculated from the random selected design variables, the effectiveness of optimum design is clarified.
TL;DR: In this paper, a finite element procedure is devised to analyze the performance of gas-lubricated spiral groove face seals operating at high speeds, based on the Galerkin weighted residual method with a new class of high-order shape functions derived from an approximate solution to the nonlinear Reynolds equation within an element.
Abstract: An efficient and accurate finite element procedure is specially devised to analyze the performance of gas-lubricated spiral groove face seals operating at high speeds. The procedure is based on the Galerkin weighted residual method with a new class of high-order shape functions, which are derived from an approximate solution to the nonlinear Reynolds equation within an element. Static and dynamic performance characteristics, such as seal opening force, flow leakage and frequency-dependent dynamic force coefficients, are determined to study the effects of high speeds on the behavior of spiral groove gas face seals.
TL;DR: In this article, a study of the behavior of elastohydrodynamic lubricated contacts subjected to rapid halting is presented, where experiments have been carried out using ultrathin interferometry coupled to a high-speed camera to measure the change in lubricant film thickness and shape during fast, controlled deceleration, both in pure sliding and pure rolling conditions.
Abstract: This paper describes a study of the behavior of elastohydrodynamic lubricated contacts subjected to rapid halting. Experiments have been carried out using ultrathin interferometry coupled to a high-speed camera to measure the change in lubricant film thickness and shape during fast, controlled deceleration, both in pure sliding and pure rolling conditions. Film collapse is seen to occur in two stages. The first persists throughout the deceleration period and, during this stage the film geometry remains almost constant across the contact. In this stage of film collapse, the film thickness lags behind the value predicted from steady-state theory, which means that when motion ceases, a thicker than expected film is present. The second stage of film collapse ensues when the entrainment speed falls below a critical value of approximately 0.002 m/s and is characterized by the formation of a central entrapment and classical, normal approach, squeeze behavior.
TL;DR: In this paper, a three-dimensional thermal-mechanical asperity contact model was developed, which takes into account steady-state heat transfer, as perity distortion due to thermal and elastic deformations, and material yield.
Abstract: The rough surface contact in a tribological process involves frictional heating and thermoelastic deformations. A three-dimensional thermal-mechanical asperity contact model has been developed, which takes into account steady-state heat transfer, asperity distortion due to thermal and elastic deformations, and material yield. The finite-element method (FEM), fast Fourier transform (FFT), and conjugate gradient method (CGM) are employed as the solution methods. The model is used to analyze the thermal-mechanical contact of typical rough surfaces and investigate the importance of thermal effects on the contact performance of surface asperities.