Showing papers in "Tribology Transactions in 2002"

Experimental Investigation of Laser Surface Texturing for Reciprocating Automotive Components

Abstract: An experimental study is presented to evaluate the effectiveness of micro-surface structure, produced by laser texturing, to improve tribological properties of reciprocating automotive components. The test rig and test specimens are described and some test results are presented. Good correlation is found with theoretical prediction of friction reduction on a simple, yet representative, test specimen. Potential benefit of the laser surface texturing under conditions of lubricant starvation is also presented. Finally, friction reduction with actual production piston rings and cylinder liner segments is demonstrated. Presented at the 57th Annual Meeting in Houston, Texas May 19–23, 2002

A Laser Surface Textured Hydrostatic Mechanical Seal

Abstract: A mechanical seal subjected to laser surface texturing over an annular portion of one of its mating rings is theoretically and experimentally investigated. The partial surface texturing provides a mechanism for hydrostatic pressure build up in the sealing dam similar to that of a radial step or face coning. Optimization of the surface texturing parameters to obtain maximum hydrostatic pressure effect is performed on a theoretical model. A test rig that allows friction torque and temperature measurements in a back-to-back double seal arrangement is used to validate the surface texturing effect. It is found that optimally textured seals generate substantially less friction and heat. Moreover, a simple unbalanced seal, limited in its pressure capacity, can be easily transformed by surface texturing to an equivalent balanced seal with much higher pressure capability. Presented at the 57th Annual Meeting Houston, Texas May 19–23, 2002

The Role of Radial Clearance on the Performance of Foil Air Bearings

Abstract: Load capacity tests were conducted to determine how radial clearance variations affect the load capacity coefficient of foil air bearings. Two Generation III foil air bearings with the same design but possessing different initial radial clearances were tested at room temperature against an as-ground PS304 coated journal operating at 30,000 rpm. Increases in radial clearance were accomplished by reducing the journal's outside diameter via an in-place grinding system. From each load capacity test the bearing load capacity coefficient was calculated from the rule-of-thumb (ROT) model developed for foil air bearings. The test results indicate that, in terms of the load capacity coefficient, radial clearance has a direct impact on the performance of the foil air bearing. Each test bearing exhibited an optimum radial clearance that resulted in a maximum load capacity coefficient. Relative to this optimum value are two separate operating regimes that are governed by different modes of failure. Bearings operating with radial clearances less than the optimum exhibit load capacity coefficients that are a strong function of radial clearance and are prone to a thermal runaway failure mechanism and bearing seizure. Conversely, a bearing operating with a radial clearance twice the optimum suffered only a 20 percent decline in its maximum load capacity coefficient and did not experience any thermal management problems. However, it is unknown to what degree these changes in radial clearance had on other performance parameters, such as the stiffness and damping properties of the bearings.

The Lubrication Effect of Micro-Pits on Parallel Sliding Faces of SiC in Water

Abstract: Silicon carbide is regarded as a promising material for sliding bearings and mechanical seals working in water. In order to improve its load carrying capacity (or anti-seizure ability) in water, micro-pits were formed on one of the contact surfaces by ion reaction etching. The effect of micro-pits on the critical load for the transition from EHL to mixed lubrication was studied experimentally in the cases of bearing type contact (with relatively rich water supply) and seal type contact (with relatively poor water supply). In order to understand the mechanisms of the lubrication effect of micro-pits, the experimental results obtained from bearing type contact and seal type contact were compared, and a theoretical analysis was carried out. Presented at the 57th Annual Meeting Houston, Texas May 19–23, 2002

Role of Third Bodies in Friction Behavior of Diamond-like Nanocomposite Coatings Studied by In Situ Tribometry

Abstract: The friction and wear behavior of amorphous diamond-like nanocomposite (DLN) coatings (C:H:Si:0) in low speed, dry sliding contact has been investigated using a home-built in situ tribometer. Tests were performed under reciprocating sliding against sapphire and steel hemispheres in dry (∼4% RH) and moist (35 to 52% RH) air at contact stresses of 0.7 and 1.1 GPa. In situ visual observations identified how third body processes affected the friction behavior of DLN coatings. For all test conditions, a transfer film began to form on the sapphire hemisphere during the first cycle, and the coefficient of friction dropped during further buildup of the transfer film. Video analysis showed most of the sliding motion took place between the transfer film on the hemisphere and the DLN coating. This velocity accommodation mode, interfacial sliding, was responsible for steady-state friction coefficients between 0.03 and 0.05 with lower values obtained at high stress and low RH. When the transfer film broke up the frict...

Influence of Colloidal Abrasive Size on Material Removal Rate and Surface Finish in SiO2 Chemical Mechanical Polishing

Abstract: This paper addresses the influence of nano-scale abrasive particle size in the polishing of thermally-grown silicon dioxide on 100 mm diameter, p-type, (100), single crystal silicon wafers. The abrasive particles are incorporated in a chemical slurry, which is used in chemical mechanical polishing (CMP). Polishing (material removal) rate was measured with six (6) slurries, each with a different mean abrasive particle diameter of 10, 20, 50, 80, 110 and 140 nm. The experimental results indicate that the material removal rate (MRR) is related to the particle size. Results confirm that there exists an optimum abrasive size (80 nm) with respect to material removal rate and surface finish, for a given set of experimental conditions. The variation of the MRR vs. particle size (on a log-log plot) varies as d3.4. In addition, the surface polished with 10 nm and 20 nm abrasives was stained by the slurries. For a pad surface roughness of 5.2 μm (Ra), the slurry containing the 80 nm particles resulted in the highest...

Ball Bearing and Tapered Roller Bearing Torque: Analytical, Numerical and Experimental Results

Abstract: The miscellaneous components of bearing torque are described analytically. When the rolling element - race contact lengths are similar, the hydrodynamic ball bearing torque component can be similar to the tapered roller bearing one. In ball bearings, the sliding speed distribution encountered at the ball/race contact is the result of two torque contributions: curvature in space of the contact ellipse and spinning effects. These two torque contributions don't exist in tapered roller bearings. However, tapered roller bearings are subjected to a roller/rib torque which is compared analytically to the two previous hall hearing torque components. The final tapered roller hearing torque is compared to hall hearing torque under various operating conditions. It is shown that there are conditions for which the tapered roller hearing torque can he smaller than the hall hearing one; the latter point is demonstrated numerically and experimentally in reported literature. Presented at the 57th Annual Meeting Houston, T...

Accurate Measurements of Pressure-Viscosity Behavior in Lubricants

Abstract: The piezoviscous effect is accurately characterized for a number of representative lubricating oil base stocks and a simple, well-defined hydrocarbon. Procedures for the generation of accurate pressure-viscosity coefficients are outlined. The reciprocal asymptotic isoviscous pressure may be measured to within perhaps 1%. The piezoviscous effect may be important to automotive fuel economy. The departure from exponential behavior at very low pressure becomes more pronounced at high temperature. Presented at the 57th Annual Meeting Houston, Texas May 19–23, 2002

A transient dynamic analysis of mechanical seals including asperity contact and face deformation

Abstract: Face seals are typically designed to be in contact at standstill. However, as speed and pressure build up, the seal faces deform from their factory flat conditions because of viscous and dry friction heating, as well as mechanical and centrifugal effects. It is imperative that such deformations form a converging gap for radial flow to ensure stable operation and to promote favorable dynamic tracking between stator and rotor. A numerical simulation is presented for the transient response of a face seal that is subjected to forcing misalignments while speeds and pressures are ramped up and down. Asperity contact forces and transient face deformation caused by viscous heating are included. A new closed-form solution is obtained for the elastoplastic contact model, which allows seamless transition between contacting and noncontacting modes of operation. The model is then used to calculate face contact forces that occur predominantly during startup and shutdown. The viscous heating model shows that the time-de...

An Analysis of Elastohydrodynamic Lubrication with Limiting Shear Stress: Part I—Theory and Solutions

Abstract: This paper investigates line contact elastohydrodynamic lubrication assuming a limiting shear stress of the fluid-contact interfaces. The film pressures and film thickness distributions are obtained for the slide-roll ratios between a cylinder and a plane. The results show that the interfacial limiting shear stress effect can directly cause a drastic film thickness reduction.

Phase transformations in silicon under dry and lubricated sliding.

Abstract: Sliding friction and wear mechanisms of silicon/silicon nitride test pairs were investigated under conditions of both dry and lubricated sliding. High-resolution surface topography mapping and electron microscopy studies revealed that microfracture was the predominant wear mechanism under dry and grease-lubricated sliding conditions. Raman spectroscopy suggested that in certain areas of the sliding contact, silicon underwent phase transformation and reached a metallic state because of high contact pressures. The extent of phase transformation was greater during the very early stages of the run-in period than during steady-state sliding regimes. The use of grease and oil as lubricants led to a substantial reduction in friction and greatly diminished wear due to microfracture. Furthermore, almost all areas on Si surfaces subjected to lubricated sliding contact underwent pressure-induced phase transformation. Both amorphous material and crystalline Si phases were identified by Raman spectroscopy. The experim...

Friction Behavior of Boric Acid and Annealed Boron Carbide Coatings Studied by In Situ Raman Tribometry

Abstract: The sliding friction behavior of boric acid and annealed boron carbide coatings has been investigated by in situ Raman tribometry. Reciprocating sliding tests were performed in air (∼20% relative humidity) at 1 mm/s with a transparent sapphire hemisphere dead weight loaded against the coated substrates. A homebuilt micro-Raman tribometer recorded the friction force as well as allowed both visualization and Raman spectroscopy of the contacts during sliding. Friction coefficients for the boric acid films remained low (μ ∼ 0.06) throughout sliding until failure (μ ∼ 0.7), at which time boric acid was lost from the contact and substrate material (aluminum) transferred to the slider. Friction coefficients for the annealed boron carbide, known to form boric acid surface films upon cooling, were initially low (0.08), then gradually increased and leveled out at about 0.2. Raman spectroscopy revealed a mixture of boric acid and carbon initially; but as the friction coefficient rose, the boric acid intensity decrea...

The Effect of Journal Roughness and Foil Coatings on the Performance of Heavily Loaded Foil Air Bearings

Abstract: Foil air bearing load capacity tests were conducted to investigate if a solid lubricant coating applied to the surface of the bearing's top foil can function as a break-in coating. Two foil coating materials, a conventional soft polymer film (polyimide) and a hard ceramic (alumina), were independently evaluated against as-ground and worn (run-in) journals coated with NASA PS304, a high-temperature solid lubricant composite coating. The foil coatings were evaluated at journal rotational speeds of 30,000 rpm and at 25 C. Tests were also performed on a foil bearing with a bare (uncoated) nickel-based superalloy top foil to establish a baseline for comparison. The test results indicate that the presence of a top foil solid lubricant coating is effective at increasing the load capacity performance of the foil bearing. Compared to the uncoated baseline, the addition of the soft polymer coating on the top foil increased the bearing load coefficient by 120% when operating against an as-ground journal surface and 85 percent against a run-in journal surface. The alumina coating increased the load coefficient by 40% against the as-ground journal but did not have any affect when the bearing was operated with the run-in journal. The results suggest that the addition of solid lubricant films provide added lubrication when the air film is marginal indicating that as the load capacity is approached foil air bearings transition from hydrodynamic to mixed and boundary lubrication.

Engagement of a Rough, Lubricated and Grooved Disk Clutch ith a Porous Deformable Paper-Based Friction Material

Abstract: The engagement of wet clutches was simulated using Berger's model (1997) and torque equations. Influencing parameters were studied such as surface roughness, fluid viscosity, friction characteristics, material permeability, moment of inertia, groove area ratio and Young's modulus. One big concern for the wet clutch engagement is engagement time which affects the friction generated heat and thus the temperature. Another major concern is the torque response that is of importance to study clutch shudder. Surface roughness, viscosity and friction curves affect the engagement time and torque response. The moment of inertia has a big influence on the engagement time rather than the torque. Permeability, groove area and Young's modulus have less effect on the torque than the other parameters. Presented as a Society of Tribologists and Lubrication Engineers Paper at the ASME/STLE Tribology Conference in Cancun, Mexico October 27–30, 2002

Effects of surface micro-geometry on the lift-off speed of an EHL contact

Abstract: With decreasing speed the film thickness in an EHL contact decreases. Below a certain speed asperity contact will take place and gradually the contact enters the mixed lubrication regime. Vice-versa, with increasing speed beyond a certain speed the film thickness has reached a level where asperity contacts have become so rare that the contact will be in the full film regime. It seems only logical to expect that the speed at which the first (or last) significant asperity interactions start to take place is influenced by the micro-geometry of the surfaces. In experiments performed on a two-disk rig under conditions of pure rolling, using one very smooth and one rough disk it was indeed observed that the “lift-off” speed defined as the speed above which full film lubrication prevails, differed significantly for surfaces with a different micro-geometry. The test results can be seen as ranking for the surface micro-geometries in terms of their film generating capability. In this paper the question is addressed if a ranking as observed in the tests can be predicted in advance, using the load conditions and the measured surface micro-geometry as input, without having to resort to full-scale numerical simulations of any sort. Based on the amplitude reduction formula proposed by Venner et al. (2000), for roughness in contacts under pure rolling a model is constructed that, given the load condition and a measured surface micro-geometry, determines the deformed micro-geometry and subsequently a measure of “probability of contact.” For a given contact this measure can be plotted as a function of speed to obtain a theoretical “lift-off” curve. For the different types of surface micro-geometries used in the tests such a curve is compared with the experimental results, showing a promising agreement in ranking.

The Effect of Shear-Thinning on Film Thickness for Space Lubricants

Abstract: The authors show that the difference between effective pressure-viscosity coefficients, obtained from film thickness, and coefficients obtained from viscometers for a PFPE space lubricant is substantially the result of shear thinning in the inlet zone of concentrated contact. Flow curves for the PFPE and a multialkylated cyclopentane are presented along with film calculations based on the Carreau model. Presented at the 57th Annual Meeting Houston, Texas May 19–23, 2002

Surface and Subsurface Cracks in Rolling Contact Fatigue of Hardened Components

Abstract: The competitive aspect of surface and subsurface fatigue crack propagation in hardened components subjected to rolling contact fatigue is highlighted, the former being greatly affected by the working conditions (in particular the presence of tangential stresses and lubricant), the latter depending mainly on the inclusions content and on the hardness profile. In order to determine which one of these kinds of damage is favoured, initial data consisting of contact load, rolling and sliding speed, theological properties of the lubricant, material hardness and inclusions content are necessary. The concurrent role of asperities and Hertzian stress field in determining surface crack propagation is explained with the approach of the “quiescent zone.” calculating the stress intensity factors range in a contact cycle and considering the pumping effect of the fluid possibly present on the contact surface. Inherent defects (especially oxides) are thought to be responsible for subsurface cracks origin and the Murakami...

Thrust-Washer Evaluation of Self-Lubricating PS304 Composite Coatings in High Temperature Sliding Contact

Abstract: PS304 self-lubricating composite coatings were successfully deposited on steel substrates at various plasma spray facilities using mixtures blended from commercially obtained constituent particles. Coatings were evaluated in thrust-washer tests against Inconel X-750 at low contact pressures to 40kPa, sliding speed of 5Amis, and either ambient temperature or 500 °C chosen to simulate conditions in airfoil bearings during startup and shutdown contact. Wear factors for all PS304 coatings tested, regardless of contact pressure and temperature, ranged from 1–3*10−4 mm3/Nm while coefficients of friction of approximately μ =0.5 were measured in all cases. While wear and friction behavior of PS304 in air foil bearings appear to have been simulated, surface roughening was observed in these thrust-washer tests which used continuous sliding contact, as opposed to the evolution of smoother surfaces observed in high-temperature foil bearings experiencing cyclic startup/shutdown. Wear-induced surface smoothening of PS3...

Fatigue Limit Concept and Life Prediction Model for Rolling Contact Machine Elements

Abstract: The weakness of the present method of fatigue limit assessment is discussed and a new approach to fatigue limit assessment using a three-parameter log-log and Weibull plot is proposed. With this new approach to the analysis of alternating fatigue test data, it is confirmed that hearing steel does not show any fatigue limit, whereas structural steel does have a distinct fatigue limit. In absence of a fatigue limit for hearing steel, a minimum life or a minimum number of stress cycles prior to failure is proposed for the analysis of fatigue life behavior under a given rolling contact fatigue load or stress, leading to a three-parameter Weibull life distribution function. The experimental data is found to fit very well to this distribution. A comparison of the stress-life exponents estimated for the structural steel and bearing steel using three methods of analysis shows the values to be very close indicating similarity in their fatigue behaviors. Presented as a Society of Tribologists and Lubrication Engine...

Antiwear Tribofilm Formation on Steel Surfaces Lubricated With Gear Oil Containing Borate, Phosphorus, and Sulfur Additives

Abstract: The formation of antiwear tribofilms plays a critical role in the longevity of automotive gears. The focus of this experimental study was on the lubrication efficacy of gear oils with different contents of borate-, phosphorus-, and sulfur-containing additives leading to the formation of protective tribofilms. Experiments were performed with AISI 52100 steel balls sliding against AISI 52100 steel disks in baths of different oils at ambient (∼32 °C) and elevated (∼100 °C) temperatures under load and speed conditions favoring sliding in the boundary lubrication regime. Friction coefficient responses accompanied by electrical contact voltage measurements provided real-time information about the formation and durability of the antiwear tribofilms. The wear resistance of the tribochemical films was quantified by wear rate data obtained from surface profilometry measurements of wear tracks on the disk specimens and sliding tests performed at ambient temperatures after the formation of the tribofilms during eleva...

Measurement of oil-film pressure in engine bearings using a thin-film sensor

Abstract: Editor's Note: Anyone who thinks that STLE isn't on the cutting edge of MEMS technology should read this paper. In it, the authors have measured oil pressures which occur in main and connecting rod bearings using vacuum deposited thin film pressure sensors measuring less than a millimeter wide and just a few microns thick. Their careful work shows that oil pressures in the main bearings can exceed 5000 psi (35 MPa) and are even higher (22,000 psi/150MPa) in connecting rod bearings. Ah, the magic of hydrodynamics. With a supply pressure of just 75 psi (0.5 MPa), the spinning crankshaft works with the oil viscosity to magnify the pressure a hundred fold or more to support the enormous forces of combustion occurring in today heavily loaded engines. This kind of advanced Tribology work goes on in many laboratories around the world and you can read about them in STLE publications. Read on and discover. Appeared in Tribology Transactions, January 2002.

100mm Diameter Self-Contained Solid/Powder Lubricated Auxiliary Bearing Operated at 30,000 rpm

Abstract: A major breakthrough development of a self-contained solid/powder lubricated auxiliary hydrodynamic bearing has recently been achieved successfully. This bearing was operated at speeds to 30,000 rpm, equivalent to three million DN, and loads to 445 N (100 1b). Uniqueness of this bearing lies in its application of dry particulate powders to provide a long life, low power loss backup hearing. Impetus behind this development is the necessity for high performance auxiliary bearing systems in magnetic bearing supported rotors. Potential applications include ground and space based Flywheel Energy Storage Systems, Auxiliary and Integrated Power Units and Gas Turbine engines. The two main technology components of this bearing are the palletized powder lubricant delivery system and the powder lubricated journal bearing design. Using established criteria, powder materials suitable for the expected operating environments were reviewed. The selected powder lubricant properties and the design tool were used to fabrica...

A Deterministic Elastohydrodynamic Lubrication Model of High-Speed Rotorcraft Transmission Components

Abstract: This paper describes a deterministic approach to analyze elastohydrodynamic lubrication (EHL) of helicopter transmission gear surfaces with asperities. A thermal, non-Newtonian, model, accompanied by three specialized models is used to study the mechanisms of film generation, pressure distribution and temperature distributions within the fluid and on the surface, in an EHL line contact. A two-slope viscosity-pressure model is used to avoid overestimation of the viscosity of the lubricant under heavy loads. The three-dimensional roughness description of an actual gear tooth surface is measured using a non-contact surface profiler. The pressure distribution, film thickness distribution and the temperature rise at the contact surface are predicted as a function of the gear operating conditions including normal load, lubricant temperature and rolling/sliding speed. Presented at the 57th Annual Meeting in Houston, Texas May 19–23, 2002

Behavior of coated carbide tools in high speed machining of a nickel base alloy

Abstract: Multilayer TiN/TiCN/TiN and single-layer TiAIN PVD coated carbide tools were used to machine a nickel base, C-263, alloy at high-speed conditions in order to investigate their performance in terms of tool life, surface finish and component forces generated during machining. The test results show that the triple layer, TiN/TiCN/TiN, coated inserts gave longer tool life when machining at higher speed and depth of cut conditions while the single layer, TiA/N, coated inserts produced better surface finish. The feed forces recorded were generally higher than the cutting forces. This could perhaps be attributed to the adverse effect of burr formation and work hardening of the workpiece associated with prolonged machining. Analysis of the test results indicate that the difference in thermal properties and tribo-chemical behaviour of both the coating and substrate materials are the major factors influencing the tribo-contact at the tool-chip interface during machining. Wear mechanisms of the coating materials can...

Behavior of EHD Films During Reversal of Entrainment in Cyclically Accelerated/Decelerated Motion

Abstract: Transient elastohydrodynamic lubrication, in which operating parameters such as speed, load or curvature vary over time, occurs in many machine elements including cams, gears and reciprocating devices. It also occurs in rolling-element bearings at the start or stop of motion. This paper presents findings of an experimental study on the behavior of EHD films during reversal of entrainment in reciprocating motion. An optical interferometric technique, which enables interference images to be captured at a rate of 1000 measurements per second, was used to monitor film thickness in the lubricated contact between a transparent flat and a steel ball run in a linear accelerated/decelerated motion. The results show that minimum film thickness does not occur at the position of zero entrainment as predicted theoretically, but with a certain time delay. This delay, as well as the minimum thickness of the film, is highly dependent upon the rate of change of entrainment speed. Comparison of experimental results with an...

Elastohydrodynamic Lubrication in Extended Parameter Ranges — Part I: Speed Effect

Abstract: Elastohydrodynamic Lubrication (EHL) has been given great attention in the last 40 years. Conventional theories by Dowson and Higginson for line contacts and Hamrock and Dowson for point contacts have been among the most important contributions and widely used in industries. However, commonly used film thickness formulae, developed more than 25–40 years ago when the computational power was very limited, were originally from curve-fitting based on limited numbers of numerical solutions obtained in relatively narrow parameter ranges. Actual operating conditions in typical engineering applications, such as gears, bearings, cams and traction drives, sometimes fall far outside those parameter ranges, and prediction through extrapolation is often difficult to give satisfactory results. As the computer technology and numerical simulation methods have been advancing greatly, one can now analyze cases in extended parameter ranges that cover various practical applications under severe conditions. This paper is Part...

Thermal Processing Effects on the Adhesive Strength of PS304 High Temperature Solid Lubricant Coatings

Abstract: In this paper the effects of post deposition heat treatments on the cohesive and adhesive strength properties of PS304, a plasma sprayed nickel-chrome based, high temperature solid lubricant coating deposited on stainless steel, are studied Plasma spray deposited coating samples were exposed in air at temperatures from 432 to 650 C for up to 500 hr to promote residual stress relief, enhance particle to particle bonding and increase coating to substrate bond strength Coating pull-off strength was measured using a commercial adhesion tester that utilizes 13 mm diameter aluminum pull studs attached to the coating surface with epoxy Pull off force was automatically recorded and converted to coating pull off strength As deposited coating samples were also tested as a baseline The as-deposited (untreated) samples either delaminated at the coating-substrate interface or failed internally (cohesive failure) at about 17 MPa Samples heat treated at temperatures above 540 C for 100 hr or at 600 C or above for more than 24 hr exhibited strengths above 31 MPa, nearly a two fold increase Coating failure occurred inside the body of the coating (cohesive failure) for nearly all of the heat-treated samples and only occasionally at the coating substrate interface (adhesive failure) Metallographic analyses of heat-treated coatings indicate that the Nickel-Chromium binder in the PS304 appears to have segregated into two phases, a high nickel matrix phase and a high chromium precipitated phase Analysis of the precipitates indicates the presence of silicon, a constituent of a flow enhancing additive in the commercial NiCr powder The exact nature and structure of the precipitate phase is not known This microstructural change is believed to be partially responsible for the coating strength increase Diffusion bonding between particles may also be playing a role Increasing the heat treatment temperature, exposure time or both accelerate the heat treatment process Preliminary measurements indicate that the heat treatment also results in a one time, permanent coating thickness increase of about 3% Based upon these results, the incorporation of a heat treatment prior to final finishing has been incorporated in the application process of this coating technology

Film Formation in EHL Point Contacts under Zero Entraining Velocity Conditions

Abstract: The contacts of adjacent balls in a retainerless bearing are subjected to the zero entrainment velocity (ZEV). The existence of an effective elastohydrodynamic lubrication (EHL) film between contacts running under ZEV conditions has long been proven experimentally. However, the classical EHL theory predicts a zero film thickness under ZEV conditions. Mechanisms, such as the thermal viscosity wedge effect and immobile film theory, have been proposed to tentatively explain the phenomenon. However, detailed numerical results are needed to provide theoretical evidence for such film formations. This paper aims to simulate, based on the viscosity wedge mechanism, the film formation of EHL point contacts under ZEV conditions. Complete numerical solutions have been successfully obtained. The results show that the thermal viscosity wedge induces a concave film profile, instead of a parallel film (Hertzian) as postulated by some previous researchers. By the simulation solver developed, the variation of film thickne...

Linear Stability Analysis for a Hydrodynamic Journal Bearing Considering Cavitation Effects

Abstract: The purpose of this paper is to present the two-dimensional linear stability analysis considering the fluid flow in both full film and cavitation regions for a plain cylindrical journal bearing. The Lund's infinitesimal perturbation procedure is applied to Elrod's universal equation for evaluation of unsteady pressure gradients. Based on JFO theory, the pressure distribution, film rupture, and reformation boundaries can be obtained using Elrod's universal equation, for a given operating position of the journal. In this work, it is assumed that for infinitesimal perturbation of a journal about the equilibrium position, the film rupture and film reformation boundaries are the same as those obtained for steady state. However, the unsteady pressure gradients in the full film region are evaluated taking into consideration the perturbed flow parameters in the cavitation region, i.e., at both rupture and reformation boundaries. The linearized stiffness and damping coefficients, whirl frequency ratio, and thresho...

Combined Influence of Journal Misalignment and Surface Roughness on the Performance of an Orifice Compensated Non-Recessed Hybrid Journal Bearing

Abstract: The combined influence of surface roughness and journal misalignment on the performance of an orifice compensated hole-entry hybrid journal bearing system is theoretically studied. The analysis considers the average Reynolds equation for a rough surface for the solution of the lubricant flow field in the clearance space of a journal bearing system. The bearing performance characteristics are presented for the various representative values of surface roughness parameter (Λ) and surface pattern parameter (γ) for a concentric design pressure ratio β* = 0.5. Performance is also compared to capillary and constant flow valve compensated bearings. The computed results indicate that the effect of journal misalignment is to lower the value of the minimum fluid-film thickness of the journal bearing system while the effect of surface roughness is to partially compensate this loss. For the chosen values of journal misalignment parameters (ϕ, δ), the constant flow valve compensated symmetric journal bearing configurat...