Showing papers in "Tribology Transactions in 1985"

Mechanism of Crack Growth in Lubricated Rolling/Sliding Contact

Abstract: In order to explain the mechanism of rolling-contact fatigue crack growth analytically, fracture mechanics are applied to a semicircular surface crack inclined at an angle to the elastic half-space loaded by Hertzian stresses. It is shown that the surface traction is the controlling factor for lubricant seepage into the crack and for shear mode crack growth rate. It is also clarified that the generation of pits results from tensile mode crack growth mainly due to the oil hydraulic pressure action.

Analysis of Surface Crack Propagation in Lubricated Rolling Contact

Abstract: Growth behavior of surface cracks formed on lubricated rolling-sliding contact surfaces is studied by calculating three-dimensional mixed-mode stress intensity factors KI, KII, and KIII. It is shown from the viewpoint of the fatigue crack propagation that the hydraulic pressure effect pointed out by Way may be accepted as a possible mechanism of surface crack growth. Some of the experimental facts on pitting are also confirmed qualitatively.

Perfluoropolyalkylether Oil Degradation: Inference of FeF3 Formation on Steel Surfaces under Boundary Conditions

Abstract: The formation of iron fluoride (FeF3) through the interaction of perfluoropolyalkylether (PEPE) oil with steel surfaces was investigated under boundary lubrication conditions. Ball-bearing rolling action was simulated by a specially designed wear-test apparatus that incorporated noncoaxial wear members to give a skid/roll ratio of ∼0.16. The contact stress was 8.3 × 108 N·m−2 (∼120 000 psi), and the speed was 1750 rpm. Under these conditions, FeF3 formation on the wear surfaces was inferred using x-ray photoelectron spectroscopic (XPS), Auger electron spectroscopic (AES), and secondary ion mass spectrometric (SIMS) surface analysis techniques. These findings support the hypothesis that, under the low oxygen environment of spacecraft earth orbit, formation of FeF3 and subsequent FeF3 catalyzed degradation of PEPE can constitute an important PFPE degradation pathway under boundary lubrication conditions. Presented at the 40th Annual Metting in Las Vegas, May 6–9, 1985

Observations on the Sliding Wear of Ceramics

Abstract: Modern design concepts for heat engines with increased thermal efficiency call for the utilization of ceramic components. In some applications, lubrication of these components will be difficult to maintain. Consequently, a need exists for an expanded understanding of the dry sliding wear behavior of ceramics. Sliding wear experiments were performed on several ceramic pairs from which wear rate data and information on the nature of the physical damage resulting from dry sliding were obtained. The wear evaluation was a pin-on-disk test. The test conditions included temperatures as high as 425°C, a surface velocity of 0.3 m/s, and a normal force of 9.0 N. Most of the specimens experienced moderate to severe damage. Damage characterized as mild wear was observed in a single room temperature test. The coefficient of friction for the damaged specimens ranged from 0.7 to 1.0, while this value was consistently 0.24 for the undamaged specimen. The implications of these results for wear mechanism are discussed. Pre...

The Reaction of Perfluoropolyalkylether Oil with FeF(3), AlF(3), and AlCl(3) at Elevated Temperatures.

Abstract: The interaction of perfluoropolyalkylether (PFPE) oil with ferric fluoride (FeF3) and other Lewis acids at elevated temperatures under inert atmosphere was investigated to determine whether the reaction results in lubricant degradation. At 35°C, ∼25°C below the onset of thermal degradation, PFPE'S reaction with FeF3 yields acyl fluoride and ketone degradation products and also a decrease in the oil's number-average molecular weight. In the presence of small quantities of water, the acyl halide products hydrolyze, resulting in carboxylic acids. The oil's reaction with aluminum fluoride at 350°C and aluminum chloride at 200°C also causes it to degrade measurably. The results indicate that PFPE oil can degrade at estimated bearing asperity contact temperatures in the presence of FeF3.

Stability threshold and steady-state response of noncontacting coned-face seals©

Abstract: The dynamic behavior of a noncontacting coned-face seal is analyzed. Stiffness and damping properties of the fluid film and flexible support including elastomeric secondary seal are fully accounted for. Stability threshold and steady-state response in the presence of rotor axial runout and assembly misalignment are investigated. An expression is provided for the critical speed above which the seal becomes dynamically unstable. For stable operation, the relative misalignment between the mating faces is given as a function of rotor runout, assembly misalignment, design parameters, and operation conditions. An expression is provided for the critical rotor runout above which the seal will fail due to face contact. Although the analysis is based on small perturbation assumption, it is shown to be valid in many practical cases. Presented as an American Society of Lubrication Engineers paper at the ASLE/ASME Lubrication Conference in San Diego, California, October 22–24, 1984

On a Negative-Ion Concept of EP Action of Organo-Sulfur Compounds

Abstract: To understand the chemical behavior of EP additives in sliding contacts, the concept of an anionic mechanism of the elementary sulfur and organo-sulfur compounds has been proposed. The model is based upon the ionization of these compounds by the action of exoelectrons. It has been shown that disulfides exhibit more efficient EP performance than monosulfides because lower energy is needed for the formation of the same number of RSΘ ions from disulfides. The corrosive action of the elementary sulfur in the friction process can be explained by the formation of ions from SΘ to S8 Θ. An attempt to interpret the difference in EP performance of diphenyl sulfide and dibenzyl sulfide has also been made as well. Presented as an American Society of Lubrication Engineers paper at the ASLE/ASME Lubrication Conference in Hartford, Connecticut, October 18–20, 1983

Computer Simulation of Elastic Rough Contacts

Abstract: A computer program is developed to analyze the contact of a rigid smooth plane and computer-simulated elastic rough surfaces. The simulated surfaces have isotropic Gaussian height distribution and bilinear autocorrelation function. Results of two cases are presented: (1) dry contact between a square elastic rough punch and a rigid smooth plane; (2) dry contact between an elastic rough half-space and a rigid smooth plane. Force-compliance relationship is compared with hat derived by Bush, Gibson, and Thomas. Real contact area ratio Ar is found to be approximately proportional to nominal contact pressure in the range 0.025 < Ar < 0.3. Presented at the 39th Annual Meeting in Chicago, Illinois May 7—10, 1984

The Dynamics of Ball Separators in Ball Bearings—Part I: Analysis

Abstract: The dynamic equations of motion of a ball-bearing separator are solved with a six degree-of-freedom model and vector matrix algebra. The dynamic model includes the effects of inelastic collisions of the separator with the balls and/or races, and also slip of the balls on the races. The digital computer model predicts separator motions, impact forces, frequencies, and all dynamic variables such as accelerations, velocities, and energy losses. The model of the ball bearing is simplified, in ways that do not significantly affect the separator dynamics, for the sake of making the analytical model and the resulting digital computer program cost effective. The analysis is adaptable to optimization of separator designs and improving performance of bearings with separator dynamic instability problem. Presented at the 39th Annual Meeting in Chicago, Illinois, May 7–10, 1984

Diagnostic monitoring of rolling-element bearings by high-frequency resonance technique©

Abstract: In the present work, investigations by high-frequency resonance technique for diagnosis of defect frequencies of rolling-element bearings are reported. Raw vibration signature of the bearings at different speeds of operation has been demodulated. Envelope detected spectrum is analyzed to evaluate various defect frequencies and their energy levels. Experimentally evaluated frequencies are compared with theoretically determined defect frequencies. These frequency values and their energy levels are used to monitor intrinsic condition of bearings as well as to establish severity of existing/developed defects in the bearings. Relative comparison of bearings of the same type are made at various operating speeds under identical conditions of operation on the basis of identified defect frequencies and severity of defects. The paper gives a realistic approach to monitor intrinsic condition of a bearing. Investigations given in the paper may have a potential for performance evaluation and may act as a reliable tool...

Thermal Elastohydrodynamic Lubrication of Line Contacts

Abstract: A numerical solution to the problem of thermal elastohydrodynamic lubrication of line contacts was obtained by using a finite difference formulation. The solution procedure consists of simultaneous solution of the thermal Reynolds equation, the elasticity equation, and the energy equation subject to appropriate boundary conditions. Pressure distribution, film shape, and temperature distribution were obtained for fully flooded conjunctions, a paraffinic lubricant, and various dimensionless speed parameters while the dimensionless load and materials parameters were held constant. Reduction in the minimum film thickness due to thermal effects (as a ratio of thermal to isothermal minimum film thickness) is given by a simple formula as a function of the thermal loading parameter Q: H(min)/H(min,I) = 10/10+ Q(0.4). Plots of pressure distribution, film shape, temperature distribution, and flow are shown for some representative cases.

The Real Area of Contact in Polymeric Magnetic Media—II: Experimental Data and Analysis

Abstract: Electrical-contact-resistance and two-beam optical-interference techniques were employed to measure the real area of contact of magnetic tapes. The former technique does not work well due to significant contributions from tunnel effect and multimolecular insulating films; the latter provides shape and size distribution of asperity-contact areas. Experiments were conducted at a pressure range of 13.8 kPa and 1.38 MPa. Normal pressure had strong dependence on both the real area of contact and the number of contact spots, and weak dependence on the mean asperity-contact diameter. This is in agreement with the theory. In the case of the two tapes tested in the pressure range, the real area of contact varied from 0.5 to 25 percent. The mean asperity-contact diameter and number of contact spots ranged from 6 to 13 μm and 200 to 2300 per mm2, respectively. The mean real pressure was in the range of 2 to 8 MPa. The real area of contact increased with an increase in the ambient temperature. Surface roughness had s...

The Measurement of Abrasive Particle Shape and Its Effect on Wear

Abstract: The wear of ground-engaging tools in agriculture is affected by various soil properties, including the angularity of the abrasive particles in the soil. In an effort to quantitatively characterize the size and shape of these particles, a new technique has been used. The method is based on a Fourier analysis of the particle profiles. It yields a set of orientation invariant descriptors which quantify the size and shape of these profiles. This technique has been applied to various types of silica sand and crushed quartzite, as well as a few soil samples. The results obtained have shown that this analysis procedure can readily distinguish particles of differing angularities. A relationship has also been developed between the particle profile size and shape descriptors and the wear rates of selected steels in the dry-sand rubber-wheel test described in ASTM Standard Practice G65. This relation has enabled us to separate the influence of size and shape on the rate of abrasion. Further work is planned, and it i...

The Role of Near-Surface Inclusions in the Pitting of Gears

Abstract: This paper presents the results of a study combining experimental and analytical techniques to characterize the role played by near-surface inclusions in the pitting of gears. Experimental test results pertaining to failures induced by inclusions are presented in photomicrographs and discussed in terms of metallurgical considerations. A model is proposed to explain the phenomena observed in roller test specimens in terms of theoretical subsurface stress distributions that include the effect of inclusions. The model is shown to be qualitatively consistent with test results concerning microstructural alterations and microcrack propagation behavior. Finally, practical considerations pertaining to material selection and further research in this area are discussed in light of the present results. Presented at the 39th Annual Meeting in Chicago, Illinois, May 7–10, 1984

Temperature Analysis in Lubricated Simple Sliding Rough Contacts

Abstract: A temperature analysis of dry sliding fully plastic contact is extended to calculate the asperity temperatures between a sliding lubricated rigid smooth plane and a stationary elastic rough surface. First, surface roughness is generated numerically to have a Gaussian height distribution and a bilinear autocorrelation function. Lai and Cheng's elastic rough contact computer program is then used to determine the asperity contact loads and geometries of real contact areas. Assuming different frictional coefficients for shearing the lubricant film at the noncontact areas, shearing the surface film at the asperity contacts and shearing the oxide film as the asperity temperature exceeds a critical temperature, asperity temperature distributions can be calculated. Eight cases in Durkee and Cheng's scuffing tests of lubricated simple sliding rough contacts are simulated by using 20 computer-generated rough surfaces. The results show that scuffing is correlated to high-temperature asperities which are above the ma...

The Dynamics of Ball Separators in Ball Bearings—Part II: Results of Optimization Study

Abstract: The dynamic equations of motion of ball-bearing separators were solved using certain simplifications to make computer analysis feasible from a cost point of view. A typical turbine engine bearing, employing solid lubrication, was used for a trade-off and optimization study of ball-separator design. The effects of varying geometric parameters of the separator were studied, along with different friction and traction coefficients and operating speeds of the bearing. The computer analysis indicated that the ball-pocket collision forces are significantly affected by the geometry of the ball separator (particularly the working clearances), and are also sensitive to the traction and friction coefficients of the materials and lubricant system. Presented at the 39th Annual Meeting in Chicago, Illinois, May 7–10, 1984

Sliding Bearing Lubricated with Ferromagnetic Fluid

Abstract: To develop a bearing which is used in clean circumstances, such as in vacuum and in a clean room, an experimental thrust bearing test device was constructed. The ferromagnetic fluids selected are colloidal suspensions of ultrafine magnetite particles in a low-vapor-pressure diester and alkylnaphthalene base fluids. The friction and wear tests with ferromagnetic lubrication were carried out with stationary cylindrical specimens constructed of permanent magnets in contact with the flat end of opposing rotating nonmagnetic cylindrical specimens. The following results were obtained: 1. The boundary lubricating effect of a ferromagnetic fluid, retained at the sliding surface by uniform magnetic field, can reduce the frictional force under low-velocity conditions and the wear caused by the mechanical contact between surfaces. 2. The hydrodynamic lubricating effect of a ferromagnetic fluid, retained at the step grooves by the magnetic attraction of permanent magnets, can greatly reduce the frictional force under...

Lubricating Performance of Organic Sulfides Under Repeated Rubbing Conditions

Abstract: Repeated four-ball tests of squalane with or without organic sulfides have been carried out to investigate the relationship between the properties of surface film formed on the rubbing surfaces and the lubricating performance of several organic sulfides. With dibenzyl disulfide and dibenzyl monosulfide, friction was remarkably reduced and load-carrying capacity raised in the second run with the additive after the first run without the additive, presumably in which only an oxide film had been formed. In contrast, for diphenyl disulfide, the repetition of rubbing tests, each with additive, was effective. EPMA, XPS(ESCA) and electron diffraction techniques have been applied to examine surface films formed during rubbing process. It is confirmed that the formation of surface films with the optimum composition of oxide and sulfide has brought about the excellent lubricating performance of these organic sulfides.

Measurement of Cage and Pocket Friction in a Ball Bearing for Use in a Simulation Program

Abstract: Few measurements have ever been made of the drag forces arising in a ball bearing due to viscous friction of the balls rotating in the cage pockets and the cage rotating inside the raceway. This paper reports measurements of both these sources of friction on simulations of just one bearing, but the data are compared with general analytical expressions for predicting the friction, and agreement is good. Finally, the data for the ball/pocket friction are compared against a theoretical model based on simple viscous shear and are shown to be in excellent agreement. Presented as an American Society of Lubrication Engineers paper et the ASLE/ASME Lubrication Conference in San Diego, California, October 22–24, 1984

Eccentricity Measurements on a Tilting-Pad Bearing

Abstract: This paper describes an experimental apparatus and procedure for measuring steady-state eccentricities in journal bearings. Eccentricity measurements for two five-pad tilting-pad bearings with load-on-pad and preloads of 0.0 and 0.2 are presented. Good agreement is shown between measured and theoretical eccentricities for a range of Sommerfeld numbers between 0.2 and 3.0. Relatively small deviations of the journal center from the load axis indicate negligible cross-coupling effects were present in the bearings. Presented at the 39th Annual Meeting in Chicago, Illinois, May 7–10, 1984

Slurry erosion of WC-Co cermets and ceramics

Abstract: Critical components in coal-liquefaction system, like letdown value trim and valve seats, are subject to severe wear from the erosive coal slurries. The slurry-erosion behavior of candidate valve trim and seat materials, like WC-Co cermets and hard ceramics (SiC, B4C), was studied by measuring the wear rates in a slurry-jet impingement test and by examining the wear craters in a scanning electron microscope. The erosion rates of the WC-Co cermets decreased monotonically with decreasing cobalt volume fraction in the range 36.9 to 5.1 Percent. The mechanism of erosion changed systematically from one involving preferential removal of binder and release of undamaged WC grains in high-binder alloys to a uniform transgranular wear of WC grains in the low-binder alloys. A sintered grade of SiC and a hot-pressed grade of B4C showed wear rates less than those of the cermets. Presented at the 39th Annual Meeting in Chicago, Illinois, May 7–10, 1984

Measurements of Squeeze-Film Bearing Forces and Pressures, Including the Effect of Fluid Inertia

Abstract: Squeeze-film dampers are commonly applied to high-speed rotating machinery, such as aircraft engines, to reduce vibration problems. The Reynolds theory of hydrodynamic lubrication has been used for the design and modeling of dampers in rotor dynamic systems despite typical modified Reynolds numbers in applications between ten and fifty. Lubrication theory is strictly valid for Reynolds numbers much less than one, which means that fluid viscous forces are much greater than inertia forces. Theoretical papers which account for fluid inertia in squeeze films have predicted large discrepancies from lubrication theory, but these results have not found wide acceptance by workers in the field. Recently, experimental results on the behavior of rotor dynamic systems have been reported which strongly support the existence of large fluid inertia forces. In the present paper, direct measurements of damper forces and pressures are presented for tile first time at high Reynolds number. Reynolds numbers up to 13 are obta...

The Real Area of Contact in Polymeric Magnetic Media—I: Critical Assessment of Experimental Techniques

Abstract: A critical assessment of techniques used to measure the real area of contact has been conducted. The techniques that are found to be suitable to measure contact area between a polymeric magnetic medium and a mating hard surface are: electrical-contact resistance and two-beam optical interference. The limitation of the electrical-contact resistance is that both surfaces must be electrically conductive. This technique only provides semiquantitative information. The two-beam optical interference technique provides complete distribution of the asperity-contact areas. Limitations of this technique are that the mating member must be optically transparent and both surfaces must be smooth. A monochromatic light of wavelength 706 nm (red) and a glass slide of high refractive index (1.93) were found to be suitable for magnetic tapes under study. All measurement techniques suffer from overestimation of the real area of contact, especially in the case of smooth magnetic tapes. Calculations for overestimation of the r...

Analysis of an oscillatory oil squeeze film containing a central gas bubble

Abstract: A squeeze-film damper, consisting of two circular plates, having only normal oscillatory relative motion is considered. The liquid lubricant between the plates is assumed to contain a single central gas bubble. The effect of the bubble on the damper performance is analyzed. Comparison is made with the performance of a pure liquid damper. Substantial deviations in peak dynamic pressures are predicted which explain discrepancies between experimental and theoretical results reported in the literature.

The combined effect of surface roughness and elastic deformation in the hydrodynamic slider bearing problem

Abstract: The paper presents the results of a numerical study concerning the combined effect of two-sided roughness and elasticity in a one-dimensional slider bearing. Based upon the assumption that Reynolds' equation holds in the presence of roughness, and wing Christensen's stochastic models for two-sided roughness, it is established that there is a strong interaction between the roughness and elasticity. The elasticity acts so as to decrease the roughness effects.

An Analysis of “Ringing Phenomena” in a Water Pump Mechanical Seal (Part II)

Abstract: Mechanical seals are used as sealing devices of water pumps in cooling systems of automobile engines. It is observed that water pump seals sometimes generate a “ringing” sound under certain conditions; however, the mechanisms of “ringing” phenomena have rarely been studied because of the difficulty in reproducing these phenomena. The present investigation is concerned with an experimental and fundamental analysis of “ringing.” As a result of observation and discussion of these phenomena, it becomes clear that this “ringing” sound is closely related to the surface condition and the “stick-slip” phenomena of rubbing surfaces of water pump seals. Presented at the 39th Annual Meeting in Chicago, Illinois, May 7–10, 1984

Contribution of Phosphorus to the Antiwear Performance of Zinc Dialkyldithiophosphates

Abstract: Four-ball wear studies show that the antiwear (low load) performance of zinc dialkyldithiophosphates (ZDPs) can be duplicated by combining a dialkyl acid phosphate and a soluble zinc compound. Antiwear performance of acid phosphates was independent of chain length for C8 to C18 but affected by chain branching and ring substitution. Zinc compound effectiveness depended on the strength of the parent acid compared to that of the acid phosphate, and its concentration in the blend (an atomic ratio of 2P:1Zn being optimum). Zinc was the most desirable metal naphthenate tested. Base oil viscosity had little effect on additive effectiveness. Added possible inorganic ZDP reaction products exhibited no antiwear activity. At higher loads in the EP regime, ZDPs lose their antiwear effectiveness, whereas both acid phosphates and sulfur compounds can reduce wear. Presented as an American Society of Lubrication Engineers paper at the ASME/ASLE Lubrication Conference in San Diego, California October 22–24, 1984

Friction, Wear, Transfer and Wear Surface Morphology of Ultra-High-Molecular-Weight Polyethylene.

Abstract: Tribological studies at 25 C in a 50-percent-relative-humidity air atmosphere were conducted using hemispherically tipped 440 C HT (high temperature) stainless steel pins sliding against ultra-high-molecular-weight polyethylene (UHMWPE) disks. The results indicate that sliding speed, sliding distance, contact stress and specimen geometry can markedly affect friction, UHMWPE wear, UHMWPE transfer and the type of wear mechanisms that occur. Adhesion appears to be the predominant wear mechanism; but after long sliding distances at slow speeds, heavy ridges of transfer result which can induce fatigue-like wear on the UHMWPE disk wear track. In one instance, abrasive wear to the metallic pin was observed. This was caused by a hard particle embedded in the UHMWPE disk wear track.

Mutual Overlap Coefficient and Wear Debris Motion in Dry Oscillating Friction and Wear Tests

Abstract: In oscillating dry friction and wear tests, mechanical parameters such as degrees of freedom and stroke amplitudes govern the formation of wear debris. A third body is formed by the wear debris within the contact. It is progressively eliminated from the contact area. The volume of wear debris lying outside the contact area corresponds to the total wear between the pin and the counterface. Wear is thus controlled by the elimination of wear debris outside the contact. The overlap of the pin and the friction track on the counterface thus controls the wear debris elimination. That overlap is characterized by the mutual overlap coefficient (MOC) which is defined as the ratio of the pin contact area to the counterface wear track. Wear debris formation and elimination was simulated with a pin made of a high-wear-rate material rubbing against an oscillating counterface. Widely different wear results and transfer film morphologies are obtained when the MOC varies between 0.66 and 0.99. Wear results are analyzed fo...

Gallium-Based Liquid-Metal Full-Film Lubricated Journal Bearings

Abstract: Experiments have been carried out on full-film journal bearings lubricated with a low-vapor pressure liquid metal (gallium-based alloy) in argon and high vacuum. Plain and spiral-groove bearings of relatively small size and without additional liquid sealing were selected. The effect of reactive gases on the liquid-metal confinement and the influence of liquid-metal properties on the loci of the shaft centers were studied. For plain bearings, it is found that the shaft center locus followed a straight line with a load angle of π/2. Subambient pressures of 25 atmospheres magnitude were achieved in the metal lubricant film. Liquid-metal leakage did not occur up to a certain speed. It is shown that Ga-based alloys can effectively be applied as a reliable lubricant in spiral-groove bearings under nonoxidizing conditions. Surface tension and cohesion strength of the metal liquid played a significant role in lubricant behavior.