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RESEARCH PAPERS

J. of Lubrication Tech. 1975;97(3):341-348. doi:10.1115/1.3452592.

This paper reports on a study of ball motion, including the measurement of ball rolling axis, in deep groove bearings operating at high speeds under thrust load conditions. The technique employed relies on viewing the test bearing, operating in the conventional fixed outer ring mode, through a rotating prism which eliminates optically the gross rotation of the separator. Videotape recordings of a selected ball, distinctively marked and illuminated stroboscopically, allows a complete analysis of ball bearing kinematics. Experimental results of separator speed, ball speed and rolling axis together with separator slip, ball slip and spin velocities at both the inner and outer raceway contacts are presented for a wide range of loads and shaft speeds up to 12,000 rev/min. These results are compared with the existing theory of Jones. Discrepancies between predicted and actual ball motion are due to the assumption made by Jones in neglecting bearing element slip. A further analysis of the experimental results including both gyroscopic torques and slip based on elastohydrodynamic traction values for the test lubricant explains actual ball motion more fully.

Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1975;97(3):350-355. doi:10.1115/1.3452596.

Hot-pressed silicon nitride was evaluated as a rolling-element bearing material. This material has a low specific gravity (41 percent that of bearing steel) and has a potential application as low mass balls for very high-speed ball bearings. The five-ball fatigue tester was used to test 12.7-mm- (0.500-in-) dia silicon nitride balls at maximum Hertz stresses ranging from 4.27 × 109 N/m2 (620,000 psi) to 6.21 × 109 N/m2 (900,000 psi) at a race temperature of 328K (130 deg F). The fatigue life of NC-132 hot-pressed silicon nitride was found to be equal to typical bearing steels and much greater than other ceramic or cermet materials at the same stress levels. A digital computer program was used to predict the fatigue life of 120-mm- bore angular-contact ball bearings containing either steel or silicon nitride balls. The analysis indicates that there is no improvement in the lives of bearings of the same geometry operating at DN values from 2 to 4 million where silicon nitride balls are used in place of steel balls.

Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1975;97(3):358-366. doi:10.1115/1.3452600.

The friction and wear characteristics of human hip joints were investigated using a pendulum-device and the Scanning Electron Microscope (SEM). The frictional phenomena of the joints oscillating under a variety of conditions were integrated with published data to provide a composite picture. As an accelerated “wear” model, joints were run “dry”, i.e., no fluid environment. This “wear” model was less severe than anticipated and subsequent damage involved only the superficial regions of the cartilage bearing material. The disruption occurred at sites where osteoarthritic damage has been detected clinically and progressed along the orientated fibrillar layers and was therefore oriented predominantly perpendicularly to joint motion.

Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1975;97(3):369-376. doi:10.1115/1.3452605.

Some theoretical consideration has been given to the use of pendulum machines when used to examine the frictional properties of human joints by incorporating them as fulcra. As a result, a new type of pendulum machine has been built which incorporates the facility to apply sudden loads to the joint on starting the swinging motion, and also the ability to measure directly the frictional torque experienced by the joint. The results obtained from natural hip joints (reported in Part I) indicate the presence of squeeze film lubrication under conditions of sudden loading. In addition, a self-generated fluid film process was observed at low loads whilst at high loads boundary lubrication appeared to be important. Artificial joints (Part II) are shown to exhibit similar lubrication properties to the natural joints but with a higher absolute value of friction. The metal on plastic type of joint is shown to exhibit a creeplike phenomenon which recovers with time.

Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1975;97(3):377-381. doi:10.1115/1.3452608.
Abstract
Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1975;97(3):383-389. doi:10.1115/1.3452611.

There has recently been disagreement on the effect of load on elastohydrodynamic film thicknesses at pressures beyond 7 × 108 Nm−2 , which was the approximate limit of earlier experiments. This disagreement which concerns a departure from established theory has been heightened by the fact that it is based on results from rather novel techniques. This paper describes an extension of well-characterized optical interferometric measurements on rolling-point contacts to pressures of over 2 × 109 Nm−2 . The central film thickness is found to fall off with load at a rate which agrees well with theory. In view of this, the results from other techniques are considered and in one case reproduced. It is concluded that the theory is essentially correct as far as it goes and possible causes of the disagreements are advanced in terms of thermal and surface roughness effects.

Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1975;97(3):390-395. doi:10.1115/1.3452614.

The extent of lubricant degradation in a sliding elastohydrodynamic contact has been investigated. The lubricant was subjected to peak Hertz pressures of approximately 109 N/m2 and average shear rates of 106 to 107 s−1 . Hydrocarbon lubricants, bulk polymers and polymer containing hydrocarbon solutions were examined. Small samples (10−8 m3 ) of test lubricant were extracted from the entrance and exit regions of the EHD contact. These samples were then analyzed to determine alterations in the molecular weight distribution. In addition, a microcapillary viscometer was developed to determine viscosity changes. Degradation resulting in up to a 70 percent viscosity loss was found in fluids which had molecular weights of over 1000. High degrees of correlation were found between molecular weight loss, viscosity loss and the energy dissipated in the contact.

Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1975;97(3):398-410. doi:10.1115/1.3452617.

Using several sources, analytic and semi-analytic solutions for frictional tractions of a lubricated line contact are presented in the appropriate non-dimensional form which is similar to that previously used by Moes for film thickness. A Newtonian lubricant with an exponential relationship between viscosity and pressure is assumed and, at this stage, the treatment is confined to fully flooded conditions. The components of frictional tractions arising from rolling (Poisseiulle) and sliding (Couette) flows are distinguished and sliding tractions in the outlet cavitated region are separated from those in the main pressure zone. Three main regimes of lubrication are studied: classical (isoviscous, undeformed), low elastic modulus (isoviscous, heavily deformed) and high elastic modulus (pressure dependent viscosity, heavily deformed). The results presented here provide a broad background of approximate results, covering a very wide range of conditions against which the results of more precise computer-based analyses can be judged. Thus the treatment reveals the existence of a range of conditions (typical of the lubrication of glassy polymers by hydrocarbon lubricants) which has been little studied and is, as yet, imperfectly understood.

Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1975;97(3):412-421. doi:10.1115/1.3452619.

Part I of this paper presented a broad semi-analytic treatment of frictional tractions in nondimensional terms; this was confined to the fully flooded situation and the present paper extends the analysis to include starved conditions. As in Part I three major conditions are considered in detail: classical (isoviscous, undeformed) low elastic modulus (isoviscous, heavily deformed) and high elastic modulus (pressure dependent viscosity, heavily deformed). The influence of starvation is presented as a series of correction curves for the rolling and sliding friction derived for fully flooded conditions. Starvation influences friction both through the extent to which the gap between the surfaces is filled by lubricant and through its influence upon the film thickness. Both factors affect rolling friction which is therefore markedly reduced by starvation so mild that there is negligible influence upon the film thickness. In contrast, sliding friction (arising either in the main pressure zone or the cavitated region) is most strongly influenced by the film thickness and is therefore markedly affected only by relatively severe starvation.

Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1975;97(3):424-428. doi:10.1115/1.3452623.

The formulation and solution for the shear stress and temperature in heavily loaded sliding elastohydrodynamic contacts is presented. The solutions are presented in dimensionless design charts. Integration over the contact area will yield the traction. Accuracy is expected to be very good over the nearly flat part of the contact area where the majority of the sliding traction is generated. The procedure presented is not appropriate for thick film lubrication, for the inlet region, or for the rolling friction of elastohydrodynamic contacts.

Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1975;97(3):430-436. doi:10.1115/1.3452626.

Laboratory tests were conducted on six-in-dia tilting pad thrust bearings to compare operating characteristics of several pad facing and backing material combinations and also to study the effects of different oil feed and discharge arrangements. Tests were conducted at various speeds and loadings, including a series of failure tests. Results of these tests are presented.

Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1975;97(3):439-448. doi:10.1115/1.3452630.

The results obtained by using lubrication theory, including inertia forces, are checked against experimental data concerning flows in relatively thin films at moderate and large Reynolds numbers. It is shown that a reasonably good agreement is obtained provided that the peculiar features of the experimental flow are properly taken into account; namely, proper consideration of the type of flow (laminar, transition, turbulent), proper evaluation of the region where lubrication flow prevails, entrance flow conditions (relating the flow into the film to the incoming flow), conditions for film rupture, cavitation or separation.

Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1975;97(3):450-460. doi:10.1115/1.3452632.

The thermoelastohydrodynamic (TEHD) behavior of a finite inclined-plane slider bearing is studied. The fluid film momentum, continuity, and energy equations are coupled to the heat conduction equations and the elasticity equations of the solid, and solved numerically. The elastic and thermal distortions of the solid as well as the variation of fluid properties with temperature are considered in the analysis. Several models for the bearing solids are treated.

Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1975;97(3):461-469. doi:10.1115/1.3452633.

This paper examines stability of the flexible single mass rotor, acted on by motion induced forces due to aero-dynamic cross-coupling and supported most generally by oil film tilting pad bearings which are in turn mounted on flexible, damped supports. Plotted results include the frequency dependent spring and damping coefficients for the 4-pad tilting pad bearing, damping coefficients for the 360-deg squeeze bearing and stability plots of rotor-bearing systems including aerodynamic cross-coupling, the 4-pad tilting pad bearing and the 150-deg partial arc bearing with various support arrangements.

Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1975;97(3):472-478. doi:10.1115/1.3452637.

The effect of dissipation heating on the apparent viscosity measured in capillary tube viscometry is described in this paper. Conditions of low Reynolds number and high shear are assumed. End corrections to the tube flow, found to be 3π/16 times the diameter of the tube, are incorporated. The flow curves show decreasing apparent viscosity when the shear stress increases. The configuration of the flow curves plotted in logarithmic presentation are found to be identical for fluids with Newtonian behavior. Convection is the predominant mechanism in removal of the heat in short capillary tube. The estimated upper bound for the shear stress obtainable in short length capillary tubes appears to be of the order of magnitude of 10 MPa limited primarily by the pressure drop associated with the constant end correction from the flat ended inlet and exit of the tube.

Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1975;97(3):479-485. doi:10.1115/1.3452640.

Shear stress independent behavior was observed for representative, synthetic, nonblended lubricants to about 4.8 × 106 N/m2 (700 psi) shear stress in high pressure viscometric measurements. This shear stress is of the same magnitude as the shear stress in sliding elastohydrodynamic contacts. It is shown that dissipation heating is the only mechanism of importance in the generation of the deviations from constant viscosity as measured with capillary tube viscometric methods. The Newtonian end corrections for the capillary tubes were found to be constant for the nonblended, liquid lubricants. Newtonian behavior will be expected of the fluids in a high shear lubrication situation. Shear induced, nonliquid behavior was found for the silicone lubricant at about 106 N/m2 and for the polymer-blended mineral oil at about 104 N/m2 at a relatively low pressure level. The observations might provide a key to an understanding of the generation of the anomalous low elastohydrodynamic film thickness as found with these lubricants. The polymer-blended oil showed shear thinning effects. The apparent viscosity was found to increase (∼30 percent) with increasing shear stress in the range of the second Newtonian viscosity level.

Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1975;97(3):486-492. doi:10.1115/1.3452641.

The variation of the viscosity of a lubricant as it passes through a concentrated contact with a Hertzian pressure profile is predicted by a simple model for the time dependent volume response of a liquid to a sudden change of applied pressure. For a wide range of operating conditions, the computed values of transient viscosity are asymmetric with respect to the center of the contact zone and are significantly lower than the equilibrium values. Three design graphs are presented which allow easy application of the results.

Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1975;97(3):494-505. doi:10.1115/1.3452645.

A linear theory of hybrid instability, due to a combination of both whirl and pneumatic hammer, in gas-lubricated porous journal bearings is presented. An approximate solution to the stability problem is obtained by the use of a Galerkin expansion. Results are presented in terms of the variation of stability parameters, such as the threshold mass, the whirl frequency ratio, etc., with the compressibility number and eccentricity ratio. In addition, the effects of permeability, supply pressure, and bearing length are investigated.

Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1975;97(3):506-509. doi:10.1115/1.3452648.

This paper summarizes the friction and wear behavior of some fluoride-metal, self-lubricating composites. Fluoride-infiltrated sintered nickel alloy composites and plasma-sprayed, co-deposited fluoride-nickel alloy composites are described. The importance of proper surface-conditioning of the composites is stressed. Performance of fluoride-metal composites in some machine application evaluations is discussed.

Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1975;97(3):512-515. doi:10.1115/1.3452653.

The results of investigations by various authors on the influence of retained austenite on seizure are briefly considered. Using as an example the investigation of the critical temperature of mineral oil in the friction of alloyed steels, it is shown that the temperature of destruction of the lubricant layer appreciably depends on the nature and content of the alloying elements and doe not strictly depend on the retained austenite content in the surface layer of steel specimens. Certain questions are considered—the influence of the contact geometry on the determination of the critical temperature in conditions of boundary lubrication, and the expediency of using austenite steel for investigating the temperature stability of lubricant layers.

Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1975;97(3):516-524. doi:10.1115/1.3452657.

A quasi-static analysis is presented for foil journal bearings designed for a NASA Brayton Cycle Turboalternator. Included in the analysis are effects of “slack” (due to flexural rigidity of the foil), of frictionally restrained extension of the foil-length in contact with cylindrical guides, of fluid inertia and compressibility, and of thermal expansion of rotor, foil and supporting structure. Comparisons are made with results of early experiments performed by Licht [1, 2] and recent data of Licht and Branger [6, 7]. Variations of film thickness, foil tension and bearing stiffness are presented graphically as functions of pertinent parameters for the case of operation in zero-gravity environment.

Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1975;97(3):526-531. doi:10.1115/1.3452660.

An approximate solution is given for the contact problem of an elastic hollow sphere indenting a solid sphere or cup with axial symmetry. The elastic deflection, maximum stress and contact radius are graphically presented as functions of a dimensionless load using hollowness ratios as parameter for the particular case that the two contacting bodies are of the same material. The numerical results include the Hertz theory as a limiting case for small hollowness ratio.

Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1975;97(3):533-537. doi:10.1115/1.3452663.

Stresses in dimensionally similar large models of 40-, 50- and 60-percent mass reduction cylindrically hollow “drilled” bearing balls were experimentally evaluated with flat strain gage rosettes. Dimensionless principal stress coefficients were calculated and were applied to estimate the bending stresses in the drilled balls of three series of full-scale bearing experiments. Stresses were highest when the applied load approached the edge of the hole, and ranged up to almost 620 × 106 N/m2 (90,000 psi) at the bore.

Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1975;97(3):539-544. doi:10.1115/1.3452666.

When to semi-infinite plates contact edge to edge, with sliding parallel to the line of contact, frictional heating can cause deformations which lead to the initial uniform-pressure contact changing to a periodic sequence of loaded patches separated by regions where the surfaces part from one another. This condition will appear near the speed at which small-disturbance instabilities occur. When it does appear there are two solutions or two configurations which satisfy the boundary conditions. One of these solutions is shown to be stable, and the other is shown to be unstable. The derivations may be applied to seals where a thermally conductive material slides on a material of significantly lower conductivity.

Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1975;97(3):546-551. doi:10.1115/1.3452669.

Equations are derived for clearance, leakage, and contact temperatures for conditions where initially flat rubbing surfaces are deformed thermally to produce a sequence of equally spaced contact patches, separated by regions where the surfaces withdraw from one another. One paradoxical result is that increased contact pressure or preload on the seal increases leakage when sliding takes place above a critical speed.

Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1975;97(3):552-556. doi:10.1115/1.3452672.

An investigation has been made of the friction and wear behavior of polycrystalline cobalt, over a wide range of rubbing conditions, to establish the general pattern of wear. Evidence has been obtained for the occurrence of three transitions, namely, mild to severe wear at low loads and speeds, severe wear back to mild at higher loads and speeds and a change to a particularly severe form of wear that has been related to the transformation of cobalt from α to β form in the vicinity of contacting asperities.

Topics: Friction , Wear , Cobalt , Stress
Commentary by Dr. Valentin Fuster

DISCUSSIONS

Commentary by Dr. Valentin Fuster
Commentary by Dr. Valentin Fuster
Commentary by Dr. Valentin Fuster
Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1975;97(3):556. doi:10.1115/1.3452673.
FREE TO VIEW
Abstract
Topics: Friction , Wear , Cobalt
Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1975;97(3):556-557. doi:10.1115/1.3452674.
FREE TO VIEW
Abstract
Topics: Friction , Wear , Cobalt
J. of Lubrication Tech. 1975;97(3):557. doi:10.1115/1.3452675.
FREE TO VIEW
Abstract
Topics: Friction , Wear , Cobalt
J. of Lubrication Tech. 1975;97(3):557. doi:10.1115/1.3452676.
FREE TO VIEW
Abstract
Topics: Friction , Wear

BOOK REVIEWS

J. of Lubrication Tech. 1975;97(3):558-559. doi:10.1115/1.3452677.
FREE TO VIEW
Abstract
Topics: Tribology
Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1975;97(3):559. doi:10.1115/1.3452678.
FREE TO VIEW
Commentary by Dr. Valentin Fuster

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