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RESEARCH PAPERS

J. of Lubrication Tech. 1981;103(2):169-179. doi:10.1115/1.3251622.

This paper presents a general critical picture of our present understanding of the frictional process. In particular it emphasizes the three main elements involved, namely the true area of contact, the nature and strength of the inerfacial bonds formed at the regions of contact, and the way in which the material around the contacting regions is sheared and ruptured during sliding. Most of the paper deals with metals but reference is also made to ceramics, lamellar solids, polymers, and elastomers. The paper concludes with a discussion of areas where further progress is desirable.

Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1981;103(2):180-187. doi:10.1115/1.3251623.

Sliding friction experiments were conducted with various iron-base alloys (alloying elements were Ti, Cr, Mn, Ni, Rh, and W) in contact with a single-crystal silicon carbide (0001) surface in vacuum. Results indicate atomic size misfit and concentration of alloying elements play a dominant role in controlling adhesion, friction, and wear properties of iron-base binary alloys. The controlling mechanism of the alloy properties is as an intrinsic effect involving the resistance to shear fracture of cohesive bonding in the alloy. The coefficient of friction generally increases with an increase in solute concentration. The coefficient of friction increases as the solute-to-iron atomic radius ratio increases or decreases from unity. Alloys having higher solute concentration produce more transfer to silicon carbide than do alloys having low solute concentrations. The chemical activity of the alloying element is also an important parameter in controlling adhesion and friction of alloys.

Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1981;103(2):188-193. doi:10.1115/1.3251624.

One of the key factors in the analysis of a wear problem is the computation of the wear coefficient for a comparison with the value to be anticipated for this application. Typical values of adhesive wear coefficients for a variety of materials and lubricants are presented, and the values compared with those arising in the wear modes of abrasion, corrosion and fretting. A major uncertainty arises from the fact that wear coefficients show considerable variation, both in repeat testing, and in the testing of different materials that presumably should have the same wear coefficient. Quantitative values for the scatter encountered in adhesive wear situations are given and discussed. Various uses of the wear coefficient in the analysis of sliding systems are illustrated.

Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1981;103(2):195-202. doi:10.1115/1.3251627.

To study the behavior of adhered fragments on rubbing surfaces, the transverse movement of a slider is measured and recorded during the wear process. The gap between the mating surfaces is enlarged gradually through the origin and growth of a transfer particle adhering to the slider and then closed suddenly by the removal of the particle. The removal process of wear particles can be observed by an optical microscope. Furthermore, an X-ray microanalysis is made on the cut section of the rubbing system just before the removal of the particle. The particle is press-slide flattened in shape and has a hair line mixed structure containing metals of both mating surfaces. The maximum lift of the slider is nearly equal to the size of the produced particle. These observations show that the adhered fragments are piling up and are being press-slide flattened between the mating surfaces until their final removal as wear particles.

Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1981;103(2):203-208. doi:10.1115/1.3251628.

The effect of running-in under low speed - high load conditions on the load carrying capacity at high speed of sliding crossed cylinders of steel AISI 52100, thin film lubricated with a marine diesel engine oil of 60°C, is described for three values of the initial composite roughness Rc , i.e. 0.14 μm, 0.42 μm and 0.71 μm. It is shown that—irrespective of the initial surface roughness—the surface of the (smaller) stationary cylinder becomes very smooth (Ra ≤ 0.1 μm), that of the (larger) rotating cylinder remaining virtually unaffected. As the local radius of curvature increases as a result of running-in, the load carrying capacity, expressed in terms of total force on the contact, increases considerably, i.e. 600 percent at Rc = 0.14 μm, 500 percent at Rc = 0.42 μm and 150 percent at Rc = 0.71 μm. This is not accompanied by a correspondingly large increase in Hertzian contact pressure at film collapse, pHc . In fact pHc increases 45 percent at Rc = 0.14 μm and 15 percent at Rc = 0.42 μm and decreases 20 percent at Rc = 0.71 μm. It is further found that run-in surfaces show the phenomenon of delayed EHD-film collapse, meaning that the transition from the (partial) EHD to the scuffing regime may take from 1 to 40 s after application of the normal force. The test method should contribute significantly to the functional characterization of lubricants and—more in particular—running-in fluids, as candidates for use in concentrated contact situations.

Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1981;103(2):211-217. doi:10.1115/1.3251632.

An RF-sputtered chrome oxide coating with metallic binders was developed. The chrome oxide coating has high-temperature capabilities and is wear resistant, and has some self-lubricating properties. A nichrome metallic binder was added in the coating to improve its ductility without significant loss in the hardness. The sputtering parameters were optimized to obtain a smooth coating with the maximum adherence. The coatings were applied using bias-sputter and sputter-deposit modes on the heat treated and annealed foil substrates. The coating applied on annealed foils using the sputter-deposit mode was smooth and had the best adherence. Metallurgical examinations showed that the coating was Ni-Cr + Cr2 O3 . The coating as applied was amorphous and it crystallized during substrate heat treatment.

Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1981;103(2):218-227. doi:10.1115/1.3251633.

Friction and wear tests were conducted on optimized sputtered Cr2 O3 and Cr2 O3 with metallic binder coatings. The coatings were applied on the bearing surface of journal foil air bearings and were tested against chrome-carbide-coated journal surfaces. The objective of the study was to develop a coating system which would withstand 9000 start-stops and high-speed rubs (maximum acceleration, 100 gs) in temperatures ranging from room temperature to 650° C. The Cr2 O3 coating completed the test sequence and the coating consisting of Cr2 O3 with metallic binders completed 3000 start-stops. The coefficient of friction of the coatings at 650° C was found to be about half that at room temperature. It was concluded, therefore, that the coatings should perform much better in a high temperature environment alone. The decrease in friction at high temperature is attributed to oxidation and interactions of the coatings and substrates at the interface temperature.

Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1981;103(2):228-235. doi:10.1115/1.3251634.

The wear of a chromium carbide hard coating, LC1B, has been investigated in CO2 , argon and air at pressures between 2 and 42 bar. In CO2 the wear rate of the shaft (but not the pin) is strongly gas pressure and load dependent. Post-test observations have suggested the presence of up to three wear regimes: (i) initial wear is short lived and probably results from the mechanical interlocking of asperities, (ii) adhesive wear involves the homogenization of surface layers and the preferential transfer of material to the static pin which then protects the pin from further wear, and (iii) mild wear which is in part abrasive, but in which oxidative wear provides the major contribution. Wear in argon is adhesive, that in air is primarily mild, but in CO2 a transition from adhesive to mild wear occurs after a sliding distance which is dependent upon sliding contact parameters and on gas pressure. The above observations and deductions have been developed analytically to explain the unusual results obtained in CO2 . It has been shown how, in CO2 , the sliding distance to the second transition (adhesive to mild wear), may be explained by the development of equations for the depletion of CO2 at the wearing interface. It is postulated that after its formation, wear debris is reactive to CO2 only for a very short time (∼ 5 × 10−9 s) and that the transition to mild wear occurs when the depleted CO2 pressure increases to a level at which a monolayer of reaction product can form in this reaction time.

Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1981;103(2):236-242. doi:10.1115/1.3251635.

Frictional properties in the contact between a hard protuberance and a metal surface covered by a soft thin metal film are examined experimentally. The protuberance used in the experiment is a hard steel ball which simulates asperities on many engineering surfaces. The load dependency of the coefficient of friction and the effects of thickness and hardness of the film on the friction are clarified. The simple empirical expression of friction, which represents the effect of the film properties, is presented, considering the deformation mechanism of the surface film.

Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1981;103(2):243-251. doi:10.1115/1.3251636.

Boundary conditions were arbitrarily specified in an earlier two dimensional (2D) analysis of contact temperature. In this new work a general three dimensional (3D) Fourier transform solution is obtained from which for specific cases, the boundary conditions can be estimated. Further, experimental verification of 3D analysis was performed using infra-red technique.

Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1981;103(2):253-260. doi:10.1115/1.3251639.

An analysis of a seal model is made where the rotating element has both fixed tilt and two-lobe waviness. The stator is assumed to be gimbal mounted and to have inertial mass. Hydrodynamic lubrication is assumed, following the short bearing or narrow seal model. Conditions are examined where the stator precesses in synchronism with the rotor rotation. Particular interest is given to operating conditions where such behavior appears to degenerate. The objective of this study is to explain a coupled, inertial/thermoelastic phenomenon observed in experiments performed by Banerjee.

Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1981;103(2):261-265. doi:10.1115/1.3251640.

The study reported in this paper is undertaken to investigate the effect of some of the physical properties of lubricants on the contact temperature and wear in heavily loaded Hertzian Contacts under sliding conditions. The surface temperature and wear in a rotating mild steel shaft are measured under different loads applied by a Tungsten Carbide slider. The carbide tip and the shaft are used as part of a dynamic thermocouple system to monitor the contact temperature. Tests are conducted for Hertzian pressures ranging from 1250 to 2140 MPa (1.81×105 –3.10×105 psi) and sliding speeds from 0.4 to 1.3 m/sec (943–3142 in./min). Temperature and wear data are given from tests with a heavy duty oil (SAE 80W-90), a high viscosity residual compound, a vegetable oil, and water miscible cutting fluid (0.0476 percent emulsifiable oil by volume). The results show that, for the considered tests, viscosity does not appear to be the significant property of the lubricant temperature rise and wear rate as indicated by the scar depth under similar test conditions.

Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1981;103(2):266-273. doi:10.1115/1.3251641.

The single-pass, transfer wear of LDPE, PVC, and PCTFE was studied as a function of the roughness of the steel counterface, and the presence or absence of a polymeric coating. A 50 nm thick film of poly(chloro-p-xylylene) was formed on the steel in a pyrolytic-vapor-deposition process. The results showed that LDPE had lower friction and wear on the coated surface than on the uncoated surface. There was no significant difference in wear or friction as a function of surface coating for PVC and PCTFE. The results were explained by considering the deformation characteristics of the polymeric coating and the three polymer sliders and the modification of the topography by the polymeric coating.

Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1981;103(2):274-281. doi:10.1115/1.3251642.

Operating characteristics for a 118-mm bore cylindrical roller bearing were calculated using the computer program CYBEAN. The predicted results of inner and outer-race temperatures and heat transferred to the lubricant generally compared well with experimental data for shaft speeds to 3 million DN (25,500 rpm), radial loads to 8900 N (2000 lb), and total lubricant flow rates to 0.0102 m3 /min (2.7 gal/min).

Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1981;103(2):284-294. doi:10.1115/1.3251647.

Fifty-seven measurements of the minimum lubricant film thickness separating the elastohydrodynamically lubricated point contact of a steel crowned roller and a flat sapphire disk were made by an optical interferometry technique. The data collected were used to evaluate the Hamrock and Dowson minimum EHD film thickness model over a practical range of contact ellipticity ratio where the major axis of the contact ellipse is aligned both parallel and perpendicular to the direction of motion. A statistical analysis of the measured film thickness data showed that the experimental data averaged 30 percent greater film thickness than the Hamrock and Dowson model predicts.

Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1981;103(2):295-301. doi:10.1115/1.3251650.

Elastohydrodynamic film thickness was measured for a 20-mm ball bearing using the capacitance technique. The bearing was thrust loaded to 90, 448, and 778 N (20, 100, and 175 lb). The corresponding maximum stresses on the inner race were 1.28, 2.09, and 2.45 GPa (185,000, 303,000, and 356,000 psi). Test speeds ranged from 400 to 14,000 rpm. Film thickness measurements were taken with four different lubricants: (a) synthetic paraffinic, (b) synthetic paraffinic with additives, (c) neopentylpolyol (tetra) ester meeting MIL-L-23699A specifications, and (d) synthetic cycloaliphatic hydrocarbon traction fluid. The test bearing was mist lubricated. Test temperatures were 300, 338, and 393 K. The measured results were compared to theoretical predictions using the formulae of Grubin, Archard and Cowking, Dowson and Higginson, and Hamrock and Dowson. There was good agreement with theory at low dimensionless speed, but the film was much smaller than theory predicts at higher speeds. This was due to kinematic starvation and inlet shear heating effects. Comparisons with Chiu’s theory on starvation and Cheng’s theory on inlet shear heating were made.

Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1981;103(2):305-313. doi:10.1115/1.3251655.

The non-Newtonian constitutive equation proposed by Winer and Bair [1] is applied in a conventional isothermal film thickness analysis of line contact lubrication of rolling elements. The present analysis provides four different dimensionless film thickness equations for four different regimes of lubrication. Due to the formulation technique used in deriving the governing pressure-gradient equation, the present study is recommended for high viscosity, high rolling speed, and low limiting shear stress cases where Newtonian models fail to match the experimental data. Comparison of the present film thickness equations with the Newtonian correspondences in each lubrication regime shows a considerable difference, but the analysis suffers from the fact that the limiting shear stress parameters of these high viscosity lubricants need to be determined experimentally. The present analysis assumes a reasonable range of limiting shear stress which is smaller than the corresponding values for low viscosity lubricants which are predominantly Newtonian in behavior (unless severe rolling and/or sliding with high loads is applied).

Commentary by Dr. Valentin Fuster

DISCUSSIONS

Commentary by Dr. Valentin Fuster

BOOK REVIEWS

J. of Lubrication Tech. 1981;103(2):319. doi:10.1115/1.3251661.
FREE TO VIEW
Abstract
Topics: Bearings
Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1981;103(2):320. doi:10.1115/1.3251662.
FREE TO VIEW
Abstract
Commentary by Dr. Valentin Fuster

LETTERS TO THE EDITOR

J. of Lubrication Tech. 1981;103(2):321. doi:10.1115/1.3251663.
FREE TO VIEW
Abstract
Commentary by Dr. Valentin Fuster

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