Effects of Surface Roughness in Lubrication

T. R. Thomas (UK) P. Poon (England) A. O. Lebeck (USA) E. Salbel (USA)

Meellng Hall FOREIGN REPORT Downloaded from http://asmedigitalcollection.asme.org/tribology/article-pdf/100/1/6/5659660/6_1.pdf by guest on 29 September 2021 D. Pnuell (Israel) Donald F. Wilcock Effects of Surface Roughness in

Manager-Tribology Department, Mechanical Technology tncorporated, Lubrication Latham, N. Y. Fellow AS ME A Review of the Fourth Leeds-Lyon Symposium

J. Hoppe (Germany)

The fourth symposium in the Leeds-Lyon series was held posium has provided a unique forum which brings together in Lyon on September 13-16, 1977. The symposium subject scientists and engineers of closely similar interests. The range was "Effects of Surface Roughness in Lubrication." of papers from theoretical to practical broadens the outlook The series began in 1974 as a means for the workers in Tri of each, and one leaves a meeting of this type with the im bology at the Institute ofTribology at Leeds, and at Mechan pression that is he well up in the particular field. Many inter ical Contacts Laboratory at INSA (lnstitut National des Sci national friendships have been begun and cemented at these ences Appliquees at Lyon) to meet together to discuss and symposia. review each others work. Each year a specialized topic is se Sessions, comprising papers and discussion, covered topics lected, and others around the world interested in that topic are of Early Concepts, Fluid Mechanics and Rough Surfaces, Ef invited to attend. The topic in 1975 was turbulence [41].1 In fects of Roughness in Lubrication Theory, Surface Topography 1976 it was wear of non-metallic materials [42]. and Running In, New Experimental Techniques, Asperity The 1977 symposium, on "Effects of Surface Roughness in Behavior in Rough Contacts, Scuffing, Fatigue Wear, Lubrication" established the Leeds-Lyon Symposium as a Roughness in Bearings, Seals and Gears, Roughness in Met viable ongoing significant meeting in tribology, attracting alworking and Roller Bearings, and General Roughness Ef authors and attendees from a wide area. The 1977 conference fects. had 120 attendees from seventeen countries, namely France Thinking back on the meeting, the writer is left with two [50], England [35], United States [10], West Germany [4], Spain broad overriding conclusions. The first is that in almost every M. R. Philips (UK) [4], Holland [3], Israel [2], Sweden [2], and one each from tribological situation, there is an optimum degree of roughness: Belgium, Denmark, India, Italy, Ireland, Norway, Poland, surfaces can very often be too smooth as well as too rough. The Switzerland and Yugoslavia. Authors from eight countries second is that we need better means of measuring and func presented 39 papers to the symposium. The distribution of tionally describing surface roughness: most profilometer papers was England [17], U.S.A. [9], France [7], Israel [2], and measurements are two dimensional in a three dimensional one each from Germany, Ireland, Poland and Sweden. world; better measuring equipment and better analysis are The selection of a single well-bounded topic for each sym- needed for future progress.

1 Numbers in brackets designate References at end of paper. Photographs of D. F. Moore, E. Felder, and D. F. Wilcock were not avail able. D. A. Jones (England)

Early Concepts containing the statistical constants expressing the surface Dowson [1] provided an intriguing and fascinating insight roughness. into some of the earlier concepts related to the interaction of While the paper is of necessity highly mathematical and rough surfaces. Many of the early theories, for example, as theoretical, striking flashes of physical insight occur. For ex sumed that friction was the result of the force required to ample, in discussing the greater load capacity predicted for separate contacting surfaces as the inclined shoulders of situations in which the rough surface is stationary and a asperities rode over each other. smoother surface is moving, he states, "Essentially, pressure Downloaded from http://asmedigitalcollection.asme.org/tribology/article-pdf/100/1/6/5659660/6_1.pdf by guest on 29 September 2021 Based on excerpts from a forthcoming book on the History build up is the result of fluid resistance to being drawn by of TriboZogy Dowson pointed out that friction was the first of convective shear into a narrowing film. For a given surface the three pillars of tribology, friction, lubrication, and wear to speed and mean film thickness, less resistance will be experi receive scientific attention. Leonardo Da Vinci (1452-1519) enced if some of the fluid is drawn along in the interstices of who wrote"... all things and everything whatsover that it be a moving rough surface." Similarly, it is convenient analytically which is interposed in the middle between objects that rub to define film thickness as the distance between the mean levels together lighten the difficulty of this friction." The paper of each surface; but from a practical point of view half the continues wit.h quotations from such well known workers as surface roughness of each surface must be subtracted from this Robert Hook (1685), Amontons (1706), Coulomb (1781), Leslie film thickness value in order to obtain a realistic estimate of (1804), and W. Bridges Adams (1853). Dowson concludes by available non-contact surface separation. pointing out: "Some of the concepts are quaint, some pur In discussions of his own and subsequent papers, Elrod poseful and accurate, but practically all are interesting. It forcefully questioned the validity of using Reynold's equation seems quite remarkable that the concepts of surface topogra in situations where the surface wavelength is small, ap K. Tonder (Norway) phy, the modelling of rough surfaces for analytical purposes proaching the film thickness in value. and the development of understanding of the influence of Chow and Saibel [3J pointed out that in treating the hy surface roughness upon friction, lubrication, and wear could drodynamic effects of surface roughness by statistical methods, have advanced so far before surface measuring instruments the roughness parameters for the two surfaces must. be char emerged in the present century." acterized by independent, stationary Gaussian random func tions, and that the length of the bearing must be large com Fluid Mechanics and Rough Surfaces pared to the correlation length of the roughness parameters. Elrod [2] in a keynote paper reviewed the theories that have The mean square deviation from the smooth case indicates been developed for expressing the fluid dynamic effects of fluctuations about the mean value and determines the im surface roughness on laminar lubricating films. The paper portance of surface roughness. They find that the upper bound provides an excellent overview and access t.o some 34 references of the root mean square deviation of load capacity is critically for anyone interested in pursuing the field in depth. dependent on the behavior of the autocorrelation of the Elrod points out that three different viewpoints have been roughness. embodied in the analyses by different workers in the field. In Rohde and Whicker [4] used a Monte Carlo method to ex one group, the common feature is the assumption that some amine the statistical effects of surface roughness in a tilted specific roughness contour (rectangular, sinusoidal, etc.) may slider configuration. A "triangular surface texture was created be treated by Reynold's equation, either by some perturbation by dividing the length of the slider into N increments and de analysis or by a direct numerical method. These analyses in termining t.he deviation of the profile at each increment, above general assume that the roughness is formed by striations or below t.he smooth mean profile, by a Monte Carlo selection running t.ransverse to the direction of sliding; and the detailed process. The results for load distribution, flow and friction were A. Dyson (UK) int.eraction bet.ween t.he surface roughness and the lubricating found to be in good agreement. with the results from asymptotic film is then followed. Roughness is usually assumed on one analysis. surface only. The second group assumes that. because of peri Chen and Sun [5] reviewed the existing methods for treating odicit.y of the roughness or short roughness wavelength, the rough surface hydrodynamic lubrication problems using st.a detailed interactions may be "smeared" or averaged. Differ tistical parameters. They concluded that a practical as well as ential equations are then developed which permit calculat.ions a general method is still not available. The method of averaging of load capacity, frict.ion, and other bearing quantities of in the solut.ion is practical only when the solution can be put in terest. The third group assumes a statistical approach, deriving analytical form; while the method of averaging the Reynold's different.ial equations analagous t.o Reynolds's equat.ion, but equation before solving has not yet been handled in a satis-

D. Dowson (UK)

, . !t./ H. S. Sayles (UK) P. M. Ku (USA) l. Rozeanu (Israel) F. T. Barwell (UK)

Journal of Lubrication Technology JANUARY 1978, VOL 100 / 7 factory manner. a form of abrasive wear in which the tips of the asperities are Dyson [7] also reviewed the status of theoretical work. In cleanly removed down to a certain level. Thomas proposes two doing so he extended the discussion into the area of EHL, functions to quantify these effects: the power spectrum and elastohydrodynamic lubrication. In contacts of this type, oc- the height distribution. Foucher, Flamand and Berthe [11] curing in rolling element bearings, gears, and cams, the fric- briefly described their method of digitizing profilometer data tional penalty is less important than it is in lubricated sliding and computing from the digitized data the distributions of bearings. Thus in EHL there is less scope for achieving ade peak heights and the distribution of asperity radii. Raffy [12] quate film thickness by modifications to the design. The film studied the running in of spur gears of unhardened steel. He thickness may be of the same order as the surface roughness, showed that roughness decreases during the early minutes of and failure by wear, fatigue or scuffing is an unpleasant pos running in but that running in with a heavy load quickly de sibility. Dyson points out that in these cases smooth surface stroys the surfaces. theory is obviously inapplicable, but that hopes for develop Jones, Sastry, and Youdam [15] found the ferrographic ment of a rough surface theory to assist in understanding these technique useful in monitoring the running in wear of an 8.83 situations and avoiding failure have not yet been realized. The liter diesel engine. Large initial wear tapered off to a low problem is compounded by the necessity of allowing for the equilibrium weight loss rate after only ten hours of testing. elasticity of individual asperities as well as of the bulk surface, Teardown and reassembly with a new piston fitted with the old

plus the random nature of the asperity sizes and shapes. piston rings again showed high initial rates of wear. Hoppe [32] Downloaded from http://asmedigitalcollection.asme.org/tribology/article-pdf/100/1/6/5659660/6_1.pdf by guest on 29 September 2021 Cheng [8] described the lubrication process around a single discussed the running-in of hydrodynamic journal bearings asperity at the entrance as well as at the central region of a such as are found in automotive engines. Using radial isotopes, lubricated Hertzian contact. He reported results on the de wear was observed to occur in the usual step-wise fashion as viation of pressure and film thickness from those predicted by load was increased in increments. Factors such as load, speed, smooth surface theory for the case of a simple sliding EHD and lubricant temperature which control the minimum oil film contact caused by the presence of a transverse asperity ridge thickness showed a direct correlation to wear. or furrow on the stationary surface. Tonder [9], whose papers are widely referenced in this field, Surface Topography showed numerical results calculated for a simple slider bearing The mechanical motions, i.e. lifting and falling, that would having surfaces with crossed striations, i.e., transverse stria- occur when one rough surface is slid over another have been tions and longitudinal striations. An inverse square root dis calculated and reported by Bowyer and Cameron [13]. Using tribution is used for the roughness probability density function. a computer model, with numerical data from actual profi The effects of roughness are seen to vanish as the surface lometer measurements of rough surfaces, wave forms were roughness, defined as the difference between maximum and produced similar to the characteristic stick-slip saw tooth vi minimum surface heights, becomes less than the minimum film bration observed in actual experiments. Greenwood and Wil thickness measured to the tops of the asperities. A transverse liamson [17] reviewed the developments in the theory of sur component on the stationary surface results in increases in face topography over the last decade, pointing out finally ". . . load, friction and side flow. A longitudinal component increases we can say with some confidence that whatever the mechanism both friction and flow in the sliding direction, and reduces side of scuffing may turn out to be, surface roughness analysis will flow. A transverse component on the moving surface provides play a major quantitative part in it. Progress indeed from the an additional increase in load which should be particularly days when all we needed was the qualitative picture of Swit beneficial for narrow bearings. zerland turned upsidedown and placed on top of Austria." Shukla and Kumar [40] derived a form of Reynold's equation Sayles and Thomas [18] used computer models of rough for rough surfaced bearings. Normal flow due to the pressure surfaces to study the size and distribution of contacts as the gradient was assumed in the areas between the surfaces, and surfaces were brought together. Material in the "overlap" a form of Darcy's law was assumed for flow between and around volume between opposing asperities was assumed to be moved the asperities. Velocities were matched at the interface between by plastic deformation below the average surface level. One the two. The theory does not include the load capability due interesting result found by these computer "experiments" was to interaction of asperities but concentrates on calculating the that the cumulative distribution of contact sizes was log-nor hydrodynamic load capability. mal over a wide range of separations. The mean contact size 2 Lebeck [6] combines a hydrodynamic solution including for one pair of surfaces increased from 0.02 mm at a separation 2 statistical roughness effects with partial load support from of twice the roughness to 0.1 mm at half the roughness. They asperity contact in predicting the performance of face seals point out that this is a very small increase in size for a change having circumferential waviness. Such waviness is common on in separation which represents an increase in load of many a micro scale, and may involve two or more peaks around the orders of magnitude. circumference. Pressure distributions over the seal face are The wear of phosphor bronze pins running against hardened calculated including cavitated regions. steel rings was found by Stout, Heath, and King [29] to be a Wilcock [28] found that while heating effects are large function not only of the scale and shape of the surface height enough to mask any hydrodynamic effect of surface roughness distributions, but also of the directionality or lay of the surface on turbulence when the films thicknesses are within an order texture. Plunge ground surfaces were found to produce far less of magnitude of the surface roughness, results from pipe flow wear than helical or traverse ground surfaces. data suggest that surface roughness may be expected to in From careful studies of the nature of the metallic contact crease the effective viscosity in the lubricant film when the film during the starting and stopping periods of plain hydrody thickness to roughness ratio is below about 100 and the namic bearings, Hailing [31] concluded that bearings having Reynolds numbers is over about 10,000. small clearances will experience a reduction of radial wear and a longer contact arc of wear. Wear, of course, is also minimized by improvements in the shaft surface finish. In studies of the influence of roughness in boundary lubri Running In cation, Georges, Kapsa and Mathia [37] found a linear relation The topographical changes that occur during running in of between the load corresponding to breakdown of the boundary surfaces were described by Thomas [10]. Two types of surface lubricant film and the mean radius of surface asperities for refinement were described, one a plastic squeezing similar to surfaces produced by blasting, peening, and lapping. King, roller burnishing which does not remove material; the other Watson, and Stout [39] have modeled lubricated wear of the

8 / VOL 100, JANUARY 1978 Transactions of the ASME type where metal is removed, for example from a phosphor roughness in such a way that oil film formation is favored and bronze surface, by relatively smooth steel rings without the can occur under loads that the original surface could not occurence of bulk plastic flow. This wear can therefore be withstand." modeled by successively deep truncation of an initial surface Moore [36] presented detailed qualitative discussions on the roughness profile. Analysis of the truncation of a Gaussian role of both large and small roughnesses in a high modulus wave indicate that the magnitude of the skewness of the am surface interacting in sliding with an elastomeric or rubber-like plitude distribution may provide a useful measurement func material. tion. The behavior of the autocorrelation function, however, has shown that it is relatively insensitive to truncation. Wear and Scuffing in Concentrated Contacts Measurements The effect of surface topography on the frictional, thermal, Rather curiously, there was relatively little discussion on and scuffing behaviors of lubricating, sliding/rolling disks was measurement of roughness at the meeting, other than com reviewed by Ku and Li [21]. The other variables that have been ments on the limited nature of profilometer data, the difficulty studied, including disk size, disk material, surface treatment, of registration so that one could follow an individual track, and oil type, oil supply configuration and flow rate, and operating the digitizing of the analog signal. Three interesting papers did conditions have tended to obscure the specific role of surface topography. However, an improved friction correlation is touch on other types of measurement of the surface. Downloaded from http://asmedigitalcollection.asme.org/tribology/article-pdf/100/1/6/5659660/6_1.pdf by guest on 29 September 2021 Leather and MacPherson [16] discussed contact resistance pointed out, ascribed to Ku, Staph, and Carper, indicating that measurements in lubricated contacts using low voltages of the the friction coefficient increases by 0.003 times the surface order of 100 millivolts. One or more pairs of asperities may be roughness expressed in micrometers. Also pointed out is the in contact, at a given time resulting in a measured low-resis fact, also reported by others, that cross-ground disks give a tance time segment on the signal. The authors develop a theory lower friction coefficient than circumferentially ground relating these quantities to the surface roughness and the type disks. of rolling/sliding motion occurring. They point out the utility Spalls, with a depth below the surface of about 200 microns, of this type of measurement in monitoring the condition of spur and micropits with a characteristic depth of only 20 microns, gear surfaces. are both observed in the tracks of disk machine specimens after Photoelastic and interferometic methods were applied by tests in pure rolling. Berthe, Michau, Flamand, and Godet [24] Mirski and Stupnicki [19] to investigate the contact stresses show that micropits are formed when the A ratio of film at individual asperity contacts between a roughened glass plate thickness to surface roughness becomes less than 1. Spalls are and a steel plate. Stresses up to 350 MN/m2 were applied. found to occur when the Hertz pressure is higher than a value Stress distributions below the surface close to Hertzian cal which depends on the material used, and that spall formation culations were observed. Pnueli [23] discussed briefly the role is accelerated when the ratio of half the peak to valley rough of surface roughness in the transmission of heat from an as ness to the film thickness becomes larger than 1.4. Elamand perity contact, referencing his earlier work (dated 1977) and Berthe [26], studying disk wear at low slide/roll ratios, without further explanation. using a synthetic diester lubricant, find that micropits are formed relatively early as the result of asperity interaction. As Elastohydrodynamics the micropit density increases, a sponge type structure is As the gross behavior of EHD contacts has become well formed which weakens the material near the surface. Later the understood, more attention is being focused on the detailed micropit cavities join to form large voids, but the depth remains behavior within the contact zone. Of particular interest is the shallow compared to the classical deep spalls that are initiated A ratio, the ratio of calculated minimum film thickness to the by subsurface fatigue. surface roughness, and the phenomena that accompany as Felder [34] reviewed six key papers relating friction, lubri perity interactions in the EHD contact zone. An excellent, ex cation and surface roughness to metal working behavior. Most ample of such work is the study by Nagaraj, Sanborn, and intriguing is the observation that the roughness of the free Winer [14] on a sliding EHD point contact between a ball and surface increases during plastic deformation when the surface a flat, under conditions where run-in and surface profile im is lubricated so as to produce hydrodynamic effects. Poon [35] provement take place. Using an infrared micro detector having discussed the influence of surface roughness on rolling element a spot size resolution of 38,umand a time response of 8 fis, the bearing vibration. ball surface temperature was monitored as the peak Hertz pressure was increased up to a level of 2.0 GPa for a steel ball Wear Systems sliding on a sapphire surface. At the higher Hertz pressures The interaction between surface roughness, film thickness, above 1,5 GPa where A < 1 temperature fluctuations are ob and the effect of additives in a white oil in disk on disk tests served which are ascribed to local heating of an asperity. with a slide/roll ratio of ten percent was studied by Phillips and Dyson [20] reported on a new theoretical treatment of roll Quinn [25], Defining D as the ratio between the combined ing/sliding disks, lubricated, under conditions approaching initial surface roughness of the two disks to the lubricant film scuffing. The disks were circumferentially ground, and he thickness, they reported a strong correlation between the life concluded that under conditions in which scuffing is imminent, to the first pit and the D ratio. When a sulphur and phosphorus the degree of inter-penetration between the two surfaces ap type EP additive was used at five percent in the base white oil, proaches that obtained in static contact. In another study of a decrease in the pitting life was found for D ratios less than load division in a disk on disk type EHD contact, Berthe, about 1.5, while an increase in life was found for D greater than Flamand, Foucher, Hassoun, and Godet [22] calculate the load 1.5. They suggest that at low D ratios the additive promotes distribution between hydrodynamic action and asperity con crack initiation and crack propagation, while at high D ratios tact. This is done by calculating hm{n for the test conditions, the additive inhibits crack propagation by a corrosive wear and periodically stopping the test to measure the surface process. Pit formation is believed to occur when a crack can profile. From this data, the degree of interaction and the load propagate faster than it can be worn away. carried by the asperities can be computed. Scuffing was ob George [27] studied the leak rate of gas through an elasto served when the ratio of asperity-carried load to total load meric static seal under compression. In order to obtain a pic approached one. The authors state that, "the role of EP ad ture of the leakage gaps between the two surfaces, George de ditives is not only to form protective films which carry the load veloped a technique for freezing the elastomer while in contact when the hydrodynamic film fails, but also to modify surface with the seal face, removing it, and measuring its surface

Journal of Lubrication Technology JANUARY 1978, VOL 100/9 roughness properties with a profilometer. A flow theory based 13 A. Bowyer and A. Cameron, Imperial College, Mechanical Engineering on the spacial frequencies of a sinusoidal pattern on each face Dept., London SE7 2BX (England), "A Computer Sliding Model of Rough Surfaces" compared satisfactorily with directly measured values of leak 14 H. S. Nagaraj, D. M. Sanborn and W. O. Winer, School of Mechanical rate. Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332 (U.S.A.), In a paper that aroused a great deal of discussion and argu "Asperity Interactions in EHD Contacts" ment, Rozeanu and Snarsky [30] reported on experiments on 15 M. H. Jones, V. Sastry and G. Youdam, University College of Swansea, Dept. of Mechanical Engineering, Singleton Park, Swansea SA2 8PP (England), a partial journal bearing to confirm their contention that re "Study of Running-in of Diesel Engines Using Particle Analysis and Spec- sidual stresses in a freshly cut or worked surface greatly in trography Oil Analysis" crease the wetting and lubricant retention properties of the 16 P. B. MacPherson and .1. A. Leather, Imperial College, Dept. of Me surface. Experiments were made on a partial bearing located chanical Engineering, London SW7 2BX (England), "The Practical Use of Electrical Measurements in Lubricated Contacts" at the top of a journal, whose lower side dipped into a pool of 17 J. Greenwood and M. Williamson, University Engineering Dept., lubricant. Oil pressure was measured near the trailing edge of Trumpington Street, Cambridge, CB2 1PZ (Fmgland), "Developments in the the bearing. Tests on a freshly cut surface showed a high Theory of Surface Topography" pressure (in millimeters of oil) which decreased rapidly with 18 H. S. Sayles and T. R. Thomas, Mechanical Engineering Dept, Teesside time. Four curves were obtained, the magnitude of the pressure Polytechnic, Middlesborough (England), "The Plastic Contact of Two Rough Surfaces" rise being proportional to the. intensity of the abrasion action 19 W. Mirski and .!. Stupnicki, Institute of Applied Mechanics, Technical that preceded test.

University of Warsaw, Nowowiejska 24-00-665, Warsaw (Poland) "Effects of Downloaded from http://asmedigitalcollection.asme.org/tribology/article-pdf/100/1/6/5659660/6_1.pdf by guest on 29 September 2021 Surface Roughness on the State of Stresses of Solids in Contact" Jones and Tate [38] presented the results of experimental 20 A. Dyson, Thornton Research Centre, Shell Research Ltd., P.O. Box I, work on the thermal and mechanical distortions in a self acting Chester CHl 3SH (England), "Failure of Circumferentially Ground Discs" gas bearing system. In passing, they observed that the end face 21 P. M. Ku, Southwest Research Institute, 8500 Culebra Road, SanAn- of the gyro rotor rim ran at two distinct temperatures. A tonio, Texas 78209 (U.S.A.) and K. Y. Li, Cheng-Kung University, Tainan, sandblasted section was observed to run 1.5°C cooler than the Taiwan, "Effects of Surface Topography on Sliding-Rolling Disc Scuffing" 22 D. Berthe, L. Flamand, D. Foucher and M. Hassoun, Laboratoire de ground section, the CLA surface roughness values being 0.45 Mecanique des Contacts, INSA 69621 ViUeurbanne (France), "Theoretical and and 1.78 micrometers respectively. experimental Investigation of Load Division in Partial EHD Effects of Oil Lak and Wilson [33] reported that solid lubricants used in Nature and Roughness on Surface Failure" 23 D. Pnueli, Technion Institute of Technology, Dept. of Materials Engi metal forming, such as waxes, soaps, polymers, soft metals and neering, Haifa, Israel, "Role of Surface Roughness in the Choice Between a graphite are transported at greater rates through the working Continuum Model and a Descrete Two-Temperature-Gradient Model for zone than are liquid lubricants. They find that the non-di Friction System" mensional transport velocity increases with the roughness ratio 24 D. Berthe, B. Michau, L. Flamand, M. Godet, Laboratoire de Mecanique between the work surface and the tool up to a roughness ratio des Contacts, INSA, 69621 Villeurbane (France), "Effect of Roughness on Pits and Micropits in Pure Roiling Lubrication" of about 10. At a roughness ratio of 1, the transport velocity is 25 F. J. Quinn and M. R. Phillips, Dept. Physics, University of Aston, half the work surface velocity, as it would be for hydrodynamic Birmingham (England), "The Effect of Surface Roughness and Lubricant Film lubrication, and at a roughness ratio of 10 the transport velocity Thickness Upon Contact Fatigue" approaches the work surface velocity. 26 L. Flamand and D. Berthe, Labortoire de Mecanique des Contacts, INSA, 69621 ViUeurbanne (France), "Different Forms of Wear at Low Slide/ Roll Ratio" References 27 A. George, Central Electricity Generating Board, Berkeiy Nuclear Laboratories, Berkeley Gloucestershire (England), "Correlation Leakage Past 1 D, Dowson, Institute of Tribology, Dept. of Mechanical Engineering, Elastomer Joint Seals and with Surface Profile Measurements" Leeds LS2 9JT, (England) "Early Concepts of Surface Topography and Their 28 D. Wilcock, Mechanical Technology Inc., 968 Albany-Shaker Road, Role in Tribology" Latham, New York 12110 (U.S.A.) "A Look at the Interaction Between Tur 2 H. Elrod, Dept. of Mechanical Engineer, Columbia University, New bulence and Surface Roughness" York, New York. 10027 (U.S.A.), Part I and Part 2 "A Review of Theories for 29 K. J. Stout, H. H. Heath and T. G. King, Leicester Polytechnic School Roughness Effects on Laminar Lubricating Films" of Mechanical and Production Engineering, P.O. Box 143, Leicester Lei 9BH 3 P. L. Chow and E. Saibel, Engineering Science Division, U. S. Army (England), "Ground Surface Finish. Its Influence on Marginally Lubricated Research Office, P.O. Box 12221, Research Triangle Park, North Carolina 27709 Wear" (U.S.A.), "The Roughness Effect in Hydrodynamic Lubrication" 30 L. Rozeanu and L. Snarsky, Technion Institute of Technology, Dept. 4 S. M. Rohde and D. Whicker, Mechanical Research Dept., General of Materials Engineering, Haifa (Israel), "Physico-Chemieal Characterisation Motors Corporation, Warren, Mi. 48090 (U.S.A.), "Some Mathematical Aspects of Surface Roughness and Its Tribological Implications" of the Hydrodynamic Lubrication Problems" 31 J. Hailing, University of Salford, Dept. of Mechanical Engineering, 5 Dah Chen Sun* and K. K. Chen, Mechanical Research Dept., Research Salford M5 4WT (England), "The Role of Surface Topography in the Friction Laboratories, General Motors Corporation, Warren, Mi 48090 (U.S.A.), "On and Wear of Plain Hydrodynamic Bearings" The Statistical Treatment of Rough Surface Hydrodynamic Lubrication 32 J. Hoppe, Mercedes, Daimler-Benz Aktiengesellschaft, 700 Stuttgart Problems" 60, Postf. 202 (Germany), "Minimum Allowable Film Thickness Surface Quality 6 A. O. Lebeck, The University of New Mexico, Bureau of Engineering and Running-In Effect in Jorunal Bearings" Research, Farris Engineering Center, Room 124, Albuquerque, New Mexico 33 S. Lak, Dept. of Machine and Tool Design, Springfield Technical 87131 (U.S.A.), "A Study of Mixed Lubrication in Contacting Mechanical Face Community College, Springfield, Mass. (U.S.A.) and W. R. D. Wilson, Dept, Seals" of Mechanical Engineering, University of Massachusetts, Amherst, Mass. 7 A. Dyson, Thorton Research Centre, Shell Research Ltd., P.O. Box 1, (U.S.A.), "Transport of Solid Lubricants by Rough Surfaces" Chester, CHI 3SH (England), "Hydrodynamic Lubrication of Rough Surfaces. 34 E. Felder, Centre de Mise en Forme des Materiaux, ENSMP, Sophia A Review of Theoretical Work" Antipolis, 0650 Valhonne (France), "Interaction Between Friction, Lubrication 8 H. Cheng, Northwestern University, Mechanical Engineering Dept., and Surface Roughness in Metal Working" Evattston, III. (U.S.A.) "On Some Aspects of Microelastohydrodynamic Lu 35 P. Poon, RHP Bearing Centre, P.O. Box 7, Chelmsford Essex CMl 1PU brication" (England), "Surface Roughness and the Rolling Element Bearing Vibration" 9 K. Tonder, University of Trondheim, Trondheim NTH (Norway), "The 36 D. F. Moore, University College of Dublin, Mechanical Engineering Dept. Lubrication of Surfaces Having a Cross Striated Roughness Pattern" Upper Merrion Street, Dublin 2 (Ireland), "Scale Effects in Elastohydrodyn- 10 T. R. Thomas, Mechanical Engineering Dept,, Teesside Polytechnic, amic Lubrication for Rubber Like Materials" Middlesborough (England), "The Characterisation of Changes in Surface To 37 J. M. Georges, P. H. Kapsa and T. Mathia, Ecole Centrale de Lyon, 36, pography in Running-In" Route de Dardilly, 69130 Eeully (France), "Roughness in Boundary Lubrica 11 D. Foucher, L. Flamand and D. Berthe, Laboratoire de Mecanique des tion" Contacts, INSA, 69621 ViUeurbanne (France), "Variation of Surface Roughness 38 D. A. Jones and D. Tate, Institute of Tribology, Dept. of Mechanical Parameters During Rtmning-in of Lubricated Hertzian Contacts" Engineering, Leeds LS2 9JT (England), "The Investigation of Various Design 12 J. C. Raffy, Centre Technique des Industries Mecanique, 10 rue Bar- Factors Control Distortion in a Simple Gas Bearing Machine" rouin, 42000 Saint-Etienne (France), "Evolution of Surface Roughness of Gear 39 T. G. King, W. Watson and K. J. Stout, Leicester Polytechnic School Teeth" of Mechanical and production Engineering, P.O. Box 143, Leicester Le 1 9BH (England), "Modelling of Micro-Geometry of Lubricated Wear" 40 J. P. Khukla and J. Kumar, Indian Institute of Technology, Kanpur 208016 (India), "Effects of Viscosity Variation and Surface Roughness in Lu * Presented by Saibel brication" 41 D. F. Wilcock, Mechanical Technology Inc., 968 Albany-Shaker Road, 10 / VOL 100, JANUARY 1978 Transactions of the ASME La tham, New York 12110, " S uper La mina r Flow in Bearings. A review of the 42 D. F. Wi lcock, Mechanical T echnology Inc., 968 Albany-Sha ke r Hoad , Second Leeds- Lyon Symposiulll , Lyons, Fra nce, Sept.ember 17- 19, 1975." Lat. ha m, New York 12110, " The Wear of Non-Metallic Materials 3rd Leeds AS ME, JOURNA L OF LUBRICAT ION TI;;CHNOLOG Y, Vol. 98, No. 1, Janua ry Lyon SymposiUln on Tl'ibology" AS ME, .JO URN AI. OF LUBRICAT ION T EC H 1976. NO LOGY, No.2, Apl'iI1977. Downloaded from http://asmedigitalcollection.asme.org/tribology/article-pdf/100/1/6/5659660/6_1.pdf by guest on 29 September 2021

Journal of Lubrication Technology JANUARY 1978, VOL 100 /11