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RESEARCH PAPERS

J. of Lubrication Tech. 1977;99(1):2-9. doi:10.1115/1.3452975.

Considering the actual roughness dimensions as well as the typical dimensions of a hydrodynamically lubricating film, the Stokes equations are used to analyze the roughness effects. The surface profile is modeled by an ergodic, stationary random process. It is revealed that the roughness effects can be determined by three parameters; viz., the rms roughness, the correlation length, and the correlation wavelength. The present results are significantly different from those in the literature, where the Reynolds equation is used for analysis.

Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1977;99(1):10-14. doi:10.1115/1.3452956.

A mathematical model for the roughening of the workpiece in a hydrodynamically lubricated metal forming process is developed. Roughening is assumed to result from local variations in the workpiece flow strength. The results of the analysis are compared with previous experimental measurements.

Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1977;99(1):15-23. doi:10.1115/1.3452973.

Utilizing the theory and numerical procedure developed by the authors in an earlier publication the influence of lubricant starvation on minimum film thickness was investigated. This study of lubricant starvation was performed simply by moving the inlet boundary closer to the contact center. From the results it was found that for the range of conditions considered the value of dimensionless inlet distance at the boundary between fully flooded and starved conditions (m*) can be expressed simply as

m*=1+3.06Rxb2Hc,F0.58
or
m*=1+3.34Rxb2Hmin,F0.56
that is, for a dimensionless inlet distance (m) less than m*, starvation occurs, and for m ≥ m*, a fully flooded condition exists. Furthermore, it has been possible to express the central and minimum film thickness for a starved condition as
Hc,S=Hc,Fm−1m*−10.29
Hmin,S=Hmin,Fm−1m*−10.25
Contour plots of the pressure and film thickness in and around the contact are shown for the fully flooded and starved lubricant condition. From these contour plots it was observed that the pressure spike becomes suppressed and the film thickness decreases substantially as starvation increases.

Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1977;99(1):24-29. doi:10.1115/1.3452974.

The micropolar fluid theory is used to analyze the elastohydrodynamic inlet zone of a line contact. The analysis, which is based on Grubin’s approximation, indicates clearly that the additive caused film thickness enhancement as observed by several researchers in heavily loaded contacts has a possible explanation in this theory.

Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1977;99(1):30-36. doi:10.1115/1.3452976.

Bearing defect data from 8,000 railroad roller bearings are analyzed to determine their defect modes and defect rate distributions. Cone bore growth, brinelling, and fatigue are identified as the predominant defect modes as bearings age at least through age 12 years. The results of the study show that, after only two years of service, ten percent of all railroad roller bearings exhibit a defect of one type or another for which at least one component would be condemned if it were in a rework shop. The present AFBMA method of calculating fatigue spalling, modified to account for lubricant film thickness effects, correlates reasonably well with the observed incidence of spalling (10 percent fatigue life of about 11 years). The problem lies in the fact that the AFBMA calculation procedure ignores the other competing defect modes which contribute far more to the overall defect rate than does spalling. The relationship between “defect rate” and “failure rate” is not direct, of course, and an examination of “condemning limit” definitions relative to the progression of bearing failure in service is needed.

Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1977;99(1):41-46. doi:10.1115/1.3452983.

The Contact Pattern Analysis technique was used to determine the actual distribution of load among rollers, misalignment, and roller edge loading effects in cylindrical roller bearings in a commercial gear train. In all the bearings in the system, the summation of the vertical components of individual roll body loads determined from Contact Pattern Analysis agreed well with the total load imposed on the bearing by the system, thereby demonstrating the practicability and accuracy of the technique. In a few cases the load distribution among rollers in the bearing and, in one case, the number of rollers loaded, were found to be far from ideal. Similarly, it was found that the direction of the bearing reaction differed significantly from the applied load direction. The misalignment as calculated from the contacts was .003 to .005 mm/mm. Also, evidence of contact truncation and roller edge loading at peak torque loads were found. Thus this systems approach, utilizing the Contact Pattern Analysis technique revealed several anomalies that suggest adjusting system parameters, such as housing stiffness and/or roller crown, to improve bearing reliability and performance. This could not have been done by any other known analytical technique.

Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1977;99(1):50-56. doi:10.1115/1.3452989.

The purpose of this investigation is to study the transmissibility characteristics of a centrally preloaded porous bearing squeeze-film damper supporting a rolling element bearing. Using the short-bearing approximation and isothermal, incompressible lubrication, transient and steady-state data are presented which show that, for the range of parameters considered, porous bearing dampers exhibit superior transmissibility characteristics over equivalent dampers using solid bearings. The data presented are for squeeze-film porous bearings having a wall thickness-to-length ratio of 0.1 and three degrees of permeability, including the case of zero permeability which corresponds to a solid bearing.

Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1977;99(1):57-64. doi:10.1115/1.3452990.

This paper examines the effect of squeeze-film damper bearings on the steady state and transient unbalance response of aircraft engine rotors. The nonlinear effects of the damper are examined, and the variance of the motion due to unbalance, static pressurization, retainer springs, and rotor preload is shown. The nonlinear analysis is performed using a time-transient method incorporating a solution of the Reynolds equation at each instant in time. The analysis shows that excessive stiffness in the damper results in large journal amplitudes and transmission of bearing forces to the engine casing which greatly exceed the unbalance forces. Reduction of the total effective bearing stiffness through static pressurization and rotor preload is considered. The reduction in stiffness allows the damping generated by the bearing to be more effective in attenuating rotor forces. It is observed that in an unpressurized damper, the dynamic transmissibility will exceed unity when the unbalance eccentricity exceeds approximately 50 percent of the damper clearance for the relatively wide range of conditions examined in this study.

Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1977;99(1):65-74. doi:10.1115/1.3452991.

A new bearing torque rig capable of qualifying and analyzing bearing torque signals for large-bore high-precision bearings is described. The servomechanical subsystem responsible for torque definition within ± 5.9 × 10−4 Nm is also described. In addition to a space proven lubricant, two lubricants were tested in this rig: KG-80 oil and Polyfluoralkylalkyl polysiloxane grease. Tests were conducted on short-time basis in open air conditions. All three lubricants were tested in a 100 mm bore high-precision angular ball bearing, with and without ball retainer. The bearing was operated at various loads and speeds. Dependence on torque and Root Mean Square-torque as function of lubricant quantity are established. Data trend reveals the existence of a region of minimum torque for oil-retainer bearing configurations. Data also imply the feasability of using the two aforementioned lubricants and the full ball complement configuration in DMA-type applications.

Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1977;99(1):75-81. doi:10.1115/1.3452992.

A mathematical analysis of a class of compliant journal bearings operating with a compressible lubricant is presented. Finite element methods are used to obtain approximate solutions, and results for the rigid case are compared to those obtained by finite difference methods. Results for the case in which the compliant bearing component is a shell show that the steady-state performance can be radically different from that predicted by the rigid bearing assumption. These differences may explain the antiwhirl characteristics exhibited by this type of bearing.

Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1977;99(1):82-88. doi:10.1115/1.3452993.

A flat sector shaped pad geometry for gas lubricated thrust bearings is analyzed considering both pitch and roll angles of the pad and the true film thickness distribution. Maximum load capacity is achieved when the pad is tilted so as to create a uniform minimum film thickness along the pad trailing edge. Performance characteristics for various geometries and operating conditions of gas thrust bearings are presented in the form of design curves. A comparison is made with the rectangular slider approximation. It is found that this approximation is unsafe for practical design, since it always overestimates load capacity.

Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1977;99(1):89-94. doi:10.1115/1.3452994.

The principle of utilizing hydrodynamic effects in diverging films for improving load capacity in gas thrust bearings is discussed. A new concept of dual action bearing based on that principle is described and analyzed. The potential of the new bearing is demonstrated both analytically for an infinitely long slider and by numerical solution for a flat sector shaped thrust bearing. It is shown that the dual action bearing can extend substantially the range of load carrying capacity in gas lubricated thrust bearings and improve their efficiency.

Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1977;99(1):95-100. doi:10.1115/1.3452995.

A gas thrust bearing consisting of flat sector shaped pads mounted on resilient metallic cantilever beams is described and analyzed. Compliance and stiffness of the bearing assembly are discussed and the effects of bearing design parameters on performance are shown. A design example is presented and a special case where zero axial movement of the runner can be obtained is pointed out.

Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1977;99(1):101-105. doi:10.1115/1.3452954.

A rigid vertical shaft was operated with known amounts of unbalance at speeds up to 30,000 rpm and gas supply pressure ratios to 4.8. From measured amplitude and phase angle data, dynamic stiffness and damping coefficients of the bearings were determined. The measured stiffness was proportional to the supply pressure, while damping was little affected by supply pressure. Damping dropped rapidly as the fractional frequency whirl threshold was approached. A small eccentricity analysis overpredicted the stiffness by 4 to 55 percent. Predicted damping was close to measured at low speeds but higher at high speeds.

Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1977;99(1):106-112. doi:10.1115/1.3452955.

A novel form of variable hydrostatic restriction is proposed which will automatically achieve a high, infinite or negative static stiffness over a substantial load range. The restrictor is formed between the bearing body and a spring mounted conical plug. The steady state performance is analyzed and design curves presented which are valid for any cone angle from zero, i.e., fixed clearance, to 90 deg which is the normal diaphragm restrictor. The dynamic response to forced sinusoidal vibrations is examined in conventional vibration analysis form and it is found that the restrictor system may be designed to act as a vibration absorber.

Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1977;99(1):113-121. doi:10.1115/1.3452957.

Turbulence makes high speed conventionally designed bearings operate with higher power loss, high temperature rise, and lower oil flow than predicted. The objective of this paper is to show that the phenomenon of turbulence can be turned to the designer’s and operator’s advantage; and that turbulent thrust bearings can be designed to operate with lower power loss than conventional design would predict, while maintaining the same minimum film thickness and safe temperature rise.

Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1977;99(1):122-127. doi:10.1115/1.3452958.

A promising new type of tilting pad journal bearing—the Fluid Pivot journal bearing—is described. The long development history of this bearing is summarized, showing how the design evolved through research and testing. Static and dynamic performance features of the bearing are presented, with sample test results compared with predictions based on an advanced computer analysis. Comparisons of the Fluid Pivot journal bearing with conventional mechanically pivoted journal bearings are given.

Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1977;99(1):129-135. doi:10.1115/1.3452961.

It is common in the analysis of fluid film bearings to neglect the effect of convective fluid inertia. There has been some interest in recent years as to the validity of this assumption in high Reynolds number turbulent flows. Analytical techniques appropriate to the solution of finite width bearing problems considering fluid inertia have been proposed by others. The authors have applied one such method to the plane inclined slider thrust bearing and found that for some situations inertial effects may be important.

Commentary by Dr. Valentin Fuster

DISCUSSIONS

Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1977;99(1):128. doi:10.1115/1.3452960.
FREE TO VIEW
Abstract
Topics: Fluids

BOOK REVIEWS

J. of Lubrication Tech. 1977;99(1):136. doi:10.1115/1.3452962.
FREE TO VIEW
Abstract
Commentary by Dr. Valentin Fuster

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