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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 253 records · Page 14
All sourcesNASA NTRSDOE OSTI
NASA NTRS1999

Experimental Determination of Load Carrying Capacity of Point Contacts at Zero Entrainment Velocity

A capacitance technique was used to monitor the film thickness separating two steel balls of a unique tribometer while subjecting the ball-ball contact to highly stressed, zero entrainment velocity (ZEV) conditions. All tests were performed under a N2 purge (R.H. < 1.0%) and utilized 52100 steel balls (R(sub a) = 0.02 mm). Tribometer operations and capacitance-to-film-thickness accuracy were verified by comparing the film thickness approximations to established theoretical predictions for test conditions involving pure rolling. Pure rolling experiments were performed under maximum contact stresses and entrainment velocities of 1.0 GPa and 1.0 m/s to 3.0 m/s, respectively. All data from these baseline tests conformed to theory. ZEV tests were initiated after calibration of the tribometer and verification of film thickness approximation accuracy. Maximum contact stresses up to 0.57 GPa were supported at zero entrainment velocity with sliding speeds from 6.0 to 10.0 m/s for sustained amounts of time up to 28.8 minutes. The protective lubricating film separating the specimens at ZEV had a thickness between 0.10 and 0.14 mm (4 to 6 min), which corresponds to an approximate L-value of 4. The film thickness did not have a strong dependence upon variations of load or speed. Decreasing the sliding speed from 10.0 m/s to 1 m/s revealed a rapid loss in load support between 3.0 and 1.0 m/s. The formation of an immobile film formed by lubricant entrapment is discussed as an explanation of the load carrying capacity at these zero entrainment velocity conditions, relevant to the ball-ball contact application in retainerless ball bearings.

Shogrin, Bradley A.↗
NASA NTRS1985

Traction forces at solid-lubricated rolling/sliding contacts

A single-element traction rig was used to measure the traction forces at a solid-lubricated contact of a ball against a flat disk at room temperature under combine rolling and sliding. The load and speed conditions were selected to match those anticipated for bearing applications in adiabatic diesel engines. Traction vs slide/roll ratio curves were similar to those for liquid lubricants but the traction forces were an order of magnitude higher. The test data were used to derive equations to predict traction force as a function of contact stress and rolling speed. The data showed that the magnitude of traction forces were almost the same for all the lubricants tested. The lubricants, should, therefore, be selected on the basis of their ability to limit the wear of contact surfaces.

Aggarwal, B. B.↗
NASA NTRS2010

Interference-Fit Life Factors for Ball Bearings

The effect of hoop stresses on the rolling-element fatigue life of angular-contact and deep-groove ball bearings was determined for common inner-ring interference fits at the ABEC-5 tolerance level. The analysis was applied to over 1150 bearing configurations and load cases. Hoop stresses were superimposed on the Hertzian principal stresses created by the applied bearing load to calculate the inner-race maximum shearing stress. The resulting fatigue life of the bearing was recalculated through a series of equations. The reduction in the fatigue life is presented as life factors that are applied to the unfactored bearing life. The life factors found in this study ranged from 1.00 (no life reduction)--where there was no net interface pressure--to a worst case of 0.38 (a 62-percent life reduction). For a given interference fit, the reduction in life is different for angular-contact and deep-groove ball bearings. Interference fits also affect the maximum Hertz stress-life relation. Experimental data of Czyzewski, showing the effect of interference fit on rolling-element fatigue life, were reanalyzed to determine the shear stress-life exponent. The Czyzewski data shear stress-life exponent c equals 8.77, compared with the assumed value of 9. Results are presented as tables and charts of life factors for angular-contact and deep-groove ball bearings with light, normal, and heavy loads and interference fits ranging from extremely light to extremely heavy.

Oswald, Fred B.↗
NASA NTRS1985

Effect of speed and press fit on fatigue life of roller-bearing inner-race contact

An analysis was performed to determine the effects of inner ring speed and press fit on the rolling element fatigue life of a roller bearing inner race contact. The effects of the resultant hoop and radial stresses on the principal stresses were considered. The maximum shear stresses below the Hertzian contact were determined for different conditions of inner ring speed, load, and geometry and were applied to a conventional ring life analysis. The race contact fatigue life was reduced by more than 90 percent for some conditions when speed and press fit were considered. The depth of the maximum shear stress remained virtually unchanged.

Coe, H. H.↗
NASA NTRS2005

Effect of Silicon Nitride Balls and Rollers on Rolling Bearing Life

Three decades have passed since the introduction of silicon nitride rollers and balls into conventional rolling-element bearings. For a given applied load, the contact (Hertz) stress in a hybrid bearing will be higher than an all-steel rolling-element bearing. The silicon nitride rolling-element life as well as the lives of the steel races were used to determine the resultant bearing life of both hybrid and all-steel bearings. Life factors were determined and reported for hybrid bearings. Under nominal operating speeds, the resultant calculated lives of the deep-groove, angular-contact, and cylindrical roller hybrid bearings with races made of post-1960 bearing steel increased by factors of 3.7, 3.2, and 5.5, respectively, from those calculated using the Lundberg-Palmgren equations. An all-steel bearing under the same load will have a longer life than the equivalent hybrid bearing under the same conditions. Under these conditions, hybrid bearings are predicted to have a lower fatigue life than all-steel bearings by 58 percent for deep-groove bearings, 41 percent for angular-contact bearings, and 28 percent for cylindrical roller bearings.

Zaretsky, Erwin V.↗
DOE OSTI2025

Dynamic condensation model of rolling droplets for high-performance heat transfer

Condensation is a critical process during vapor-liquid phase change in relation to heat transfer. To achieve a high heat transfer coefficient, the classical model for dropwise condensation requires a low contact angle and low contact angle hysteresis, failing to align with experimental observations on a hydrophobic and slippery quasi-liquid surface (QLS). Here, we report a dynamic condensation model that incorporates high-frequency condensate removal by emphasizing the role of timescale during droplet growth and shedding. Our model agrees well with the experimental result that a surface with high contact angle and low contact angle hysteresis promotes condensation, particularly during rolling-propelled condensate removal. Particle image velocimetry reveals that rolling droplets on a hydrophobic QLS exhibit 4-fold higher shedding speeds than the sliding droplets on a hydrophilic QLS, leading to significant heat transfer enhancement. This work deepens our theoretical understanding of condensation heat transfer and provides advanced physics-informed design rationales for water and energy systems.

42 ENGINEERING↗
NASA NTRS1951

Preliminary Investigation of Molybdenum Disulfide-air-mist Lubrication for Roller Bearings Operating to DN Values of 1 x 10(exp 6) and Ball Bearings Operating to Temperatures of 1000 F

The effectiveness of molybdenum disulfide MoS2 as a bearing lubricant was determined at high temperature and at high speeds. A 1-inch-bore ball bearing operated at temperatures to 1000 F, a speed of 1725 rpm, and a thrust load of 20 pounds when lubricated only with MoS2-air mist. A 75-millimeter-bore cageless roller bearing, provided with a MoS2-syrup coating before operation, operated at DN values to 1 x 10(exp 6) with a load of 368 pounds.

BEARINGS, ANTI - FRICTION↗
NASA NTRS1951

Comparison of High-Speed Operating Characteristics of Size 215 Cylindrical-Roller Bearings as Determined in Turbojet Engine and in Laboratory Test Rig

A comparison of the operating characteristics of 75-millimeter-bore (size 215) cylindrical-roller one-piece inner-race-riding cage-type bearings was made using a laboratory test rig and a turbojet engine. Cooling correlation parameters were determined by means of dimensional analysis, and the generalized results for both the inner- and outer-race bearing operating temperatures are compared for the laboratory test rig and the turbojet engine. Inner- and outer-race cooling-correlation curves were obtained for the turbojet-engine turbine-roller bearing with the same inner- and outer-race correlation parameters and exponents as those determined for the laboratory test-rig bearing. The inner- and outer-race turbine roller-bearing temperatures may be predicted from a single curve, regardless of variations in speed, load, oil flow, oil inlet temperature, oil inlet viscosity, oil-jet diameter or any combination of these parameters. The turbojet-engine turbine-roller-bearing inner-race temperatures were 30 to 60 F greater than the outer-race-maximum temperatures, the exact values depending on the operating condition and oil viscosity; these results are in contrast to the laboratory test-rig results where the inner-race temperatures were less than the outer-race-maximum temperatures. The turbojet-engine turbine-roller bearing, maximum outer-race circumferential temperature variation was approximately 30 F for each of the oils used. The effect of oil viscosity on inner- and outer-race turbojet-engine turbine-roller-bearing temperatures was found to be significant. With the lower viscosity oil (6x10(exp -7) reyns (4.9 centistokes) at 100 F; viscosity index, 83), the inner-race temperature was approximately 30 to 35 F less than with the higher viscosity oil (53x10(exp -7) reyns (42.8 centistokes) at 100 F; viscosity index, 150); whereas the outer-race-maximum temperatures were 12 to 28 F lower with the lower viscosity oil over the DN range investigated.

BEARINGS, ANTI-FRICTION↗
NASA NTRS1965

The rolling tire under load

Dynamic pressure distributions calculated for contact patch areas of elastically supported cylindrical shell used to model pneumatic tire

CYLINDRICAL SHELL↗
NASA NTRS1980

Simplified fatigue life analysis for traction drive contacts

A simplified fatigue life analysis for traction drive contacts of arbitrary geometry is presented. The analysis is based on the Lundberg-Palmgren theory used for rolling-element bearings. The effects of torque, element size, speed, contact ellipse ratio, and the influence of traction coefficient are shown. The analysis shows that within the limits of the available traction coefficient, traction contacts exhibit longest life at high speeds. Multiple, load-sharing roller arrangements have an advantageous effect on system life, torque capacity, power-to-weight ratio and size.

Rohn, D. A.↗
NASA NTRS1980

Simplified fatigue life analysis for traction drive contacts

A simplified fatigue life analysis for traction drive contacts of arbitrary geometry is presented. The analysis is based on the Lundberg-Palmgren theory used for rolling-element bearings. The effects of torque, element size, speed, contact ellipse ratio, and the influence of traction coefficient are shown. The analysis shows that within the limits of the available traction coefficient, traction contacts exhibit longest life at high speeds. Multiple, load-sharing roller arrangements have an advantageous effect on system life, torque capacity, power-to-weight ratio and size.

Rohn, D. A.↗
NASA NTRS1983

Predicted and experimental performance of large-bore high-speed ball and roller bearings

The values of inner and outer race temperature, cage speed, and heat transferred to the lubricant or bearing power loss, calculated using the computer programs Shaberth and Cybean, with the corresponding experimental data for the large bore ball and roller bearings were compared. After the development of computer program, it is important that values calculated using such program are compared with actual bearing performance data to assess the programs predictive capability. Several comprehensive computer programs currently in use are capable of predicting rolling bearing operating and performance characteristics. These programs accept input data of bearing internal geometry, bearing material and lubricant properties, and bearing operating conditions. The programs solve several sets of equations that characterize rolling element bearings. The output produced typically consists of rolling element loads and Hertz stresses, operating contact angles, component speed, heat generation, local temperatures, bearing fatigue life, and power loss. Two of these programs, Shaberth and Cybean were developed.

Coe, H. H.↗
NASA NTRS1993

Computer program for analysis of high speed, single row, angular contact, spherical roller bearing, SASHBEAN. Volume 1: User's guide

The computer program SASHBEAN (Sikorsky Aircraft Spherical Roller High Speed Bearing Analysis) analyzes and predicts the operating characteristics of a Single Row, Angular Contact, Spherical Roller Bearing (SRACSRB). The program runs on an IBM or IBM compatible personal computer, and for a given set of input data analyzes the bearing design for it's ring deflections (axial and radial), roller deflections, contact areas and stresses, induced axial thrust, rolling element and cage rotation speeds, lubrication parameters, fatigue lives, and amount of heat generated in the bearing. The dynamic loading of rollers due to centrifugal forces and gyroscopic moments, which becomes quite significant at high speeds, is fully considered in this analysis. For a known application and it's parameters, the program is also capable of performing steady-state and time-transient thermal analyses of the bearing system. The steady-state analysis capability allows the user to estimate the expected steady-state temperature map in and around the bearing under normal operating conditions. On the other hand, the transient analysis feature provides the user a means to simulate the 'lost lubricant' condition and predict a time-temperature history of various critical points in the system. The bearing's 'time-to-failure' estimate may also be made from this (transient) analysis by considering the bearing as failed when a certain temperature limit is reached in the bearing components. The program is fully interactive and allows the user to get started and access most of its features with a minimal of training. For the most part, the program is menu driven, and adequate help messages were provided to guide a new user through various menu options and data input screens. All input data, both for mechanical and thermal analyses, are read through graphical input screens, thereby eliminating any need of a separate text editor/word processor to edit/create data files. Provision is also available to select and view the contents of output files on the monitor screen if no paper printouts are required. A separate volume (Volume-2) of this documentation describes, in detail, the underlying mathematical formulations, assumptions, and solution algorithms of this program.

Aggarwal, Arun K.↗
NASA NTRS1973

Study of ball bearing torque under elastohydrodynamic lubrication

Spinning and rolling torques were measured in an angular-contact ball bearing with and without a cage under several lubrication regimes in a modified NASA spinning torque apparatus. Two lubricants were used, a di-2 ethylhexyl sebacate and a synthetic paraffinic oil, at shaft speeds of 1000, 2000, and 3000 rpm and bearing loads from 10 lbs to 90 lbs. An analytical model was developed from previous spinning friction models to include rolling with spinning under lubrication regimes from thin film to flooded conditions. The bearing torque values have a wide variation, under any condition of speed and load, depending on the amount of lubricant present in the bearing. The analytical model compared favorably with experimental results under several lubrication regimes.

Townsend, D. P.↗
NASA NTRS1973

Study of ball bearing torque under elastohydrodynamic lubrication

Spinning and rolling torques were measured in an angular-contact ball bearing with and without a cage under several lubrication regimes in a modified NASA spinning torque apparatus. Two lubricants were used - a di-2 ethylhexyl sebacate and a synthetic paraffinic oil, at shaft speeds of 1000, 2000, and 3000 rpm and bearing loads from 45 newtons (10 lb) to 403 newtons (90 lb). An analytical model was developed from previous spinning friction models to include rolling with spinning under lubrication regimes from thin film to flooded conditions. The bearing torque values have a wide variation, under any condition of speed and load, depending on the amount of lubricant present in the bearing. The analytical model compared favorably with experimental results under several lubrication regimes.

Townsend, D. P.↗
NASA NTRS1987

Heat generation in Aircraft tires under yawed rolling conditions

An analytical model was developed for approximating the internal temperature distribution in an aircraft tire operating under conditions of yawed rolling. The model employs an assembly of elements to represent the tire cross section and treats the heat generated within the tire as a function of the change in strain energy associated with predicted tire flexure. Special contact scrubbing terms are superimposed on the symmetrical free rolling model to account for the slip during yawed rolling. An extensive experimental program was conducted to verify temperatures predicted from the analytical model. Data from this program were compared with calculation over a range of operating conditions, namely, vertical deflection, inflation pressure, yaw angle, and direction of yaw. Generally the analytical model predicted overall trends well and correlated reasonably well with individual measurements at locations throughout the cross section.

Dodge, Richard N.↗
NASA NTRS1996

Three-dimensional roller locking sprags

A torque coupling sprag system which provides contact between the sides of at least one groove and at least two contact surfaces angled with respect to the central axial direction of at least one rotatable 3-D sprag member located between a drive member and a reaction member. The surface contacts between the members include various combinations of surface segments arranged in a predetermined manner to define a desired configuration. The contact radius of the 3-D sprag member is significantly larger than its rolling radius; however, radii can be varied in size and shape independently of each other, particularly the contact radius.

Vranish, John M.↗
NASA NTRS1980

Surface temperatures and glassy state investigations in tribology

Measurements were made of the limiting shear stress for two naphthenic oils of differing molecular weight and three blends of the lower molecular weight oil and polymers of differing molecular weight. All reached the same limiting shear stress for the same temperature and pressure; although the polymer solutions reduced the limiting shear stress by about fifteen percent. A falling body viscometer was constructed to operate to 230 C and to 0.6 GPa and another was constructed to extend the pressure range to 1.1 GPa. A concentrated contact simulator was developed which allows recording of the traction force while the slide-roll ratio is continuously varied and the rolling speed is maintained essentially constant. Measurement of lubricant minimum film thickness of elliptical EHD contacts of various aspect ratios were made by optical interferometry. The experimental data were thirty percent greater than that predicted by the Hamrock and Dowson model. Preliminary development of the application of a scanning infrared radiation system to a tribological system was completed.

Bair, S.↗