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Results for “ROLLING CONTACT”

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 181 records · Page 10
All sourcesNASA NTRSDOE OSTI
NASA NTRS1975

Wear and interfacial transport of material

The paper is a review of adhesion or bonding across an interface between two solids in contact, transfer or transport to one or both surfaces, wear with tangential motion, and the effect of surface films on adhesion, transfer, and wear. The discussion is limited to the case of adhesive wear which deals with the interfacial transport of material from one surface to another. The data presented suggest that the resulting interfacial adhesive bond for metals in contact is generally stronger than the cohesive bond in the cohesively weaker of the two materials so that upon separation of the surfaces transfer will occur from the cohesively weaker material to the cohesively stronger; that with tangential motion of two metal surfaces in contact such as encountered with sliding, rolling, or rubbing contact, the frictional energy can be dissipated in a number of ways, where heating of the surfaces can produce metallurgical changes such as alloying; and that the presence of adsorbed and reacted films on the surface of metals and alloys even in frictions of a monolayer can reduce interfacial bonding, adhesion, and transfer.

Buckley, D. H.↗
NASA NTRS1977

Microstructural and wear properties of sputtered carbides and silicides

Sputtered Cr3C2, Cr3Si2, and MoSi2 wear-resistant films (0.05 to 3.5 microns thick) were deposited on metal and glass surfaces. Electron transmission, electron diffraction, and scanning electron microscopy were used to determine the microstructural appearance. Strong adherence was obtained with these sputtered films. Internal stresses and defect crystallographic growth structures of various configurations within the film have progressively more undesirable effects for film thicknesses greater than 1.5 microns. Sliding contact and rolling element bearing tests were performed with these sputtered films. Bearings sputtered with a duplex coating (0.1-micron-thick undercoating of Cr3Si2 and subsequently 0.6-micron coating of MoS2) produced marked improvement over straight MoS2 films.

Spalvins, T.↗
NASA NTRS1978

The practical impact of elastohydrodynamic lubrication

Elastohydrodynamic lubrication has had its most significant impact on, among all the types of concentrated contact mechanisms, rolling element bearings. EHL technology, through its inclusion in computer codes, now provides us with more effective methods for optimizing bearing design and for predicting bearing life, power loss, temperature and dynamic behavior. Bearing life prediction has advanced to a much more sophisticated level as compared to the calculation of fatigue life based on Lundberg-Palmgren theory. Application of elastohydrodynamics to gearing has, more or less, been limited to the calculation of pitch point film thicknesses. Techniques for calculating film thicknesses over the entire range of tooth meshes for arbitrarily shaped gear teeth (noninvolute, spur, helical, etc.) need to be developed. Elastomer seals with both unidirectional and reciprocating motion offer a fruitful application for the elastohydrodynamics of low modulus materials.

Anderson, W. J.↗
NASA NTRS1990

Spiral lead platen robotic end effector

A robotic end effector is disclosed which makes use of a rotating platen with spiral leads used to impact lateral motion to gripping fingers. Actuation is provided by the contact of rolling pins with the walls of the leads. The use of the disclosed method of actuation avoids jamming and provides excellent mechanical advantage while remaining light in weight and durable. The entire end effector is compact and easily adapted for attachment to robotic arms currently in use.

Beals, David C.↗
NASA NTRS1972

Cross flow in a starved EHD contact

An analysis of lubrication cross flow effects under starved elastohydrodynamic conditions is presented. Starvation is defined as any operating condition such that an increase in oil available to the contact will result in an increase in film thickness. Starved EHD behavior is considered in several situations: (1) when no new oil enters the contact, and (2) when a step change in one of the rolling parameters is introduced at an equilibrium contact. Based on the fact that important oil flow within the Hertz zone is across the rolling contact direction, it is possible to formulate a simple theory which explains quantitatively some aspects of starved ball bearing behavior.

Kingsburg, E. P.↗
NASA NTRS2015

Superelastic Ball Bearings: Materials and Design to Avoid Mounting and Dismounting Brinell Damage in an Inaccessible Press-fit Application-: Detailed Analysis - II

Rolling element bearings utilized in precision rotating machines require proper alignment, preload, and interference fits to ensure overall optimum performance. Hence, careful attention must be given to bearing installation and disassembly procedures to ensure the above conditions are met. Usually, machines are designed in such a way that bearings can be pressed into housings or onto shafts through the races without loading the rolling elements. However, in some instances, either due to limited size or access, a bearing must be installed or removed in such a way that the load path travels through the rolling elements. This can cause high contact stresses between the rolling elements and the races and introduces the potential for Brinell denting of the races. This paper is a companion to the Part I paper by the authors that discusses material selection and the general design philosophy for the bearing. Here, a more in-depth treatment is given to the design of a dent-resistant bearing utilizing a superelastic alloy, 60NiTi, for the races. A common bearing analysis tool based on rigid body dynamics is used in combination with finite element simulations to design the superelastic bearing. The primary design constraints are prevention of denting and avoiding the balls riding over the edge of the race groove during a blind disassembly process where the load passes through the rolling elements. Through an iterative process, the resulting bearing geometry is tailored to improve axial static load capability compared to a deep-groove ball bearing of the same size. The results suggest that careful selection of materials and bearing geometry can enable blind disassembly without damage to the raceways, which is necessary in the current application (a compressor in the International Space Station Environmental Control and Life Support System), and results in potential design flexibility for other applications, especially small machines with miniature bearings.

metals↗
NASA NTRS1985

Thermal traction contact performance evaluation under fully flooded and starved conditions

Ultra high speed traction tests were performed on two traction fluids commonly employed. Traction data on these fluids is required for purposes of traction drive design optimization techniques. To obtain the traction data, an existing twin disc traction test machine was employed. This machine was modified to accommodate the range of test variables. All the data reported was obtained under conditions of side slip, a technique whereby only low power levels are required to simulate real traction drive contacts. Theoretical traction predictions were performed for a representative number of curves that showed the influence of rolling velocity, of contact pressure and of aspect ratio. To establish the accuracy of the thermal model the predictions were performed ith increasing levels of independence of experimentally determined parameters. In the final resulting prediction only two non linear thermal parameters were used for the prediction of 15 different traction curves covering the entire range of variables as used in the investigation, with the exception of the influence of asperity traction. Comparison of these theoretical curves and corresponding experimental traces show very good agreement.

Tevaarwerk, J. L.↗
NASA NTRS1991

Quantifying oil filtration effects on bearing life

Rolling-element bearing life is influenced by the number, size, and material properties of particles entering the Hertzian contact of the rolling element and raceway. In general, rolling-element bearing life increases with increasing level of oil filtration. Based upon test results, two equations are presented which allow for the adjustment of bearing L(sub 10) or catalog life based upon oil filter rating. It is recommended that where no oil filtration is used catalog life be reduced by 50 percent.

Needelman, William M.↗
NASA NTRS1975

Silicon nitride used as a rolling-element bearing material

Rolling-element fatigue tests were conducted with hot-pressed silicon nitride to determine its ability to withstand concentrated contacts in rolling-element bearings. If hot-pressed silicon nitride is used for both balls and races, attention must be paid to fitting both shaft and bearing housing.

Parker, R. J.↗
NASA NTRS2018

Lifetimes of Multiply Alkylated Cyclopentane Oil in Contact with Various Metals, Evaluated with Vacuum Spiral Orbit Tribometer

The dependence of the lifetimes of small quantities of a Multiply Alkylated Cyclopentane (MAC) lubricant oil, Pennzane (Registered Trademark) 2001A (Nye Lubricants, Inc.), in rolling and sliding contact with different metals was evaluated with a vacuum spiral orbit tribometer. The metals were the bearing alloys 52100 steel, 440C steel, 17-4 PH steel and Nitinol 60 and the elements chromium, vanadium and titanium. The lifetimes of the lubricant oil on different metals fell into distinct groups with 52100 greater than 440C approx. Nitinol 60 greater than 17-4 PH for the order of the lifetimes of the steels and chromium greater than vanadium greater than titanium for the order of the lifetimes for the elements. The limited life of the small quantities of oil is assumed to be due to its consumption by the tribochemical reaction of the oil with the different metal bearing materials. The lifetimes are then inversely related to the reaction rates of the oil molecules with the various metals: the longest life of 52100 steel having the lowest reaction rate and the shortest life of titanium having the highest reaction rate. Mechanisms for the tribochemical reactions are discussed.

lubrication↗