Search NASA⌕ Search

SEARCH · Search NASA

Results for “Friction”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 433 records · Page 24
All sourcesNASA NTRSDOE OSTI
NASA NTRS1972

Studies on the frictional behavior of magnetic recording tapes

Methods were developed for measuring frictional forces acting on a magnetic tape in motion or at rest, as well as the extent of stick slip. The effects of factors such as temperature, humidity, kind of gaseous atmosphere, and tape speed on the frictional interaction between various tapes and heads were investigated. Results were instrumental in the selection of a tape for the Mariner Mars 1971 spacecraft. Studies are reported on the stick slip behavior of tapes and the performance of a metallic tape, compared with the usual plastic tapes.

Kalfayan, S. H.↗
NASA NTRS1972

Effect of polarity of electric current on friction behavior of two gallium-lubricated tantalum slipring assemblies

Computer-processed data from low-speed (10 rpm) slipring experiments with two similar (but of opposite polarity) gallium-lubricated tantalum slipring assemblies (hemisphere against disk) carrying 50 amperes dc in vacuum (10 to the minus 9th power torr) showed that the slipring assembly with the anodic hemisphere had significantly lower peak-to-peak values and standard deviations of coefficient-of-friction samples (a measure of smoothness of operation) than the slipring assembly with the cathodic hemisphere. Similar data from an experiment with the same slipring assemblies running currentless showed more random differences in the frictional behavior between the two assemblies.

Przybyszewski, J.↗
NASA NTRS1972

Pressure-gradient effects on hypersonic turbulent skin friction and boundary-layer profiles.

Local skin friction, total-temperature profiles, and pitot-pressure profiles were measured on the wall of a Mach-7.4 wind tunnel. The wall to adiabatic wall temperature ratio was varied from 0.3 to 0.5. Boundary-layer characteristics were compared with those predicted by a finite-difference method. Local skin friction was predicted to within 15%. Pressure-gradient effects on the temperature and Mach number distributions and the shape factor (displacement thickness/momentum thickness) were underpredicted, but the velocity distributions were closely predicted.

Hopkins, E. J.↗
NASA NTRS1971

Possible flow regimes of adiabatic one-dimensional compressible fluid flow with friction in convergent and divergent ducts.

An analytical solution for the compressible one-dimensional flow in convergent and divergent ducts with friction is obtained. It is found that a nondimensional parameter, N, can be formed using the friction factor, duct half-angle and the ratio of specific heats of the gas. Seven flow regimes are describable with the solution, based on certain bounds on the magnitude of N. The regimes are discussed and corollary data are presented graphically.

Shouman, A. R.↗
NASA NTRS1973

The atomic nature of polymer-metal interactions in adhesion, friction and wear

Adhesion experiments with polytetra-fluoroethylene (PTFE) and polyimide contacting tungsten indicate that the polymers bond chemically to the clean metal surface. Polymer chain fragments which transfer to the surface of tungsten in field ion microscopy adhesion studies are highly oriented. Auger emission spectroscopy of PTFE transfer films to various metal surfaces indicates that the PTFE is bonded to the metal surface via the carbon atom. With PTFE in sliding contact with different orientations of aluminum, metal orientation is found to influence surfaces in sliding. The lowest friction and least amount of surface damage is detected on the highest atomic density (111) plane. The friction process itself can initiate polymer film formation from simple organic molecules.

Buckley, D. H.↗
NASA NTRS1972

Friction at small displacement.

Low contact resistance between metal surfaces is often observed in spite of interposed lubricant and/or oxide films. To study this effect an apparatus is used with which normal force and tangential microdisplacement are applied between a small lead rider and a gold flat with various surface film conditions. Under nonoxidized and nonlubricated conditions, and with either oxide or stearic acid lubricant film alone, friction is high and contact resistance is low. With oxide and lubricant together, friction is much lower and slide is smooth, but contact resistance remains low and Ohm's law is obeyed. The results are consistent with Greenwood's theory of contact resistance for a cluster of minute metallic contact spots within the load-supporting area. The contact resistance of such a cluster is indistinguishable, for practical purposes, from that given by complete metallic contact.

Campbell, W. E.↗
NASA NTRS1973

Friction, wear, and noise of slip ring and brush contacts for synchronous satellite use.

A program is being conducted for testing of slip rings for synchronous orbit application. Instrumentation systems necessary for monitoring electrical noise, friction, and brush wear at atmospheric pressure and at less than 50 nanotorr have been developed. A multiplex scheme necessary for the simultaneous recording of brush displacement, friction, and electrical noise has also been developed. Composite brushes consisting of silver-molybdenum disulfide-graphite and silver-niobium diselenide-graphite have been employed on rings of coin silver and rhodium plate. Brush property measurements made included measurement of density, electrical resistivity, shear strength, and microstructure.

Lewis, N. E.↗
NASA NTRS1974

A general review of concepts for reducing skin friction, including recommendations for future studies

Four main concepts which have significantly reduced skin friction in experimental studies are discussed; suction, gaseous injection, particle additives, and compliant wall. It is considered possible that each of these concepts could be developed and applied in viable skin friction reduction systems for aircraft application. Problem areas with each concept are discussed, and recommendations for future studies are made.

Fischer, M. C.↗
NASA NTRS1974

Internal friction measurement in high purity tungsten single crystal

Internal friction peaks observed after small deformation in high purity tungsten single crystals between liquid helium temperature and 800 K in the frequency range 30-50 KHz, are studied as a function of orientation. An orientation effect is observed in the internal friction spectra due to the creation of internal stresses. The elementary processes related to these peaks are discussed in terms of kink generation and geometric kink motion on screw and edge dislocations in an internal stress field.

Rieu, G. E.↗
NASA NTRS1974

Dynamic-scanning-electron-microscope study of friction and wear

A friction and wear apparatus was built into a real time scanning electron microscope (SEM). The apparatus and SEM comprise a system which provides the capability of performing dynamic friction and wear experiments in situ. When the system is used in conjunction with dispersive X-ray analysis, a wide range of information on the wearing process can be obtained. The type of wear and variation with speed, load, and time can be investigated. The source, size, and distribution of wear particles can be determined and metallic transferal observed. Some typical results obtained with aluminum, copper, and iron specimens are given.

Brainard, W. A.↗
NASA NTRS1974

The atomic nature of polymer-metal interactions in adhesion, friction and wear

The adhesion, friction, and wear behavior of the solid polymers PTFE and polyimide in contact with various metals were studied using field ion microscopy, Auger emission spectroscopy, and scanning electron microscopy. Results indicate that the polymers will transfer to a clean tungsten surface on simple tough contact, forming a chemical bond. With PTFE, it is hypothesized that the bonding is of the carbon to the metal surface, while with the polyimide, both oxygen and carbon bonding to the tungsten surface are possible. In sliding contact, the friction process itself can initiate polymer film formation. The formation of such films has been suggested as a form of extreme pressure lubrication.

Buckley, D. H.↗
NASA NTRS1974

Study of Friction Properties of Lunar Surface Material and Its Analogs

A description is given of instruments for determining the friction properties of the surficial layer of lunar surface material returned by the Luna 16 automatic lunar station, as well as the friction properties of its analogs: andesite-basaltic sand and basalts. The experimental method and results are presented.

Ye A Dukhovskoy↗
NASA NTRS1975

Experimental measurements of skin friction on upper surface blown wing

An experimental investigation was conducted to obtain skin-friction measurements on a wing with a circular jet exhausting above it. A Preston tube was used to determine the local shear stress at a point on the wing's upper surface. Data were obtained for four nozzle pressures and four vertical displacements of the jet above the wing. The results indicated that the highest skin-friction values occurred with the jet closest to the wing and with the highest nozzle pressure. These data trends were validated by calculations which combined two-dimensional, turbulent boundary-layer theory with axisymmetric co-flowing jet theory.

Miner, D. D.↗
NASA NTRS1975

Friction and wear of metals in contact with pyrolytic graphite

Sliding friction experiments were conducted with gold, iron, and tantalum single crystals sliding on prismatic and basal orientations of pyrolytic graphite in various environments, including vacuum, oxygen, water vapor, nitrogen, and hydrogen bromide. Surfaces were examined in the clean state and with various adsorbates present on the graphite surfaces. Auger and LEED spectroscopy, SEM, and EDXA were used to characterize the graphite surfaces. Results indicate that the prismatic and basal orientations do not contain nor do they chemisorb oxygen, water vapor, acetylene, or hydrogen bromide. All three metals exhibited higher friction on the prismatic than on the basal orientation and these metals transferred to the atomically clean prismatic orientation of pyrolytic graphite. No metal transfer to the graphite was observed in the presence of adsorbates at 760 torr. Ion bombardment of the graphite surface with nitrogen ions resulted in the adherence of nitrogen to the surface.

Buckley, D. H.↗
NASA NTRS1975

Friction and wear of carbon-graphite materials for high energy brakes

Caliper-type brakes simulation experiments were conducted on seven different carbon-graphite material formulations against a steel disk material and against a carbon-graphite disk material. The effects of binder level, boron carbide (B4C) additions, graphite fiber additions, and graphite cloth reinforcement on friction and wear behavior were investigated. Reductions in binder level and additions of B4C each resulted in increased wear. The wear rate was not affected by the addition of graphite fibers. Transition to severe wear and high friction was observed in the case of graphite-cloth-reinforced carbon sliding against a disk of similar composition. This transition was related to the disruption of a continuous graphite shear film that must form on the sliding surfaces if low wear is to occur. The exposure of the fiber structure of the cloth constituent is believed to play a role in the shear film disruption.

Bill, R. C.↗
NASA NTRS1976

Friction and wear of titanium alloys and copper alloys sliding against titanium 6-percent-aluminum - 4-percent-vanadium alloy in air at 430 C

Experiments were conducted to determine the friction and wear characteristics of aluminum bronzes and copper-tin, titanium-tin, and copper-silver alloys sliding against a titanium-6% aluminum-4% vanadium alloy (Ti-6Al-4V). Hemispherically tipped riders of aluminum bronze and the titanium and copper alloys were run against Ti-6Al-4V disks in air at 430 C. The sliding velocity was 13 cm/sec, and the load was 250 g. Results revealed that high tin content titanium and copper alloys underwent significantly less wear and galling than commonly used aluminum bronzes. Also friction force was less erratic than with the aluminum bronzes.

Wisander, D. W.↗
NASA NTRS1976

The metal to metal interface and its effect on adhesion and friction

The nature of the interface, adhesion and friction properties of noble metals, platinum metals, Group IV (B) metals and transition metals were considered. The surface chemical activity of the noble and platinum metals is shown to effect metal to metal interfaces as does a valance bonding in the transition metals. With the Group IV (B) metals the degree of metallic nature of the elements is shown to effect interfacial behavior. The effect of surface segregation of alloy constituents such as silicon in iron and its influence on the metal to metal interface is discussed. In addition the effect of alloy constituents on changes in bulk properties such as transformations in tin are shown to effect interfacial adhesion and friction behavior.

Buckley, D. H.↗