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At least 1,531 records · Page 85
All sourcesNASA NTRSDOE OSTI
NASA NTRS1974

Observations on the deformation-induced beta internal friction peak in bcc metals

During a study of the effects of electron irradiation on the tungsten alpha mechanism, internal friction data were obtained. The data indicate that the mechanism underlying the beta peak does not possess the relaxation parameters generally associated with a simple dislocation process. The significance of the experimental results in the light of beta observations in other metals is discussed. It is suggested that the beta peaks in deformed bcc metals are the anelastic result of the thermally-activated relaxation of deformation-induced imperfections.

Dicarlo, J. A.↗
NASA NTRS1973

Solar tidal friction and satellite loss

This paper treats the dynamical evolution of a satellite orbiting a primary that is being despun by solar tidal friction. The results are then applied to Mercury and Venus. It is concluded that a wide variety of satellites would not have survived the solar tidal braking of these planets. Hence, the absence of satellites around Mercury and Venus is not a compelling reason for thinking that this has always been the situation. Satellites are lost by orbital decay and impact with the primary. It is likely that Mercury would retain a record of such an event on its surface.

Ward, W. R.↗
NASA NTRS1975

A hot-wire surface gage for skin friction and separation detection measurements

A heated-element, skin-friction gage employing a very low thermal conductivity support is described. It is shown that the effective dimension of the gage in the stream direction in only 0.06 mm, including the effects of heat conduction in the supporting material. Because of its small size, the calibration of the gage is independent of the kind of boundary-layer flow (whether laminar or turbulent) and is insensitive to pressure gradients. Construction tolerances can be maintained so that a single universal calibration can be applied. Multiple gages, sufficiently closely spaced so as to interfere with each other, are shown to provide accurate determinations of the locations of the points of boundary-layer separation and reattachment.

Rubesin, M. W.↗
NASA NTRS1974

Ball motion and sliding friction in an arched outer race ball bearing

The motion of the ball and sliding friction in an arched outer-race ball bearing under thrust load is determined. Fatigue life evaluations were made. The analysis is applied to a 150 millimeter bore ball bearing. The results indicated that for high speed-light load applications the arched bearing has significant improvement in fatigue life over that of a conventional bearing. An arching of 0.254 mm (0.01 in.) was found to be an optimal. For an arched bearing it was also found that a considerable amount of spinning occurs at the outer race contacts.

Hamrock, B. J.↗
NASA NTRS1975

Experimental verification of turbulent skin friction reduction with compliant walls

Preliminary compliant wall skin friction test results obtained in a low-turbulence pressure tunnel are reported. Compliant surface skins consisted of 0.0025 cm thick mylar, stretched under tension and area-bonded or longitudinally strip-bonded with silicone rubber adhesive to polyurethane foam. Mean velocity and fluctuating survey data were obtained with a single slanted hot wire. Mean velocity profiles for the area-bonded mylar surface skins indicated up to a 20% reduction in boundary-layer thickness (and lower momentum thickness) over rigid surfaces. This reduction in boundary-layer thickness indicates that a drag reduction occurred. In addition, a 16% reduction in wall shear was evident for the mylar/compressor foam compliant surface.

Weinstein, L. M.↗
NASA NTRS1975

Friction and abrasion of elastomeric materials

An abrasion apparatus is described. Experimental measurements are reported for four representative elastomeric materials, including a typical high-quality tire tread material and a possible replacement material for aircraft tire treads based on transpolypentenamer (TPPR). Measurements are carried out at different levels of frictional work input, corresponding to different severities of wear, and at both ambient temperature and at 100 C. Results indicate the marked superiority in abrasion resistance of the material based on TPPR, especially at 100 C, in comparison with the other materials examined.

Gent, A. N.↗
NASA NTRS1975

In-flight friction and wear mechanism

A unique mechanism developed for conducting friction and wear experiments in orbit is described. The device is capable of testing twelve material samples simultaneously. Parameters considered critical include: power, weight, volume, mounting, cleanliness, and thermal designs. The device performed flawlessly in orbit over an eighteen month period and demonstrated the usefulness of this design for future unmanned spacecraft or shuttle applications.

Devine, E. J.↗
NASA NTRS1976

Simulated studies of wear and friction in total hip prosthesis components with various ball sizes and surface finishes

Experiments were conducted on a newly designed total hip joint simulator. The apparatus closely simulates the complex motions and loads of the human hip in normal walking. The wear and friction of presently used appliance configurations and materials were determined. A surface treatment of the metal femoral ball specimens was applied to influence wear. The results of the investigation indicate that wear can be reduced by mechanical treatment of metal femoral ball surfaces. A metallographic examination and surface roughness measurements were made.

Swikert, M. A.↗
NASA NTRS1975

Flush-mounted hot-wire gage for skin friction and separation detection measurements

A heated-element skin-friction gage employing a very low thermal-conductivity support is described. It is shown that the effective dimension of the gage in the stream direction is only 0.06 mm, including the effects of heat conduction in the supporting material. Because of its small size, the calibration of the gage is independent of the kind of boundary-layer flow (whether laminar or turbulent) and is insensitive to pressure gradients. Construction tolerances can be maintained so that a single universal calibration can be applied. Multiple gages, sufficiently closely spaced so as to interfere with each other, are shown to provide accurate determinations of the location of the points of boundary-layer separation and reattachment.

Rubesin, M. W.↗
NASA NTRS1976

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

The paper considers the interface between two bulk metals and the effect of this interface on adhesive bonding, resistance to tangential displacements, friction and the interfacial transport from one surface to another. Using Auger emission spectroscopy, field ion microscopy, and low energy electron diffraction techniques, the influence of surface orientation, lattice registry, crystal lattice structure and defects, metal surface chemistry and alloying on the characteristics of the interface was studied for noble, platinum, transition, and Group 4B metals. With dissimilar metals in contact, epitaxial transfer of the cohesively weaker to the cohesively stronger metal has been observed. Surface chemical activity of the noble and platinum metals is shown to affect interfacial behavior as does a valence bonding in the transition metals, and the degree of metallic nature in the Group 4B elements. Alloying elements, e.g., Si and Fe, can alter interfacial behavior by segregation to the surface of metals or by altering bulk properties such as crystal transformation kinetics.

Buckley, D. H.↗
NASA NTRS1977

Effect of ion-plated films of germanium and silicon on friction, wear, and oxidation of 52100 bearing steel

Friction and wear experiments were conducted with ion plated films of germanium and silicon on the surface of 52100 bearing steel both dry and in the presence of mineral oil. Both silicon and germanium were found to reduce wear, with germanium being more effective than silicon. An optimum film thickness of germanium for minimum wear without surface crack formation was found to be approximately 400 nanometers (4000 A). The presence of silicon and germanium on the 52100 bearing steel surface improved resistance to oxidation.

Buckley, D. H.↗
NASA NTRS1977

Friction and wear behavior of graphite fiber reinforced polymide composites

The friction and wear rate characteristics of 50/50 (weight percent) graphite fiber polyimide composites were studied by sliding metallic hemispherically tipped riders against disks made from the composites. Two different polyimides and two different graphite fibers were evaluated. Also studied were such variables as the effect of moisture in an air atmosphere; the effect of temperature; and the effect of different sliding speeds. In general, wear to the the metallic riders was negligible, and composite wear increased at a constant rate as a function of number of sliding cycles.

Fusaro, R. L.↗
NASA NTRS1977

X-Ray photoelectron spectroscopy study of radiofrequency-sputtered titanium, carbide, molybdenum carbide, and titanium boride coatings and their friction properties

Radiofrequency sputtered coatings of titanium carbide, molybdenum carbide and titanium boride were tested as wear resistant coatings on stainless steel in a pin on disk apparatus. X-ray photoelectron spectroscopy (XPS) was used to analyze the sputtered films with regard to both bulk and interface composition in order to obtain maximum film performance. Significant improvements in friction behavior were obtained when properly biased films were deposited on deliberately preoxidized substrates. XPS depth profile data showed thick graded interfaces for bias deposited films even when adherence was poor. The addition of 10 percent hydrogen to the sputtering gas produced coatings with thin poorly adherent interfaces. Results suggest that some of the common practices in the field of sputtering may be detrimental to achieving maximum adherence and optimum composition for these refractory compounds.

Brainard, W. A.↗
NASA NTRS1976

Apparatus for measuring internal friction Q factors in brittle materials

A flexural analog of the torsion pendulum for measuring the Young's modulus and the internal friction Q factor of brittle materials has been developed for Q greater than 10 to the 3rd measurements at a zero static stress and at 10 to the -7th strains of brittle materials in the Hz frequency range. The present design was motivated by the desire to measure Q in fragile lunar return samples at zero static stress to shed light on the anomalously low attenuation of seismic waves on the moon. The use of the apparatus is demonstrated with data on fused silica and on a terrestrial analog of lunar basalt.

Tittmann, B. R.↗
NASA NTRS1976

Internal friction and velocity measurements

The Q of a lunar basalt sample was measured under varying vacuum conditions, and it was found that even at pressures as low as 10 to the -7th to 10 to the -10th torr, substantial increases in Q with decreasing pressure are observed, while the resonant frequency increases only slightly. This suggests that only small amounts of volatiles are sufficient to increase the internal friction (lower the Q) dramatically. The technique of vibrating encapsulated samples in the torsional mode was used to measure Q of terrestrial rocks as a function of hydrostatic pressure under lunar vacuum conditions. Young's modulus measurements in the temperature range 25-600 C under a variety of conditions including high vacuum show no evidence of any irreversibility upon temperature cycling and no indication that the high Q-values obtained are associated with any permanent structure changes such as the formation of lossless 'welded' contacts.

Tittmann, B. R.↗
NASA NTRS1977

Friction and wear behavior of graphite fiber reinforced polyimide composites

The friction and wear rate characteristics of 50/50 (weight per cent) graphite fiber-polyimide composites were studied by sliding metallic hemispherically tipped riders against disks made from the composites. Two different polyimides and two different graphite fibers were evaluated. Also studied were such variables as the effect of adding 10 per cent weight additions of powdered (CF-1.1)n, CdI2, or CdO, the effect of moisture in an air atmosphere, the effect of temperature, and the effect of different sliding speeds. In general, wear to the metallic riders was negligible and composite wear increased at a constant rate as a function of number of sliding cycles.

Fusaro, R. L.↗
NASA NTRS1977

Friction factor for isothermal and nonisothermal flow through porous media

Measurements were performed to determine the pressure drops for gaseous flow through porous materials of different microstructures, porosities, and thickness under isothermal and nonisothermal conditions at various temperature levels. Results were satisfactorily correlated by a simple equation relating the friction factor to the Reynolds number and porosities.

Koh, J. C.↗
NASA NTRS1978

Friction and wear of several compressor gas-path seal movements

Rub interaction experiments were conducted on a series of sintered and plasma sprayed compressor gas path seal materials in contact with Ti-6Al-4V blade tip and knife edge rotors. The most rub tolerant materials investigated were sintered Nichrome and plasma sprayed nickel 25 percent graphite. The effectiveness of providing a compliant substrate for dense seal material coatings was also demonstrated. In general, it was observed that rotor wear and high frictional energy generation rates accompanied smearing or surface densification of the materials investigated. The onset of smearing was sensitive to rub interaction parameters and seal geometry. Two complementary models were proposed to account for the smearing trends. One is based on thermal effects, the other on particulate escape effects. They were shown to be consistent with the experimental evidence at hand, and together they predict that smearing, with the onset of high energy rub conditions, is favored when incursion rates (radial motion) are low, incursion depths are high, the seal geometry is of a knife-edge character, and the seal particle size is small.

Bill, R. C.↗