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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 199 records · Page 11
All sourcesNASA NTRSDOE OSTI
NASA NTRS1978

NASTRAN analysis of a wheel-rail loading on its foundation

One type of azimuth bearing for a large ground antenna (100 m) will consist of steel wheels, mounted at four corners of the alidade, rolling on a circular flat rail which provides the vertical restraints; a radial constraining bearing at the center of the alidade provides the horizontal restraints. One important design feature is the compressive stresses in the grout or concrete foundation under the wheel-rail load. A finite element analysis check was made of a particular design that consists of a steel rail resting on a concrete foundation. Symmetry was assumed as much as possible in order to minimize the models, but meaningful element sizes were used. Recently developed isoparametric hexahedron elements available in the NASTRAN computing program, which minimizes the number of elements required while maintaining the accuracy of the computed stresses, were used with two versions of NASTRAN. Test cases to check with the analytical solutions were made. A side loading was also applied to calculate the increase in the concrete stresses.

Katow, M. S.↗
NASA NTRS1979

Operational loopwheel suspension systems for Mars Rover demonstration model: Loopwheel failure report

The results are presented from the analysis of a failure which occurred in the fiberglass loop of one of the Loopwheel traction elements delivered to the Jet Propulsion Laboratory (JPL) for use on the JPL Mars Rover demonstration model. The loop failed in compression in the outer fibers forming a hinge which, through cycling, caused the inner fibers to break. The probable cause of this failure was the load being introduced as point loads at the center of the loop causing high compressive stresses and early buckling. To decrease the stress level and delay buckling, the tread lugs can be reshaped so that the entire lug contacts the ground when the loop is loaded. This can be accomplished through removal of lug material, starting with zero removal at the outer edge and linearly increasing to one-half of the lug thickness at the center.

West, E. J. M.↗
NASA NTRS1978

Lunar mare ridge orientation - Implications for lunar tectonic models

Four circular mare basins were selected for ridge orientation analysis: Crisium, Imbrium, Serenitatis and Tranquillitatis. In each basin a central area was identified in which ridges were neither concentric with basin edges nor seemed to be extensions of significant highland structural trends. Ridge orientations in these central areas and in the remaining marginal areas were measured separately and rose diagrams plotted for each. Rose diagrams of ridge orientations in the four circular mare basins show a narrow dispersion with a statistical average nearly north. Trends of basin margin ridges have a high deviation and are polymodal with maxima in the northwest, north and northeast directions. Mare ridges which display a preferred northern trend result from an east-west compressive stress field.

Fagin, S. W.↗
NASA NTRS1980

Effects of method of loading and specimen configuration on compressive strength of graphite/epoxy composite materials

Three test schemes were examined for testing graphite/epoxy (Narmco T300/5208) composite material specimens to failure in compression, including an adaptation of the IITRI "wedge grip" compression fixture, a face-supported-compression fixture, and an end-loaded-coupon fixture. The effects of specimen size, specimen support arrangement and method of load transfer on compressive behavior of graphite/epoxy were investigated. Compressive stress strain, strength, and modulus data obtained with the three fixtures are presented with evaluations showing the effects of all test parameters, including fiber orientation. The IITRI fixture has the potential to provide good stress/strain data to failure for unidirectional and quasi-isotropic laminates. The face supported fixture was found to be the most desirable for testing + or - 45 s laminates.

Clark, R. K.↗
NASA NTRS1982

Unidirectional Flexural Pivot

Flexural pivot deflects in only one angular direction (either clockwise or counterclockwise) and has a longer operating life than many previous designs. Pivot consists of two rings interconnected by three flat metal parallelograms welded into grooves or slots in inside diameters of rings. Springs flex to relieve compressive stress imparted by angular rotation.

Bahiman, H.↗
NASA NTRS1982

Elastic Surface Wrinkling

Instability phenomena in elastic surfaces subject to compressive stresses are examined theoretically in new report. Theory is potentially applicable to such practical problems as aircraft panel flutter, nondestructive testing, piezoelectric transducer design, distortion of optical surfaces, and tolerance studies of very precise machine parts.

Zak, M.↗
NASA NTRS1982

Glass for Solid State Devices

Glass film has low intrinsic compressive stress for isolating active layers of magnetic-bubble and other solid-state devices. Solid-state device structure incorporates low-stress glasses as barrier and spacer layers. Glass layers mechanically isolate substrate, conductor, and nickel/iron layers.

Bailey, R. F.↗
NASA NTRS1984

Walnut Hulls Clean Aluminum

Hulls inflict minimal substrate damage. Walnut hulls found to be best abrasive for cleaning aluminum surfaces prior to painting. Samples blasted with walnut hulls showed no compressive stress of surface.

Colberg, W. R.↗
NASA NTRS1983

Experimental creep data for a built-up aluminum/titanium structure subjected to heating and loading

Experimental creep, temperature, and strain data resulting from a laboratory experiment on a built-up aluminum/titanium structure are presented. The structure and the experiment are described in detail. A heating and loading experiment lasting approximately six hours is conducted on a test structure. Considerable creep strain resulted from compressive stresses in the heated skin. Large residual stresses were found after the experiment was completed. The residual stresses in the substructure frames were large enough to preclude further cycles of creep experiments with this built-up structure because of concern that the frame webs would buckle.

Jenkins, J. M.↗
NASA NTRS1983

Unidirectional flexural pivot

A pair of generally coaxial mutually rotatable cylindrical outer ring members are held in spaced-apart relationship by three parallelogram-shaped, relatively thin, flexible, flat planar spring elements. These spring elements are substantially inextensible in length and are joined to the inside of the outer ring members and held in position by arcuate inner ring segments, three for each outer ring members, which respectively span an arc of substantially 120. The parallelogram shape of the spring elements provides a slanted interconnection between the outer ring members. The direction of slant, moreover, determines in which direction the spring elements can flex or bend unidirectionally to relieve the compression stress imparted thereto by any mutual angular rotation of the outer ring members.

Bahiman, H.↗
NASA NTRS1984

Tensile Fracture of Ductile Materials

For brittle materials, circular voids play an important role relative to fracture, intensifing both tensile and compressive stresses. A maximum intensified tensile stress failure criterion applies quite well to brittle materials. An attempt was made to explore the possibility of extending the approach to the tensile fracture of ductile materials. The three dimensional voids that exist in reality are modelled by circular holes in sheet metal. Mathematical relationships are sought between the shape and size of the hole, after the material is plastically deformed, and the amount of deformation induced. Then, the effect of hole shape, size and orientation on the mechanical properties is considered experimentally. The presence of the voids does not affect the ultimate tensile strength of the ductile materials because plastic flow wipes out the stress intensification caused by them. However, the shape and orientation of the defect is found to play an important role in affecting the strain at fracture.

Pai, D. M.↗
NASA NTRS1984

Method and apparatus for gripping uniaxial fibrous composite materials

A strip specimen is cut from a unidirectional strong, brittle fiber composite material, and the surfaces of both ends of the specimen are grit blasted. The specimen is then placed between metal load transfer members having grit blasted surfaces. Sufficient compressive stress is applied to the load transfer members to prevent slippage during testing at both elevated temperatures and room temperatures. The need for adhesives, load pads, and other secondary composite processing is eliminated. This gripping system was successful in tensile testing, creep rupture testing, and fatigue testing uniaxial composite materials at 316 C.

Whittenberger, J. D.↗
NASA NTRS1983

Carbon, oxygen and their interaction with intrinsic point defects in solar silicon ribbon material: A speculative approach

Some background information on intrinsic point defects is provided and on carbon and oxygen in silicon in so far as it may be relevant for the efficiency of solar cells fabricated from EFG ribbon material. The co-precipitation of carbon and oxygen and especially of carbon and silicon self interstitials are discussed. A simple model for the electrical activity of carbon-self-interstitial agglomerates is presented. The self-interstitial content of these agglomerates is assumed to determine their electrical activity and that both compressive stresses (high self-interstitial content) and tensile stresses (low self-interstitial content) give rise to electrical activity of the agglomerates. The self-interstitial content of these carbon-related agglomerates may be reduced by an appropriate high temperature treatment and enhanced by a supersaturation of self-interstitials generated during formation of the p-n junction of solar cells. Oxygen present in supersaturation in carbon-rich silicon may be induced to form SiO, precipitates by self-interstitials generated during phosphorus diffusion. It is proposed that the SiO2-Si interface of the precipates gives rise to a continuum of donor stables and that these interface states are responsible for at least part of the light inhancement effects observed in oxygen containing EFG silicon after phosphorus diffusion.

Goesele, U.↗
NASA NTRS1983

Cooling and deformation of sulfur flows

A simple one-dimensional cooling analysis is used to consider the cooling of a flow of pure sulfur on the Ionian surface by a combination of upward radiation and downward conduction, and some speculations on the nature of surface structures and optical properties for such a flow are made. It is concluded that surface folding caused by compressive stresses, crustal foundering due to tensile fracturing and density inversions, and local turbulence may result in regularly spaced surface ridges periodically interrupted by upwellings of liquid sulfur onto the frozen surface of the flow. The model suggests that although the color of the surface crust of a quickly quenched sulfur flow will not necessarily reflect the local internal temperature of the flow, diapiric upwellings and convection from beneath this crust should indicate the progressive cooling of the inner, more fluid zones of the flow.

Fink, J. H.↗
NASA NTRS1986

Measure of displacement around holes in composite plates subjected to quasi-static compression

Contour maps of thickness changes were obtained for three quasi-isotropic graphite-epoxy plates with central holes, loaded in compression. Thickness changes were determined for six load increments from nearly zero to within a few percent of the failure load. The largest change of thickness occurred near the hole but not at the boundary of the hole. Below 90 percent of the failure load, the thickness changes were nearly proportional to load. Irregularities of thickness changes occurred in zones of compressive stresses and they were attributed to localized fiber buckling. A new optical technique was developed to measure thickness changes with high sensitivity. It utilizes a comparatively simple means of holographic interferometry on both sides of the specimen, followed by additive moire to obtain thickness changes as the sum of the out-of-plane displacements. Sensitivity was 12.5 x 10 to the -6 power in. per fringe order. The fringe patterns represent thickness changes uniquely, even when specimen warpage and consequent out-of-plane displacements are very large.

Duke, J. C., Jr.↗
NASA NTRS1986

Postbuckling behavior of longitudinally compressed orthotropic plates with three-dimensional flexibility

Postbuckling results for the average longitudinal compressive stress vs applied displacement are obtained for aluminum (isotropic), aluminum/epoxy (quasi-isotropic), and 45-deg graphite/epoxy (orthotropic) plates using classical (Kirchhoff) and conventional transverse shearing theories. An analysis of the results obtained shows that, in the postbuckling range, the classical theory cannot provide reasonably accurate results even for thin plates.

Stein, M.↗
NASA NTRS1986

Orientation, relative age, and extent of the Tharsis Plateau ridge system

The orientations of the Tharsis Plateau ridge system on Mars and the symmetry of the inferred compressive stress field, the relative ages of the compressional events that generated the ridges, and the extent of Tharsis-related compressional deformation are investigated. Models for the origin of stresses in the Tharsis region are studied in relation to the formation of the ridges. The data indicate either that the Tharsis ridge system did not form in response to a single regional compressional event with a single stress center or that the majority of the ridge system did form in a single event but with locally controlled deflections in the generally radially oriented stress field. Superposition relationships and relative ages suggest that the compressional stresses that produced the ridges occurred after the emplacement of the ridged plains volcanic units but did not extend beyond the time of emplacement of the Syria Planum Formation units or the basal units of the Tharsis Montes Formation.

Watters, T. R.↗
NASA NTRS1987

Martian volcanism: Festoon-like ridges on terrestrial basalt flows and implications for Mars

The Fink and Fletcher, and Fink model was used to assess and compare flow rheology for two terrestrial basalt flows and one Martian flow with previous studies. Based on the morphologic similarities between the Martian flows and the Icelandic flows and knowledge of the emplacement of the terrestrial flows, the flows west of Arsia Mons are considered to have been emplaced as large sheet flows from basaltic flood style eruptions. Festoon ridges represent folding of the surface crust in the last stages of emplacement when viscosities would be high due to cooling. Alternatively, the lava may have had a high crystallinity or was erupted at low temperatures. In addition, increased compressive stress behind halted flow fronts or in ponded areas may have contributed to ridge formation.

Theilig, E.↗