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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 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
NASA NTRS1984

Nondestructive evaluation of residual stress in low-carbon steel, introduction

The degree of insensitivity of the temperature dependence method to variations in preferred orientations in A508 low carbon steel specimens was determined. A pulsed phase locked loop was used to measure ultrasonic velocity in these specimens in the temperature range of 50 C below and above room temperature. Results are given in tables and indicate that the temperature dependence of ultrasonic longitudinal velocity in four specimens cut at different angles remains unchanged as a function of orientation within + or -2%. The variation of temperature dependence of ultrasonic shear velocity in the A508 steel as a function of applied stresses was also measured. Results show that values at zero stress are equal regardless of whether the polarization direction is parallel or perpendicular to the direction in which the stress is applied.

Source record↗
NASA NTRS1984

Strain analysis of the Leoville chondrite and conditions in asteroidal interiors

Deformed chondrules in the Leoville carbonaceous chondrite define a preferred orientation, also recognized previously in other CV3 chondrites. Identifying the strain mechanism is necessary for understanding the conditions which caused this compressional shortening. Luckly, the major mineralogical constituent of CV3 meteorites is olivine, for which experimental data on strain mechanisms exist. The conditions that caused strain in the olivine were obviously applicable to the whole meteorite. Possible mechanisms of olivine deformation are cataclasis, low temperature plasticity, power low creep, and diffusional flow, each of which occurs under different combinations of temperature and deviatoric stress. Cataclasis can be ruled out on the basis of its high deviatoric stress requirements; some fractures occur in chondrule olivines, but these may have formed during excavation or impact. Low temperature plasticity and power low creep occur by means of various types of lattice dislocations. However, methods of thermal decoration and chemical etching of dislocations failed to indicate evidence for either mechanism. Thus, the inference is that diffusional flow, characteristic of low to moderately high temperatures and low deviatoric stress, was the major deformation mechanism.

Cain, P. M.↗
NASA NTRS1984

X-radiography of slices of the Allende Meteorite

A 2.2 kg fragment of the Allende Meteorite was derinded and sliced by bandsawing. Several X-radiographs were made of all slices. The following features are resolved: grains of blocky troilite (bright spots), troilite rimmed chondrules (bright halos), chondrules with central vugs (dim halos), white aggregates (dark patches), and dark inclusions (medium dark patches). The number of FeS grains larger than about 0.5 mm is one per 6 + or - 1 gram of this fragment. Their concentration appears to be uniform at the 1 kg weight level, but is not uniform at the 100 g level. The number of FeS rimmed chondrules is one per 10 g. Their concentration is also nonuniform at the 100 g weight level. The number of white aggregates is roughly one per 20 g. These disc shaped objects show a distinct preferred orientation of the axis orthogonal to the plane of the disc. Chondrules with central vugs are numerous. Linear and curved arrays of chondrules, up to a few cm long, were observed. An interpretation of the observed features is given.

Smith, M. J.↗
NASA NTRS1984

Microstructural development of protective Al2O3 scales

Microstructural characteristics of Al2O3 scales grown as protective coatings on NiCrAl alloys used in jet engines are described. The alloys were pure or doped with 0.3 percent Zr or Y and oxidized in 1 atm air at 1100 C for 0.1, 1 or 20.0 hr. The scales were then examined under a microscope. Transient epitaxial scales, formed during the 0.1 hr treatment and containing Ni, Cr and Al, consisted of a mosaic of subgrains and precipitates of different phases. The Y and Zr dopants had no effect on the nucleation site locations. The appearance of intergranular porosity at 0.1 hr was exacerbated after the 1 hr treatment. A bimodal void distribution appeared after 20 hr, when no porosity was evident. The detection of local areas of preferred orientation is taken as a spur to further studies of scale growth to gain control of the grain size or even to produce single crystal scales.

Smialek, J. L.↗
NASA NTRS1986

Adsorption of O2, SO2, and SO3, on nickel oxide - Mechanism for sulfate formation

Calculations based on the atom superposition and electron delocalization molecular orbital technique suggest that O2 will adsorb preferentially end-on at an angle 45 deg from normal on a nickel cation site on the (100) surface of NiO. SO2 adsorption is also stronger on the nickel site; SO2 bonds through the sulfur atom in a plane perpendicular to the surface. Adsorption energies for SO3 on the nickel and oxygen sites are comparable in the preferred orientation in which the SO3 plane is parallel to the surface. The calculations suggest that the strength of adsorption varies as O2 greater than SO2 greater than SO3. On activation, SO3 adsorbed to an O(2-) site forms a trigonal pyramidal SO4 species which yields, with a low barrier, a tetrahedral sulfate anion. Subsequently the anion reorients on the surface. Alternative mechanisms which require the formation of Ni(3+) or O(-) are discussed. NiSO4 thus formed may play a passivating role for the corrosion of Ni at low temperatures in the SO2 + O2 + SO3 atmospheres and an active role at high temperatures, as discussed in the experimental literature.

Mehandru, S. P.↗
NASA NTRS1986

X-ray investigations related to the shock history of the Shergotty achondrite

The shock stress suffered by naturally shocked materials from the Shergotty achondrite was studied using X-ray diffraction techniques and experimentally shocked augite and enstatite as standards. The Shergotty pyroxenes revealed the formation of continuous diffraction rings, line broadening, preferred orientation of small scale diffraction domains, and other evidence of substantial lattice disorders. As disclosed by the application of Debye-Scherrer techniques, they are hybrids between single crystals and fine-grained random powders. The pyroxene lattice is very resistant to shock damage on smaller scales. While measurable lattice disaggregation and progressive fragmentation occur below 25 GPa, little additional damage is suffered from application of pressures between 30 to 60 GPa, making pressure calibration of naturally shocked pyroxenes via X-ray methods difficult. Powder diffractometer scans on pure maskelynite fractions of Shergotty revealed small amounts of still coherently diffracting plagioclase, which may contribute to the high refractive indices of the diaplectic feldspar glasses of Shergotty.

Horz, F.↗
NASA NTRS1986

Periodic amplitude variations in Jovian continuum radiation

An analysis of periodic variations in the amplitude of continuum radiation near 3 kHz trapped in the Jovian magnetosphere shows structure with periods near both five and ten hours. Contrary to a plausible initial idea, the continuum amplitudes are not organized by position of the observer relative to the dense plasma sheet. Instead, there seem to be preferred orientations of system III longitude with respect to the direction to the sun which account for the peaks. This implies a clock-like modulation of the continuum radiation intensity as opposed to a searchlight effect. The importance of the dipole longitude-solar wind alignment to the amplitude of the continuum radiation implies the source region of the radiation is near the magnetopause and may indirectly tie the generation of the radio waves to the clocklike modulation of energetic electron fluxes from Jupiter.

Kurth, W. S.↗
NASA NTRS1987

Chemically assisted ion beam etching of polycrystalline and (100)tungsten

A chemically assisted ion-beam etching technique is described which employs an ion beam from an electron-bombardment ion source and a directed flux of ClF3 neutrals. This technique enables the etching of tungsten foils and films in excess of 40 microns thick with good anisotropy and pattern definition over areas of 30 sq mm, and with a high degree of selectivity. (100) tungsten foils etched with this process exhibit preferred-orientation etching, while polycrystalline tungsten films exhibit high etch rates. This technique can be used to pattern the dispenser cathode surfaces serving as electron emitters in traveling-wave tubes to a controlled porosity.

Garner, Charles↗
NASA NTRS1987

The effect of texture on the crack growth resistance of alumina

The crack growth resistance of a textured, extruded alumina body was compared with that of an isotropic, isopressed body of similar grain size, density, and chemistry. R-curve levels reflected the preferred orientation; however, R-curve slopes (dK sub IR/d Delta a) were the same in all instances, implying a similar crack growth resistive mechanism. Three orthogonal orientations of crack growth in the two structures exhibited similar forms of K sub IR versus Delta-a curves, for which a schematic diagram for polycrystalline ceramics is proposed.

Salem, Jonathan A.↗
NASA NTRS1988

Three-dimensional trajectory analyses of two drop sizing instruments: PMS OAP and PMS FSSP

Flow induced distortions of water drop fluxes and speeds seen by the instruments were predicted by use of three dimensional flow and trajectory calculation methods. Sensitivities were determined for the instruments, in isolation and mounted under the wing of an airplane, to: water drop diameter (2 to 1000 microns), angle of attack and free stream air speed. For the optical array probe in isolation and on the airplane at 0 deg angle of attack, flux distortions of practical consequence are not found. At 4 deg airplane angle of attack, partial flow stagnation under the uptilted wing causes significant decreases in both flux and speed for cloud size droplets. For the forward scattering spectrometer probe in isolation, only marginally significant sensitivities to free stream air speed are found, and no sensitivity is found to angle of attack. Both speed and flux of cloud size droplets are predicted to be undermeasured by from 12 to 24 percent depending on airplane angle of attack. For the wing-mounted instruments, effects of flow about the instruments themselves are found to be equal in importance to effects of flow about the airplane. Preferred orientation (canting) angles of distorted water drops are found to be functions of drop size, angle of attack and air speed.

Norment, Hillyer G.↗
NASA NTRS1987

Analytical electron microscopy of extraterrestrial materials - Results from microtome sections of carbonaceous chondrites and interplanetary dust particles

The paper describes a method for embedding, sectioning, and observing two types of extraterrestrial materials, including hydrated interplanetary dust particles (IDPs) and carbonaceous chondrite meteorites. The technique, which produces large thin areas suitable for both high-resolution imaging and thin-film microanalysis, was applied to study the petrology of the IDP Ames-DE C86-11, the Murchison carbonaceous chondrite matrix, and the Allende dark inclusion. The technique makes it possible to maintain delicate interfaces, boundaries, and phase relationships between grains. Because phases are held in place, layer lattice silicates and other minerals with strong preferred orientations can be viewed in any orientation, including the orientation normal to their basal planes.

Blake, D. F.↗
NASA NTRS1987

Roosevelt County 027 - A low-shock ureilite with interstitial silicates and high noble gas concentrations

The RC027 lightly-shocked ureilite contains less than 1 percent of a fine-grained interstitial silicate that has an igneous texture indicating crystallization from an interstitial liquid. RC027 is also noted to exhibit the strongest olivine preferred-orientation thus far observed in a ureilite; its fabric is characteristic of fabrics formed by tabular minerals in a fluid laminar flow regime, and is unlike those formed by synectonic recrystallization and plastic flow. The elemental and isotopic compositions of noble gases in RC027 are typical of previously analyzed ureilites.

Goodrich, Cyrena Anne↗
NASA NTRS1987

Telescope structures - An evolutionary overview

A development history is presented for telescope structural support materials, design concepts, equatorial and altazimuthal orientational preferences, and mechanical control system structural realizations. In the course of 50 years after Galileo, the basic configurations of all reflecting telescopes was set for the subsequent 300 years: these were the Cassegrain, Gregorian, and Newtonian designs. The challenge of making a lightweight ribbed pyrex glass primary mirror for the 5-m Palomar telescope was met by von Karman's use of finite element analysis. Attention is given to the prospects for a 20-m deployable space-based reflecting telescope.

Meinel, Aden B.↗
NASA NTRS1989

Crack growth resistance of textured alumina

The crack growth resistance of a textured, extruded alumina body was compared with that of anisotropic, isopressed body of similar grain size, density, and chemistry. R-curve levels reflected the preferred orientation; however, R-curve slopes were the same in all instances, implying a similar crack growth-resistive mechanism. Three orthogonal orientations of crack growth in the two structures exhibited similar forms of K(IR) versus Delta-a curves, for which a schematic diagram for polycrystalline ceramics is proposed.

Salem, Jonathan A.↗
NASA NTRS1988

Three-dimensional trajectory analyses of two drop sizing instruments - PMS OAP and PMS FSSP

Flow induced distortions of water drop fluxes and speeds seen by the instruments were predicted by use of three dimensional flow and trajectory calculation methods. Sensitivities were determined for the instruments, in isolation and mounted under the wing of an airplane, to: water drop diameter (2 to 1000 microns), angle of attack and free stream air speed. For the optical array probe in isolation and on the airplane at 0 deg angle of attack, flux distortions of practical consequence are not found. At 4 deg airplane angle of attack, partial flow stagnation under the uptilted wing causes significant decreases in both flux and speed for cloud size droplets. For the forward scattering spectrometer probe in isolation, only marginally significant sensitivities to free stream air speed are found, and no sensitivity is found to angle of attack. Both speed and flux of cloud size droplets are predicted to be undermeasured by from 12 to 24 percent depending on airplane angle of attack. For the wing-mounted instruments, effects of flow about the instruments themselves are found to be equal in importance to effects of flow about the airplane. Preferred orientation (canting) angles of distorted water drops are found to be functions of drop size, angle of attack and air speed.

Norment, Hillyer G.↗
NASA NTRS1990

Modification of the background flow by roll vortices

Use of observed wind profiles, such as those obtained from ascent or descent aircraft soundings, for the identification of the expected roll modes is hindered by the fact that these modes are able to modify the wind profiles. When such modified wind profiles are utilized to estimate the critical values of the dynamic and thermodynamic forcing rates, large errors in the preferred orientation angles and aspect ratios of the rolls may result. Nonlinear analysis of a 14 coefficient spectral model of roll circulations shows that the primary modification of the background wind is the addition of a linear component. When the linear profile having the correct amount of shear is subtracted from the observed cross-roll winds, then the pre-roll wind profile can be estimated. A preliminary test of this hypothesis is given for a case in which cloud streets were observed during FIRE.

Shirer, Hampton N.↗
NASA NTRS1991

Reliability analysis of structural ceramics subjected to biaxial flexure

The reliability of alumina disks subjected to biaxial flexure is predicted on the basis of statistical fracture theory using a critical strain energy release rate fracture criterion. Results on a sintered silicon nitride are consistent with reliability predictions based on pore-initiated penny-shaped cracks with preferred orientation normal to the maximum principal stress. Assumptions with regard to flaw types and their orientations in each ceramic can be justified by fractography. It is shown that there are no universal guidelines for selecting fracture criteria or assuming flaw orientations in reliability analyses.

Chao, Luen-Yuan↗
NASA NTRS1991

Molecular dynamics of phenol at the liquid-vapor interface of water

Results of molecular dynamics calculations on phenol at the water liquid-vapor interface are presented. The density profile of the center of mass of phenol exhibits a maximum 1 A from the Gibbs surface toward the vapor phase, indicating that the molecule is surface-active. Changes in the profile caused by the interface extend 6 A from the Gibbs surface into the liquid, significantly more than change in the density profile of water. The most probable orientation of the solute at the surface is such that its symmetry axis is perpendicular to the interface with the OH substituent pointing toward the liquid. An additional simulation with benzene shows that this molecule at the surface most often adopts orientations parallel to the interface. Deeper in the liquid all the solutes are preferentially ordered perpendicular to the surface. In the interfacial region the orientational preferences of the solute are primarily determined by cavity formation needed to accommodate the hydrophobic portion of the dissolved molecule.

Pohorille, Andrew↗