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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 1,459 records · Page 81

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NASA NTRS1974

High gas velocity burner tests on silicon carbide and silicon nitride at 1200 C

Ten SiC materials and five Si3N4 materials were exposed in a Mach 1-gas-velocity burner simulating a gas-turbine engine environment. All materials studied are commercially available. Cyclic tests up to 100 hours' duration were conducted at specimen temperatures of 1200 C. A specimen geometry was used that develops thermal stresses during thermal cycling in a manner similar to blades and vanes of a gas turbine engine. Materials were compared on a basis of weight change, dimensional reductions, metallography, fluorescent-penetrant inspection, X-ray diffraction analyses, failure mode, and general appearance. One hot-pressed SiC, one reaction-sintered SiC, and three hot-pressed Si3N4 materials survived the program goal of 100 one-hour cycles of exposures. Of the materials that failed to meet the program goal, thermal fatigue was identified as the exclusive failure mode.

Sanders, W. A.↗

NASA NTRS1975

Early detection of fatigue damage in composite materials

Early detection of fatigue damage in composite materials by nondestructive inspection (NDI) techniques has been demonstrated for glass/epoxy, graphite/glass/epoxy, and graphite/epoxy composites. Modulus and temperature were monitored and a correlation between them observed. Axial modulus and torsional modulus changes were a function of the laminate orientation. Torsional modulus measurements and coin tap tests were performed at 0, 1 million, 5 million, and 10 million cycles, on axial fatigue specimens. Three distinct regions were noted. In the primary region a small but rapid change in stiffness was noted in the first few thousand cycles. This was followed by a secondary region of little or no stiffness change. The tertiary region was characterized by an increasing rate of stiffness change leading to fracture. NDI procedures including holographic interferometry, ultrasonics, penetrant, and X-ray radiography were evaluated for fatigue damage detection.

Salkind, M. J.↗

NASA NTRS1975

Internal optical losses in very thin CW heterojunction laser diodes

Theoretical calculations are presented showing the relationship between the internal laser absorption and structural parameters appropriate for CW room-temperature lasers. These diodes have submicron-thick recombination regions, and very small spacings between the heat sink and the recombination region to minimize the thermal resistance. The optical loss is shown to be strongly dependent on the degree of radiation confinement to the active region. In particular, absorption in the surface GaAs layer providing the ohmic contact becomes very significant when the intermediate (AlGa)As layer is reduced below about 1 micron. It is further shown that excessive penetration into the GaAs regions gives rise to anomalies in the far-field radiation profiles in the direction perpendicular to the junction plane.

Butler, J. K.↗

NASA NTRS1975

Diffusion length measurement using the scanning electron microscope

The present work describes a measuring technique employing the scanning electron microscope in which values of the true bulk diffusion length are obtained. It is shown that surface recombination effects can be eliminated through application of highly doped surface field layers. The effects of high injection level and low-high junction current generation are investigated. Results obtained with this technique are compared to those obtained by a penetrating radiation (X-ray) method, and a close agreement is found. The SEM technique is limited to cells that contain a back surface field layer.

Weizer, V. G.↗

NASA NTRS1974

Impact cratering models and their application to lunar studies - A geologist's view

Impact cratering models are discussed which were derived from: (1) laboratory hypervelocity experiments in cohesive materials; (2) laboratory impact experiments in noncohesive materials such as sand; and (3) terrestrial meteorite impact craters (specifically the Ries Crater, the largest well-preserved terrestrial meteorite crater). Salient features of these three categories of models are compared in order to point out unresolved controversies and inconsistencies. Arguments and evidence are presented to support the conclusions that (1) penetrations of secondary impacts are insignificant and are not likely to stir up much local material, (2) the laboratory hypervelocity experiments are perhaps the best model for lunar glass-lined microcraters, (3) laboratory impact experiments in noncohesive materials such as sand are the best model for impacts in lunar regolith, and (4) the Ries is considered the best model for large lunar impact craters. From analogy with the Ries, it appears that lateral and low-angle transport of ejecta and accelerated lateral growth are important in formation of large impact craters.

Chao, E. C. T.↗

NASA NTRS1974

The role of horizontal transport as evaluated from the Apollo 15 and 16 orbital experiments

Despite the large amount of accumulated data there is still considerable debate about the role of various processes in the formation of the lunar surface. One of the processes frequently discussed is that of horizontal transport and how it affected surface chemistry and surface features. The orbital experiments flown on Apollo 15 and 16 enable us to consider the extent of horizontal transport. In particular, the X-ray experiment because of its low penetration depth permits us to make at least crude estimates of the extent of horizontal transport.

Adler, I.↗

NASA NTRS1974

Hydrogen and fluorine in the surfaces of lunar samples

The resonant nuclear reaction F-19(p, alpha gamma)O-16 has been used to perform depth-sensitive analyses for both fluorine and hydrogen in lunar samples. The resonance at 0.83 MeV (center-of-mass) in this reaction has been applied to the measurement of the distribution of trapped solar protons in lunar samples to depths up to 0.45 microns. These results are interpreted in terms of terrestrial H2O surface contamination and of a redistribution of the implanted solar H which has been influenced by heavy radiation damage in the surface region. Results are also presented for an experiment to test the penetration of H2O into laboratory glass samples which have been irradiated with O-16 to simulate the radiation-damaged surfaces of lunar glasses. Fluorine determinations have been performed in a 1-micron surface layer on lunar samples using the same F-19(p, alpha gamma)O-16 resonance. The data are discussed from the standpoint that observed fluorine concentrations are a mixture of true lunar fluorine and Teflon contamination.

Leich, D. A.↗

NASA NTRS1974

High-frequency lunar teleseismic events

A small number of seismic signals, including some of the strongest observed to date, have been identified as representing a fourth principal category of natural lunar seismic events with characteristics distinct from those produced by normal meteoroid impacts, deep moonquakes, and thermal moonquakes. These signals are much richer in high frequencies than other events observed at comparable distances, and display relatively impulsive P- and S-wave beginnings, indicating negligible seismic-wave scattering near the source. Source depths of these events may range between 0 and perhaps 300 km. These and other characteristics could represent either (1) meteoroids impacting upon outcrops of competent lunar crystal rock, (2) rare impacting objects that penetrate to competent rock below a scattering zone, or (3) shallow tectonic moonquakes.

Nakamura, Y.↗

NASA NTRS1975

Height of helium emission in the chromosphere

Filtergrams of the limb show the He I D3 chromosphere as a shell which is separated from the limb by a gap. The height of maximum D3 contribution occurs at about 1350 km above the limb and is independent of the intensity of the D3 emission. We interpret this effect as the height to which coronal EUV radiation is capable of penetrating the atmosphere.

Pope, T.↗

NASA NTRS1975

Ionosphere-magnetosphere coupling. II - Electric fields

An attempt is made to fit individual observations and theories into the broader network of magnetosphere-ionosphere-atmosphere couplings as they affect the general behavior of quasi-static electric fields in the magnetosphere and ionosphere. Particular attention is given to high-latitude processes, however, mid-latitude penetration of electric fields of magnetospheric origin during disturbed periods is discussed.

Banks, P. M.↗

NASA NTRS1975

Rocket-borne particle, field, and plasma observations in the cleft region

Results are reported for comprehensive observations of magnetic and electric fields together with ambient and suprathermal plasmas above the dayside auroral oval with rocket-borne instrumentation which penetrated the cleft region. Measurements were also obtained equatorward and poleward of the cleft. Convection velocities as inferred from electric-field measurements were generally toward noon equatorward of the cleft and were antisunward over the polar cap. Observations of electron temperatures, electric fields, and low-frequency electrostatic noise provide strong evidence of a plasma instability (Farley-Buneman) in the E-layer associated with the appearance of the 'slant E condition' identified in ground-acquired ionograms. The positions of these measurements relative to that of the cleft were firmly established via the determination of the plasma environment with an electrostatic analyzer.

Ungstrup, E.↗

NASA NTRS1975

A multichannel implantable telemetry system for flow, pressure, and ECG measurements

The design, principles of operation, and performance of an implantable miniaturized (48 cu cm in volume) multiplex telemetry system for simultaneous measurement of up to eight physiological parameters (including cardiovascular data) are described. Integrated circuits are used to reduce the size, complexity, and cost of fabrication. Power consumption is reduced using recently developed complementary MOS devices. PWM technique is selected as it is relatively easy to implement, lends itself to ICs, and provides an accurate means of transmitting data. The system is totally implantable within the chest of a test animal, with no wire penetrating through the skin. It is shown that the described system permits repeated measurement of the physiological effects of a variety of interventions in awake unanesthetized animals.

Fryer, T. B.↗

NASA NTRS1975

Electromagnetic fields and torque for a rotating gyroscope with a superconducting shield

In a proposed experiment, a measurement is to be made of the angular precession of a rotating superconducting gyroscope for the purpose of testing different general-relativity theories. For various reasons having to do with the design of the experiment, the superconducting shield surrounding the gyroscope is not spherically symmetric and produces a torque. There are two distinct features of the shield which lead to a torque on the gyroscope. First, its shape is a sphere intersected by a plane. If the angular momentum of the gyroscope is not parallel to the rotational symmetry axis of the shield, there is a torque which is calculated. Second, there are small holes in the spherical portion of the shield. The earth's field can penetrate through these holes and give an additional torque which is also calculated. In the actual experiment, these torques must be accurately known or made very small in order to obtain meaningful results. The present calculation is sufficiently general for application over a wide range of experimental design parameters.

Ebner, C.↗

NASA NTRS1975

Transport and emplacement of crater and basin deposits

Material is ejected from impact craters in ballastic trajectories; it impacts first near the crater rim and then at progressively greater ranges. Ejecta from craters smaller than approximately 1 km are laid predominantly on top of the surrounding surface. With increasing crater size, more and more surrounding surface will be penetrated by secondary cratering action, and these preexisting materials will be mixed with primary crater ejecta. Ejecta from large craters, and especially basin-forming events, not only excavate preexisting local materials, but also are capable of moving large amounts of material away from the crater. Thus mixing and lateral transport give rise to continuous deposits that contain materials from within and outside the primary crater. As a consequence, ejecta of basins and large highland craters have eroded and mixed highland materials throughout geologic time and deposited them in depressions inside and between older crater structures.

Oberbeck, V. R.↗

NASA NTRS1975

Pioneer 11's encounter with Jupiter and mission to Saturn

Results of Pioneer 11's encounter with Jupiter are reviewed, and present plans for its approach to Saturn are discussed. The spacecraft is described together with its instrumentation, Jupiter-encounter operations, and scientific investigations. Scientific objectives at Saturn are outlined, including imaging of the planet, magnetospheric studies, measurements of Titan's mass and ephemeris, estimates of the mass of Saturn's rings, and penetration of the ring plane, particularly the D ring.

Dyer, J. W.↗

NASA NTRS1974

Convective heat transfer to low-temperature fluids

Research into forced and natural convection processes in low-temperature (cryogenic) fluids is reviewed with primary emphasis on forced convection. Boundaries of the near-critical region are defined, fluid properties near the critical state are discussed, and heat-transfer processes around the critical point are described. The thermodynamics of the critical point is analyzed together with transport properties of a near-critical fluid, and the quantum states of low-temperature molecular hydrogen (para and ortho) are discussed. Experimental work on heat transfer in free, natural, and forced convection systems is briefly summarized. Graham's (1969) penetration model for near-critical fluids is outlined, near-critical heat transfer is discussed in relation to conventional geometric effects, and the effects of curvature on the properties of near-critical hydrogen are noted. Theoretical considerations in free and forced convection are examined.

Graham, R. W.↗

NASA NTRS1976

Fracture mechanics for weld acceptance

Criteria include specifications for allowable cracklike defect lengths, undercut, underfill, suckback, mismatch, peaking in butt welds, root penetration, weld beam dimensions, lap joint dimensions, and acceptable defect sizes and densities for double and single fillet welds.

Bolstad, C. A.↗

NASA NTRS1975

Skylab M551 metals melting experiment

The objectives of the M551 Metals Melting Experiment were to: (1) study behavior of molten metal, (2) characterize metals melted and solidified in the low gravity space environment compared to one-gravity of earth, and (3) determine feasibility of joining metals in space. The experiment used the electron beam (EB) and chamber of the M512 apparatus to make a dwell puddle and a melt in a rotating disc of varying thickness. Hence, the EB performed cut-through, full and partial penetration melts, in addition to a resolidified button. The three disc materials were aluminum 2219-T87, 304 stainless steel, and pure tantalum to provide a wide range of density and melting conditions. Observations to date include the proof that EB welding, cutting, and melting can be done successfully in low gravity. Earlier, some welding authorities had postulated that without gravity the EB would force the molten puddle out of contact. However, the experiment proved that surface tension forces predominate. From the viewpoint of cast-solidification, small, equiaxed grains in Skylab specimens compared to large, elongated grains in ground based specimens were observed. The former are thought to be associated with constitutional supercooling and nucleation where the latter are associated with dendritic solidification. In further support of the more equiaxed grain growth in Skylab, symmetric subgrain patterns were frequently observed where there was much less symmetry in ground based specimens.

Poorman, R. M.↗