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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 667 records · Page 37
All sourcesNASA NTRSDOE OSTI
NASA NTRS1972

Subcritical crack growth of selected aerospace pressure vessel materials

This experimental program was undertaken to determine the effects of combined cyclic/sustained loads, stress level, and crack shape on the fatigue crack growth rate behavior of cracks subjected to plane strain conditions. Material/environment combinations tested included: 2219-T87 aluminum plate in gaseous helium, room air, and 3.5% NaCl solution at room temperature, liquid nitrogen, and liquid hydrogen; 5Al-2.5 Sn (ELI) titanium plate in liquid nitrogen and liquid hydrogen and 6AL-4V (ELI) STA titanium plate in gaseous helium and methanol at room temperature. Most testing was accomplished using surface flawed specimens instrumented with a clip gage to continuously monitor crack opening displacements at the specimen surface. Tapered double cantilever beam specimens were also tested. Static fracture and ten hour sustained load tests were conducted to determine fracture toughness and apparent threshold stress intensity values. Cyclic tests were performed using sinusoidal loading profiles at 333 MHz (20 cpm) and trapezoidal loading profiles at both 8.3 MHz (0.5 cpm) and 3.3 MHz (0.2 cpm). Data were evaluated using modified linear elastic fracture mechanics parameters.

Hall, L. R.↗
NASA NTRS1977

The influence of growth speed, orientation and environment on fracture of aligned Al-CuAl2

There has been considerable interest in the mechanical properties of aligned eutectics as functions of microstructure, orientation between reinforcement and stress axis, and temperature of testing. However, little is known about the behavior of these alloys in aggressive environments, such as liquid metals, with the exception of a recent paper on embrittlement of several eutectic alloys in gallium and gallium-indium alloys. This paper is concerned with the effects of a liquid Ga-16%In solution on tensile behavior of an aligned Al-CuAl2 eutectic.

Skiff, P. K.↗
NASA NTRS1977

Vibrations of incompressible liquid-plastic tank combinations using a series representation of the liquid

A series representation is presented of the dynamic behavior of incompressible non-viscous liquids contained in partially filled elastic shells of revolution. Using a series in which each term satisfies exactly Laplace's equation, the liquid portion of the problem becomes an integral equation on the wetted wall of the shell. Physical insight required in selecting the terms of the series is such that selection may be readily programed on a computer. Liquid-shell vibration interaction is investigated by modifying an existing shell of revolution vibration program with the series expansion of the liquid pressure loading on the wetted shell wall. Application of the modified program is demonstrated on a hemispherical tank and a realistic scaled model of a launch vehicle tank having a more complex geometry. Comparison of the present analysis with a NASTRAN finite element analysis for a hemispherical tank, and comparison with test results for a launch vehicle tank shows excellent agreement and rapid convergence of the series representation of the liquid to the true solution.

Housner, J. M.↗
NASA NTRS1979

Simulated lidar return from a one-dimensional stratospheric aerosol model

Results are presented for theoretical calculations of lidar backscatter at wavelengths of 0.6943 and 1.06 microns from the stratospheric aerosol. The computations are based on the size distribution, particle number density, and particle composition predicted by a one-dimensional model of the stratospheric aerosol layer that assumes that the primary source of sulfur to the stratosphere is biogenic OCS released at ground level. The aerosol particles are taken to be spherical liquid H2SO4-H2O solution droplets with solid cores, which undergo condensation, evaporation, coagulation, sedimentation, and vertical eddy mixing. The theoretical backscatter profiles are compared with experimental results obtained from actual lidar observations of the stratospheric aerosol layer before and after the eruption of Volcan de Fuego in October 1974. The model predictions are shown to be in good agreement with the average of a number of observations.

Hamill, P.↗
NASA NTRS1981

Excited ozone is a possible source of atmospheric N2O

Consideration is given to the possibility that internally excited ozone formed in the three-body recombination reaction between oxygen atoms and molecules may be a potential source of atmospheric N2O through a gas-phase reaction with nitrogen molecules. Determinations of the wavelength dependence of the quantum yield for N2O formation from the photolysis of dilute solutions of O3 in liquid N2 and of the O(1D) quantum yield in the gas-phase photolysis of O3 are interpreted as suggesting the possibility of the excited ozone reaction, and a new expression for N2O quantum yield is derived. An expression for the production rate of N2O through the proposed reaction is then obtained and used to calculate atmospheric concentrations and fluxes of N2O. The theoretical profile obtained is found to agree better with experimental data than that obtained without the excited ozone reaction taken into account and to demonstrate a wide variability in N2O mixing ratios. In addition, the existence of the new N2O source is noted to imply a significantly smaller flux of N2O from surface microbiological activities, and provide a possible physical basis for latitudinal and temporal N2O variations and an additional stability for the ozone layer.

Prasad, S. S.↗
NASA NTRS1983

Process research of non-CZ silicon material

High risk, high payoff research areas associated with the Westinghouse process for producing photovoltaic modules using non- CZ sheet material were investigated. All work was performed using dendritic web silicon. The following tasks are discussed and associated technical results are given: (1) determining the technical feasibility of forming front and back junctions in non-CT silicon using dopant techniques; (2) determining the feasibility of forming a liquid applied diffusion mask to replace the more costly chemical vapor deposited SiO2 diffusion mask; (3) determining the feasibility of applying liquid anti-reflective solutions using meniscus coating equipment; (4) studying the production of uniform, high efficiency solar cells using ion implanation junction formation techniques; and (5) quantifying cost improvements associated with process improvements.

Source record↗
NASA NTRS1983

Homogeneous crystal nucleation in binary metallic melts

A method for calculating the homogeneous crystal nucleation frequency in binary metallic melts is developed. The free energy of crystallization is derived from regular solution models for the liquid and solid and is used, together with model-based estimates of the interfacial tension, to calculate the nucleation frequency from the classical theory. The method can account for the composition dependence of the maximum undercooling observed in a number of experiments on small droplet dispersions. It can also be used to calculate the driving force for crystal growth and to obtain more precise estimates of the homogeneous crystal nucleation frequency in glass-forming alloys. This method, although approximate, is simple to apply, and requires only knowledge of the phase diagram and a few readily available thermodynamic quantities as input data.

Thompson, C. V.↗
NASA NTRS1985

Mass Transport Phenomena Between Bubbles and Dissolved Gases in Liquids Under Reduced Gravity Conditions

The long term objective of the experiment is to observe the dissolution of isolated, immobile gas bubbles of specified size and composition in a solvent liquid of known concentration in the reduced gravity environment of earth orbit. Preliminary bubble dissolution experiment conducted both in the NASA Lewis 2.2 sec drop tower and in normal gravity using SO2 - Toluene system were not completely successful in their objective. The method of gas injection and lack of bubble interface stabiliy experienced due to the extreme solubility of SO in Toluene has the effects of changing the problem from that of bubble dissolution to one of bubble formation stability and subsequent dissolution in a liquid of unknown initial solute concentration. Current work involves further experimentation in order to refine the bubble injection system and to investigate the concept of having a bubble with a critical radius in a state of unstable equilibrium.

Dewitt, K. J.↗
NASA NTRS1985

The casting of semi-permeable membranes in a microgravity environment

The National Electric Company of Venezuela, C.A.D.A.F.E., is sponsoring the development of this experiment which represents Venezuela's first scientific experiment in space. The experience can be classified as an educational one which could add knowledge to the fundamental study of polymeric membranes. Presently, semi-permeable membranes are being manufactured from several different kind of polymers all over the world and specific applications have been identified in fluid separation processes such as reverse osmosis, ultrafiltration and electrodyalisis. Although, the ultrastructure of asymetric and composite membranes have been under intensive study, still there are many questions about the factors affecting this structure and their degree of correlation. Nevertheless, there is indication that the entire morphological structure of polymeric membranes could be affected by the differences in specific gravity between the cast solution and the coagulation liquid, normally used in the membranes preparation process. The casting of semi-permeable membranes in space might help to identify the effect of gravity upon the structure of these membranes. It is important to recognize that the casting process involves changes of states (liquid-gas, liquid-solid) and that in a micro gravity environment, there will be a reduction on buoyancy-driven natural convection and density gradients

Ivan Vera↗
NASA NTRS1986

Viscometer for low frequency, low shear rate measurements

A computer-controlled torsion-oscillator viscometer with low 0.5 Hz frequency and very low 0.05/s shear rate is designed to precisely study shear-sensitive fluids such as microemulsions, gels, polymer solutions and melts, colloidal solutions undergoing coagulation, and liquid mixtures near critical points. The viscosities are obtained from measurements of the logarithmic decrement of an underdriven oscillator. The viscometer is found to have a resolution of 0.2 percent when used with liquid samples and a resolution of 0.4 percent when used with a dense gaseous sample. The design is compatible with submillikelvin temperature control.

Berg, R. F.↗
NASA NTRS1987

Physical properties of immiscible polymers

The demixing of immiscible polymers in low gravity is discussed. Applications of knowledge gained in this research will provide a better understanding of the role of phase segregation in determining the properties of polymer blends made from immiscible polymers. Knowledge will also be gained regarding the purification of biological materials by partitioning between the two liquid phases formed by solution of the polymers polyethylene glycol and dextran in water. Testing of new apparatus for space flight, extension of affinity phase partitioning, refinement of polymer chemistry, and demixing of isopycnic polymer phases in a one gravity environment are discussed.

Harris, J. Milton↗
NASA NTRS1989

Efficient estimation of diffusion during dendritic solidification

A very efficient finite difference method has been developed to estimate the solute redistribution during solidification with diffusion in the solid. This method is validated by comparing the computed results with the results of an analytical solution derived by Kobayashi (1988) for the assumptions of a constant diffusion coefficient, a constant equilibrium partition ratio, and a parabolic rate of the advancement of the solid/liquid interface. The flexibility of the method is demonstrated by applying it to the dendritic solidification of a Pb-15 wt pct Sn alloy, for which the equilibrium partition ratio and diffusion coefficient vary substantially during solidification. The fraction eutectic at the end of solidification is also obtained by estimating the fraction solid, in greater resolution, where the concentration of solute in the interdendritic liquid reaches the eutectic composition of the alloy.

Yeum, K. S.↗
NASA NTRS1995

Surface-atmosphere interactions on Titan compared with those on the pre-biotic Earth

The surface and atmosphere of Titan constitute a system which is potentially as complex as that of the Earth, with the possibility of precipitation, surface erosion due to liquids, chemistry in large surface or subsurface hydrocarbon resevoirs, surface expressions of internal activity, and occasional major impacts leading to crustal melting. While none of the above have been observed as yet, the composition, density and thermal properties of Titan's atmosphere make it uniquely suited in the outer solar system as a place where such processes may occur. The one attribute of the Earth not expected on Titan is biological activity, which has had a profound effect on the evolution of the Earth's surface-atmosphere system. The earliest environment of Titan could have been warm enough for liquid ammonia-water solutions to exist on or near surface; pre-biotic organic processes may have taken place in such an environment. After a few hundred million years surface ammonia-water would have disappeard. Therefore, study of Titan through Cassini/Huygens mission, planned for launch in 1997, primarily affords the opportunity to understand planet-side surface-atmophsre interactions in the presence of fluids but in the absence of life. More speculative is the possibility that endogenic and exogenic heating continue to provide short-lived environments on Titan wherein pre-biotic organic processes in the presence of water happen.

Lunine, J. I.↗
NASA NTRS1996

Phase Diagram of HgTe -ZnTe Pseudobinary and Density, Heat Capacity, and Enthalphy of Mixing of Hg(sub 1-x)Zn(sub x)Te Pseudobinary Melts

In this article, the solidus temperatures of the Hg(sub 1-x) Zn(sub x)Te pseudobinary phase diagram for several compositions in the low x region were measured by differential thermal analysis and the HgTe-ZnTe pseudobinary phase diagram was constructed. The densities of two HgZnTe melts, x = 0.10 and 0.16, were determined by an in situ pycnometric technique in a transparent furnace over, respectively, 110 and 50 C ranges of temperature. The thermodynamic properties of the melts, such as the heat capacity and enthalpy of mixing, were calculated for temperatures between the liquidus and 1500 C by assuming an associated solution model for the liquid phase.

Su, Ching-Hua↗
NASA NTRS1996

Venus Gravity Handbook

This report documents the Venus gravity methods and results to date (model MGNP90LSAAP). It is called a handbook in that it contains many useful plots (such as geometry and orbit behavior) that are useful in evaluating the tracking data. We discuss the models that are used in processing the Doppler data and the estimation method for determining the gravity field. With Pioneer Venus Orbiter and Magellan tracking data, the Venus gravity field was determined complete to degree and order 90 with the use of the JPL Cray T3D Supercomputer. The gravity field shows unprecedented high correlation with topography and resolution of features to the 2OOkm resolution. In the procedure for solving the gravity field, other information is gained as well, and, for example, we discuss results for the Venus ephemeris, Love number, pole orientation of Venus, and atmospheric densities. Of significance is the Love number solution which indicates a liquid core for Venus. The ephemeris of Venus is determined to an accuracy of 0.02 mm/s (tens of meters in position), and the rotation period to 243.0194 +/- 0.0002 days.

Konopliv, Alexander S.↗
NASA NTRS1998

Real-Time X-Ray Transmission Microscopy for Fundamental Studies Solidification

High resolution real-time X-ray Transmission Microscopy, XTM, has been applied to obtain information fundamental to solidification of optically opaque metallic systems. We have previously reported the measurement of solute profile in the liquid, phase growth, and detailed solid-liquid interfacial morphology of aluminum based alloys with exposure times less than 2 seconds. Recent advances in XTM furnace design have provided an increase in real-time magnification (during solidification) for the XTM from 4OX to 16OX. The increased magnification has enabled for the first time the XTM imaging of real-time growth of fibers and particles with diameters of 5 micrometers. We have applied this system to study of the kinetics of formation and morphological evolution of secondary fibers and particles in Al-Bi monotectic alloys to observe a previously unreported velocity dependent thermo-capillary depletion mechanism for Bi rich liquid which can penetrate many fiber diameters into the solid-liquid interface. In this talk we will discuss application of the XTM to the study the fundamentals of monotectic and eutectic solidification, the enhancement of XTM data with precise solid liquid interfacial temperature and thermal gradient measurement techniques, and the application of this technology to the study of the fundamentals of solidification in microgravity,

Curreri, Peter A.↗
NASA NTRS2000

Combinatorial Optimization of Heterogeneous Catalysts Used in the Growth of Carbon Nanotubes

Libraries of liquid-phase catalyst precursor solutions were printed onto iridium-coated silicon substrates and evaluated for their effectiveness in catalyzing the growth of multi-walled carbon nanotubes (MWNTs) by chemical vapor deposition (CVD). The catalyst precursor solutions were composed of inorganic salts and a removable tri-block copolymer (EO)20(PO)70(EO)20 (EO = ethylene oxide, PO = propylene oxide) structure-directing agent (SDA), dissolved in ethanol/methanol mixtures. Sample libraries were quickly assayed using scanning electron microscopy after CVD growth to identify active catalysts and CVD conditions. Composition libraries and focus libraries were then constructed around the active spots identified in the discovery libraries to understand how catalyst precursor composition affects the yield, density, and quality of the nanotubes. Successful implementation of combinatorial optimization methods in the development of highly active, carbon nanotube catalysts is demonstrated, as well as the identification of catalyst formulations that lead to varying densities and shapes of aligned nanotube towers.

Cassell, Alan M.↗