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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 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
NASA NTRS1975

Effect of service usage on tensile, fatigue, and fracture properties of 7075-T6 and 7178-T6 aluminum alloys

A study has been made to determine the effects of extensive service usage on some basic material properties of 7075-T6 and 7178-T6 aluminum alloy materials. The effects of service usage were determined by comparing material properties for new material (generally obtained from the literature) with those for material cut from the center wing box of a C-130B transport airplane with 6385 flight-hours of service. The properties investigated were notched and unnotched fatigue strengths, fatigue-crack-growth rate, fracture toughness, and tensile properties. For the properties investigated and the parameter ranges considered (crack length, stress ratio, etc.), the results obtained showed no significant difference between service and new materials.

Everett, R. A., Jr.↗
NASA NTRS1974

Thermoelectric properties of 80 a/o Si-20 a/o Ge alloy

This paper discusses the time and temperature dependence of the thermoelectric properties of n- and p-type 80 at. % Si-20 at. % Ge alloy. It is shown that the time-temperature behavior of the properties of both polarity types of this alloy can be described by means of a diffusion-limited dopant precipitation model due to Lifshitz and Slyozov (1961). An experimental program for the determination of the long-term behavior of the properties of the alloy is described in terms of the Lifshitz-Slyozov model, and the thermoelectric properties of the alloy are given for temperatures in the range from room temperature to 1000 C as a function of time up to and including twelve years. The data given for the p-type alloy represent the first time-dependent thermoelectric property data ever published for the p-type silicon-germanium alloys.

Raag, V.↗
NASA NTRS1976

Effect of casting geometry on mechanical properties of two nickel-base superalloys

An investigation was performed to determine mechanical properties of two rhenium-free modifications of alloy TRW, and to evaluate the suitability of the alloy for use in a small integrally cast turbine rotor. The two alloys were initially developed using stress rupture properties of specimens machined from solid gas turbine blades. Properties in this investigation were determined from cast to size bars and bars cut from 3.8 by 7.6 by 17.8 cm blocks. Specimens machined from blocks had inferior tensile strength and always had markedly poorer rupture lives than cast to size bars. At 1,000 C the cast to size bars had shorter rupture lives than those machined from blades. Alloy R generally had better properties than alloy S in the conditions evaluated. The results show the importance of casting geometry on mechanical properties of nickel base superalloys and suggest that the geometry of a component can be simulated when developing alloys for that component.

Johnston, J. R.↗
NASA NTRS1976

The effect of thermal exposure on the mechanical properties of aluminum-graphite composites

To promote the development of aluminum-graphite composites with improved properties for aerospace applications, composite samples were fabricated by solid-state diffusion bonding of liquid-phase Al-infiltrated Thornel 50 fibers, and their mechanical properties were measured at room temperature in the as-received condition, after temperature exposure and after thermal cycling. The interface structure in aluminum-graphite composites and its effect on the composite properties, the effect of thermal cycling on the tensile properties of the composites, and the characteristics of failures of the composites in tension is discussed. The studied composites exhibited tensile properties corresponding well with those predicted by the rule of mixtures. Thermal cycling between 20 C and 500 C, as well as the formation of the Al4C3 at the Al-graphite interfaces at temperatures above 500 C resulted in degradation of the composite strength. Scanning electron microscopy of fractured surfaces indicated that the relatively weak interface governs the mode of failure in tension.

Khan, I. H.↗
NASA NTRS1976

Effective thermal property improves phase change paint data

The phase-change coating technique presents itself as a valuable tool in determining the heat transfer rate over the surface of small complex wind tunnel models. A numerical technique is described which shows that an effective thermophysical property - the square root of the product of thermal conductivity, density, and specific heat - may significantly improve the accuracy of the phase-change coating technique with allowance for model inhomogeneity and temperature dependency in a transient environment. Results of the measured steady-state variation of the effective thermophysical property with temperature and the effect of surface heating rate on the effective thermophysical property are plotted for a representative homogeneous model material and for an extreme nonhomogeneous model material. The use of an effective thermophysical property to reduce phase-change paint data is recommended. The analysis also confirms that the apparatus described by Corwin and Kramer (1975) can be used to measure directly this effective thermophysical property for use in wind tunnel model heat-transfer measurements.

Drummond, J. P.↗
NASA NTRS1979

A new approach to the correlation of boundary layer mass transfer rates with thermal diffusion and/or variable properties

A rational approach to the correlation of boundary layer mass transport rates, applicable to many commonly encountered laminar flow conditions with thermal diffusion and/or variable properties, is outlined. The correlation scheme builds upon already available constant property blowing/suction solutions by introducing appropriate correction factors to account for the additional ('pseudo' blowing and source) effects identified with variable properties and thermal diffusion. Applications of the scheme to the particular laminar boundary layer mass transfer problems considered herein (alkali and transition metal compound vapor transport) indicates satisfactory accuracy up to effective blowing factors equivalent to about one third of the 'blow off' value. As a useful by-product of the variable property correlation, we extend the heat-mass transfer analogy, for a wide range of Lewis numbers, to include variable property effects.

Srivastava, R.↗
NASA NTRS1979

The effects of strain and temperature on the dynamic properties of elastomers

This paper presents the results of a program of analysis and tests to determine the dynamic properties of elastomers as a function of strain and ambient temperature. Measurements were also made to determine the temperature distribution in the elastomer samples during the tests. These measured properties were compared with analytical predictions based on a visco-elastic model designed to take into account the self-heating of the materials as a function of strain. The test method used was well-established Base Excitation Resonant Mass Technique. The specimens tested were two cylindrical button compression specimens and a shear specimen. Strain was shown to be an important parameter in determining the dynamic properties of the elastomers. In general, these properties were much more sensitive to strain than to frequency. The self-heating effect was found to account for a portion of the strain sensitivity of these properties.

Darlow, M. S.↗
NASA NTRS1979

Mechanical property characterization of intraply hybrid composites

An investigation of the mechanical properties of intraply hybrids made from graphite fiber/epoxy matrix hybridized with secondary S-glass or Kevlar 49 fiber composites is presented. The specimen stress-strain behavior was determined, showing that mechanical properties of intraply hybrid composites can be measured with available methods such as the ten-degree off-axis test for intralaminar shear, and conventional tests for tensile, flexure, and Izod impact properties. The results also showed that combinations of high modulus graphite/S-glass/epoxy matrix composites exist which yield intraply hybrid laminates with the best 'balanced' properties, and that the translation efficiency of mechanical properties from the constituent composites to intraply hybrids may be assessed with a simple equation.

Chamis, C. C.↗
NASA NTRS1984

Materials properties data base computerization

Material property data plays a key role in the design of jet engine components. Consistency, accuracy and efficient use of material property data is of prime importance to the engineering community. The system conception, development, implementation, and future plans for computer software that captures the Material Properties Handbook into a scientific data base are described. The engineering community is given access to raw data and property curves, display of multiple curves for material evaluation and selection, direct access by design analysis computer programs, display of the material specification, and a historical repository for the material evolution. The impact of this activity includes significant productivity gains and cost reductions; all users have access to the same information nd provides consistent, rapid response to the needs of the engineering community. Future plans include incorporating the materials properties data base into a network environment to access information from other data bases and download information to engineering work stations.

Baur, R. G.↗
NASA NTRS1984

A comparison of the properties of highly polarized QSOs versus low-polarization QSOs

An optical linear-polarization survey testing the relationships between polarization and other properties of QSOs is presented. Polarimetric observations of 239 QSOs have been made. Data from the literature are used to analyze the relationships between polarization and radio, optical, and X-ray properties. The highly polarized QSOs are generally compact radio sources, are associated with radio properties such as low-frequency variability and superluminal motion, exhibit large-amplitude rapid photometric variability, have steep nonthermal optical continua, and may show excess X-ray emission. No relationship is seen between polarization and redshift, optical luminosity, or the equivalent width of emission lines. The results are discussed in the context of both isotropic and anisotropic (beaming) models. While the associations between the optical and radio properties of highly polarized QSOs provide strong motivation for the anisotropic model, the lack of associations with redshift, optical luminosity, and emission-line strength is inconsistent with this model. It is concluded that the highly polarized QSOs are probably fundamentally different in their physical properties from low-polarization QSOs.

Moore, R. L.↗
NASA NTRS1984

Changes in spectral properties of detached leaves

If leaf senescence can be delayed for several days without significant changes in spectral properties, then samples of leaves at remote test sites could be prepared and shipped to laboratories to measure spectral properties. The changes in spectral properties of detached leaves were determined. Leaves from red birch and red pine were immersed in water or 0.001 M benzylaminopurine (BAP) and stored in plastic bags in the dark at either 5 or 25 C. Total directional-hemispherical reflectance and transmittance of the adaxial surface of birch leaves were measured over the 400 to 1100 nm wavelength region with a spectroradiometer and integrating sphere. Pine needles were taped together and reflectance of the mat of needles was measured. Spectral properties changed less than 5% of initial values during the first week when leaves were stored at 5 C. Storage at 25 C promoted rapid senescence and large changes in spectral properties. BAP delayed, but did not stop, senescence at 25 C.

Daughtry, C. S. T.↗
NASA NTRS1985

Effect of reduction of strategic Columbium addition in 718 Alloy on the structure and properties

A series of alloys was developed having a base composition similar to Inconel 718, with reduced Cb levels of 3.00 and 1.10 wt% Cb. Substitutions of 3.0% W, 3.0W + 0.9V or Mo increased from 3.0% to 5.8% were made for the Cb in these alloys. Two additional alloys, one containing 3.49% Cb and 1.10% Ti and another containing 3.89% Cb and 1.29% Ti were also studied. Tensile properties at rooom and elevated temperatures, stress-rupture tests, and an analysis of extracted phases were carried out for each of the alloys. Additions of solid solution elements to a reduced Cb alloy had no significant effect on the properties of the alloys under either process condition. The solution and age alloys with substitutions of 1.27% i at 3.89% Cb had tensile properties similar top hose of the original alloy and stress-rupture properties superior to the original alloy. The improved stress-rupture properties were the result of significant precipitation of Ni3Ti-gamma prime in the alloy, which is more stable than gamma' at the elevated temperatures. At lower temperatures, the new alloy benefits from gamma' strengthening. With more precise control and proper processing, the reduced Cb direct-age alloy could substitute for Alloy 718 in high strength applications.

Ziegler, K. R.↗
NASA NTRS1985

Solid Rocket Motor Case (SRMC) dynamic sensitivity to changes in composite properties

Traditional composite lamination theory was used to compute the constitutive matrices using a potential range of lamina properties. Sensitivity of vibrational frequencies was examined for variations in constituent materials and geometric properties. The material component interactions examined were the lamina longitudinal and transverse Young's modulus, the lamina Poisson's ratio, and the shear modulus. Fiber and resin properties were related to the frequency response through lamina properties. Geometric properties examined are void ratio and helical wind angle. Capabilities and applications of the SPAR and NASTRAN computer codes are examined for laminated cylindrical shells.

Tolbert, R. N.↗
NASA NTRS1985

Microwave Dielectric and Propagation Properties of Vegetation Canopies

A vegetation canopy is a highly inhomogeneous medium at microwave frequencies, and because the scattering elements (leaves, stalks, fruits, and branches) have a nonuniform distribution in orientation, the canopy is likely to exhibit nonisotropic attenuation properties. In some canopies, the stalk may contain the overwhelming majority of the plant's biomass, which suggests that an incident radar wave would be differentially attenuated by the canopy depending on the direction of the incident electric field relative to the stalks' orientation. The propagation properties of a vegetation canopy play a central role in modeling both the backscattering behavior observed by an imaging radar and the emission observed by a radiometer. These propagation properties are in turn governed by the dielectric properties and the size, shape, and slope distributions of the scatteres. In spite of the critical need for canopy propagation models and experimental data, very few investigations had been conducted (prior to this study) to determine the extinction properties of vegetation canopies, either by constituent type (leaves, stalks, etc.) or as a whole.

Ulaby, F. T.↗
NASA NTRS1985

Study on effects of powder and flake chemistry and morphology on the properties of Al-Cu-Mg-X-X-X powder metallurgy advanced aluminum alloys

The effects of alloy chemistry and particulate morphology on consolidation behavior and consolidated product properties in rapid solidification processed, powder-metallurgical Al-3Li-1.5Cu-1Mg-0.5Co-0.2Zr and Al-4.4Cu-1.5Mg-Fe-Ni-0.2Zr extrusions and forgings were studied. Microstructures and mechanical properties of both alloys are largely unaffected by particulate production method (vacuum atomization, ultrasonic atomization, or twin-roller quenching) and by particulate solidification rates between 1000 and 100,000 K/s. Consolidation processing by canning, cold compaction, degassing, and hot extrusion is sufficient to yield mechanical properties in the non-Li-containing alloy extrusions which are similar to those of 7075-Al, but ductilities and fracture toughnesses are inferior owing to poor interparticle bonding caused by lack of a vacuum-hot-pressing step during consolidation. Mechanical properties of extrusions are superior to those of forgings owing to the stronger textures produced by the more severe hot working during extrusion. The effects on mechanical properties of dispersoid size and volume fraction, substructural refinement, solid solution strengthening by Mg, and precipitate size and distribution are elucidated for both alloy types.

Meschter, P. J.↗
NASA NTRS1987

Containerless high temperature property measurements by atomic fluorescence

Containerless high temperature processing and material property measurements are discussed. Researchers developed methods for non-contact suspension, heating, and property measurement for materials at temperatures up to 3,680K, the melting point of tungsten. New, scientifically interesting results were obtained in Earth-based research. These results and the demonstration of new methods and techniques form a basis for further advances under the low gravity environment of space where containerless conditions are more easily achieved. Containerless high temperature material property investigations that have been completed in this and our earlier projects include measurements of fluorine LaB sub 6 reaction kinetics at 1,000 to 1,500K; optical property measurements on sapphire (Al2O3) at temperatures up to the melting point (2,327K); and vapor pressure measurements for LaB sub 6 at 2,000 to 2,500K, for molybdenum up to 2,890K and for tungsten up to 3,680K. Gas jet levitation which is applicable to any solid material, and electromagnetic levitation of electrical conductors were used to suspend the materials of interest. Non-contact heating and property measurements were achieved by optical techniques, i.e., laser heating, laser induced fluorescence measurements of vapor concentrations, and optical pyrometry for specimen temperatures.

Nordine, Paul C.↗
NASA NTRS1987

Review of thermal properties of graphite composite materials

Flammability, thermal, and selected mechanical properties of composites fabricated with epoxy and other thermally stable resin matrices are described. Properties which were measured included limiting-oxygen index, smoke evolution, thermal degradation products, total-heat release, heat-release rates, mass loss, flame spread, ignition resistance, thermogravimetric analysis, and selected mechanical properties. The properties of 8 different graphite composite panels fabricated using four different resin matrices and two types of graphite reinforcement are described. The resin matrices included: XU71775/H795, a blend of vinyl polystyryl pyridine and bismaleimide; H795, a bismaleimide; Cycom 6162, a phenolic; and PSP 6022M, a polystyryl pyridine. The graphite fiber used was AS-4 in the form of either tape or fabric. The properties of these composites were compared with epoxy composites. It was determined that the blend of vinyl polystyryl pyridine and bismaleimide (XU71775/H795) with the graphite tape was the optimum design giving the lowest heat release rate.

Kourtides, D. A.↗
NASA NTRS1988

Processing, texture and mechanical properties of sintered silicon carbide

With regard to its favorable properties, in particular those shown at high temperatures, silicon carbide is of great interest for applications related to the construction of engines and turbines. Thus, silicon carbide could replace heat-resisting alloys with the objective to achieve a further increase in operational temperature. The present investigation is concerned with approaches which can provide silicon carbide material with suitable properties for the intended applications, taking into account the relations between characteristics of the raw material, material composition, sinter conditions, and results of the sintering process. The effects of density and texture formation on the mechanical properties are studied. It is found that a dense material with a fine-grained microstructure provides optimal mechanical properties, while any deviation from this ideal condition can lead to a considerable deterioration with respect to the material properties.

Landfermann, H.↗