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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 559 records · Page 31
All sourcesNASA NTRSDOE OSTI
NASA NTRS1981

Effect of Yttria additives on properties of pressureless-sintered silicon nitride

Si3N4-base ceramics were made from milled Si3N4 containing 11.1 wt% SiO2 and oxide additives by pressureless sintering at 1760 C. The four-point-average moduli of rupture were 460, 515, and 515 MPa at room temperature and 270, 256, and 227 MPa at 1400 C for compositions with 3.67, 7.22, and 14.0 wt% Y2O3, respectively. The oxidation resistance of these compositions decreased with increasing Y2O3 in the 600 to 1400 C range, and no surface oxide cracking or spalling was noted. Partial substitution of Al2O3 for Y2O3 reduced both strength and oxidation resistance.

Arias, A.↗
NASA NTRS1981

The variability of winds over the ocean

The present state of knowledge of the synoptic scale, the mesoscale, and the microscale in describing the winds, especially over the ocean, is summarized both in terms of conventional data and remotely sensed properties and effects of the winds. A description is then given of some of the areas posing problems in modeling each scale and interpreting the various kinds of measurements that are made. It is noted that not much is known about the wind, especially in the mesoscale, that affects the ability to use remotely sensed data in an optimum way.

Pierson, W. J.↗
NASA NTRS1981

Active regions from the photosphere to the chromosphere

The structures and physical conditions in that portion of a solar active region extending from the photosphere to the corona are considered. A horizontally averaged model of a solar plage is developed which is in reasonable agreement with observations, and significant discrepancies existing between quiet sun models and UV and IR spectra are noted which cast doubt on the reliability of such models. The nature of the flux tubes comprising the small-scale structure of the active regions is discussed, and the concept of filling factor is described as a basis for a flux tube model explaining changes in spectral properties. The effects of two-dimensional radiative transfer are examined for flux tubes of various cross-sectional size, and it is found that the neglect of explicit horizontal radiative interactions is a good approximation to the two-dimensional treatment. The radiative power loss from active regions is discussed for homogeneous and flux tube models, and a significant difference in total heating requirements is found. Finally, attention is given to the characteristics of the transition zone.

Chapman, G. A.↗
NASA NTRS1982

Martian surface properties indicated by the opposition effect

Radiative transfer expressions are used to derive average surface particle single-scattering albedos, phase functions and porosities from a photometric comparison of Viking Orbiter opposition measurements of the Martian Arabia, Syrtis Major and Elysium Planitia regions with several generic features. The best functional fit to the data includes consideration of atmospheric scattering, two-particle populations and surface roughness. It is found that (1) the presence of high albedo, high porosity surface particles is ubiquitous, (2) opposition surge is absent in the Syrtis Major region, and (3) the Chryse areas possess the largest surface roughness.

Thorpe, T. E.↗
NASA NTRS1982

Numerical simulation of the flow and fuel-air mixing in an axisymmetric piston-cylinder arrangement

The implicit factored method of Beam and Warming was employed to describe the flow and the fuel-air mixing in an axisymmetric piston-cylinder configuration during the intake and compression strokes. The governing equations were established on the basis of laminar flow. The increased mixing due to turbulence was simulated by appropriately chosen effective transport properties. Calculations were performed for single-component gases and for two-component gases and for two-component gas mixtures. The flow field was calculated as functions of time and position for different geometries, piston speeds, intake-charge-to-residual-gas-pressure ratios, and species mass fractions of the intake charge. Results are presented in graphical form which show the formation, growth, and break-up of those vortices which form during the intake stroke and the mixing of fuel and air throughout the intake and compression strokes. It is shown that at bore-to-stroke ratio of less than unity, the vortices may break-up during the intake stroke. It is also shown that vortices which do not break-up during the intake stroke coalesce during the compression stroke. The results generated were compared to existing numerical solutions and to available experimental data.

Shih, T. I. P.↗
NASA NTRS1982

Influence of quality control variables on failure of graphite/epoxy under extreme moisture conditions

Tension tests on graphite/epoxy composites were performed to determine the influence of various quality control variables on failure strength as a function of moisture and moderate temperatures. The extremely high and low moisture contents investigated were found to have less effect upon properties than did temperature or the quality control variables of specimen flaws and prepreg batch to batch variations. In particular, specimen flaws were found to drastically reduce the predicted strength of the composite, whereas specimens from different batches of prepreg displayed differences in strength as a function of temperature and extreme moisture exposure. The findings illustrate the need for careful specimen preparation, studies of flaw sensitvity, and careful quality control in any study of composite materials. Previously announced in STAR as N80-33493

Clements, L. L.↗
NASA NTRS1984

Computer analysis of effects of altering jet fuel properties on refinery costs and yields

This study was undertaken to evaluate the adequacy of future U.S. jet fuel supplies, the potential for large increases in the cost of jet fuel, and to what extent a relaxation in jet fuel properties would remedy these potential problems. The results of the study indicate that refiners should be able to meet jet fuel output requirements in all regions of the country within the current Jet A specifications during the 1990-2010 period. The results also indicate that it will be more difficult to meet Jet A specifications on the West Coast, because the feedstock quality is worse and the required jet fuel yield (jet fuel/crude refined) is higher than in the East. The results show that jet fuel production costs could be reduced by relaxing fuel properties. Potential cost savings in the East (PADDs I-IV) through property relaxation were found to be about 1.3 cents/liter (5 cents/gallon) in January 1, 1981 dollars between 1990 and 2010. However, the savings from property relaxation were all obtained within the range of current Jet A specifications, so there is no financial incentive to relax Jet A fuel specifications in the East. In the West (PADD V) the potential cost savings from lowering fuel quality were considerably greater than in the East. Cost savings from 2.7 to 3.7 cents/liter (10-14 cents/gallon) were found. In contrast to the East, on the West Coast a significant part of the savings was obtained through relaxation of the current Jet A fuel specifications.

Breton, T.↗
NASA NTRS1984

The Effect of Matrix and Fiber Properties on Impact Resistance

The basic material properties which control impact damage are identified and testing techniques are assessed. It is demonstrated that static indentation tests can provide better information about failure processes than impact tests, and they are simpler to conduct. In thin and thick laminates, it was found that the matrix shear strength controls the onset of delamination damage and that the fiber strength controlled the penetration phase. In thin laminates, tough matrices do little to enhance impact resistance.

Elber, W.↗
NASA NTRS1986

Dynamic moduli and localized damage in composites

The scatter of elastic waves due to a thin, flat ellipsoidal inhomogeneity, either penny shaped or elliptical is discussed. An average theorem appropriate for dynamic effective mass density and effective moduli was developed via a self-consistent scheme. Effective material properties of two-component media consisting of randomly distributed spheres are given here as a special case.

Fu, L. S.↗
NASA NTRS1986

The effect of Thematic Mapper spectral properties on land cover mapping for hydrologic modeling

The accuracy of unsupervised land-cover classification from all seven Landsat TM bands and from six combinations of three or four bands is evaluated using images of the Clinton River Basin, a suburban watershed near Detroit. Data from aerial TMS photography, USGS topographic maps, and ground surveys are employed to determine the classification accuracy. The mapping accuracy of all seven bands is found to be significantly better (6 percent overall, 12 percent for residential areas, and 13 percent for commercial districts) than that with bands 2, 3, and 4; but almost the same accuracy is obtained by including at least one band from each major spectral region (visible, NIR, and mid-IR).

Gervin, J. C.↗
NASA NTRS1988

Flow-field Survey of an Empennage Wake Interacting with a Pusher Propeller

The flow field between a model empennage and a 591-mm-diameter pusher propeller was studied in the Ames 7- by 10-Foot Wind Tunnel with directional pressure probes and hot-wire anemometers. The region probed was bounded by the empennage trailing edge and downstream propeller. The wake properties, including effects of propeller operation on the empennage wake, were investigated for two empennage geometries: one, a vertical tail fin, the other, a Y-tail with a 34 deg dihedral. Results showed that the effect of the propeller on the empennage wake upstream of the propeller was not strong. The flow upstream of the propeller was accelerated in the streamwise direction by the propeller, but the empennage wake width and velocity defect were relatively unaffected by the presence of the propeller. The peak turbulence in the wake near the propeller tip station, 0.66 diameter behind the vertical tail fin, was approximately 3 percent of the free-stream velocity. The velocity field data can be used in predictions of the acoustic field due to propeller-wake interaction.

Horne, W. Clifton↗
NASA NTRS1990

Application of the pentaiodide strong base resin disinfectant to the U.S. space program

A pentaiodide resin is described which has 70 percent of its weight composed of elemental iodine, has a relatively low iodine residual, and may offer superior disinfection capability for applications on long-duration space vehicles. Such a disinfectant is crucial for use on spacecraft for long periods of time where water would be recycled through various systems. The pentaiodide resin is capable of devitalizing 1 x 10 to the 9th bacteria per ml in aqueous suspension within 10 seconds of contact with the resin bed. A number of organisms have already been tested and the resin continues to prove effective. Resin properties and composition are discussed and a detailed account of the first investigation of the pentaiodide resin as a disinfectant against the intestinal parasite Giardia lamblia is provided.

Marchin, George L.↗
NASA NTRS1991

Effect of the rotational-vibrational excitation on molecular diameters

The kinetic molecular diameters of rotationally and vibrationally excited diatomic molecules and molecular ions are derived as functions of the rotational and vibrational quantum numbers of the molecules. Typical molecular diameters are studied in two cases: in low-temperature gas, where the molecular diameter is independent of the degree of rotational-vibrational excitation of the molecules, and in high-temperature gas, where the molecular diameter depends on the degree of rotational-vibrational excitation of the molecules. The rotational-vibrational excitation of molecules is shown to have a meaningful effect on the collisional properties of gases. The effect is stronger in gases of weakly-bound molecules.

Kang, S. H.↗
NASA NTRS1991

Laboratory photometric measurement of particulate soils out to very large phase angles

In the present study, the objectives were to develop the laboratory methods and tools to conduct photometric observations of dark particulate samples over a large range of phase angles and to demonstrate whether forward scattering behavior can be seen in a surface constructed of low albedo material. The researchers also examined the adequacy of various model formulations of P (alpha) to describe the effective scattering properties of their sample.

Helfenstein, Paul↗
NASA NTRS1991

Temperature effects on high strain rate properties of graphite/epoxy composites

A unidirectional graphite epoxy material (AS4/3501-6) was characterized at strain rates ranging from 5 x 10(exp 6) s(exp -1) to 5(exp -1), at room temperature and at 128 C. Results are presented in the form of stress-strain curves to failure. The longitudinal properties remain nearly unchanged with strain rate and temperature. The transverse modulus increases with strain rate but decreases with temperature. The transverse strength and transverse ultimate tensile strain have a positive rate sensitivity at low rates, which changes to negative at intermediate rates and returns to positive rate sensitivity at the highest rates tested. A temperature-time equivalence principle was applied and master curves were obtained for the transverse mechanical properties. The in-plane shear modulus and in-plane shear strength have a positive rate sensitivity. The ultimate intralaminar shear strain has a positive rate sensitivity at low rates, which changes to negative at high rates. At the elevated temperature of 128 C, the ultimate shear strain is 25 to 30 percent higher than the room temperature value, but its strain rate dependence is moderate.

Yaniv, G.↗
NASA NTRS1991

An approximate analytical solution for interlaminar stresses in angle-ply laminates

An improved approximate analytical solution for interlaminar stresses in finite width, symmetric, angle-ply laminated coupons subjected to axial loading is presented. The solution is based upon statically admissible stress fields which take into consideration local property mismatch effects and global equilibrium requirements. Unknown constants in the admissible stress states are determined through minimization of the complementary energy. Typical results are presented for through-the-thickness and interlaminar stress distributions for angle-ply laminates. It is shown that the results represent an improved approximate analytical solution for interlaminar stresses.

Rose, Cheryl A.↗
NASA NTRS1993

An approximate solution for interlaminar stresses in composite laminates

An efficient approximate solution for interlaminar stresses in finite width, symmetric and unsymmetric laminated composites subjected to axial and/or bending loads is presented. The solution is based upon statically admissible stress fields which take into consideration local property mismatch effects and global equilibrium requirements. Unknown constants in the assumed stress states are determined through minimization of the laminate complementary energy. Typical results are presented for through-thickness and interlaminar stress distributions for angle-ply and cross-ply laminates subjected to axial loading. It is shown that the present formulation represents an improved, efficient approximate solution for interlaminar stresses.

Rose, Cheryl A.↗
NASA NTRS1993

Variation of the energy release rate as a crack approaches and passes through an elastic inclusion

The variation of the energy release rate (ERP) at the tip of a crack penetrating an elastic inclusion is analyzed using an approach involving modeling the random array of microcracks or other defects by an elastic inclusion with effective elastic properties. Computations are carried out using a finite element procedure. The eight-noded isoparametric serendipity element with the shift of the midpoint to the quarter-point is used to simulate the singularity at the crack tip, and the crack growth is accommodated by implementing a mesh regeneration technique. The ERP values were calculated for various crack tip positions which simulate the process of the crack approaching and penetrating the inclusion.

Li, Rongshun↗