Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “Effective properties”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 847 records · Page 47
All sourcesNASA NTRSDOE OSTI
NASA NTRS1973

Enriched aluminide coatings for dispersion strengthened nickel materials

Improved aluminide/barrier coating combinations for dispersion strengthened nickel materials were investigated. The barrier materials involved alloys with refractory metal content to limit interdiffusion between the coating and the substrate, thereby minimizing void formation. Improved aluminide coatings involved the dispersion of aluminum-rich compounds. Coatings were tested in argon at 1533 K (2300 F) for 100 hours and in cyclic oxidation at 1422 K (2100 F). Two coatings on TDNiCr completed 300 hours of oxidation testing, none on TDNi. Selected coating combinations were evaluated in Mach 1 burner rig testing using JP-4 fuel and air at 1422 K (2100 F) and 1477 K (2200 F) for 350 and 100 hours, respectively. Static oxidation in 1-hour cycles was conducted at 1533 K (2300 F) for 100 hours. For comparison purposes a physical vapor deposition (PVD) NiCrAlY coating was tested concurrently. Only the NiCrA1Y coating survived the 1477 K (2200 F)/100-hour burner rig test and 275 hours of the 350-hour 1422 K (2100 F) test. Elevated temperature exposure reduced room temperature tensile properties but had little effect on elevated temperature properties.

Levinstein, M. A.↗
NASA NTRS1974

The thermal and mechanical properties of a low-density glass-fiber-reinforced elastomeric ablation material

An evaluation of the thermal and mechanical properties was performed on a molded low-density elastomeric ablation material designated as Material B. Both the virgin and charred states were examined to provide meaningful inputs to the design of a thermal protection system. Chars representative of the flight chars formed during ablation were prepared in a laboratory furnace from 600 K to 1700 K and properties of effective thermal conductivity, heat capacity, porosity and permeability were determined on the furnace chars formed at various temperature levels within the range. This provided a boxing of the data which will enable the prediction of the transient response of the material during flight ablation.

Engelke, W. T.↗
NASA NTRS1975

Deposition rate and substrate temperature effects on the structure and properties of bulk-sputtered OFHC Cu and Cu-0.15Zr

Bulk-sputtered OFHC Cu and Cu-0.15 Zr used as inner walls of advanced regeneratively cooled thrust chambers are evaluated as to microstructure, surface topography, and fractography. It is found that under conditions of low substrate temperature, crystallite size and openness of the structure increase with increasing deposition rate for both materials. At elevated temperatures, an equiaxed ductile structure of OFHC Cu is produced only at low deposition rates; at higher deposition rate, open structures are observed with recrystallized equiaxed grains within large poorly bonded crystallites. The Cu-0.15 Zr alloy sputtered from the hollow cathode using a diode discharge shows open-type structures for all conditions evaluated. The use of a triode discharge in generating a dense non-voided structure of Cu-0.15 Zr is discussed.

Hecht, R. J.↗
NASA NTRS1975

OGO-6 observations of 5577 A

A brief review is given of the data obtained by the horizon-scanning 5577-A airglow photometer flown aboard OGO 6. Data are presented which show the contributions to the 5577-A emission from the F-1 region and the Chapman airglow layer. Emission rates are calculated for both regions on the basis of the dissociative-recombination and Chapman reactions, and the atomic oxygen density and downward flux are inferred from the emission rates and several assumptions concerning the temperature dependence of the rate constants. Latitude variations in the emission rates are discussed along with variations in the altitude of the 5577-A airglow. It is shown that there is a large semiannual variation in the average effective transport properties of the lower thermosphere, that the atomic oxygen profiles near 110 km suggest a maximum in eddy diffusion at about that altitude, and that systematic variations in the altitude of the atomic oxygen maximum probably do not exceed 2 km.

Donahue, T. M.↗
NASA NTRS1977

Improved accuracy with phase-change paints

Technique, using effective thermophysical property, significantly improves accuracy when phase-change coating methods are used to determine heat transfer rate over surface of small complex models.

Drummond, J. D.↗
NASA NTRS1977

Analysis of shear test method for composite laminates

An elastic plane stress finite element analysis of the stress distributions in four flat test specimens for in-plane shear response of composite materials subjected to mechanical or thermal loads is presented. The shear test specimens investigated include: slotted coupon, cross beam, losipescu, and rail shear. Results are presented in the form of normalized shear contour plots for all three in-plane stess components. It is shown that the cross beam, losipescu, and rail shear specimens have stress distributions which are more than adequate for determining linear shear behavior of composite materials. Laminate properties, core effects, and fixture configurations are among the factors which were found to influence the stress distributions.

Bergner, H. W., Jr.↗
NASA NTRS1978

Thermal environment effects on strength and impact properties of boron-aluminum composites

A systematic study was conducted regarding the degradation of fracture strength and impact energy in commercial B-Al composites in both static and cyclic thermal environments. The composites used in the study contained approximately 50 vol % boron fibers, unidirectionally aligned in either a 6061 Al or 1100 Al matrix. The tensile strengths of the composites after 3000 thermal cycles as a function of upper cycle temperature are presented in graphs. The temperature at which the strengths of 6061 Al matrix, B-Al composites were significantly degraded after 3000 cycles was noticeably higher than that for the 1100 Al matrix composites. Static heating at 420 C resulted in no significant strength degradation for the 6061 Al matrix composites. In the case of 1100 matrix composites, some degradation was observed at 420 C but markedly less than in the composites cycled to 420 C.

Grimes, H. H.↗
NASA NTRS1978

Some effects of ablation on transport properties in the Jovian atmosphere

In this paper the transport properties at the inner and outer boundary for mixing between ablation products and a Jovian-like atmosphere are calculated. The dominant species at these boundaries are C, H, O, He, H+, and e. Accurate potential energy curves are obtained for the fifteen possible two-body interactions among these species by fitting good semiempirical potentials for which transport collision cross sections have been tabulated to accurate experimental and theoretical information. Results are obtained for the viscosity and translational thermal conductivity of the pure species and the binary diffusion coefficients from 1000 K to 25,000 K. In addition, the mixture translational thermal conductivity and viscosity are calculated at the inner and outer mixing boundaries. This information is required for calculating flowfield properties and surface heating. The most important conclusion is that the translational thermal conductivity is substantially lower at the inner mixing boundary than it is at the outer mixing boundary.

Biolsi, L.↗
NASA NTRS1979

Qualitative and quantitative flow visualization technique using ozone

The paper describes a new flow-visualization technique based on the absorption of ultraviolet light by ozone. Ozone is an excellent tracer, because as a gas it has the same effective physical properties as air. Ozone strongly absorbs the principal line (253.7 nm) of a mercury lamp, so that when an ozone-traced flow passes between a mercury lamp and a fluorescent screen, a sharp, shadow-like image of the ozone tracer is cast on the screen. Quantitative photometry can be carried out by replacing the screen with ultraviolet detectors that yield the path-integrated column density of ozone in the flow. High-speed quantitative point monitoring (10 Hz at 10 ppb O3) is possible with capillary probes and chemiluminescent analysis.

Dickerson, R. R.↗
NASA NTRS1980

Study of the effects of impurities on the properties of silicon materials and performance of silicon solar cell

Zinc is a major residue impurity in the preparation of solar grade silicon material by the zinc vapor reduction of silicon tetrachloride. It was found that in order to get a 17 percent AMl cell efficiency, the concentration of the zinc recombination centers in the base region of silicon solar cells must be less than 4 x 10 to the 11th power Zn/cu cm in the p-base n+/p/p+ cell and 7 x 10 to the 11th power Zn/cu cm in the n-base p+/n/n+ cell for a base dopant impurity concentration of 5 x 10 to the 14th power atoms/cu cm. If the base dopant impurity concentration is increased by a factor of 10 to 5 x 10 to the 15th power atoms/cu cm, then the maximum allowable zinc concentration is increased by a factor of about two for a 17 percent AMl efficiency. The thermal equilibrium electron and hole recombination and generation rates at the double acceptor zinc cancers were obtained from previous high field measurements as well as new measurements at zero field. The rates were used in the exact d.c. circuit model to compute the projections.

Sah, C. T.↗
NASA NTRS1980

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 sensitivity, and careful quality control in any study of composite materials.

Clements, L. L.↗
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.↗