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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 739 records · Page 41
All sourcesNASA NTRSDOE OSTI
NASA NTRS1973

Effect of Cristobalite on the Mechanical Properties of Silica RSI Materials

The strength of various silica surface insulation materials was measured after high temperature heat treatment to develop substantial crystalline phases, and after low temperature thermal cycling through the alpha-beta cristobalite transformation. It appears that the presence of cristobalite in the structural elements (the fibers) is highly detrimental to tensile strength. When crystallization does not occur in silica material, the strength improves with heat treatment.

Khandelwal, P. K.↗
NASA NTRS1972

Limited cavitation and the related scale effects problem.

It is indicated that the study of limited cavitation can be divided into two parts, namely, the factors which influence the pressure field, and those which influence the bubble dynamics. Major aspects of cavitation nuclei and bubble dynamics are summarized. An analysis is presented of the effects of velocity, size and fluid properties, including the thermodynamic effect. The effects of turbulence, roughness and polymer additives are presented. These include new data on roughness and estimates of the effects of turbulence and polymer additives on jets. An analysis of nonvaporous cavitation with new data on vortex cavitation is presented. Implications concerning scale effects are given.

Holl, J. W.↗
NASA NTRS1974

The effect of ultrasonics on the strength properties of carbon steel processed by cold plastic deformation

A study was made of the influence of ultrasounds on the mechanical properties of OLT 35 carbon steel tubes cold-drawn on a plug ultrasonically activated by longitudinal waves. Experimental results indicate that: 1. The reduction in the values of the flow limit and tensile strength is proportional to the increase in acoustic energy introduced into the material subjected to deformation. 2. The diminution in influence of ultrasounds on tensile strength and flow rate that is due to an increased degree of deformation is explained by a reduction in specific density of the acoustic energy at the focus of deformation. 3. The relations calculated on the basis of the variation in the flow limit and tensile strength as a function of acoustic energy intensity was verified experimentally.

Atanasiu, N.↗
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 NTRS1977

Effects of illumination on the conductivity properties of spacecraft insulating materials

Experimental data on the dark and illuminated conductivities of Kapton V and polyvinylidene fluoride (PVF2) films are described as well as the changes in insulating properties produced in Kapton H, Kapton V, PVF2, and FEP Teflon films as result of prolonged exposure to solar illumination. An overall summary of the results of tests is presented. A general introduction and a description of the experimental apparatus and procedures used are also given.

Adamos, R. C.↗
NASA NTRS1980

Effects of hypodynamia on the hemocoagulative properties of the vascular wall and myocardium

The hemocoagulative properties of the aorta (laminar), myocardium, hollow veins, and fibrinolytic capacity of tissues were studied in 14 rabbits subjected to 7 days of restricted mobility and compared to those of 10 control animals. Two tables of results show that, as a result of hypodynamia, the thromboplastic activity of the inner and middle layers of the aorta together with the destruction of endothelium increases the hemocoagulative potential and creates the threat of thrombogenesis. There is also an increase in fibrin-stabilizing activity for all tissues.

Inchina, V. I.↗
NASA NTRS1983

The effects of vegetation and soil hydraulic properties on passive microwave sensing of soil moisture: Data report for the 1982 fiels experiments

Field experiments to (1) study the biomass and geometrical structure properties of vegetation canopies to determine their impact on microwave emission data, and (2) to verify whether time series microwave data can be related to soil hydrologic properties for use in soil type classification. Truck mounted radiometers at 1.4 GHz and 5 GHz were used to obtain microwave brightness temperatures of bare vegetated test plots under different conditions of soil wetness, plant water content and canopy structure. Observations of soil moisture, soil temperature, vegetation biomass and other soil and canopy parameters were made concurrently with the microwave measurements. The experimental design and data collection procedures for both experiments are documented and the reduced data are presented in tabular form.

Oneill, P.↗
NASA NTRS1984

Effects of thermal cycling on magnetic properties of lunar analogs

An experimental study has been performed to determine whether stresses associated with thermal cycling cracks can affect the coercivity of remanence carried by iron in lunar samples. Initially, samples were cycled up to 100 times in a refrigerator over a period of about 30 min per cycle. In a second set of experiments, samples were dipped directly into liquid nitrogen up to 100 times at about 1 min per cycle. Comparison of AF demagnetization curves of weak field anhysteretic remanent magnetization before and after cycling revealed no systematic differences. Calculations based on a model of spherical iron grains within olivine or troilite indicate that it is unlikely that the iron will crack under thermal stress. Thus, thermal cycling does not appear to provide an explanation for increasing the stability of remanence in samples from the lunar surface.

Barron, A. M.↗
NASA NTRS1987

Spectroscopic comparison of effects of electron radiation on mechanical properties of two polyimides

The differences in the radiation durabilities of two polyimide materials, Du Pont Kapton and General Electric Ultem, are compared. An explanation of the basic mechanisms which occur during exposure to electron radiation from analyses of infrared (IR) and electron paramagnetic resonance (EPR) spectroscopic data for each material is provided. The molecular model for Kapton was, in part, established from earlier modeling for Ultem (pp. 1293-1298 of IEEE Transactions on Nuclear Science, December 1984). Techniques for understanding the durability of one complex polymer based on the understanding of a different and equally complex polymer are demonstrated. The spectroscopic data showed that the primary radiation-generated change in the tensile properties of Ultem (a large reduction in tensile elongation) was due to crosslinking, which followed the capture by phenyl radicals of hydrogen atoms removed from gem-dimethyl groups. In contrast, the tensile properties of Kapton remained unchanged because radical-radical recombination, a self-mending process, took place.

Long, Edward R., Jr.↗
NASA NTRS1986

Effects of instrument characteristics on cloud properties retrieved from satellite imagery data

The relationships between sensor resolution and derived cloud properties in satellite remote sensing were studied by comparisons of cloud characteristics determined by spatial coherence analysis of AVHRR and GOES data. The latter data were simulated from 11 microns AVHRR data and were assigned a resolution (8 sq km) half that of the AVHRR. Day and nighttime passes were considered for single-layer maritime cloud systems. Sample radiance vs local standard deviation plots of 1024 points are provided for the same area from AVHRR and GOES-East sensors, demonstrating a qualitative agreement.

Baldwin, D. G.↗
NASA NTRS1993

Turbulent flow in a channel with transverse rib heat transfer augmentation

Turbulent flow in a 2D channel with repeated rectangular rib roughness was numerically simulated using a low Reynolds number form of the k-epsilon turbulence model. Friction factors and average Stanton numbers were calculated for various pitch to rib height ratios and bulk Reynolds numbers. Comparisons with experiment were generally adequate, with the predictions of friction superior to those for heat transfer. The effect of variable properties for channel flow was investigated, and the results showed a greater effect for friction than for heat transfer. Comparison with experiment yielded no clear conclusions. The turbulence model was also validated for a related problem, that of flow downstream of an abrupt pipe expansion.

Chang, B. H.↗
NASA NTRS1993

Effects of process variables on the properties of YBa2Cu3O(7-x) ceramics formed by investment casting

An investment casting process has been developed to produce net-shape, superconducting ceramics. In this work, a factorial experiment was performed to determine the critical process parameters for producing cast YBa2Cu3O7 ceramics with optimum properties. An analysis of variance procedure indicated that the key variables in casting superconductive ceramics are the particle size distribution and sintering temperature. Additionally, the interactions between the sintering temperature and the other process parameters (e.g., particle size distribution and the use of silver dopants) were also found to influence the density, porosity, and critical current density of the fired ceramics.

Hooker, M. W.↗