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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 325 records · Page 18
All sourcesNASA NTRSDOE OSTI
NASA NTRS1991

Superplastic formability of Al-Cu-Li alloy Weldalite (TM) 049

Extensive research during the past decade shows that several aluminum lithium alloys can be processed to attain a microstructure that enables superplasticity. The high tensile stress of Al-Cu-Li alloy Weldalite (TM) 049 in the T4 and T6 tempers offers tremendous potential for attaining exceptional post-SPF (superplastic formability) properties. The used SPF material is Weldalite, which was shown to induce SPF behavior in other Al-Cu-Li alloys. The superplastic behavior and resulting post-SPF mechanical properties of this alloy, which was designed to be the next major structural alloy for space applications, were evaluated. The results indicate that Weldalite alloy does indeed exhibit excellent superplasticity over a wide range of temperatures and strain rates and excellent post-SPF tensile strength at various potential service temperatures.

Ma, Bao-Tong↗
NASA NTRS1991

The effect of temperature on the fracture toughness of Weldalite(TM) 049

The uncertain effect of temperature is characterized on the deformation and fracture behavior of Weldalite(TM) 049 from cryogenic to elevated temperatures. Fracture resistance is measured and the determination of fracture mechanisms emphasized, including slip plane cracking, high angle boundary delamination, subgrain boundary cracking, and microvoid coalescence. Microstructure is controlled to produce either predominantly T(sub 1) or T(sub 1) + delta (after Blankenship and Starke) and to examine the effect of dislocation-precipitate interaction on fracture toughness.

Lach, Cynthia L.↗
NASA NTRS1991

Identification of strengthening phases in Al-Cu-Li alloy Weldalite (tm) 049

Microstructure property relationships were determined for a family of ultrahigh strength weldable Al-Cu-Li based alloys referred to as Weldalite (tm) alloys. The highest strength variant of this family, Weldalite 049, has a high Cu/Li wt pct. ratio with a nominal composition of Al-6.3Cu-1.3Li-0.4Ag-0.4Mg-0.14Zr. Increasing the alloy's lithium content above 1.3 wt pct. resulted in a decrease in both yield and ultimate tensile strength. Strength was shown to be strongly dependent on lithium content, with a maximum in strength occurring in the range of about 1.1 to 1.4 wt pct. lithium. The strengthening phases present in Weldalite 049 (1.3Li) and an Al-6.3Cu-1.9Li-0.4Mg-0.14Zr alloy were identified using transmission electron microscopy (TEM).

Source record↗
NASA NTRS1991

Weldability of Weldalite (tm) 049 with and without TiB2 reinforcement

The effects are assessed of TiB2 reinforcement and parent alloy Li content on the weldability of Weldalite (tm) 049 type alloys. Welding trials were performed using either AC or DC polarity gas tungsten arc (GTA) welding according to described procedures. The welding was performed under conditions of high restraint on 5 cm (2 in) wide x 25.4 cm (10 in) long plates machined from the 0.952 cm (0.375 in) extruded bar parallel to the extrusion direction. A 37.5 deg bevel was machined on the center edge of the extruded bar. Cut rod filler wire was machined from three alloys, and one commercially available 2319 filler wire was also used. The preliminary assessment of the weldability revealed no propensity for hot cracking under conditions of high restraint. This result is significant, because hot cracking has been reported for all other leading aluminum lithium alloys welded with certain conventional filler alloys. The strengths for Weldalite parent welded with parent filler obtained were higher than those for alloys used in launch systems, such as 2219 and 2014 welded with 2319 and 4043 fillers, respectively. Even higher values were obtained by variable polarity plasma arc welding (e.g., 54 ksi (372 MPa) mean tensile strength).

Source record↗
NASA NTRS1991

Effect of Li level, artificial aging, and TiB2 reinforcement on the fracture toughness of Weldalite (tm) 049-type alloys

Plane strain fracture toughness (K sub IC) was evaluated for Weldalite (tm) 049 with and without TiB2 reinforcement. For the nonreinforced variant, changes in toughness were measured for various aging conditions and lithium levels. Toughness testing was carried out on fatigue precracked compact tension (CT) specimens at 24 C, as per ASTM standard E-399. Toughness was measured as a function of aging time at 160 C for the two Weldalite 049(1.3) heats. The composition of these heats differed only in that 0.03 wt pct. Ti was added to one as an additional grain refiner. Both heats showed a decrease in toughness with increasing aging time, although toughness values for one were significantly higher than for the other. This greater toughness may be due to a subtle change in the grain size resulting for the presence of Ti or, alternatively, to differences in texture or substructure formed during extrusion.

Source record↗
NASA NTRS1990

CFIE MM solution for TE and TM incidence on a 2-D conducting body with dielectric filled cavity

The problem of determining the scattering cross section of an arbitrarily shaped two-dimensional conducting body with an arbitrarily shaped dielectric-filled cavity is considered. The problem is solved using a method-of-moments (MM) solution for the combined field integral equations (CFIE). The particular form of the method of moments solution used has here uses a minimum number of expansion coefficients. Results are given for TE and TM incident waves.

Goggans, Paul M.↗
NASA NTRS1990

Selection of Landsat TM band and band-ratio combinations to maximize lithologic information in color composite displays

Correlation analyses of Landsat TM data for arid areas and laboratory spectral data for various combinations of minerals indicate that band combination 1-4-7 maximally differentiates lithologic materials in most scenes, but that band combination 1-5-7 is preferable for scenes in which hydroxyl-rich minerals are prominent or of specific interest. Among band ratio combinations, 3/1 - 5/4 - 5/7 ranks high for optimal information display.

Crippen, Robert E.↗
NASA NTRS1991

Eye-safe coherent laser radar system at 2.1 microns using Tm,Ho:YAG lasers

An eye-safe pulsed coherent laser radar has been developed by using single-frequency Tm,Ho:YAG lasers and heterodyne detection. Returns from a mountainside located 145 km from the laser radar system and the measurement of wind velocity to ranges exceeding 20 km have been demonstrated with transmitted pulse energies of 22 mJ.

Henderson, Sammy W.↗
NASA NTRS1991

Single-mode lasing of Ho:Tm:YAG at 2.091 microns in a monolithic crystal

This paper demonstrates single-longitudinal-mode lasing of Ho:Tm:YAG at 2.091 microns in a diode-laser-pumped monolithic crystal. Heterodyne detection at 2.1 microns is demonstrated, and energy diffusion effects on spatial hole burning are discussed. Temperature tuning over 4.5 A is demonstrated.

Storm, Mark E.↗
NASA NTRS1991

Experiments and theory for a Tm:Ho:YAG laser end pumped by a Cr:GSAG laser

A Cr:GSAG-laser-pumped Tm:Ho:YAG laser has been fabricated and tested. A maximum output energy of 14 mJ with a slope efficiency of 33.6 percent was obtained using a 98-percent reflective output coupler. A comprehensive rate equation model has been developed to describe laser performance. Details of the experimental measurements and model are presented.

Kim, Kyong H.↗
NASA NTRS1991

An SSME high pressure oxidizer turbopump diagnostic system using G2(TM) real-time expert system

An expert system which diagnoses various seal leakage faults in the High Pressure Oxidizer Turbopump of the SSME was developed using G2(TM) real-time expert system. Three major functions of the software were implemented: model-based data generation, real-time expert system reasoning, and real-time input/output communication. This system is proposed as one module of a complete diagnostic system for Space Shuttle Main Engine. Diagnosis of a fault is defined as the determination of its type, severity, and likelihood. Since fault diagnosis is often accomplished through the use of heuristic human knowledge, an expert system based approach was adopted as a paradigm to develop this diagnostic system. To implement this approach, a software shell which can be easily programmed to emulate the human decision process, the G2 Real-Time Expert System, was selected. Lessons learned from this implementation are discussed.

Guo, Ten-Huei↗
NASA NTRS1992

Postflight aerothermodynamic analysis of Pegasus(tm) using computational fluid dynamic techniques

The objective was to validate the computational capability of the NASA Ames Navier-Stokes code, F3D, for flows at high Mach numbers using comparison flight test data from the Pegasus (tm) air launched, winged space booster. Comparisons were made with temperature and heat fluxes estimated from measurements on the wing surfaces and wing-fuselage fairings. Tests were conducted for solution convergence, sensitivity to grid density, and effects of distributing grid points to provide high density near temperature and heat flux sensors. The measured temperatures were from sensors embedded in the ablating thermal protection system. Surface heat fluxes were from plugs fabricated of highly insulative, nonablating material, and mounted level with the surface of the surrounding ablative material. As a preflight design tool, the F3D code produces accurate predictions of heat transfer and other aerodynamic properties, and it can provide detailed data for assessment of boundary layer separation, shock waves, and vortex formation. As a postflight analysis tool, the code provides a way to clarify and interpret the measured results.

Kuhn, Gary D.↗
NASA NTRS1991

Backscatter RCS for TE and TM excitations of dielectric-filled cavity-backed apertures in two-dimensional bodies

Transverse electric (TE) and transverse magnetic (TM) scattering from dielectric-filled, cavity-backed apertures in two-dimensional bodies are treated using the method of moments technique to solve a set of combined-field integral equations for the equivalent induced electric and magnetic currents on the exterior of the scattering body and on the associated aperture. Results are presented for the backscatter radar cross section (RCS) versus the electrical size of the scatterer for two different dielectric-filled cavity-backed geometries. The first geometry is a circular cylinder of infinite length which has an infinite length slot aperture along one side. The cavity inside the cylinder is dielectric filled and is also of circular cross section. The two cylinders (external and internal) are of different radii and their respective longitudinal axes are parallel but not collocated. The second is a square cylinder of infinite length which has an infinite length slot aperture along one side. The cavity inside the square cylinder is dielectric-filled and is also of square cross section.

Goggans, Paul M.↗
NASA NTRS1991

Efficient energy extraction from a diode-pumped Q-switched Tm,Ho:YLiF4 laser

The operation of a diode-laser pumped thulium, holmium yttrium-lithium-fluoride laser (Tm,Ho:YLF) in Q-switched mode is reported. Output energies of 200 microjoules in pulses of 22 ns duration are recorded at Q-switch frequencies commensurate with an effective upper laser level lifetime of 6 ms. This lifetime is appreciably longer than that observed in other hosts permitting stored energy extraction of 64 percent, close to the projected maximum performance from these materials.

Mcguckin, B. T.↗
NASA NTRS1992

Landsat-TM identification of Amblyomma variegatum (Acari: Ixodidae) habitats in Guadeloupe

The feasibility of identifying specific habitats of the African bont tick, Amblyomma variegatum, from Landsat-TM images was investigated by comparing remotely sensed images of visible farms in Grande Terre (Guadeloupe) with field observations made in the same period of time (1986-1987). The different tick habitates could be separated using principal component analysis. The analysis clustered the sites by large and small variance of band values, and by vegetation and moisture indexes. It was found that herds in heterogeneous sites with large variances had more ticks than those in homogeneous or low variance sites. Within the heterogeneous sites, those with high vegetation and moisture indexes had more ticks than those with low values.

Hugh-Jones, M.↗
NASA NTRS1992

Efficient CW diode-pumped Tm, Ho:YLF laser with tunability near 2.067 microns

A conversion efficiency of 42 percent and slope efficiency of approximately 60 percent relative to absorbed pump power are reported from a continuous wave diode-pumped Tm, Ho:YLF laser at 2 microns with output power of 84 mW at sub-ambient temperatures. The emission spectrum is etalon tunable over a range of 16/cm centered on 2.067 microns, with fine tuning capability of the transition frequency with crystal temperature at a measured rate of about -0.03/cm-K. The effective emission cross section is measured to be 5 x 10 exp -21 sq cm. These and other aspects of the laser performance are discussed in the context of calculated atmospheric absorption characteristics in this spectral region and potential use in remote sensing applications.

Mcguckin, B. T.↗
NASA NTRS1992

Identification of central Kenyan Rift Valley Fever virus vector habitats with Landsat TM and evaluation of their flooding status with airborne imaging radar

Rift Valley Fever (RVF) is a mosquito-borne virus that affects livestock and humans in Africa. Landsat TM data are shown to be effective in identifying dambos, intermittently flooded areas that are potential mosquite breeding sites, in an area north of Nairobi, Kenya. Positive results were obtained from a limited test of flood detection in dambos with airborne high resolution L, C, and X band multipolarization SAR imagery. L and C bands were effective in detecting flooded dambos, but LHH was by far the best channel for discrimination between flooded and nonflooded sites in both sedge and short-grass environments. This study demonstrates the feasibility of a combined passive and active remote sensing program for monitoring the location and condition of RVF vector habitats, thus making future control of the disease more promising.

Pope, K. O.↗
NASA NTRS1992

Phase shift of TE and TM modes in an optical fiber due to axial strain (exact solution)

Axial strain may be determined by monitoring the phase shift of modes of a variety of optical fiber sensors. In this paper, the exact solution of a circular optical fiber is used to calculate the phase shift of the TE and TM modes. Whenever an optical fiber is stressed, the optical path length, the index of refraction, and the propagation constants of each fiber mode change. In consequence, the modal phase term, beta(ln)z, of the fields is shifted by an amount Delta phi. In certain cases, it is desirable to control the phase shift term in order to make the fiber either more or less sensitive to certain kinds of strain. It is shown that it can be accomplished by choosing appropriate fiber parameters.

Egalon, Claudio O.↗