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At least 1,531 records · Page 85

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NASA NTRS1992

Radioactivities of Long Duration Exposure Facility (LDEF) materials: Baggage and bonanzas

Radioactivities in materials onboard the returned Long Duration Exposure Facility (LDEF) satellite were studied by a variety of techniques. Among the most powerful is low-background Ge-semiconductor detector gamma-ray spectrometry, illustrated here by results obtained at the Lawrence Berkeley Laboratory's (LBL) Low Background Facilities. The observed radioactivities are of two origins: those radionuclides produced by nuclear reactions with the radiation field in orbit, and radionuclides present initially as 'contaminants' in materials used for construction of the spacecraft and experimental assemblies. In the first category are experiment-related monitor foils and tomato seeds, and such spacecraft materials as aluminum, stainless steel, and titanium. In the second category are aluminum, beryllium, titanium, vanadium, and some special glasses.

Smith, Alan R.↗

NASA NTRS1992

Measurements of induced radioactivity in some LDEF samples

Twenty-six stainless steel trunnion samples, five aluminum end support retainer plate samples, two aluminum keel plate samples, and two titanium clips were analyzed. The shielded high purity germanium detectors used had efficiencies of 33, 54, and 80 percent at 1332 keV. Detector efficiencies as a function of energy and corrections for self-absorption in the samples were determined with calibrated sources and unactivated control samples. Several measurements were made on most samples. In the trunnion samples, Mn-54 and Co-57 were seen and limits were obtained for other isotopes. The results agree well with 1-D activation calculations for an anisotropic trapped proton model. In the aluminum and titanium samples, Na-22 was detected. Other results are presented.

Moss, C. E.↗

NASA NTRS1991

A reevaluation of spectral ratios for lunar mare TiO2 mapping

The empirical relation established by Charette et al. (1974) between the 400/560-nm spectral ratio of mature mare soils and weight percent TiO2 has been used extensively to map titanium content in the lunar maria. Relative reflectance spectra of mare regions show that a reference wavelength further into the near-IR, e.g., above 700 nm, could be used in place of the 560-nm band to provide greater contrast (a greater range of ratio values) and hence a more sensitive indicator of titanium content. An analysis of 400/730-nm ratio values derived from both laboratory and telescopic relative reflectance spectra suggests that this ratio provides greater sensitivity to TiO2 content than the 400/560-nm ratio. The increased range of ratio values is manifested in higher contrast 400/730-nm ratio images compared to 400/560-nm ratio images. This potential improvement in sensivity encourages a reevaluation of the original Charette et al. (1974) relation using the 400/730-nm ratio.

Johnson, Jeffrey R.↗

NASA NTRS1992

Combined compressive and shear buckling analysis of hypersonic aircraft sandwich panels

The combined-load (compression and shear) buckling equations were established for orthotropic sandwich panels by using the Rayleigh-Ritz method to minimize the panel total potential energy. The resulting combined-load buckling equations were used to generate buckling interaction curves for super-plastically-formed/diffusion-bonded titanium truss-core sandwich panels and titanium honeycomb-core sandwich panels having the same specific weight. The relative combined-load buckling strengths of these two types of sandwich panels are compared with consideration of their sandwich orientations. For square and nearly square panels of both types, the combined load always induces symmetric buckling. As the panel aspect ratios increase, antisymmetric buckling will show up when the loading is shear-dominated combined loading. The square panel (either type) has the highest combined buckling strength, but the combined load buckling strength drops sharply as the panel aspect ratio increases. For square panels, the truss-core sandwich panel has higher compression-dominated load buckling strength. However, for shear dominated loading, the square honeycomb-core sandwich panel has higher shear-dominated combined load buckling strength.

Ko, William L.↗

NASA NTRS1993

Solid Lubricant For Alumina

Outer layer of silver lubricates, while intermediate layer of titanium ensures adhesion. Lubricating outer films of silver deposited on thin intermediate films of titanium on alumina substrates found to reduce sliding friction and wear. Films provide effective lubrication for ceramic seals, bearings, and other hot sliding components in advanced high-temperature engines.

Dellacorte, Christopher↗

NASA NTRS1992

A Ground-based Search for Lunar Resources Using High-resolution Imaging in the Infrared

When humans return to the Moon, lunar resources will play an important role in the successful deployment and maintenance of the lunar base. Previous studies have illustrated the abundance of resource materials available on the surface of the Moon, as well as their ready accessibility. Particularly worth considering are the lunar regional (2,000-30,000 sq km) pyroclastic deposits scattered about the lunar nearside. These 30-50-m-thick deposits are composed of fine-grained unconsolidated titanium- and iron-rich mafic glasses and may be used as bulk feedstock for the beneficiation of oxygen, iron, titanium, sulfur, and other solar wind gases, or simply used as is for construction and shielding purposes. A groundbased observing survey of the resource-rich regions on the lunar nearside using a new imaging technique designed to obtain much higher resolution images, and more precise compositional analyses than previously obtainable is proposed.

Coombs, C. R.↗

NASA NTRS1992

Determination of lunar ilmenite abundance from remotely sensed data

Of fundamental importance in the utilization of indigenous resources for a future permanently manned lunar base is the identification and mapping of the abundance distribution of the mineral ilmenite, which is currently considered the most readily identifiable and most easily accessible source of oxygen needed for human consumables and spacecraft propellant. Solid state detector array technology now permits the use of ground based multispectral remote sensing techniques to produce maps with better than one kilometer spatial resolution and uncertainties of about two weight-percent TiO2 abundance. An empirical relationship between the weight-percent abundance of titanium dioxide and the 400/560 nm spectral ratio measured in returned lunar samples was used. Because this abundance correlation is valid only for mature lunar mare regolith, the distribution of immature mafic minerals which were found to be correlated primarily with steep slopes exposing bedrock was qualitatively mapped. The first mapping phase focused on the entire lunar nearside at 5.3 km per pixel, and on experiments with more sensitive spectral ratios. Relative spectrophotometry was employed to aid in identifying wavelengths that provide greater spectral contrast. It was found that the 400/730 nm ratio improved the abundance sensitivity by 37 percent, while the 950/730 nm ratio improved mafic mineral contrast about 100 percent. The second mapping phase utilized a large experimental CCD at 280 m per pixel to map the high titanium regions identified in the phase one mapping. The high resolution maps provide data on the small scale (500 m) variations in abundance and their relationship to morphological units.

Larson, S. M.↗

NASA NTRS1993

Radioactivities induced in some LDEF samples

Radioactivities induced in several Long Duration Exposure Facilities (LDEF) samples were measured by low-level counting at Los Alamos and elsewhere. These radionuclides have activities similar to those observed in meteorites and lunar samples. Some trends were observed in these measurements in terms of profiles in trunnion layers and as a function of radionuclide half-life. Several existing computer codes were used to model the production by the protons trapped in the Earth's radiation belts and by the galactic cosmic rays of some of these radionuclides, Mn-54 and Co-57 in steel, Sc-46 in titanium, and Na-22 in alloys of titanium and aluminum. Production rates were also calculated for radionuclides possibly implanted in LDEF, Be-7, Be-10, and C-14. Enhanced concentrations of induced isotopes in the surfaces of trunnion sections relative to their concentrations in the center are caused by the lower-energy protons in the trapped radiation. Secondary neutrons made by high-energy trapped protons and by galactic cosmic rays produce much of the observed radioactivities, especially deep in an object. Comparisons of the observed to calculated activities of several radionuclides with different half-lives indicate that the flux of trapped protons at LDEF decreased significantly at the end of the mission.

Reedy, Robert C.↗

NASA NTRS1991

Practical approaches for application of hi-temperature strain gages on high temperature composites

Four major areas of interest with respect to utilizing strain gages on carbon/carbon (with SiC surfaces) and titanium matrix composites are addressed. Strain gage and adhesive combinations on carbon/carbon (C/C) at temperatures from minus 190 C to 540 C, half-bridge gaging for reducing apparent strain on C/C using Poisson's ratio and bending configurations, review of the 'field installation' techniques developed for gaging a C/C hypersonic generic elevon, and results of initial strain gaging efforts on titanium matrix composites are discussed. Current research in developing techniques for increasing the maximum temperature for strain gages on carbon/carbon are reviewed.

Moore, Thomas C., Sr.↗

NASA NTRS1992

Nonlinear acoustics and the thermal expansivity of glass

The paper shows the intrinsic relationship between acoustical nonlinearity and the thermal expansivity of crystalline solids (a thermal measure of anharmonicity) from consideration of the 'static' radiation field generated by the vibrating lattice (atomic) sources of the crystal. A modification of the theory to account for long-range structural disorder in glass is proposed and applied to an explanation of the zero thermal expansivity at the cross-over temperature in silicate and titanium silicate glasses. Experimental evidence which validates the essential features of the theory is presented. An application of nonlinearity measurement, based on these results, to the processing of ULE glass, where the addition of titanium in various amounts is used to establish the temperature at which the zero thermal expansivity occurs, is suggested.

Cantrell, John H.↗

NASA NTRS1993

Interfacial reactions in titanium/SCS fiber composites during fabrication

The objectrive of the study was to determine the effect of titanium concentration and different pyrocarbon fiber coatings on the morphology and the extent of fiber-matrix reactions in Ti/SiC composites fabricated by rapid infrared forming (RIF). It is found that the extent of fiber-matrix reactions in Ti/SiC composites fabricated by the RIF technique is noticeably affected by both an increase in Ti content and by the processing temperature. Uncoated SiC fibers extensively react with the titanium alloy matrix at 1200 C, whereas no reaction occurs when coated SiC fibers are used.

Warrier, S. G.↗

NASA NTRS1985

Siloxane containing polyimides with improved processability

Siloxane containing polyimides were prepared in an effort to improve processability of linear aromatic polyimides and toughness of addition curing imide oligomers. Linear aromatic polyimides were endcapped with varying proportions of a silane; a diaminosiloxane was copolymerized with an aromatic diamine; polyimide oligomers were endcapped with reactive groups; and acetylene terminated siloxane-containing oligomers were blended with linear siloxane-containing polyimides. The resins were used to prepare moldings, titanium to titanium adhesive bonds, and graphite reinforced composites. In each case, physical properties and other characteristics were compared to those of chemically similar polyimides with no siloxane incorporation. The resins, in most cases, performed better at room temperature than the corresponding polyimide. At elevated temperatures, for high siloxane content, the performance deteriorated.

Maudgal, Shubha↗

NASA NTRS1992

Chemistry and properties of poly(arylene ether 1,3,4-oxadiazole)s and poly(arylene ether 1,2,4-triazole)s

Poly(arylene ether)s containing l,3,4-oxadiazole and 1,2,4-triazole units were prepared by the aromatic nucleophilic displacement reaction of bisphenol oxadiazole and bisphenol triazole compounds with activated aromatic dihalides. The polymers exhibited glass transition temperatures (Tg) ranging from 182 to 242 C, and several polymers exhibited melting transitions (Tm) ranging from 265 to 390 C. Inherent viscosities ranged from 1.02 to 3.40 dl/g, indicating relatively high molecular weights. Thin films exhibited tensile strengths, moduli, and elongations at 23 C of 90-110 MPa, 2.7-3.6 GPa, and 4-7 percent, respectively. Titanium-to-titanium tensile shear specimens of a poly(arylene ether 1,3,4-oxadiazole) exhibited tensile shear strengths at 23 and 150 C of 22.1 and 17.9 MPa, respectively.

Connell, J. W.↗

NASA NTRS1993

An investigation of the effect of surface impurities on the adsorption kinetics of hydrogen chemisorbed onto iron

The goal of this program was to develop an understanding of heterogeneous kinetic processes for those molecular species which produce gaseous hydrogen degradation of the mechanical properties of metallic structural materials. Although hydrogen degradation of metallic materials is believed to result from dissolved protonic hydrogen, the heterogeneous hydrogen interface transport processes often dominate the kinetics of degradation. The initial step in the interface transport process is the dissociative chemisorption of the molecular species at the metal surface followed by hydrogen absorption into and transport through the bulk. The interaction of hydrogen with the surfaces of alpha-2(Ti3Al) titanium aluminide, gamma(TiAl) titanium aluminide, and beryllium were studied.

Shanabarger, Mickey R.↗

NASA NTRS1995

T/BEST: Technology Benefit Estimator Select Features and Applications

A Technology Benefit Estimator (T/BEST) system has been developed to provide a formal method to assess advanced aerospace technologies and quantify the benefit contributions for prioritization. An open-ended, modular approach is used to allow for upgrade and insertion of advanced technology modules. T/BEST's software framework, beginner-to-expert operation, interface architecture, and key analysis modules are discussed. In this paper, selected features and applications of T/BEST are demonstrated. Sample cases pertaining to structural analysis of titanium and composite blades are presented. The performance of hot and cold composite fan blades is also discussed. The cost required to manufacture titanium and composite fan blades is estimated.

Generazio, Edward R.↗

NASA NTRS1996

Materials Research for High Speed Civil Transport and Generic Hypersonics-Metals Durability

This report covers a portion of an ongoing investigation of the durability of titanium alloys for the High Speed Civil Transport (HSCT). Candidate alloys need to possess an acceptable combination of properties including strength and toughness as well as fatigue and corrosion resistance when subjected to the HSCT operational environment. These materials must also be capable of being processed into required product forms while maintaining their properties. Processing operations being considered for this airplane include forming, welding, adhesive bonding, and superplastic forming with or without diffusion bonding. This program was designed to develop the material properties database required to lower the risk of using advanced titanium alloys on the HSCT.

Schulz, Paul↗

NASA NTRS1996

Ignition and Combustion of Bulk Metals in a Microgravity Environment

This annual report summarizes the latest results obtained in a NASA-supported project to investigate the effect of gravity on the ignition and combustion of bulk metals. The experimental arrangement used for this purpose consists of a 1000-W xenon lamp that irradiates the top surface of cylindrical titanium and magnesium specimens, 4 mm in diameter and 4 mm in height, in a quiescent, pure-oxygen environment at 1 atm. Reduced gravity is obtained from the NASA LeRC DC-9 aircraft flying parabolic trajectories. Values of critical and ignition temperatures are obtained from thermocouple records. Qualitative observations and propagation rates are extracted from high-speed cinematography. Emission spectra of gas-phase reactions are obtained with an imaging spectrograph/diode array system. It was found that high applied heating rates and large internal conduction losses generate critical and ignition temperatures that are several hundred degrees above the values obtained from isothermal experiments. Because of high conduction and radiation heat losses, no appreciable effect on ignition temperatures with reduced convection in low gravity is detected. Lower propagation rates of the molten interface on titanium and of ignition waves on magnesium are obtained at reduced gravity. These rates are compared to theoretical results from heat conduction analyses with a diffusion/convection controlled reaction. The close agreement found between experimental and theoretical values indicates the importance of the influence of natural convection-enhanced oxygen transport on combustion rates. Lower oxygen flux and lack of oxide product removal in the absence of convective currents appear to be responsible for longer burning times of magnesium diffusion flames at reduced gravity. The accumulation of condensed oxide particles in the flame front at low gravity produces a previously unreported unsteady explosion phenomenon in bulk magnesium flames. This spherically symmetric explosion phenomenon seems to be driven by increased radiation heat transfer from the flame front to an evaporating metal core covered by a porous, flexible oxide coating. These important results have revealed the significant role of gravity on the burning of metals, and are now being used as the database for future experiments to be conducted with different metals at various pressures, oxygen concentrations and gravity levels.

Branch, M. C.↗

NASA NTRS1994

Ignition and Combustion Characteristics of Pure Bulk Metals: Normal-Gravity Test Results

An experimental apparatus has been designed for the study of bulk metal ignition under elevated, normal and reduced gravity environments. The present work describes the technical characteristics of the system, the analytical techniques employed, the results obtained from the ignition of a variety of metals subjected to normal gravity conditions and the first results obtained from experiments under elevated gravity. A 1000 W xenon short-arc lamp is used to irradiate the top surface of a cylindrical metal specimen 4 mm in diameter and 4 mm high in a quiescent pure-oxygen environment at 0.1 MPa. Iron, titanium, zirconium, magnesium, zinc, tin, and copper specimens are investigated. All these metals exhibit ignition and combustion behavior varying in strength and speed. Values of ignition temperatures below, above or in the range of the metal melting point are obtained from the temperature records. The emission spectra from the magnesium-oxygen gas-phase reaction reveals the dynamic evolution of the ignition event. Scanning electron microscope and x-ray spectroscopic analysis provide the sequence of oxide formation on the burning of copper samples. Preliminary results on the effect of higher-than-normal gravity levels on the ignition of titanium specimens is presented.

Abbud-Madrid, A.↗