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  • Other Sources  (576)
  • ASTRONOMY  (294)
  • COMPOSITE MATERIALS  (282)
  • 1990-1994  (576)
  • 1991  (576)
  • 1
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    Repair of oxidation protection coatings on carbon-carbon using preceramic polymers (1991)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: The paper describes a field-applicable technique for the repair of damage to SiC protective coatings on carbon/carbon composites, using commercial preceramic polymers, such as perhydropolysilazane developed by the Southwest Research Institute and several commercial polymers (NICALON, PS110, PS116, PS117, NCP-200, and PHPS were tested). After being applied on the damaged panel and oxidized at 1400 C, these polymers form either SiC or Si3N4 (or a mixture of both). It was found that impact damaged carbon/carbon specimens repaired with perhydropolysilazane exhibit substantial oxidation resistance. Many of the other tested preceramic polymer were found to be unsuitable for the purpose of repair due to either low ceramic yield, foaming, or intumescence.
    Keywords: COMPOSITE MATERIALS
    Type: In: Damage and oxidation protection in high temperature composites. Vol. 1; Proceedings of the Symposium, 112th ASME Winter Annual Meeting, Atlanta, GA, Dec. 1-6, 1991 (A93-53937 23-24); p. 131-138.
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  • 2
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    Fatigue life prediction of an intermetallic matrix composite at elevated temperatures (1991)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: A strain-based fatigue life prediction method is proposed for an intermetallic matrix composite (IMC) under tensile cyclic loadings at elevated temperatures. Styled after the 'Universal Slopes' method, the model utilizes the composite's tensile properties to estimate fatigue life. Factors such as fiber volume ratio (Vf), number of plys and temperature dependence are implicitly incorporated into the model through these properties. The model constants are determined by using unidirectional fatigue data at temperatures of 425 and 815 C. Fatigue lives from two independent sources are used to verify the model at temperatures of 650 and 760 C. Cross-ply lives at 760 C are also predicted. It is demonstrated that the correlation between experimental and predicted lives is within a factor of two.
    Keywords: COMPOSITE MATERIALS
    Type: In: Failure mechanisms in high temperature composite materials; Proceedings of the Symposium, 112th ASME Winter Annual Meeting, Atlanta, GA, Dec. 1-6, 1991 (A93-31351 11-24); p. 45-54.
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  • 3
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    Void control in the crystallization of lithium fluoride (1991)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: The effect of tungsten-coated graphite fibers on the radiant heat transfer characteristics of salt-fiber composites was studied by measuring the onset of melting as a function of applied furnace power. As the fiber concentration was increased from 0 to 5.40 percent fiber by weight, the furnace temperature required to melt the lithium fluoride also increased. Upon cooling, each of the crystalline salt-fiber composites were cut open with a diamond saw to expose the void. Optical photographs of the voids revealed a trend in void location and size, with the largest void, and the least change in the outer dimension of the boule upon cooling, occurring in the sample with the most fiber.
    Keywords: COMPOSITE MATERIALS
    Type: In: Space nuclear power systems; Proceedings of the 8th Symposium, Albuquerque, NM, Jan. 6-10, 1991. Pt. 1 (A93-13751 03-20); p. 49-54.
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  • 4
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    Delamination behavior of quasi-isotropic graphite epoxy laminates subjected to tension and torsion loads (1991)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: Sixteen and thirty-two ply quasi-isotropic laminates fabricated from AS4/3501-6 were subjected to pure tension, simultaneous tension and torsion, and torsion fatigue. Layups tested were (45 sub n/-45 sub n/0 sub n/90 sub n) sub s, with n = 2 or 4. A torsion damage pattern consisting of a localized matrix crack and delaminations was characterized, and the measured torsional stiffnesses were compared with calculated values. It was found that a combination of tension and torsion led to failure at smaller loads than either type of deformation acting alone. Further work is required to determine the exact form of the failure criterion.
    Keywords: COMPOSITE MATERIALS
    Type: In: AHS National Technical Specialists' Meeting on Rotorcraft Structures, Williamsburg, VA, Oct. 29-31, 1991, Proceedings (A93-27951 10-05); 15 p.
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  • 5
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    The Next Generation Space Telescope - A large UV-IR successor to HST (1991)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: Attention is given to the science goals of the Next Generation Space Telescope (NGST), namely, detection and spectroscopy of gas giant planets to earthlike planets around nearby stars, study of nearby star-forming complexes with resolutions of 5-50 AU in the visible and IR, measurement of stellar populations in a variety of environments, spatial resolution and mapping of complex structures in the inner narrow line regions for AGN and QSOs, and investigation of the structure and evolution of galaxies at redshifts greater than 1. The NGST characteristics, milestones, long-term strategy, and launch capability are also discussed.
    Keywords: ASTRONOMY
    Type: Space Astronomical Telescopes and Instruments; Apr 01, 1991 - Apr 04, 1991; Orlando, FL; United States
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  • 6
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    Astro-archaeology - The white dwarfs and hot subwarfs (1991)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: By 'astroarcheology' is presently meant the effort to ascertain the Galaxy's past in light of what is found in its most ancient, white dwarf constituents. Attention is given to the controversial role of the hot subdwarfs and the theory of white dwarf spectral evolution, as well as to the concept of the 'Whole Earth Telescope', involving continuous photometric coverage of rapidly varying astronomical sources and thereby eliminating the otherwise troublesome diurnal gaps in data. Much higher resolution of the power spectra of these objects is attainable by these means than any current alternative.
    Keywords: ASTRONOMY
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  • 7
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    Germanium detector vacuum encapsulation (1991)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: This paper describes an encapsulation technology that should significantly improve the viability of germanium gamma-ray detectors for a number of important applications. A specialized vacuum chamber has been constructed in which the detector and the encapsulating module are processed in high vacuum. Very high vacuum conductance is achieved within the valveless encapsulating module. The detector module is then sealed without breaking the chamber vacuum. The details of the vacuum chamber, valveless module, processing, and sealing method are presented.
    Keywords: ASTRONOMY
    Type: International Symposium on Gamma-Ray Line Astrophysics; Dec 10, 1990 - Dec 13, 1990; Paris; France
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  • 8
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    Observational aspects of stellar radio flares (1991)
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    Publication Date: 2019-08-28
    Description: The study of stellar flares in the radio regime provides a nearly unique observational perspective, as the emission generally arises from the particle acceleration region. Continuum and spectral studies of radio burst emission for several classes of stars are reviewed, and some preliminary connections with the quiescent radio emission from flare stars are made. Further, the radio observations are placed in a broader observational context provided by X-ray, UV, and optical observations.
    Keywords: ASTRONOMY
    Type: Societa Astronomica Italiana, Memorie (ISSN 0037-8720); 62; 321-336
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  • 9
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    Study of astrophysics from the Lunar Outpost (1991)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: This paper describes the strategy of the NASA astronomical program that would follow if observations were performed from a Lunar Outpost. Contemporaneous observations across the entire electromagnetic spectrum are the underlying strategies of this astronomical program. To conduct these observations, Spacelab, Explorers, suborbital programs, Great Observatories, and Space Station Freedom are utilized, along with unique moon-based astronomical facilities. It is concluded that addition of the evolutionary facilities studied for the Lunar Outpost element would increase the sensitivity and angular resolution of the astronomical program by orders of magnitude.
    Keywords: ASTRONOMY
    Type: Advances in Space Research (ISSN 0273-1177); 11; 2, 19
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  • 10
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    Radioactivities and gamma-rays from supernovae (1991)
    In:  Other Sources
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    Publication Date: 2019-08-27
    Description: An account is given of the implications of several calculations relevant to the estimation of gamma-ray signals from various explosive astronomical phenomena. After discussing efforts to constrain the amounts of Ni-57 and Ti-44 produced in SN 1987A, attention is given to the production of Al-27 in massive stars and SNs. A 'delayed detonation' model of type Ia SNs is proposed, and the gamma-ray signal which may be expected when a bare white dwarf collapses directly into a neutron star is discussed.
    Keywords: ASTRONOMY
    Type: International Symposium on Gamma-Ray Line Astrophysics; Dec 10, 1990 - Dec 13, 1990; Paris; France
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