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At least 343 records · Page 19

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NASA NTRS1977

A Weibull characterization for tensile fracture of multicomponent brittle fibers

Necessary to the development and understanding of brittle fiber reinforced composites is a means to statistically describe fiber strength and strain-to-failure behavior. A statistical characterization for multicomponent brittle fibers is presented. The method, which is an extension of usual Weibull distribution procedures, statistically considers the components making up a fiber (e.g., substrate, sheath, and surface) as separate entities and taken together as in a fiber. Tensile data for silicon carbide fiber and for an experimental carbon-boron alloy fiber are evaluated in terms of the proposed multicomponent Weibull characterization.

Barrows, R. G.↗

NASA NTRS1979

Material growth and characterization directed toward improving III-V heterojunction solar cells

In addition to the existing materials growth laboratory, the photolithographic facility and the device testing facility were completed. The majority of equipment for data acquisition, solar cell testing, materials growth and device characterization were received and are being put into operation. In the research part of the program, GaAs and GaA1As layers were grown reproducibly on GaAs substrates. These grown layers were characterized as to surface morphology, thickness and thickness uniformity. The liquid phase epitaxial growth process was used to fabricate p-n junctions in Ga(1-x)A1(x)As. Sequential deposition of two alloy layers was accomplished and detailed analysis of the effect of substrate quality and dopant on the GaA1As layer quality is presented. Finally, solar cell structures were formed by growing a thin p-GaA1As layer upon an epitaxial n-GaA1As layer. The energy gap corresponding to the long wavelength cutoff of the spectral response characteristic was 1.51-1.63 eV. Theoretical calculations of the spectral response were matched to the measured response.

Stefanakos, E. K.↗

NASA NTRS1979

Status of materials characterization studies

In the context of the spacecraft charging technology investigation, studies were made to characterize the response of typical spacecraft surface materials to the charging environment. The objective is to obtain an understanding of the charging and discharging behavior of such materials for the reliable prediction of spacecraft response to charging environments and as a guide for the design of future spacecraft. Materials were characterized in terms of such basic properties as resistivity and secondary emission and in terms of charging and discharging behavior in simulated charging environments.

Purvis, C. K.↗

NASA NTRS1978

Interface reaction and characterization in B/Al composites

Interfacial reactions, strength degradation, and fracture morphology have been characterized in B/Al(1100) and B/Al(6061) composite systems at a volume fraction of 0.55. Reaction was promoted by isothermal exposure at 350 C or 500 C for times up to 860,000 s. Tetragonal AlB12 was identified as the reaction product in the 6061 matrix and hexagonal AlB2 in the 1100 matrix. Interface development is analyzed based on a moving boundary model modified by the addition of ternary elements. While strength decreases in both systems, the time dependence of elevated-temperature exposure is different in the two matrix materials. In the 45 deg fiber orientation, failure occurs primarily by matrix shear, whereas in the 90 deg fiber orientation, fracture morphology is characterized by a mixture of fiber splitting, ductile matrix fracture, and failure at fiber-matrix interfaces.

Kim, W. H.↗

NASA NTRS1979

Characterization of PMR polyimides - Correlation of ester impurities with composite properties

The presumed relationship of chemical impurities to final composite properties is the rationale for most chemical characterization studies. This study examines this relationship for PMR-polyimide resin. Ester/acid solutions of one monomer were aged at selected temperatures and chemical changes were monitored spectroscopically. At selected intervals, graphite fiber reinforced composite panels were fabricated. Changes in resin processing characteristics and composite properties were determined. The correlation of these data are discussed as are related characterization studies of PMR-polyimide resin.

Lauver, R. W.↗

NASA NTRS1980

The accelerated characterization of viscoelastic composite materials

Necessary fundamentals relative to composite materials and viscoelasticity are reviewed. The accelerated characterization techniques of time temperature superposition and time temperature stress superposition are described. An experimental procedure for applying the latter to composites is given along with results obtained on a particular T300/934 graphite/epoxy. The accelerated characterization predictions are found in good agreement with actual long term tests. A postcuring phenomenon is discussed that necessitates thermal conditioning of the specimen prior to testing. A closely related phenomenon of physical aging is described as well as the effect of each on the glass transition temperature and strength. Creep rupture results are provided for a variety of geometries and temperatures for T300/934 graphite/epoxy. The results are found to compare reasonably with a modified kinetic rate theory.

Griffith, W. I.↗

NASA NTRS1980

Microstructural characterization of the HRSI thermal protection system for space shuttle

Components of the space shuttle high temperature reusable surface insulation (HRSI) system were microscopically characterized, both separately and as a system, to obtain information needed for stress analysis models of the thermal protection system. A tension specimen of the HRSI system was loaded in steps and was microscopically observed at each load condition to demonstrate the tension failure mode associated with strain isolation pad (SIP) behavior. A local failure occurred which should be associated with transfer of load through transverse fibers in the SIP. Stress concentrations attributed to the SIP behavior necessitated strengthening of the HRSI by densification of the RSI at the bondline. An HRSI tile was microscopically characterized after the densification process. The densified surface layer blended into the RSI which caused a gradual change in density. The gradation in density does not appear to represent a sharp discontinuity in elastic modulus between the densified layer and the parent material.

Ransone, P. O.↗

NASA NTRS1979

Characterization of submicron matrix phyllosilicates from Murray and Nogoya carbonaceous chondrites

The combined techniques of high-resolution transmission electron microscopy and energy-dispersive X-ray analysis have been used to study dispersed, submicron phyllosilicates and the 'poorly characterized phase' of C2 matrix material. Morphologies and structure types observed are similar to terrestrial chrysotile. Distinctive morphologies and 7.3-A characteristic basal spacings combined with composition information rule out phyllosilicates other than serpentine group minerals as the predominant phyllosilicate material. The 'poorly characterized phase' is composed of chemically similar very fine-grained phyllosilicate and amorphous material. The observation of interstratified phyllosilicate material sheds additional doubt on compositional data which is not accompanied by structural data from the same particle.

Mckee, T. R.↗

NASA NTRS1981

National Transonic Facility Fan Blade prepreg material characterization tests

The test program for the basic prepreg materials used in process development work and planned fabrication of the national transonic facility fan blade is presented. The basic prepreg materials and the design laminate are characterized at 89 K, room temperature, and 366 K. Characterization tests, test equipment, and test data are discussed. Material tests results in the warp direction are given for tensile, compressive, fatigue (tension-tension), interlaminar shear and thermal expansion.

Klich, P. J.↗

NASA NTRS1982

An investigation of adhesive/adherend and fiber/matrix interactions. Part A: Surface characterization of titanium dioxide, titantium and titanium 6% Al to 4% V powders: Interaction with water, hydrogen chloride and polymers

The titanium dioxide surface is discussed. Polymer adhesive are also discussed. Titanium powders are considered. Characterization techniques are also considered. Interactions with polymers, water vapor, and HCl are reported. Adsorbents are characterized.

Siriwardane, R. V.↗

NASA NTRS1982

Characterization of advanced electric propulsion systems

Characteristics of several advanced electric propulsion systems are evaluated and compared. The propulsion systems studied are mass driver, rail gun, MPD thruster, hydrogen free radical thruster and mercury electron bombardment ion engine. These are characterized by specific impulse, overall efficiency, input power, average thrust, power to average thrust ratio and average thrust to dry weight ratio. Several important physical characteristics such as dry system mass, accelerator length, bore size and current pulse requirement are also evaluated in appropriate cases. Only the ion engine can operate at a specific impulse beyond 2000 sec. Rail gun, MPD thruster and free radical thruster are currently characterized by low efficiencies. Mass drivers have the best performance characteristics in terms of overall efficiency, power to average thrust ratio and average thrust to dry weight ratio. But, they can only operate at low specific impulses due to large power requirements and are extremely long due to limitations of driving current. Mercury ion engines have the next best performance characteristics while operating at higher specific impulses. It is concluded that, overall, ion engines have somewhat better characteristics as compared to the other electric propulsion systems.

Ray, P. K.↗

NASA NTRS1983

LANDSAT-4 evaluation program and scientific characterization activities

The characterization objectives of the LANDSAT 4 Science Office at GSFC are to: (1) determine the accuracy and precision of sensor and spacecraft performance, image data quality, and derived information; (2) recommend LANDSAT 4 system improvements; and (3) communicate results to the research community. In-house activities are directed toward full access and utilization of the prelaunch and in-orbit engineering test data on the sensor and spacecraft. Principle scientists in remote sensing are involved as part of a major scientific characterization effort, and workshops were held for these investigative teams. A symposium is scheduled prior to turnover of the TM to NOAA.

Barker, J. L.↗

NASA NTRS1981

Soil spectral characterization

The spectral characterization of soils is discussed with particular reference to the bidirectional reflectance factor as a quantitative measure of soil spectral properties, the role of soil color, soil parameters affecting soil reflectance, and field characteristics of soil reflectance. Comparisons between laboratory-measured soil spectra and Landsat MSS data have shown good agreement, especially in discriminating relative drainage conditions and organic matter levels in unvegetated soils. The capacity to measure both visible and infrared soil reflectance provides information on other soil characteristics and makes it possible to predict soil response to different management conditions. Field and laboratory soil spectral characterization helps define the extent to which intrinsic spectral information is available from soils as a consequence of their composition and field characteristics.

Stoner, E. R.↗

NASA NTRS1983

Synthesis and characterization of bisimide amines and bisimide amine-cured epoxy resins

An attempt is made to develop tough, moisture resistant, high char yield epoxy resins by means of novel bisimide amine (BIA) hardener curing agents and a state-of-the-art epoxy resin system. The BIAs are isolated as mixtures containing monomer, oligomer, and polymeric species, and then characterized by elemental analysis and high pressure liquid chromatography. The bisimide amine-cured epoxies (IMEs) were characterized with respect to moisture absorption, thermal properties, and physical and mechanical properties, as well as in the role of matrices in Celion 6000/IME composites. The relative toughness characteristics of each IME formulation was measured by the 10 deg off-axis tensile test, measuring the uniaxial tensile strength, shear strength, and shear-strain-to-failure of the composite systems.

Scola, D. A.↗

NASA NTRS1984

Fundamental Remote Sensing Science Research Program. Part 1: Scene Radiation and Atmospheric Effects Characterization Project

Brief articles summarizing the status of research in the scene radiation and atmospheric effect characterization (SRAEC) project are presented. Research conducted within the SRAEC program is focused on the development of empirical characterizations and mathematical process models which relate the electromagnetic energy reflected or emitted from a scene to the biophysical parameters of interest.

R E Murphy↗

NASA NTRS1984

Proceedings of the Flat-plate Solar Array Project Research Forum on the High-speed Growth and Characterization of Crystals for Solar Cells

The High-Speed Growth and Characterization of Crystals for Solar Cells Research Forum was held on July 25-27, 1983, at the Sandpiper Bay Hotel in ort St. Lucie, Florida. The Research Forum was arranged into eight interactive sessions and addressed theoretical and experimental phenomena, applications, and characterization including stress/strain and other problem areas that limit the rate of growth of crystals suitable for processing into efficient, cost-effective solar cells. The Flat-Plate Solar Array Project of the Jet Propulsion Laboratory sponsored the meeting: Thirty-five invited papers were presented. Discussion periods followed each presentation. These Proceedings are a record of the papers and the discussions.

Katherine A. Dumas↗

NASA NTRS1984

Overview of Characterization Techniques for High Speed Crystal Growth

Features of characterization requirements for crystals, devices and completed products are discussed. Key parameters of interest in semiconductor processing are presented. Characterization as it applies to process control, diagnostics and research needs is discussed with appropriate examples.

Ravi, K. V.↗

NASA NTRS1982

Characterization and degradation studies on synthetic polymers for aerospace application

The anti-misting additive for jet fuels known as FM-9 (proprietary polymer) was characterized by elemental analysis, solubility studies and molecular weight determination. Physical properties of surface tension, viscosity, specific gravity and other physical parameters were determined. These results are compared with properties of polyisobutylene and fuels modified with the same; the misting characteristics of polyisobutylene and FM-9 in Jet A fuel are included. Characterization and degradation of phthalocyanine and its derivatives were accomplished by use of a mass spectrometer and a pyroprobe solid pyrolyzer. Metal phthalocyanine tetracarboxylic acids and phthalocyanine-tetraamine cured epoxies were studied. Epoxy/graphite composite panels were exposed to a NASA-Ames radiant panel fire simulator in the flaming and non-flaming modes; toxic gases of HCN and HZS were measured along with oxygen, Co2, Co, and organic gases.

Hsu, M. T. S.↗