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At least 739 records · Page 41
All sourcesNASA NTRSDOE OSTI
NASA NTRS1999

Acoustic Emission Signals in Thin Plates Produced by Impact Damage

Acoustic emission (AE) signals created by impact sources in thin aluminum and graphite/epoxy composite plates were analyzed. Two different impact velocity regimes were studied. Low-velocity (less than 0.21 km/s) impacts were created with an airgun firing spherical steel projectiles (4.5 mm diameter). High-velocity (1.8 to 7 km/s) impacts were generated with a two-stage light-gas gun firing small cylindrical nylon projectiles (1.5 mm diameter). Both the impact velocity and impact angle were varied. The impacts did not penetrate the aluminum plates at either low or high velocities. For high-velocity impacts in composites, there were both impacts that fully penetrated the plate as well as impacts that did not. All impacts generated very large amplitude AE signals (1-5 V at the sensor), which propagated as plate (extensional and/or flexural) modes. In the low-velocity impact studies, the signal was dominated by a large flexural mode with only a small extensional mode component detected. As the impact velocity was increased within the low velocity regime, the overall amplitudes of both the extensional and flexural modes increased. In addition, a relative increase in the amplitude of high-frequency components of the flexural mode was also observed. Signals caused by high-velocity impacts that did not penetrate the plate contained both a large extensional and flexural mode component of comparable amplitudes. The signals also contained components of much higher frequency and were easily differentiated from those caused by low-velocity impacts. An interesting phenomenon was observed in that the large flexural mode component, seen in every other case, was absent from the signal when the impact particle fully penetrated through the composite plates.

Prosser, William H.↗
NASA NTRS1964

Particle populations in space.

Space radiation flux, composition and energy spectra data that must be considered in design of manned spacecraft

COSMIC RADIATION↗
NASA NTRS1999

The Features of Self-Assembling Organic Bilayers Important to the Formation of Anisotropic Inorganic Materials in Microgravity Conditions

There is a growing need for inorganic anisotropic particles in a variety of materials science applications. Structural, optical, and electrical properties can be greatly augmented by the fabrication of composite materials with anisotropic microstructures or with anisotropic particles uniformly dispersed in an isotropic matrix. Examples include structural composites, magnetic and optical recording media, photographic film, certain metal and ceramic alloys, and display technologies including flat panel displays. While considerable progress has been made toward developing an understanding of the synthesis of powders composed of monodispersed, spherical particles, these efforts have not been transferred to the synthesis of anisotropic nanoparticles. The major objective of the program is to develop a fundamental understanding of the growth of anisotropic particles at organic templates, with emphasis on the chemical and structural aspects of layered organic assemblies that contribute to the formation of anisotropic inorganic particles.

Talham, Daniel R.↗
NASA NTRS2002

Composition of Impact Melt Debris from the Eltanin Impact Strewn Field, Bellingshausen Sea

The impact of the km-sized Eltanin asteroid into the Bellingshausen Sea produced mm- to cm-sized vesicular impact melt-rock particles found in sediment cores across a large area of the ocean floor. These particles are composed mainly of olivine and glass with minor chromite and traces of NiFe-sulfides. Some particles have inclusions of unmelted mineral and rock fragments from the precursor asteroid. Although all samples of melt rock examined have experienced significant alteration since their deposition in the late Pliocene, a significant portion of these particles have interiors that remain pristine and can be used to estimate the bulk composition of the impact melt. The bulk composition of the melt-rock particles is similar to the composition of basaltic meteorites such as howardites or mesosiderite silicates, with a contribution from seawater salts and a siderophile-rich component. There is no evidence that the Eltanin impact melt contains a significant terrestrial silicate component that might have been incorporated by mixing of the projectile with oceanic crust. If terrestrial silicates were incorporated into the melt, then their contribution must be much less than 10 wt%. Since excess K, Na, and CI are not present in seawater proportions, uptake of these elements into the melt must have been greatest for K and least for CI, producing a K/CI ratio about 4 times that in seawater. After correcting for the seawater component, the bulk composition of the Eltanin impact melt provides the best estimate of the bulk composition of the Eltanin asteroid. Excess Fe in the impact melt, relative to that in howardites, must be from a significant metal phase in the parent asteroid. Although the estimated Fe:Ni:Ir ratios (8:1:4 x 10(exp -5)) are similar to those in mesosiderite metal nodules (10:1:6 x 10(exp -5), excess Co and Au by factors of about 2 and 10 times, respectively, imply a metal component distinct from that in typical mesosiderites. An alternative interpretation, that siderophiles have been highly fractionated from a mesosiderite source, would require loss of about 90% of the original metal from the impact melt and the sediments, and is unsupported by any observational data. More likely, the excess Fe in the melt rocks is 'representative of the amount of metal in the impacting asteroid, which is estimated to be 4+/- 1 wt%.

Kyte, Frank T.↗
NASA NTRS1980

Development of a solvent processed insensitive propellant

Two types of low vulnerability propellants are studied which are distinguished by whether the binder is a rubber, such as polyurethane or CTBN, or a plasticizable polymer such as ethyl cellulose or cellulose acetate. The former propellants are made by a partial cure extrusion process while the latter are made by the conventional solvent process. Emphasis is given to a cellulose binder (plasticizer) RDX composition. The type of binder used, the particle size of the RDX and the presence of small quantities of nitrocellulose in the solvent processed compositions have important influences on the mechanical and combustion characteristics of the propellant. The low temperature combustion is of particular concern because of potential breakup of the grains that can lead to instability.

Trask, R.↗
NASA NTRS1992

Atmospheric nuclei in the remote free-troposphere

An extensive flight series to survey aerosol present in the upper-troposphere was undertaken aboard the NASA DC-8 as part of the Global Backscatter Experiment. Aerosol with diameters greater than 3 nm were counted and sized with a combination of condensation nuclei counters and optical particle counters. Aerosol number and mass concentrations were separately identified with regard to both refractory and volatile components. Regions of the free-troposphere with the lowest mass concentrations were generally found to have the highest number concentrations and appeared to be effective regions for new particle production. These new particle concentrations appear inversely related to available aerosol surface area, and their volatility suggests a sulfuric acid composition. The long lifetime of these new particles aloft can result in their growth to sizes effective as CN and CCN that can be mixed throughout the troposphere.

Clarke, Antony D.↗
NASA NTRS1994

Aerosol Abundances and Optical Characteristics in the Pacific Basin Free Troposphere

During NASA's Global Backscatter Experiment (GLOBE) mission flights in November 1989 and May 1990, a DC-8 research aircraft probed the Pacific Basin free troposphere for about 90 flight hours in each month between +72 and -62 degrees latitude, +130 and -120 degrees longitude, and up to 39,000 feet pressure altitudes. Aerosols were sampled continuously in situ by optical particle counters to measure concentration and particle size, and during 48 10-min intervals during each mission by wire impactors for concentration, size, composition, phase and shape analyses. The optical particle counters cover a particle diameter range between 0.3 and 20 microns; wire impactors extend the range down to 0.03 microns. Results of particle number, size, shape, together with the assumption of a refractive index corresponding to (NH4)2SO4 to account for the prevalence of aerosol sulfur, were utilized in a Mie algorithm to calculate aerosol extinction and backscatter for a range of wavelengths (0.385 less than lambda less than 10.64 microns). Computations for 22 randomly selected size distributions yield coefficients of extinction E(0.525) = (2.03 +/- 1.20) x 10(exp -4) km(exp -1) and backscatter beta(0.525) = (6.45 +/- 3.49) x 10(exp -6) km(exp -1) sr(exp -1) in the visible, and E(10.64) = (8.13 +/- 6.47) x 10(exp -6) km(exp -1) and beta(10.64) = (9.98 +/- 10.69) x 10(exp -8) km(exp -1) sr(exp -1) in the infrared, respectively. Large particles (D greater than 0.3 microns) contribute two-thirds to the total extinction in the visible (lambda = 0.525 microns), and almost 100% in the infrared (lambda = 10.64 microns). These results have been used to define an IR optical aerosol climatology of the Pacific Basin free troposphere, from which it follows that the infrared backscatter coefficient at lambda = 9.25 microns wavelength fluctuates between 5.0 x 10(exp -10) and 2.0 x 10(exp -7) km(exp -1) sr(exp -1) with a modal value 2.0 x 10(exp -8) km(exp -1) sr(exp -1).

Pueschel, R. F.↗
NASA NTRS1969

An investigation of volcanic depressions. Part 1: Airfall and intrusive pyroclastic deposits. Part 2: Subaerial pyroclastic flows and their deposits

Pyroclastic ejecta and the deposits they form were classified in many ways, and many interpretations were given to individual terms. Some classifications are based on the modes of orgin and deposition of the ejecta; others emphasized the chemical and physical composition of the ejecta. Particle-size was used as the prime basis of subdivision, and the same size-limits were used as those employed in the classification of sediments and sedimentary rocks.

Williams, H.↗
NASA NTRS1974

Galactic heavy cosmic rays with 5 less than E less than 130 MeV/nucleon

With stacks of Lexan and cellulose triacetate exposed outside the lunar modules on Apollo 16 and 17, a study was made of the spectra and composition of low-energy particles in interplanetary space. For the period from Apr. 16 to 23, 1972 (Apollo 16), measurements were made of the spectra of the elements 6 less than or equal to Z less than or equal to 28 at energies 40 less than or equal to E less than or equal to 150 MeV/nucleon. For the period from Dec. 11 to 13, 1972 (Apollo 17), a study was made of CNO, NeMgSi, and elements with Z greater than 16 at energies 5 less than or equal to E less than or equal to 40 MeV/nucleon. Using the abundance of charges 17 less than or equal to Z less than or equal to 25 relative to iron as a tracer, it is found that the bulk of the heavy particles in interplanetary space at E greater than 10 MeV/nucleon are of galactic rather than solar origin. The relative abundances of the various charge groups are independent of energy from about 2 GeV/nucleon down to about 30 MeV/nucleon.

Price, P. B.↗
NASA NTRS1979

Materials and structural aspects of advanced gas-turbine helicopter engines

The key to improved helicopter gas turbine engine performance lies in the development of advanced materials and advanced structural and design concepts. The modification of the low temperature components of helicopter engines (such as the inlet particle separator), the introduction of composites for use in the engine front frame, the development of advanced materials with increased use-temperature capability for the engine hot section, can result in improved performance and/or decreased engine maintenance cost. A major emphasis in helicopter engine design is the ability to design to meet a required lifetime. This, in turn, requires that the interrelated aspects of higher operating temperatures and pressures, cooling concepts, and environmental protection schemes be integrated into component design. The major material advances, coatings, and design life-prediction techniques pertinent to helicopter engines are reviewed; the current state-of-the-art is identified; and when appropriate, progress, problems, and future directions are assessed.

Freche, J. C.↗
NASA NTRS1979

Post-Skylab activities

The Apollo Soyuz Test Program is described. A modification of the Skylab furnace was developed for the ASTP mission that had a maximum temperature of 1200 C, a programmed cool down to give more uniform growth rates, and a He quench system to shorten the time required to reach allowable touch temperature. The Space Processing Applications Rocket (SPAR) program was initiated to provide some continuity in flight experimentation. Liquid mixing, immiscible alloy solidification, composite materials, bubbles and dispersed particles during solidification, and containerless processing techniques were studied in the SPAR program.

Source record↗
NASA NTRS1979

International planetary patrol observations of Saturn's rings. II - Four color phase curves and their analysis

New phase curves for Saturn's rings at an intermediate tilt angle B of about 17 deg are presented. Quantitative results for each of the A and B rings are reported in terms of the opposition effect, phase coefficient, and best logarithmic fit to the phase curve. There was no significant difference between the shape of the phase curves for the two rings in each of the four colors, and a four-parameter multiple scattering model of the rings was consistent with the observations. In this model, the difference in the phase curves for different colors can be explained by a variation in the single scattering albedo with wavelength. The observations allow the particles to have the same composition in the A and B rings, so that their different photometric behavior is explained by differences in optical depth and volume density in the two rings.

Esposito, L. W.↗
NASA NTRS1979

Voyager 2 - Energetic ions and electrons in the Jovian magnetosphere

The passage of Voyager 2 through the Jovian magnetosphere demonstrated that this magnetosphere is highly variable, even as close as 10 Jupiter radii from the planet. The cosmic-ray subsystem measured the flux, elemental composition, and anisotropy of energetic particles. Its high sensitivity was particularly valuable during the long passage through the magnetotail, where particle fluxes were orders of magnitude less than in the inner magnetosphere and approached interplanetary values. The new data confirm earlier observations that the Jovian magnetosphere is a giant accelerator of particles - electrons, protons, and heavy ions, including sulfur. Both spatial and temporal changes are observed in the magnetosphere as compared to prior observations with Pioneer 10 and 11 and Voyager 1. It is suggested that the 10-hr modulation of interplanetary Jovian electrons may be associated with the arrival at the dawn magnetopause of a rarefaction region each planetary rotation.

Vogt, R. E.↗
NASA NTRS1980

Satellite studies of N/D-2/ emission and ion chemistry in aurorae

The incident particle flux ion and neutral composition data taken on the AE-D satellite have been used to investigate the quantal emission of N2(plus) at 4278 A, N(D-2) at 5200 A, and the ion chemistry in aurorae. The results of a time dependent auroral model have been compared to the data. The calculated 4278 A emission of N2(plus), the 5200 A emission of N(D-2), the densities of O2(plus), NO(plus), N2(plus), O(plus), and the electron density are generally in agreement with the measured values. These results are consistent with the branching ratios and quenching rates deduced from previous studies of the N(D-2) densities in the day-time, mid-latitude ionosphere. It is found that in an auroral arc, the measured atomic oxygen density is lower than predicted by the MSIS model.

Rusch, D. W.↗
NASA NTRS1980

Modulation of terrestrial ion escape flux composition /by low-altitude acceleration and charge exchange chemistry/

Motivated by recent observations of highly variable hot plasma composition in the magnetosphere, control of the ionospheric escape flux composition by low-altitude particle dynamics and ion chemistry has been investigated for an e(-), H(+), O(+) ionosphere. It is found that the fraction of the steady state escape flux which is O(+) can be controlled very sensitively by the occurrence of parallel or transverse ion acceleration at altitudes below the altitude where the neutral oxygen density falls rapidly below the neutral hydrogen density and the ionospheric source of O(+) tends to be rapidly converted by charge exchange to H(+). The acceleration is required both to overcome the gravitational confinement of O(+) and to violate charge exchange equilibrium so that the neutral hydrogen atmosphere appears 'optically' thin to escaping O(+). Constraints are placed on the acceleration processes, and it is shown that O(+) escape is facilitated by observed ionospheric responses to magnetic activity.

Moore, T. E.↗