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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 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
NASA NTRS1984

Shock wave properties of anorthosite and gabbro

Hugoniot data on San Gabriel anorthosite and San Marcos gabbro to 11 GPA are presented. Release paths in the stress-density plane and sound velocities are reported as determined from particl velocity data. Electrical interference effects precluded the determination of accurate release paths for the gabbro. Because of the loss of shear strength in the shocked state, the plastic behavior exhibited by anorthosite indicates that calculations of energy partitioning due to impact onto planetary surfaces based on elastic-plastic models may underestimate the amount of internal energy deposited in the impacted surface material.

Boslough, M. B.↗
NASA NTRS1984

Transient behavior of a flare-associated solar wind. I - Gas dynamics in a radial open field region

A numerical investigation is conducted into the way in which a solar wind model initially satisfying both steady state and energy balance conditions is disturbed and deformed, under the assumption of heating that correspoonds to the energy release of solar flares of an importance value of approximately 1 which occur in radial open field regions. Flare-associated solar wind transient behavior is modeled for 1-8 solar radii. The coronal temperature around the heat source region rises, and a large thermal conductive flux flows inward to the chromosphere and outward to interplanetary space along field lines. The speed of the front of expanding chromospheric material generated by the impingement of the conduction front on the upper chromosphere exceeds the local sound velocity in a few minutes and eventually exceeds 100 million cm/sec.

Nagai, F.↗
NASA NTRS1985

Pulse-Width-to-Analog-Voltage Converter

Peak output voltage varies linearly with input-pulse duration. Circuit converts pulses of varying widths (as from sound-velocity instrumentation or tachometers) into analog voltages. Peak voltage increases in proportion to pulse width. Voltage used to drive an x-y plotter or storage oscilloscope. Pulse-width-to-voltage converter has peak output voltage that varies with duration of input pulses.

Sosack, G. S.↗
NASA NTRS1984

Low-frequency sound absorption measurements in air

Thirty sets of sound absorption measurements in air at a pressure of 1 atmosphere are presented at temperatures from 10 C to 50 C, relative humidities from 0 to 100 percent, and frequencies from 10 to 2500 Hz. The measurements were conducted by the method of free decay in a resonant tube having a length of 18.261 m and bore diameter of 0.152 m. Background measurements in a gas consisting of 89.5 percent N2 and 10.5 percent Ar, a mixture which has the same sound velocity as air, permitted the wall and structural losses of the tube to be separated from the constituent absorption, consisting of classical rotational and vibrational absorption, in the air samples. The data were used to evaluate the vibrational relaxation frequencies of N2 and/or O2 for each of the 30 sets of meteorological parameters. Over the full range of humidity, the measured relaxation frequencies of N2 in air lie between those specified by ANSI Standard S1.26-1978 and those measured earlier in binary N2H2O mixtures. The measured relaxation frequencies could be determined only at very low values of humidity, reveal a significant trend away from the ANSI standard, in agreement with a prior investigation.

Zuckerwar, A. J.↗
NASA NTRS1983

Prediction of structures and magnetic orientations in solid alpha and beta-O2

A quasi-harmonic-lattice-dynamics method coupled with a pattern-recognition optimization scheme is used to determine the minimum energy structures and magnetic orientations of solid oxygen. It is shown that the magnetic interaction is responsible for the stability of alpha-O2 with respect to beta-O2 at zero temperature and pressure. The calculated alpha-O2 lattice parameters, magnetic orientations, and sublimation energy are in good agreement with experiment. Phonon dispersion curves are calculated at vector k not equal to zero and the acoustic sound velocities are determined. The rms translational and orientational fluctuations from equilibrium are also calculated. The beta-O2 phase is described by constraining the magnetic moments so that the magnetic Hamiltonian preserves the hexagonal symmetry of the crystal. The calculated lattice parameters are in good agreement with the experiments, and a three-sublattice, quasi-helical magnetic orientation is predicted from structural and energetic considerations.

Etters, R. D.↗
NASA NTRS1985

Shock wave properties of anorthosite and gabbro

Huyoniot data on San Gabriel anorthosite and San Marcos gabbro to 11 GPA are presented. Release paths in the stress-density plane and sound velocities are reported as determined from partial velocity data. Electrical interference effects precluded the determination of accurate release paths for the gabbro. Because of the loss of shear strength in the shocked state, the plastic behavior exhibited by anorthosite indicates that calculations of energy partitioning due to impact onto planetary surfaces based on elastic-plastic models may underestimate the amount of internal energy deposited in the impacted surface material.

Boslough, M. B.↗
NASA NTRS1985

Low-frequency absorption of sound in air

Thirty sets of sound absorption measurements in air at a pressure of 1 atmosphere are presented at temperatures from 10 C to 50 C, relative humidities from 0 to 100 percent, and frequencies from 10 to 2500 Hz. The measurements were conducted by the method of free decay in a resonant tube having a length of 18.261 m and bore diameter of 0.152 m. Background measurements in a gas consisting of 89.5 percent N2 and 10.5 percent Ar, a mixture which has the same sound velocity as air, permitted the wall and structural losses of the tube to be separated from the constituent absorption, consisting of classical rotational and vibrational absorption, in the air samples. The data were used to evaluate the vibrational relaxation frequencies of N2 and/or O2 for each of the 30 sets of meteorological parameters. Over the full range of humidity, the measured relaxation frequencies of N2 in air lie between those specified by ANSI Standard S1.26-1978 and those measured earlier in binary N2H2O mixtures. The measured relaxation frequencies could be determined only at very low values of humidity, reveal a significant trend away from the ANSI standard, in agreement with a prior investigation.

Zuckerwar, A. J.↗
NASA NTRS1985

Containerless Studies of Nucleation and Undercooling

The long term research goals are to perform experiments to determine the achievable limits of undercooling, the characteristics of heterogeneous nucleation, and the physical properties of significantly undercooled melts. The techniques used are based on the newly developed containerless manipulation methods afforded by acoustic levitation. Ground based investigations involved 0.1 to 2 mm specimens of pure metals and alloys (In, Ga, Sn, Ga-In, ...) as well as glass-forming organic compounds (O-Terphenyl). A currently operating ultrasonic high temperature apparatus has allowed the ground-based levitation of 1 to 2 mm samples of solid aluminum at 550 deg C in an argon atmosphere. Present work is concentrating on the undercooling of pure metal samples (In, Sn), and on the measurements of surface tension and viscosity of the undercooled melts via shape oscillation techniques monitored through optical detection methods. The sound velocity of undercooled O-Terphenyl is being measured in an immiscible liquid levitation cells.

Trinh, E. H.↗
NASA NTRS1985

Nondestructive ultrasonic measurement of bolt preload using the pulsed-phase locked-loop interferometer

Achieving accurate preload in threaded fasteners is an important and often critical problem which is encountered in nearly all sectors of government and industry. Conventional tensioning methods which rely on torque carry with them the disadvantage of requiring constant friction in the fastener in order to accurately correlate torque to preload. Since most of the applied torque typically overcomes friction rather than tensioning the fastener, small variations in friction can cause large variations in preload. An instrument called a pulsed phase locked loop interferometer, which was recently developed at NASA Langley, has found widespread use for measurement of stress as well as material properties. When used to measure bolt preload, this system detects changes in the fastener length and sound velocity which are independent of friction. The system is therefore capable of accurately establishing the correct change in bolt tension. This high resolution instrument has been used for precision measurement of preload in critical fasteners for numerous applications such as the space shuttle landing gear and helicopter main rotors.

Allison, S. G.↗
NASA NTRS1986

Analytical ultrasonics for characterization of metallurgical microstructures and transformations

The application of contact (piezoelectric) and noncontact (laser generation and detection) ultrasonic techniques for dynamic investigation of precipitation hardening processes in aluminum alloys, as well as crystallization and phase transformation in rapidly solidified amorphous and microcrystalline alloys is discussed. From the variations of the sound velocity and attenuation the precipitation mechanism and kinetics were determined. In addition, a correlation was established between the observed changes in the velocity and attenuation and the mechanical properties of age-hardenable aluminum alloys. The behavior of the elastic moduli, determined ultrasonically, were found to be sensitive to relaxation, crystallization and phase decomposition phenomena in rapidly solidified metallic glasses. Analytical ultrasonics enables determination of the activation energies and growth parameters of the reactions. Therefrom theoretical models can be constructed to explain the changes in mechanical and physical properties upon heat treatment of glassy alloys. The composition dependence of the elastic moduli in amorphous Cu-Zr alloys was found to be related to the glass transition temperature, and consequently to the glass forming ability of these alloys. Dynamic ultrasonic analysis was found to be feasible for on-line, real-time, monitoring of metallurgical processes.

Rosen, M.↗
NASA NTRS1984

Recent progress in the measurement of temperature and salinity by optical scattering

Recent progress is described in the use of Brillouin and Raman scattering for the measurement of temperature and salinity in the ocean. The use of Brillouin scattering is described for the measurement of the sound velocity, and the use of Raman scattering is described for the independent measurement of the temperature and salinity. Coupling these techniques permits the assessment of both temperature and salinity. The experimental techniques are described together with the results of recent experiments and an assessment of the errors to be expected.

Collins, D. J.↗
NASA NTRS1986

Inequalities for frequency-moment sum rules of electron liquids

The relations between the various frequency-moment sum rules of electron liquids, which include even-power moments, are systematically examined by using the Cauchy-Schwarz and Hoelder inequalities. A relation involving the isothermal sound velocity and the kinetic and potential energies is obtained from one of the inequalities in the long-wavelength limit, and is generalized to arbitrary spatial dimensions.

Iwamoto, N.↗
NASA NTRS1988

The single crystal elastic constants of hexagonal SiC to 1000 C

The relationships between the sound velocities in the cubic and hexagonal crystal structures and the tensor transformations for the two structures are applied to determine the elastic stiffnesses for the hexagonal structures of SiC to 1000 C. These results are then applied to calculate the polycrystalline elastic moduli, E and G, and their temperature variations. The calculated values for E and G at 20 C are 420 and 180 GPa; for (dE/dT) and (dG/dT), the values are -0.020 and -0.007 GPa/C, respectively.These agree well with published experimental values for E and G of dense polycrystalline alpha silicon carbides.

Li, Z.↗
NASA NTRS1989

Thermophysical properties of Helium-4 from 0.8 to 1500 K with pressures to 2000 MPa

Tabular summary data of the thermophysical properties of fluid helium are given for temperatures from 0.8 to 1500 K, with pressures to 2000 MPa between 75 and 300 K, or to 100 MPa outside of this temperature band. Properties include density, specific heats, enthalpy, entropy, internal energy, sound velocity, expansivity, compressibility, thermal conductivity, and viscosity. The data are calculated from a computer program which is available from the National Institute of Standards and Technology. The computer program is based on carefully fitted state equations for both normal and superfluid helium.

Arp, Vincent D.↗
NASA NTRS1990

Enhanced ultrasonic attenuation of Tl-Ca-Ba-Cu-O at the superconducting transition

Temperature-dependent ultrasonic attenuation measurements have been performed on polycrystalline samples of Tl-Ca-Ba-Cu-O at various frequencies. An attenuation anomaly was observed close to the superconducting transition temperature T(c) (103 K) whose temperature position was frequency-independent. The attenuation decreased exponentially with temperature in the superconducting state for both transverse and longitudinal waves. It was also found that the temperature-dependent sound velocity showed a slope change around T(c).

Sun, K. J.↗
NASA NTRS1991

The shock wave equation of state of brucite Mg(OH)2

New shock equation of state (EOS) data on magnesium hydroxide between 12 and 60 GPa is presented. It is found that the brucite EOS data between 12 and 97 GPa can be fit with a single linear U(s) - u(p) relationship: U(s) = 4.76(0.11) + 1.35(0.05)u(p). The third order Birch-Murnaghan equation parameters are K(os) = 51 + or - 4 GPa and K(os)prime = 5.0 + or - 0.4. The first partial release states measured for brucite Mg(OH)2 are reported. Calculated phase boundaries using the EOS data are found to be consistent with the experimental data and indicate that brucite is unlikely to be stable under lower mantle conditions. At high pressure, bulk sound velocities calculated for MgO and Mg(OH)2 are very similar, indicating that the presence of hydrous assemblages in the lower mantle may not produce anomalous bulk seismic velocities. A comparison of densities in brucite and other high-pressure phases under mantle conditions shows that the water content of the lower mantle is between 0 and 3 wt pct.

Duffy, Thomas S.↗
NASA NTRS1991

Acoustoelastic characterisation of materials

Recent developments in the use of nonlinear acoustoelastic techniques for the characterization of materials are reviewed, with particular attention given to the quantitative modeling of the acoustoelastic properties of multiphase alloys in terms of material composition. Topics discussed include general theory of acoustoelasticity, models of two-phase systems, measurement techniques, acoustic nonlinearity parameters and material properties, stress-temperature dependence of sound velocity, and low field magnetoacoustics. The discussion is illustrated by results obtained for steels and aluminum alloys with second phase precipitates.

Cantrell, J. H.↗