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At least 1,315 records · Page 73

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NASA NTRS1983

Characterization of Interlaminar Crack Growth in Composites with the Double Cantilever Beam Specimen

A project to examine the double cantilever beam specimen as a quantitative test method to assess the resistance of various composite materials to interlaminar crack growth is discussed. A second objective is to investigate the micromechanics of failure for composites with tough matrix resins from certain generic types of polymeric systems: brittle thermosets, toughened thermosets, and thermoplastics. Emphasis is given to a discussion of preliminary results in two areas: the effects of temperature and loading rate for woven composites, and the effects of matrix toughening in woven and unidirectional composites.

Hunston, D. L.↗

NASA NTRS1985

LSS 2018: A double-lined spectroscopic binary central star with an extremely large reflection effect

LSS 2018, the central star of the planetry nebulae DS1, was found to be a double-lined spectroscopic binary with a period of 8.571 hours. Light variations with the same period were observed in U, B, and V; in the wavelength regions defined by the two IUE cameras; and in the strength of the CIII 4647 emission line. The light variations can be accurately predicted by a simple reflection effect, and an analysis of the light curves yields the angular diameter and effective temperature of the primary, the radii of the two stars in terms of their separation, and the inclination of the system. Analysis of the radial velocities then yields the masses of the two stars, their separation, the distance of the system, the absolute magnitude of the primary, and the size of the nebula.

Drilling, J. S.↗

NASA NTRS1985

Dissociative and double photoionization cross sections of NO from threshold to 120 A

The partial photoionization cross sections for producing the NO(+) parent ion and the O(+), N(+), and NO2(+) fragment ions from neutral NO are presented from 120 to 614 A. The results indicate predissociation of the c(sup3) pi (21.72 eV) and B prime (sup 1) sigma (+) (22.73 eV) electronic states of NO(+). The photoionization threshold for double ionization was found to be 39.4 + or 0.12 eV.

Samson, J. A. R.↗

NASA NTRS1984

The width-tapered double cantilever beam for interlaminar fracture testing

The width-tapered double-cantilever-beam (WTDCB) specimen configuration used to determine the Mode-I interlaminar fracture energy (IFE) of composites has special advantages for routine development work and for quality-assurance purposes. These advantages come primarily from the simplicity of testing and the fact that the specimen is designed for constant change in compliance with crack length, so that the computation of Mode-I IFE is independent of crack length. In this paper, a simplified technique for fabrication and testing WTDCB specimens is described. Also presented are the effects of fiber orientation and specimen dimensions, a comparison of data obtained using the WTDCB specimens and other specimen geometries, and comparison of data obtained at different laboratories. It is concluded that the WTDCB gives interlaminar Mode-I IFE essentially equal to other type specimens, and that it can be used for rapid screening in resin-development work and for quality assurance of composite materials.

Bascom, W. D.↗

NASA NTRS1984

Numerical simulations of double layers and auroral electric fields

Recent one-dimensional and two-dimensional numerical simulations of double layers (DLs) in the electric fields of the auroral plasma are reviewed, with reference to observational data. It is found that two-dimensional DLs driven by current sheets of finite thickness have different characteristics, depending on whether the layer thickness is less than or much greater than the ion gyroradius: When thickness is less than ion gyroradius, V-shaped DLs form with nearly equal parallel and perpendicular potential drops; when layer thickness is much greater than ion gyroradius the major parallel potential drop occurs outside the current sheet and the perpendicular electric fields are localized at the edges of the current sheet. It is shown that some features of the simulated fields, such as the amplitudes and scale lengths, are qualitatively similar to those observed in space.

Singh, N.↗

NASA NTRS1983

High sensitivity high resolution double scatter 1-30 MeV gamma ray telescope

The design and performance of the double-scatter 1-30-MeV gamma-ray telescope developed at the University of California for balloon-borne observations are reported and illustrated with drawings, diagrams, and graphs. The telescope comprises an upper array of 16 6.03 x 6.03 x 100-cm plastic scintillator bars viewed by photomultiplier tubes (PMTs) at both ends, a lower array (at 100-cm distance) of 16 4.83 x 4.83 x 100-cm NaI(Tl) bars viewed at both ends by PMTs, and four 122 x 122 x 0.64-cm plastic sheets viewed by four PMTs each as charged-particle anticoincidence shielding. The operating principle of the telescope, the tests conducted on the NaI(Tl) bars, the on-board data-processing electronics, and the overall performance are characterized. Performance parameters include area 1 sq m, field of view pi sr, 4-sigma sensitivity above 1 MeV 0.00004 gamma/sq cm sec over 25 h, angular resolution about 3.5 deg FWHM, and energy resolution 10 percent at 1 MeV and 6 percent at 6 MeV.

Zych, A. D.↗

NASA NTRS1985

High-performance double-focusing mass spectrometer

Double focusing was first employed when mass spectrometers of a simpler design were not capable any longer to satisfy increasing demands in mass spectroscopy. One of the successful instruments of the 1930's was the mass spectrometer designed by Mattauch and Herzog (1934). The compactness of the Mattauch-Herzog geometry became particularly important in connection with studies involving the employment of rockets, satellites, or space probes. Another advantage of the considered spectrometer is related to the capability of measuring several masses of ions simultaneously. The instrument design was, therefore adopted for some rocket flights to the upper atmosphere, the investigation of the upper atmosphere of Mars, and for studying the upper atmosphere of Venus. Attention is given to laboratory applications involving the instrument in a somewhat enlarged version, and aspects of instrument operation and performance.

Nier, A. O.↗

NASA NTRS1985

Response of double wall composite shells

This paper presents an analytical study of double wall laminate cylindrical shell response to random loads. A soft viscoelastic core with dilatational modes included is used. The theory of laminate shells is simplified by assumptions similar to those in the Donnell-Mushtari development for isotropic shells. Modal solutions of simply supported shells are obtained. Modal frequencies and deflection response spectral densities are determined. It is found that this approach allows for easy parametric evaluation and that by proper selection of dynamic parameters, viscoelastic core characteristics and fiber reinforcement orientation, vibration response can be reduced.

Vaicaitis, R.↗

NASA NTRS1985

Double symbol error rates for differential detection of narrow-band FM

This paper evaluates the double symbol error rate (average probability of two consecutive symbol errors) in differentially detected narrow-band FM. Numerical results are presented for the special case of MSK with a Gaussian IF receive filter. It is shown that, not unlike similar results previously obtained for the single error probability of such systems, large inaccuracies in predicted performance can occur when intersymbol interference is ignored.

Simon, M. K.↗

NASA NTRS1985

LSS 2018 - A double-lined spectroscopic binary central star with an extremely large reflection effect

LSS 2018, the central star of the planetary nebulae DS1, was found to be a double-lined spectroscopic binary with a period of 8.571 hours. Light variations with the same period were observed in U, B, and V; in the wavelength regions defined by the two IUE cameras; and in the strength of the CIII 4647 emission line. The light variations can be accurately predicted by a simple reflection effect, and an analysis of the light curves yields the angular diameter and effective temperature of the primary, the radii of the two stars in terms of their separation, and the inclination of the system. Analysis of the radial velocities then yields the masses of the two stars, their separation, the distance of the system, the absolute magnitude of the primary, and the size of the nebula.

Drilling, J. S.↗

NASA NTRS1985

Double-diffusive convection with sidewalls

Stommel et al. (1956) have first described an instability, known as thermosolutal convection, thermohaline convection, or double-diffusive convection. This instability may occur in the case of a fluid in a gravitational field with two diffusing components present. The present study is concerned with the effect of sidewalls on flow in the fingering regime in the absence of applied horizontal gradients. The work was motivated by numerical results obtained on the basis of a simulation of thermosolutal convection occurring during the unidirectional solidification of a binary alloy. In this case, the unperturbed solute field in the liquid ahead of the solidifying planar interface has an exponential vertical profile because of the rejection or preferential incorporation of solute by the solid phase.

Mcfadden, G. B.↗

NASA NTRS1985

Self-locking double retention redundant full pin release

A double retention redundant pull pin release system is disclosed. The system responds to a single pull during an intentional release operation. A spiral threaded main pin is seated in a mating bore in a housing, which main pin has a flange fastened thereon at the part of the main pin which is exterior to the housing. Accidental release tends to rotate the main pin. A secondary pin passes through a slightly oversized opening in the flange and is seated in a second bore in the housing. The pins counteract against one another to prevent accidential release. A frictional lock is shared between the main and secondary pins to enhance further locking of the system. The secondary pin, in response to a first pull, is fully retracted from its bore and flange hole. Thereafter the pull causes the main pin to rotate free of the housing to release, for example, a parachute mechanism.

Killgrove, T. O.↗

NASA NTRS1986

Investigation of fiber bridging in double cantilever beam specimens

The possibility to eliminate fiber bridging or at least to reduce it, and to evaluate an alternative approach for determination of in situ mode 7 fracture toughness values of composite matrix materials were investigated. Double cantilever beam (DCB) specimens were made using unidirectional lay-ups of T6C/Hx205 composite material in which the delaminating halves were placed at angles of 0, 1.5, and 3 degrees to each other. The small angles between the delaminating plies were used to avoid fiber nesting without significantly affecting mode I teflon insert. The DCB specimens were fabricated and it was found that: (1) the extent which fiber bridging and interlaminar toughness increase with crack length can be reduced by slight cross ply at the delamination plane to reduce fiber nesting; (2) some fiber bridging may occur even in the absence of fiber nesting; (3) the first values of toughness measured ahead of the thin teflon insert are very close to the toughness of the matrix material with no fiber bridging; (4) thin adhesive bondline of matrix material appears to give toughness values equal to the interlaminar toughness of the composite matrix without fiber bridging.

Johnson, W. S.↗

NASA NTRS1986

Flow in out-of-plane double S-bonds

Developing flows in two out-of-plane double S-bend configurations have been measured by laser-Doppler anemometry. The first duct had a rectangular cross-section 40mmx40mm at the inlet and consisted of a uniform area 22.5 deg. - 22.5 deg. S-duct upstream with a 22.5 deg.- 22.5 deg. S- diffuser downstream. The second duct had a circular cross-section and consisted of a 45 deg. - 45 deg. uniform area S-duct upstream with a 22.5 deg. -22.5 deg. S-diffuser downstream. In both configurations the ratio of the mean radius of curvature to the inlet hydraulic diameter was 7.0, the exit-to-inlet area ratio of the diffusers was 1.5 and the ducts were connected so that the centerline of the S-duct lay in a plane normal to that of the S-diffuser. Streamwise and cross-stream velocity components were measured in laminar flow for the rectangular duct and in turbulent flow for both configurations; measurements of the turbulence levels, cross-correlations and wall static pressures were also made in the turbulent flow cases. Secondary flows of the first kind are present in the first S-duct and they are complemented or counteracted by the secondary flows generated by the area expansion and by the curvature of the S-diffusers downstream. Cross-stream velocities with magnitudes up to 0.19 and 0.11 of the bulk velocity were measured in the laminar and turbulent flows respectively in the rectangular duct and six cross-flow vortices were evident at the exit of the duct in both flow cases. The turbulent flow in the circular duct was qualitatively similar to that in the rectangular configuration, but the cross-stream velocities measured at the exit plane were smaller in the circular geometry. The results are presented in sufficient detail and accuracy for the assessment of numerical calculation methods and are listed in tabular form for this purpose.

Schmidt, M. C.↗

NASA NTRS1985

Double-injection, deep-impurity switch development

The overall objective of this program was the development of device design and process techniques for the fabrication of a double-injection, deep-impurity (DI) sup 2 silicon switch that operates in the 2-10 kV range with conduction current values of 5 A at 2 kV and 1 A at 10 kV. Other major specifications include a holding voltage of 10 V with no gate current, 10 microsec switching time, and power dissipation of 50 W at 75 C. It was decided to concentrate on the lateral circular devices in order to optimize the gold diffusion. This resulted in devices that are much better switches (approx.1 micro sec switching time), and in a gold diffusion process that is much more controllable than those previously developed. Some results with injection-gated devices were also obtained. The current conduction for V less than VT was analyzed and seen to agree, for the most part, with Lampert's theory. Various sections of this report describe the device designs, wafer-processing techniques, and various measurements which include ac and dc characteristics and four-point probe.

Whitson, D. W.↗

NASA NTRS1986

A mechanical property and stress corrosion evaluation of VIM-ESR-VAR work strengthened and direct double aged Inconel 718 bar material

Presented are the mechanical properties and the stress corrosion resistance of triple melted vacuum induction melted (VIM), electro-slag remelted (ESR), and vacuum arc remelted (VAR), solution treated, work strengthened and direct double aged Inconel 718 alloy bars 4.00 in. (10.16) and 5.75 in. (14.60 cm) diameter. Tensile, charpy v-notched impact, and compact tension specimens were tested at ambient temperature in both the longitudinal and transverse directions. Longitudinal tensile and yield strengths in excess of 220 ksi (1516.85 MPa) and 200 ksi (1378.00 MPa) respectively, were realized at ambient temperature. Additional charpy impact and compact tension tests were performed at -100 F (-73 C). Longitudinal charpy impact strength equalled or exceeded 12.0 ft-lbs (16.3 Joules) at ambient and at -100 F(-73 C) while longitudinal compact (LC) tension fracture toughness strength remained above 79 ksi (86.80 MPa) at ambient and at -100 F(-73 C) temperatures. No failures occurred in the longitudinal or transverse tensile specimens stressed to 75 and 100 percent of their respective yield strengths and exposed to a salt fog environment for 180 days. Tensile tests performed after the stress corrosion test indicated no mechanical property degradation.

Montano, J. W.↗

NASA NTRS1986

Double photon excitation of high-Rydberg atoms as a long-lived submillimeter detector

A method and apparatus for detecting submillimeter or IR radiation is disclosed. A rare gas, such as xenon, is supplied at its ground state via a pressurized cylinder and an adjustable leak valve into a cryogenically cooled detection area. The ground state of xenon is double photon excited to a particularized level of the Rydberg series by a resonance lamp and a laser. The doubly excited gas is then further excited by the radiation to be measured. A field ionization and an ion measurement indicative of the radiation intensity is achieved.

Chutjian, A. N.↗

NASA NTRS1985

Native hole trap in bulk GaAs and its association with the double-charge state of the arsenic antisite defect

A dominant hole trap has been identified in p-type bulk GaAs employing deep level transient and photocapacitance spectroscopies. The trap is present at a concentration up to about 4 x 10 to the 16th per cu cm, and it has two charge states with energies 0.54 + or - 0.02 and 0.77 + or - 0.02 eV above the top of the valence band (at 77 K). From the upper level the trap can be photoexcited to a persistent metastable state just as the dominant midgap level, EL2. Impurity analysis and the photoionization characteristics rule out association of the trap with impurities Fe, Cu, or Mn. Taking into consideration theoretical results, it appears most likely that the two charge states of the trap are the single and double donor levels of the arsenic antisite As(Ga) defect.

Lagowski, J.↗