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At least 1,153 records · Page 64
All sourcesNASA NTRSDOE OSTI
NASA NTRS1984

Electrical conductivity studies on CuBr containing Al2O3 particles

The conductivity of CuBr was studied and the role of a second phase, Al2O3, dispersed in CuBr was tested. CuBr melts at 493 C and exhibits three phases in the solid state. CuBr is a good ionic conductor with a transport number for copper ions of virtually unity with weighed proportions of the appropriate chemicals used. The CuBr materials were heated above melting point of CuBr, and the samples were sandwiched between copper electrodes. The ac conductivity, was determined at 1 kHz between 25 and 440 C depending on the sample. It was shown that at low temperatures, the conductivity for CuBr (Al2O3) increased by as much as 100, whereas in the beta phase the conductivity of CuBr containing Al2O3 decreased. The electrical conductivity studies are in agreement with earlier data.

Dubec, P. M.↗
NASA NTRS1984

Preparation and characterization of a siloxane containing bismaleimide

A novel siloxane containing bismaleimide has been prepared by reacting maleic anhydride, benzophenonetetracarboxylic dianhydride and bis(gamma-aminopropyl)tetramethyldisiloxane. Characterization of this monomer was done by comparing its nuclear magnetic resonance spectrum (NMR) to those of model compounds. Solubility of the prepolymer was tested in amide, chlorinated and ether solvents. Films were cast from solution as well as by melt processing and a cure cycle was determined. Infrared spectrum (IR) of the resulting film was obtained. Thermal polymerization was investigated by differential scanning calorimetry (DSC). Thermal properties of the cured resin were followed by means of thermogravimetric analysis (TGA), torsional braid analysis (TBA) and dynamic mechanical analysis (DMA). Thermomechanical analysis (TMA) was used to study the effect of postcure on the glass transition temperature (Tg) of the resin. Adhesive strength of the resin was obtained at ambient temperature.

Maudgal, S.↗
NASA NTRS1984

Synthesis and characterization of phosphorus-containing polyamides and copolyamides based on 1-(dialkoxyphosphinyl)methyl-2,4- and -2,6-diaminobenzenes

Phosphorus containing polyamides and copolyamides were prepared from 1-(dialkoxyphosphinyl)methyl-2,4- and -2,6-diaminobenzenes. The polymers produced were characterized by infrared and proton nuclear magnetic resonance spectroscopy, differential scanning calorimetry, and thermogravimetric analysis. Their thermal properties were compared with those of the corresponding common polyamides. In addition, by determining the limiting oxygen index value of some of these polyamides, their fire resistance was evaluated.

Mikroyannidis, J. A.↗
NASA NTRS1984

Synthesis of tin-containing polyimide films

A series of tin-containing polyimide films derived from either 3,3',4,4'-benzophenone tetracarboxylic acid dianhydride or pyromellitic dianhydride and 4,4'-oxydianiline have been synthesized and their electrical properties examined. Highest quality materials (i.e., homogeneous, smooth surface, flexible) with the best electrical properties were doped with either SnCl2.2H2O or (n-Bu)2SnCl2. In all cases, extensive reactivity of the tin dopant with water, air or polyamic acid during imidization is observed. Lowered electrical surface resistivities appear to be correlatable with the presence of surface tin oxide on the film surface.

Ezzell, S. A.↗
NASA NTRS1984

Phosphorus-containing imide resins - Modification by elastomers

The syntheses and general features of addition-type maleimide resins based on bis(m-aminophenyl)phosphine oxide and tris(m-aminophenyl)phosphine oxide have been reported previously. These resins have been used to fabricate graphite cloth laminates having excellent flame resistance. These composites did not burn even in pure oxygen. However, these resins were somewhat brittle. This paper reports the modification of these phosphorus-containing resins by an amine-terminated butadiene-acrylonitrile copolymer (ATBN) and a perfluoroalkylene diaromatic amine elastomer (3F). An approximately two-fold increase in short beam shear strength and flexural strength was observed at 7 percent ATBN concentration. The tensile, flexural, and shear strengths were reduced when 18 percent ATBN was used. Anaerobic char yields of the resins at 800 C and the limiting oxygen indexes of the laminates decreased with increasing ATBN concentration. The perfluorodiamine (3F) was used with both imide resins at 6.4 percent concentration. The shear strength was doubled in the case of the bisimide with no loss of flammability characteristics. The modified trisimide laminate also had improved properties over the unmodified one. The dynamic mechanical analysis of a four-ply laminate indicated a glass transition temperature above 300 C. Scanning electron micrographs of the ATBN modified imide resins were also recorded.

Varma, I. K.↗
NASA NTRS1984

Polyimides containing oxyethylene units. II - Polymerization of 3.3', 4.4'-benzophenonetetra carboxylic dianhydride and pyromellitic dianhydride

The study is concerned with the polymerization of diamines 2a-d with readily available dianhydrides, i.e., 3,3',4,4'-benzophenonetetracarboxylic dianhydride (BTDA) and pyromellitic dianhydride (PMDA). The synthesis and polymerization of asymmetric diamines containing substituted alkylene ether linkages are also investigated. It is assumed that the flexibility introduced into the polymer chain through the use of such diamines would result in moderate glass transition temperatures that would allow the systems to be melt processed. Mixtures of diamines are also copolymerized so as to further disrupt the polymer's symmetry and recurrence regularity. The properties of the resulting polymers are briefly discussed.

Harris, F. W.↗
NASA NTRS1985

Analysis of an oscillatory oil squeeze film containing a central gas bubble

A squeeze-film damper, consisting of two circular plates, having only normal oscillatory relative motion is considered. The liquid lubricant between the plates is assumed to contain a single central gas bubble. The effect of the bubble on the damper performance is analyzed. Comparison is made with the performance of a pure liquid damper. Substantial deviations in peak dynamic pressures are predicted which explain discrepancies between experimental and theoretical results reported in the literature.

Haber, S.↗
NASA NTRS1985

Acoustic shocks in a variable area duct containing near sonic flows

Acoustic shock waves in a variable area duct which contains near sonic flows are considered. The problem is modeled after an aeroengine inlet. Area variation of a duct and high Mach number mean the flow reduces acoustical energy yielding substantial noise reduction. One possible reason for this is acoustic shock. The use of an explicit accurate numerical method which captures shocks is described. Comparison of the results are made with an existing asymptotic theory for Mach numbers close to unity. When shock occurs reduction of sound pressure levels are shown by example.

Hariharan, S. I.↗
NASA NTRS1984

Effect of metal ions on positron annihilation characteristics in metal ion containing epoxies

In the course of developing improved moisture-resistant epoxy resins, two different types of epoxy resins containing variable mole ratios of chromium ions per polymer repeat unit were developed. Positron annihilation characteristics have been investigated in these resins as a function of their metal ion content. In both cases, the presence of metal ions reduces the lifetime as well as the intensity of the long life component. The long life component intensity reduction is considerably more pronounced than the lifetime reduction. These results have been discussed in terms of increased unpaired electron density at Ps formation sites due to the presence of chromium ions in the matrix.

Singh, J. J.↗
NASA NTRS1985

Analysis of stress-strain, fracture, and ductility behavior of aluminum maxtrix composites containing discontinuous silicon carbide reinforcement

Mechanical properties and stress-strain behavior were evaluated for several types of commercially fabricated aluminum matrix composites, containing up to 40 vol pct discontinuous SiC whisker, nodule, or particulate reinforcement. The elastic modulus of the composites was found to be isotropic, to be independent of type of reinforcement, and to be controlled solely by the volume percentage of SiC reinforcement present. The yield/tensile strengths and ductility were controlled primarily by the matrix alloy and temper condition. Type and orientation of reinforcement had some effect on the strengths of composites, but only for those in which the whisker reinforcement was highly oriented. Ductility decreased with increasing reinforcement content; however, the fracture strains observed were higher than those reported in the literature for this type of composite. This increase in fracture strain was probably attributable to cleaner matrix powder, better mixing, and increased mechanical working during fabrication. Comparison of properties with conventional aluminum and titanium structural alloys showed that the properties of the low-cost, lightweight composites demonstrated very good potential for application to aerospace structures.

Mcdanels, D. L.↗
NASA NTRS1986

Self-Contained Neutral-Buoyancy Suit

Report discusses self-contained diving suit used in simulations of zero-gravity maneuvers in space suit. Method, called neutral-buoyancy immersion, useful in preparing astronauts for extravehicular activity.

Boswell, B. E.↗
NASA NTRS1986

Fire-Resistant Polyimides Containing Phosphorus

Limiting oxygen index increased. Copolyimide with a group containing phosphorus synthesized from 1-2,4-diaminobenzene, m-phenylenediamine, and tetracarboxylic dianhydride. Copolymer more fire resistant than corresponding polyimide without phosphorus.

Mikroyannidis, J.↗
NASA NTRS1985

Manufacture of dense sintered bodies containing silicon nitride

Sintered bodies containing 1-32.5 Si oxide and 1.5 wt.% SiC (Si oxide/SiC wt. ratio 3/2) are prepared and kept in a 10-3000 kg/2 sq. cm. N (g) atmosphere at 1500-2300 degrees, while simultaneously maintaining the CO (g) partial pressure around the body lower than the nitrogenation equil. pressure to give a dense sintered body. The prepared dense sintered body has high strength at high temperatures. Thus, SiC 40, oxide 30 and Si3N4 30 wt% were fired to a body which was kept in 1500 kg/sq. cm. N (g) for 20 h at 2000 degrees to give a dense sintered body having high bending strength at high temperatures.

Hirota, K.↗
NASA NTRS1985

Supernova remnants containing neutron stars

X-ray observations of Crab Nebula-like supernova remnants are summarized. Five remnants are found to contain internal neutron stars - four isolated and one in a binary system. Another five remnants have central unresolved X-ray sources which are probably neutron stars. Thus approximately 10 remnants are now known to have their origin in gravitational collapse. Another 22 remnants show some Crab-like properties, but the existence of a central compact object or pulsar is doubtful or unconfirmed. The four fast isolated pulsars in SNR are also compared with five X-ray detected radio pulsars.

Seward, F. D.↗
NASA NTRS1985

Measurement and analysis of distribution coefficients in Fe-Ni alloys containing S and/or P. II - K(Ir), K(Ge), and K(Cu)

Crystals of Fe-Ni-S-P alloys containing Ir, Ge, and Cu in small amounts were grown by plane front solidification. The electron microprobe was used to measure the compositions of these alloys. The Ir, Ge, and Cu distribution coefficients were determined by an analytical procedure from the composition data. The distribution coefficients of Ir, Ge, and Cu vary from 1.20 to 11.0, 0.75 to 2.1, and 0.06 to 0.84, respectively. K(Ir) and K(Ge) increase and K(Cu) decreases with the S content of the liquid. K(Cu) increases and K(Ir) and K(Ge) decrease with the P content of the liquid. Mathematical expressions have been formulated to relate the Ir, Ge, and Cu distribution coefficients to the S and P contents of the liquid. These distribution coefficients are important to the study of the solidification behavior of iron meteorites.

Sellamuthu, R.↗
NASA NTRS1985

A clamped rectangular plate containing a crack

The general problem of a rectangular plate clamped along two parallel sides and containing a crack parallel to the clamps is considered. The problem is formulated in terms of a system of singular integral equations and the asymptotic behavior of the stress state near the corners is investigated. Numerical examples are considered for a clamped plate without a crack and with a centrally located crack, and the stress intensity factors and the stresses along the clamps are calculated.

Tang, R.↗
NASA NTRS1985

Stability of finite-difference models containing two boundaries or interfaces

The stability of finite difference models of hyperbolic initial boundary value problems is connected with the propagation and reflection of parasitic waves. Wave propagation ideas are applied to models containing two boundaries or interfaces, where repeated reflection of trapped wave packets is a potential new source of instability. Various known instability phenomena are accounted for in a unified way. Results show: (1) dissipativity does not ensure stability when three or more formulas are concatenated at a boundary or internal interface; (2) algebraic GKS instabilities can be converted by a second boundary to exponential instabilities only when an infinite numerical reflection coefficient is present; and (3) GKS-stability and P-stability can be established in certain problems by showing that all numerical reflection coefficients have modulus less than 1.

Trefethen, L. N.↗