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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 289 records · Page 16
All sourcesNASA NTRSDOE OSTI
NASA NTRS1977

Exploratory study on the effects of novel diamine curing agents and isocyanate precursors on the properties on new epoxy and urethane adhesives

Aromatic diamines based on diphenyl sulfone and benzophenone were studied as epoxy adhesive curing agents. Previously found differences in adhesive strengths for meta vs para orientation were not found in these series. The use of aluminum and alumina as fillers in a m,m prime-methylene dianiline-cured epoxy adhesive was not found to be beneficial to adhesive strength. Alumina filled adhesives had much lower strength than unfilled adhesives. The unfilled m,m prime-methylene dianiline-based epoxy adhesive had excellent resistance to moisture relative to a p,p prime-methylene dianiline-based adhesive and maintained good strengths up to 250 F. A glass fiber composite based on a m,m prime-methylene dianiline-cured epoxy appeared to be equivalent to the p,p prime-methylene dianiline-cured epoxy as judged by short beam shear tests.

Glasgow, D. G.↗
NASA NTRS1977

The correlation of ultrasonic attenuation and shear strength in graphite-polyimide composites

The buffer rod technique for measuring attenuation in thin specimens is modified here to apply to specimens having intermediate thicknesses and high attenuation. The described procedure, which requires only one accessible surface of the material, was used to determine the initial attenuation values of ultrasonic waves in short beam shear specimens of graphite-polyimide composite material. It is shown that there is good correlation between the initial attenuation values and the shear strengths of the specimens determined by the standard short beam shear test method. The modified ultrasonic buffer block technique offers much potential for service as a quantitative, nondestructive, quality assurance test for composite materials.

Hayford, D. T.↗
NASA NTRS1980

Evaluation of SRM flex bearing materials and processes

Tensile, peel, and shear testing was performed on combinations of primers, adhesives, tycements and rubber compounds cured at various times and temperatures. The materials used in the fabrication of the solid rocket motor flex bearing as well as in other systems were evaluated. A compatibility study between adhesives and tycements was initiated. The flex bearing mold design was reviewed by our tooling experts.

Wood, T. E.↗
NASA NTRS1979

Development of an improved toughness hyperpure silica reflective heat shield

High purity three dimensionally woven silica-silica materials were evaluated for use as a tough reflective heat shield for planetary entry probes. A special weave design was selected to minimize light piping effects through the heat shield thickness. Various weave spacings were evaluated for densification efficiency with an 0.7 micron particle size high purity silica. Spectral hemispherical reflectance was measured from 0.2 to 2.5 microns at room temperature. Reflectance increases due to densification and purity of material were measured. Reflectance of 3D hyperpure silica was higher than 3D astroquartz silica for all wavelengths. Mechanical properties were measured in beam flexure and beam shear tests. Results indicated strengths lower than reported for slip cast fused silica. Low strengths were attributed to low densities achieved through vacuum impregnation.

Rusert, E. L.↗
NASA NTRS1976

Evaluation of advanced microelectronic fluxless solder-bump contacts for hybrid microcircuits

Technology for interconnecting monolithic integrated circuit chips with other components is investigated. The advantages and disadvantages of the current flip-chip approach as compared to other interconnection methods are outlined. A fluxless solder-bump contact technology is evaluated. Multiple solder-bump contacts were formed on silicon integrated circuit chips. The solder-bumps, comprised of a rigid nickel under layer and a compliant solder overlayer, were electroformed onto gold device pads with the aid of thick dry film photomasks. Different solder alloys and the use of conductive epoxy for bonding were explored. Fluxless solder-bump bond quality and reliability were evaluated by measuring the effects of centrifuge, thermal cycling, and high temperature storage on bond visual characteristics, bond electrical continuity, and bond shear tests. The applicability and suitability of this technology for hybrid microelectronic packaging is discussed.

Mandal, R. P.↗
NASA NTRS1982

PMR-15 polyimide modifications for improved prepreg tack

The use of mixed solvents and of modified monomeric ester reactants was investigated as a means of improving the tack and drape retention characteristics of PMR-15 polyimide prepreg. Methanol, ethanol, 1-propanol and 1-butanol were used to prepare the esters, prepreg solutions, and T-300 graphite fabric and Celion 6000 unidirectional fiber prepregs. The tack retention characteristics of the T-300 fabric prepreg after exposure to simulated use conditions were determined using a simple lap shear test. Drape was qualitatively assessed by visually monitoring the deformability of the prepreg. Thermo-oxidative stability and mechanical properties retention of the Celion 6000 grahite fiber composites were determined as a function of exposure time in air at 600 F.

Vannucci, R. D.↗
NASA NTRS1984

Graduate engineering research participation in aeronautics

Graduate student engineering research in aeronautics at Old Dominion University is surveyed. Student participation was facilitated through a NASA sponsored university program which enabled the students to complete degrees. Research summaries are provided and plans for the termination of the grant program are outlined. Project topics include: Failure modes for mechanically fastened joints in composite materials; The dynamic stability of an earth orbiting satellite deploying hinged appendages; The analysis of the Losipescu shear test for composite materials; and the effect of boundary layer structure on wing tip vortex formation and decay.

Roberts, A. S., Jr.↗
NASA NTRS1985

Adhesive evaluation of LARC-TPI and a water-soluble version of LARC-TPI

The results of a study to evaluate two Langley Research Center thermoplastic polimide (TPI) materials, identified as TPI/MTC for the material from Mitsui Toatsu Chemicals Inc. and TPI/H2O for the material from United Technologies Research Center, as high temperature thermoplastic adhesives and primers for bonding titanium (6AL-4V) adherends are discussed. A limited characterization of the materials was performed using a Diffuse Reflectance-Fourier Transform Infrared Spectroscopy (DR-FTIR) technique. Thermomechanical Analysis (TMA) and torsional braid techniques were used to determine glass transition temperature. The adhesive's strength, as determined by simple lap shear tests, as used to evaluate the effects of long term thermal exposure (up to 1000 hrs) at 204 deg C and a 72-hour water-boil.

Progar, D. J.↗
NASA NTRS1985

STPI/LARC: A 200 deg C polyimide adhesive

A copolyimide, STPI/LARC, was prepared from the reaction of 3,3'4'benzophenonetetracarboxylic dianhydride (BTDA), equimolar quantities of m-phenylenediamine and 4,4'-oxydianiline, and a small amount of phthalic anhydride to control the molecular weight. The processability and adhesive properties of STPI/LARC were compared to those of a commercially available form of LARC-TPI. LARC-TPI, a thermoplastic polyimide, from the reaction of BTDA and 3,3'-diaminobenzophenone, had previously shown promise as a high temperature structural adhesive. Lap shear specimens were fabricated using adhesive tape prepared from each of the two polymers. Lap shear tests were performed at room temperature, 177 C, and 204 C before and after exposure to a 72-hour water-boil and to aging at 204 C.

Progar, D. J.↗
NASA NTRS1985

Solid-state Bonding of Superplastic Aluminum Alloy 7475 Sheet

Experimental works were carried out to study the feasibility of solid state bonding of superplastic aluminum 7475 sheet. Amount of deformation, bonding time, surface cleaning method and intermediate layer were the process parameters investigated. Other parameters, held constant by the superplastic forming condition which is required to obtain a concurrent solid state bonding, are bonding temperature, bonding pressure and atmosphere. Bond integrity was evaluated through metallographic examination, X-ray line scan analysis, SEM fractographic analysis and lap shear tests. The early results of the development program indicated that sound solid state bonding was accomplished for this high strength 7475 alloy with significant amounts of deformation. A thin intermediate layer of the soft 5052 aluminum alloy aided in achieving a solid state bonding by reducing the required amount of plastic deformation at the interface. Bond strength was substantially increased by a post bond heat treatment.

Byun, T. D. S.↗
NASA NTRS1983

Analysis of the stress state in an Iosipescu sheartest specimen

The state of stress in an Iosipescu shear test specimen is analyzed, utilizing a finite element computer program. The influence of test fixture configuration on this stress state is included. Variations of the standard specimen configuration, including notch depth, notch angle, and notch root radius are modeled. The purpose is to establish guidelines for a specimen geometry which will accommodate highly orthotropic materials while minimizing stress distribution nonuniformities. Materials ranging from isotropic to highly orthotropic are considered. An optimum specimen configuration is suggested, along with changes in the test fixture.

Walrath, D. E.↗
NASA NTRS1986

Adhesive evaluation of thin films of LARC-TPI and LARC-TPI with 5 mol % ODA

A commercially available LARC-TPI film and an experimentally prepared film of LARC-TPI with 5 mol % of 4,4'-oxydianiline (ODA), designated as LARC-TPI/ODA in the report, supplied by Mitsui Toatsu Chemicals, Incorporated (MTCI), Japan, were evaluated as thermoplastic adhesive films for bonding Ti-6Al-4V. The LARC-TPI/ODA had been shown by MTCI to possess more flow than thermoplastic LARC-TPI and was, therefore, evaluated and compared to the LARC-TPI. Lap shear strength was used to evaluate the materials as adhesives. They were characterized after fracture by determining the glass transition temperature, Tg. The mode of failure was also reported. Thermal exposure at 204C for 500 and 1000 hrs and a 72-hour water-boil were conducted on lap shear specimens prepared with the two adhesive films. Lap shear tests were conducted at RT, 177C, 204C, and 232C before and after exposures.

Progar, D. J.↗
NASA NTRS1986

Adhesive evaluation of LARC-TPI and a water-soluble version of LARC-TPI

The results of a study to evaluate two Langley Research Center thermoplastic polimide (TPI) materials, identified as TPI/MTC for the material from Mitsui Toatsu Chemicals Inc. and TPI/H2O for the material from United Technologies Research Center, as high temperature thermoplastic adhesives and primers for bonding titanium (6AL-4V) adherends are discussed. A limited characterization of the materials was performed using a Diffuse Reflectance-Fourier Transform Infrared Spectroscopy (DR-FTIR) technique. Thermomechanical Analysis (TMA) and torsional braid techniques were used to determine glass transition temperature. The adhesive's strength, as determined by simple lap shear tests, was used to evaluate the effects of long term thermal exposure (up to 1000 hrs) at 204 deg C and a 72-hour water-boil.

Progar, D. J.↗
NASA NTRS1986

A finite element overlay technique for modeling pinned composite joints

A finite element technique using overlaid plane stress elements is presented for modeling a pinned composite joint. The technique allows for discrete modeling of the pin and web regions of the joint in a two-dimensional (2-D) finite element analysis. Thus, predictive capability is substantially increased without the added complexity of a three-dimensional (3-D) analysis. The overlay technique requires a thorough evaluation of the model constraints between the joint components. Bearing panels are used to account for a reduced compressive modulus under bearing loads. Application of the plane stress overlay technique to the Filament Wound Case (FWC) Program is discussed. The experimental approach to determine bearing panel moduli using a double lap shear test is detailed, and finite element results are correlated with full-scale FWC joint test results.

Colvin, G. E.↗
NASA NTRS1987

Evaluation of polyimide films as adhesives

A commercially available LARC-TPI film and an experimentally prepared film of LARC-TPI with 5 mol pct of 4,4-prime-oxydianiline (ODA), designated as LARC-TPI/ODA, were evaluated as thermoplastic adhesive films for bonding Ti-6Al-4V. Lap shear strength was used to evaluate the materials as adhesives. They were characterized after fracture by determining the glass transition temperature, T(g). The mode of failure is also reported. Thermal exposure at 240 C for 500 and 1000 h and a 72-h water-boil were conducted on lap shear specimens prepared with the two adhesive films. Lap shear tests were conducted at room temperature, 177 C, 204 C, and 232 C before and after exposures.

Progar, Donald J.↗
NASA NTRS1991

Nonlinear response of resin matrix laminates using endochronic theory

The nonlinear response of laminated, resin matrix fibrous composites is modeled using orthotropic endochronic theory. The theory is formulated in terms of elastic constants and endochronic parameters characterizing the linear and nonlinear response, respectively, of unidirectional composites. All constants and parameters can be determined from normal (tension and/or compression) and shear tests on unidirectional and off-axis specimens. The nonlinear constitutive response relations for the unidirectional lamina are presented and the procedure for determining constants and parameters from test is described. The results are then used to predict the nonlinear response of unidirectional laminae and angle-ply laminates. Comparison between theory and experiment for compression loading of AS4/3502 graphite-epoxy, angle-ply laminates shows excellent correlation.

Mathison, S. R.↗
NASA NTRS1992

Enhanced damping of Alfven waves in the solar corona by a turbulent wave spectrum

The effect of a background spectrum of Alfven waves on the rate of dissipation of a test shear Alfven wave is numerically calculated. The results demonstrate that as the classical resistivity eta and classical viscosity mu become small, the damping rate of the Alfven wave remains large and depends only on the amplitude for the scalar potential of the wave spectrum and the wavenumber of the Alfven wave. The damping rate is virtually independent of eta and mu. The wave spectrum need not be turbulent or stochastic to affect the damping rate. The dissipation rate is nonlinear enhanced by nonstochastic spectra as well as by stochastic spectra if two conditions are met. First, the perpendicular magnetic field associated with Alfven wave spectrum must exceed a certain collision-frequency threshold and second, for nonstochastic spectra only, the magnetic field must exceed a threshold proportional to the parallel wavenumber of the shear Alfven wave. These conditions can be easily satisfied in the solar corona.

Kleva, Robert G.↗
NASA NTRS1985

A thermoplastic copolyimide

A copolyimide, STPI/LARC, was prepared from the reaction of 3,3'4,4'-benzophenonetetracarboxylic dianhydride (BTDA), equimolar quantities of m-phenylenediamine and 4,4'-oxydianiline, and a small amount of phthalic anhydride to control the molecular weight. The processability and adhesive properties of STPI/LARC were compared to those of a commercially available form of LARC-TPI. LARC-TPI, a thermoplastic polyimide, from the reaction of BTDA and 3,3'-diaminobenzophenone, had previously shown promise as a high temperature structural adhesive. Lap shear specimens were fabricated using adhesive tape prepared from each of the two polymers. Lap shear tests were performed at room temperature, 177 C, and 204 C before and after exposure to a 72-hour water-boil and to aging at 204 C.

Progar, D. J.↗