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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 1,117 records · Page 62

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NASA NTRS1979

Effects of moisture on apparent flexure strength and on torsion and flexure fatigue properties of graphite-epoxy composites

The effects of moisture and temperature on unidirectional and multi-ply laminates of T300/934 and AS/3501 graphite-epoxy systems were investigated. Properties studied were static flexure strength and flexure and torsion fatigue strengths at room temperature and at 74 C. Specimens with increased moisture content showed a reduced static flexure strength; water as the test environment had only a negligible influence. In flexure fatigue and torsion fatigue, the water environment caused somewhat reduced fatigue strengths at room temperature and significantly greater degradation in 74 C water. The failure mode in all cases was interlaminar delamination.

Sumsion, H. T.↗

NASA NTRS1980

Two-dimensional O2 adsorbed on graphite

Properties of two-dimensional O2 adsorbed on graphite are calculated in the extremely low-coverage delta region and for monolayers, with use of pattern-recognition optimization and Monte Carlo techniques. Equilibrium configurations and orientations, orientational order-disorder, melting, and dissociation transitions are predicted at various O2 densities. Phase characteristics, including a plastic crystallite phase, are compared with experiment.

Etters, R. D.↗

NASA NTRS1980

The spectral opacity of triatomic carbon measured in a graphite tube furnace over the 280 to 600 nm wavelength range

The paper presents the measurements of linear triatomic carbon opacity (C3) made in a graphite tube furnace to extend the wavelength range of Brewer and Engelke (1962) to the 280-600 nm range. An electrooptical method was used to determine C3 absorption in argon at 2720 to 3060 K; a quartic polynomial regression expression was derived to provide a complete temperature profile from pyrometer measurements. The C3 spectra were plotted for several opacity levels. It was concluded that the extension of the spectral range to the near u.v. levels made it easier to identify C3 particles.

Snow, W. L.↗

NASA NTRS1980

Graphite-epoxy panel compression strength reduction due to local impact

The effects of low velocity impact on the compressive strength of graphite/epoxy structures are reviewed. Extensive tests were conducted on sandwich beams, laminated plates and stiffened panels. Conditions for failures were investigated by impact tests on statically loaded test specimens. Lightly loaded graphite structures (such as aircraft secondary structure) were insensitive to impact damage. In more heavily loaded structures, (such as wing panels), appreciable reductions in compressive strength occurred. The implications of the tests for structural design are discussed by comparing panel masses for designs where ultimate strains were reduced due to impact considerations with the masses of designs with higher ultimate strains. Preliminary test data are presented to show the possibility of improvements in damage to tolerance achievable by using an alternate matrix material.

Card, M. F.↗

NASA NTRS1980

Graphite fiber surface treatment to improve char retention and increase fiber clumping

Composites containing carbon and graphite fibers can release fibers into the atmosphere during a fire. This release can potentially cause failure in some types of electrical equipment. Reduced fiber dispersion during and after combustion will reduce risks. Epoxidized char forming systems were synthesized which will react with commercially available surface treated carbon fiber. Fibers modified with these char formers retained adhesion in a specific epoxy matrix resin. Small scale combustion testing indicates that using these char former modified fibers in laminates will help to reduce the dispersement of fibers resulting from exposure to fire without sacrificing resin to fiber adhesion.

Paul, J. T., Jr.↗

NASA NTRS1980

Microwave limb sounder, graphite epoxy support structure

The manufacturing and processing procedures which were used to fabricate a precision graphite/epoxy support structure for a spherical microwave reflecting surface are described. The structure was made fromm GY-70/930 ultra high modulus graphite prepreg, laminated to achieve an isotropic in plane thermal expansion of less than + or - 0.1 PPM/F. The structure was hand assembled to match the interface of the reflective surface, which was an array of 18 flexure supported, aluminum, spherically contoured tiles. Structural adhesives were used in the final assembly to bond the elements into their final configuration. A eutectic metal coating was applied to the composite surface to reduce dimensional instabilities arising from changes in the composite epoxy moisture content due to environmental effects. Basic materials properties data are reported and the results of a finite element structural analysis are referenced.

Pynchon, G.↗

NASA NTRS1980

Graphite composite truss welding and cap section forming subsystems. Volume 1: Executive summary

A rolltrusion process was developed for forming of a hybrid, single-ply woven graphite and glass fiber cloth, impregnated with a polysulfone resin and coated with TI02 pigmented P-1700 resin into strips for the on-orbit fabrication of triangular truss segments. Ultrasonic welding in vacuum showed no identifiable effects on weld strength or resin flow characteristics. An existing bench model cap roll forming machine was modified and used to roll form caps for the prototype test truss and for column test specimens in order to test local buckling and torsional instability characteristics.

Source record↗

NASA NTRS1981

Physical aging in graphite epoxy composites

The matrix dominated mechanical behavior of a graphite epoxy composite was found to be affected by sub Tg annealing. Postcured + or - 45 deg 4S specimens of Thornel 300 graphite/Narmco 5208 epoxy were quenched from above Tg and given a sub Tg annealing at 140 C for times up to 10 to the 5th power min. The ultimate tensile strength, strain to break, and toughness of the composite material were found to decrease as functions of sub Tg annealing time. No weight loss was observed during the sub Tg annealing. The time dependent change in mechanical behavior is explained on the basis of free volume changes that are related to the physical aging of the nonequilibrium glassy network epoxy. The results imply possible changes in composite properties with service time.

Kong, E. S. W.↗

NASA NTRS1981

Research on graphite reinforced glass matrix composites

A broad group of fibers and matrices were combined to create a wide range of composite properties. Primary material fabrication procedures were developed which readily permit the fabrication of flat plate and shaped composites. Composite mechanical properties were measured under a wide range of test conditions. Tensile, flexure mechanical fatigue, thermal fatigue, fracture toughness, and fatigue crack growth resistance were evaluated. Selected fiber-matrix combinations were shown to maintain their strength at up to 1300 K when tested in an inert atmosphere. Composite high temperature mechanical properties were shown to be limited primarily by the oxidation resistance of the graphite fibers. Composite thermal dimensional stability was measured and found to be excellent.

Prewo, K. M.↗

NASA NTRS1980

Spatial distribution of volatile compounds in graphite composites

The distribution of water and other volatile compounds such as acetone and phenol was measured as a function of depth in four graphite resin matrix composites. Precision abrasion mass spectrometry was used to qualitatively and quantitatively characterize the indigenous volatile compounds in the as received condition and after drying in an environmentally controlled oven. The total amount of water in the composites varied from 0.12 wt% to 1.1 wt% and the times required to dry the samples ranged from less than 96 h to much greater than 555 h.

Grayson, M. A.↗

NASA NTRS1980

Silicone modified resins for graphite fiber laminates

Six silicone modified resins were selected for evaluation in unidirectional filament wound graphite laminates. Neat samples of these resins had 1,000 C char residues of 6-63%. The highest flexural values measured for the laminates were a strength of 1,220 MPa and a modulus of 105 GPa. The highest interlaminar shear strength was 72 MPa.

Frost, L. W.↗

NASA NTRS1980

Increased fracture toughness of graphite-epoxy composites through intermittent interlaminar bonding

The objective of this study was to increase the fracture toughness of multilayer continuous-filament graphite-epoxy composites. The method used is intermittent interlaminar bonding which can lead to a large increase in the fracture surface area. Intermittent bonding was achieved through introduction of thin perforated Mylar between the layers of the composite. For the optimum condition, fracture toughness was increased from about 100 kJ/sq m for untreated specimens to an average of about 500 kJ/sq m, while tensile strength dropped from 500 MPa to 400 MPa, and elastic modulus remained the same at about 75 GPa. An approximate analysis is presented to explain the improvement in toughness.

Jea, L.-C.↗

NASA NTRS1980

Ultrasonic evaluation of impact-damaged graphite fiber composite

Unidirectional Hercules AS/3501-6 graphite fiber epoxy composites are subjected to repeated controlled low-velocity drop-weight impacts in the laminate direction. The degradation is ultrasonically monitored using through-thickness attenuation and a modified stress wave factor, SWF. There are correlations between the number of drop-weight impacts, the residual tensile strength, the through-thickness attenuation and the SWF.

Williams, J. H., Jr.↗

NASA NTRS1980

Ultrasonic attenuation and velocity in AS/3501-6 graphite fiber composite

The ultrasonic group velocity and attenuation were measured as a function of frequency for longitudinal and shear waves in the Hercules epoxy matrix (3501-6) and in the principal directions of the unidirectional Hercules graphite fiber epoxy composite (AS/3501-6). Tests were conducted in the frequency ranges 0.25-14 MHz and 0.5-3 MHz for longitudinal and shear wave modes, respectively. While the attenuation increased with frequency for all wave modes, the group velocity was independent of frequency for all wave modes. In studying the effects of transducer-specimen interface couplant and pressure, it was found that for each transducer, there exists a frequency-dependent 'saturation pressure' corresponding to the maximum output amplitude of the signal.

Williams, J. H., Jr.↗

NASA NTRS1981

Postbuckling and failure characteristics of selected flat rectangular graphite-epoxy plates loaded in compression

Results of an experimental study of the postbuckling response and failure characteristics of 16- and 24-ply quasi-isotropic and 24-ply orthotropic flat rectangular graphite-epoxy plates loaded in compression are examined. Some of the specimens had circular drilled holes or were subjected to low-speed impact damage. The ratio of failure load to buckling load was found to be higher for specimens with lower initial buckling strains than for specimens with higher initial buckling strains. Some specimens supported more than five times their initial buckling load before failing. The specimens failed along a nodal line of the buckling mode in an induced shear failure mode. Holes and impact damage had a more adverse effect on the postbuckling strength of specimens with high initial buckling strains than on the strength of specimens with lower initial buckling strains.

Starnes, J. H., Jr.↗

NASA NTRS1981

Graphitic carbon in the Allende meteorite - A microstructural study

High-resolution transmission electron microscopy shows that carbon in the Allende carbonaceous chondrite meteorite is predominantly a poorly crystalline graphite. Such material is of interest as an important carrier of the isotopically anomalous noble gases found in carbonaceous chondrites.

Smith, P. P. K.↗

NASA NTRS1981

Effective masses, relaxation times, and carrier mobilities in some chloride intercalants of graphite

The effective masses, carrier scattering times and carrier mobilities have been measured in selected graphite intercalation compounds using the Shubnikov-de Haas effect at a series of temperatures between 4 and 50 K. Effective masses are less than or equal to 0.1 of the free-electron mass, scattering times are about 10 to the -13th/s and carrier mobilities are on the order of 10,000 sq cm/V s.

Woollam, J. A.↗

NASA NTRS1980

Fillers for improved graphite fiber retention by polymer matrix composites

This program was designed to develop technology for fabrication of graphite/epoxy composites containing selected boron and boron-containing fillers, determine the effects of the fillers on physical and mechanical properties of composites, and evaluate the effectiveness of the boron fillers for fiber retention when the composites are exposed to fire conditions followed by impact. Fillers evaluated were crystalline and amorphous boron, boron carbide, and aluminum boride. The fillers were evaluated by mixing with Narmco 5208 resin matrix at quantities up to 5%. Graphite composites were fabricated and evaluated with respect to their mechanical properties, resistance to humidity, and burning characteristics. Also, the mechanism by which the fillers prevented fiber release was studied.

Sheppard, C. H.↗