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Quantum oscillations as a function of magnetic field in the Hall effect and thermoelectric power are studied in two samples of pressure-annealed pyrolytic graphite. Only the oscillations originating from minority-Fermi-surface carriers are discussed. Frequencies of the de Haas-van Alphen type are measured over a wide range of angles between the magnetic field and the c axis of the Brillouin zone. Results are given graphically and analyzed.
Comparison of graphite ablation experiment results in the diffusion-controlled oxidation and sublimation regimes with results of an equilibrium chemistry, film coefficient ablation analysis. Mass transfer and energy transfer effects are considered. Tests were conducted in an arcjet facility at convective heating rates of 600 to 800 W/sq cm, radiative heating rates up to 2900 W/sq cm, with test specimen surface pressures of 0.06, 0.1, and 0.3 atm in an air stream. The experimental and analytical mass loss and surface temperature results agreed well when the carbon vapor thermodynamic properties from the JANAF tables are used in the analysis.
This paper discusses a resin developed for use in autoclave molding of polyimide graphite composite stiffened, titanium alloy structures. Both primary and secondary bonded structures were evaluated that were produced by autoclave processing. Details of composite processing, adhesive formulary, and bonding processes are provided in this paper, together with mechanical property data for structures. These data include -65 F, room temperature, and 600 F shear strengths; strength retention after aging; and stress rupture properties at 600 F under various stress levels for up to 1000 hours duration. Typically, shear strengths in excess of 16 ksi at room temperature with over 60% strength retention at 600 F were obtained with titanium alloy substrates.
The first crystal X-ray polarimeter to be used for X-ray astronomy is described. Polarization is measured by modulation of the X rays diffracted at an average 45 deg glancing angle from large, curved graphite crystal panels as these rotate about an axis parallel to the incident X-ray flux. Arrangement of the crystal panels, the design of the detector, and the signal-processing circuitry were optimized to minimize systematic effects produced by off-axis pointing of the rocket and cosmic ray induced events. The in-flight performance of the instrument in relation to the observed background signal is discussed.
Powdered polymer is finely ground. Second polymer, soluble, is mixed with appropriate solvent. Milled polymer and graphite filaments are added to soluble polymer-solvent solution to create slurry. Slurry is dried, and when ready for processing, the soluble, binder-polymer is removed by heat during precure or cure cycle.
The state-of-the-art of graphite/polyimide structures was evaluated and key design and fabrication issues to be considered in future hardware programs are defined. The fabrication and testing at 500 F of a graphite/polyimide center wing box beam using OV-10A aircraft criteria was accomplished. The baseline design of this box was developed in a series of studies of other advanced composite materials: glass/epoxy, boron/epoxy, and boron/polyimide. The use of this basic design permits ready comparison of the performance of graphite/polyimide with these materials. Modifications to the baseline composite design were made only in those areas effected by the change of materials. Processing studies of graphite fiber polyimide resins systems resulted in the selection of a Modmor II/Gemon L material.
Filament wound NOL rings, 4-inch and 8-inch diameter closed-end vessels involving three epoxy resin systems and three graphite fibers were tested to develop property data and fabrication technology for filament wound graphite/epoxy pressure vessels. Vessels were subjected to single-cycle burst tests at room temperature. Manufacturing parameters were established for tooling, winding, and curing that resulted in the development of a pressure/vessel performance factor (pressure x volume/weight) or more than 900,000 in. for an oblate spheroid specimen.
Sliding friction experiments were conducted with amorphous and fully graphitized carbons sliding on copper and on films of chromium and aluminum on copper. Auger emission spectroscopy analysis was used to monitor carbon transfer to the metal surfaces. Friction and wear were also measured. Metal surfaces were examined both in the clean state and with normal oxides present. Results indicate that different metals have an important effect on friction, wear, and transfer characteristics. With amorphous carbon, the least chemically active metal gave the highest wear and amount of carbon transfer. Both forms of carbon gave lower friction and wear and lower transfer rates when in contact with clean, as opposed to oxide-covered, chromium surfaces. With copper, the reverse was true; cleaning was detrimental.
The potential of polyphenylquinoxaline (PPQ)/graphite composites to serve as structural material at 316 C (600 F)has been demonstrated using a block copolymer, BlCo(13), PPQ derivative. Initially, thirteen polyphenylquinoxalines were evaluated. From this work, four candidate polymers were selected for preliminary evaluation as matrices for HMS graphite fiber reinforced composites. The preliminary composite evaluation enabled selection of one of the four polymers for advanced composite preparation and testing. Using an experimentally established cure schedule for each of the four polymers, preliminary laminates of 50% resin volume content, prepared without postcure, were tested for flexure strength and modulus, interlaminar shear strength (short beam), and tensile strength and modulus at ambient temperature. A block copolymer (Bl Co 13) derived from one mole p-bis (phenylglyoxalyl) benzene, one fourth mole 3,3'-diaminobenzidine and three-fourths mole 3,3', 4,4'-tetraminobenzophenone was selected for extensive study. Tensile, flexural, and interlaminar shear values were obtained after aging and testing postcured BlCo(13) laminates at 316 C (600 F). The potential of PPQ/graphite laminates to serve as short term structural materials at temperatures up to 371 C (700 F) was demonstrated through weight loss experiments.
The design, development, fabrication, and qualification load testing of the reflector support truss for Applications Technology Satellites F and G are described. Because the truss is stability-critical, high modulus graphite epoxy composite was used to provide a minimum weight structure. The work was performed under the sponsorship of the NASA Goddard Space Flight Center with Fairchild Industries as the prime contractor.
A friction and wear life study was conducted on the use of a polyimide (PI) varnish as a binder for the solid lubricant, graphite fluoride (CF sub 1.1) sub n. Also studied were the lubricating properties of PI thin films with no solid lubricant additives. For comparison, similar experiments on PI-bonded MoS2 and burnished films of MoS2 or (CF sub 1.1) sub n were conducted. The best results were obtained with the PI-bonded (CF sub 1.1) sub n films. The polyimide thin films (with no solid lubricant additives) did not lubricate well at 25 C; however, when heated to 100 C, low friction and long wear lives were obtained.
The momentum transfer and blow-off vapor yield resulting from the deposition of a pulsed high-power electron beam onto a plane graphite target with surface temperatures of 300 K and 5000 K are examined experimentally. The results show that with identical electron beams the momentum transfer and vapor yield are between two and three times larger when irradiating the 5000 K surface as compared with the 300 K surface.
The potential of polyphenylquinoxaline (PPQ)/graphite composites to serve as structural material at 316 C (600 F) has been demonstrated using a block copolymer, BICo(1:3), PPQ derivative. Initially, 13 polyphenylquinoxalines were evaluated. From this work, four candidate polymers were selected for preliminary evaluation as matrices for HMS graphite fiber reinforced composites. The preliminary composite evaluation enabled selection of one of the four polymers for advanced composite preparation and testing. Using an experimentally established cure schedule for each of the four polymers, preliminary laminates of 50% resin volume content, prepared without postcure, were tested for flexure strength and modulus, interlaminar shear strength (short beam), tensile strength, and modulus of ambient temperature. The potential of PPQ/graphite laminates to serve as short term structural materials at temperatures up to 371 C (700 F) was demonstrated through weight loss experiments.
Coupled mass loss and heat transfer was studied experimentally for thin two inch diameter graphite disks heated as high as 2800 F in a flow of ambient air at velocities of 97 to 717 ft/sec. Oxidation was predominately reaction rate controlled with rate constants which were determined experimentally for POCO AXF 5Q, ATJ, ATJS, and an AVCO 3D Orthogonal material. The specimen thermal response was used with an energy balance to obtain the influence of mass loss and chemical reactions on the heat transfer. Specimen heating due to exothermic reactions correlates qualitatively with an approximate theory.
Small scale combined load fatigue tests were conducted on twelve unidirectional graphite-glass scrim-epoxy composite specimens. The specimens were 1 in. (2.54 cm) wide by 0.1 in. (.25 cm) thick by 5 in. (12.70 cm) long. The fatigue data was developed for the preliminary design of the spar for a bearingless helicopter main rotor. Three loading conditions were tested. Combinations of steady axial, vibratory torsion, and vibratory bending stresses were chosen to simulate the calculated stresses which exist at the root and at the outboard end of the pitch change section of the spar. Calculated loads for 150 knots (77.1 m/sec) level flight were chosen as the baseline condition. Test stresses were varied up to 4.4 times the baseline stress levels. Damage resulted in reduced stiffness; however, in no case was complete fracture of the specimen experienced.
Processing techniques and design data were characterized for a graphite/epoxy composite system that is useful from 75 K to 450 K, and a graphite/polyimide composite system that is useful from 75 K to 589 K. The Monsanto 710 polyimide resin was selected as the resin to be characterized and used with the graphite fiber reinforcement. Material was purchased using the prepreg specification for the design data generation for both the HT-S/710 and HM-S/710 graphite/polyimide composite system. Lamina and laminate properties were determined at 75 K, 297 K, and 589 K. The test results obtained on the skin-stringer components proved that graphite/polyimide composites can be reliably designed and analyzed much like graphite/epoxy composites. The design data generated in the program includes the standard static mechanical properties, biaxial strain data, creep, fatigue, aging, and thick laminate data.
In situ polymerization of monomers was used to prepare graphite-fiber-reinforced polyphenylquinoxaline composites. Six different monomer combinations were investigated. Composite mechanical property retention characteristics were determined at 316 C (600 F) over an extended time period.
A technique has been developed which permits laboratory simulation of graphite condensation in the envelopes of cool, late sequence stars. Processes in the stellar envelope were simulated by allowing hydrogen-carbon mixtures of typical circumstellar composition and temperature to expand freely into vacuum, cooling and supersaturating the vapor. Expansion products were determined mass spectrometrically through the use of molecular beam techniques. The results of laboratory expansions were scaled to those occurring near M and N stars by comparing the number of collisional events in each case. Kinetic considerations indicate that the important rate process in rarefied envelopes will be C2 formation; consequently scaling by termolecular collisions was employed. Results of this study imply that envelope expansions near M giants contribute at most .01 of the observed interstellar grain density. In the case of pulsating N stars, on the other hand, the results are not inconsistent with previous predictions of essentially complete carbon condensation.