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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 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
NASA NTRS1979

Resin/fiber thermo-oxidative interactions in PMR polymide/graphite composites

The amounts of resin weight loss and fiber weight loss in four PMR-polyimide graphite fiber composites were calculated from the composite weight losses and the fiber/resin ratios of the composites after long term thermo-oxidative aging in 600 F air. The accelerating effect of graphite fiber on resin weight loss, compared to neat resin weight loss, indicated the presence of a deleterious resin/fiber thermo-oxidative interaction, presumably due to fiber impurities. Similarly, the decelerating effect of the protective matrix resin on fiber weight loss, compared to bare fiber weight loss, was also demonstrated. The amount of hydrazine-indigestible resin and the amount of loose surface graphite fiber that formed during 600 deg F exposure of the composites were quantitatively determined. The indigestible residual resin was also qualitatively studied by scanning electron microscopy.

Alston, W. B.↗
NASA NTRS1979

Synthesis of improved moisture resistant polymers

The use of difluoromaleimide-capped prepolymers to provide improved moisture resistant polymers was investigated. Six different prepolymer formulations were prepared by two different methods. One method utilized the PMR approach to polyimides and the second method employed the normal condensation route to provide fully imidized prepolymers. Polymer specimens cured at 450 F exhibited adequate long-term stability in air at 400 F. Moisture absorption studies were conducted on one polymer formulation. Neat Polymer specimens exhibited weight gains of up to 2% (w/w) after exposure to 100% relative humidity at 344K (160 F) for 400 hours.

Orell, M. K.↗
NASA NTRS1978

Effects of hydrothermal exposure on a low-temperature cured epoxy

Thermal mechanical analysis was employed to monitor the penetration temperature of a low-temperature epoxy resin (EPON 826/D230). Both neat resin and E-glass composite samples were examined. The effects of cure temperature variation and moisture content on the apparent glass transition temperature were determined.

Lauver, R. W.↗
NASA NTRS1980

Analyses of moisture in polymers and composites

A suitable method for the direct measurement of moisture concentrations after humidity/thermal exposure on state of the art epoxy and polyimide resins and their graphite and glass fiber reinforcements was investigated. Methods for the determination of moisture concentration profiles, moisture diffusion modeling and moisture induced chemical changes were examined. Carefully fabricated, precharacterized epoxy and polyimide neat resins and their AS graphite and S glass reinforced composites were exposed to humid conditions using heavy water (D20), at ambient and elevated temperatures. These specimens were fixtured to theoretically limit the D20 permeation to a unidirectional penetration axis. The analytical techniques evaluated were: (1) laser pyrolysis gas chromatography mass spectrometry; (2) solids probe mass spectrometry; (3) laser pyrolysis conventional infrared spectroscopy; and (4) infrared imaging thermovision. The most reproducible and sensitive technique was solids probe mass spectrometry. The fabricated exposed specimens were analyzed for D20 profiling after humidity/thermal conditioning at three exposure time durations.

Ryan, L. E.↗
NASA NTRS1980

Oxygen index tests of thermosetting resins

The flammability characteristics of nine thermosetting resins under evaluation for use in aircraft interiors are described. These resins were evaluated using the Oxygen Index (ASTM 2863) testing procedure. The test specimens consisted of both neat resin and glass reinforced resin. When testing glass-reinforced samples it was observed that Oxygen Index values varied inversely with resin content. Oxygen values were also obtained on specimens exposed to temperatures up to 300 C. All specimens experienced a decline in Oxygen Index when tested at an elevated temperature.

Gilwee, W. J., Jr.↗
NASA NTRS1981

Two-stage combustion for reducing pollutant emissions from gas turbine combustors

Combustion and emission results are presented for a premix combustor fueled with admixtures of JP5 with neat H2 and of JP5 with simulated partial-oxidation product gas. The combustor was operated with inlet-air state conditions typical of cruise power for high performance aviation engines. Ultralow NOx, CO and HC emissions and extended lean burning limits were achieved simultaneously. Laboratory scale studies of the non-catalyzed rich-burning characteristics of several paraffin-series hydrocarbon fuels and of JP5 showed sooting limits at equivalence ratios of about 2.0 and that in order to achieve very rich sootless burning it is necessary to premix the reactants thoroughly and to use high levels of air preheat. The application of two-stage combustion for the reduction of fuel NOx was reviewed. An experimental combustor designed and constructed for two-stage combustion experiments is described.

Clayton, R. M.↗
NASA NTRS1981

Critical parameters for coarse coal underground slurry haulage systems

Factors are identified which must be considered in meeting the requirements of a transportation system for conveying, in a pipeline, the coal mined by a continuous mining machine to a storage location neat the mine entrance or to a coal preparation plant located near the surface. For successful operation, the slurry haulage the system should be designed to operated in the turbulent flow regime at a flow rate at least 30% greater than the deposition velocity (slurry flow rate at which the solid particles tend to settle in the pipe). The capacity of the haulage system should be compatible with the projected coal output. Partical size, solid concentration, density, and viscosity of the suspension are if importance as well as the selection of the pumps, pipes, and valves. The parameters with the greatest effect on system performance ar flow velocity, pressure coal particle size, and solids concentration.

Maynard, D. P.↗
NASA NTRS1981

Investigation of the effect of resin material on impact damage to graphite/epoxy composites

The results of an experimental program are described which establishes the feasibility and guide lines for resin development. The objective was to identify the basic epoxy neat resin properties that improve low velocity impact resistance and toughness to graphite-epoxy laminates and at the same time maintain useful structural laminate mechanical properties. Materials tests from twenty-three toughened epoxy resin matrix systems are included.

Palmer, R. J.↗
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 NTRS1981

The effects of organosulfur compounds upon the storage stability of Jet A fuel

This study examined the effect of sulfur-containing compounds on the storage stability of Jet A turbine fuel. It was found that alkyl sulfides and disulfides increased the fuel's stability while all thiols and thiophene derivatives tested decreased fuel stability (increased deposit formation) at temperatures and sulfur concentrations selected. Linear Arrhenius plots of sulfur-spiked fuel samples demonstrated that deposit formation decreased with increased slope for all alkyl sulfides, alkyl disulfides, thiols, and thiophene derivatives. A plot of insoluble deposit vs. concentration of added alkyl sulfide produces a negative slope. It appears that the inhibiting mechanism for alkyl sulfides is a result of the compound's reactivity with intermediate soluble precursors to deposit in the fuel. A method of approximating the relative basicity of weak organosulfur bases was developed via measurement of their resonance chemical shifts in proton NMR. Linear plots of log gm. deposit vs. change in chemical shift (shift differences between sulfur bases neat and complexed with I2) were found for alkyl sulfides and alkyl thiols. This suggests the possibility that increased deposit formation is due to base catalysis with these compound classes.

Heneman, F. C.↗
NASA NTRS1981

Fundamental studies of antimisting fuels

Research is currently being undertaken to determine the various physical characteristics of antimisting fuel. It is an endeavor to prevent post-crash fuel mist fires. The following studies were done: (1) drop and jet breakup studies using an image processing technique, (2) flammability of fuel mist under simulated plane crash conditions; (3) skin friction measurements; (4) determination of the tensile viscosity of non-Newtonian antimisting fuel as a function of the extensional rate; and (5) water compatibility measurements. The results indicate that the mechanism which prevents antimisting fuel breakup is related to the time-dependent tensile viscosity of antimisting fuel under stress. Drag reduction phenomenon was also observed at Reynolds numbers higher than 20,000. Uptake of water by the antimisting fuel is higher than that for the neat fuel. In addition, its rate of absorption depends on the concurrent degree of agitation.

Sarohia, V.↗
NASA NTRS1980

Impact penetration studies of graphite/epoxy laminates

A study was conducted to provide an initial insight into the role of the matrix in impact energy absorption of graphite/epoxy laminates. A single epoxy system, NARMCO 5208, in both composite and cured neat-resin form was studied with a constant velocity impact test apparatus. The parameters investigated include resin cure temperature, fiber type, ply thickness and orientation, and impact velocity. The results from the study show that matrix chemistry, as obtained by cure temperature changes, has a significant effect upon the failure mode and energy absorption during impact.

Sykes, G. F.↗
NASA NTRS1983

High-Performance Matrix Resins

State-of-the-art PMR polyimides provide good strength and light weight in wide variety of critical applications. However, improved processability and elevated temperature thermo-oxidative stability are desired in such polyimide systems. Resins, intended for use in advanced composites, adhesives, and neat resin articles, show improvements in both processability and elevatedtemperature stability over state-of-the-art PMR-15 polymers.

Pater, R. H.↗
NASA NTRS1981

The effect of resin on the impact damage tolerance of graphite-epoxy laminates

The effect of the matrix resin on the impact damage tolerance of graphite-epoxy composite laminates was investigated. The materials were evaluated on the basis of the damage incurred due to local impact and on their ability to retain compression strength in the presence of impact damage. Twenty-four different resin systems were evaluated. Five of the systems demonstrated substantial improvements compared to the baseline system including retention of compression strength in the presence of impact damage. Examination of the neat resin mechanical properties indicates the resin tensile properties influence significantly the laminate damage tolerance and that improvements in laminate damage tolerance are not necessarily made at the expense of room temperature mechanical properties. Preliminary results indicate a resin volume fraction on the order of 40 percent or greater may be required to permit the plastic flow between fibers necessary for improved damage tolerance.

Williams, J. G.↗
NASA NTRS1982

Vibration damping characteristics of graphite/epoxy composites for large space structures

Limited data on extensional and flexural damping of small specimens of graphite/epoxy and unreinforced epoxy resin were obtained. Flexural damping was measured using a forced vibration technique based on resonant flexural vibration of shaker excited double cantilever specimens. Extensional damping was measured by subjecting similar specimens to low frequency sinusoidal oscillation in a servohydraulic tensile testing machine while plotting load versus extensional strain. Damping was found to vary slowly and continuously over the frequency range 0.01 - 1000 Hz, and no drastic transitions were observed. Composite damping was found to be less than neat resin damping. Comparison of small specimen damping values with assembled column damping values seems to indicate that, for those materials, material damping is more important than joint damping. The data reported was limited not by the test apparatus, but by signal conditioning and data acquisition. It is believed that filtering of the strain gage signals and the use of digital storage with slow playback will make it possible to extend the frequency and amplitude ranges significantly.

Gibson, R. F.↗
NASA NTRS1982

The properties of novel bisimide amine cured epoxy/Celion 6000 graphite fiber composites

The study is concerned with the further development of bisimide amine cured epoxy resins first reported by Serafini et al. (1979). Attention is given to properties of the neat resins and composites made with these novel epoxy resins and Celion 6000 graphite fibers. The use of bisimide amine hardeners to cure epoxy resins causes a significant improvement in the char-forming characteristics of the cured resin. Compared to epoxy resins cured with a conventional amine, such as 4,4'-diaminodiphenylsulfone, the bisimide cured epoxies exhibit about a twofold improvement in the aerobic char yield at 800 C. The levels of moisture absorption exhibited by the bisimide amine cured epoxies were found to be considerably lower than those exhibited by state-of-the-art epoxies (0.5 wt.% versus 2.0%).

Scola, D. A.↗
NASA NTRS1982

Cure kinetics of epoxy matrix resin by differential scanning calorimetry

A study was made on the cure kinetics of an epoxy neat-resin (Narmco 5208) using Differential Scanning Calorimetry (DSC). Two interrelated analytical methods were applied to dynamic DSC data for evaluating the kinetic parameters, such as activation energy, E, the order of reaction, n, and the total heat of polymerization (or crosslinking), delta H sub t. The first method was proposed by Ellerstein (1968), and uses a thorough differential-integral analysis of a single DSC curve to evaluate the kinetic parameters. The second method was proposed by Kissinger (1957), and uses multiple DSC curves obtained at various heating rates to evaluate E regardless of n. Kinetic analysis of Narmco 5208 epoxy resin showed that the reaction order, n, is substantially affected by the rate of heating; i.e., n is approximately 2 at slow scan rates but is reduced to 1.5 at higher scan rates. The activation energy, E, is not affected by the scan rate, and the average value of E is 25.6 + or - 1.8 kcal/mole.

Cizmecioglu, M.↗