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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 235 records · Page 13
All sourcesNASA NTRSDOE OSTI
NASA NTRS2005

Graphite Sheet Coating for Improved Thermal Oxidative Stability of Carbon Fiber Reinforced/PMR-15 Composites

Expanded graphite was compressed into graphite sheets and used as a coating for carbon fiber reinforced PMR-15 composites. BET analysis of the graphite indicated an increase in graphite pore size on compression, however the material was proven to be an effective barrier to oxygen when prepegged with PMR-15 resin. Oxygen permeability of the PMR-15/graphite was an order of magnitude lower than the compressed graphite sheet. By providing a barrier to oxygen permeation, the rate of oxidative degradation of PMR-15 was decreased. As a result, the composite thermo-oxidative stability increased by up to 25%. The addition of a graphite sheet as a top ply on the composites yielded little change in the material's flexural strength or interlaminar shear strength.

Campbell, Sandi↗
NASA NTRS1980

Advanced resin systems for graphite epoxy composites

The value of resin/carbon fiber composites as lightweight structures for aircraft and other vehicle applications is dependent on many properties: environmental stability, strength, toughness, resistance to burning, smoke produced when burning, raw material costs, and complexity of processing. A number of woven carbon fiber and epoxy resin composites were made. The epoxy resin was commercially available tetraglycidylmethylene dianiline. In addition, composites were made using epoxy resin modified with amine and carboxyl terminated butadiene acrylonitrile copolymer. Strength and toughness in flexure as well as oxygen index flammability and NBS smoke chamber tests of the composites are reported.

Gilwee, W. J.↗
NASA NTRS1986

Anticorrelation of Shubnikov-deHaas amplitudes and negative magnetoresistance magnitudes in intercalated pitch based graphite fibers

In pitch based carbon fibers at low temperatures, simultaneous presence of a negative magnetoresistance and the Shubnikov-deHaas effect are found. The strengths of these effects correlate inversely. These results can be understood in terms of the amount of order vs disorder in the fiber, as described by Guigon and Oberlin from structural studies.

Woollam, John A.↗
NASA NTRS1985

Develop and demonstrate manufacturing processes for fabricating graphite filament reinforced polymide (Gr/PI) composite structural elements

A study was conducted to assess the merits of using graphite/polyimide, NR-150B2 resin, for structural applications on advanced space launch vehicles. The program was divided into two phases: (1) Fabrication Process Development; and (2) Demonstration Components. The first phase of the program involved the selection of a graphite fiber, quality assurance of the NR-150B2 polyimide resin, and the quality assurance of the graphite/polyimide prepreg. In the second phase of the program, a limited number of components were fabricated before the NR-150B2 resin system was removed from the market by the supplier, Du Pont. The advancement of the NR-150B2 polyimide resin binder was found to vary significantly based on previous time and temperature history during the prepregging operation. Strength retention at 316C (600F) was found to be 50% that of room temperature strength. However, the composite would retain its initial strength after 200 hours exposure at 316C (600F). Basic chemistry studies are required for determining NR-150B2 resin binder quality assurance parameters. Graphite fibers are available that can withstand high temperature cure and postcure cycles.

Chase, V. A.↗
NASA NTRS1979

Feasibility study on the development of tough, moisture-resistant laminating resins

The potential of cyanate resins as replacement for epoxy resins in composites with graphite fiber reinforcement was investigated in an effort to provide improved moisture resistance and toughness in laminating systems at a projected cost, handleability, and processing requirements equivalent to 400 K (260 F) curing epoxies. Monomer synthesis, formulation, blending, resin preparation, catalysis studies, prepreg preparation, laminate fabrication, and testing are discussed. A graphite fiber reinforced laminate was developed with 95 percent retention of the original 363 K (180 F) flexural strength and 70 percent retention of the 363 K (180 F) short beam shear strength after 500 hour exposure to 95 + 7 relative humidity at 324 K (120 F).

Brand, R. A.↗
NASA NTRS1983

Orthotic devices using lightweight composite materials

Potential applications of high strength, lightweight composite technology in the orthotic field were studied. Several devices were designed and fabricated using graphite-epoxy composite technology. Devices included shoe plates, assistive walker devices, and a Simes prosthesis reinforcement. Several other projects having medical application were investigated and evaluations were made of the potential for use of composite technology. A seat assembly was fabricated using sandwich construction techniques for the Total Wheelchair Project.

Harrison, E., Jr.↗
NASA NTRS1984

The effect of space environment exposure on the properties of polymer matrix composite materials (A0180)

The objective of this experiment is to determine the effect of various lengths of exposure to a space environment on the mechanical properties of selected commercial polymer matrix composite materials. Fiber materials will include graphite, boron, S-glass, and PRD-49. The mechanical properties to be investigated are orthotropic elastic constants, strength parameters (satisfying the tensor polynomial relation), coefficients of thermal expansion, impact resistance, crack propagation, and fracture toughness. In addition, the effect of laminate thickness on property changes will also be investigated.

Tennyson, R. C.↗
NASA NTRS1983

Shock processing of interstellar grains

Theoretical and observational evidence is presented that shock processing of interstellar dust grains by supernova blast waves affects both heavy element depletions and ultraviolet extinction curves. By coupling a realistic model of grain sizes and populations with a radiative shock code, significant grain destruction at velocities as low as 40 km/s is demonstrated. Nonthermal sputtering and grain-grain collisions destroy relatively more large grains than small, and more silicates than graphite. Consequently, both the 2175 A extinction 'bump' and the far-ultraviolet normalized extinction are increased in strength. Ultraviolet extinction studies with the International Ultraviolet Explorer of nine stars near three supernova remnants (the Monoceros Loop, Shajn 147, and Vela) exhibit strong 2175 A bumps and normal or high far-ultraviolet extinction. Diffuse bands, if they are created by small grains, should show little correlation with such activity.

Seab, C. G.↗
NASA NTRS1998

Progressive Failure And Life Prediction of Ceramic and Textile Composites

An engineering approach to predict the fatigue life and progressive failure of multilayered composite and textile laminates is presented. Analytical models which account for matrix cracking, statistical fiber failures and nonlinear stress-strain behavior have been developed for both composites and textiles. The analysis method is based on a combined micromechanics, fracture mechanics and failure statistics analysis. Experimentally derived empirical coefficients are used to account for the interface of fiber and matrix, fiber strength, and fiber-matrix stiffness reductions. Similar approaches were applied to textiles using Repeating Unit Cells. In composite fatigue analysis, Walker's equation is applied for matrix fatigue cracking and Heywood's formulation is used for fiber strength fatigue degradation. The analysis has been compared with experiment with good agreement. Comparisons were made with Graphite-Epoxy, C/SiC and Nicalon/CAS composite materials. For textile materials, comparisons were made with triaxial braided and plain weave materials under biaxial or uniaxial tension. Fatigue predictions were compared with test data obtained from plain weave C/SiC materials tested at AS&M. Computer codes were developed to perform the analysis. Composite Progressive Failure Analysis for Laminates is contained in the code CPFail. Micromechanics Analysis for Textile Composites is contained in the code MicroTex. Both codes were adapted to run as subroutines for the finite element code ABAQUS and CPFail-ABAQUS and MicroTex-ABAQUS. Graphic user interface (GUI) was developed to connect CPFail and MicroTex with ABAQUS.

Xue, David Y.↗
NASA NTRS1994

Milestone 5 test report. Task 5, subtask 5.2: Tile to foam strength tests

This report summarizes work that has been performed to date on the strength of a cryotank insulation system using Rohacell foam and TUFI-coated AETB-12 ceramic tiles directly bonded to a simulated graphite-epoxy tank wall. Testing utilized a custom specimen design which consists of a long tensile specimen with eccentric loading to induce curvature similar to the curvature expected due to 'pillowing' of the tank when pressurized. A finite element model was constructed to predict the specific element strains in the test article, and to assist with design of the test specimen to meet the specific goals of curvature and laminate strain. The results indicate that the heat treated 3.25-pcf density Rohacell foam does not provide sufficient strength for the induced stresses due to curvature and stress concentration at the RTV bondline to the TUFI tile. The test was repeated using higher density non-heat treated Rohacell foam (6.9 pcf) without foam failure. The finite element model was shown to predict specimen behavior, and validation of the model was successful. It is pertinent to mention that the analyses described herein accurately predicted the failure of the heat treated foams and based on this analysis method it is expected that the untreated 3.25 pcf Rohacell foam will be successful.

Greenberg, H. S.↗
NASA NTRS1985

Properties of autoclaved Gr/PI composites made from improved tack PMR-15 prepreg

Autoclave processing studies were conducted, using improved tack PMR-15 prepreg, to determine the effect of tack enhancing PMR resin modifications on composite processability and mechanical properties. Improved tack graphite fiber reinforced PMR-15 prepregs were prepared and exposed to ambient conditions for various times and then autoclave molded into composites. Composite specimens were prepared and tested for flexural and interlaminar shear strengths at room temperature and 316 C. The retention of flexural and interlaminar shear strength as a function of exposure in air at 316 C was also determined. The results show that the modified PMR resin solutions provide prepreg with improved tack and drape retention characteristics without adversely affecting processability or mechanical properties of autoclave molded graphite fiber reinforced PMR-15 composites.

Vannucci, R. D.↗
NASA NTRS1985

Effect of low-velocity or ballistic impact damage on the strength of thin composite and aluminum shear panels

Impact tests were conducted on shear panels fabricated from 6061-T6 aluminum and from woven fabric prepreg of Du Pont Kevlara fiber/epoxy resin and graphite fiber/epoxy resin. The shear panels consisted of three different composite laminates and one aluminum material configuration. Three panel aspect ratios were evaluated for each material configuration. Composite panels were impacted with a 1.27-cm (0.05-in) diameter aluminum sphere at low velocities of 46 m/sec (150 ft/sec) and 67 m/sec (220 ft/sec). Ballistic impact conditions consisted of a tumbled 0.50-caliber projectile impacting loaded composite and aluminum shear panels. The results of these tests indicate that ballistic threshold load (the lowest load which will result in immediate failure upon penetration by the projectile) varied between 0.44 and 0.61 of the average failure load of undamaged panels. The residual strengths of the panels after ballistic impact varied between 0.55 and 0.75 of the average failure strength of the undamaged panels. The low velocity impacts at 67 m/sec (220 ft/sec) caused a 15 to 20 percent reduction in strength, whereas the impacts at 46 m/sec (150 ft/sec) resulted in negligible strength loss. Good agreement was obtained between the experimental failure strengths and the predicted strength with the point stress failure criterion.

Farley, G. L.↗
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 NTRS1975

Numerical analysis and parametric studies of the buckling of composite orthotropic compression and shear panels

A computer program is presented which was developed for the combined compression and shear of stiffened variable thickness orthotropic composite panels on discrete springs: boundary conditions are general and include elastic boundary restraints. Buckling solutions are obtained by using a newly developed trigonometric finite difference procedure which improves the solution convergence rate over conventional finite difference methods. The classical general shear buckling results which exist only for simply supported panels over a limited range of orthotropic properties, were extended to the complete range of these properties for simply supported panels and, in addition, to the complete range of orthotropic properties for clamped panels. The program was also applied to parametric studies which examine the effect of filament orientation upon the buckling of graphite-epoxy panels. These studies included an examination of the filament orientations which yield maximum shear or compressive buckling strength for panels having all four edges simply supported or clamped over a wide range of aspect ratios. Panels with such orientations had higher buckling loads than comparable, equal weight, thin skinned aluminum panels. Also included among the parameter studies were examinations of combined axial compression and shear buckling and examinations of panels with rotational elastic edge restraints.

Housner, J. M.↗
NASA NTRS1975

Quiet Clean Short-haul Experimental Engine (QCSEE) under-the-wing engine composite fan blade design

The design and analysis of a composite fan blade for the under the wing (UTW) QCSEE is presented. The blade is designed for a variable pitch, 18 bladed rotor and is constructed from a hybrid composite combination of materials consisting of Kevlar-49, type AS graphite, boron, and S-glass fibers in a PR288 epoxy resin matrix. The blade has an attached platform which is constructed of AS-graphite, PR288 epoxy resin matrix and aluminum honeycomb. The blade is designed to satisfy aerostability and cyclic life and strength requirements with a light weight construction. The attached platform is designed for a fail-safe condition in that it is retainable by the blade, under centrifugal force loading, even in the event of blade to platform bond separation. Details of the blade design and the results of stress, vibration, and impact analysis are included.

Source record↗
NASA NTRS1991

Probabilistic micromechanics for metal matrix composites

A probabilistic micromechanics-based nonlinear analysis procedure is developed to predict and quantify the variability in the properties of high temperature metal matrix composites. Monte Carlo simulation is used to model the probabilistic distributions of the constituent level properties including fiber, matrix, and interphase properties, volume and void ratios, strengths, fiber misalignment, and nonlinear empirical parameters. The procedure predicts the resultant ply properties and quantifies their statistical scatter. Graphite copper and Silicon Carbide Titanlum Aluminide (SCS-6 TI15) unidirectional plies are considered to demonstrate the predictive capabilities. The procedure is believed to have a high potential for use in material characterization and selection to precede and assist in experimental studies of new high temperature metal matrix composites.

Engelstad, S. P.↗
NASA NTRS1995

Intercalated-Graphite-Fiber Composites

Electrically conducting composites made from bromine-intercalated graphite fibers in epoxy matrix. Bromine-intercalated graphite fibers have conductivity of about 20,000 ohm-1cm-1 and found to be stable in presence of moisture fibers even submerged for indefinite times) and at reasonably high temperature (200 degrees C). Conventional epoxy resins can be used with such fibers. Composite materials containing 50 percent bromine-intercalated graphite fibers have promising properties. Mechanical properties of composites similar to composites made with pristine fibers: Tensile and flexural strengths and Young's and bending moduli essentially unchanged, and interlaminar shear strengths slightly enhanced. Thermal conductivities of composites also show very little degradation. However, electrical conductivities of composites increase, which invites application of composites in electrical grounding planes and in shields against electro-magnetic interference.

Gaier, James R.↗