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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 937 records · Page 52
All sourcesNASA NTRSDOE OSTI
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 NTRS1980

Positron annihilation studies of moisture in graphite-reinforced composites

The positron lifetime technique of monitoring absorbed moisture is applied to several composites, including graphite/polymides which are candidates for high-temperature (over 260 C) applications. The experimental setup is a conventional fast-slow coincidence system wherein the positron lifetime is measured with respect to a reference time determined by the detection of a nuclear gamma ray emitted simultaneously with the positron. From the experiments, a rate of change of positron mean lifetime per unit mass of water can be determined for each type of specimen. Positron lifetime spectra are presented for a graphite/polyimide composite and for a pure polyimide.

Singh, J. J.↗
NASA NTRS1980

Graphite polyimide fabrication research for supersonic cruise aircraft

Advanced fabrication processes and adhesive bonding methods have been developed for the fabrication of full scale fiberglass-polyimide honeycomb stiffened HTS-1 graphite/PMR-15 polyimide panels that meet the design criteria for an upper wing panel of the NASA YF-12 aircraft. Detailed manufacturing, bonding, and autoclave cure procedures are presented. Nondestructive test methods including pulse echo and through-transmission ultrasonic C-scan and laser holography were developed to detect flaws in components and the completed panels. Panels were tested in shear at room temperature and 533 K (500 F) following a variety of thermal exposures to obtain load, deflection and failure analysis data.

Freeman, W. T., Jr.↗
NASA NTRS1982

Electrical Connector for Graphite Heating Elements

Connection method applies force to two interfaces: that between heating element proper and heating-element support members and between heating-element support members and metal conductor. Inner rod of new connector system is maintained in tension by a spring (for example, Belleville washers). Connection is sufficiently complaint so tension remains within desired range, regardless of thermal expansion and contraction of various elements.

Mackintosh, B. H.↗
NASA NTRS1980

Data reduction and analysis for the graphite crystal X-ray spectrometer and polarimeter experiment flown aboard OSO-8 spacecraft

The documentation and software programs developed for the reception, initial processing (quickbook), and production analysis of data obtained by solar X-ray spectroscopy, stellar spectroscopy, and X-ray polarimetry experiments on OSO-8 are listed. The effectiveness and sensitivity of the Bragg crystal scattering instruments used are assessed. The polarization data polarimetric data obtained shows that some X-ray sources are polarized and that a larger polarimeter of this type is required to perform the measurements necessary to fully understand the physics of X-ray sources. The scanning Bragg crystal spectrometer was ideally suited for studying rapidly changing solar conditions. Observations of the Crab Nebula and pulsar, Cyg X-1, Cyg X-2, Cyg X-3, Sco X-1, Cen X-3, and Her X-1 are discussed as well as of 4U1656-53 and 4U1820-30. Evidence was obtained for iron line emission from Cyg X-3.

Novick, R.↗
NASA NTRS1982

Thermal expansion of graphite-epoxy between 116 K and 366 K

A Priest laser interferometer was developed to measure the thermal strain of composite laminates. The salient features of this interferometer are that: (1) it operates between 116 K and 366 K; (2) it is easy to operate; (3) minimum specimen preparation is required; (4) coefficients of thermal expansion in the range of 0-5 micro epsilon/K can be measured; and (5) the resolution of thermal strain is on the order of micro epsilon. The thermal response of quasi-isotropic, T300/5208, grahite-epoxy composite material was studied with this interferometer. The study showed that: (1) for the material tested, thermal cycling effects are negligible; (2) variability of thermal response from specimen to specimen may become significant at cryogenic temperatures; and (3) the thermal response of 0.6 cm and 2.5 cm wide specimens are the same above room temperature.

Short, J. S.↗
NASA NTRS1982

Effect of 1.33 Mev gamma radiation and 0.5 Mev electrons on the mechanical properties of graphite fiber composites

Epoxy/graphite fiber, polyimide/graphite fiber, and polysulfone/graphite fiber composites were exposed to 1.33 Mev gamma irradiation and 0.5 Mev electron bombardment for varying periods of time. The effects of the irradiation treatments on the breaking stress and Young's modulus were studied by a three point bending test. Effects were small; both electron radiation up to 5000 Mrad and gamma radiation up to 350 Mrad resulted in slight increases in both stress and modulus.

Fornes, R. E.↗
NASA NTRS1981

Sub-T/g/ annealing studies of advanced epoxy-matrix graphite-fiber-reinforced composites

Annealing at temperatures below the glass transition temperature (sub-T/g/ annealing) in structural epoxy network glasses is found to affect long-term mechanical properties of symmetrically (+ or - 45 deg) reinforced 16-lamina graphite/epoxy composites. Post-cured specimens of Thornel 300 graphite/Narmco 5208 epoxy are sub-T(g) annealed at 140 C for about 10, 100, 1000, 10,000, and 100,000 min with a prior quenching above T(g). The ultimate tensile strength, strain-to-break, and static toughness of the composite materials are found to decrease as a function of sub-T(g) annealing time, while no weight loss is observed. Time-dependent changes in properties are explained by a physical aging concept based on free-volume decreases in the nonequilibrium glassy state of network epoxies, and results imply that changes in composite properties may occur with the service time.

Kong, E. S. W.↗
NASA NTRS1982

Effects of thermal cycling on residual mechanical properties of C6000/PMR-15 graphite polyimide

An experimental study to determine the effects of thermal cycling on residual mechanical properties of a graphite/polyimide composite has been conducted. Interlaminar shear, flexure and compression strengths were measured at room temperature and 316 C on unidirectional and quasi-isotropic laminates subjected to 150 and 500 thermal cycles between -156 C and 316 C. Thermal cycling produced transverse microcracks and delaminations in the laminates. The linear density of the microcracks (35/cm) was about the same after 150 and 500 cycles. Although the crack density did not change from 150 to 500 cycles, crack growth did occur with intralamina cracks growing into adjacent lamina. The matrix controlled properties of the quasi-isotropic laminate at both room temperature and 316 C were significantly reduced by thermal cycling. However, the properties of the unidirectional laminate were significantly reduced only at 316 C.

Tompkins, S. S.↗
NASA NTRS1982

Application of a gripping system to test a uniaxial graphite fiber reinforced composite /PMR 15/Celion 6000/ in tension at 316 C

A gripping system has been developed to test uniaxial, 0 deg orientation PMR 15/Celion 6000 composites at elevated temperatures. The method involves compression of grit-blasted laminate between grit-blasted metal to give a non-slipping interface for load transfer. Tensile testing at both 316 C and room temperature indicated that deformation was elastic to fracture and that the variation in tensile properties for one laminate is the same as that for several panels. In addition, the tensile properties for uniaxial PMR 15/Celion 6000 are identical at 316 C and room temperature. For nominally 51 volume percent fiber, the elastic modulus is 119.6 GPa, the fracture stress is 1370 MPa, and the strain to fracture is about 1.15 percent. In addition, data are presented which indicate that the gripping system can be used for long term, elevated temperature testing of composite materials.

Whittenberger, J. D.↗
NASA NTRS1982

Effect of Ionizing Radiation on the Mechanical and Structural Properties of Graphite Fiber Reinforced Composites

Graphite/epoxy (T300/5208) and graphite/polyimide composites (C6000/PMR 15) were exposed to various levels of 0.5 MeV electron radiation with the maximum dose being 10,000 Mrad. A three point bending test was used to evaluate the ultimate stress and modulus of the composites. In all composites except transverse samples of C6000/PMR 15 ultimate stress values remained approximately constant or increased slightly. The modulus values remained approximately constant for all composite types regardless of the radiation level. Interfacial aspects of composites were studied. Interlaminar shear tests were performed on T300/5208 and C6000/PMR 15 composites irradiated to 10,000 Mrad. There was an initial increase in interlaminar shear strength (up to 1,000 Mrad) followed by a sharp decrease with further radiation exposure. Using scanning electron microscopy no visual differences in the mode of fracture could be detected between ruptured control samples and those exposed to various levels of radiation. Electron spectroscopy for chemical analysis (ESCA) revealed little change in the surface elements present in control and highly irradiated T300/5208 composite samples.

Wolf, Kay Woodroof↗
NASA NTRS1983

Mechanisms of degradation of graphite composites in a simulated space environment

Attention is given to degradation mechanisms for graphite/polysulfone and graphite/epoxy laminates exposed to ultraviolet and high-energy electron radiation in vacuum up to 960 equivalent sun hours and to 10 to the 9th rads, respectively. The materials showed good electron radiation stability as indicated by the low G values for gas formation and no evidence of mechanical property changes. Quantum yields for gas formation indicate poor stability to ultraviolet radiation. Mechanical property measurements did not show significant changes up to 960 ESH, with the possible exception of P1700/C6000. The main products of irradiation were identified as hydrogen and methane, along with high levels of CO and CO2.

Giori, C.↗
NASA NTRS1983

Dynamic mechanical characterization of cure of a polyimide-graphite fiber composite (PMR 15/Celion 6000)

Dynamic mechanical studies of thermosetting PMR 15 polyimide/Celion 6000 composites were used to characterize cure behavior. Variation in composite shear modulus with cure time for laminates partially cured under 3.45 MPa pressure was compared with that of laminates fully cured under pressure to select a partially cured system whose behavior corresponded with that of the pressure-cured composites. An empirical kinetic model was developed that relates relative composite shear moduli to cure time and temperature. This model, coupled with standard statistical techniques, was used in the determination of an overall activation energy, E = 145 kj/mole (35 kcal/mole) and order of reaction, n, for the cure reaction(s). The empirical relationship defining dynamic modulus as a function of time and temperature remained linear well into the glassy region. Changes in dynamic glass-transition temperature and in the breadth of the transition peaks with cure time are discussed. Shear modulus and damping were found to be more sensitive measures of relative extent of cure than Fourier transform infrared spectroscopy.

Hurwitz, F. I.↗
NASA NTRS1983

Mechanical Property Characterization of F-100/934 Graphite-Epoxy Composite Material

Procedures for quality control, fabrication techniques, specimen machining, test methodologies, and data collection and interpretation were defined using Thornel P-100 carbon fiber combined with Fiberite's 934 epoxy resin in unidirectional tape form. Tests on the prepreg material, including gel time, resin solids content, tack, volatile content, and flow are detailed. The steps of the fabrication and machining processes are described. Both destructive and nondestructive techniques were employed to assess the properties of the cured laminates. Tests to determine tensile strength and modulus, compressive strength and modulus, interlaminar and inplane shear strength, and flexural strength and modulus are discussed. The results of these experiments are compared with data generated by other researchers.

Clinton, R. G., Jr.↗
NASA NTRS1983

Rubber-toughened polyfunctional epoxies - Brominated vs nonbrominated formulated for graphite composites

A new, commercially available, trifunctional epoxy resin (tris-(hydroxyphenyl)-methane triglycidyl ether) was modified with synthetic rubber to increase the impact resistance of epoxy/graphite composites. These composites were reinforced with commercially available satin-weave carbon cloth using two formulations of epoxies (brominated and nonbrominated) containing various amounts of carboxy-terminated butadience acrylonitrile (CTBN) rubber that had been prereacted with epoxy resin. The impact resistance was determined by measuring the interlaminar shear strength of the composites after impact. The mechanical properties, such as flexural strength and modulus at room temperature and at 93 C, were also determined. Measurements were taken of the flammability and glass transition temperature (Tg); and a thermal-gravimetric analysis was made.

Nir, Z.↗
NASA NTRS1984

Nonlinear response and failure characteristics of clamped internally pressurized graphite-epoxy cylindrical panels

The nonlinear response and failure characteristics of internally pressurized 4- to 16-ply cylindrical panels of graphite/epoxy are experimentally and analytically studied. Tests simulated the skin of a typical transport aircraft fuselage under loading to eventual failure. Aluminum test specimens were similarly tested and compared. All graphite/epoxy panels are found to withstand the internal pressures applied, which are well above the proof pressure loading expected for transport fuselage structures.

Boitnott, R. L.↗