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At least 343 records · Page 19

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NASA NTRS1973

Phenylquinoxaline copolymers

The preparation of a series of homopolymers and block and random type phenylquinoxaline copolymers is described together with their important characteristics and preliminary measurements of composite properties. Phenylquinoxaline homopolymers consisting of low, intermediate, and high molecular weight versions were prepared from the reaction of 3,3'-diaminobenzidine (DAB) and 3,3',4,4'-tetraaminobenzophenone (TAB), each with p-bis(phenylglyoxalyl)benzene as solutions (18% solids content) in a 1:1 mixture of m-cresol and xylene. Three random and three block copolymers were prepared from the reaction of various amounts of DAB and TAB with p-bis(phenylglyoxalyl)benzene. The copolymers were prepared with DAB to TAB distribution ratios of 3:1, 1:1, and 1:3. The work was performed primarily to determine if phenylquinoxaline copolymers exhibit any advantage over the homopolymers for use as functional or structural resins, especially as a matrix material in combination with a high-modulus graphite fiber reinforcement.

Hergenrother, P. M.↗

NASA NTRS1975

Shortgrass prairie spectral measurements

The spectral methods of vegetation analysis not only measure herbage biomass on a nondestructive basis but also can be adapted to aircraft and satellite devices to map the spatial distribution over an area in an efficient and economical fashion. This study reviews the ground-based in situ field spectrometry in the 0.350-0.800 micron region of the spectrum. A statistical analysis of in situ spectroreflectance data from sample plots of the shortgrass prairie shows that green biomass, chlorophyll concentration, and leaf water content are directly interrelated to that composite property of the plot which is called functioning green biomass. Spectrocorrelation data indicate the spectral regions of optimum sensitivity for a remote estimation of the green biomass, chlorophyll, and leaf water content. The near-infrared region of the spectrum shows a high positive spectrocorrelation to these three sample parameters, regardless of the amount of standing dead vegetation.

Tucker, C. J.↗

NASA NTRS1975

Colloquium on Planetary Satellites, 28th, Cornell University, Ithaca, N.Y., August 18-21, 1974, Proceedings

The papers consider the orbits, physical properties, composition, origin, and evolution of the natural satellites of the solar system from the viewpoint of celestial mechanics. Topics include a computer technique for developing analytic expressions for the coordinates and partial derivatives of Jupiter's Galilean satellites, a theory of the motion of the Galilean satellites, a comparison between photographic observations of the positions of the Galilean satellites and Sampson's tables, astrolabe observations of several transits of the Galilean satellites, the orbital resonance among the Galilean satellites, the motion of the Martian satellites from ground-based observations and Mariner-9 TV data, and a general method for predicting eclipses of natural planetary satellites. Individual items are announced in this issue.

Burns, J. A.↗

NASA NTRS1978

Brazed boron-silicon carbide/aluminum structural panels

Fluxless brazing process minimizes degradation of mechanical properties composite material of silicon carbide coated boron fibers in an aluminum matrix. Process is being used to fabricate full-scale Boron-Silicon Carbide/Aluminum-Titanium honeycomb core panels for flight testing and ground testing.

Arnold, W. E., Jr.↗

NASA NTRS1979

Stability of PMR-polyimide monomer solutions

The stability of alcohol solutions of norborneyl capped PMR-polyimide resins was monitored during storage at ambient and subambient temperatures. Chemical changes during storage were determined spectroscopically using nuclear magnetic resonance. Resin processability and cured resin quality were determined by fabrication of unidirectional, graphite fiber composites using aged solutions and testing of selected composite properties. PMR-15 solutions exhibit nominally two weeks of useful life and PMR-2 solutions exhibit nominally two days of useful life at ambient conditions. The limiting factor is precipitation of imide reaction produces from the monomer solutions. Both solutions exhibit substantially longer useful lifetimes in subambient storage. PMR-15 shows no precipitation after several months storage at subambient temperatures. PMR-2 solutions do exhibit precipitates after extended subambient storage, however, the precipitates formed under these conditions can be redissolved. The chemical implications of these observations are discussed.

Lauver, R. W.↗

NASA NTRS1979

Recent developments in PMR polyimides at NASA Lewis

The following areas of PMR polyimide research were reviewed: (1) prepreg tack and drape; (2) cure temperature; (3) solution characterization; and (4) elevated temperature composite properties. Recent hardware applications of PMR-15 by various fabricators were also reviewed.

Serafini, T. T.↗

NASA NTRS1981

High char yield epoxy curing agents

Class of imide-amine curing agents preserves structural integrity, prevents fiber release, and is fully compatible with conventional epoxy resins; agents do not detract from composite properties while greatly reducing char yield. Materials utilizing curing are used in aerospace, automotive, and other structural components where deterioration must be minimized and fiber release avoided in event of fire.

Delvigs, P.↗

NASA NTRS1979

Second generation PMR polyimide/fiber composites

A second generation polymerization monomeric reactants (PMR) polyimdes matrix system (PMR 2) was characterized in both neat resin and composite form with two different graphite fiber reinforcements. Three different formulated molecular weight levels of laboratory prepared PMR 2 were examined, in addition to a purchased experimental fully formulated PMR 2 precurser solution. Isothermal aging of graphite fibers, neat resin samples and composite specimens in air at 316 C were investigated. Humidity exposures at 65 C and 97 percent relative humidity were conducted for both neat resin and composites for eight day periods. Anaerobic char of neat resin and fire testing of composites were conducted with PMR 15, PMR 2, and an epoxy system. Composites were fire tested on a burner rig developed for this program. Results indicate that neat PMR 2 resins exhibit excellent isothermal resistance and that PMR 2 composite properties appear to be influenced by the thermo-oxidative stability of the reinforcing fiber.

Cavano, P. J.↗

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 NTRS1983

The Uranian satellites - Surface compositions and opposition brightness surges

The present, 5 percent-resolution spectrophotometry for the Uranian satellites Ariel, Umbriel, Titania and Oberon cover the 1.43-2.57 wavelength region and confirm the presence of a spectrally dominant water ice component in their surfaces. The 1.5- and 2.0-micron water absorption band depths and continuum reflectance indicate significant differences among the surface compositional properties of the four satellites, and comparisons of the spectra with those of other solar system bodies and of laboratory water ice spectra imply the presence of a significant nonwater ice component on/in their surfaces. The nature of this nonwater ice component is suggested by the data to be similar to that of such substances as carbon black. Near-IR opposition brightness surges of Ariel, Titania and Oberon are found to be among the largest in the solar system.

Brown, R. H.↗

NASA NTRS1983

The Integrated Technology and Flight Research Rotor Technology demonstrators for the 1985-1995 timeframe

The purposes and progress in the Integrated Technology Rotor/Flight Research Rotor (ITR/FRR) Project, a joint effort by the U.S. Army and NASA, are outlined. The project goal is to integrate the disciplines of rotor design, aerodynamics, structures, materials, dynamics, and acoustics, to remove the risks in applying the technology, and to develop an advanced flight research rotor which permits significant variation in the rotor properties. Composite rotors are believed to be capable of displaying infinite fatigue lifetimes with fail-safe characteristics, and bearingless hubs simplify hub designs. The programs will also consider the flight control, propulsion, and structures. Concept definition contracts are presently distributed among five companies, and preliminary designs will lead to model tests in 1984.

Bousman, W.↗

NASA NTRS1984

Space debris impact experiment (S0001)

The specific objectives of this experiment are to establish the population and size distribution of meteoroids in the mass range from 10 to the minus 10 power to 10 to the minus 4 power G, to establish the current population of man-made debris in the same mass range, and to obtain data on the physical properties (composition and density) of meteoroids.

Humes, D. H.↗

NASA NTRS1985

Improved Thermal-Diffusivity-Measuring Apparatus

Accuracy at high temperature improved. Furnace heats specimen to experimental temperature, and flash tube raises specimen temperature by small amount and for short time so diffusivity (composite property of heat capacity and conductivity) determined. Specimen mount ensures minimum heat loss during temperature-rise measurement. Measurement temperatures up to 1,000 degrees C realized with fused-quartz light pipe and up to 1,600 degrees C with sapphire light pipe.

Wood, C.↗

NASA NTRS1984

Solvent Resistant Thermoplastic Composite Matrices

The following approaches improved the solvent resistance and raised the Tg of thermoplastics: end-capping aligomers with ethynyl groups; incorporating ethynyl groups pendent along the polymer chain; and correcting polymers containing pendent ethynyl groups with a low molecular weight diethynyl compound. The following conclusions were reached: (1) film and composite properties off an ethynyl-terminated sulfone were better than those of UDEL (trademark); (2) fracture energy of an ethynyl-terminated sulfone was lower than that of UDEL (trademark); (3) residual palladium in the cured ethynyl-terminated sulfone lower the thermooxidative stability of the cured resin; (4) the properties of a phenoxy resin were altered considerably by placing pendent ethynyl groups along the polymer chain; and (5) property trade-offs must be considered when thermoplastics are modified via reactant groups.

Hergenrother, P. M.↗

NASA NTRS1985

Polymer matrix and graphite fiber interface study

Hercules AS4 graphite fiber, unsized, or with EPON 828, PVA, or polysulfone sizing, was combined with three different polymer matrices. These included Hercules 3501-6 epoxy, Hercules 4001 bismaleimide, and Hexcel F155 rubber toughened epoxy. Unidirectional composites in all twelve combinations were fabricated and tested in transverse tension and axial compression. Quasi-isotropic laminates were tested in axial tension and compression, flexure, interlaminar shear, and tensile impact. All tests were conducted at both room temperature, dry and elevated temperature, and wet conditions. Single fiber pullout testing was also performed. Extensive scanning electron microphotographs of fracture surfaces are included, along with photographs of single fiber pullout failures. Analytical/experimental correlations are presented, based on the results of a finite element micromechanics analysis. Correlations between matrix type, fiber sizing, hygrothermal environment, and loading mode are presented. Results indicate that the various composite properties were only moderately influenced by the fiber sizings utilized.

Adams, D. F.↗

NASA NTRS1985

Thermo-oxidative stability of graphite fiber/PMR-15 polyimide composites at 350 deg C

A series of graphite fiber/PMR-15 polyimide composites were subjected to isothermal aging at 350 C in flowing air (100 cc/min and 1000 cc/min) over a 520 hr time period. The graphite fibers were analyzed by ISS/SIMS techniques before composite fabrication. Fibers exposed at the surface of the composite due to the isothermal aging process were also analyzed by the ISS/SIMS method. Component and composite weight less studies were also conducted for similarly exposed materials. Optical micrograph investigations of composites to follow the progress of the thermo-oxidative process were also conducted. Flexural and interlaminar shear strengths of the imaged and aged composites were measured. The relationship of component and composite properties as they relate to the thermo-oxidative behavior of the materials was discussed.

Scola, D. A.↗

NASA NTRS1989

Composite sizing and ply orientation for stiffness requirements using a large finite element structural model

A NASTRAN bulk dataset preprocessor was developed to facilitate the integration of filamentary composite laminate properties into composite structural resizing for stiffness requirements. The NASCOMP system generates delta stiffness and delta mass matrices for input to the flutter derivative program. The flutter baseline analysis, derivative calculations, and stiffness and mass matrix updates are controlled by engineer defined processes under an operating system called CBUS. A multi-layered design variable grid system permits high fidelity resizing without excessive computer cost. The NASCOMP system uses ply layup drawings for basic input. The aeroelastic resizing for stiffness capability was used during an actual design exercise.

Radovcich, N. A.↗

NASA NTRS1990

Functionalized poly(arylene ethers) as toughness modifiers for bismaleimides

A family of novel, low molecular weight functionalized poly(arylene ether) resins has been investigated to ascertain its members' toughness-imparting contribution to neat bismaleimide (BMI) resin and BMI-matrix laminate composite properties. Attention is given to the contribution of the reactive poly(arylene ether)'s backbone chemistry to fracture toughness, as well as to the comparative influence of high and low molecular weight reactive poly(arylene ether) types on the modified BMI resin systems. The modified BMIs possess a polyphase morphology, with good adhesion between the thermoplastic nodules and the host thermoset systems.

Stenzenberger, H. D.↗