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At least 253 records · Page 14

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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.↗

NASA NTRS1991

Ethynyl terminated imidothioethers and resins therefrom

Ethynyl terminated imidothioethers (ETIs) are prepared by the reaction of a dimercaptan, such as 4,4'-dimercaptodiphenyl ether, and an ethynyl containing maleimide, such as N-(3-ethynylphenyl)maleimide. Blends of these ETIs and ethynyl terminated polymeric materials, such as ethynyl terminated sulfones and ethynyl terminated arylene ethers, are also prepared. These resin blends exhibit excellent processability, and the cured blends show excellent fracture toughness and solvent resistance, as well as excellent adhesive and composite properties.

Hergenrother, Paul M.↗

NASA NTRS1990

LaRC-I-TPI - A status report on a new high performance, thermoplastic polyimide

A new thermoplastic polyimide designated LaRC-I-TPI has been prepared from 4,4'-isophthaloyldiphthalic anhydride (IDPA) and 1,3-phenylenediamine (m-PDA), phthalic anhydride endcapped or unendcapped. It is closely related to the well-known commercial LaRC-TPI. A survey of the synthesis and some thermal, film, adhesive, fracture toughness, and composite properties of this new polyimide is presented. While both materials have similar properties at comparable stages of development, LaRC-I-TPI should be less expensive to manufacture as a result of the use of lower cost readily available monomers.

Pratt, J. Richard↗

NASA NTRS1990

Factors which influence tensile strength of a SiC/Ti-24Al-11Nb (at. pct) composite

Tensile and fiber pullout tests were used in conjunction with SEM to investigate structural and processing effects on SiC fiber, a neat Ti-24Al-11Nb matrix alloy, and a composite fabricated from the two. The effects of oxygen content, fiber spacing, fiber volume fraction, fiber-matrix reaction thickness, Teflon content, and matrix powder size, appear to be smaller than the effects of variability in fiber strength. Fiber spacing did not influence radial crack formation, interfacial bond shear strength, or stress-strain behavior in the composite. The temperature dependence of composite properties was investigated over the 23-815 C range.

Brindley, P. K.↗

NASA NTRS1992

A micromechanics-based progressive failure model for laminated composite structures

A micromechanics-based mechanistic model for progressive failure analysis of laminated composite shell structures is developed. A finite-element program for laminated shell analysis is coupled with a micromechanical elasticity solution for predicting failure and effective composite properties. The laminate model is based on a third-order shell theory which allows for both transverse normal and shearing deformations. Results are presented for the progressive failure of a (0/90(4)s graphite/epoxy laminate under uniaxial tension. The effect of fiber volume fraction in the 90-deg plies on laminate behavior was studied, and it was found that decreasing the fiber-volume fraction in the off-axis plies did not affect the laminate stiffness or the ultimate failure load, but significantly increased the load at which initial failure occurred.

Averill, R. C.↗

NASA NTRS1993

Micromechanics of crenulated fibers in carbon/carbon composites

The influence of crenulated noncircular fibers on the micromechanical stress states due to a transverse strain and to a temperature change in carbon/carbon composites is examined using the finite element method. Stresses at the interface of both fully bonded and fully disbonded fibers having two crenulation amplitudes and with two fiber volume fractions are presented. In each case, these interface stresses are compared to stresses at the interface of circular fibers which have the same degree of disbond and fiber volume fraction and are under the same loading conditions. For the disbonded cases, deformed meshes showing locations of fiber/matrix contact are also included. In addition to the interface stress states, selected composite properties are also computed and compared in each case examined. Interest in studying noncircular fibers stems from a desire to increase the transverse properties of carbon/carbon by introducing a mechanical interlocking between the fiber and the matrix. Results presented here indicate that this interlocking does in fact occur. Evidence from the interface stress data suggests, however, that any possible advantage of this interlocking may be outweighed by the disadvantage of stress concentrations which arise at the interface due to the crenulated geometry of the fibers.

Carapella, E. E.↗

NASA NTRS2000

Technological Readiness of Ceramic Matrix Composites: A Review

This review intends to provide a snapshot of the state of industry of ceramic matrix composites (CMC). It is therefore organized in terms of design needs, composite properties, system capabilities, and technological availability. This publication will cover CMCs in use and development, with technological readiness levels (TRL) from laboratory testing of coupons to flight proven hardware.

Neergaard, Lynn↗

NASA NTRS2000

Method to Prepare Processable Polyimides with Non-Reactive Endgroups Using 1,3-bis(3-Aminophenoxy) Benzene

Polyimide copolymers were obtained containing 1,3-bis(3-aminophenoxy)benzene (APB) and other diamines and dianhydrides and terminating with the appropriate amount of a non-reactive endcapper, such as phthalic anhydride. Homopolymers containing only other diamines and dianhydrides which are not processable under conditions described previously can be made processable by incorporating various amounts of APB, depending on the chemical structures of the diamines and dianhydrides used. Polyimides that are more rigid in nature require more APB to impart processability than polyimides that are less rigid in nature. The copolymers that result from using APB to enhance processability have a unique combination of properties including excellent thin film properties, low pressure processing (200 psi and below), improved toughness, improved solvent resistance, improved adhesive properties, improved composite mechanical properties, long term melt stability (several hours at 390 C), and lower melt viscosities.

Jensen, Brian J.↗

NASA NTRS2004

Water in Terrestrial Planets: Always an Oxidant?

Water is commonly assumed to be an oxidant in many planetary settings. Because it can affect Fe-FeO-Fe2O3 equilibria and thus bulk compositional properties of planets and asteroids, this is an important ingredient to understand. The role of water in two settings will be addressed - magmas, and mantles during accretion - along with the implications for planet growth and evolution.

Righter, K.↗