2,390 research outputs found
Fabrication of composite fan blades using PMR A-type polyimide resin and graphite fiber reinforcement
PMR polyimides are safe, easy to handle, can be processed with relatively wide process controls, and offer excellent mechanical properties, with thermo-oxidative stability. Procedures, staging and cure schedules fully dense, crackfree, dimensionally controlled, complex structure: high tip speed fan blades 1.27 cm (0.5 in) thick
PMR polyimide/graphite fiber composite fan blades
Ultrahigh speed fan blades, designed in accordance with the requirements of an ultrahigh tip speed blade axial flow compressor, were fabricated from a high strength graphite fiber tow and a PMR polyimide resin. The PMR matrix was prepared by combining three monomeric reactants in methyl alcohol, and the solution was applied directly to the reinforcing fiber for subsequent in situ polymerization. Some of the molded blades were completely finished by secondary bonding of root pressure pads and an electroformed nickel leading edge sheath prior to final machining. The results of the spin testing of nine PMR fan blades are given. Prior to blade fabrication, heat resin tensile properties of the PMR resin were examined at four formulated molecular weight levels. Additionally, three formulated molecular weight levels were investigated in composite form with both a high modulus and a high strength fiber, both as-molded and postcured, in room temperature and 232 C transverse tensile, flexure and short beam shear. Mixed fiber orientation panels simulating potential blade constructions were also evaluated. Flexure tests, short beam shear tests, and tensile tests were conducted on these angle-plied laminates
Fiber reinforced PMR polyimide composites
Commercially obtained PMR-15 polyimide prepregs with S-glass and graphite fiber reinforcements were evaluated along with in-house prepared glass and graphite cloth PMR 2 materials. A novel autoclave approach was conceived and used to demonstrate that both the PMR systems respond to 1.4 MPa (200 psi) autoclave pressures to produce void free composites equivalent to die molded laminates. Isothermal gravimetric analysis and subsequent mechanical property tests indicated that the PMR 2 system was significantly superior in thermo-oxidative stability, and that S-glass reinforcements may contribute to the accelerated degradation of composites at 316 C (600 F) when compared to graphite fiber reinforced composites. Fully reversed bending fatigue experiments were conducted with a type of fixture unused for organic matrix composites. These studies indicated that the graphite fiber composites were clearly superior in fatigue resistance to the glass fiber reinforced material and that PMR matrix composite systems yield performance of the same order as composite materials employing other families of matrices
Composite impact strength improvement through a fiber/matrix interphase
Research was conducted to improve the impact strength and toughness of fiber/resin composites by means of a fiber coating interphase. Graphite fiber/epoxy resin composites were fabricated with four different fiber coating systems introduced in a matrix-fiber interphase. Two graphite fibers, a high strength and a high modulus type, were studied with the following coating systems: chemical vapor deposited boron, electroless nickel, a polyamide-imide resin and a thermoplastic polysulfone resin. Evaluation methods included the following tests: Izod, flexure, shear fracture toughness, longitudinal and transverse tensile, and transverse and longitudinal compression. No desirable changes could be effected with the high strength fiber, but significant improvements in impact performance were observed with the polyamide-imide resin coated high modulus fiber with no loss in composite modulus
The COBE DIRBE Point Source Catalog
We present the COBE DIRBE Point Source Catalog, an all-sky catalog containing
infrared photometry in 10 bands from 1.25 microns to 240 microns for 11,788 of
the brightest near and mid-infrared point sources in the sky. Since DIRBE had
excellent temporal coverage (100 - 1900 independent measurements per object
during the 10 month cryogenic mission), the Catalog also contains information
about variability at each wavelength, including amplitudes of variation
observed during the mission. Since the DIRBE spatial resolution is relatively
poor (0.7 degrees), we have carefully investigated the question of confusion,
and have flagged sources with infrared-bright companions within the DIRBE beam.
In addition, we filtered the DIRBE light curves for data points affected by
companions outside of the main DIRBE beam but within the `sky' portion of the
scan. At high Galactic latitudes (|b| > 5 degrees), the Catalog contains
essentially all of the unconfused sources with flux densities greater than 90,
60, 60, 50, 90, and 165 Jy at 1.25, 2.2, 3.5, 4.9, 12, and 25 microns,
respectively, corresponding to magnitude limits of approximately 3.1, 2.6, 1.7,
1.3, -1.3, and -3.5. At longer wavelengths and in the Galactic Plane, the
completeness is less certain because of the large DIRBE beam and possible
contributions from extended emission. The Catalog also contains the names of
the sources in other catalogs, their spectral types, variability types, and
whether or not the sources are known OH/IR stars. We discuss a few remarkable
objects in the Catalog. [abridged]Comment: Accepted for publication in the Astrophysical Journal Supplement. The
full tables are available at http://www.etsu.edu/physics/bsmith/dirbe
The core structure of presolar graphite onions
Of the ``presolar particles'' extracted from carbonaceous chondrite
dissolution residues, i.e. of those particles which show isotopic evidence of
solidification in the neighborhood of other stars prior to the origin of our
solar system, one subset has an interesting concentric
graphite-rim/graphene-core structure. We show here that single graphene sheet
defects in the onion cores (e.g. cyclopentane loops) may be observable edge-on
by HREM. This could allow a closer look at models for their formation, and in
particular strengthen the possibility that growth of these assemblages proceeds
atom-by-atom with the aid of such in-plane defects, under conditions of growth
(e.g. radiation fluxes or grain temperature) which discourage the graphite
layering that dominates subsequent formation of the rim.Comment: 4 pages, 7 figures, 11 refs, see also
http://www.umsl.edu/~fraundor/isocore.htm
Laser spectroscopy of hyperfine structure in highly-charged ions: a test of QED at high fields
An overview is presented of laser spectroscopy experiments with cold,
trapped, highly-charged ions, which will be performed at the HITRAP facility at
GSI in Darmstadt (Germany). These high-resolution measurements of ground state
hyperfine splittings will be three orders of magnitude more precise than
previous measurements. Moreover, from a comparison of measurements of the
hyperfine splittings in hydrogen- and lithium-like ions of the same isotope,
QED effects at high electromagnetic fields can be determined within a few
percent. Several candidate ions suited for these laser spectroscopy studies are
presented.Comment: 5 pages, 1 figure, 1 table. accepted for Canadian Journal of Physics
(2006
Impact of clinical severity of stroke on the severity and recovery of visuospatial neglect (vol 13, 0198755, 2018)
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