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  • Articles  (134)
  • Springer  (134)
  • American Chemical Society (ACS)
  • American Institute of Physics (AIP)
  • Blackwell Publishing Ltd
  • Cell Press
  • International Union of Crystallography (IUCr)
  • Oxford University Press
  • Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics  (134)
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  • Articles  (134)
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  • 1
    ISSN: 1572-8935
    Keywords: Blends ; PEEK ; PEI ; Infrared spectroscopy ; Conformation ; Intermolecular interaction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract The intermolecular interaction and the conformation in miscible blends of poly(ether ether ketone) (PEEK) and poly(ether imide) (PEI) have been investigated by Fourier-transform infrared (FTIR) spectroscopy. The intensity of the C=O out-of-phase stretching (1725 cm−1) of PEI shows a minimum at 70 wt% PEI, whereas that of the C=O in-phase stretching (1778 cm−1) is not perturbed by blending. These intensity variations have been attributed to the effect of blending on the coplanarity of the two imide rings bridged by the phenylene group. Change in coplanarity of these two imide rings alters the intensity of the C=O out-of-phase stretching, but it can not affect the intensity of the C=O in-phase stretching. When the two imide rings are perpendicular to each other, the intensity of the C=O out-of-phase stretching is shown to reach the minimum, corresponding to the observation at 70 wt% PEI. The difference spectra (blend - PEEK - PEI) reveal that the bands associated with the diphenyl ether groups in PEEK are modified by blending with PEI. It is proposed that the favorable interaction takes place between the oxygen lone-pair electrons of the ether group in PEEK and the electron-deficient imide rings in PEI.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Journal of polymer research 6 (1999), S. 21-26 
    ISSN: 1572-8935
    Keywords: Poly(ether ether ketone) ; Poly(ether imide) ; Blend ; Spherulite growth rate ; Surface free energy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract Growths of poly(ether ether ketone) (PEEK) spherulites from both pure melt and its miscible blends with poly(ether imide) (PEI) have been studied by polarized optical microscopy. The nucleation density of PEEK spherulites was depressed upon blending with PEI, which can be attributed to the reduction in degree of supercooling arising from equilibrium melting point depression. A modified Lauritzen-Hoffman (L-H) theory was adopted to analyze the growth kinetics. Regime III-II transition was observed with the transition temperature decreasing with increasing PEI composition. Assuming free rotations of the virtual bonds in PEEK molecule, the side surface free energy of 12.0 erg/cm2 was calculated from the characteristic ratio. The fold surface free energy of 188 erg/cm2 and work of chain folding of 12.3 kcal/mol were then obtained from the modified L-H analysis.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Advanced performance materials 3 (1996), S. 309-324 
    ISSN: 1572-8765
    Keywords: creep ; modelling ; modulus ; molecular modelling ; polymers ; viscoelasticity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The use of molecular-level materials modelling techniques in the development of advanced performance polymers is discussed, with particular emphasis upon bridging the large difference in the scales of dimensions between atomic structure and fabricated parts. The advantages and disadvantages of bulk quantitative structure-property relations and atomistic modelling are assessed, and the method of group interaction modelling is suggested as a means of bridging the dimensional scales. After a brief introduction to the concept of group interaction modelling, examples of modelling the engineering properties of polymers are presented which are difficult to model quantitatively by any other means. The important phase transitions from the crystal and glassy states of matter to those of rubber- and liquidlike states are shown quantitatively to be due to the same isoenergetic condition. The viscoelastic properties of a polymer are critical for many applications and expressions are derived for the loss and storage components of the complex modulus, with reference to failure initiation conditions. The effect of crosslinking in thermosets upon the glass transition temperature and viscoelastic properties is outlined. Finally, the scaling of time from atomic vibrations to the years involved in creep and ageing effects are discussed.
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Journal of reducing space mission cost 1 (1998), S. 9-25 
    ISSN: 1572-9621
    Keywords: barter system ; Cassini ; cost containment ; instrument development ; project management ; resource allocation ; science management ; space payloads.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Using economic incentives to control costs is a new concept for space missions. The basic tenets of market-based approaches run counter to typical centralized management techniques often utilized for complex space missions. NASA's Cassini mission to Saturn used a market trading system to assist the Science Instrument Manager in guiding the development of the spacecraft's science payload. This system allowed science instrument teams to trade resources among themselves to best manage their resources (mass, power, data rate, and budget). Thus, Cassini Project management was no longer responsible for adjudicating and reallocating resources that result from instrument development problems. Instrument teams were responsible for directly managing their resources and if they ran into a development problem it was their responsibility to resolve their problem by descoping or through the use of a 'resource exchange.' Under the trading system, instrument cost growth was less than 1% and the total payload mass was under its allocation by 7%. This result is in stark contrast to the 50%–100% increases in these resources on past missions.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Journal of reducing space mission cost 1 (1998), S. 119-132 
    ISSN: 1572-9621
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Market-based systems are those systems in which currency is used to express demand for a limited resource. In these systems, users `own' currency and exchange it for a desired commodity. Though used for thousands of years, market-based applications to space missions are still in their infancy. The first successful application was in 1992 with the Cassini Mission to Saturn. In this case, the sum total of mass and dollars for the science instruments had to fit within the allocated resource envelope. Results from the use of a market-based system show that the entire science payload grew from original estimates by only +1% for cost, and by −7% for mass. The next application was for Space Shuttle Secondary Payloads. In this application, available shuttle lift mass, number of lockers for secondary payloads, and available astronaut time had to be allocated between 5 NASA Users. Experiments showed that a market-based system can reduce the size of the required workforce needed to produce a manifest of the same quality as one produced `by committee.' Finally, a market-based system was experimentally applied to LightSAR science planning, a proposed joint NASA/Commercial RADAR mission. In this application, users were able to produce a conflict-free timeline of events remotely, of high science value, in about half the time required by more traditional methods.
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  • 6
    ISSN: 1432-0630
    Keywords: 74.60 ; 74.70
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract The temperature and magnetic-field dependences of the remanent magnetization have been determined from far-field measurements for thallium ceramic samples. The current flow that gives rise to the observed magnetization is intragranular. The results are consistent with flux-creep-controlled transport with a distance between pinning centers of ∼- 1/2/μm. Using near-field measurements, the superconducting properties are found to be heterogeneous on a scale of ≫ 1 mm. Magnetic domains have been induced by pplying spatial variation in the applied field.
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Journal of materials science 19 (1984), S. 3554-3573 
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract An understanding of the detailed mechanisms which control the migration of grain boundaries through multiphase materials is limited. In this article, the forces which may cause grain-boundary migration (such as those due to recrystallization, grain growth and a redistribution of chemical species) together with effects which oppose this motion (such as solute drag and particle pinning) are reviewed. Theories of grain-boundary migration are presented and, in particular, the influence of grain-boundary structure on these models is discussed. It is shown that experimental studies of grain-boundary migration in bicrystals offer the best opportunity of relating migration mechanisms to the grain-boundary structure. In the light of this an attempt is made to develop an experimental approach by which the interaction of a migrating boundary with a dispersion of particles might be studied.
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Journal of materials science 14 (1979), S. 850-862 
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Cross-linked poly(dienes) (polychloroprene, polyisoprene and polybutadiene) are shown to exhibit crazing when subjected to low strain-rate tensile tests at low temperatures. Conditions for crazing to occur in the polybutadienes are examined. It is found that observable crazing occurs providing the rubbers are (a) slightly oriented, (b) stretched below their glass transition temperature (T g) and (c) deformed in an environment which is close to its liquefaction or sublimation point. Gases evolved after low temperature testing are shown to be dissolved gases from the test environment. The interrelationship between the mechanical properties of the rubbers, quantity of gas absorbed and the radicals formed by scission of the network molecules is explored.
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  • 9
    ISSN: 1573-4889
    Keywords: SCALE FRACTURE ; OXIDE SCALES ; ALUMINA
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The isothermal- and cyclic-oxidation behavior ofthermal barrier coating (TBC) systems consisting ofvacuum plasma-sprayed (VPS) Ni-22Cr-10Al-1Y (wt.%) bondcoatings and air plasma-sprayed (APS)Y2O3-stabilized ZrO2 (YSZ) top coatings (onsingle-crystal superalloys) was investigated. Themicrostructures, flaw contents, and fracture behavior ofthe Al2O3 scales formed duringoxidation testing at 1150°C were characterized (by analysis of coating andscale fracture surfaces and metallographic crosssections). Significant localized fracture and bucklingof the Al2O3 scales that formedalong the bond-coat-top-coat interfaces were observed after cyclic oxidationof TBCs. However, substantial amounts of localized scaledamage did not induce rapid TBC failure. Decohesion ofthe columnar alumina scales on the rough bond-coat surfaces occurred by both internalAl2O3 fracture (parallel to themetal surface) and oxide-metal delamination. There weremicrostructural indications ofAl2O3 scale crack healing bysintering into planar arrays of voids. Alumina scales that formed onconvex NiCrAlY surfaces (with radii of 50 μm or less)often contained significant amounts of internal voids(along grain boundaries) after cyclic oxidation, whereas scales formed by isothermal oxidationcontained few visible voids. Accelerated void growth inAl2O3 scales on the irregularNiCrAlY surfaces appeared to be creep-related and wasattributed to the synergistic effects of geometric and thermalstresses.
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    Journal of materials science 21 (1986), S. 803-809 
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The development of uniaxial orientation by solid-state extrusion at 60 to 90° C has been evaluated for both the amorphous and crystalline components of a polyethylene terephthalate). Analyses involved X-ray diffraction, birefringence and visable dichroism. The dichroism was evalulated from a host dye molecule. The initial PET film for draw was amorphous and isotropic. Orientation functions for the amorphous and the developed crystalline phases are reported at a series of draw ratios up to 4.4.
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