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  • 1
    Electronic Resource
    Electronic Resource
    Microvelocity sensor for instantaneous velocity determination (1989)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 60 (1989), S. 3692-3697 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A new microvelocity sensor unit was developed to measure the instantaneous velocity of a high velocity impactor during the penetration process. The concept of this device is based on the induced current generated in a coil due to the passage of a magnet. A special digital circuit was designed to yield a spatial resolution of better than 0.05 in. by eliminating the problem of signal overlap. The precise time delays obtained from these signals can be used to determine the slowing down or energy loss of a high-velocity projectile. The details of this sensor unit will be described and its resolution will be demonstrated. A light gas gun was used to propel aluminum projectiles to velocities up to 320 m/s. Energy loss of these high-velocity projectiles in composites reinforced with polyethylene, polyester, and graphite fabrics as well as pure Kevlar fabric was measured using this system. Results show that this microvelocity sensor is capable of identifying various energy-loss processes during the impact of high-velocity projectiles.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1140476
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  • 2
    Electronic Resource
    Electronic Resource
    Anomalous electrical and optical properties of polymeric carbons (1995)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 66 (1995), S. 1951-1953 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Semiconducting polymeric carbons were prepared by pyrolyzing phenol formaldehyde resin in a nitrogen atmosphere between 500 to 800 °C for 0.5 to 48 h. Their logarithmic resistivity values were found to vary linearly with the temperature in the range of 20 to 200 °C. Properties such as switching, radiative recombination, and Mott's minimum metallic conductivity were observed in these materials. These three characteristics, which are common with the inorganic amorphous semiconductors, suggest that these polymeric carbons can be included in the class of materials which satisfy the Ioffe–Regel condition, kL≈1 (where k is the electron wave vector and L is the mean-free path). The switching and the radiative recombination phenomena observed in these materials provide experimental proof for the double injection model proposed by N. F. Mott [Adv. Phys. 16, 4 (1967)] for describing conduction processes in amorphous chalcogenide semiconductors. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.113287
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  • 3
    Electronic Resource
    Electronic Resource
    The oxidation behaviour of low-temperature heat-treated carbon fibres (1997)
    Springer
    Journal of materials science 32 (1997), S. 2811-2819 
    Details
    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 oxidation behaviour of partially carbonized polyacrylonitrile fibres was studied primarily by both dynamic and isothermal thermogravimetric analysis. These fibres, referred to as quasi-carbon fibres (QCFs), were obtained by pyrolysis of a polyacrylonitrile precursor at a heat-treatment temperature (HTT) ranging from 400–950°C. Results indicated that QC fibres exhibited increased thermal stability with increasing HTT. The oxidation behaviour was strongly related to the microstructure of QC fibres. An empirical model was developed to simulate the real oxidation process. Two different oxidation mechanisms were operational in QC fibres; one with a more moderate oxidation rate and the other with an auto-acceleration effect. Only the QC fibres that were heat treated above 650°C to develop an extended two-dimensional graphite-like structure, exhibited an auto-acceleration effect.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1018612214572
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  • 4
    Electronic Resource
    Electronic Resource
    Electrical conduction in thermoplastic elastomer matrix composites containing catalytic chemical vapour deposited carbon whisker (1995)
    Springer
    Journal of materials science 30 (1995), S. 4879-4883 
    Details
    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 Electrical conduction in carbon whisker/thermoplastic elastomer (TPE) composites was found to be a thermally activated process. The carbon whiskers used were obtained by a catalytic chemical vapour deposition (CCVD) technique conducted at 500 °C and the TPE was a styrene-ethylene butylene-styrene (S-EB-S) block copolymer. The resistivity, (ϱ), versus 1/T curves of the composites exhibited two regions with distinct slopes with an inflection at the glass transition temperature,T g, of the elastomer, EB; Region I 〈T g and II 〉T g. The thermally activated conduction mechanism of these composites is explained on the basis of electron transport in low-mobility solids with a large number of trap sites, Intra- and intermolecular motion of the polymer chains can result in the electron transport from such trap sites and were correlated to the observed activation energies. Intramolecular motion in region I, was related to the thermally assisted hopping with the activation energy, ΔE A, of 0.067 and 0.030 eV for 33% and 52% whisker volume fraction composites, respectively. Similarly, ΔE A due to the intermolecular segmental chain motions in region II for 33% and 52% whisker volume fraction composites was related to the equilibrium rate of trapping-detrapping of electrons from 0.240 and 0.138 eV deep traps.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01154498
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  • 5
    Electronic Resource
    Electronic Resource
    Switching behaviours in semiconducting carbon fibres (1996)
    Springer
    Journal of materials science 15 (1996), S. 99-101 
    Details
    ISSN: 1573-4811
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00291437
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  • 6
    Electronic Resource
    Electronic Resource
    Microstructure origin of strength and toughness of 2-d C/C composites (1997)
    Springer
    Journal of materials science 16 (1997), S. 1319-1322 
    Details
    ISSN: 1573-4811
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Abstracts are not published in this journal
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1018503714726
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  • 7
    Electronic Resource
    Electronic Resource
    Controlled energy dissipation in fibrous composites. II: Microscopic failure mechanisms (1991)
    Brookfield, Conn. : Wiley-Blackwell
    Polymer Composites 12 (1991), S. 57-65 
    Details
    ISSN: 0272-8397
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Mechanical properties and microscopic fracture mechanisms of continuous fiber reinforced polymer composites were investigated. Perforated polyimide films (e.g. Kapton®) were added between composite prepreg layers to modify the interlaminar bonding strength. Addition of highly perforated films can increase the toughness of unidirectional glass/epoxy composites without an appreciable reduction in strength. The fibrous composites studied exhibit two fracture modes (compressive and tensile) when failed by three-point bending. In general, the compressive failure mode preceded the tensile failure mode. Real-time acoustic emission (AE) analysis was found to provide more fracture information which is otherwise not discernible from mechanical testing alone. The crack initiation stress level and the subsequent crack propagation mode were identified by real-time AE during deformation and by post-failure scanning electron microscopy fracture surface analysis.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pc.750120109
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  • 8
    Electronic Resource
    Electronic Resource
    Properties and processing characteristics of dielectric-filled epoxy resins (1989)
    Brookfield, Conn. : Wiley-Blackwell
    Polymer Composites 10 (1989), S. 205-214 
    Details
    ISSN: 0272-8397
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: A family of casting composites, epoxy resins with mineral fillers, having a range of electrical properties, are being developed. In such composites, the dielectric constant is controlled primarily by varying the filler material in composition and proportions. The present work reports on the mechanical properties of composites made with two types of filler, an alumina powder (XA3500 from ALCOA) and a BaTiO3/TiO2 ceramic powder (ATD-50 from Ampex). Dependence of mechanical properties on curing agents was also determined. Filler contents from 0 to 40 percent volume were used. Epoxy systems contained single epoxy resin with both amine and anhydride hardeners. Processing of the anhydride-cured systems was easier than that of the amine-based systems because of their lower viscosity and longer gel time of the former. However, the anhydride-cured systems required higher processing temperatures. Curing kinetics and molecular bonding were investigated using a combination of differential scanning calorimetry, dynamic mechanical thermal analysis, and scanning electron microscopy. Activation energies of 11.2 kcal/mole and 12.1 kcal/mole were obtained for the curing of the amine-based and the anhydride-based composites respectively, and a small difference in the glass transition temperature was also observed. These effects can be attributed to the difference in the structure of the curing agents. The epoxy resin cured with NMA is less ductile compared with those cured with MTHPA or MHHPA due to slight chemical modification on the ring structures. This dependence of ductility on curing agent was observed in specimens with different filler contents. Although the presence of the filler materials was found to enhance the mechanical properties of the epoxy, the fracture mode in these materials is still brittle.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pc.750100402
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  • 9
    Electronic Resource
    Electronic Resource
    Simultaneous interpenetrating networks for tough matrix composites (1994)
    Brookfield, Conn. : Wiley-Blackwell
    Polymer Composites 15 (1994), S. 479-487 
    Details
    ISSN: 0272-8397
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Graphite fiber reinforced epoxy composites normally exhibit low impact strength, poor delamination resistance, and low damage tolerance. Because delamination is a matrix-dominated failure mode, tougher matrix resins may be utilized to reduce or eliminate the adverse effects of delamination on the structural integrity of fiber composites. The effects of modifying epoxy network morphology by introducing polyurethane in the form of an interpentrating network were studied. The compatibility, toughness, and tensile properties of the matrix as well as the properties of the resultant laminates were evaluated. One of the conclusions arising was that the interpenetrating network morphology results in superior resin and composites toughness with increasing polyurethane content. However, the benefits of increased resin toughness did not necessarily translate into proportionally increased composite owing to the geomertical limitations placed on the plastic deformation zones in laminates.
    Additional Material: 15 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pc.750150613
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  • 10
    Electronic Resource
    Electronic Resource
    Mechanical properties of carbon fiber reinforced polyester/urethane hybrid network compositesBased in part on the MS thesis of J. L. Yu. (1994)
    Brookfield, Conn. : Wiley-Blackwell
    Polymer Composites 15 (1994), S. 488-495 
    Details
    ISSN: 0272-8397
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Hybrid resins of unsaturated polyester/urethane were synthesized and characterized. Both the toughness and stiffness of the polyester were improved significantly by incorporating 20 wt% urethane. Unsaturated polyester, styrene, and ethane showed good compatibility during blending and probably formed a simultaneous interpenetrating network (IPN) during polymerization. The resultant IPN morphology possessed a unique glass transition temperature. This IPN morphology not only imparted great fracture resistance to the otherwise brittle polyester, but also changed the fracture mode of new resin composites. The molecular weight of unsaturated polyesters did not have significant effect on the mechanical properties, but did exert an apparent influence on the fracture mode. During the cure process the side reaction, an amine reaction, could be suppressed addition of suitable promoter and catalyst.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pc.750150614
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