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  • 1
    Electronic Resource
    Electronic Resource
    Thermal and mechanical induced stresses in superconducting YBa2Cu3Ox coatings on fibers (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 1337-1344 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Thermal stresses induced during cooling from the fabrication temperature of a fiber with a noncubic superconducting ceramic coating are analyzed theoretically. The coating considered has a preferred crystallographic orientation such that the c axis of the coating material is perpendicular to the fiber surface which, in turn, results in different thermal expansion coefficients in the radial and the tangential directions in the coating. The thermal stresses are shown to result both from the mismatch between the fiber and the coating, and from the thermal expansion anisotropy of the coating. Stresses due to bending of the fiber/coating to form a superconducting component are also addressed. A critical radius of curvature of bending is obtained below which segmentation of the coating is predicted.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.349590
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  • 2
    Electronic Resource
    Electronic Resource
    Recent Advances in Whisker-Reinforced Ceramics (1990)
    Palo Alto, Calif. : Annual Reviews
    Annual Review of Materials Research 20 (1990), S. 179-195 
    Details
    ISSN: 0084-6600
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1146/annurev.ms.20.080190.001143
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  • 3
    Electronic Resource
    Electronic Resource
    Mechanical reliability of ceramic windows in high frequency microwave heating devices (1984)
    Springer
    Journal of materials science 19 (1984), S. 3778-3785 
    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 mechanical reliability was evaluated for the specific alumina and beryllia ceramics now used as microwave windows in the high-power (⩾200 kW) high-frequency (⩾60 GHz) gyrotron tubes being developed for plasma heating in fusion systems. Previous analysis of the stresses generated in the various window configurations and tube operating conditions indicated that significant tensile stresses are generated in the ceramic window by dielectric heating. As a result, we characterized both the static fatigue behaviour in the fluorocarbon fluid used to cool gyrotron windows and the inert strength distributions for these two ceramics. These data were then analysed in order to construct reliability diagrams for these two materials. Such diagrams revealed that the use of these specific ceramic materials will be limited by their time to failure at the tensile stresses imposed on them under the gyrotron operating conditions (60 GHz or greater and ⩾200 kW in a continuous wave (CW), TE02 mode (i.e., radial power distribution in beam exhibits two maxima). The fatigue behaviour and inert strengths of both materials could be improved by increasing their density (〉97% of theoretical) and employing a uniform fine (⩽10μm) grain size. Such material improvements would permit significant increases in the mechanical reliability of the gyrotron microwave window.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00552291
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  • 4
    Electronic Resource
    Electronic Resource
    Mechanical reliability of ceramic windows in high frequency microwave heating devices (1984)
    Springer
    Journal of materials science 19 (1984), S. 3767-3777 
    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 temperature and stress distributions generated in ceramic window materials currently employed in microwave gyrotron tubes were determined for a variety of operating conditions. Face-cooled windows of both polycrystalline BeO and polycrystalline Al2O3 were considered. The actual analysis involved three steps. First, a computer program was used to determine the electric field distribution within the window at a given power level and frequency. This program was capable of describing both the radial and axial dependence of the electric field. Second, the field distribution was used to derive an expression for the heat generated per unit volume per unit time within the window due to dielectric losses. A generalized heat conduction computer code was then used to compute the temperature distribution based on the heat generation function. Finally, the stresses were determined from the temperature profiles using a finite-element computer program. Primary emphasis was given to determining the effect of frequency upon the resulting thermal stress distribution. In addition, the effects of increasing window diameter and enhancing heat removal from the windows were considered.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02396950
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  • 5
    Electronic Resource
    Electronic Resource
    Mechanical reliability of ceramic windows in high frequency microwave heating devices (1984)
    Springer
    Journal of materials science 19 (1984), S. 3767-3777 
    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 temperature and stress distributions generated in ceramic window materials currently employed in microwave gyrotron tubes were determined for a variety of operating conditions. Face-cooled windows of both polycrystalline BeO and polycrystalline Al2O3 were considered. The actual analysis involved three steps. First, a computer program was used to determine the electric field distribution within the window at a given power level and frequency. This program was capable of describing both the radial and axial dependence of the electric field. Second, the field distribution was used to derive an expression for the heat generated per unit volume per unit time within the window due to dielectric losses. A generalized heat conduction computer code was then used to compute the temperature distribution based on the heat generation function. Finally, the stresses were determined from the temperature profiles using a finite-element computer program. Primary emphasis was given to determining the effect of frequency upon the resulting thermal stress distribution. In addition, the effects of increasing window diameter and enhancing heat removal from the windows were considered.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00552290
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  • 6
    Electronic Resource
    Electronic Resource
    Mechanical behaviour of MgO-partially stabilized ZrO2 ceramics at elevated temperatures (1987)
    Springer
    Journal of materials science 22 (1987), S. 973-980 
    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 Transformation toughened partially stabilized zirconia ceramics containing magnesia exhibit quite high fracture toughness (K lc ⩾ 8 MPa m1/2) at temperatures of up to 500° C. The observed temperature dependences of the toughness and the fracture strength are consistent with that of the transformation behaviour. The high toughness of these materials results in a significant reduction in the sensitivity of the flexure strength to crack size increases. Exposure of these materials at 1000° C for prolonged periods results in flexure strength changes associated with the generation of the monoclinic phase by tetragonal precipitate destabilization and eutectoid decomposition. However, when exposed at 500° C, neither the phase contents nor the flexure strength are altered for exposures of up to 1000 h.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01103538
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  • 7
    Electronic Resource
    Electronic Resource
    Cyclic fatigue-crack propagation in a silicon carbide whisker-reinforced alumina composite: role of load ratio (1993)
    Springer
    Journal of materials science 28 (1993), S. 3258-3266 
    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 characteristics of subcritical crack growth by cyclic fatigue have been examined in a silicon carbide whisker-reinforced alumina composite, with specific reference to the role of load ratio (ratio of minimum to maximum applied stress intensity, R=K min/K max); results are compared with similar subcritical crack-growth data obtained under constant load conditions (static fatigue). Using compact-tension samples cycled at ambient temperatures, cyclic fatigue-crack growth has been measured over six orders of magnitude from ∼10−11–10−5 m cycle−1 at load ratios ranging from 0.05–0.5. Growth rates (da/dN) display an approximate Paris power-law dependence on the applied stress-intensity range (ΔK), with an exponent varying between 33 and 50. Growth-rate behaviour is found to be strongly dependent upon load ratio; the fatigue threshold, ΔK TH, for example, is found to be increased by over 80% at R=0.05 compared to R=0.5. These results are rationalized in terms of a far greater dependency of growth rates on K max(da/dN ∞ K max 30 ) compared to ΔK(da/dN ∞ ΔK 5), in contrast to fatigue behaviour in metallic materials where generally the reverse is true. Micromechanisms of crack advance underlying such behaviour are discussed in terms of timedependent crack bridging involving either matrix grains or unbroken whiskers.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00354244
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  • 8
    Electronic Resource
    Electronic Resource
    Effect of oxidizing and coal-slag environments upon the time-dependent strength behaviour of a sintered SiC (1986)
    Springer
    Journal of materials science 21 (1986), S. 2678-2684 
    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 time-dependent variations in the high-temperature mechanical properties of a sintered SiC were investigated. The strength of C-ring specimens was determined as a function of temperature and applied stress in oxidizing atmospheres, and the results indicated that both crackblunting and crack-growth processes were operative when modest stress levels were applied. These results were consistent with the concept of a stress-intensity threshold. In the slag environment, localized reactions between the slag and SiC led to the formation of large surface pits which promoted a time-dependent drop in strength.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00551472
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  • 9
    Electronic Resource
    Electronic Resource
    Adaptation of the DCB test for determining fracture toughness of brazed joints in ceramic materials (1987)
    Springer
    Journal of materials science 22 (1987), S. 3297-3303 
    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 We have developed a test, based on a modified applied moment double cantilever beam specimen, to measure the fracture toughness of brazed joints between ceramics and ceramics and metals. Evaluation of samples directly brazed with experimental brazing filler metals showed that the brazed interfaces were generally as tough as the ceramics alone, with toughness increasing proportionally to the toughness of the ceramics. Although the specimen and techniques have so far been used only for direct brazes (no surface pretreatment of the ceramic), we suggest that they would also be valid for joints involving metallization of the ceramics prior to brazing.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01161195
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  • 10
    Electronic Resource
    Electronic Resource
    Mechanical properties of β-Si3N4 whisker reinforced α′-SiAlON ceramics (1995)
    Springer
    Journal of materials science 30 (1995), S. 6023-6027 
    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 effects of β-Si3N4 whisker additions on the mechanical properties of α′-SiAlON ceramics were studied. The room temperature fracture toughness and fracture strength of the composites increased with increasing whisker content, and were 6.5 MPa m1/2 and 900 MPa, respectively, for the addition of 30 vol% whiskers. Although creep resistance of the composites was not enhanced at 1200°C, the whisker additions were observed to be beneficial in reducing the oxidation induced slow crack growth of α′-SiAlON that occurred at 1300 °C, and thereby, improved the creep resistance of the composites at 1300°C.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01151523
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