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  • 1
    Electronic Resource
    Electronic Resource
    Effect of Fiber Bridging Stress on the Fracture Resistance of Silicon-Carbide-Fiber/Zircon Composites (2000)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 83 (2000), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The room-temperature fracture-resistance behavior (R-curve) of unidirectional silicon-carbide-fiber-reinforced zircon-matrix composites has been studied experimentally and numerically. The composites showed strong rising R-curve behavior from experimental results that used in situ crack-length measurements taken via optical microscopy as well as the compliance method. A numerical calculation, based on the available models, then was performed to determine the bridging-stress function from the experimental R-curve. In addition, the effect of the residual stress and constituent properties on the bridging-stress function also has been considered in the numerical calculations. These results have indicated that the bridging-stress function, which controls the fracture resistance of ceramic composites, can be obtained from the carefully measured R-curve.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.2000.tb01355.x
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  • 2
    Electronic Resource
    Electronic Resource
    Single and Double Deflections of Cracks at the Carbon-Carbon/BN Coating Interfaces in Ceramic-Matrix Composites (1998)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 81 (1998), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: A finite element technique is used to study the effects of coating properties on the deflection and penetration of cracks which terminate perpendicular to the bimaterial interfaces in SCS6-zircon composites having three coatings (two carbon coatings and one boron nitride) on the fibers. Although, the change in the thickness of coatings has a very small effect on the stress ratio (ratio of hoop stresses along a crack and at the interface) and the energy release rate ratio (ratio of energy release rates for crack penetration and crack deflection), the magnitudes of the stresses and energy release rates change substantially. The finite element results are compared with experimental observations of Kumaria et al. on the nature of crack propagation behavior in these composites. Our finite element results explained the evidence of the doubly deflected cracks at the carbon-carbon interface as experimentally seen by Kumaria et al.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.1998.tb02486.x
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  • 3
    Electronic Resource
    Electronic Resource
    Newtonian Viscosity of Amorphous Silicon Carbonitride at High Temperature (1998)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 81 (1998), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The creep viscosity of chemical-precursor-derived silicon carbonitride (SiCN), which is known to remain predominantly amorphous at temperatures below 1400°C, was measured in the temperature range 1090-1280°C. Experiments were done in uniaxial compression at constant loads in pure nitrogen atmosphere. The creep behavior exhibited three stages. In stage I the strain rate decreased rapidly with time and deformation was accompanied by densification. In stage II the samples exhibited a steady-state creep rate. In stage III, which commenced after long-term deformation, creep gradually declined to rates that were below the sensitivity of our apparatus. The relative density of the specimens during stage II and stage III remained constant at ≅2.3 g/cm3. The shear viscosity in stage II was nearly Newtonian and was measured to be 1.3 × 1013-5.0 1013 Pa·s at 1280°C, which is approximately 103 times the value for fused silica. The creep-hardened as well as uncrept specimens contained silicon nitride crystallites. The volume fraction of these crystals was variable but always less than 5%. Such a small volume fraction of crystals does not explain the dramatic creep-hardening behavior in stage III, even if it is assumed that the crystals formed during creep deformation in stage II.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.1998.tb02489.x
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  • 4
    Electronic Resource
    Electronic Resource
    Amorphous Silicoboron Carbonitride Ceramic with Very High Viscosity at Temperatures above 1500°C (1998)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 81 (1998), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Recently, the viscosity of a predominantly amorphous silicon carbonitride (Si1.7C1.0±0.1N1.5) alloy with an apparent glass-transition temperature (Tg) of 1400°–1500°C was studied. In this study, the creep behavior of silicoboron carbonitride (Si2B1.0C3.4N2.3), which seems to have a Tg value of 〉1700°C, was examined. Both materials exhibited a three-stage creep behavior. In stage I, the creep rate declined, because of densification. In stage II, the strain rate approaches a steady state. In stage III, it resumes a declining strain rate, which ultimately decreased below the measurement limit of the system. At 1550°C in stage II, the viscosity of silicoboron carbonitride was six orders of magnitude higher than that of fused silica. Among the Si-C-N ceramics, only chemical-vapor-deposited and reaction-bonded silicon carbides seem to have greater creep resistance than the silicoboron carbonitrides at temperatures 〉1550°C.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.1998.tb02780.x
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