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    SUBCRITICAL CRACK GROWTH UNDER MODE I, II, AND III LOADING FOR COCONINO SANDSTONE

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    Author
    Ko, Tae Young
    Issue Date
    2008
    Keywords
    Coconino sandstone
    Constant stress-rate test
    Mode I
    Mode II
    Mode III
    Subcritical crack growth
    Advisor
    Kemeny, John
    Committee Chair
    Kemeny, John
    
    Metadata
    Show full item record
    Publisher
    The University of Arizona.
    Rights
    Copyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.
    Abstract
    In systems subjected to long-term loading, subcritical crack growth is the principal mechanism causing the time-dependent deformation and failure of rocks. Subcritical crack growth is environmentally-assisted crack growth, which can allow cracks to grow over a long period of time at stresses far smaller than their failure strength and at tectonic strain rates. The characteristics of subcritical crack growth can be described by a relationship between the stress intensity factor and the crack velocity. This study presents the results of studies conducted to validate the constant stress-rate test for determining subcritical crack growth parameters in Coconino sandstone, compared with the conventional testing method, the double torsion test. The results of the constant stress-rate test are in good agreement with the results of double torsion test. More importantly, the stress-rate tests can determine the parameter A with a much smaller standard deviation than the double torsion test. Thus the constant stress-rate test seems to be both a valid and preferred test method for determining the subcritical crack growth parameters in rocks. We investigated statistical aspects of the constant stress-rate test. The effects of the number of tests conducted on the subcritical crack growth parameters were examined and minimum specimen numbers were determined. The mean and standard deviation of the subcritical crack growth parameters were obtained by randomly selecting subsets from the original strength data. In addition, the distribution form of the subcritical crack growth parameters and the relation between the parameter n and A were determined. We extended the constant stress-rate test technique to modes II and III subcritical crack growth in rocks. The experimental results of the modes I, II and III tests show that the values of the subcritical crack growth parameters are similar to each other. The subcritical crack growth parameter n value for Coconino sandstone has the range of 34 to 38 and the parameter A has the range of 1.02x10⁻² to 6.52x10⁻² m/s. The effect of confining stress, specimen size, and water saturation on subcritical crack growth under mode II loading has also been investigated. Finally strength parameters for Coconino sandstone were determined experimentally, including tensile strength, uniaxial compressive strength, cohesion, internal friction angle, in-plane / our-of-plane shear strength and the fracture toughness under mode I, II, and III loading.
    Type
    text
    Electronic Dissertation
    Degree Name
    Ph.D.
    Degree Level
    doctoral
    Degree Program
    Mining Geological & Geophysical Engineering
    Graduate College
    Degree Grantor
    University of Arizona
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