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    Effect of fatigue-induced microdamage on the compressive properties of bovine trabecular bone

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    Heney, Adric
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    Abstract
    Understanding the effect of microdamage accumulation on the failure mechanisms of bone is important

    for treatment and prevention in degenerative diseases such as osteoporosis. The common sites of fracture

    in osteoporotic patients – arm, vertebra, hip – have large proportions of trabecular bone, which make

    them of particular interest. Degenerative bone diseases disrupt bone’s natural remodeling ability, meaning

    the microdamage which is normally repaired begins to accumulate, increasing a patient’s risk of fracture.

    The current study aims to investigate the effect of microdamage accumulation on subsequent monotonic

    tests-to-failure using cored bovine trabecular bone samples. Various levels of microdamage were induced

    via pre-determined quantities of compressive fatigue loading on cored samples, which were subsequently

    tested in a uniaxial, compressive, test-to-failure. A parabolic relationship was found in the yield strain

    (from the test-to-failure) plotted against the reduction in modulus from fatigue loading, as well as in the

    normalized yield stress (from the test-to-failure) plotted against the reduction in modulus from fatigue

    loading. These results support the hypothesis that increases in yield strain at low quantities of fatigue

    induced damage could be attributed to a microdamage stress relieving mechanism in which small

    microdamage sites nucleate rather than growing larger sites. The results are indicative that a critical

    amount of this proposed mechanism exists, after which point further microdamage accumulation becomes

    detrimental to the mechanical properties obtained in subsequent compressive testing-to-failure. Once this

    critical amount of fatigue-induced damage is induced, a significant decrease in the subsequent yield strain

    is noted representing the growth and coalescence of few, large microdamage sites that become

    responsible for yielding in the test-to-failure.

    X-ray micro-computed tomography was used in an attempt to characterize damage propagation during

    post-yield loading of select trabecular bone samples during monotonic failure testing. Qualitative three

    dimensional imaging suggests that two distinct damage propagation types may exist: the first appearing to

    originate from the centre of trabeculae, while the second appears to originate from trabecular surfaces.
    URI for this record
    http://hdl.handle.net/1974/26684
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    • Department of Mechanical and Materials Engineering Graduate Theses
    • Queen's Graduate Theses and Dissertations
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