Browsing by Author "Currey, John D."

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    Mechanical properties of nacre and highly mineralized bone
    (Royal Society, 2001-01-07) Currey, John D.; Zioupos, Peter; Peter, Davies; Casinos, Adrià
    We compared the mechanical properties of ‘ordinary’ bovine bone, the highly mineralized bone of the rostrum of the whale Mesoplodon densirostris, and mother of pearl (nacre) of the pearl oyster Pinctada margaritifera. The rostrum and the nacre are similar in having very little organic material. However, the rostral bone is much weaker and more brittle than nacre, which in these properties is close to ordinary bone. The ability of nacre to outperform rostral bone is the result of its extremely well–ordered microstructure, with organic material forming a nearly continuous jacket round all the tiny aragonite plates, a design well adapted to produce toughness. In contrast, in the rostrum the organic material, mainly collagen, is poorly organized and discontinuous, allowing the mineral to join up to form, in effect, a brittle stony material.
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    Notch sensitivity of mammalian mineralized tissues in impact
    (The Royal Society, 2004-03-07) Currey, John D.; Brear, Kevin; Zioupos, Peter
    The toughness of bone is an important feature in preventing it from fracturing. We consider the notch sensitivity in impact, and the associations between brittleness, notch sensitivity and post–yield energy absorption of mammalian mineralized tissues. Specimens of bone–like tissues covering a wide range of mineralization were broken, either notched or un–notched, in impact. The greater the mineral content, the greater was the notch sensitivity. Also, the more brittle tissues dissipated the least post–yield energy and were the most notch sensitive. It is suggested that since antler bone, the least mineralized of all known mammalian mineralized tissues, seems to be notch insensitive in impact, no adaptive purpose would be served by having mineralized tissues of a lower mineralization than antler. This may explain the lower cut–off in mineralization seen in mammals
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    Strain patterns during tensile, compressive, and shear fatigue of human cortical bone and implications for bone biomechanics
    (Wiley, 2006-09-22) Winwood, K.; Zioupos, Peter; Currey, John D.; Cotton, J. R.; Taylor, M.
    It is a common theme in basic bone biomechanics and in biomechanical applications that much of the behavior can be determined and is dictated by the level of strain, whether this pertains to bone physiology, bone remodeling, osseoinduction, osseointegration, or the development of damage. The development of damage, demonstrated by stiffness loss measurements, has already been reported in detail in the literature. However, the systematic study of the development of “plastic” (residual) strains, which are associated with the inelastic mechanical behavior of bone tissue, has generally been overlooked. The present study compares the rates at which the elastic (ea) and plastic components (ep) of strain developed during tensile, compressive, and shear fatigue in human cortical bone of six individuals aged between 53 and 79 years. The overall hypothesis of this investigation is that there is a common underlying factor in the damage‐related behavior of bone, which may allow us to link together the various aspects of the damage related behavior of bone. The rate of development of plastic strain (Δep/ΔN) and the rate of growth in elastic strain amplitude (Δea/ΔN) are described as a function of the stress (σ), and/or stress normalized by the modulus of elasticity (σ/E). The implications of our findings are discussed with respect to simple models/mechanisms, which may underlie the observed behavior. © 2006 Wiley Periodicals, Inc. J Biomed Mater Res, 2006
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    Strain rate dependence of work of fracture tests on bone and similar tissues: reflections on testing methods and mineral content effects
    (Elsevier, 2019-08-22) Currey, John D.; Brear, Kevin; Zioupos, Peter
    This paper is concerned with the effect of different strain rate on the Work of Fracture (Wf) of various vertebrate mineralised tissues, controlling for the effect of mineral content and Young's modulus of elasticity. Using specimens of uniform shape and size values for the Work of Fracture of specimens tested at various deformation rates, and also the energy absorbed by notched specimens in impact, are reported. The results indicated that, of those tested, for most bone specimens the Work of Fracture measurements were constant like in the case for a ‘material property’. Variations due to loading conditions (deformation rate) were small, with the exemption of antler, which is relatively poorly mineralised and in which the Work of Fracture values increased by a factor of 4 across the range from quasistatic loading to impact. The Tattersall and Tappin (1966) test has shown itself to offer some great advantages: if the quest is for a fracture toughness test for an unknown tissue it offers reliability, it is perhaps more forgiving to handling errors, it also suffers less of the influence of strain rate effects and uses relatively simple instrumentation. It is also able to demonstrate the remarkable toughness of antler bone which other more commonly used fracture toughness methods cannot do.