Load transfer in bovine plexiform bone determined by synchrotron x-ray diffraction
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M.R. Daymond Department of Mechanical and Materials Engineering, Queen’s University, Kingston, Ontario K7L 3N6, Canada
J.D. Almer X-Ray Operations and Research (XOR), Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois 60439
P.M. Mummery School of Materials, The University of Manchester, Manchester M1 7HS, United Kingdom (Received 25 June 2007; accepted 15 November 2007)
High-energy synchrotron x-ray diffraction (XRD) has been used to quantify load transfer in bovine plexiform bone. By using both wide-angle and small-angle XRD, strains in the mineral as well as the collagen phase of bone were measured as a function of applied compressive stress. We suggest that a greater proportion of the load is borne by the more mineralized woven bone than the lamellar bone as the applied stress increases. With a further increase in stress, load is shed back to the lamellar regions until macroscopic failure occurs. The reported data fit well with reported mechanisms of microdamage accumulation in bovine plexiform bone.
I. INTRODUCTION
Laminar or plexiform bone is a type of bone characteristic of quickly growing large animals such as cows and is composed of two distinct bone regions: woven or parallel-fibred bone, which can be formed rapidly and has a disorganized collagen fibril arrangement, and lamellar bone, which is formed at a much slower rate but with mineralized collagen fibrils that are highly organized and are arranged in lamellae (sheets). In bovine plexiform bone, laminae that are around 200 m thick surround a network of blood vessels, and on either side of the laminae, layers of woven or parallelfibred bone are found.1 Hence, the bone is composed of two distinct phases that have very different collagen/mineral organizations and are separated on a submillimeter length scale. The woven bone is more mineralized,2 and at high loads (close to the yield strength of bone) its failure has been associated with microcracking.1 More recently, microdamage accumulation and failure under loads much lower than the yield has been associated with lamellar bone.3 Such studies show that the overall micromechanical response of plexiform bone is affected by the differing responses of both the woven and lamellar regions. a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2008.0068 J. Mater. Res., Vol. 23, No. 2, Feb 2008
The aforementioned studies on bovine plexiform bone describe the manner in which microcracking can occur in both woven and lamellar bone, but there have been no studies on load partitioning or transfer during deformation. In this investigation, we sought to further enhance understanding of damage accumulation and failure of plexiform bone by using high-energy synchrotron x-ray diffraction (XRD) to determine the evolution of strains in both the mineral and collagen phases under in situ compression. By using wide-angle x-ray scattering (WAXS) as well as small-angle x-ray scattering (SAXS) XRD, strains in mineral and collagen could be investigated, res
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