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Mechanistic Aspects of Fracture of Human Cortical Bone

Published online by Cambridge University Press:  17 March 2011

Ravi K. Nalla ,
Jamie J. Kruzic ,
John H. Kinney  and
R. O. Ritchie
Ravi K. Nalla
Affiliation:
Materials Sciences Division, Lawrence Berkeley National Laboratory, and Materials Science & Engineering Department, University of California, Berkeley, CA 94720
Jamie J. Kruzic
Affiliation:
Materials Sciences Division, Lawrence Berkeley National Laboratory, and Materials Science & Engineering Department, University of California, Berkeley, CA 94720
John H. Kinney
Affiliation:
Lawrence Livermore Nat. Laboratory, andUniversity of California, San Francisco, CA 94143
R. O. Ritchie
Affiliation:
Materials Sciences Division, Lawrence Berkeley National Laboratory, and Materials Science & Engineering Department, University of California, Berkeley, CA 94720
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Abstract

There has been growing interest of late in the fracture properties of human bone. As understanding such properties in the context of the hierarchical microstructure of bone is of obvious importance, this study addresses the evolution of the in vitro fracture toughness with crack extension (Resistance-curve behavior) in terms of the salient mechanisms involved. Fracture-mechanics based measurements were performed on compact-tension specimens hydrated in Hanks' Balanced Salt Solution using cortical bone from mid-diaphyses of 34-41 year-old human humeri. Post-test observations of the crack path were made by optical microscopy and three-dimensional X-ray computed tomography. The fracture toughness was found to rise linearly with crack extension with a mean crack-initiation toughness of Ko ∼ 2.0 MPa√m for crack growth in the proximal-distal direction. The increasing cracking resistance had its origins in several toughening mechanisms, most notably crack bridging by uncracked ligaments. Uncracked-ligament bridging, which was observed by tomography in the wake of the crack, was identified as the dominant toughening mechanism responsible for the observed Rcurve behavior through compliance-based experiments. The extent and nature of the bridging zone was examined quantitatively using multi-cutting compliance experiments in order to assess the bridging stress distribution. The results obtained in this study provide an improved understanding of the mechanisms associated with the failure of cortical bone, and as such are of importance from the perspective of developing a realistic framework for fracture risk assessment, and for determining how the increasing propensity for fracture with age can be prevented.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 823: Symposium W – Biological and Bioinspired Materials and Devices , 2004 , W8.2
Copyright
Copyright © Materials Research Society 2004

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