Research Papers

Wedge Indentation Fracture of Cortical Bone: Experimental Data and Predictions

[+] Author and Article Information
Saeid Kasiri1

Trinity Centre for Bioengineering, Trinity College Dublin, Dublin 2, Dublin, Irelandkasirigs@tcd.ie

Ger Reilly

Biomedical Devices and Assistive Technologies Research Group, Dublin Institute of Technology, Dublin 1, Ireland

David Taylor

Trinity Centre for Bioengineering, Trinity College Dublin, Dublin 2, Dublin, Ireland


Corresponding author.

J Biomech Eng 132(8), 081009 (Jun 28, 2010) (6 pages) doi:10.1115/1.4001883 History: Received September 09, 2009; Revised May 04, 2010; Posted May 27, 2010; Published June 28, 2010; Online June 28, 2010

The fracture of bone due to indentation with a hard, sharp object is of significance in surgical procedures and certain trauma situations. In the study described below, the fracture of bovine bone under indentation was measured experimentally and predicted using the theory of critical distances (TCDs), a theory, which predicts failure due to cracking in the vicinity of stress concentrations. The estimated indentation fracture force was compared with the experimental results in three different cutting directions. Under indentation, the material experiences high levels of compression and shear, causing cracks to form and grow. The direction of crack growth was highly dependent on the bone’s microstructure: major cracks grew in the weakest possible structural direction. Using a single value of the critical distance (L=320μm), combined with a multiaxial failure criterion, it was possible to predict the experimental failure loads with less than 30% errors. Some differences are expected between the behavior of human bone and the bovine bone studied here, owing to its plexiform microstructure.

Copyright © 2010 by American Society of Mechanical Engineers
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Figure 1

Principle of the PM. If the stress at a distance L/2 from the notch root reaches a critical value, failure will occur by crack propagation.

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Figure 2

Different indentation directions used in the testing program: longitudinal (C-L), transverse (L-R) and tangential (R-C). The codes are according to the ASTM-E399. For example R-C means the direction perpendicular to the radial axis and in parallel with the circumferential axis.

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Figure 3

Experimental force-indentation results for longitudinal indentation using the 20 deg-300 μm blade

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Figure 4

Sample after testing to failure, stained to reveal cracking. Cracks in the longitudinal direction start from the boundary of contact, and then they merge and propagate in the longitudinal direction. Some permanent, inelastic deformation caused by the indenter can be seen at the surface.

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Figure 5

Results of the FE model of longitudinal indentation with the 20 deg-700 μm blade: shear stress at the fracture force. Half the geometry was modeled due to symmetric conditions. The fracture line is shown, starting from the contact boundary and oriented in the longitudinal direction.

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Figure 6

The experimental and predicted fracture forces for different indenters in various directions. The horizontal axis presents the different wedge angles in three different indentation directions.

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Figure 7

Crack propagation in tangential indentation direction for sharp blade with the wedge angle of 20 deg

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Figure 8

Cracking patterns revealed by staining after indentation in the transverse direction; evidence of multiple cracks running in the longitudinal direction: a piece of bone has spalled off the surface (top right)

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Figure 9

The force-indentation behavior in transverse indentation for 20 deg-50 μm blade. Force passes through a series of maxima and minima (1 cycle shown here). The figure also shows the finite element model verification with the experimental data.



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