Understanding the mechanical properties of human femora is of great importance for the development of a reliable fracture criterion aimed at assessing fracture risk. Earlier ex vivo studies have been conducted by measuring strains on a limited set of locations using strain gauges (SGs). Digital image correlation (DIC) could instead be used to reconstruct the full-field strain pattern over the surface of the femur. The objective of this study was to measure the full-field strain response of cadaver femora tested at a physiological strain rate up to fracture in a configuration resembling single stance. The three cadaver femora were cleaned from soft tissues, and a white background paint was applied with a random black speckle pattern over the anterior surface. The mechanical tests were conducted up to fracture at a constant displacement rate of 15 mm/s, and two cameras recorded the event at 3000 frames per second. DIC was performed to retrieve the full-field displacement map, from which strains were derived. A low-pass filter was applied over the measured displacements before the crack opened in order to reduce the noise level. The noise levels were assessed using a dedicated control plate. Conversely, no filtering was applied at the frames close to fracture to get the maximum resolution. The specimens showed a linear behavior of the principal strains with respect to the applied force up to fracture. The strain rate was comparable to the values available in literature from in vivo measurements during daily activities. The cracks opened and fully propagated in less than 1 ms, and small regions with high values of the major principal strains could be spotted just a few frames before the crack opened. This corroborates the hypothesis of a strain-driven fracture mechanism in human bone. The data represent a comprehensive collection of full-field strains, both at physiological load levels and up to fracture. About 10,000 points were tracked on each bone, providing superior spatial resolution compared to ∼15 measurements typically collected using SGs. These experimental data collection can be further used for validation of numerical models, and for experimental verification of bone constitutive laws and fracture criteria.
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November 2014
Research-Article
Full-Field Strain Measurement During Mechanical Testing of the Human Femur at Physiologically Relevant Strain Rates
Lorenzo Grassi,
Lorenzo Grassi
Division of Solid Mechanics,
Lund University
,Lund 22363
, Sweden
Department of Biomedical Engineering,
e-mail: lorenzo.grassi@bme.lth.se
Lund University
,BMC D13, Sölvegatan 19
,Lund 22184
, Sweden
e-mail: lorenzo.grassi@bme.lth.se
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Sami P. Väänänen,
Sami P. Väänänen
Department of Applied Physics,
University of Eastern Finland
,Kuopio 70211
, Finland
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Saber Amin Yavari,
Saber Amin Yavari
Faculty of Mechanical, Maritime, and
Materials Engineering,
Materials Engineering,
Delft University of Technology
,Delft 2628 CD
, The Netherlands
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Jukka S. Jurvelin,
Jukka S. Jurvelin
Department of Applied Physics,
University of Eastern Finland
,Kuopio 70211
, Finland
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Harrie Weinans,
Harrie Weinans
Faculty of Mechanical, Maritime, and
Materials Engineering,
Materials Engineering,
Delft University of Technology
,Delft 2628 CD
, The Netherlands
Department of Orthopaedics,
UMC Utrecht 3508 GA
, The Netherlands
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Matti Ristinmaa,
Matti Ristinmaa
Division of Solid Mechanics,
Lund University
,Lund 22363
, Sweden
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Amir A. Zadpoor,
Amir A. Zadpoor
Faculty of Mechanical, Maritime, and
Materials Engineering,
Materials Engineering,
Delft University of Technology
,Delft 2628 CD
, The Netherlands
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Hanna Isaksson
Hanna Isaksson
Division of Solid Mechanics,
Lund University
,Lund 22363
, Sweden
Department of Biomedical Engineering,
Lund University
,Lund 22184
, Sweden
Department of Orthopaedics,
Lund University
,Lund 22184
, Sweden
Search for other works by this author on:
Lorenzo Grassi
Division of Solid Mechanics,
Lund University
,Lund 22363
, Sweden
Department of Biomedical Engineering,
e-mail: lorenzo.grassi@bme.lth.se
Lund University
,BMC D13, Sölvegatan 19
,Lund 22184
, Sweden
e-mail: lorenzo.grassi@bme.lth.se
Sami P. Väänänen
Department of Applied Physics,
University of Eastern Finland
,Kuopio 70211
, Finland
Saber Amin Yavari
Faculty of Mechanical, Maritime, and
Materials Engineering,
Materials Engineering,
Delft University of Technology
,Delft 2628 CD
, The Netherlands
Jukka S. Jurvelin
Department of Applied Physics,
University of Eastern Finland
,Kuopio 70211
, Finland
Harrie Weinans
Faculty of Mechanical, Maritime, and
Materials Engineering,
Materials Engineering,
Delft University of Technology
,Delft 2628 CD
, The Netherlands
Department of Orthopaedics,
UMC Utrecht 3508 GA
, The Netherlands
Matti Ristinmaa
Division of Solid Mechanics,
Lund University
,Lund 22363
, Sweden
Amir A. Zadpoor
Faculty of Mechanical, Maritime, and
Materials Engineering,
Materials Engineering,
Delft University of Technology
,Delft 2628 CD
, The Netherlands
Hanna Isaksson
Division of Solid Mechanics,
Lund University
,Lund 22363
, Sweden
Department of Biomedical Engineering,
Lund University
,Lund 22184
, Sweden
Department of Orthopaedics,
Lund University
,Lund 22184
, Sweden
Manuscript received May 8, 2014; final manuscript received August 13, 2014; accepted manuscript posted August 27, 2014; published online September 17, 2014. Assoc. Editor: David Corr.
J Biomech Eng. Nov 2014, 136(11): 111010 (8 pages)
Published Online: September 17, 2014
Article history
Received:
May 8, 2014
Revision Received:
August 13, 2014
Accepted:
August 27, 2014
Citation
Grassi, L., Väänänen, S. P., Amin Yavari, S., Jurvelin, J. S., Weinans, H., Ristinmaa, M., Zadpoor, A. A., and Isaksson, H. (September 17, 2014). "Full-Field Strain Measurement During Mechanical Testing of the Human Femur at Physiologically Relevant Strain Rates." ASME. J Biomech Eng. November 2014; 136(11): 111010. https://doi.org/10.1115/1.4028415
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