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Full-field Strain Measurement During Mechanical Testing of the Human Femur at Physiologically Relevant Strain Rates

Grassi, Lorenzo LU ; Väänänen, Sami P; Amin Yavari, Saber; Jurvelin, Jukka S; Weinans, Harrie; Ristinmaa, Matti LU ; Zadpoor, Amir A and Isaksson, Hanna LU (2014) In Journal of Biomechanical Engineering 136(11).
Abstract
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. 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... (More)
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. 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 represents a comprehensive collection of full-field strains, both at physiological load levels and up to fracture. About 10000 measurements were collected for each bone, providing superior spatial resolution compared to ~15 measurements typically collected using strain gauges. These experimental data collection can be further used for validation of numerical models, and for experimental verification of bone constitutive laws and fracture criteria. (Less)
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author
organization
publishing date
type
Contribution to journal
publication status
published
subject
keywords
Proximal femur fracture, Biomechanics, Digital Image Correlation, ex vivo destructive test
in
Journal of Biomechanical Engineering
volume
136
issue
11
publisher
American Society Of Mechanical Engineers (ASME)
external identifiers
  • wos:000342750600011
  • scopus:84907615407
ISSN
0148-0731
DOI
10.1115/1.4028415
language
English
LU publication?
yes
id
d30c7350-67b5-4d90-a012-a5c517484660 (old id 4611757)
date added to LUP
2014-09-04 08:45:09
date last changed
2017-07-30 04:13:19
@article{d30c7350-67b5-4d90-a012-a5c517484660,
  abstract     = {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. 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 represents a comprehensive collection of full-field strains, both at physiological load levels and up to fracture. About 10000 measurements were collected for each bone, providing superior spatial resolution compared to ~15 measurements typically collected using strain gauges. These experimental data collection can be further used for validation of numerical models, and for experimental verification of bone constitutive laws and fracture criteria.},
  articleno    = {111010},
  author       = {Grassi, Lorenzo and Väänänen, Sami P and Amin Yavari, Saber and Jurvelin, Jukka S and Weinans, Harrie and Ristinmaa, Matti and Zadpoor, Amir A and Isaksson, Hanna},
  issn         = {0148-0731},
  keyword      = {Proximal femur fracture,Biomechanics,Digital Image Correlation,ex vivo destructive test},
  language     = {eng},
  number       = {11},
  publisher    = {American Society Of Mechanical Engineers (ASME)},
  series       = {Journal of Biomechanical Engineering},
  title        = {Full-field Strain Measurement During Mechanical Testing of the Human Femur at Physiologically Relevant Strain Rates},
  url          = {http://dx.doi.org/10.1115/1.4028415},
  volume       = {136},
  year         = {2014},
}