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TECHNICAL PAPERS: Bone/Orthopedics

The Effect of Damage on the Viscoelastic Behavior of Human Vertebral Trabecular Bone

[+] Author and Article Information
Todd L. Bredbenner1

Mechanical and Aerospace Engineering, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, OH 44106-7222todd.bredbenner@swri.org

Dwight T. Davy

Mechanical and Aerospace Engineering, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, OH 44106-7222

1

Corresponding author. Current address Reliability and Materials Integrity Section, Southwest Research Institute, PO Box 28510, San Antonio, TX 78228-0510.

J Biomech Eng 128(4), 473-480 (Jan 14, 2006) (8 pages) doi:10.1115/1.2205370 History: Received January 26, 2004; Revised January 14, 2006

The present study examines the viscoelastic behavior of cancellous bone at low strains and the effects of damage on this viscoelastic behavior. It provides experimental evidence of interaction between stress relaxation behavior and the effect of accumulated damage. The results suggest that damage is at least orthotropic in trabecular bone specimens under uniaxial loading. Simple linear models of viscoelasticity described the time-dependent stress-strain behavior at low strains before and after specimen damage, although better fits of these models were obtained prior to damage. Modeling the observed changes in relaxation times with damage accumulation appears necessary to successfully predict the post-damage viscoelastic response.

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Copyright © 2006 by American Society of Mechanical Engineers
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Figures

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Figure 1

Relative positioning of transverse extensometers. The transverse extensometers are pictured, showing extension arms with pairs of opposed contacts in orthogonal transverse directions.

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Figure 2

Specimen in experimental testing fixture. Three extensometers and axial load cell are pictured, along with a mock specimen, in the experimental testing setup.

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Figure 3

Experimental loading protocol. The loading protocol consists of tensile loading pulses with 60sec hold periods followed by zero-strain recovery periods of 180sec. Diagnostic pulses at low strain amplitudes were used to evaluate material properties without alteration of the specimen and the damaging pulse amplitude was chosen to damage the specimen in a controlled manner. (Figure is not to scale.)

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Figure 4

One-dimensional representations of generalized Maxwell bodies. Simple linear models of viscoelastic solids were described by three parameters (left) or five parameters (right) describing the stiffness and damping characteristics of the model.

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Figure 5

Predicted and experimental stress response for undamaged specimen. The pre-damage stress response (diagnostic pulse 1) for a typical specimen (SI-05) is shown. Plots of the stress response predictions using three or five viscoelastic parameters are indistinguishable from each other. For clarity, only the three-parameter prediction is shown here.

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Figure 6

Predicted and experimental stress response for damaged specimen. The post-damage stress response (diagnostic pulse 2) for a typical specimen (SI-05) is shown. Plots of the stress response predictions using three or five viscoelastic parameters are indistinguishable from each other. For clarity, only the three-parameter post-damage prediction is shown here.

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