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TECHNICAL PAPERS

Fatigue Microdamage in Bovine Trabecular Bone

[+] Author and Article Information
Tara L. A. Moore

Harvard-MIT Division of Health Sciences and Technology, Massachusetts Institute of Technology, Cambridge, MA 02139Orthopedic Biomechanics Lab, Beth Israel Deaconess Medical Center, Boston, MA 02215

Lorna J. Gibson

Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139

J Biomech Eng 125(6), 769-776 (Jan 09, 2004) (8 pages) doi:10.1115/1.1631584 History: Received June 07, 2002; Revised July 02, 2003; Online January 09, 2004
Copyright © 2003 by ASME
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Figures

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Stress-strain loops for a typical fatigue test, with the specimen loaded at Δσ/E0=0.007 to εmax=−2.5%. The figure shows the measurement of the secant modulus, Esec, the plastic strain in a single cycle, Δεpl, the residual strain, εres, and the maximum strain, εmax.
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Examples of damage patterns observed, including (a) diffusely stained area, without visible cracks, (b) single crack, (c) parallel cracks, (d) cross-hatching, (e) complete trabecular fracture, and (f) local region of damage in the specimen.
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Examples of damage patterns observed. All images are taken from a single specimen tested to −2.0% strain at Δσ/E0=0.007. (a) diffusely stained area, without visible cracks, (b) single crack, (c) parallel cracks, (d) cross-hatching, and (e) complete trabecular fracture.
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Plot of total number of (a) damaged trabeculae per total section area and (b) damaged area fraction vs. maximum compressive strain, εmax. The numbers in the legend represent the normalized stress level. Data at each strain level spread slightly for clarity. Microdamage increases with increasing maximum strain, εmax, after yield. The data for monotonic loading 25 are included for comparison.
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Number of damaged trabeculae per total section area increased with increasing modulus reduction (decreasing normalized reloading modulus, Er/E0). Results are similar for other microdamage parameters.
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Patterns of microdamage observed in bone specimens, tested to two normalized stress levels. Number of specimens=5 for each column. The numbers above each column represent the average number of cycles, N, needed to reach the maximum strain. (a) Δσ/E0=0.008. No specimens were tested to strain levels less than εmax=−1.3% at this normalized stress. (b) Δσ/E0=0.005.
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Plot of number of damaged trabeculae containing complete fractures, normalized by total section area. Each line represents a moving average consisting of five values. The number of fractures increases with increasing specimen strain. A threshold number of cycles is needed for fractures to form. This threshold increases with decreasing maximum specimen strain, εmax.
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Extent of damage across the trabecular strut, rounded to the nearest one-quarter for specimens tested at a normalized stress of Δσ/E0=0.005. Values were estimated to the nearest quarter. The trabecular damage extends all the way across the specimen approximately half the time. Relatively few cracks extend 75% of the distance across the trabecula. Results are typical for other normalized stress levels.
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Progression of damage in typical sections. Each mark represents a damaged trabecula. All specimens shown here were tested (when applicable) at the same normalized stress level of Δσ/E0=0.006. (a) εmax=−0.8%, (b) εmax=−1.1%, (c) εmax=−1.3%, (d) εmax=−1.65%, (e) εmax=−2.0%, (f) εmax=−2.5%.

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