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RESEARCH PAPERS

Creep Contributes to the Fatigue Behavior of Bovine Trabecular Bone

[+] Author and Article Information
S. M. Bowman, D. W. Cheng, W. C. Hayes

Orthopedic Biomechanics Laboratory, Department of Orthopedic Surgery, Charles A. Dana Research Institute, Harvard Thorndike Laboratory, Beth Israel Deaconess Medical Center and Harvard Medical School, Boston, MA 02215

X. E. Guo

Bone Bioengineering Laboratory, Center for Biomedical Engineering, Columbia University, New York, NY 10027

T. M. Keaveny

Orthopedic Biomechanics Laboratory, Department of Mechanical Engineering, University of California, Berkeley, CA 94720

L. J. Gibson

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

T. A. McMahon

Division of Engineering and Applied Sciences, Harvard University, Cambridge, MA 02138

J Biomech Eng 120(5), 647-654 (Oct 01, 1998) (8 pages) doi:10.1115/1.2834757 History: Received November 12, 1996; Revised February 18, 1998; Online January 23, 2008

Abstract

Repetitive, low-intensity loading from normal daily activities can generate fatigue damage in trabecular bone, a potential cause of spontaneous fractures of the hip and spine. Finite element models of trabecular bone (Guo et al., 1994) suggest that both creep and slow crack growth contribute to fatigue failure. In an effort to characterize these damage mechanisms experimentally, we conducted fatigue and creep tests on 85 waisted specimens of trabecular bone obtained from 76 bovine proximal tibiae. All applied stresses were normalized by the previously measured specimen modulus. Fatigue tests were conducted at room temperature; creep tests were conducted at 4, 15, 25, 37, 45, and 53°C in a custom-designed apparatus. The fatigue behavior was characterized by decreasing modulus and increasing hysteresis prior to failure. The hysteresis loops progressively displaced along the strain axis, indicating that creep was also involved in the fatigue process. The creep behavior was characterized by the three classical stages of decreasing, constant, and increasing creep rates. Strong and highly significant power-law relationships were found between cycles-to-failure, time-to-failure, steady-state creep rate, and the applied loads. Creep analyses of the fatigue hysteresis loops also generated strong and highly significant power law relationships for time-to-failure and steady-state creep rate. Lastly, the products of creep rate and time-to-failure were constant for both the fatigue and creep tests and were equal to the measured failure strains, suggesting that creep plays a fundamental role in the fatigue behavior of trabecular bone. Additional analysis of the fatigue strain data suggests that creep and slow crack growth are not separate processes that dominate at high and low loads, respectively, but are present throughout all stages of fatigue.

Copyright © 1998 by The American Society of Mechanical Engineers
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