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Fragility Assessment of Bovine Cortical Bone Using Scratch Tests
Published on: November 30, 2017
The fatigue strength of compact bone in torsion
D Taylor1, P O'Reilly, L Vallet
1Department of Mechanical & Manufacturing Engineering, Trinity College, Dublin, Ireland. dtaylor@tcd.ie
Journal of Biomechanics
|July 2, 2003
Summary
Bone fatigue strength is significantly lower in torsion than in compression. This finding, explained by a microcrack growth model, highlights the role of shear stress in bone failure and stress fractures.
Area of Science:
- Biomechanics
- Materials Science
- Orthopedics
Background:
- Bone fatigue failure is a critical factor in stress fractures and implant loosening.
- Understanding anisotropic bone properties under cyclic loading is essential for predicting skeletal integrity.
Purpose of the Study:
- To investigate the fatigue behavior of bone under cyclic torsion.
- To compare torsional fatigue strength with compressive fatigue strength.
- To develop a theoretical model predicting fatigue failure based on microcrack growth.
Main Methods:
- Cyclic torsion fatigue tests on bovine compact bone samples.
- Cyclic compression fatigue tests on chicken tibiae.
- Testing of intact chicken metatarsals under torsion.
- Development of a theoretical model incorporating microcrack growth and stress intensity factors.
Main Results:
- Torsional fatigue strength of bone is more than twofold lower than compressive fatigue strength.
- Similar strength reductions were observed in chicken metatarsals compared to tibiae under torsion.
- The theoretical model accurately predicted experimental results, emphasizing microcrack growth parallel to the longitudinal axis.
Conclusions:
- Longitudinal shear stress significantly contributes to bone fatigue failure, contrary to common assumptions.
- The derived effective stress range, accounting for Mode I and Mode II stresses, explains the reduced torsional fatigue strength.
- These findings have implications for understanding in vivo bone fatigue, stress fractures, and bone adaptation mechanisms.
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