Anisotropic yield behavior of bone under combined axial force and torque

Area of Science:

• Biomechanics
• Materials Science
• Orthopedic Research

Background:

• Cortical bone exhibits complex mechanical behavior under multiaxial loading.
• Understanding bone's yield criteria is crucial for predicting fracture and designing implants.
• Existing failure criteria for composites may apply to bone tissue.

Purpose of the Study:

• To experimentally determine the yield behavior of cortical bone under combined tension, compression, and torsion.
• To evaluate the applicability of established failure criteria to cortical bone.
• To identify the most accurate criterion for predicting bone yield under combined loading.

Main Methods:

• Testing bovine and human cortical bone samples (tibial and femoral) under combined loading.
• Utilizing a strain offset technique to identify the common yield point.
• Applying strain rates (0.01-0.06 s-1) to minimize viscoelastic effects.

Main Results:

• Experimental yield loci were generated for human and bovine cortical bone.
• The Tsai-Wu criterion demonstrated the best agreement with the experimental data.
• Hill's criterion accurately described specific loading combinations (compression-torsion, tension-torsion).

Conclusions:

• The Tsai-Wu criterion is a suitable model for predicting the yield behavior of cortical bone under combined loading.
• Combined loading significantly influences bone's mechanical response.
• Further validation of failure criteria for bone biomechanics is warranted.