Inelastic strain accumulation in cortical bone during rapid transient tensile loading

Area of Science:

• Biomechanics
• Biomaterials Science
• Orthopedic Research

Background:

• Cortical bone's mechanical properties are crucial for skeletal function.
• Understanding bone's response to rapid loading is vital for injury prevention and treatment.

Purpose of the Study:

• To investigate the tensile stress-strain behavior of human and bovine cortical bone under rapid, high-amplitude load cycles.
• To determine if nonlinear stress-strain behavior observed in creep loading also occurs during transient loading at physiological rates.

Main Methods:

• Experimental study using machined bovine and human cortical bone samples.
• Subjected samples to rapid load cycles (+/- 420 MPa/s) with load reversal at pre-selected strain levels.
• Measured axial and transverse strain behavior to assess nonlinearity and residual strain.

Main Results:

• Cortical bone demonstrated significant nonlinearity in axial strain during the first load cycle, while transverse strain remained largely linear.
• A substantial portion of maximum nonlinear strain accumulated after load reversal in both human (29.1%) and bovine (35.1%) bone.
• Significant residual axial and volumetric strains were observed upon unloading, indicating internal damage.

Conclusions:

• Nonlinear stress-strain behavior in cortical bone occurs during transient loading at physiological rates, mirroring creep loading behavior.
• Damage accumulation, evidenced by internal voids and new surfaces, is a primary driver of this nonlinear behavior.
• Residual volume increases and structural disruptions may act as a stimulus for bone's biological repair mechanisms.