A strain rate dependent model with decreasing Young's Modulus for cortical human bone

Area of Science:

• Biomechanics
• Materials Science
• Orthopedics

Background:

• Conflicting literature exists on human cortical bone's elastic modulus response to strain rate.
• Some studies attribute strain rate dependence to viscoelastic properties, while others suggest non-viscoelastic mechanisms.

Purpose of the Study:

• Investigate the dynamic mechanical behavior of human cortical bone specimens.
• Develop a strain rate-dependent model to explain experimental findings.
• Clarify the role of viscoelasticity versus other mechanisms in bone's mechanical response.

Main Methods:

• Uniaxial tensile tests were performed on 21 human rib cortical bone specimens from 12 male post-mortem subjects.
• A comprehensive strain rate-dependent model was developed and applied.
• Viscoelastic models were analyzed for their applicability to bone material.

Main Results:

• A significant decrease in Young's modulus was observed with increasing strain rate (from ~18 GPa at 0.10 s⁻¹ to ~8 GPa at 0.50 s⁻¹).
• This decrease was not consistent with predictions from common viscoelastic models for small strains.
• The observed behavior aligns with findings linking microcracking damage to strain rate.

Conclusions:

• The study concludes that the decrease in elastic modulus with strain rate in human cortical bone is primarily due to microcracking, not viscoelastic effects.
• Existing viscoelastic models may not accurately represent the complex mechanical behavior of bone.
• Further research into microcracking mechanisms is warranted for a complete understanding of bone's dynamic properties.