Continuum damage interactions between tension and compression in osteonal bone.

Area of Science:

• Biomechanics
• Materials Science
• Orthopedics

Background:

• Osteoporosis and other skeletal diseases pose significant burdens on aging populations.
• Decreased bone mechanical competence leads to increased fracture incidence and mortality, particularly after age 65.
• Understanding how bone damage accumulates under various loading conditions and affects bone strength is crucial.

Purpose of the Study:

• To investigate continuum damage interactions between tensile and compressive loading modes in bone.
• To develop and identify material constants for a novel constitutive model describing bone's mechanical response to combined loading histories.
• To quantify the impact of damage accumulated in one loading mode on mechanical behavior in another.

Main Methods:

• Performed loading-reloading experiments to measure stiffness, plastic strains, and stress-strain curves.
• Applied tensile and compressive overloading to assess subsequent mechanical responses.
• Developed a piecewise 1D constitutive model to characterize bone's response to combined loading.

Main Results:

• Tensile overloading (60% damage at 0.65% plastic strain) caused a 20% stiffness reduction under compression.
• Compressive overloading (60% damage at 0.75% plastic strain) resulted in a 50% stiffness reduction under tension.
• Previous tensile overload did not affect compressive hardening, but previous compressive overload significantly reduced tensile reloading strength.

Conclusions:

• Damage accumulated under one loading mode significantly affects mechanical behavior under a different loading mode.
• A novel constitutive model was proposed to capture these loading mode-dependent damage and plasticity behaviors.
• Incorporating these findings into finite element models can enhance fracture risk analysis for bones and bone implants.