Fatigue damage-fracture mechanics interaction in cortical bone

Area of Science:

• Biomaterials Science
• Orthopedic Biomechanics
• Materials Science

Background:

• Fatigue loading accumulates damage in bone, potentially leading to macrocrack initiation and catastrophic failure.
• Understanding the impact of fatigue damage on bone fracture mechanics is crucial for predicting skeletal integrity.

Purpose of the Study:

• To investigate how fatigue damage influences crack growth parameters in bovine cortical bone.
• To determine the relationship between accumulated fatigue damage and the mechanical properties governing bone fracture.

Main Methods:

• Bovine cortical bone specimens were subjected to fatigue loading to induce varying levels of damage, indicated by stiffness loss.
• Notched specimens (both fatigued and unfatigued) were tested under monotonic three-point bending to failure.
• Key fracture parameters including critical stress intensity factor (K(I)) and work to critical load (W(Q)) were quantified.

Main Results:

• Fatigue-damaged bone exhibited significantly lower critical stress intensity factor (K(I)) and work to critical load (W(Q)) compared to undamaged bone.
• Percent stiffness loss showed significant negative correlations with K(I), W(Q), maximum load (Pmax), deflection at maximum load (Δmax), structural stiffness (Smax), Wmax, and load at 1.4 mm deflection (P(1.4)).
• Load-deflection curves of damaged bone could be transformed to those of undamaged bone via a specific shift, suggesting a unified fracture behavior model.

Conclusions:

• Fatigue damage substantially reduces cortical bone stiffness, resistance to crack initiation, and overall load-carrying capacity.
• A single governing principle appears to describe the effect of fatigue damage on cortical bone fracture behavior.
• These findings have implications for understanding bone fragility and designing treatments for bone-related injuries.