Figure 3. Fracture toughness testing of cortical bone.

The single-edge notched beam (SENB) is typically loaded in three-point bending until a crack emanating from a micro-notch propagates through the specimen (A). In the magnified photo, the sharpened notch creates a stress concentration to start crack growth. As the loading rate of human cortical SENBs increases from low and high, the final fracture displacement decreases (B). In the schematic of an R-curve, the determination of J_Ic is based on a construction line (e.g., a slope = yield strength, σ_y, of cortical bone) and characterizes fracture toughness at crack growth initiation while J-int is fracture toughness at fracture instability (C).