A Critical Distance Analysis of the Effect of Crack Length on Toughness and Fatigue in Compact Bone

The plane strain fracture toughness, K_IC, has a constant value for long cracks, but when specimens containing short cracks are tested it is often found that the measured toughness is less than the long-crack value, and tends to decrease with decreasing crack length. A similar effect occurs when measuring the cyclic stress intensity range, ΔK, corresponding to a given rate of crack growth da/dN. Some experimental data are available in the published literature to show that cortical bone displays these short-crack effects for crack lengths of the order of millimeters or less. The hypothesis of the present work was that these effects can be predicted using an approach known as the Theory of Critical Distances. This is the first time that this approach has been used to predict short crack effects in bone.