Ductility and brittleness of bone

Human, bovine and equine bones show brittle to ductile transitions as a function of strain rate. The transition is not sharp, but occurs around a strain rate of 10−1 s−1.At lower rates, the strength increases proportional to the logarithm of the strain rate, at higher rates it decreases. Additionally, the work of fracture peaks around 10−1 s−1. Thermal activation analysis gives an activation volume of (1 nm)3, an activation enthalpy of 1 eV and an activation energy of about 0.5 eV. Plastic deformation occurs both within and between collagen fibrils. In the fibrils, the existence of screw dislocations parallel to the collagen molecules with a Burger’s vector of 1 nm length is postulated. Deformation occurs by thermally activated kink pair formation in these defects.