Initiation Fracture Toughness of Human Cortical Bone as a Function of Loading Rate

Abstract

During injury causing events such as impact, blunt trauma, penetration or blast, the human body is subjected to high rate loading. These events will deform and damage human tissue, frequently causing tearing in soft tissues and cracking/fracture in hard tissue (bone) due to the inherent brittleness of bone. For the development of accurate fracture models for computer simulation of bone fracture and also to understand the failure mechanisms of hard tissues during blast and impact events, it is necessary to investigate the failure behavior (fracture) of hard tissues at different loading rates, including high loading rates. In this study, the Mode I fracture behavior of cortical bone from the human femur, perpendicular to the long axis, is investigated as a function of loading rate, including dynamic loading rates which are accomplished with a modified Kolsky bar. The bone fracture specimens were extracted from three different human donors, ages 36, 50, and 43. For all three donors, the fracture toughness increases as loading rate increases from quasi-static to intermediate. As loading rate increases from intermediate to dynamic rates, the initiation fracture toughness decreased on average, while remaining higher than at quasi-static rate. The observed variations in initiation fracture toughness with donor age for each loading rate did not show any specific trends. The initiation fracture toughness of cortical bone is dependent on the path of the crack relative to the internal bone structure.