Rising Crack-Growth-Resistance Behavior in Cortical Bone: Implications for Toughness Measurements

Application of fracture mechanics to bone was undertaken to provide a better estimate of bone’s resistance to fracture as traditional strength of materials tests failed to provide a realistic measure due to the presence of inherent flaws and fatigue microcracks in bone (1). Consequently, over the last decade a number of fracture mechanics studies have characterized bone’s resistance to fracture in terms of critical stress intensity factor and critical strain energy release rate measured at the onset of a fracture crack (1–3). These studies, although useful, provide a limited insight into fracture behavior of bone as, unlike classical brittle materials, bone is a microcracking solid that derives its resistance to fracture during the process of crack propagation from microfracture mechanisms occurring behind the advancing crack front (4). More significantly age and disease-related alterations in the content and arrangement of bone, that cause reduced post-yield properties, are unlikely to be realized from initiation tests as such tests are limited to events at yielding.