Issue 10

D.Taylor et alii, Frattura ed Integrità Strutturale, 10 (2009) 12-20; DOI: 10.3221/IGF-ESIS.10.02 19 Figure 7 : The geometry used to study defects of various shapes and sizes in a typical long bone – the focus path is the line on which TCD calculations are carried out. Typical predictions showing the effect on damage evolution of including ingrowth of bone into the defect, and bone repair processes. (a) (b) Figure 8 : (a) Variation of peak damage amount with Young’s modulus of the bone graft material; (b) Specification for the safe value of E o (i.e. the value above which failure will not occur) as a function of hole size. C ONCLUDING REMARKS his work has shown that the TCD can be used to study fracture and fatigue problems in bone. Classic problems which the TCD has been able to solve in other materials, such as notch-initiated fracture and fatigue and the short crack problem, have been successfully addressed in this material. Even though bone shows large variations in its mechanical properties, it seems that L remains approximately constant, of the order of 0.3-0.4mm, which is very convenient when making predictions. This value reflects the role of osteons and other microstructural features in impeding crack growth and thus controlling toughness and fatigue. Current work has been limited to cases where crack growth occurs across the bone, i.e. in the transverse direction: longitudinal crack growth requires separate study. We have also limited ourselves to cortical bone: the failure of spongy, cancellous bone is also of great interest and merits further attention. The TCD can be employed as part of a practical software tool to aid orthopaedic surgeons in the planning of operations and of post-operative treatments. A CKNOWLEDGEMENTS e are grateful to the Higher Education Authority of Ireland for provision of funding for part of the work described above, which was conducted in collaboration with the Institute of Technology, Sligo, Ireland. T W