Issue 10

D.Taylor et alii, Frattura ed Integrità Strutturale, 10 (2009) 12-20; DOI: 10.3221/IGF-ESIS.10.02 15 conducted a different analysis of bone, to predict indentation fracture, for which a non-linear material model was needed, we found that T=1 [13]. S HORT CRACK BEHAVIOUR IN FATIGUE AND BRITTLE FRACTURE t is well known than short cracks often display behaviour which does not conform to linear elastic fracture mechanics. For example, the values of toughness (K c ) and fatigue threshold (  K th ) for short cracks are often smaller than the material-constant values measured from long cracks. Data in which the measured K c (or  K th ) is plotted as a function of crack length are known as resistance curves, or R-curves. Figs 2 and 3 show R-curve data for bone, for brittle fracture and fatigue respectively, along with predictions using the TCD. In this case the analysis can be made very easily using the Line Method, because predictions for the case of a small crack (length a ) in an infinite body can be expressed using the following simple equation: La a K K c ca   (2) Figure 2 : Two sets of data showing the variation of measured fracture toughness as a function of crack length for bone along with TCD predictions. For more details se e [17]. 0 1 2 3 4 5 6 0 1 2 3 4 5 6 7 Crack Length (mm) Fracture Toughness Kc (MPa.m^0.5) TCD Prediction Lakes 0 0.5 1 1.5 2 2.5 3 0 0.02 0.04 0.06 0.08 Crack Length (mm) Fracture Toughness Kc (MPa.m^1/2) TCD Prediction Mullins I