Figure 4.
Differences in fracture toughness with age. Loading a notched femur caused a crack to propagate through the cortex (a). The initial notch angle was determined from μCT images (centroid is an average among slices above and below notch), and the angle at which the crack propagation became unstable was determined from SEM images (centroid determined directly from SEM image). At the initiation of crack growth, the critical stress intensity factor Kc was higher at 12-mo. and 24-mo. than at 6-mo. (b). Fracture toughness at instability did not vary with age (c). However, the work to propagate the crack through the bone was much lower for aged rats than the young adult and 12-mo. rats. *p<0.05 vs. 6-mo.