Abstract:
Bone fracture is a severe health concern; therefore, understanding the causes of bone fracture are crucial. This
paper investigates the microstructure and fracture behaviour of cadaveric cortical bone of two different groups
(Young, n= 6; Aged, n=7). The microstructure is obtained from µ-CT images, and the material parameters are
measured with nanoindentation. Fracture behaviour in transverse and longitudinal orientations is investigated
experimentally and numerically. The results show that the Haversian canal (HC) size increases and the osteon
wall thickness (OWT) decreases significantly in the aged group, whereas a nonsignificant difference is found in
tissue properties. The crack initiation (Jic) and crack growth (Jgrow) toughness of the aged group are found to be
significantly lower (p<0.01) than the young group in the transverse orientation; however, for the longitudinal
orientation, only the value of Jic in the aged group is found significantly lower. Further, a 4-phase XFEM (based
on micro-CT image) model is developed to investigate the crack propagation behaviour in both orientations. For
the transverse orientation, results show that in the aged group, the crack initially follows the cementline and then
penetrates the osteon, whereas, in the young group, it propagates along the cementline. These results are in
agreement with experimental results where the decrease in Jgrow is more significant than the Jic in the aged group.
This study suggests that ageing leads to a larger HC and reduced OWT, which weakens the crack deflection
ability and causes fragility fracture. Further, the XFEM results indicate that the presence of a small microcrack in
the vicinity of a major crack tip causes an increase in the critical stress intensity factor.
