Modelling fracture processes in bones 285
failure in many biological materials is described based on an elastic damage
criterion (Budyn and Hoc, 2007) that in human cortical bone is governed by
the strain-based criterion (Nalla et al ., 2005). In these models, the onset of
fracture is based on the critical maximum principal strain. A value of 0.6%
was chosen to initiate the cracks in the homogenized material as well as in all
the microstructural constituents (Bayraktar et al ., 2004). In a similar model,
it was shown that cracks can be initiated perpendicular to the maximum
principal stress direction, that is, mode I in tension (Budyn and Hoc, 2007).
Therefore, an initial microcrack of length 100 μ m was placed at the middle
of upper and ...