Crack propagation under three different
intial strain conditions (mode 1) was simulated (5%, 5.5% and 6%
strain).
The average kinetic energy per atom vs. time is shown figure 5. The kinetic
energy of the system behaves as expected and matches the results from
the IMD simulations (see setup ). At low strains
( <4.8%) the crack doesn't propagate because the energy isn't
sufficient to break Si-Si bonds. At high strains the crack becomes
unstable due to shock waves and there is a need to create incremental loading
in order to achieve stable crack propagation.

Fig. 5
Green, blue and red curves represent 6%, 5.5% and 5% strains
respectively.

The strain energy release rate ()
of the system was calculated using eq. 12 :

while the height of the specimen equals
256.101 Angstrom, E=169, Poisson ratio = 0.36 and E*=194.16GPa [8].

Fig. 6 shows snapshots of the crack at
different timesteps (26,800 , 36,800 ,46,800, 56,800). It can be seen
from the red curve that the crack is propagating at a constant speed.

Fig. 6 Snapshots of crack
propagation showing constant crack propagation.

Fig. 7 A snapshot of the
specimen. Only atoms with potential energy above a certain threshold
are visible. It is observed that the crack free surfaces (green) have
high surface energy and that the energy distribution surrounding the
crack tip behaves similarly to Irwin's theory.
Strain 5%, timestep 26,800.

Dynamic crack propagation along the {110} plane in the [110] direction
is presented in the following movie for 5% strain:

References:
[8]
What is the Young's Modulus of silicon? W. D. Nix et al. J. Micro/
Sys. Vol 19 No.2 2010