  In this paper, the effect of twin boundaries on the crack growth behaviour of
single crystal BCC Fe has been investigated using molecular dynamics
simulations. The growth of an atomically sharp crack with an orientation of
(111)$<$110$>$ (crack plane/crack front) has been studied under mode-I loading
at constant strain rate. In order to study the influence of twin boundaries on
the crack growth behaviour, single and multiple twin boundaries were introduced
perpendicular to crack growth direction. The results indicate that the
(111)$<$110$>$ crack in single crystal BCC Fe grows in brittle manner. However,
following the introduction of twin boundaries, a noticeable plastic deformation
has been observed at the crack tip. Further, increasing the number of twin
boundaries increased the amount of plastic deformation leading to better crack
resistance and high failure strains. Finally, an interesting relationship has
been observed between the crack growth rate and flow stress.
