Atomistic study of lattice trapping behavior for brittle fracture in bcc-iron

The lattice trapping behavior for brittle fracture in bcc-iron has been studied by atomistic simulations. A pronounced anisotropy for brittle cleavage fracture of a mode I crack is observed in the discrete atomistic scale, and the preferred direction for cleavage is along the 〈1 1 0〉 direction on both {1 0 0} and {0 1 1} planes. The analysis of the atomic structure indicates that, due to the shear effect at the crack tip, the stacking faults or partial dislocations are formed before crack cleavage occurs. For the crack with a 〈1 1 0〉 crack front, shear occurs easily along the slip direction of bcc crystals, whereas for the crack with a 〈1 0 0〉 front, shear can only occur along the non-slip direction, and a strong lattice trapping is exhibited. We conclude that the anisotropy for cleavage fracture and the lattice trapping behavior are closely related with the slip systems of bcc crystals.