Dislocation emission from a crack tip in a body-centered cubic lattice under quasi-static mode-I loading was modelled by means of 2-dimensional (plane strain) molecular dynamic simulations, using 2 different interatomic potentials. The calculated crack opening displacements between the atoms were compared with the crack opening displacements in continuum treatments. The simulations confirmed that the crack opening displacement consisted of 3 components. One contribution arose from the applied stress, one was the plastic contribution arising from dislocation emission (which increased the crack opening displacement) and the other was the shielding contribution. Since the maximum crack opening responded to all of these contributions, it could be considered to be a fracture parameter which was suitable for the determination of fracture toughness at micro-crack initiation. The stress conditions for dislocation emission and crack initiation were different for the various atomistic models. This was explained in terms of differing barriers to the breaking of bonds between second-nearest neighbors. This led to differing energies of the unstable stacking fault; according to the Rice model. Both atomistic models obeyed known ductility criteria.

Atomistic Modelling of the Contribution of Dislocations to Crack Opening Displacements. A.Machová, F.Kroupa: Materials Science and Engineering A, 1997, 234-236, 185-8