Brittle fracture processes modelled on the atomic scale

Atomistic techniques are used to study brittle fracture processes. The discreteness of the lattice, which manifests itself in the lattice trapping effect, is shown to be important not only for the distinction between different crack propagation directions on one individual cleavage plane but also for the selection of the cleavage plane itself. The (100)-[001] crack system in NiAl is presented as an example which clearly shows that the Griffith criterion is only a necessary condition for brittle fracture and not sufficient. The role of the interatomic force law is studied in the second part of the paper. The non-linearity of the interatomic interaction is shown to strongly influence the critical load to fracture blunted cracks and also reduces the speed of dynamically running cracks significantly below the (linear elastic) continuum limit.