ABSTRACT

We study the problem of atomic scale fracture using the recently developed
quasicontinuum method in which there is a systematic thinning of the
atomic-level degrees of freedom in regions where they are not needed.
Fracture is considered in two distinct settings. First, a study is made
of cracks in single crystals, and second, we consider a crack advancing
towards a grain boundary (GB) in its path. In the investigation of single
crystal fracture, we evaluate the competition between simple cleavage and
crack-tip dislocation emission. In addition, we examine the ability of
analytic models to correctly predict fracture behaviour, and find that the
existing analytical treatments are too restrictive in their treatment of
nonlinearity near the crack tip. In the study of GB-crack interactions, we
have found a number of interesting deformation mechanisms which attend the
advance of the crack. These include the migration of the GB, the emission of
dislocations from the GB, and deflection of the crack front along the GB
itself. In each case, these mechanisms are rationalized on the basis of
continuum mechanics arguments.