  Are the cohesive laws of interfaces sufficient for modelling fracture in
polycrystals using the cohesive zone model? We examine this question by
comparing a fully atomistic simulation of a silicon polycrystal to a finite
element simulation with a similar overall geometry. The cohesive laws used in
the finite element simulation are measured atomistically. We describe in detail
how to convert the output of atomistic grain boundary fracture simulations into
the piecewise linear form needed by a cohesive zone model. We discuss the
effects of grain boundary microparameters (the choice of section of the
interface, the translations of the grains relative to one another, and the
cutting plane of each lattice orientation) on the cohesive laws and polycrystal
fracture. We find that the atomistic simulations fracture at lower levels of
external stress, indicating that the initiation of fracture in the atomistic
simulations is likely dominated by irregular atomic structures at external
faces, internal edges, corners, and junctions of grains. Thus, cohesive
properties of interfaces alone are likely not sufficient for modelling the
fracture of polycrystals using continuum methods.
