  We study propagating mode-I fracture in two dimensional amorphous materials
using atomistic simulations. We used the continuous random network (CRN) model
of an amorphous material, creating samples using a two dimensional analogue of
the WWW (Wooten, Winer & Weaire) Monte-Carlo algorithm. For modeling fracture,
molecular-dynamics simulations were run on the resulting samples. The results
of our simulations reproduce the main experimental features. In addition to
achieving a steady-state crack under a constant driving displacement (which had
not yet been achieved by other atomistic models for amorphous materials), the
runs show micro-branching, which increases with driving, transitioning to
macro-branching for the largest drivings. Beside the qualitative visual
similarity of the simulated cracks to experiment, the simulation also succeeds
in explaining the experimentally observed oscillations of the crack velocity.
