  The break-up of a two-dimensional circular disc by normal and oblique impact
on a hard frictionless plate is investigated by molecular dynamics simulations.
The disc is composed of numerous unbreakable randomly shaped convex polygons
connected together by simple elastic beams that break when bent or stretched
beyond a certain limit. It is found that for both normal and oblique impacts
the crack patterns are the same and depend solely on the normal component of
the impact velocity. Analysing the pattern of breakage, amount of damage,
fragment masses and velocities, we show the existence of a critical velocity
which separates two regimes of the impact process: below the critical point
only a damage cone is formed at the impact site (damage), cleaving of the
particle occurs at the critical point, while above the critical velocity the
disc breaks into several pieces (fragmentation). In the limit of very high
impact velocities the disc suffers complete disintegration (shattering) into
many small fragments. In agreement with experimental results, fragment masses
are found to follow the Gates-Gaudin-Schuhmann distribution (power law) with an
exponent independent of the velocity and angle of impact. The velocity
distribution of fragments exhibit an interesting anomalous scaling behavior
when changing the impact velocity and the size of the disc.
