  The brittle fragmentation of spheres is studied numerically by a 3D Discrete
Element Model. Large scale computer simulations are performed with models that
consist of agglomerates of many spherical particles, interconnected by
beam-truss elements. We focus on a detailed description of the fragmentation
process and study several fragmentation mechanisms involved. The evolution of
meridional cracks is studied in detail. These cracks are found to initiate in
the inside of the specimen with quasi-periodic angular distribution and give a
broad peak in the fragment mass distribution for large fragments that can be
fitted by a two-parameter Weibull distribution. The results prove to be
independent of the degree of disorder in the model, but mean fragment sizes
scale with velocity. Our results reproduce many experimental observations of
fragment shapes, impact energy dependence or mass distribution, and
significantly improve the understanding of the fragmentation process for impact
fracture since we have full access to the failure conditions and evolution.
