  Crack propagation is studied in a two dimensional decagonal model
quasicrystal. The simulations reveal the dominating role of highly coordinated
atomic environments as structure intrinsic obstacles for both dislocation
motion and crack propagation. For certain overloads, these obstacles and the
quasiperiodic nature of the crystal result in a specific crack propagation
mechanism: The crack tip emits a dislocation followed by a phason wall, along
which the material opens up.
