From crystalline to glassy: Crack propagation modes in decagonal quasicrystals

The propagation of mode-I cracks in a two-dimensional decagonal model quasicrystals is studied by molecular dynamics simulations. The samples are endowed with an atomically sharp seed crack and a temperature gradient. Subsequently the crack is loaded by linear scaling of the displacement field. The response of the crack running into regions of increasing temperature is monitored. For low temperatures below 30% of the melting temperature Tm the model-quasicrystals fails by brittle fracture. We observe that the crack follows the path of dislocation nucleated at its tip. The crack propagates along well defined planes and circumvents tightly bound clusters. In the medium temperature regime from 30% to 70% Tm the crack is blunting spontaneously by dislocation emission. In the range of 70%-80% Tm the quasicrystals fails by nucleation, growth and coalescence of micro-voids. This gradual, dislocation-free crack extension is caused by plastic deformation which is mediated by localized rearrangements comparable to so-called shear transformation zones in amorphous solids.