Temperature dependence of crack propagation in a two-dimensional model quasicrystal

The propagation of cracks in two-dimensional decagonal model quasicrystals is studied under mode I loading by means of molecular dynamics simulations. In particular, we investigate the dependence on temperature, applied load and underlying structure. The samples are endowed with an atomically sharp crack and strained by linear scaling of the displacement field. Three different regimes of propagation and discernible with increasing temperature. For low temperatures the crack velocity increases monotonically with increasing applied load. We observe that the crack follows the path of dislocations nucleated at its tip. For temperatures above 0.3 T-m, where T-m is the melting temperature, the crack does not remain atomically sharp but becomes blunt spontaneously. In the temperature range between 0.7 T-m and 0.8 T-m the quasicrystal fails by nucleation, growth and coalescence of microvoids. This gradual dislocation-free crack extension is caused by plastic deformation which is mediated by localized rearrangements comparable with the so-called shear transformation zones. These are also observed in amorphous solids. Thus, at low temperatures the crack propagates along crystallographic planes just as in periodic crystals, whereas at high temperatures a glass-like behaviour is dominant.