Crack propagation in quasicrystals

Numerical simulations have been performed on the propagation of mode-I cracks in both ordered and randomized two-dimensional decagonal model quasicrystals. In particular, the dependence on temperature, applied load and underlying structure has been investigated. The samples are endowed with an atomically sharp crack and subsequently loaded by linear scaling of the displacement field. The response of the system is followed by molecular dynamics simulations. For temperatures below 30% of the melting temperature T_m the crack velocity grows monotonically with the applied load and the model quasicrystal shows brittle fracture. For large overloads the crack becomes unstable and branches. In this low temperature regime crack tip velocities are in the range of 20% - 50% of the shear wave velocity v_s. For temperatures above 30% of T_m the crack does not remain atomically sharp but blunts spontaneously. To circumvent this and to nevertheless study a sharp crack a linear temperature gradient is established along a strip. From the low temperature regime, where a sharp tip can be stabilized, the crack is driven into a region of elevated temperature. In the range of 70% -80% T_m the failure mode of the quasicrystal changes to a void formation process. Thus at low temperatures the crack propagates along crysta lographic planes just like in periodic crystals, whereas a glass-like behaviour is dominant at high temperatures.