Molecular dynamics simulations of crack propagation in quasicrystals

In a large number of experiments it has been proven that plastic deformation of quasicrystals can occur by a dislocation mechanism. By use of molecular dynamics simulations we have investigated the application of shear stress to a three-dimensional model quasicrystal in which we had built in an edge dislocation of the Peierls-Nabarro type. To determine suitable Burgers vectors we have calculated the gamma surface, i.e. the misfit energy obtained by a rigid shift of two sample halves along a glide plane. The sample was an approximant of the Ammann-Kramer-Penrose-Tiling decorated according to Henley and Elser (Phil. Mag. B 53 (1986), 59). It consisted of 1 504 080 atoms interacting via Lennard-Jones-Potentials. We performed simulations in the microcanonical ensemble at zero temperature. To detect the dislocation line we have used several visualization methods. We have plotted only particles with a potential energy above a threshold leading to pictures of both the atoms in the dislocation core and in the stacking fault in the wake of the dislocation. To distinguish among them we have used image processing algorithms. The displacement field of the configuration has also been computed. We have observed climb and glide motion of the dislocation. The climb motion is caused mainly by boundary effects due to the sample geometry. The glide motion shows kinks due to structural elements that act as pinning centers. The width of the kinks is about 20 quasilattice constants.