Temperature Dependence of Dislocation Motion and Crack Propagation in a Two-Dimensional Binary Model Quasicrystal
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Temperature dependence of dislocation motion and crack propagation in a twodimensional binary model quasicrystal
Galib Krdzalic, Marco Brunelli , Hans-Rainer Trebin Institut für Theoretische und Angewandte Physik der Universität Stuttgart, Pfaffenwaldring 57, D-70550 Stuttgart, Germany
ABSTRACT A twodimensional binary model quasicrystal (Roth-Mikulla tiling) was subjected to shear of constant rate (Lees-Edwards boundary conditions). Lennard-Jones forces were applied between the atoms and the evolution of the system was followed by isothermal molecular dynamics simulations. Temperature was controlled by a Nosé-Hoover thermostat. Dislocation dipoles were created followed by phason walls, which broadened with increasing shear. Widening happens by transversal shear induced diffusion. It starts with the onset of failure and is saturating after reaching two planes of high interface energy parallel to the glide plane. Thus a structurally damaged layer arises along which viscous glide is developing. The transverse diffusion constant follows an Arrhenius law at low temperature. With increasing temperature it is bending to a flatter slope similar as in the model of phason induced diffusion by Kalugin and Katz. First results of temperature-dependent crackpropagation are reported, too.
INTRODUCTION The interest in mechanical properties of quasicrystals stems from many stressexperiments [1] which reveal the following remarkable properties: • • •
There is a brittle-to-ductile transition at about 80% of the melting temperature. With increasing strain quasicrystals show softening. During dislocation motion phasons are created and the structure is changed.
To understand aspects of these phenomena on a microscopic level, we are studying dislocation motion and crack propagation in twodimensional quasicrystalline model systems by numerical molecular dynamics simulations. Previous work [2] was concerned with plastic deformation at one low and one elevated temperature and with fracture at zero temperature. Now we have systematically investigated dislocation motion in a wide range of temperatures and have observed a scenario which might be of interest to be reported. Also a few results of a similar study on crack propagation are presented.
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Fig. 1. The model quasicrystal used is the Roth-Mikulla binary tiling. Left: Atom representation. Middle: Bond representation. Full lines are connecting the tenfold clusters. The broken line is an "easy" line not touching clusters. Right: If a basic flip occurs in one of two adjacent rhombs, a nonconvex hexagon is arising in the bond representation.
MODEL SYSTEM a) Equilibrium structure and dynamics The model system is a decagonal quasicrystal with two kinds of atoms: the RothMikulla tiling. It is obtained by decoration of the Tübingen triangle tiling and is depicted either directly by a plot of the atoms, or in the bond representation, where next neighbor A-B bonds are drawn (Fig. 1). The bond representation is a rhombic tiling, different from the Penrose tiling. The model quasicrystal
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