ICAMS / Interdisciplinary Centre for Advanced Materials Simulation
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On-the-fly analysis of large-scale molecular dynamics simulations: calculating lattice rotation and dislocation density tensors from atomistic data

Date: 30.11.2009
Place: Fall Meeting of the Materials Research Society (MRS), Boston, USA

Alexander Hartmaier
Jun Hua
Christoph Begau

Large-scale molecular dynamics simulations have been widely used to investigate the mechanical behavior of materials. But complex datasets generated during the atomistic simulations involving the positions of many million atoms make quantitative data analysis quite a challenge. This paper presents a novel method to determine dislocations in the crystal and also quantifies the corresponding Burgers vectors. This is achieved by combining geometrical methods to determine the atoms lying in the dislocations cores, like for example the common neighbor analysis or the bond angle analysis, with the slip vector analysis. The first methods are used to filter out the atoms lying in undisturbed regions of the crystal; the latter method yields the relative slip of the remaining atoms and thus indicates the Burgers vector of those atoms lying in the dislocation cores. A topological simplification of atom positions in the dislocation cores into geometrical line segments allows us to calculate local lattice rotations as well as the Nye dislocation density tensor from atomistic data during the simulation. Large-scale atomistic simulations of nanoindentation reveal the full potential of this advanced analysis method. Based on the gained data, the density of geometrically necessary dislocations (GND) is evaluated and expressed as a function of the deformed volume, the indentation depth and the indenter size. Also the dislocation-grain boundary interaction can be investigated with a drastically improved precision. Hence, this method is expected to provide valuable input for multi-scale modeling schemes.

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