Regensburg 2013 – wissenschaftliches Programm

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MM: Fachverband Metall- und Materialphysik

MM 34: Topical Session: Fundamentals of Fracture - Fracture at the Atomistic Scale

MM 34.4: Vortrag

Mittwoch, 13. März 2013, 12:30–12:45, H4

Multiscale Simulation of Brittle Fracture in Oxides and Semiconductors — •James Kermode — King's College London, Physics Department, London, WC2R 2LS, United Kingdom

Fracture is probably the most challenging `multi-scale' problem: crack propagation is driven by the concentration of a long-range stress field at an atomically sharp crack tip. This creates a complex dynamical system with strongly coupled length scales. An accurate description of the chemical processes occurring in the small crack tip region is therefore essential, as is the inclusion of a much larger region in the model systems. Both these requirements can be met by combining a quantum mechanical (at the DFT level) description of the crack tip with a classical atomistic model that captures the long-range elastic behaviour of the surrounding crystal matrix, using a QM/MM (quantum mechanics/molecular mechanics) technique such as the `Learn on the Fly' (LOTF) scheme. Here, we consider silicon and silica as prototypical semiconductor and oxide materials, respectively. The elastic and thermodynamic behaviour of silicon can be accurately described with simple interatomic potentials, while for silica a polarizable force field is required. Examples of the application of these techniques to fracture problems include low-speed dynamical fracture instabilities in silicon, interactions between moving cracks and material defects such as dislocations or impurities, very slow crack propagation via kink formation and migration, and chemically activated fracture, where cracks advance under the concerted action of stress and corrosion by chemical species such as oxygen or water.