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MM: Fachverband Metall- und Materialphysik

MM 62: Topical Session: Fundamentals of Fracture - Stochastic Aspects

MM 62.4: Vortrag

Donnerstag, 14. März 2013, 18:15–18:30, H4

Thermally Activated Fluctuating Dynamics of Dislocations in a Low-Stress Zone — •Thomas Swinburne — EURATOM/CCFE Fusion Association, OX14 3DB — Department of Physics, Imperial College London, SW7 2AZ

A crack is an intense dislocation source, and the propagation of the crack is controlled by the mobile dislocations forming the atmosphere extending into the far-field low stress zone. The mobility of dislocations is believed to control brittle to ductile transition [Hirsch, Roberts and Samuels 1989, Hartmaier and Gumbsch 1999].

To explore the transition from brittle to ductile fracture it thus becomes essential to investigate dislocation mobility under vanishing applied stress, a regime typically considered inaccessible to atomistic simulation of bcc metals due to the kink limited motion of screw dislocations. This is overcome through specially adapted large-scale atomistic simulations which enforce the existence of individual kinks on a dislocation line. The temperature dependence of the resultant kink motion contradicts decades of theoretical work and leads to new conclusions on dislocation friction.

A stochastic line model is capable of quantitatively capturing the diverse range of temperature dependent effects seen in atomistic simulation providing the line is crystallographically discrete, introducing a new length scale into thermally activated plasticity. The model, fully parametrised from atomistic simulation, is used to predict the thermally activated response of mobile dislocations to vanishing applied stress.