Discrete Dislocation Dynamics

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The discrete dislocation dynamics method will be used to gain new insight in the plasticity of small scale specimens by analysing the evolution of dislocation ensembles under different loading conditions. The main focus will be on the role of grain boundaries (GBs) and imposed stress or strain gradients on the emerging dislocation structure. In reporting period 1 of FOR1650, it has been found that the plastic deformation of a GB -- modelled as impenetrable in DDD -- can only be described in a continuum framework assuming a finite and strain dependent grain boundary yield strength. However, it is yet unclear how such a grain boundary yield strength can be formulated. Extensive discrete dislocation dynamics simulations will allow to derive a better understanding of this behaviour by a systematic variation of misorientation and plastic properties (e.g initial dislocation density) of the involved grains. The role of the elastic interaction between dislocations in the neighbouring grains shall be characterized in detail. Furthermore the orientation and microstructure dependence of dislocation multiplication mechanisms within a dislocation network will be explored. Topological and statistical measures shall be developed for quantitatively characterizing dislocation microstructures, while going beyond simple density measures and "junction counting". The expected results will also allow guiding the development of continuum descriptions of plasticity, e.g. the handling of GBs and the key mechanism needed for the formulation of the interaction of slip systems in dislocation continuum theories. For improved computational efficiency a MPI parallelisation of the DDD code shall be realized which would allow simulating poly-crystalline samples.