CDD as a Mesoscopic Field Theory: Dynamic Closure and Multiphysics Extension

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CDD as developed in the previous reporting period is a mesoscopic field theory which describes dislocation microstructure evolution in terms of density-like field variables. Due to its relations with the classical continuum theory of dislocations, CDD gives natural access to mesoscopic internal stresses above the single-dislocation scale. At the same time, the theory requires dynamic closure relationships which express the local dislocation velocities as nonlinear and in general non-local functionals of the dislocation fields. In physical terms, these closure relationships provide an averaged representation of the interactions of individual dislocations in a continuum setting.The first line of research pursued in the present project uses an entirely novel approach to the problem of dynamic closure, by departing from commonly used phenomenological approximations and using instead a data-driven research paradigm to parameterise generic nonlinear functions on the basis of data extracted from large-scale discrete dislocation dynamics simulations.The second line of research in this project will bridge the gap between CDD and experiments and demonstrate direct technological relevance of our model: coupling CDD with other mesoscopic field theories in the sense of a multiphysics approach allows e.g. to predict and analyze the coupled evolution of defect and phase microstructures in advanced alloy systems. This will be demonstrated for the coupling of CDD with a phase field approach in order to describe the coupled stress-driven dynamics of dislocation creep and directional coarsening in gamma/gamma´ alloys.