  A computational approach has been developed for analyzing the characteristics
of 3D dislocation substructures generated by the vector-density based continuum
dislocation dynamics (CDD). In this CDD framework, the dislocation density on
the individual slip systems is represented by vector fields with a unique
dislocation line direction at each point in space. The evolution of these
density fields is governed by a set of transport equations coupled with crystal
mechanics. Such a detailed picture of the dislocation system enables mesoscale
plasticity simulations based on dislocation properties. Here, a computational
approach based on streamline construction is proposed to obtain the
characteristics of dislocation substructures generated by CDD. Streamlines are
obtained by travelling along the tangent of the vector density and velocity
fields of the dislocation system, and can be used to construct the dislocation
lines and their paths in the deformed crystal in 3D. As explained in the text,
the streamlines are computed by solving a set of partial differential
equations. Here we use this approach to extract microstructure parameters from
the CDD simulations that are relevant to substructure-sensitive crystal
plasticity models. These parameters include the average mean free path and
mobile dislocation segment length, as well as the dislocation wall volume
fraction, and the corresponding distributions. The results show that both the
mobile dislocation segment length and dislocation mean free path decrease with
the applied strain, which is consistent with the models used in the literature,
and that the mobile dislocation segment length follows a log-normal
distribution.
