Ice crystals are interesting model materials for 3D4 modelling: it is easy to build large single crystals and plasticity is mostly confined in the basal slip systems of the HCP structure.
Here, the simulation box is taken as a cylinder with an axis colinear to the c direction of the HCP structure. A torsion momentum is applied around the c axis. Screw dislocations are shearing the crystal from the external radius, where the stress is the highest, towards the symmetry axis. A regular dislocation arrangement is observed with a regular spaced array : a pure torsion boundary. The number of dislocation lines on the 3 activated slip systems is directly related to the applied momentum.