Formation of fragments with medium-angle boundaries in shear bands: Computer simulation

The conditions for the formation of fragments with medium-angle boundaries in shear bands are analyzed using computer simulation. It is shown that the main condition for the transformation of weakly disoriented dislocation structures into a fragmented structure is the suppression of active plastic deformation in a subgrain by the elastic fields of disclinations appearing at subgrain boundary junctions as a result of mismatch of plastic rotations in individual subgrain boundaries. Under these conditions, during continued straining in the surrounding matrix, such a subgrain behaves as an undeformed inclusion and experiences a crystallographic rotation. The disorientation of the subgrain continuously increases, thereby transforming initial small-angle dislocation boundaries into medium-angle and (in the limit) large-angle boundaries.