An experimental study of the formation of typical dislocation patterns in polycrystalline copper under cyclic shear

The typical slip patterns and dislocation substructures of polycrystalline copper under cyclic torsion were experimentally investigated. The cyclic stress–strain curve of the material consisted of three regions, resembling those of single crystal copper oriented for single slip. During the formation of persistent slip bands, cross slip bands between primary slip bands were often observed. Under cyclic torsion at a high shear strain amplitude, cross slip between slip bands of each slip system was an important process for the collapse of dislocation tangles into dislocation cell walls. During the transient stage of the formation of dislocation cells, the stress amplitude was inversely proportional to the average diameter of dislocation cells. This relationship is identical to that between the saturated stress magnitude and the corresponding dislocation cell size. The formation of typical dislocation patterns in copper under cyclic loading is closely associated with cross slip of screw dislocations.