Dislocation-Induced Internal Stresses

Abstract

Long-range internal stresses (LRIS) are widely suggested to exist in plastically deformed materials as a result of dislocation distribution heterogeneity and polarization. Important examples of plastically induced dislocation microstructures are cell and subgrain walls in monotonically deformed materials and edge-dislocation dipole bundles and walls in cyclically deformed materials. Evidence for internal stresses in dislocation microstructures was observed early and the existence of LRIS is commonly supposed responsible for important properties such as the Bauschinger effect in reversed and cyclic deformation. On the other side, other experiments including dipole separation observations and convergent beam electron diffraction experiments are less supportive of LRIS. This is why we recently revisited the question of LRIS using X-ray microbeam diffraction experiments for oriented monotonically and cyclically deformed Cu single crystals. From synchrotron radiation at the Advanced Photon Source it was possible to determine elastic strains in very small volumes within the dislocation cell interiors, and most recently, within the cell walls. These experiments clearly show the existence of LRIS in the dislocation cell structure albeit, at modest levels. The magnitude and statistical variation of these stresses are detailed, and further explored using dislocation dynamics simulations. Our new results are placed in the context of earlier experiments.