Dislocation Cellular Structures

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This is a fundamental study of the role of cellular dislocation structures in the deformation and fracture of materials. It is an outgrowth of previous work on the fundamental mechanisms controlling the steady-state response of cellular dislocation structures produced by fatigue. Since dislocation cellular microstructures and their behaviors are archetypical of the inhomogeneous structures and inhomogeneous behaviors that characterize the deformation of many ductile crystalline materials, the scope of this work is broadened to study dislocation cellular microstructures as phenomena. From the theoretical point of view, several issues are addressed, such as internal stress development, the stabilizing forces that lead to a dynamic steady state, the evolution of cell structures from restricted random dislocation activity, the motion of cell walls, the detailed dislocation mechanisms for slip and dynamic recovery and the onset of instabilities that lead to fracture. Experimentally, this project addresses two of what are believed to be the most significant issues related to cell structures that can be settled experimentally, namely the effects of deformation cell structures (or their absence) in fracture toughness and the effects of partial (or recovery) anneals on the behavior of isothermally formed cellular dislocation structures. The former will be very valuable to the fracture community and its ongoing examination of the shielding concept, while the latter will address the contribution of vacancies and internal stresses to the observed mechanical response of fatigued metals.