Plastic Behavior of Aluminum and Dislocation Patterning Based on Continuum Dislocation Dynamic (CDD)
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INTRODUCTION
METALLIC and many non-metallic solids exhibit crystal structure. Most crystals exhibit defects and imperfections that can be in the form of point, line, surface or volume type[1–3]; these imperfections are distributed all over the material and considerably affect its properties.[4,5] Dislocations are line defects that move under load and initiate the plastic deformation process.[6] The amount of dislocations inside a specific volume is measured by the dislocation density which is defined as the total length of dislocation lines per volume of grain.[4] Since the amount of dislocations in a unit volume of material, as well as their motion and their interaction with other dislocations (and other defects), affect the material’s properties, clear understanding of their behavior is required to predict the plastic deformation of crystalline structures. Therefore, the microstructure of the material is the key parameter in deformation behavior of metals during plastic flow NAVID KERMANSHAHIMONFARED and IOANNIS MASTORAKOS are with the Department of Mechanical and Aeronautical Engineering, Clarkson University, Potsdam, NY, 13699. Contact e-mail: [email protected] HESAM ASKARI is with the Department of Mechanical Engineering, University of Rochester, Rochester, NY 14627. Manuscript submitted April 10, 2019.
METALLURGICAL AND MATERIALS TRANSACTIONS A
(plastic deformation).[7,8] This understanding can be critical to the design of new alloys and structures with tailored properties resulted by the manipulation of dislocation motion and interaction.[9,10] For this purpose various theoretical frameworks and models have been introduced to study the effect of the dislocation motion on the plastic deformation of metals.[11–17] These models span a variety of applications, time scales, and length scales from the atomic to the macroscale. The atomistic models are focusing on ensemble of individual atoms and their interactions. They are limited to million of atoms that represent small portion of structure due to computational limitation.[18] Unlike the atomistic models, the continuum dislocation dynamics (CDD) frameworks are based on the motion of individual dislocations (gliding and climbing), and on interactions between dislocations of various types considering specific interaction mechanisms[19,20]; because these mechanisms are taking place at the mesoscale, CDD is used to describe dislocation motion at larger length scales.[21,22] In CDD methods, depending on the framework and in order to facilitate the modeling, the dislocation densities are divided into various types such as mobile and immobile dislocations, screw and edge, positive and negative etc.[9,23] The evolution of the dislocation densities is described by a system of nonlinear partial differential equations that includes terms for various dislocation interaction mechanisms.[24–26] For example,
in Walgraef’s model, which is formed on the balanced state of mass and momentum of dislocations, the dislocation populations are divided into mobile and immobile dislocati
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