Coupled atomistic-mesoscopic model of polycrystalline plasticity
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Coupled atomistic-mesoscopic model of polycrystalline plasticity Fabrizio Cleri* and Gregorio D’Agostino Ente Nuove Tecnologie, Energia e Ambiente (ENEA), Divisione Materiali Centro Ricerche Casaccia, CP 2400, I-00100 Roma, Italy *also with Istituto Nazionale per la Fisica della Materia (INFM), Roma, Italy Alessandra Satta and Luciano Colombo Istituto Nazionale per la Fisica della Materia (INFM), and Dipartimento di Fisica, Università di Cagliari S.P. Monserrato-Sestu, 09057 Monserrato, Cagliari, Italy ABSTRACT We discuss a microstructure evolution framework which couples atomic-level information about extended-defect interactions into a mesoscopic model; the latter, in turn, describes the dy-namic evolution of a statistical population of grain boundaries and dislocations. Atomistic simulations are carried out by means of molecular dynamics simulations on both isolated and interacting dislocations, grain boundaries, triple junctions, microcracks; the reference material for such studies is, at present, Silicon with the Stillinger-Weber potential. The mesoscale model describes the motion of discrete triple junctions (and, consequently, of the continuous network of adjoining grain boundaries) embedded in a continuous medium containing a homogenous, evolving distribution of dislocations. INTRODUCTION The description of microstructural evolution under external forces, e.g. temperature and stress, is a central subject of materials science (see e.g. [1-3]). By definition, materials microstruc-ture comprises any extended defects beyond point-like: line-defects, such as dislocations and disclinations, bidimensional defects, such as grain boundaries and phase boundaries, three-dimensional, such as inclusions, precipitates, voids and microcracks, can occur into different conditions as a function of temperature, stress, strain and strain-rate, and can furthermore transform into each other under the action of both the external forces and the internal driving forces. The macroscopic behavior resulting from such a complex interaction encompasses deformation, recovery and different stages of recrystallization [3]. The first level, i.e., deformation, occurring under several different experimental conditions, is without any doubt the less known. Our knowledge of the deformed state, e.g., after cold working, hot pressing, sintering and so on, is still so poor that most of the conclusions which can be drawn about recovery and recrystallization, and thus about real-world materials microstructure, have a strong parametric dependence on the deformation variables. On the other hand, macroscopic deformation results from a complex interplay of microscopic phenomena under strongly nonequilibrium conditions, a thing which makes any new experiment more likely to add a new problem instead of solving existing ones. Much work is yet to be done also on the theoretical side given that, after the introduction of the concept of dislocation about seventy years ago, we are still lacking a fundamental theory of the plastic response. AA7.6.1
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