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Over the past decades, discrete dislocation dynamics simulations have been shown to reliably predict the evolution of dislocation microstructures for micrometer-sized metallic samples. Such simulations provide insight into the governing deformation mechanisms and the interplay between different physical phenomena such as dislocation reactions or cross-slip. This work is focused on a detailed analysis of the influence of the cross-slip on the evolution of dislocation systems. A tailored data mining strategy using the 'discrete-to-continuous (D2C) framework' allows to quantify differences and to quantitatively compare dislocation structures. We analyze the quantitative effects of the cross-slip on the microstructure in the course of a tensile test and a subsequent relaxation to present the role of cross-slip in the microstructure evolution. The precision of the extracted quantitative information using D2C strongly depends on the resolution of the domain averaging. We also analyze how the resolution of the averaging influences the distribution of total dislocation density and curvature fields of the specimen. Our analyzes are important approaches for interpreting the resulting structures calculated by dislocation dynamics simulations. [ABSTRACT FROM AUTHOR]

Dislocation junctions are considered to control the hardening behavior of crystalline materials during plastic deformation. Here the influence of the glissile junction on the plastic deformation of microscale samples is investigated, based on discrete dislocation dynamics simulation results. It is found that with increasing dislocation density ρ , sample size d , which can be collapsed into a single dimensionless parameter d ρ , and an increasing number of activated slip systems due to different global crystallographic orientations, the glissile junction forms frequently and can bow out easily, acting as an effective source. The resulting new dislocations are mobile and contribute to the macroscopic plastic deformation on the order of 30–60%. In the size regime from 0.5 to 2 μm and dislocation densities in the range of 10 12 – 10 14 m - 2 , the glissile junction is therefore an important source for generating mobile dislocation density. Furthermore a significant correlation between stress drops and activity of dislocations originating from glissile junctions is found. A rate formulation is proposed to include these findings in crystal plasticity or continuum dislocation density frameworks. [ABSTRACT FROM AUTHOR]

This review examines the size effects observed in the mechanical strength of thin metal films and small samples such as single-crystalline pillars, whiskers, and wires. Experimental results from mechanical testing and electron microscopy studies, as well as recent insights from discrete dislocation dynamics simulations, are presented. The size dependency of deformation may be separated into three regimes: the nanometer regime of roughly 100 nm and below, an intermediate regime between 100 nm and approximately 1 μm, and a bulk-like regime. We argue that there is no scaling law with one universal power-law exponent encompassing the entire range. Instead, there are a number of different mechanisms and underlying effects, e.g., the initial dislocation microstructure or loading conditions. The complex interaction of these mechanisms leads to the typically observed scaling behavior. [ABSTRACT FROM AUTHOR]

Abstract: 3D finite element simulations of 9-grain multicrystalline aggregates are performed within the framework of the classical continuum crystal plasticity and discrete dislocation dynamics. The results are processed in a statistical way by ensemble averaging. The comparison is made at three levels: macroscopic stress–strain curves, average stress values per grain, local values of stress and plastic strain. The comparison shows that some similarities are observed in the stress and strain distributions in both simulations approaches. But there are also large discrepancies caused by the discrete nature of plasticity in DDD. The DDD simulations provide higher stress levels in the aggregate due to the small number of dislocation sources and to the stress field induced by individual dislocations. [Copyright &y& Elsevier]

The strength and hardening of metallic materials are dictated by the motion and interactions of dislocations. Individual dislocations intersect, react, and frequently form junctions, defining a defect topology that is the basis of subsequent deformation. While immobilized dislocation locks are intuitively considered as potent strengthening structures, simulations suggest that glissile reactions are a predominant contributor to hardening among the four types of dislocation reactions in face-centered cubic crystals, even though the resulting dislocations are inherently mobile. To date, the prevailing understanding of glissile reactions has been primarily based on classical geometric models of perfect dislocations and simulations thereof. Understandings of the reaction pathways and detailed experimental characterization of glissile reactions are lacking, leaving the potential topological variations shrouded in mystery. This study details molecular dynamics simulations of glissile reaction involving dissociated partial dislocations, and the direct experimental characterization of the dislocation configurations resulting from glissile reactions in deformed pure aluminum using transmission electron microscopy. The experimentally-determined structure was reconstructed in 3D and parametrically studied in discrete dislocation dynamics simulations, revealing varying topological evolutions under different loading conditions. Further statistical analyses on an ensemble of simulated dislocations revealed the essential role of stress states and cross-slip in affecting the probability of glissile reaction and the fraction of mobile dislocation nodes. These findings point to avenues for the development of dislocation-based constitutive theories of plasticity. [Display omitted] [ABSTRACT FROM AUTHOR]