Papers by Keyword: Dislocation Dynamics

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Authors: Juan Daniel Muñoz-Andrade
Abstract: The goal of this work is to describe the cosmic micromechanics connection with irreversible deformation processes in spatially extended polycrystalline systems, where the nature of the crystalline structure of the universe in a relativistic framework at Max Plank scale and Edwin Hubble scale play and important role. In this physical construction by applying the theoretical model of Muñoz-Andrade the activation energy for irreversible deformation processes in spatially extended polycrystalline systems is obtained. Consequently, the main results of this work are analyzed in the context of the unified interpretation of Hubble flow, plastic flow and super plastic flow.
Authors: Masaki Tanaka, Yumi Hoshino, Alexander Hartmaier, Kenji Higashida
Abstract: Two dimensional simulations of discrete dislocation dynamics were carried out to clarify a shielding effect due to dislocations at a crack tip. The configuration of dislocations around the crack tip was calculated under the conditions of mode I tensile load at high temperatures. The stress field around the crack tip due to dislocations was found to be compressive, accommodating mode I stress intensity at the crack tip. In order to experimentally confirm the stress accommodation, infrared photoelastic observation was also performed in a specimen pre-deformed at high temperatures. The experimental result is in good agreement with a simulated infrared photoelastic image derived from the stress field calculated.
Authors: Zhuo Zhuang, Zhan Li Liu, Xiao Chuan You, Y. Guo
Abstract: With the development of material science, especially as MEMS/NEMS are playing a more and more important role in modern engineering, some mechanical behaviors of materials, e.g., fracture, shear instability, need to be investigated from multidisciplinary perspective. The molecular dynamics (MD) simulations are performed on single-crystal copper block under simple shear to investigate the size and strain rate effects on the mechanical responses of face-centered cubic (fcc) metals. It is shown that the yield stress decreases with the specimen size and increases with the strain rate. Based on the theory of dislocation nucleation, a modified power law is proposed to predict the scaling behavior of fcc metals. In the MD simulations with different strain rates, a critical strain rate exists for each single-crystal copper block of given size, below which the yield stress is nearly insensitive to the strain rate. A hyper-surface is therefore formulated to describe the combined size and strain rate effects on the plastic yield stress of fcc metals.
Authors: Ichiro Yonenaga, Kazuo Nakajima
Abstract: Deformation Characteristics in High-Purity Si Crystals Subjected to Bending Tests Were Studied. Specimens Were Deformed at the Temperatures Higher than 800°C without Brittle Fracture under Application of a High Stress up to 350 Mpa. Stress-Strain Behavior and the Yield Stresses Depend on the Temperature and the Strain Rate. The Results Were Discussed in Terms of the Dislocation Dynamics and Dislocation Mobility to Provide Fundamental Knowledge for Wafer Manufacturing.
Authors: Akiyuki Takahashi, Naoki Soneda, A. Nomoto, G. Yagawa
Abstract: This paper describes dislocation dynamics simulation of grain boundary effects on yield behavior of metals, such as α-Fe bcc metal. Since the stress field arising from the grain boundary has not been well understood yet, the geometrical effect of the grain boundary can be handled in the simulation by the use of rigid boundary condition. The dislocation pileups can be observed near the grain boundary in the result of the DD simulation. And the yield stress in the crystal having the grain boundary becomes larger than that in the crystal having free surface. This result tells us that the Hall-Petch effect can actually describe well the effects of the grain boundary on the yield behavior of metals.
Authors: Karri V. Mani Krishna, Prita Pant
Abstract: Dislocation Dynamics (DD) simulations are used to study the evolution of a pre-specified dislocation structure under applied stresses and imposed boundary conditions. These simulations can handle realistic dislocation densities ranging from 1010 to 1014 m-2, and hence can be used to model plastic deformation and strain hardening in metals. In this paper we introduce the basic concepts of DD simulations and then present results from simulations in thin copper films and in bulk zirconium. In both cases, the effect of orientation on deformation behaviour is investigated. For the thin film simulations, rigid boundary conditions are used at film-substrate and film-passivation interfaces leading to dislocation accumulation, while periodic boundaries are used for bulk grains of Zr. We show that there is a clear correlation between strain hardening rate and the rate of increase of dislocation density.
Authors: W. Pantleon
Abstract: Plastic deformation creates orientation differences in grains of originally uniform orientation. These disorientations are caused by a local excess of dislocations having the same sign of the Burgers vector. Their increase with increasing plastic strain is modeled by dislocation dynamics taking into account different storage mechanisms. The predicted average disorientation angles across different types of boundaries are in close agreement with experimental data for small and moderate plastic strains. At large plastic strains after severe plastic deformation, saturation of the measured average disorientation angle is observed. This saturation is explained as an immediate consequence of the restriction of experimentally measured disorientation angles to angles below a certain maximum value imposed by crystalline symmetry. Taking into account the restrictions from crystalline symmetry for modeled disorientation angles does not only lead to an excellent agreement with experimental findings on Ni after high pressure torsion, but also rationalizes the work-hardening behavior at large plastic strains as well as a saturation of the flow stress.
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