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首页> 外文学位 >Formation and stability of dislocation boundaries and cell structures using multiscale discrete dislocation and gradient crystal plasticity.
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Formation and stability of dislocation boundaries and cell structures using multiscale discrete dislocation and gradient crystal plasticity.

机译：使用多尺度离散位错和梯度晶体可塑性形成位错边界和晶胞结构及其稳定性。

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摘要

Dislocation boundaries are an important dislocation structure created during plastic deformation of metals. Since these are formed at the beginning of plastic deformation, they play a vital role in the creation of subsequent microstructural pattern. Considerable research has been directed towards understanding of the behavior of dislocation boundaries. Unfortunately, most of the theoretical work available in open literature considers simplified dislocation boundaries configuration leading to the use of two-dimensional models. In addition, dislocation boundaries are formed as a result of various dislocation motion processes, which are three-dimensional in nature. Therefore in order to gain a better understanding of dislocation boundary behavior, one must perform three-dimensional analysis of experimentally observed dislocation boundaries, which is the main objective of this study.; In this research, the behavior of nearly planar geometrically necessary dislocation boundaries (GNBs) is investigated. The internal dislocation structure of the dislocation boundary is determined using experimentally known dislocation boundary normal and misorientation angle/axis, which is then used to construct the dislocation boundary for a discrete dislocation (DD) analysis. A dislocation boundary constructed in this manner reflects the characteristics of the dislocation boundary in the experiments. The dislocation boundary behavior is investigated using a multi-scale model, which couples discrete dislocation plasticity with finite element. The results are presented for two different dislocation boundaries termed "21" and "10". Comprehensive analysis of a single dislocation boundary is performed to investigate various numerical factors and set guidelines for simulation of such dislocation boundaries. It is shown that the use of plausible model boundary conditions removes the 'hump' observed in the self-stress field of dislocation boundaries of finite size. Next, the interaction behavior of two dislocation boundaries is analyzed, which shows that local stress in the space between dislocation boundaries depends on the separation distance. In addition, results are presented for interaction of a mobile extrinsic dislocation with a dislocation boundary using a quasi-static method and dynamic simulations. Finally, a gradient crystal plasticity model is outlined that incorporates the effect of length scale associated with dislocation boundaries into a continuum model.
机译：位错边界是金属塑性变形过程中产生的重要位错结构。由于它们是在塑性变形开始时形成的，因此它们在随后的微结构图案的产生中起着至关重要的作用。已经进行了大量研究以了解位错边界的行为。不幸的是，公开文献中可用的大多数理论工作都考虑了简化的位错边界配置，从而导致了二维模型的使用。另外，由于各种位错运动过程而形成位错边界，这些位错运动过程本质上是三维的。因此，为了更好地理解位错边界行为，必须对实验观察到的位错边界进行三维分析，这是本研究的主要目的。在这项研究中，研究了几乎平面的几何必要位错边界（GNB）的行为。使用实验已知的位错边界法线和方向错误的角度/轴确定位错边界的内部位错结构，然后将其用于构造位错边界以进行离散位错（DD）分析。以这种方式构造的位错边界反映了实验中位错边界的特征。使用多尺度模型研究位错边界行为，该模型将离散的位错可塑性与有限元耦合。给出了两个不同位错边界的结果，分别称为“ 21”和“ 10”。进行单个位错边界的综合分析以研究各种数值因素并为此类位错边界的模拟设定指导原则。结果表明，使用合理的模型边界条件可以消除在有限尺寸的位错边界的自应力场中观察到的“驼峰”。接下来，分析了两个位错边界的相互作用行为，表明位错边界之间空间中的局部应力取决于分离距离。另外，使用准静态方法和动态模拟，给出了移动外部位错与位错边界相互作用的结果。最后，概述了梯度晶体可塑性模型，该模型将与位错边界相关的长度尺度的影响纳入了连续模型。

著录项

  • 作者

    Khan, Shafique Mohammed Ahmed.;

  • 作者单位

    Washington State University.;

  • 授予单位 Washington State University.;
  • 学科 Engineering Mechanical.; Engineering Materials Science.
  • 学位 Ph.D.
  • 年度 2003
  • 页码 145 p.
  • 总页数 145
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类 机械、仪表工业;工程材料学;
  • 关键词

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