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Dislocation-based crystal plasticity finite element modelling of polycrystalline material deformation.

机译：基于位错的多晶​​材料变形的晶体塑性有限元建模。

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摘要

The objective of this research is to develop an understanding of the mechanical behavior and dislocation microstructure evolution of copper single and polycrystals, and to delineate the physical and mechanical origins of spatially-localized plastic deformation. Traditional approaches to the study of plastic instabilities have either been based on kinematic considerations, such as finite strain effects and geometric softening, or physics-based concepts. In this study, we develop a framework that combines both approaches. A rate-independent crystal plasticity model was developed to incorporate micromechanics, crystallinity and microstructure into a continuum description of finite strain plasticity. A comprehensive dislocation density model based on rate theory is employed to determine the strain hardening behavior within each plastic slip system for the fcc crystal structure. Finite strain effects and the kinematics of crystal plasticity are coupled with the dislocation-density based model via the hardening matrix in crystal plasticity.;ABAQUS/CAE is employed as a finite element method solver, and several user's subroutines were developed to model fcc crystals with 2 and 12 slip systems. The developed material models are applied to study single and polycrystal deformation behavior of copper. Interfaces between the ABAQUS user's subroutine Umat and the ABAQUS main code are developed to allow further extension of the current method.;The results of the model are first compared to earlier simulations of localized shear bands in a single copper crystal showing the association of the shear band with defects, as illustrated by Asaro. Current simulations for bicrystals indicate that shear band localization initiates at the triple point junction between the two crystals and the free surface. Simulations carried out for polycrystals clearly illustrate the heterogeneous nature of plastic strain, and the corresponding spatial heterogeneity of the mobile dislocation density. The origins of the spatial heterogeneities are essentially geometric, as a result of constraints on grain rotation (finite strain effects), geometric softening due to plastic, unloading of neighboring crystals. The physical origins of plastic instabilities manifest themselves in the coupling between the dislocation densities and the localized kinematically-induced softening.
机译：这项研究的目的是发展对铜单晶和多晶力学行为和位错微观结构演变的理解，并描绘空间局部塑性变形的物理和机械起源。研究塑性不稳定性的传统方法要么基于运动学考虑，例如有限应变效应和几何软化，要么基于物理的概念。在这项研究中，我们开发了一个结合了两种方法的框架。建立了与速率无关的晶体可塑性模型，将微力学，结晶度和微结构纳入有限应变可塑性的连续描述中。基于速率理论的综合位错密度模型用于确定fcc晶体结构在每个塑料滑模系统中的应变硬化行为。通过晶体塑性中的硬化矩阵，将有限应变效应和晶体塑性运动学与基于位错密度的模型相结合。； ABAQUS / CAE被用作有限元方法求解器，并开发了多个用户子程序来模拟具有2和12滑移系统。所开发的材料模型用于研究铜的单晶和多晶变形行为。开发了ABAQUS用户子程序Umat和ABAQUS主代码之间的接口，以允许进一步扩展当前方法;该模型的结果首先与单个铜晶体中局部剪切带的早期模拟进行了比较，显示了剪切的关联如Asaro所示的缺陷带。当前对双晶的模拟表明，剪切带局部化始于两个晶体与自由表面之间的三点连接处。对多晶进行的模拟清楚地说明了塑性应变的异质性，以及相应的移动位错密度的空间异质性。由于晶粒旋转的限制（有限应变效应），塑性导致的几何软化，相邻晶体的卸载，空间异质性的起源基本上是几何的。塑性不稳定性的物理成因表现在位错密度与局部运动诱发的软化之间的耦合上。

著录项

  • 作者

    Liu, Chunlei.;

  • 作者单位

    University of California, Los Angeles.;

  • 授予单位 University of California, Los Angeles.;
  • 学科 Engineering Mechanical.;Engineering Materials Science.
  • 学位 Ph.D.
  • 年度 2006
  • 页码 105 p.
  • 总页数 105
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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