Stress-Induced Grain Boundary Migration in Polycrystalline Copper

We use three-dimensional (3D) grain-continuum models to study grain boundary migration, treating each grain with anisotropic elastic properties. Grain boundary speeds are computed using a finite element method to calculate differences in strain energy density across grain boundaries. Body-fitted finite element meshes are used. An interface tracking program, PLENTE, is used to develop starting structures and move the grain boundaries based on these speeds. We demonstrate this procedure on textured films consisting of 〈100〉 and 〈111〉 fiber textured film. We also apply the model to a short section of a Cu line embedded in oxide. We conclude with a discussion on the relative impact of different driving forces for grain boundary motion.     

连续体模型-研究大规模电力系统机电动态的一种新方法

随着同步相量测量技术的发展和对电力系统的深入研究,人们认识并观察到电力系统中的功角扰动以远低于光速的速度传播。大规模电力系统的连续体模型突破了对传统认识的局限性,用波动理论这一崭新的视角研究电力系统的机电动态。本文根据经典物理学中矢量场理论,推导出电力系统连续体模型中的非线性波动方程,求出均匀电力系统在平衡点附近的解析解,分析了机电波传播幅度变化的内在机理。最后用一个由64台发电机组成的环形仿真系统,证明了大规模电力系统连续体系机电波模型的正确性。作为一种新的数学模型,连续体系模型能够揭示电力系统机电动态的内在规律。     

一种立方对称晶体结构的唯象连续非线性本构模型及其分析

基于立方对称结构的晶体特点，本文建立一种唯象连续非线性本构模型，推导出一些主要方向如（００１）、（０１１）和（１１１）受单向载荷时的表达式。并对所建模型的适用性进行了分析，指出在较高温度状态时所建模型能较准确地描述Ｎｉ基单晶的非线性变形。     

An anisotropic damage model for tensile fatigue

Fatigue damage in materials is considered to be the effect of material degradation, and the dispersion in fatigue life is attributed to variability in microstructure. This paper presents a numerical model to simulate fatigue damage evolution using continuum damage mechanics to characterize material degradation. An explicit microstructure topology representation is achieved using Voronoi tessellations. Unlike conventional models which use a scalar approximation for damage, this model treats the damage variable as an anisotropic tensor. The model is used to simulate tensile fatigue failure in thin steel specimen. The fatigue life estimations from the model compares well with published experimental results. The results predict a high variability in fatigue life that is characteristic of metals and alloys, as compared with the existing isotropic damage models available in the literature. The model was also used to study the influence of material inhomogeneity on fatigue life dispersion.     

Goal‐oriented adaptivity for linear elastic micromorphic continua based on primal and adjoint consistency analysis

Microscopic considerations are drawing increasing attention for modern simulation techniques. Micromorphic continuum theories, considering micro degrees of freedom, are usually adopted for simulation of localization effects like shear bands. The increased number of degrees of freedom clearly motivates an application of adaptive methods. In this work, the adaptive FEM is tailored for micromorphic elasticity. The proposed adaptive procedure is driven by a goal‐oriented a posteriori error estimator based on duality techniques. For efficient computation of the dual solution, a patch‐based recovery technique is proposed and compared to a reference approach. In order to theoretically ensure optimal convergence order of the proposed adaptive procedure, adjoint consistency of the FE‐discretized solution for the linear elastic micromorphic continua is shown. For illustration, numerical examples are provided. Copyright © 2017 John Wiley & Sons, Ltd.     

A boundary density evolutionary topology optimization of continuum structures with smooth boundaries

Based on the variable density method, this article proposes a boundary density evolutionary topology optimization method. The method uses a material interpolation model without penalization. Combined with the density grading filtering method, an optimal topology with only 0/1 cells can be obtained. Compared with the solid isotropic microstructures with penalization method (SIMP), no penalty factor is required in the material interpolation model; compared with the evolutionary structural optimization method (ESO), intermediate-density elements are allowed in the optimization process, but the concept of gradually removing the low-utilization materials near the boundary in the ESO method is retained. After the optimal result is obtained, the structural boundary element is processed by the level set of nodal strain energy, and the optimization result with smooth boundaries similar to the level set method (LSM) can be obtained. The proposed method has the superiority of the variable density method, and it also combines the advantages of the evolutionary method and the level set method, so which is named as boundary density evolution (BDE) method. The four static and one dynamic optimization examples illustrate the stability and efficiency of the proposed method.     

A stress-influence-function with adaptive strength feature approach for stress constrained continuum topology optimization via small-loop sequential strategy

Recently, the stress-influence-function (SIF) approach is presented for stress constrained continuum topology optimization. The SIF approach provides an alternative for continuum topology optimization with stress constraints. However, the SIF approach is not good at controlling the maximum stress of the elements compared to the conventional approach. In the study, the stress-influence-function with adaptive strength feature (SIF-ASF) approach via small-loop sequential strategy is proposed to achieve better control on the maximum elemental stress. First, the stress constrained continuum topology optimization formulation is given and the SIF approach is briefly introduced. Then the SIF-ASF approach is proposed for stress constrained continuum topology optimization, in which the strength feature in the stress influence function is adjusted in each iterative step of the optimization process. The adjoint-vector based sensitivity analysis to the design variables is further discussed. Three numerical examples are given to illustrate the applicability and validity of the proposed SIF-ASF approach. It is shown that the proposed SIF-ASF approach can achieve better control on the maximum elemental stress than the SIF approach. Moreover, the proposed SIF-ASF approach may obtain a lighter structure than the conventional approach.     

基于CDM的复合材料层合板插层补强强度分析

文章针对复合材料插层补强层合板损伤破坏问题,基于各向异性材料连续介质损伤力学方法,引入材料损伤状态变量对复合材料损伤情况进行描述,建立了复合材料插层补强三维非线性渐进损伤模型;利用该模型对复合材料插层补强层合板的损伤破坏进行了准确预测.重点对补强设计中插层材料铺层比例和补强半径两个设计参数进行了研究,得到了复合材料开口层合板理想的插层材料铺层比例及补强半径范围.     

双瑞利衰落下等增益合并接收系统性能分析

基于双瑞利衰落模型,对等增益合并多支路接收系统的中断特性和平均误符号率性能展开研究.导出了等增益合并输出信噪比n阶矩的封闭表达武,基于Padé逼近原理得到了其相应矩生成函数的近似公式,采用基于矩生成函数的方法得到了系统中断概率和平均误符号率的近似表示武.仿真结果验证了理论方法和数学分析的有效性和准确性.     

常见炸药分子的溶剂化效应

用密度泛函理论（ DFT）和极化连续介质模型（ PCM）研究了7种溶剂对22种常见炸药分子的特征键键长、硝基电荷、偶极矩、溶剂化能及键离解能的影响。结果表明,溶剂能极化炸药分子,改变其电子结构,影响其几何结构和能量。对介电常数为0～10．36的溶剂,随溶剂极性增大,炸药分子的特征键长及溶剂化能减少,而硝基负电荷及偶极矩增加。