塑性梯度体元及应变局部化启动机制分析

利用代表性体元可较好地反映出并非理想连续均匀的岩土介质破坏前强度和变形行为。但当材料出现高的应变梯度(应变局部化)时,在体元上的应力、应变呈现高次非线性变化,代表性体元不能如实地反映出介质的力学性能。提出一种可包含局部化变形的研究基元——塑性梯度体元(Plasticity Gradient Volume Element),塑性应变在其内可用微分形式表达。该体元不但可反映介质的平均力学响应,而且可反映应变呈高次非线性变化时的影响。随着硬(软)化模量从正值变为负值,变形模式将由均匀变形模式变为局部化变形模式,这就是应变局部化的启动机制。

弥散型核燃料元件热应力的计算模拟

针对弥散型燃料板的具体形状,选择了一种能够反映其实际变形特征的三维代表性体积单元作为研究对象;利用有限元法对其热力耦合行为进行了弹塑性分析,研究了热应力在燃料和基体中的分布特征.

构造上正交各向异性半球形凸起凹凸板等效刚度研究

根据半球形凹凸板周期性将其划分得到代表性体元结构.首先研究代表性体元的刚度特性,利用变形等效原理、均质化和刚度组合法得到半球形凹凸板的等效刚度.然后将得到的三个主向刚度代入四边简支板Navier解中求解板中心挠度.通过有限元数值模拟解和Navier解进行对比分析,从而验证该文得到的主向刚度的准确性.然后讨论了代表性体元的材料尺寸对所得等效刚度的影响.随着代表性体元边长与凸起半径的比值逐渐增大,所得结果精度越来越高,且等效刚度公式适用于不同厚度的半球形凹凸板.最后给出了较为简洁的工程应用公式,并给出了凸起半径的近似取值范围和工程应用算例.

纤维增强复合材料模量细观分析方法探讨

细观力学采用代表性体元（RVE）模型分析长纤维增强复合材料的性能参数E1、E2和G12,但传统的推导过程偏离了原本的RVE模型,纤维比（Volume Fraction）也被曲解。本文严格遵循典型RVE模型和纤维比定义,对复合材料性能参数进行了推导,提高了结果精度,与实验结果相比更为一致。

Calculation of Strain Amplification Matrix for Strain Invariant Failure Theory Based on Representative Volume Element Models with Periodical Boundary Condition

Strain invariant failure theory (SIFT) is a micro-mechanics-based failure theory for multi-scale failure analysis of composite materials originally proposed by Gosse and Christensen. In this paper, the approach for obtaining strain amplification matrix which is a key step for the execution of SIFT is improved by adopting representative volume element (RVE) finite element models considering periodical boundary condition, based on which more actual deformation mode is reflected. The deformation modes and strain data at the characteristic points of the centroid cell of multi-cell RVE model are analyzed and taken as a reference. It can be concluded that more reasonable deformation mode and relationship between the micro-mechanical and macro-mechanical strain states are obtained by employing the new model. Finally, numerical examples are provided to illustrate the determination of strain amplification factors within the RVEs considering periodical boundary condition at the characteristic points. © 2017, Shanghai Jiaotong University and Springer-Verlag GmbH Germany.