RANDOM MICROSTRUCTURE FINITE ELEMENT METHOD FOR EFFECTIVE NONLINEAR PROPERTIES OF COMPOSITE MATERIALS

Some theoretical methods have been reported to deal with nonlinear problems of composite materials but the accuracy is not so good. In the meantime, a lot of nonlinear problems are difficult to be managed by the theoretical methods. The present study aims to use the de veloped method, the random microstrtucture finite element method, to deal with these nonlinear problems. In this paper, the random microstructure finite element method is used to deal with all three kinds of nonlinear property problems of composite materials. The analyzed results suggest that the influences of the nonlinear phenomena on the effective properties of composite materials are significant and the random microstructure finite element method is an efficient tool to investigate the nonlinear problems.     

Stochastic homogenization method for heterogeneous materials under finite deformation on thermoelasticity

Stochastic homogenization of heterogeneous materials is addressed in the context of thermoelasticity at finite deformation, where the uncertainty in the microstructure is fully considered. The stochastic homogenization in finite thermoelasticity is presented by the multi-scale finite element combined with the Monte-carlo method, and the macroscopically random effective mechanic and thermal properties are solved by using a two-step technique. The numerical characteristics of random effective properties such as stress tensor, heat flux tensor, deformation gradient are then derived. Finally, the feasibility of the method proposed in this work is validated with a numerical example, in which the mean values and the coefficient of variations of random effective quantities under different correlative and boundary conditions are obtained. The distributions of random effective quantities within a representative volume element under different correlative and boundary conditions are also discussed. Obviously, the randomness and correlation existing in the microstructure are not neglected during the process of homogenization of heterogeneous materials under finite deformation.     

一种三维线弹性随机数值均化方法

对小变形下具有随机微观结构非均质材料的数值均化问题进行了研究.当考虑材料微观结构形态、各组分性质的随机性及相关性时,基于多尺度有限元方法和蒙特卡罗法,建立了非均质材料的随机均化模型.求出了不同边界条件下的随机有效量及其数字特征值以及有效量之间所具有的相关性.考察了随机微观结构参数对随机有效量以及表征体积单元中应力分布的影响.结果表明,在分析非均质材料的宏观有效力学性质时,考虑材料微观结构中客观存在的随机性和相关性非常重要.     

周期性复合材料热力耦合性能的多尺度方法

基于多尺度方法预报了周期性复合材料的热传导系数、弹性模量和热膨胀系数.针对复合材料热力耦合问题,分别引入了细观和宏观两种尺度坐标描述细观单胞的非均匀化构造和宏观均匀化结构,利用小参数摄动展开技术,建立了复合材料内部温度场和位移场的多尺度表达式,给出了复合材料有效热传导系数、有效刚度系数和有效热膨胀系数的均匀化方程.利用有限元数值模拟分析了夹杂百分含量、形状、排列方式以及间距的变化对复合材料有效性能的影响.     

基于单胞数字化模型的三维编织复合材料本构关系数值模拟

在渐近均匀化理论基础上，确立了基于单胞数字化模型的复合材料宏观等效弹性性能的三维数值分析方法（DCB—FEA）．该方法采用三维光栅化技术将三维单胞模型转化为三维光栅图形（数字化模型），并将光栅图形直接转化为三维有限元求解网格，产生的离散单元具有相同的几何尺寸和规则的形状，单元刚度矩阵的数量将减少为单胞材料的个数．此外，单胞数字化模型仅需记录每个离散单元的材料种类，其他参数如单元节点编号、节点坐标等均可在求解过程中自动生成，周期性边界条件也可以自动施加．随着分辨率的提高，单胞数字化模型将产生更多数量的单元，特别是对于三维单胞模型，集成整体刚度矩阵时需要大量的计算机内存．采用基于Element-by-element策略的预处理共轭梯度法（EBE—PCG），有限元方程的求解在单元级上进行，避免了整体刚度矩阵的集成．通过对三维编织复合材料的线弹性本构关系的数值模拟，表明该方法可得到较为准确的复合材料等效模量。     

一种快速生成三维混凝土骨料模型的混合实现方法

三维随机骨料混凝土模型是由骨料、砂浆基体以及界面层组成的三相复合材料,基于Fortran和ANSYS软件提出了一种快速生成含高体分比球形骨料混凝土模型的混合实现方法,并在此基础上生成三维椭球形骨料（卵石）模型、凸多面体骨料（碎石）模型以及混合模型。算例结果表明,这种新方法可以快速生成三级配球形颗粒混凝土模型所需的骨料数据,相应的骨料投放含量能达到65%左右。混合方法可将骨料颗粒和界面层分离开来,在有限元网格剖分时避免了复杂的单元属性判别。通过对椭球形骨料模型和凸多面体骨料模型的有限元数值模拟,进一步验证了该混合方法的有效性。     

含缺陷三维编织复合材料有效性能研究

本文研究了含缺陷情况下的一种三维编织材料的有效力学性能.本文构建了该三维编织复合材料的单胞模型,并采用基于非均匀单元的有限元方法计算了该材料单胞的应力分布.得出了该材料的模量和泊松比等有效力学性能参数,并与用相同方法得出的不含缺陷情况对应的结果进行了比较.研究表明,本文采用的方法对于具有复杂材料分布特征且含有缺陷的三维编织复合材料的力学性能分析非常有效.数值计算结果说明,三维编织材料中的缺陷使得材料整体的力学属性有一定的降低,但是缺陷对各有效力学属性分量的影响程度不同.     

秸秆混凝土-薄壁型钢组合墙体的抗侧力有限元分析

秸秆混凝土-薄壁型钢组合墙体是一种新型组合墙,在保温、阻燃、吸声等方面有着优越的性能．通过ABAQUS大型通用有限元软件建立了一系列不同构造形式的秸秆混凝土-薄壁型钢组合墙体的有限元模型,并根据真实实验的方法模拟了加载和施加边界条件．在分析模型水平承载力和延性的基础上,提出了较为合理的结构构造措施．     

随机FG-CNTRC结构的动力特性分析

为考查功能梯度碳纳米管增强复合材料结构中组分材料物理参数及组分分布随机性对结构固有频率的影响,采用高阶剪切变形理论及广义混合律建立了碳纳米管在不同排布方式下梁结构的有限元动力学模型;运用一阶摄动法引入随机变量参数,建立了随机有限元模型,确定了结构固有频率数字特征与随机组分材料物理参数及组分分布数字特征之间的关系。结果表明,组分材料物理参数随机性对结构固有频率分散性的贡献远大于组分分布随机性的贡献;随着碳纳米管体积分数的增加,碳纳米管X型功能梯度排布下结构固有频率的分散性由衰减转为迅速增加,O型功能梯度排布下结构固有频率分散性仍处于衰减状态。     

Dynamic characteristics analysis for the random FGM beam

The uncertainty in effective physical properties is inherent since the manufacturing and fabrication processes of FGM (Functionally Graded Materials) are extremely complex. Based on the high-order shear deformation theory, the finite element model is developed for the FGM beam with material properties varying in the axial direction, taking into account the shear deformation. Using the moment method of the random function, the statistics of dynamic characteristics for the FGM beam is calculated, and the effect of random constituent material properties on the dynamic characteristics for the FGM beam is systemically investigated in the case of different volume fraction indexes. The Monte-Carlo method is used to verify the presented method. Numerical results show the dominant effect of the constituent volume fraction index on the dispersion in dynamic characteristics, and the dispersion in modal frequencies becomes higher when more material properties are considered random, and the dispersion in mode shapes depends mainly on the randomness of constituent material mass densities, while the volume fraction index and random elastic modulus of constituent materials have little influence on mode shapes.     

Stochastic homogenized thermal properties of composites with an uncertain microstructure

Random homogenization analysis of the effective thermal properties of a three-dimensional composite material with unidirectional fibers is presented by combining the equivalent inclusion method with the Random Factor Method (RFM). The randomness of the micro-structural morphology and constituent material properties as well as the correlation among these random parameters are completely accounted for, and stochastic effective thermal properties as thermal expansion coefficients as well as their correlation are then found. Results from the RFM and the Monte-Carlo Method (MCM) are compared. The impact of randomness and correlation of the micro-structural parameters on the random homogenized results is revealed by two methods simultaneously, with some important conclusions obtained.     

具随机刚度梁结构的重特征值计算

利用一种新的方法来研究具随机刚度梁结构的重特征值问题。将材料物理量的随机场扩展为K．L（Karhtmen-Loeve）正交展式，运用矩阵技巧处理重特征值对应的特征向量，采用二阶收敛的非正交多项式展开式表示梁结构的重特征值和特征向量，建立了类似于摄动法的一系列确定性的递推方程，求解这些递推方程，得到了重特征值的均值和均方差。悬臂、简支和固支梁的算例表明：递推随机有限元法的结果能在较宽的随机涨落范围内较好地逼近蒙特卡罗模拟法的结果，而且相对于蒙特卡罗模拟法而言可以节省大量计算时间。     

二维复合材料微结构的力学响应计算

复合材料的力学响应数值计算对于多元多向异质体材料微结构的“性能导向型”设计、材料微结构失效的评估与预测具有重要的意义。利用自主开发的材料微观组织结构仿真软件ProDesign构造出二维复合材料微结构的代表性体积单元,通过C语言、Python脚本混合编程的方式,实现对商业有限元软件ABAQUS前处理的二次开发,使之用于复合材料微结构几何模型的建立、材料属性与晶粒取向的赋值、边界条件的定义以及有限元网格的划分,从而有效地实现二维复合材料微结构的细观应力响应计算。     

Nonlinear finite element analysis of steel-concrete composite beams

Design criteria proposed by presentcodes for steel-concrete composite beams are required to satisfy bothultimate and serviceability limit states. To check thelatter, a correct assessment of creep and shrinkageeffects on stress and deflection response is very impor-tant. If the internal force redistribution caused byshrinkage and creep of concrete is not taken into fullconsideration, normal use and safety of the structuremay be affected.The adverse effect of shrinkage and creep in con-crete on …     

Design and Synthesis of Ti-ZrO2 Functionally Graded Materials

Functionally graded materials (FGMs) based on titanium-zirconia system have been prepared by powder metallurgical method. The graded interlayer number and the compositional distribution have been designed by elastic finite element method. The inierfacial microstructure between layers, the combining state of phases between Ti and ZrO2 have been investigated by means of XRD (X-ray dif fraction), SEM (scanning electron microscope), EDS (energy dispersive spectrometer) and so on. The co-existing region of Ti and ZrO2 has been determined by thermodynamic calculation to control the sintering atmosphere. The experimental results show that the joint between Ti and ZrO2 phases is physical in this composite and ZrO2, mainly exists as tetragonal phase. The microstructure of Ti-ZrO2, system FGM exhibits a transition from a zirconia particle dispersion in a titanium matrix to an inverse dispersion of titanium in zirconia. The gradient structure of titanium and zirconia can relieve thermal stress.     

钢混凝土组合梁-钢管混凝土柱节点性能

为了研究钢混凝土组合梁-钢管混凝土柱节点的力学性能和半刚性特性,制作了4个比例为1∶3的节点模型进行试验,借助有限元分析软件ABAQUS建立了节点的有限元模型进行数值计算,分别进行了试验结果与数值计算的相应测点的应变、位移等结果的对比分析.通过试验与数值计算彼此校核,得到了与试验相符的有限元模型.在此模型的基础上,建立了该组合梁柱节点只含几何参数的相对弯矩-转角曲线模型.     

基于细观层次的混凝土抗压强度与尺寸效应的数值模拟

为了实现混凝土试件抗压强度与尺寸效应的仿真计算分析,在细观尺度下,把混凝土看作是由砂浆、粘结带和骨料组成的三相复合材料,细观尺度下的各相物理力学参数都以试验数据为依据,用随机骨料模型代表混凝土细观结构,利用有限元法和混凝土细观力学的本构关系,借助于计算机强大的运算能力,对混凝土复杂的力学行为进行数值模拟.通过计算发现:...     

基于计算均匀化的夹杂颗粒复合材料参数研究

夹杂颗粒复合材料分布形态各异,为确定其力学参数,基于计算均匀化方法,结合随机周期复合材料模型生成算法,提出了一种由表征单元体计算夹杂颗粒复合材料弹性模量的方法,研究了夹杂颗粒分布形态、尺寸和含量对复合材料力学参数的影响。复合材料在颗粒随机分布时表现为各向同性,在颗粒沿一定方向分布时表现为各向异性;复合材料力学参数随单元体尺寸增大逐渐稳定;弹性模量随颗粒含量增加而增大,泊松比随颗粒含量增加而减小。结果表明计算均匀化是研究复合材料力学参数的有效方法。     

钢筋混凝土叠合结构二次受力过程数值分析

二阶段制造和二次受力是叠合结构的关键特征。基于ABAQUS软件,考虑钢筋和混凝土材料本构关系的非线性,定义了联结单元分析钢筋与混凝土之间的粘结滑移关系,确定了切向弹簧单元和主、被动接触表面分析新旧混凝土叠合面之间的粘结滑移关系,通过初始条件定义施加预应力形成初始应力场,引入生死单元模拟叠合结构的二阶段制造和二次受力过程。通过数值分析,验证有限元分析方法的正确性和可靠性,为叠合结构在实际工程中的应用以及其有限元分析提供参考。     

热连轧带钢层流冷却过程温度场模拟

轧后冷却过程中,卷取温度对带钢最终的微观组织和力学性能有重要影响。针对带钢轧后的层流冷却过程,分别采用有限差分法和有限元法,建立了带钢厚度方向的温度场模型,并将模型计算值与实测值进行对比。结果表明,两种方法建立的模型均能较准确地反映层流冷却过程中带钢的瞬态温度分布,为进一步分析带钢的微观组织转变和力学性能提供了依据。