The Kantorovich macro-or-mesoscopic refined solution for the heterogeneous functionally gradient material complex structure

Regarding the plate problems, such approximate solutions as Rayleigh-Ritz method, Galerkin method and Levi method are generally employed to solve the problems of the plates fixed and supported on four sides, plates simply supported on four sides or the combination of the two. This paper intends to solve the bending problem of FGM complex structure which is locally fixed and supported by a round revolving axis. It is a triangular structure plate bearing combined loads. The solutions mentione…     

梯度功能材料的断裂准则

基于断裂力学的能量释放率理论 ,研究了平面应变条件下梯度功能材料的Ⅰ ,Ⅱ型复合裂纹问题 .讨论了裂纹尖端附近的应力场和应力强度因子 ,建立了具有一般性的梯度功能材料的断裂准则即能量释放率判据 .     

Method of lines for functionally gradient materials

The method of lines(MOL) for solving the problems of functionally gradient materials(FGMs) was studied. Navier‘s equations for FGMs were derived, and were semi-discretized into a system of ordinary differential equations(ODEs) defined on discrete lines with the finite difference. By solving the system of ODEs, the solutions to the problem can be obtained. An example of three-point bending was given to demonstrate the application of MOL for a crack problem in the FGM. The computational results show that the more accurate results can be obtained with less computational time and resources. The obvious difficulties of numerical method for crack problems in FGMs, such as the effect of material nonhomogeneity and the existence of high gradient stress and strain near a crack tip, can be overcome without additional consideration if this method is adopted.     

Active contours with normally generalized gradient vector flow external force

Gradient vector flow(GVF) is an effective external force for active contours,but its isotropic nature handicaps its performance.The recently proposed gradient vector flow in the normal direction(NGVF) is anisotropic since it only keeps the diffusion along the normal direction of the isophotes;however,it has difficulties forcing a snake into long,thin boundary indentations.In this paper,a novel external force for active contours called normally generalized gradient vector flow(NGGVF) is proposed,which generalizes the NGVF formulation to include two spatially varying weighting functions.Consequently,the proposed NGGVF snake is anisotropic and would improve active contour convergence into long,thin boundary indentations while maintaining other desirable properties of the NGVF snake,such as enlarged capture range,initialization insensitivity and good convergence at concavities.The advantages on synthetic and real images are demonstrated.     

功能梯度材料静态断裂的CGS方法实验研究

利用相干梯度敏感方法对功能梯度材料I型静态断裂特性进行实验研究,并利用有限元软件进行数值模拟.假设材料性能沿裂纹方向分别按两种不同的规律变化:1)弹性模量和密度指数规律变化;2)弹性模量线性变化,密度保持常数.保持泊松比不变,首先推导两种变化规律功能梯度材料I型静态裂纹的相干梯度敏感方法控制方程;然后根据实验结果,提取应力强度因子等断裂参数,分析不同梯度变化规律对材料断裂性能的影响;最后与有限元模拟计算结果相结合,对功能梯度材料I型静态裂尖的K主导区范围进行了分析.     

功能梯度材料的数字散斑相关方法实验研究

利用数字散斑相关方法对功能梯度材料I型静态断裂特性进行实验研究,并利用有限元软件进行数值模拟.首先通过在环氧树脂中添加玻璃微珠,利用重力沉降法制备功能梯度材料试件.为对比材料梯度对静态断裂行为的影响,准备了三种梯度变化规律的试件.然后对功能梯度材料试件进行3点弯曲实验,通过CCD采集试件散斑场,利用数字散斑相关方法计算应力强度因子.通过与有限元模拟结果进行对比,验证了实验结果的正确性.最后分析不同梯度变化规律对材料断裂性能的影响,证明材料弹性梯度对位于弹性模量较小边的静态裂纹具有保护作用.     

梯度功能材料的体积分数和物性系数的研究状况

介绍了国外有关梯度功能材料的体积分数和物性系数问题的研究状况,并对其研究特点进行了评述.     

Effects of the component and fiber gradient distributions on the strength of cement-based composite materials

1　IntroductionTheconceptofthefunctionallygradientmaterial(FGM)wasfirstproposedtwodecadesagobyMasayukietal[1] tohelpthedesignofheat resistantsystemsofspacecraftswhentheytraveledthroughtheastrosphere .Sincethen ,extensiveresearchesandapplicationsofFGMhavebeenconducted ,especiallyonceramicandmetalmaterials[2 6] ,butthestudyonthecement basedfunction allygradientmaterial (CFGM)onlystartedrecently[7] .FGMismadeoftwoormoredistinctmaterialsusingavarietyofadvancedcompositetechniquesanditscompo n…     

广义凸向量最优化问题的对偶理论

本文利用 Hanson-Mond 的一般广义凸性条件,在任意维实赋范线性空间建立了向量最优化问题的对偶理论。     

对称型梯度功能材料的瞬态热应力强度因子

采用摄动法推导出无限大对称型梯度功能材料平板的一维非定常温度场及非定常热应力场的解析表达式 ,并采用权函数法计算了受热冲击的含双边裂纹的对称型梯度功能材料平板的瞬态热应力强度因子 .通过两种Al2 O3 TiC系梯度功能陶瓷平板表面冷却条件下的计算实例并与均质陶瓷材料对比 ,分析了材料的热 物理性能分布规律对瞬态热应力强度因子的影响 ,并提出高抗热震性梯度功能陶瓷的设计原则     

应用Daubechies小波理论求解应力大梯度梁

介绍了采用常规有限元法求解应力大梯度问题的缺点,指出小波理论具有多尺度、多分辨及紧支性等特性,应用小波理论计算应力大梯度问题将明显优于传统有限元法.以求解受集中荷载的平面弯曲梁为例,阐述了采用Daubechies小波理论进行计算时矩阵方程的建立及采用系数转换法施加本质边界条件的过程.分析系数转换法带来的不足,并结合广义变分原理对目前常用的Daubechies小波方法进行改进.通过实际算例中Daubechies小波方法的计算结果与理论解的对比验证应力大梯度问题计算中小波方法的有效性.     

一种新的功能梯度材料实体建模方法

在总结相关建模方法的基础上,提出了一种新的功能梯度材料实体建模方法,即将离散堆积理论运用到形体建模中,同时采用“体积法”在CATIA里很方便地创建离散化的几何模型。功能梯度材料建模基于梯度源理论,选取三维空间中的几何特征作为梯度源和给定材料分布方程,确定实体材料分布信息。为了满足材料建模的需要,将已有的3种布尔运算扩充到6种。论文最后给出了设计实例。     

等效焓降法理论剖析与扩展

根据汽轮机组回热系统的热平衡计算,分析了等效焓降法理论,说明了等效焓降法是以蒸汽初、终参数和蒸汽流量不变,回热系统特征量为常数,且满足小扰动理论为前提条件的回热系统的局部足量求解方法.论述了该方法的使用条件、使用范围和使用价值.将等效焓降法和热偏差法有机结合,推导出扩展的能损分析理论,通过在火电厂实际应用证明,该方法是有效的.     

细观力学能量等效模量方法与微极弹性力学

夹杂多相复合体的能量等效模量介质，是细观力学研究脆性材料损伤的主要方法之一．通过研究细观结构变化的物理和力学过程，引入某种平均化方法寻出材料的宏观性质．从宏观唯象角度引入各阶张量形式的连续场变量研究夹杂复合体的损伤，目前尚属空白．本文将夹杂多相复合体同引入内部结构的微极介质等效，通过微极弹性力学中的应力(σ)、力偶应力张量(m)和Helmholtz自由度密度φ，给出了描述夹杂多相复合体损伤的等效模量解析表达式．将取决于各相几何、物理性质和平均化方法的平均应变柔度张量用与连续分布场张量m相关的柔度张量代替．     

The nonlocal theory solution of a Mode-I crack in functionally graded materials

The behavior of a Mode-I finite crack in functionally graded materials is investigated using the non-local theory. To make the analysis tractable, it is assumed that the shear modulus varies exponentially with coordinate vertical to the crack. The problem in this paper can be solved through the Fourier transform with the help of two pairs of dual integral equations, in which the unknown variables are jumps of dis- placements across crack surfaces. To solve dual integral equations, the jumps of displacements...     

Geometric structure of generalized controlled Hamiltonian systems and its application

The main purpose of this paper is to provide a systematic geometric frame for generalized controlled Hamiltonian systems. The pseudo-Poisson manifold and the co-manifold are proposed as the statespace of the generalized controlled Hamiltonian systems. A Lie group, called N-group, and its Lie algebra, called N-algebra, are introduced for the structure analysis of the systems. Some properties, including spectrum, structure-preservation, etc. are investigated. As an example the theoretical results are applied to power systems. The stabilization of excitation systems is investigated.     

平板结构预应力等效结点荷载计算探讨

目前的预应力平板结构计算模式，对于预应力效应的计算多采用等效荷载法的概念，不适宜进行结构平面布置不规则、预应力束集中布置、有效预应力沿预应力束变化较大等情况下的内力分析计算，探求一种较好的预应力束作用分析模式成为急需解决的问题。本文基于预应力结构两阶段受力思想和有限元分析理论，针对预应力阶段的后张预应力混凝土平板结构，从混凝土体受力分析出发，运用虚功等效原理，推导了预应力束在预应力阶段所产生的等效结点荷载积分表达式，从而为平板结构预应力效应的计算提供了一种新的求解思路。另外从预应力束受力分析出发，运用虚位移原理，并区分有粘结与无粘结情况，提出了另一种形式更为简洁的预应力等效结点荷载积分表达式。     

基于水泥净浆流变性的振动-剪切等效理论

为了分析振动条件下水泥净浆的流变特性,解释水泥净浆流变性模型的转化机制,提出适用于振动条件下水泥净浆流变性分析的振动-剪切等效理论. 根据修正HI理论和回转黏度仪径向分层算法,计算振动条件下回转黏度仪内水泥净浆流场的剪切速率,将振动台正弦振动过程转化为对水泥净浆的剪切过程. 采用自制回转黏度仪,开展20 Hz振动频率下的HI参数标定试验和30 Hz振动频率下的水泥净浆黏度试验. 结果表明,HI参数标定结果与数值计算结果之间的误差约为7%,水泥净浆的试验黏度与数值计算的黏度之间的误差为8%并趋于收敛状态. 增大振动频率,水泥净浆的黏度逐渐减小并达到峰值,流变性模型逐渐由Bingham模型转变为Hershel-Bulkley模型,最后转变为Power-Law模型.     

The non-local theory solution of a Griffith crack in functionally graded materials subjected to the harmonic anti-plane shear waves

In this paper, the dynamic stress field near crack tips in the functionally graded materials subjected to the harmonic anti-plane shear stress waves was investi- gated by means of the non-local theory. The traditional concepts of the non-local theory were extended to solve the fracture problem of functionally graded materials. To make the analysis tractable, it was assumed that the material properties vary exponentially with coordinate parallel to the crack. By use of the Fourier transform, the problem can be solved with the help of a pair of dual integral equations, in which the unknown variable was the displacement on the crack surfaces. To solve the dual integral equations, the displacement on the crack surfaces was expanded in a series of Jacobi polynomials. Unlike the classical elasticity solutions, it is found that no stress singularities are present at crack tips. The non-local elastic solutions yield a finite hoop stress at crack tips, thus allowing us to use the maximum stress as a fracture criterion. The magnitude of the finite dynamic stress field depends on the crack length, the parameter describing the functionally graded materials, the circular frequency of the incident waves and the lattice parameter of materials.     

单自由度平面连杆机构等效转动惯量计算公式

在平面连杆系统动力分析及仿真中,需要对平面连杆机构系统建立等效的动力学模型,其中等效转动惯量是一个很重要的量,因此建立平面连杆机构等效转动惯量的解析计算公式是非常必要的。在系统动能相等的条件下,以质点系动能和刚体绕质心转动动能为基础,引入多余坐标,通过平面连杆机构的非线性稳定的几何约束消去多余速度,导出了以原动件的位移为广义坐标和其他构件的位移为多余坐标表示的等效转动惯量的计算公式,并以一个实例来说明等效转动惯量公式的使用,为平面连杆机构的过渡过程动态仿真提供了理论基础。