高体积分数颗粒增强复合材料有效线性与非线性介电性质的研究

基于两球相互作用的近似解,提出了一种解析方法来预测颗粒增强复合材料的线性有效介电性质,该方法可以应用于颗粒体积分数较高(可达50%)的情况．利用割线方法还研究了该类复合材料的非线性有效性质．结果表明当外加电场较弱时该文提出的方法与Stroud和Hui的方法比较接近,当外场较强时与Yu和Hui的方法一致．     

具有非均匀界面相的颗粒和纤维增强复合材料弹性静力学问题的解析解

通过将以位移表示的平衡方程转化为黎卡提方程,得到了具有非均匀界面相的颗粒和纤维增强复合材料非均匀界面相内弹性场的解析解·　所得的解析解是弹性模量呈幂次方变化的非均匀界面相解的通用形式·　任意给定1个幂指数,可以得到具有非均匀界面相的颗粒和纤维增强复合材料体积模量的解析表达式·　通过改变幂指数及幂次方项的系数,此解析解可适用于具有多种不同性质的非均匀界面相·　结果表明:界面相模量和厚度对复合材料模量有很大的影响,当界面相存在时,粒子将出现一种"尺寸效应"·     

颗粒增强复合材料热应力分析的双层嵌套模型

建立了一个把增强颗粒球和基体空心球嵌入等效复合介质空腔中的“双层嵌套模型”,研究了颗粒增强材料自高温冷却下来时,不同相中热应力的分布特点。推出了热应力在弹性和弹塑性状态的各种表达式。研究表明,随着温度降低,增强体受到压应力,基体材料中存在的静水应力为拉应力。温度继续下降,将出现自增强颗粒与基体界面向外扩展的屈服区。随增强相体积分数增大,增强颗粒受到的压应力和基体中的静水拉应力减小,增强颗粒与基体界面屈服的起始温差增大,而基体材料全面屈服的温差却减小。     

考虑基体粘弹性与介电弛豫的铁电复合材料的本构模型*——Ⅰ.理论

基于细观力学方法和Laplace变换 ,将仅适用于基体为线弹性和线性介电性的铁电复合材料的本构模型推广至基体为粘弹性和介电弛豫情况 ,建立了考虑基体粘弹性和介电弛豫的铁电复合材料的本构模型 .     

颗粒增强复合材料的几何模型数值模拟方法研究

为了在细观层次上模拟混凝土和土石混合体等颗粒增强复合材料,假设颗粒为凸多面体.首先研究由随机八面体随机变形得到任意凸多面体及其参数方程的方法,然后研究凸多面体内部与外部的判定条件、点到多面体的距离和两多面体之间距离的计算方法,从而得到了一个生成具有大量多面体随机分布区域的方法.为了提高模拟区域中多面体的含量,还给出了下降算法.实验表明：可以按二级配生成多面体含量达35%（体积比）的模拟区域,为从细观层次研究混凝土、土石混合体等颗粒增强复合材料,提供了创建几何模型的方法.     

基于杂交应力元法的颗粒增强复合材料Monte-Carlo模拟

杂交应力元假设的高阶应力场可以用较疏的网格获得较高的计算精度.采用四叉树网格离散非均质计算域,四叉树杂交应力单元悬挂节点的位移协调条件自动满足,且得益于单元类型数量有限,单元刚度矩阵可以预计算,以便在实际计算时直接读取调用,大幅提高了计算效率.考虑夹杂的随机性对颗粒增强复合材料力学性能的影响,采用均匀化方法和Monte-Carlo方法,研究了随机夹杂的体积比、数量、长宽比对材料均质等效模量的影响,结果表明,复合材料的等效弹性模量随夹杂体积比、数量、长宽比的增大而增大,且对体积比最敏感.     

考虑基体粘弹性和介电弛豫的铁电复合材料的本构模型*——Ⅱ.实验、计算和分析

对基体具有粘弹性和介电弛豫的铁电复合材料进行了实验分析 ,并用本文第一部分建立的本构模型对其进行了计算 .实验结果与计算值的比较表明 :建立的本构模型能够较好地反映这类铁电复合材料的力电耦合行为 ,基体的粘弹性和介电弛豫对铁电复合材料的影响是不能忽略的 .     

纤维增强聚合物加固木柱的非线性稳定性分析

考虑加固层中纤维增强聚合物布（FRP布）拉伸与压缩时的不同弹性模量,基于梁大挠度变形假定,首先建立了FRP加固细长木梁大挠度弯曲的一般数学模型,给出了考虑梁弯曲二阶效应的非线性控制方程．其次,研究了FRP布加固细长简支木柱的非线性稳定性问题,得到了FRP加固简支木柱的临界载荷公式．理论证明了其过屈曲解的存在性,并利用摄动法,得到了临界载荷附近过屈曲状态的渐近解析解．进行了参数分析,结果表明：FRP加固层对临界载荷有显著的影响,而对其无量纲过屈曲状态影响较小．     

Constitutive model of ferroelectric composites with a viscoelastic and dielectric relaxation matrix I

Based on micromechanics and Laplace transformation, a constitutive model of ferroelectric composites with a linear elastic and linear dielectric matrix is developed and extended to the ferroelectric composites with a viscoelastic and dielectric relaxation matrix. Thus, a constitutive model for ferroelectric composites with a viscoelastic and dielectric relaxation matrix has been set up Project supported by the National Natural Science Foundation of China (Grant No. 19891180).     

粘弹性动力问题中的一种新的时域递进算法

提出一种新的求解粘弹性动力问题的时域递进技术,在离散时段内将各物理量展开,导出有限元形式的递推计算格式。对不同的时间步长,可做自适应计算,以保证计算精度。数值验证给出了令人满意的结果。     

Constitutive models of ferroelectric composites with a viscoelastic and dielectric relaxation matrix (II)

Experimental analysis of ferroelectric composites with a viscoelastic and dielectric relaxation matrix is carried out, and the electromechanical coupling behavior of the ferroelectric composites is calculated by means of the constitutive model proposed in this paper. Comparisons between the experimental results and the calculations show that the constitutive model can reflect the electromechanical coupling behavior of the ferroelectric composites. The analysis indicates that the effect of viscoelasticity and dielectric relaxation of the matrix on the electromechanical coupling behavior of ferroelectric composites cannot be neglected.     

Reliability Estimation of Optimal Viscoelastic Composite Shells in Critical-Time Calculations

The problem of reliability estimation for optimal viscoelastic composite shells in critical-time calculations is considered. The weight minimization of a viscoelastic composite shell, with constraints on deflections at the critical time, leads to a system deforming unstably, whose deflections grow in time with an increasing rate. A method for estimating the reliability of such shells in calculating the critical time is discussed. This time is regarded as a random variable depending on many, roughly equivalent, factors. An analysis of the reliability is carried out for different values of coefficients of variation, occurring in practice.     

Micromechanics of Damage Accumulation in a 2.5D Woven C-Fiber/SiC Ceramic Composite

The morphology of a C/PyC/SiC ceramic composite is studied and its microdamage mechanisms are revealed. Some models based on the micromechanical fracture mechanics are proposed to describe the possible damage processes. The influence of the observed microdamage on the stiffness reduction is studied. It is shown that the delamination between the layers and the cracks in the coating alone cannot explain the stiffness reduction observed in tests. Debonding between the SiC coating and pyrocarbon is suggested as another mechanism of the stiffness reduction.     

Local Buckling around an Interfacial Crack in a Viscoelastic Sandwich Plate

Buckling around an interfacial crack in a clamped sandwich plate is studied. The layers of the plate are assumed to be linearly viscoelastic, isotropic, and homogeneous. The investigations are carried out within the framework of a piecewise homogeneous body model with the use of a three-dimensional linearized theory of stability. The corresponding boundary value problems are solved numerically by employing the FEM and the Laplace transform. The calculated critical times are presented for various problem parameters. In this case, the upper and lower layers are assumed to be viscoelastic and are described by Rabotnov operators, whereas the midlayer is regarded as purely elastic. The influence of rheological parameters on the critical time is also analyzed.     

Numerical simulation of the rheological properties of granular composites by using a structural approach

Composites with an elastomeric matrix containing rigid particles of diameter 10–1000 μm are studied. One of possible mechanisms of the rheological behavior of such filled systems, related to the origination and growth of vacuoles near the rigid inclusions in a viscous matrix, is considered. For simulating the mechanism of formation of rheological properties of the filled elastomers, we use a structural cell in the form of an elastomeric cylinder, whose height and diameter are equal in magnitude, with a rigid spherical inclusion at its center. Deformation of the cells is examined with the observance of boundary conditions providing the preservation of their close packing. The inclusion is assumed to be rigid, and the matrix properties are described by equations of the linear hereditary viscoelasticity theory. The formation of vacuoles is described by using the approach suggesting that an initial debonding begins to propagate when the energy accumulated in the extended matrix reaches a value sufficient to create a new interface. The heterogeneity of the composite is simulated by taking into account the variability of the local filler concentration. Creep curves obtained for composite cells with different content of the solid phase are presented. Comparisons between the numerical and experimental results show a satisfactory agreement. Translated from Mekhanika Kompozitnykh Materialov, Vol. 44, No. 6, pp. 895–906, November–December, 2008.     

Numerical Prediction of the Strain State of Thermoset Matrix/Mineral Filler Composite Plates

The numerical prediction of the fields of inelastic strains (the linear invariant of the tensor of inelastic strains) in thermoset polyester/marble filler composite plates is discussed. A uniformly distributed load is applied to the plates, which lie on a steel base. The strain fields are predicted by means of the boundary element method by using creep test data for the composites and the polyester matrix itself. Identical creep tests were performed for two ages of the materials (1 month and 13 years), which allowed evaluating the aging effect. The study is carried out in two stages. At the first stage, the application of the generalized Maxwell-Gurevich equation to the thermoset matrix/mineral filler composite is demonstrated. The model parameters determined from the experimental creep data is used for the second stage, where the state of inelastic strains in the plates is predicted by applying the boundary element method. The influence of composite formulation (filler content) and physical aging of the polyester matrix on the state of inelastic strains in the plates is shown.__________Russian translation published in Mekhanika Kompozitnykh Materialov, Vol. 41, No. 2, pp. 145–156, March–April, 2005.     

碳纤维的形状效应和界面效应对复合材料等效热弹性性能的影响

碳纤维增强聚合物基复合材料是一种应用广泛的工程材料,其性能优异与否直接影响着工程应用的安全和可靠性. 碳纤维的形状效应和界面效应被认为是影响碳纤维复合材料力学性能的重要因素. 因此,开展碳纤维形状效应和界面效应的深入研究,对于碳纤维增强聚合物基复合材料的优化设计和工程应用具有重要意义. 为了揭示碳纤维形状效应和界面效应对碳纤维复合材料热弹性性能的影响,该文采用细观力学有限元方法建立了一个代表性体积单元(RVE)模型,通过模拟材料内部微观结构,研究了不同碳纤维形状和含量、界面相含量和界面相性能对碳纤维复合材料等效热弹性性能的影响. 结果表明,碳纤维形状效应对复合材料宏观纵向弹性模量和纵向热膨胀系数几乎没有影响,而对横向弹性模量、横向剪切模量、纵向剪切模量和横向热膨胀系数影响较大,尤其是随着碳纤维含量的增加影响更为明显. 随着界面相含量的增加,当界面效应表现为硬界面效应时,复合材料的纵向与横向弹性模量均会随之增加,而当界面效应表现为软界面效应时,复合材料的纵向与横向弹性模量均会随之减小. 当界面相热膨胀系数小于基体热膨胀系数时,复合材料的纵向与横向热膨胀系数均会随界面相含量的增加而减少,而当界面相热膨胀系数大于基体热膨胀系数时,复合材料的纵向与横向热膨胀系数均会随界面相含量的增加而增加.