等效介质理论数值法计算复合材料的热膨胀系数

本文用一套等效介质理论的数值方法计算了球状微粒掺杂之各向同性复合材料及单向纤维增强之横观各向同性复合材料之线热膨胀系数,得到合理的结果,并与Schapery式、Kerner式之计算及实验值作出比较,显示了等效介质理论于复合材料热弹性能计算之适用性.      

核壳粒子复合材料的等效磁导率

为了预测复合材料的等效磁导率,建立了填充核壳粒子复合材料等效磁导率的物理模型,应用电磁场理论推导了核壳粒子以单一介质球代替的等效方法并推广得到椭球核壳粒子情况.基于平均极化理论和Maxwell-Garnett理论给出了核壳粒子以特定浓度随机分布于复合材料时等效磁导率的预测公式,通过数值计算分析了核壳粒子浓度、结构参数以及磁导率对复合材料等效磁导率的影响.数值计算与实验结果吻合很好,验证了该等效方法用于复合材料电磁特性优化设计的有效性.     

等效介质理论用于单向纤维增强复合材料弹性性能的数值计算

本文把一套等效介质理论简化成为一数值方法,用于横观各向同性组分构成的单向纤维增强复合材料弹性性能的计算。我们计算了几个单向纤维增强的系统并把计算值与实验值作出比较,得到很好的符合。     

纤维复合材料的电磁反射系数计算

为了探讨用于制造飞机的纤维复合材料的电磁特性,运用等效层模型分析了纤维复合材料的等效电磁参数,利用传输线理论推导了材料的反射系数计算公式并计算了不同参数下材料的反射系数。将计算结果与有限元方法对实际材料的数值计算结果进行了比较,发现在材料结构周期(纤维间距)远小于波长时,等效层模型的计算结果与有限元法的结果吻合良好。     

金属-介质壳核结构复合材料吸波特性的仿真和分析

基于有效媒质理论,采用有限元法计算了二维金属-介质壳核结构复合材料模型的等效介电常数.分析了金属层电导率、金属层厚度、填充比、内核材料及衬底介电常数对复合材料等效介电常数的影响.仿真结果表明,金属-介质复合材料具有2个吸收峰,且通过改变金属层电导率可以在射频至红外频段灵活调整复合材料吸收峰的位置;复合材料的吸收峰与其显微结构密切相关.有效介质理论是研究和分析复合材料吸波特性的有力工具.     

复合材料电磁参数计算的理论研究进展

介绍了计算复合材料等效电磁参数的相关理论及其应用条件和适用范围,着重介绍了有效介质理论的相关公式及思想,并总结和评价了国内外关于复合材料电磁参数计算的研究现状.     

等效介质理论在各向同性复合材料的弹性性能上的应用

本文介绍了我们不久前发展的一套应用于复合材料性能的等效(有效)介质理论,并且把它合理地扩展到研究二相各向同性复合材料的弹性性能。作为例子,我们计算了含球状空隙及含球状刚性微粒固体的剪切模量,得到这两个情况下模量与掺入物体积比的直接关系式。计算结果并与实验比较,得到很好的符合。     

复合吸声材料中的微粒对吸声性能影响的研究

1引言 吸声材料现已由单相向含微粒的多相复合材料发展,因粒子的散射和波型转换的作用,可使复合材料吸声器具有优良的吸声性能.吸声性能是与基材和微粒材料的力学参数、微粒的形状、结构、体积比和分布概率等因素有关.计及这些因素的影响,对吸声性能进行预报的研究是很有意义的.由于媒质的不均匀性、界面的不规则性很难用严格波动理论进行声场计算,因而只能采用近似方法.在上世纪60年代中Chaban[1]提出"假设来自多个非相互作用的散射粒子的散射场等效于体积等于所有散射粒子所占体积之和的单个散射体的散射场"的物理模型,计算复合材料的等效弹性模量和密度以来,出现多种近似计算方法,其中由J.G.Berryman[2]和M.R.Haberman[3]等人提出的基于自洽(self-consistent,SC)理论并与统计力学结合起来的计算复合材料的低频等效模量的算法与实验复合较好.本文用[2,3]的算法计算等效模量,并预报复合材料吸声器的吸声系数.     

颗粒填充二元复合材料等效介电特性的修正通用有效介质计算公式

介电特性在复合材料的电磁效应研究和材料设计中具有重要的作用。本工作在研究传统通用有效介质(GEM,General Effective Medium)公式的局限性基础上,提出了用于预测和计算颗粒填充二元复合材料等效介电特性的修正通用有效介质(MGEM,Modified General Effective Medium)公式。运用MC-FEM(Monte Carlo-Finite Element Method)方法分析计算各种参数条件下颗粒随机填充二元复合材料的等效介电特性,并与MGEM公式计算结果进行比较,验证MGEM公式的正确性和有效性。此外,还将MGEM的预测结果与部分经典理论公式的计算结果、部分文献报道的实验测量数据进行了比较。研究表明,在不同介电常数比(1/50~50)和不同体积分数(0~1)的情况下,MGEM公式预测结果与MC-FEM模型结果完全吻合,与实验测量结果基本一致,为颗粒填充二元复合材料等效介电性能分析提供了一种具有较高计算精度的理论计算方法。     

复合材料热传导系数均匀化计算的实现方法

均匀化理论可以有效预测周期性结构复合材料的等效热传导系数,然而其控制方程的载荷项形式特殊,通用有限元软件中没有对应的载荷形式,难以直接求解.提出一种本构关系及场变量的类比方法,证明了在此类比下等效热传导系数均匀化方程与等效弹性模量均匀化方程是等价的.根据求解等效弹性模量均匀化方程的热应变法,提出一种新的等效热传导系数均匀化方程数值求解方法.以ABAQUS为平台,预测单向纤维复合材料以及金属蜂窝夹芯板的等效热传导系数,计算结果与参考值吻合良好.该方法为基于通用有限元软件的复合材料等效热传导系数的均匀化计算提供了简便途径.     

The impact strength of fibre composites

Two models have been developed which predict the crack initiation energy, notched impact strength and unnotched impact strength of fibre composites. One is applicable to composites containing short fibres and the other to composites containing long fibres. Data obtained with randomly oriented short fibre composites were consistent with the one model. The other model has been verified using composites containing uniaxially oriented long fibres and long fibres oriented randomly in a plane. The success of the model demonstrates that the high notched impact strength with long fibres is due to the redistribution of stress away from the stress concentrating notch, the extra stress that can be held by the fibre relative to the matrix and the work required to pull fibres out of the matrix during crack propagation. The parameters which have been shown to control the fracture energy are composite modulus, fibre length, fibre volume fraction, effective fibre diameter, fibre tensile strength and the coefficient of friction during fibre pull-out from the matrix. The matrix toughness on the other hand usually has no effect at all for composites containing fibres randomly oriented in two dimensions and only a minor effect in exceptional cases. The shear strength of the fibre-matrix bond has only an indirect effect in that it controls the number of fibres which pull out rather than fracture.     

C/ZA-12复合材料的摩擦磨损性能研究

本文研究了用挤压铸造法制备的C/ZA-12复合材料的摩擦磨损性能.对碳纤维体积分数和载荷改变时,复合材料的摩擦系数、磨损量的变化规律作了较细致的分析,并对影响其磨损性能的因素进行了讨论.      

C／ZA－12复合材料的摩擦磨损性能研究

本文研究了用挤压铸造法制备的Ｃ／ＺＡ－１２复合材料的摩擦磨损性能。对碳纤维体积分数和载荷改变时，复合材料的摩擦系数、磨损量的变化规律作了较细致的分析，并对影响其磨损性能的因素进行了讨论。     

A mechanistic approach to damage in short-fiber composites based on micromechanical and continuum damage mechanics descriptions

A micro-macro mechanistic approach to matrix cracking in randomly oriented short-fiber composites is developed in this paper. At the micro-scale, the virgin and reduced elastic properties of the reference aligned fiber composite are determined using micromechanical models [Proc. Roy Soc. Lond. A241 (1957) 376; Acta Metall. 21 (1973) 571; Mech. Mater. 2 (1983) 123], and are then distributed over all possible orientations in order to compute the stiffness of the random fiber composite containing random matrix microcracks. After that the macroscopic response is obtained by means of a continuum damage mechanics formulation, which extends the thermodynamics based approach in [Comp. Sci. Technol. 46 (1993) 29] to randomly oriented short-fiber composites. Damage accumulations leading to initiation and propagation of a macroscopic crack are modeled using a vanishing element technique. The model is validated against the published experimental data and results [Comp. Sci. Technol 55 (1995) 171]. Finally, its practical application is illustrated through the damage analysis of a random glass/epoxy composite plate containing a central hole and under tensile loading.     

Micro-Mechanical Parameters in Short Fibre Composite

The aim of this paper is to analyse the contribution of micro-mechanical parameters, on the macroscopic behaviour of a short fibre reinforced thermoplastic composites (SFRTC). By developing an algorithm to provide a representative random micro-structure, a comparative analysis of different micro-mechanical parameters, such as aspect ratio (AR) and fibre orientation (FO), was conducted and compared with the existing analytical models. A study of different aspect ratios and different fibre orientations has been carried out in order to examine their effect on the linear elastic properties of SFRTC. Aspect ratios from one to ten have been analysed for the cases of fully oriented 0° fibres, miss-oriented fibres and randomly oriented fibres. A representative volume element (RVE) was used to investigate the effect of the representative size. Results were analysed statistically through X ² test, and the subsequent representative realisations were compared with the theoretical predictions.     

Elastic Constants of Particle and Fiber Reinforced Metal Matrix Composites

Abstract

A model has been developed to predict the elastic moduli in composites reinforced with both particles and fibers. In the model the matrix material and the particles, which are assumed to be homogeneously distributed, form an effective matrix. The characteristics of this effective matrix is calculated using a theory formulated by Ledbetter and Datta. The effective matrix is then considered to be reinforced with fibers lying in one plane but randomly oriented in that plane. The effect of the 2-dimensionally random orientation of the fibers on the elastic moduli of the composites is determined in two steps. First the composite cylinders model by Hashin and Rosen for an aligned fiber system is employed, and then a geometric averaging procedure suggested by Christensen and Waals is performed. Using this model, the Young's and shear moduli were calculated for three samples with different aluminum matrices and volume fractions of particles (9, 13, and 17%) but the same fiber content (6%). The same elastic moduli were also determined using ultrasonic velocity measurements. The agreement between calculated and measured elastic moduli is found to be very good. Also, the elastic anisotropics between directions of the fiber rich plane and that normal to the plane could be predicted by the model.     

Elastic constants of particle and fiber reinforced metal matrix composites

A model has been developed to predict the elastic moduli in composites reinforced with both particles and fibers. In the model the matrix material and the particles, which are assumed to be homogeneously distributed, form an effective matrix. The characteristics of this effective matrix is calculated using a theory formulated by Ledbetter and Datta. The effective matrix is then considered to be reinforced with fibers lying in one plane but randomly oriented in that plane. The effect of the 2-dimensionally random orientation of the fibers on the elastic moduli of the composites is determined in two steps. First the composite cylinders model by Hashin and Rosen for an aligned fiber system is employed, and then a geometric averaging procedure suggested by Christensen and Waals is performed. Using this model, the Young's and shear moduli were calculated for three samples with different aluminum matrices and volume fractions of particles (9, 13, and 17%) but the same fiber content (6%). The same elastic moduli were also determined using ultrasonic velocity measurements. The agreement between calculated and measured elastic moduli is found to be very good. Also, the elastic anisotropies between directions of the fiber rich plane and that normal to the plane could be predicted by the model.This article is dedicated to Professor Dr. Paul Höller on the occasion of his 65th birthday.     

对尼龙短纤维-丁苯橡胶复合材料模量的影响因素及模量的预测

本文讨论了几种因素对尼龙短纤维补强弹性体的杨氏模量的影响。在Halpin-Tsai方程的基础上提出了一个半经验方程,用来预测复合材料的模量,该方程的预测值与实验结果有较好的一致性。      

Measuring the elastic properties of high-modulus fibres

The measurement of the elastic constants of several highly oriented thermoplastic polymer fibres is described. The method makes use of the hot-compaction process, developed and patented in this laboratory, which enables a solid section of highly oriented polymer to be produced from an aggregate of highly oriented fibres. As only a small fraction of the original fibre is melted and recrystallized during the process, the compacted materials offer a unique opportunity for measuring fibre properties in the bulk. An ultrasonic immersion technique is used to measure the elastic properties of the compacted materials, from which the properties of the polymer fibres are inferred. The experimentally determined fibre elastic properties have been compared with other oriented polymer materials to assess any similarities in elastic anisotropy between different methods for producing fibre orientation, and compared with theoretical upper limits for the fibre elastic properties based on theoretical estimates for the polymer crystal unit cell appropriately averaged for hexagonal symmetry using the aggregate model.     

Effect of inclusion shape on the effective elastic moduli for composites with imperfect interface

Summary Bounds on the effective elastic moduli for isotropic composites consisting of randomly oriented spheroidal inclusions with imperfect matrix-inclusion interface are proposed based on Hashin's extremum principle. Phenomenally, these bounds are the first-order ones for such composites, and contain the effect of the size and shape of inclusions, and the elastic properties of constituent phases and interfaces. In the limit cases, these bounds reduce to those known ones. The effect of inclusion shape and interface imperfection on the bounds is discussed with some numerical results for a WC/Co metal-matrix composite.