Bifurcations in the mechanics of hypoelastic composite materials

This paper analyses the modification of a hypoelastic material behavior at the small variations of the material parameters, using elements of the bifurcation theory. The considered material is obtained by the combination of two granular hypoelastic materials, which have the memory of the initial stress state, and their stress work depends on stress history. Its constitutive equation is deduced by means of the constitutive equations of the component materials. In consequence, mechanical properties of those two materials are interpenetrated, generating, for the new material, domains of stability, as well as surfaces in stress space, surfaces on which the strain–stress system is not invertible. It results that it is necessary to choose correctly the component materials, their share and the process of forming the new material, so that the imposed solicitation by the operation conditions should be accessible to a composite material. When we are modelling, the choice of the component materials means the choice of their constitutive equations—the share of the component materials will fix the stability domain of the composite material—the forming process chosen correctly will determine that the initial stress state (from which the loading path will start) should be in the stability domain of the material.     

Multi-scale modeling in damage mechanics of composite materials

This paper addresses the multi-scale modeling aspects of damage in composite materials. The multiplicity of the scales of the operating mechanisms is discussed and clarified by taking examples of damage in a unidirectional ceramic matrix composite and in a cross ply polymer matrix composite laminate. Two multi-scale modeling strategies––the hierarchical and the synergistic––are reviewed in the context of deformational response. Finally, the “big picture” as it relates to the cost-effective manufacturing of composite structures intended for long-term performance is outlined and desired future direction in multi-scale modeling is discussed.     

Application of the principles of linear fracture mechanics to the composite materials

Application of the principles of linear fracture mechanics to the orthotropic composite materials is examined. It is shown that fracture toughness of unidirectional composites is independent of crack length but dependent on crack-fiber orientation. For experimental verification of the above principles, uni-directional glass epoxy material (Scotchply 1002) was used. The fracture toughness of Scotchply 1002 for different crack-fiber orientations is obtained by utilizing Solid Sap finite element program and compact tension specimens. An empirical formula relating the fracture toughness of the material for different crack-fiber orientation is found.

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Résumé On examine l'application du principe de la mécanique linéaire de rupture aux matériaux composites orthotropes. On montre que la ténacité à la rupture de composites unidirectionnels est indépendante de la longueur de la fissure mais dépend de l'orientation des fibres par rapport à cette fissure. Pour vérifier de manière expérimentale les principes ci-dessus, on a utilisé un matériau en verre epoxy unidirectionnel (Scotchply 1002). La ténacité à la rupture du Scotchply 1002 pour différentes orientations fibre/fissure a été obtenue en utilisant un programme à élément fini Solid Sap et des éprouvettes de traction compactes. On a trouvé une formule empirique mettant en relation la ténacité à la rupture du matériau pour différentes orientations fibre/fissure.

     

A 3-D fracture mechanics approach to the strength of composite materials

The first ply failure in composite laminates are studied by 3-D fracture mechanic approach. The fracture model is based on a crack embedded in one of the inner layers. Numerical results for the case of “angle ply” laminates are based on a general 3-D finite difference program.Stress intensity factors and fracture energy are evaluated by the $\text{J-}\text{integral}$ 2-D and 3-D methods as well as by the stresses and energy balance. It was found that the $\text{J(2-}\text{D}\text{)}$ method can be applied to 3-D problems while the $\text{J(3-}\text{D}\text{)}$ method is not suitable for the numerical computation.The influence of geometrical properties of the crack and the layers on the various stress intensity factors is presented and discussed. Change in failure mechanism of the weakest ply was proved by experiments to fit with numerical results. It was found that the weakest layer is strengthened by the others, a fact which has been verified experimentally and hasn't been explained by other approaches.     

无机填料的改性及其在复合材料中的应用

阐述了填料表面改性技术即偶联剂处理技术、表面活性剂处理技术、等离子体处理技术的最新研究进展 ,介绍了几种典型无机填料在复合材料中的应用现状以及填料粒径、形状和含量对填充效果的影响     

A multi-continuum theory for composite elastic materials

Summary A continuum theory for composite materials is presented in which the composite constituents are modeled by superimposed continua which undergo thermal and mechanical interactions. Kinematical notions, field equations and a constitutive theory are developed, including consequences of material frame indifference and material symmetry which restrict the form of the response functions. The final result is a set of linearized equations for thermal and mechanical processes in laminated or fiber reinforced composite elastic materials.

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Eine Mehrphasen-Kontinuumstheorie elastischer Verbundwerkstoffe

Zusammenfassung Eine Kontinuumstheorie dev Verbundwerkstoffe wird angegeben in der die einzelnen Bestandteile durch überlagerte Kontinuen, die sich thermisch und mechanisch beeinflussen, dargestellt werden. Kinematische Begriffe, Feldgleichungen und eine Werkstofftheorie werden entwickelt einschließlich der Folgerungen aus dem Prinzip der Bezugsindifferenz und der Werkstoffsymmetrie. Das Resultat besteht aus einem System, von linearisierten Gleichungen für thermische und mechanische Prozesse in geschichteten oder faserverstärkten elastischen Verbundwerkstoffen.

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With 2 Figures     

结构吸波复合材料透波层的研究

采用弓形法测试反射率,研究透波层的厚度、材质对结构吸波复合材料电磁性能的影响。结果显示,在4~18GHz范围内,厚度对其吸波性能具有显著影响,厚度分别为0.25、0.50和1.25mm的透波层,其结构吸波复合材料的最大吸收峰分别为-37.03,-33.45和-33.22dB;随厚度的增加,吸收峰的位置随向低频段显著漂移,-10dB的有效吸收带宽也显著变窄,分别为11.5,11和6.5GHz;与厚度相比,材质对结构吸波复合材料电磁性能影响较小。     

纳米核-壳型含能复合粒子的制备及应用研究进展

通过对比分析核-壳型纳米复合粒子的制备技术和应用领域,阐述了不同复合粒子所适合的制备方法,这些制备技术具有广阔发展前景.通过对比几种典型的纳米含能复合材料的结构及其性能,分析了这种类型的复合方式对改变单一超细含能粒子易团聚的性质、改善了含能材料综合性能等方面的积极作用;并分析了该材料制备技术在其它含能复合材料中的应用潜...     

Computational damage mechanics for composite materials based on mathematical homogenization

This paper is aimed at developing a non‐local theory for obtaining numerical approximation to a boundary value problem describing damage phenomena in a brittle composite material. The mathematical homogenization method based on double‐scale asymptotic expansion is generalized to account for damage effects in heterogeneous media. A closed‐form expression relating local fields to the overall strain and damage is derived. Non‐local damage theory is developed by introducing the concept of non‐local phase fields (stress, strain, free energy density, damage release rate, etc.) in a manner analogous to that currently practiced in concrete [1, 2], with the only exception being that the weight functions are taken to be C⁰ continuous over a single phase and zero elsewhere. Numerical results of our model were found to be in good agreement with experimental data of 4‐point bend test conducted on composite beam made of Blackglas™/Nextel 5‐harness satin weave. Copyright © 1999 John Wiley & Sons, Ltd.     

航空发动机复合材料的应用与研究

由于航空工业的迅猛发展,航空发动机复合材料应运而生,本文简单介绍了航空发动机复合材料的发展状况,以及主要的发展趋势,分析了发动机材料的各自独特的特性,并突显了复合材料在航空发动机发展中重要地位,为未来航空发动机的相关研究和研发奠定基础,使航空发动机相关制造工艺上再上一个新台阶。     

A bimodal plasticity theory of fibrous composite materials

Summary It is shown that elastic-plastic response of metal matrix composites reinforced by aligned continuous fibers can be described in terms of two distinct modes. In the matrix-dominated mode, the composite deforms primarily by plastic slip in the matrix, on planes which are parallel to the fiber axis. In the fiber-dominated mode, both phases deform together in the elastic and plastic range. Constitutive equations are derived for the matrix-dominated mode of deformation in composites with elastic-perfectly plastic matrices. Response in the fiber-dominated mode is approximated by the self-consistent and Voigt models. The two deformation modes give different branches of the overall yield surface which identify the state of stress that activates a particular mode, and indicate the conditions for mode transition in a given composite system. The matrix-dominated mode is found to exist in systems reinforced by fibers of large longitudinal shear stiffness, such as boron or silicon carbide. Systems reinforced by more compliant fibers, such as graphite, appear to deform exclusively in the fiber-dominated mode. The results show good agreement with experimental data, and with predictions obtained from a more accurate material model. They also help to reconcile several different plasticity theories of fibrous composites, and suggest limits of their validity.With 9 FiguresPrepared for the Symposium on Plasticity: Foundations and Future Directions. In Memory of Aris Phillips. January 28–30, 1987. University of Florida, Gainesville, U.S.A.     

Micromechanical approach to damage mechanics of composite materials with fabric tensors

The purpose of this study is to apply continuum damage mechanics – introduced through the concept of fabric tensors – to composite materials within the framework of the theory of elasticity. A directional data model of damage mechanics for composite materials will be developed using fabric tensors. The introduction of fabric tensors into the analysis of damage of composite materials will allow for an enhanced and better understood physical meaning of damage. The micromechanical approach will be used here to relate the damage effect through fabric tensors to the behavior of composite materials. In this approach, damage mechanics is introduced separately to the constituents of the composite material through different constituents’ damage effect tensors. The damaged properties of the composite system as a whole can then be obtained by proper homogenization of the damaged properties of the constituents.

The derivation of a generalized formulation of damage evolution will be shown here in a mathematically consistent manner that is based on sound thermodynamic principles. Numerical examples will be presented to show applicability. In addition, damage evolution for the one-dimensional tension case is also illustrated.     

A new fracture mechanics theory for orthotropic materials like wood

A new fracture mechanics theory is derived based on a new orthotropic-isotropic transformation of the Airy stress function, making the derivation of the Wu-“mixed mode I-II” fracture criterion possible, based on the failure criterion of a flat elliptic crack. As a result of this derivation, the right fracture energy and theoretical relation between mode I and II stress intensities and energy release rates are obtained.     

A review of recent research on mechanics of multifunctional composite materials and structures

In response to the marked increase in research activity and publications in multifunctional materials and structures in the last few years, this article is an attempt to identify the topics that are most relevant to multifunctional composite materials and structures and review representative journal publications that are related to those topics. Articles covering developments in both multiple structural functions and integrated structural and non-structural functions since 2000 are emphasized. Structural functions include mechanical properties like strength, stiffness, fracture toughness, and damping, while non-structural functions include electrical and/or thermal conductivity, sensing and actuation, energy harvesting/storage, self-healing capability, electromagnetic interference (EMI) shielding, recyclability and biodegradability. Many of these recent developments are associated with polymeric composite materials and corresponding advances in nanomaterials and nanostructures, as are many of the articles reviewed. The article concludes with a discussion of recent applications of multifunctional materials and structures, such as morphing aircraft wings, structurally integrated electronic components, biomedical nanoparticles for dispensing drugs and diagnostics, and optically transparent impact absorbing structures. Several suggestions regarding future research needs are also presented.     

Damage mechanics of composite materials: I— Measurements of damage and strength

A new approach for modelling the strength of notched composites has been developed. The approach is based on the assumption that subcritical damage modifies the notch-tip stress field and that the state of subcritical damage just before failure, referred to as the terminal damage state (TDS), must have a significant influence on notched strength. The TDS was monitored for a wide range of cross-ply graphite reinforced epoxy specimens using real-time radiography. A finite element model incorporating the TDS was used to determine the modified notch-tip stress field. A simple tensile stress failure criterion has been found to predict failure very well provided that the effect of subcritical damage is considered in this way. The effect of both layup and notch size on strength can be entirely accounted for by the effect these parameters have on the terminal damage state. In the first paper of a four-part series, radiographs of c. 60 specimens have been used to characterize the notch-tip damage zone and to establish a qualitative relationship between terminal damage and notched strength.     

CaCO_3晶须研究及其在复合材料中的应用

介绍了CaCO3晶须的性能特点以及作为增强填充物在国内外有机和无机复合材料领域应用研究的新进展,并结合作者在水泥基材料领域对CaCO3晶须的最新应用和初步试验结果,从多个方面进行了探讨和分析。在这些复合材料里面CaCO3晶须均能够起到良好的补强增韧作用,并赋予材料新的特性和功能,而且价格低廉、绿色环保、有利于环境可持续发展,具有非常重要的实际应用价值、广阔的市场和应用前景。