Showing papers on "Micromechanics published in 2002"
TL;DR: The foundations of classical homogenization techniques, which aim at predicting the overall behavior of heterogeneous materials from that of their constituents, are reviewed in this paper, with a focus on linear elasticity.
Abstract: The foundations of classical homogenization techniques, which aim at predicting the overall behavior of heterogeneous materials from that of their constituents, are reviewed. After introductory definitions and a methodological preamble, attention is focused on linear elasticity, for which the basic principles of estimating and bounding the overall properties are introduced and illustrated. In this context, special recourse is made for that to the solution of the inclusion and inhomogeneity problems as reported by Eshelby in 1957. Approaches proposed recently to account in a better way for the structural morphology of the considered materials are briefly mentioned. The case of linear elasticity with eigenstrains is then discussed: several applications, including heterogeneous thermoelasticity, can be investigated within this framework. Finally, outlines of nonlinear micromechanics are briefly reported from a historical point of view: from rate-independent elastoplasticity to nonlinear elasticity and viscoplasticity, examples of a fruitful interaction between the search for new estimates and the derivation of rigorous bounds are given and the crucial question of the description of intraphase heterogeneity is emphasized. Viscoelastic coupling and rate-dependent effects are briefly discussed in conclusion.
628 citations
TL;DR: In this article, the PVA-ECC was developed for the context of material design under the guidance of micromechanical tools, where the fiber/matrix interface may be engineered to accommodate the requirements imposed by the micro-mechanical models, thus highlighting the importance of interface tailoring on composite performance.
Abstract: This paper presents the development of the PVA-ECC in the context of material design under the guidance of micromechanical tools. Specifically, this work illustrates how the fiber/matrix interface may be engineered to accommodate the requirements imposed by the micromechanical models, thus highlighting the importance of interface tailoring on the composite performance. This micromechanics-based material design approach is broadly applicable to achieving high-performance composites with low fiber content for cost-effective structural applications.
625 citations
TL;DR: In this paper, a self-healing polymeric composite material that can recover as much as 90 percent of its virgin fracture toughness has been developed, based on biological systems in which damage triggers an autonomic healing response.
Abstract: Inspired by biological systems in which damage triggers an autonomic healing response, a polymer composite material that can heal itself when cracked has been developed. In this paper we summarize the self-healing concept for polymeric composite materials and we investigate fracture mechanics issues consequential to the development and optimization of this new class of material. The self-healing material under investigation is an epoxy matrix composite, which incorporates a microencapsulated healing agent that is released upon crack intrusion. Polymerization of the healing agent is triggered by contact with an embedded catalyst. The effects of size and concentration of the catalyst and microcapsules on fracture toughness and healing efficiency are investigated. In all cases, the addition of microcapsules significantly toughens the neat epoxy. Once healed, the self-healing polymer exhibits the ability to recover as much as 90 percent of its virgin fracture toughness.
549 citations
TL;DR: In this article, the potential of lattice models for micromechanics applications is discussed, and a detailed presentation of one-dimensional and planar lattice model for classical continua is given.
Abstract: This review presents the potential that lattice ~or spring network! models hold for micromechanics applications. The models have their origin in the atomistic representations of matter on one hand, and in the truss-type systems in engineering on the other. The paper evolves by first giving a rather detailed presentation of one-dimensional and planar lattice models for classical continua. This is followed by a section on applications in mechanics of composites and key computational aspects. We then return to planar lattice models made of beams, which are a discrete counterpart of non-classical continua. The final two sections of the paper are devoted to issues of connectivity and rigidity of networks, and lattices of disordered ~rather than periodic! topology. Spring network models offer an attractive alternative to finite element analyses of planar systems ranging from metals, composites, ceramics and polymers to functionally graded and granular materials, whereby a fiber network model of paper is treated in considerable detail. This review article contains 81 references. @DOI: 10.1115/1.1432990#
449 citations
Book•
20 Nov 2002
TL;DR: In this paper, the 3D Fibre Preforms (3D FRP composites) were modeled for 3D woven composites and knitted composites, including Braided Composite Materials and Knitted Composite Materials.
Abstract: Introduction: Background Introduction to 3D FRP composites Manufacture of 3D Fibre Preforms: Weaving Braiding Knitting Stitching Preform Consolidation Liquid moulding techniques Resin selection Tooling Component quality. Micromechanics Models for Mechanical Properties: Fundamentals in micromechanics Unit cell models for 2D woven composites Models for 3D woven composites Unit cell models for braided and knitted composites. 3D Woven Composites: Microstructural properties of 3D woven composites In-plane mechanical properties of 3D woven composites Interlaminar fracture properties of 3D woven composites 3D woven distance fabric composites. Braided Composite Materials: In-plane mechanical properties Fracture toughness and damage performance Fatigue performance Modelling of braided composites. Knitted Composite Materials: In-plane mechanical properties Interlaminar fracture toughness Impact performance Modelling of knitted composites. Stitched Composites: The Stitching process Mechanical properties of stitched composites Interlaminar properties of stitched composites Stitched composite joints. Z-Pinned Composites Fabrication of Z-pinned composites Mechanical properties of Z-pinned composites Delamination resistance and damage tolerance of Z-pinned composites Z-Pinned sandwich composites.
413 citations
TL;DR: In this paper, multiwalled carbon nanotubes (MWNT) reinforced epoxy composite thin films were prepared by a microfabrication process and their elastic modulus was determined using a shaft-loaded blister test and linear and nonlinear elasticity models.
Abstract: Multiwalled carbon nanotubes (MWNT) reinforced epoxy composite thin films were prepared by a microfabrication process and their elastic modulus was determined using a shaft-loaded blister test and linear and nonlinear elasticity models. Compared to net resin thin films, a 20% increase in elastic modulus was seen when 0.1 wt % MWNTs were added, suggesting MWNT alignment by spin coating. Electron microscopic observations of the fracture surfaces suggested high interfacial shear stress between MWNTs and the epoxy matrix, a result supported by both molecular mechanics simulation and micromechanics calculations.
279 citations
TL;DR: In this paper, a model was developed to predict the buckling of platelets in reinforced materials under compressive loading, and a critical strain above which platelet buckling, and hence a reduction in the compressive modulus relative to the tensile modulus, would be expected to occur.
273 citations
TL;DR: In this article, a general three-dimensional micromechanical approach to modeling anisotropic damage of brittle materials such as concrete, rocks, or certain ceramics is presented.
Abstract: A general three-dimensional micromechanical approach to modeling anisotropic damage of brittle materials such as concrete, rocks, or certain ceramics is presented. Damage is analyzed as a direct consequence of microcracks growth. Following a rigorous scale change methodology, the macroscopic free energy of the microcracked medium is built considering either open and closed microcracks. Moreover, the microcracks opening/closure criterion as well as the moduli recovery conditions (unilateral effects) are addressed in stress-based and strain-based formulations. An alternative derivation of the homogenized properties, based on the well-known Eshelby method, is also presented and extended here to closed cracks. From the micromechanical analysis, an energy-based yield condition is formulated and illustrated in various stress subspaces. Assuming that the normality rule applies, we then present the damage evolution law and the rate form of the constitutive model. The main capabilities and advantages of the micromechanical model are illustrated through various examples in which material microstructure evolutions are presented.
216 citations
TL;DR: In this paper, the authors model concrete as a composite formed by a matrix with embedded spherical particles and evaluate the effective elastic moduli of this composite on the basis of the generalized selfconsistent scheme (GSCS).
186 citations
TL;DR: In this article, a methodology has been developed to arrive at a sufficiently small micro-structural window that can be regarded as a volume element of a non-uniform micro-structure of a ceramic matrix composite (CMC) containing a range of fiber sizes, and fiber-rich and -poor regions at the length scale of about 100 μm.
167 citations
TL;DR: An enhanced version of the damage mesomodel for laminates (DML) is introduced in this article, which has been developed over the last 15 years at Cachan, and is fully compatible with classical micromechanics models.
TL;DR: In this paper, a homogenization method is used to determine the formulation of the behavior of both saturated and unsaturated porous media, making it possible to assess the validity of the effective stress concept as a function of the properties of the porous media at the microscopic scale.
Abstract: The homogenization method is used to determine the formulation of the behaviour of both saturated and unsaturated porous media. This approach makes it possible to assess the validity of the effective stress concept as a function of the properties of the porous media at the microscopic scale. Furthermore, the influence of the morphologies of the solid and fluid phases on the macroscopic behaviour is studied. The strain induced by drying is examined as a function of the morphological properties. Copyright © 2002 John Wiley & Sons, Ltd.
TL;DR: In this article, the authors investigated the stiffness anisotropy of asphalt mixtures using micromechanics-based models and found that the orientations of the longest axes of aggregates are easier to measure and better descriptors of stiffness than the contact normals.
Abstract: The mechanical behavior of many bound granular materials, such as asphalt mixtures, is anisotropic in nature. However, the majority of the current mechanical tests and analytical models for asphalt mixtures are based on the assumption of isotropic material properties. This study investigates the stiffness anisotropy of asphalt mixtures using micromechanics-based models. The models’ parameters are obtained by quantifying the internal structure anisotropy in terms of the preferred orientation of longest axes and contact normals of aggregates. Image analysis techniques are used to conduct the internal structure measurements. The orientations of the longest axes are found to be easier to measure, and better descriptors of anisotropy, than the contact normals. Finite-element analyses of the internal structure are also used to provide insight into the mixture stiffness anisotropy. The mixture properties are selected to represent a wide range of temperatures. The stiffness in the horizontal direction is shown to be as high as 30% more than the stiffness in the vertical direction. The stiffness anisotropy decreases with a decrease in the mixture temperature. The finite-element results are shown to have very good correlation with the results of the micromechanics model derived based on the orientation of the longest axes of aggregates.
TL;DR: Onck et al. as mentioned in this paper proposed a homogenization procedure that enables the derivation of macroscopic Cosserat constitutive equations based on the underlying microstructural morphology and material behavior.
TL;DR: In this article, the effect of the shape of fiber cross-section and fiber volume fraction on the various damping coefficients was studied through the application of viscoelastic correspondence principle to the model based on Eshelby's method and Mori-Tanaka approach.
Abstract: The paper incorporates some micromechanical investigations for the prediction of damping coefficients of two-phase continuous fiber reinforced composite. The effect of the shape of fiber cross-section and fiber volume fraction on the various damping coefficients viz. η11, η22, η33, η12, η13, and η23 is studied through the application of viscoelastic correspondence principle to the model based on Eshelby's method and Mori–Tanaka approach. The damping coefficients expressed as loss factors are predicted using several other micromechanical models like, Unified micromechanics, Haplin–Tsai, Hashin, and Tsai. Loss factors for composite reinforced with cylindrical continuous fiber are also determined by 2D micromechanical FEM/strain energy approach and compared with the predictions made by other methods/theories.
TL;DR: In this article, a new damage deactivation rule is developed, directly based on mechanics of micro-cracks behavior, considering both closure effects and the corresponding elastic energy storage, which allows a progressive effect and a better description of the residual strain.
TL;DR: In this article, a lattice-based micromechanics approach is proposed to characterize the cracking performance of asphalt concrete and a random truss lattice model is introduced and investigated for simulating the following: linear elastic and visco-elastic deformation of homogeneous materials in axial compression and shear loading experiments, linear elastic deformation and the stress field in heterogeneous materials, and damage evolution in elastic solids under an indirect tensile test.
Abstract: A lattice-based micromechanics approach is proposed to characterize the cracking performance of asphalt concrete. A random truss lattice model was introduced and investigated for simulating the following: (a) linear elastic and viscoelastic deformation of homogeneous materials in axial compression and shear loading experiments, (b) linear elastic deformation and the stress field in heterogeneous materials in an axial compression loading experiment, and (c) damage evolution in elastic solids under an indirect tensile test. The simulation results match well with the theoretical solutions and show excellent promise in predicting cracking patterns in the indirect tensile test. A brief discussion about ongoing work is also presented.
TL;DR: In this paper, a framework for automatic generation of quadrilateral finite element meshing of planar Voronoi tessellation is proposed, resulting in a powerful set of tools to be used in the rather wide field of micromechanics.
TL;DR: In this article, the effect of coalescence on shear band development and associated fracture mode in plane strain is analyzed numerically using a recent elastic-viscoplastic Gurson-like model that accounts for void shape evolution, coalescence and post-coalescence micromechanics along with isotropic hardening and orthotropic plasticity.
Abstract: The macroscopic fracture in plane strain is known to be shear-like in ductile materials. In most structural materials, fracture starts after diffuse necking, at the centre of the specimen, by micro-void coalescence giving rise afterwards to the macroscopic shear fracture mode. In this paper, the effect of coalescence on shear band development and on associated fracture mode in plane strain is analysed numerically. The calculations are performed using a recent elastic-viscoplastic Gurson-like model that accounts for void shape evolution, coalescence and post-coalescence micromechanics along with isotropic hardening and orthotropic plasticity for the matrix behaviour. The latter is introduced to represent the actual flow properties of hot-worked materials. No kinematic hardening or nucleation formulation is used in order to focus attention on coalescence effects and to discuss, with respect to experiments, published results based on kinematic hardening and nucleation effects. The most important finding is the synergistic effect of plastic anisotropy and post-coalescence yield surface curvature upon the onset of a shear band after the fracture sets in at the centre of the specimen.
TL;DR: In this paper, a micromechanical model based on a probabilistic approach is implemented in the finite element code CASTEM 2000 to develop numerical simulations that efficiently predict the overall damaged behaviour of random oriented fiber composites.
TL;DR: In this paper, two micromechanics models, referred to as "XY PEMFRC model" and "YX PEM F reinforced composite model", are presented to investigate the electro-magneto-thermo-elastic properties for piezoelectric-magnetic fiber reinforced composite (PEM-FRC) materials operating in the linear regime.
Abstract: Two micromechanics models, referred to as ‘XY PEMFRC model’ and ‘YX PEMFRC model’, are presented to investigate the electro-magneto-thermo-elastic properties for piezoelectric-magnetic fiber reinforced composite (PEMFRC) materials operating in the linear regime. These models exhibit full coupling relations between electric, magnetic, thermal and elastic fields. The required closed-form formulas for these two models are derived using the linear electro-magneto-thermo-elastic constitutive equations under the iso-field assumptions and multiple loading condition, and then are employed to study the effects of the piezoelectric-magnetic fiber volume fraction V f and cross-sectional shape on the effective constants. A numerical study is conducted to discuss the convergence of the present models for a PEMFRC rectangle-cylinder unit cell. Quantitative and qualitative comparisons show that there is an excellent agreement between the present results and those using the Mori–Tanaka mean field approach [J Intelligent Mater Syst Struct 9 (1998) 404].
TL;DR: In this article, the elastic constants of a lotus-type porous copper composite material were determined using a combination of resonance ultrasound spectroscopy and electromagnetic acoustic resonance methods, and it was shown that the elastic properties of various types of porous metals can be predicted and designed using micromechanics modeling.
TL;DR: In this paper, a micromechanics model based on the Mori-Tanaka method was developed to estimate the elastic modulus of underfill materials and an explicit expression of the underfill modulus was derived as a function of filler content and the properties of the matrix and the fillers.
Abstract: In this paper, a micromechanics model based on the Mori-Tanaka method was developed to estimate the elastic modulus of underfill materials. An explicit expression of the underfill modulus was derived as a function of filler content and the properties of the matrix and the fillers. Predictions of the modulus from this theory were compared with experimentally measured values. Excellent agreement was observed.
TL;DR: In this paper, an effective hyperelastic constitutive model for particle-filled elastomer composites based on the microstructural deformation and physical mechanism of the magnetostrictive particles embedded in the hypergraphs was developed.
TL;DR: In this paper, the Ramaswamy-Stouffer constitutive equations for metals have been modified to model the strain rate dependent inelastic deformation of ductile polymers, including hydrostatic stress effects.
Abstract: A research program is in progress to develop strain rate dependent deformation and failure models for the analysis of polymer matrix composites subject to high strain rate impact loads. The Ramaswamy–Stouffer viscoplastic constitutive equations for metals have been modified to model the strain rate dependent inelastic deformation of ductile polymers, including hydrostatic stress effects. These equations have been incorporated into a mechanics of materials based micromechanics model that was developed to analyze uniaxial composites at various fiber orientation angles. The Hashin failure criteria have been implemented into the micromechanics to predict ply failure strengths. The deformation response and ply failure strengths for the representative composite AS4/PEEK have been successfully predicted for a variety of fiber orientations and strain rates.
TL;DR: In this article, the damage process of microscale to macroscale in coarse-grained granite specimens under uniaxial compressive stress was studied by using a newly developed experimental system that allows us to observe the damaging process continuously.
TL;DR: In this article, a numerical procedure for the computation of the overall macroscopic elasticity moduli of linear composite materials with periodic micro-structure was proposed, where the deformation of the microstructure is coupled with the local deformation at a typical point of the macro-continuum by three alternative constraints of the microscopic fluctuation field.
Abstract: The paper investigates a numerical procedure for the computation of the overall macroscopic elasticity moduli of linear composite materials with periodic micro-structure. We consider a homogenized macro-continuum with locally attached representative micro-structure which characterizes a representative cell of a composite. The deformation of the micro-structure is assumed to be coupled with the local deformation at a typical point of the macro-continuum by three alternative constraints of the microscopic fluctuation field. The underlying key approach is a finite element discretization of the boundary value problem for the fluctuation field on the micro-structure of the composite. This results into a distinct closed-form representation of the overall elasticity moduli in terms of a Taylor-type upper bound term and a characteristic softening term which depends on global fluctuation stiffness matrices of the discretized micro-structure. With this representation in hand, overall moduli of periodic composites can be computed in a straightforward manner for a given finite element discretization of the micro-structure. We demonstrate the concept for three types of periodic composites and compare the results with well-known analytical estimates.
TL;DR: In this article, the role of each component of a refractory subjected to severe thermal loading through the use of micromechanics is highlighted, and a micro-thermomechanical analysis is used to study the behavior of brittle two-phase ceramics subjected to thermal shock.
TL;DR: In this paper, bounds for the effective elastic moduli of granular materials in terms of micromechanical parameters are derived based on variational principles. But the results of discrete element simulations are used to compare the obtained bounds with the actual moduli.