Showing papers on "Micromechanics published in 1997"
Book•
01 Jan 1997
TL;DR: The What and Why of Fibrous Composites as mentioned in this paperibrous composites have been studied extensively in the literature, e.g., in the context of solid mechanics and 3-dimensional constitutive equations.
Abstract: The What and the Why of Fibrous Composites. Concepts of Solid Mechanics. 3--D Constitutive Equations. Plane Stress Constitutive Equations. Lamination Theory. Test Methods. Material Response. Interlaminar Stresses. Failure and Damage. Laminated Tubes. Micromechanics. Appendices. Indexes.
896 citations
19 Mar 1997
TL;DR: In this paper, the authors define fibres, fabrics and fillers matrix resins and fibre/matrix adhesion as constituents of composite materials and apply them in a variety of applications.
Abstract: Introduction - definitions, classifications and applications. Part 1 Constituents: fibres, fabrics and fillers matrix resins and fibre/matrix adhesion. Part 2 Mechanics: micromechanics mechanics of laminated structures mechanics of woven fabric composites fracture and damage mechanics in laminated composites. Part 3 Processing: processing for laminated structures press moulding processes filament winding the pultrusion process for continuous automated manufacture of engineered composite profiles processing of thermoplastic matrix composites processing of particle-reinforced metal matrix composites joining and repair of aircraft composite structures machining of composite materials. Part 4 Properties and performance: laminated polymer matrix composites random fibre composites selection guidelines for metal matrix composites ceramic matrix composites cement matrix composites. Part 5 Testing: mechanical property measurements nondestructive tests. Part 6 Engineering with composite materials: design methodology and practices materials selection, preliminary design and sizing for composite laminates design guidelines for laminated composites.
385 citations
TL;DR: In this paper, a crack bridging model accounting for slip-hardening interfacial shear stress is derived for randomly oriented discontinuous flexible fibers in cement-based composites, based on a micromechanics analysis of single fiber pull-out.
Abstract: A new crack bridging model accounting for slip-hardening interfacial shear stress is derived for randomly oriented discontinuous flexible fibers in cement-based composites, based on a micromechanics analysis of single fiber pull-out. The complete composite bridging stress versus crack opening curve (σB − δ relation) and associated fracture energy are theoretically determined. A micromechanics-based criterion which governs the existence of post-debonding rising branch of the σB − δ curve is obtained. Implications of the present model on various composite properties, including uniaxial tensile strength, flexural strength, ductility and critical fiber volume fraction for strain-hardening, are discussed together with an example of a 2% polyethylene fiber reinforced cement composite. It is found that the present model can very well describe the slip-hardening behavior during fiber pull-out which originates from fiber surface abrasion at fiber/matrix interface. In addition, the new model predicts accurately the enhanced toughness in terms of both ultimate tensile strain and fracture energy of the composite and resolves the deficiency of constant interface shear stress model in predicting the crack opening and ultimate strain, which are critical for material design of pseudo strain hardening engineered cementitious composites (ECCs).
302 citations
TL;DR: In this paper, the authors investigated void growth and coalescence under physical states similar to those found in highly stressed regions ahead of a crack and showed that micro void cavitation and link-up will increasingly dominate the failure process resulting in a brittle-like ductile rupture mode in which very little energy is expended.
Abstract: Void growth and coalescence under physical states similar to those found in highly stressed regions ahead of a crack is investigated. The analysis introduces a representative material volume containing several large voids and a population of microvoids present from the very beginning, all of which are modeled as discrete entities. Plastic yielding has pervaded the material volume of interest. The underlying micromechanics of final rupture is dominated by a succession of rapidly growing microvoids. This involves the synergistic interaction between elasticity associated with high stress triaxiality, stiffness softening caused by plastic yielding and a rich supply of length scales arising from voids of vastly different sizes. A primary feature of the coalescence phase is an unstable deformation mode whereby a minute, benign void rapidly enlarges reaching a size set by the characteristic length of the locally elevated stress field. The process begins with a large void growing in concert with the plastic strain. Simultaneously, a local zone of high stress concentration emanates from the large void and spreads across the material raising the stresses at nearby microvoids. As a result, the hydrostatic stress surrounding one or more microvoids is raised to a level that activates an unstable deformation mode in which the stored elastic energy drives the plastic expansion of the microvoid. Although the overall stress decreases rapidly, small zones of high stress concentration are generated near growing voids—causing even smaller nearby microvoids to grow rapidly. This process continues until the submicron ligament fails by microcleavage or by shearing along crystallographic planes. Plastic yielding plays a crucial role in the above process by lowering the stress level required for the unstable-like growth mode of microvoids. The process outlined above appears to be the main operative mechanism in several observed failure modes in metal alloys. The morphologies of fracture surfaces dominated by flat dimpled rupture and voidsheet formation can be elucidated by the present work. For high-strength metals, our studies suggest that microvoid cavitation and link-up will increasingly dominate the failure process resulting in a brittle-like ductile rupture mode in which very little energy is expended.
168 citations
TL;DR: In this paper, a single-filament model of a commercial glass-fiber-reinforcement manufacturing process was used to apply methacryloxy and amino silanes with one, two, and three silanols (mono-ol, diol, and triol) to two different glass fibers in a molecular model.
138 citations
01 Jun 1997
TL;DR: In this paper, the statistical distribution of the constituent phases of the considered random inhomogeneous materials is available, but only partial information on the statistical distributions of the component phases is available.
Abstract: One of the main specific aspects of continuum micromechanics is related to the fact that one has generally to deal with ill-defined bodies: only partial information on the statistical distribution of the constituent phases of the considered random inhomogeneous materials is available
122 citations
Book•
01 Jan 1997
TL;DR: In this article, the authors present seminal papers in micromechanics, up to and including papers written in 1990, arranged by topic, with an introduction to each section written by expert and editor, William Trimmer.
Abstract: Description: Electrical Engineering Micromechanics and MEMS Classic and Seminal Papers to 1990 Micromechanics is a rich, diverse field that draws on many different disciplines and has potential applications in medicine, fields will find uses for micromechanics in the next ten years. Micromechanics and MEMS gives you convenient access to the fundamental papers in this rapidly growing field. Until now, papers written during the earlier stages of this field have been difficult to retrieve. Micromechanics and MEMS presents seminal papers in micromechanics, up to and including papers written in 1990. This volume gives you an historical perspective of the field and insight into where the field is heading. The papers are arranged by topic, with an introduction to each section written by expert and editor, William Trimmer. Topics covered include:
112 citations
TL;DR: In this article, an analytical method called the selective averaging method (SAM) was proposed for prediction of the thermoelastic constants of textile composite materials, where the unit cell of the composite is divided into slices (mesoscale), and the slices are subdivided into elements (microscale).
110 citations
TL;DR: In this article, an attempt has been made to establish macroscopic constitutive relations of ferroelectric single crystals in terms of micromechanics approaches on the basis of analyzing the coupled microscopic electroelastic fields and using the internal variable theory, the domain switching conditions, the evolution of microstructures, the incremental mechanical and electrical relations are formulated, the model is then used to approximately simulate the nonlinear behavior of polycrystalline ferroelectrics.
106 citations
TL;DR: In this paper, a micromechanics-based Helmholtz free energy is obtained in the framework of irreversible thermodynamics, and a kinetic relationship, a martensitic nucleation criterion and the reorientation criterion are obtained.
TL;DR: In this paper, the density distribution of geometrically necessary dislocations, which accompany the gradient of plastic slip strain on slip systems, is evaluated by a finite-element technique.
Abstract: The density distribution of geometrically necessary dislocations, which accompany the gradient of plastic slip strain on slip systems, is evaluated by a finite-element technique. As a numerical example, the bending of a single-crystal plate is analysed. The result obtained for the density distribution of dislocations shows good agreement with that obtained by micromechanics theory.
TL;DR: In this paper, a physically based computational micromechanics model was developed to study random and discrete microstructures in functionally graded materials (FGMs), and the influences of discrete microstructure on residual stress distributions at grain size level were examined with respect to material gradient and FGM volume percentage.
TL;DR: In this paper, a computationally efficient method for analyzing the performance of short-fiber reinforcement in cementitious composites is presented, where each fiber is modeled as a discrete entity.
TL;DR: In this paper, a simple, 3D yield function that is quadratic in stresses was proposed to describe the plastic behavior of fiber composites, which relaxes the two usually used assumptions that hydrostatic stress does not influence plastic deformation and that the total plastic dilatation is incompressible.
Abstract: A simple, 3-D yield function that is quadratic in stresses was proposed to describe the plastic behavior of fiber composites. It relaxes the two usually used assumptions that hydrostatic stress does not influence plastic deformation and that the total plastic dilatation is incompressible. It is also general in nature to allow for composites with various fiber volume fractions and different fiber arrays. The applicability of this quadratic yield function to fiber composites was examined, and the accuracy of the elasto-plasticity model was verified by using the macro stress-strain data generated by a 3-D nonlinear micromechanics model. Because this anisotropic plasticity model is simple and is in the general form of those widely used in existing numerical plasticity codes, it can easily be incorporated into the existing codes with little effort.
TL;DR: In this paper, a finite element based micromechanical method is developed for computing the plate stiffness coefficients (A, B, D matrices) and coefficients of thermal expansion (α's and β's) of a textile composite modeled as a homogeneous plate.
Abstract: A novel finite element based micromechanical method is developed for computing the plate stiffness coefficients (A, B, D matrices) and coefficients of thermal expansion (α's and β's) of a textile composite modeled as a homogeneous plate. Periodic boundary conditions for the plate model, which are different from those for the continuum model, have been derived. The micromechanics methods for computing the coefficients of thermal expansion are readily extended to compute the thermal residual stresses due to curing. The methods are first verified by applying to several examples for which solutions are known, and then applied to the case of woven composites. The plate stiffness coefficients computed from direct micromechanics are compared with those derived from the homogenized elastic constants in conjunction with the classical plate theory. It is found that the plate stiffness coefficients of textile composites, especially the B and D matrices, cannot be predicted from the homogenized elastic constants and ...
TL;DR: In this article, an integrated micromechanics approach using modern observation and image processing tools may provide the necessary information about the internal mechanisms and variables involved in cracking, damaging and fracture phenomena in strongly heterogeneous materials.
TL;DR: In this paper, Cheng and He [Int. J. Engng Sci., 1995, 33, 389] showed that the micropolar Eshelby tensors are size-dependent both for the inside and for the outside of the circular cylinder.
TL;DR: In this article, the elastic-plastic response of short-fiber composites with a preferred orientation of the reinforcement, i.e., a texture, is predicted. But the authors focus on a simple micromechanics model to predict the elastic response.
TL;DR: In this paper, a micromechanical approach is proposed to predict the initial tensile response under uniaxial loading of a bonded two-dimensional fibrous network consisting of two kinds of fibers.
Abstract: A micromechanical approach is proposed in this work to predict the initial tensile response under uniaxial loading of a bonded two-dimensional fibrous network consisting of two kinds of fibers. The...
TL;DR: In this paper, a review of the application of analytical optical microscopy to the analysis of composite micromechanics in a number of different composites systems is presented, including single-fibre pull-out test, crack bridging with an array of fibres, stress concentrations around a hole in a unidirectional composite and a high-volume fraction woven composite.
Abstract: A review is presented of the application of analytical optical microscopy to the analysis of composite micromechanics in a number of different composites systems. A description is given of the use of Raman spectroscopy to follow fibre deformation in a variety of different aramid/epoxy composite test-pieces. Various examples are presented including the single-fibre pull-out test, crack bridging with an array of fibres, stress concentrations around a hole in a unidirectional composite and a high-volume fraction woven composite. In each case it is shown that the Raman technique gives a unique opportunity to measure local fibre strain leading to the possibility of analysing fully the deformation micromechanics. In addition it is shown how, for alumina-based fibres such as PRD-166, well-defined fluorescence spectra can be obtained and that the stress-induced fluorescence band shifts allow deformation micromechanics to be studied for PRD-166 fibres in a glass matrix. In particular it is shown how it is possible to determine the level of thermal residual strain and follow the effect of externally imposed deformation upon the level of residual strain.
TL;DR: In this article, the elastic properties and stress distributions of plain-weave composites under in-plane tensile loading were investigated for the configurations of single lamina, iso-phase laminate, out-of-position laminate and random phase laminate.
TL;DR: A multicontinuum approach to structural analyses of composites is described in this article, where a continuum field is defined to represent each constituent material along with the traditional continuum field associated with the composite.
Abstract: A multicontinuum approach to structural analyses of composites is described. A continuum field is defined to represent each constituent material along with the traditional continuum field associated with the composite. Finite element micromechanics is used to establish relationships between composite and constituent field variables. These relationships uncouple the micromechanics from structural solutions and render an efficient means of extracting constituent information during the course of a finite element structural analysis. Equations are developed for the case of a linear elastic reinforcing material embedded in a linear viscoelastic matrix and verified by comparison with results of finite element micromechanics.
TL;DR: In this article, a Karman type nonlinear theory of laminated composite plates with weakened interfacial bonding is developed, where each weakly bonded interface is modelled by a spring-layer model which has recently been used efficiently in the field of micromechanics of composites.
TL;DR: In this article, a mathematical model that captures the effects of microstructure on the macromechanical response of granular materials was presented, where the overall imposed stresses determine the overall strain response.
TL;DR: In this paper, a higher-order theory for the response of a functionally graded composite plate subjected to a through-thickness thermal gradient is employed to optimize the composite's microstructure.
Abstract: A recently developed higher-order theory for the response of a functionally graded composite plate subjected to a through-thickness thermal gradient is employed to optimize the composite's microstructure. The higher-order theory explicitly couples the microstructural and macrostructural effects, thereby providing a rational methodology for analyzing the response of functionally graded materials, typically analyzed using the standard uncoupled micromechanics approach, which often produces erroneous results. Herein, the higher-order theory is incorporated into an optimization algorithm to determine optimal through-thickness distributions of the reinforcement phase in a composite plate subjected to a thermal gradient that minimize the inplane moment resultant, and thus the tendency of the plate to bend about an axis. The results indicate that the manner of constraining the plate from bending due to the thermal gradient is a major factor that governs the optimal reinforcement phase distributions.
TL;DR: In this article, the pressure-induced conducting mechanisms of conductive adhesives were investigated and a deformation analysis revealed a logarithmic pressure-resistance relationship and is capable of addressing the conducting phenomena for both rigid and deformable particle systems within a contact mechanics framework.
Abstract: Micromechanics models which aim to provide an understanding of conductive adhesive materials from the level of micro-particles (less than 30 mm) are presented in this paper. The pressure-induced conducting mechanisms are investigated. A deformation analysis reveals a logarithmic pressure-resistance relationship and is capable of addressing the conducting phenomena for both rigid and deformable particle systems within a contact mechanics framework. This logarithmic relationship also provides analytical support for findings reported in the literature of conductive adhesive research. It is observed that electrical contacts are made by squashing conducting particles for a deformable particle system while the particle penetration creates a crater in metallization to make contacts for a rigid particle system. The current analysis provides simple closed-form solutions for the elastic deformation of single-particle contacts and based on the assumption that the contact forces are evenly distributed in a conductive film, the pressure-resistance responses are correlated to the particle volume fraction. The high volume fraction, while ensuring that there are a sufficient number of particles to make contacts, may limit the particle deformation due to overall increased stiffness, resulting in the increased resistance on a per particle basis. The current analysis also offers insight into design considerations whereby limited amount of deformation (low processing temperature) and sufficiently low electrical resistance are to be simultaneously satisfied. For the mechanical performance, the uniaxial nonlinear stress-strain relationship is obtained for conductive adhesive systems in terms of polymer and particle material properties. The Mori-Tanaka's method is utilized to account for particle-particle and particle-matrix interactions. The behaviour in thermal expansion within the elasto-plastic deformation range is also obtained in a similar fashion. In all these calculations, only a very simplified finite element analysis for the problem of a particle embedded into an infinitely extended matrix material needs to be carried out.
TL;DR: In this paper, a set of micromechanics equations for the analysis of particulate reinforced composites is developed using the mechanics of materials approach, which are used to compute homogenized or equivalent thermal and mechanical properties of composite in terms of the properties of the constituent materials.
Abstract: A set of micromechanics equations for the analysis of particulate reinforced composites is developed using the mechanics of materials approach. Simplified equations are used to compute homogenized or equivalent thermal and mechanical properties of particulate reinforced composites in terms of the properties of the constituent materials. The microstress equations are also presented here to decompose the applied stresses on the overall composite to the microstresses in the constituent materials. The properties of a 'generic' particulate composite as well as those of a particle reinforced metal matrix composite are predicted and compared with other theories as well as some experimental data. The micromechanics predictions are in excellent agreement with the measured values.
TL;DR: In this paper, a simplified micromechanics model and a damage evolution function are incorporated into a finite-element analysis program for laminated fibrous composite structures in order to investigate the effects of microscale damages on the structural response.