scispace - formally typeset
Search or ask a question

Showing papers on "Micromechanics published in 1995"


Journal ArticleDOI
TL;DR: In this paper, the influence of matrix properties on composite pseudo-strain-hardening has been studied and a new class of ECCs with improved elastic modulus by the addition of fine aggregates to the cementitious matrix is proposed.
Abstract: Pseudo-strain-hardening behaviour under direct tensile loading in short fibre reinforced cement composites designed with quantitative guidance from micromechanics has been demonstrated experimentally, and conditions for the ductile behaviour of such engineered cementitious composites (ECC) have been formulated theoretically. In this paper special focus is placed on the influence of matrix properties on composite pseudo-strain-hardening. An experimental program is undertaken to study the dependence of the matrix properties on its mix compositions governed by water/cement and the sand/cement ratios. The theoretical and experimental knowledge thus obtained are combined to propose an innovative procedure for the design of composites using different types of matrix. The study is motivated by the need to develop a new class of ECCs with improved elastic modulus by the addition of fine aggregates to the cementitious matrix. Finally, a new composite is designed, and shown experimentally to exhibit the desirable features of pseudo-strain-hardening behaviour and improved elastic modulus.

370 citations


Journal ArticleDOI
TL;DR: In this paper, a general purpose micromechanics analysis that discretely models the yarn architecture within the textile repeating unit cell was developed to predict overall, three-dimensional, thermal and mechanical properties, damage initiation and progression, and strength.
Abstract: A general purpose micromechanics analysis that discretely models the yarn architecture within the textile repeating unit cell was developed to predict overall, three-dimensional, thermal and mechanical properties, damage initiation and progression, and strength. This analytical technique was implemented in a user-friendly, personal computer-based, menu-driven code called Textile Composite Analysis for Design (TEXCAD). TEXCAD was used to analyze plain weave and 2 × 2, 2-D triaxial braided composites. The calculated tension, compression, and shear strengths correlated well with available test data for both woven and braided composites. Parametric studies were performed on both woven and braided architectures to investigate the effects of parameters such as yarn size, yarn spacing, yarn crimp, braid angle, and overall fiber volume fraction on the strength properties of the textile composite.

205 citations


Journal ArticleDOI
TL;DR: In this paper, a micromechanics model that includes the effects of the fibre-matrix interface is used in a simple cumulative damage scheme to predict the tensile fatigue behavior of composite laminates.

133 citations


01 Mar 1995
TL;DR: In this article, a micromechanical theory for the thermoelastic response of functionally graded composites with non-uniform fiber spacing in the through-thickness direction is further extended to enable analysis of material architectures characterized by arbitrarily nonuniform fibre spacing in two directions.
Abstract: A recently developed micromechanical theory for the thermoelastic response of functionally graded composites with nonuniform fiber spacing in the through-thickness direction is further extended to enable analysis of material architectures characterized by arbitrarily nonuniform fiber spacing in two directions. In contrast to currently employed micromechanical approaches applied to functionally graded materials, which decouple the local and global effects by assuming the existence of a representative volume element at every point within the composite, the new theory explicitly couples the local and global effects. The analytical development is based on volumetric averaging of the various field quantities, together with imposition of boundary and interfacial conditions in an average sense. Results are presented that illustrate the capability of the derived theory to capture local stress gradients at the free edge of a laminated composite plate due to the application of a uniform temperature change. It is further shown that it is possible to reduce the magnitude of these stress concentrations by a proper management of the microstructure of the composite plies near the free edge. Thus by an appropriate tailoring of the microstructure it is possible to reduce or prevent the likelihood of delamination at free edges of standard composite laminates.

124 citations


Journal ArticleDOI
TL;DR: In this paper, a self-consistent method has been proposed to estimate the effective properties of composite materials with respect to volume fraction distributions, and it is shown that certain assumed property distributions presented in the literature must be used with care as they are not physically realizable for certain material combinations.

120 citations


Journal ArticleDOI
TL;DR: In this article, a micromechanical formulation is presented for the prediction of the overall thermo-inelastic behavior of multiphase composites which consist of short fibers, which is an extension of the generalized method of cells that was previously derived for inelastic composites with continuous fibers, and the reliability was critically examined in several situations.

120 citations


Journal ArticleDOI
TL;DR: In this article, the effect of matrix degradation on the overall behavior of randomly oriented discontinuous-fibre composites (RODFC) is analyzed based on the modified Mori-Tanaka model.

101 citations


Journal ArticleDOI
TL;DR: In this article, a simple three-dimensional plasticity model was developed to describe the plastic response of unidirectional composite materials and the orthotropic parameters in the model were determined from the stress/strain responses of composites subjected to various experimental loading conditions.

71 citations


Journal ArticleDOI
TL;DR: In this paper, a theoretical approach is proposed to estimate the elastic moduli of three-phase composites consisting of a matrix phase reinforced by two-phase particles, based on a simple extension to nondilute concentrations of the mechanical concentration factors obtained from the recent analysis of the average elastic fields in a double inclusion by Hori and Nemat-Nasser (1993).
Abstract: A theoretical approach is proposed to estimate the elastic moduli of three-phase composites consisting of a matrix phase reinforced by two-phase particles. The theoretical predictions are based on a simple extension to nondilute concentrations of the mechanical concentration factors obtained from the recent analysis of the average elastic fields in a double inclusion by Hori and Nemat-Nasser (1993). The proposed micromechanics theory can account for the effects of shapes and concentrations of both the particles and the dispersed phase in the particles. Theoretical estimates of the concentration factors and the effective elastic moduli are obtained in closed form and are diagonally symmetric and fall within the Hashin-Shtrikman-Walpole bounds for all cases considered. The theoretical predictions are in excellent agreement with experimental results obtained from pulse-echo and rod-resonance measurements of the elastic moduli of a three-phase composite consisting of an aluminum matrix reinforced by mullite/alumina particles.

71 citations


Journal ArticleDOI
TL;DR: In this paper, a micromechanics model is developed to predict the in-plane effective thermal conductivities of plain-weave fabric composites based on a thermal-electrical analogy.

61 citations


Journal ArticleDOI
TL;DR: In this article, a micromechanics-based, three-dimensional damage model for microcrack-weakened brittle solids is developed based on modified mixed-mode growth criteria of microcracks, the evolution of DMG as well as the overall effective compliance tensor of damaged materials are formulated.

Journal ArticleDOI
TL;DR: In this article, effective properties and local stress variations of elastic fiber composites are studied by means of the homogenization method, and two different methods, "the displacement method" and "the force method" for solving the so called cell problem are derived, applied and compared.

Journal ArticleDOI
TL;DR: In this paper, a micromechanics model was developed for damage and failure analyses of laminated fibrous composite structures, which allowed the load transfer from cracked matrix to surrounding fibers until the fibers came to failure.

01 Oct 1995
TL;DR: In this article, two models are presented to predict the homogeneous elastic constants and coefficients of thermal expansion of a textile composite unit-cell, based on finite element analysis and selective averaging.
Abstract: The objective is to develop micromechanical models for predicting the stiffness and strength properties of textile composite materials. Two models are presented to predict the homogeneous elastic constants and coefficients of thermal expansion of a textile composite. The first model is based on rigorous finite element analysis of the textile composite unit-cell. Periodic boundary conditions are enforced between opposite faces of the unit-cell to simulate deformations accurately. The second model implements the selective averaging method (SAM), which is based on a judicious combination of stiffness and compliance averaging. For thin textile composites, both models can predict the plate stiffness coefficients and plate thermal coefficients. The finite element procedure is extended to compute the thermal residual microstresses, and to estimate the initial failure envelope for textile composites.

Journal ArticleDOI
TL;DR: In this paper, a higher-order theory for functionally graded materials has been developed that explicitly couples the microstructural and macrostructural effects, thereby providing both a rational methodology for analyzing the response of this new class of materials and a means for evaluating the uncoupled RVE-based micromechanics approach.

Journal ArticleDOI
TL;DR: Several micromechanics models for the determination of composite moduli are investigated in this article, including the dilute solution, self-consistent method, generalized selfconsistent methods, and Mori-Tanaka's method.
Abstract: Several micromechanics models for the determination of composite moduli are investigated in this paper, including the dilute solution, self-consistent method, generalized self-consistent method, and Mori-Tanaka's method. These micromechanical models have been developed by following quite different approaches and physical interpretations. It is shown that all the micromechanics models share a common ground, the generalized Budiansky's energy-equivalence framework. The difference among the various models is shown to be the way in which the average strain of the inclusion phase is evaluated. As a bonus of this theoretical development, the asymmetry suffered in Mori-Tanaka's method can be circumvented and the applicability of the generalized self-consistent method can be extended to materials containing microcracks, multiphase inclusions, non-spherical inclusions, or non-cylindrical inclusions. The relevance to the differential method, double-inclusion model, and Hashin-Shtrikman bounds is also discussed. The application of these micromechanics models to particulate-reinforced composites and microcracked solids is reviewed and some new results are presented.

Journal ArticleDOI
TL;DR: In this article, an experimental study of the compression fracture of unidirectional composites (T300/914, T800/5245C, M40J/913, GY70/V108 and AS4/PEEK) shows that fibre kinking is the main failure mode.

Journal ArticleDOI
TL;DR: In this article, the elastic properties of unidirectional fiber composites were investigated using the composite cylinder model and the results of the effective elastic moduli and microstresses within the constituents were compared with existing numerical solutions, both with and without partial interphase failure.
Abstract: The present work is concerned with the theoretical study of the elastic properties of unidirectional fiber composites. The approach to calculate the effective moduli of composite materials is generally based upon the premise of a representative volume element, or an element in which the strain and stress averages taken over large enough subregions of the specimen are the same for any such subregion. For purposes of computation, some model of a fiber composite must be assumed. The objective of this study is to demonstrate that the composite cylinder model can provide a good simulation for the representative volume element to define the response of a unidirectional composite for a wide range of elastic moduli and volume fraction provided the displacements are prescribed on the external surfaces. Results of the effective elastic moduli and microstresses within the constituents are compared with existing numerical solutions, both with and without partial interphase failure, to demonstrate the effectiveness of...

Journal ArticleDOI
TL;DR: In this article, a micromechanics model is developed to predict the tensile strength of unidirectional composites, where the local stresses are calculated using shear lag analysis, including the effects of interfacial debonding.
Abstract: A micromechanics model has been developed to predict the tensile strength of unidirectional composites. The local stresses are calculated using shear lag analysis, including the effects of interfacial debonding. The tensile strength of the composite is estimated by considering the accumulation of fiber fractures as a function of applied load. A new parameter called ‘efficiency’ of the interface is introduced to account for the effectiveness of load transfer from the matrix to the fiber. A simple scheme is described to estimate this efficiency parameter η using the experimentally measured tensile stiffness in the concentric cylinders model. It is postulated that the interface can be completely characterized by two parameters: interfacial shear strength τi and efficiency of the interface η. Results indicate that the interfacial strength and efficiency can be optimized to maximize the tensile strength of a unidirectional composite. The proposed model was used to predict tensile strength of three different sets of materials that possessed carefully tailored interphase variations. The predicted tensile strengths agree well with the experimental data. The predicted failure modes in these material systems are also consistent with experimental observations.

Journal ArticleDOI
TL;DR: In this article, the concept of contiguity, which is a measure of phase continuity, is applied to Mori-Tanaka micromechanics theory and it is shown that contiguit of the second phase increases with volume fraction, leading eventually to a reversal in the roles of the inclusion and matrix.
Abstract: Predictions using current micromechanics theories for the effective moduli of particulate-reinforced composites tend to break down at high volume fractions of the reinforcing phase. The predictions are usually well below experimentally measured values of the Young's modulus for volume fractions exceeding about 0.6. In this paper, the concept of contiguity, which is a measure of phase continuity, is applied to Mori—Tanaka micromechanics theory. It is shown that contiguity of the second phase increases with volume fraction, leading eventually to a reversal in the roles of the inclusion and matrix. In powder metallurgy practice, it is well known that at high volume fractions, sintering and consolidation of the reinforcement make it increasingly continuous and more like the matrix phase, while the former matrix tends to become more like the inclusion phase. The concept of contiguity applied to micromechanics theory results in very good agreement between the predicted Young's modulus and experimental data on tungsten carbide particulate-reinforced cobalt.

Journal ArticleDOI
TL;DR: In this article, a generic unit cell model which includes a unique fiber substructuring concept is proposed for the development of micromechanics equations for continuous fiber reinforced ceramic composites.
Abstract: A generic unit cell model which includes a unique fiber substructuring concept is proposed for the development of micromechanics equations for continuous fiber reinforced ceramic composites. The unit cell consists of three constituents: fiber, matrix and an interphase. In the present approach, the unit cell is further subdivided into several slices and the equations of micromechanics are derived for each slice. These are subsequently integrated to obtain ply level properties. A stand-alone computer code containing the micromechanics model as a module is currently being developed specifically for the analysis of ceramic matrix composites. Towards this development, equivalent ply property results for a SiC (silicon carbide fiber)/Ti-15-3 (titanium matrix) composite with a 0.5 fiber volume ratio are presented and compact with those obtained from customary micromechanics models to illustrate the concept. Also, comparisons with limited experimental data for the ceramic matrix composite, SiC/RBSN (Reaction Bonded Silicon Nitride) with a 0.3 fiber volume ratio are given to validate the concepts

Journal ArticleDOI
TL;DR: In this paper, Raman spectroscopy has been used to study the deformation micromechanics of the single-fibre pull-out test for a carbon fiber/epoxy resin system using surface-treated and untreated versions of the same type of PAN-based fibre.
Abstract: Raman spectroscopy has been used to study the deformation micromechanics of the single-fibre pull-out test for a carbon fibre/epoxy resin system using surface-treated and untreated versions of the same type of PAN-based fibre. It has been possible to determine the detailed strain distribution along embedded fibres and it has been found that it varies with the level of strain in the fibre outside the resin block. The variation of interfacial shear stress along the fibre/matrix interface has been determined using the balance of forces equilibrium and this has been compared with the single values of interfacial shear strength determined from conventional pull-out analyses. It has been demonstrated that it is possible to identify situations where the interface is well-bonded, partially debonded or fully debonded and also to follow the failure mechanisms in detail. It has been found that the level of interfacial adhesion is better for the surface-treated fibre and that, for the untreated fibre, interfacial failure takes place by the cohesive failure of a weakly-bonded surface skin that appears to be removed by the surface pretreatment process.

Journal ArticleDOI
TL;DR: In this article, the Stroh formalism is used to develop a general solution for an infinite, anisotropic piezoelectric medium with an elliptic inclusion; the coupled elastic and electric fields both inside the inclusion and on the boundary of the matrix are given.

Journal ArticleDOI
TL;DR: In this article, an improved micromechanics analysis is developed for the stress transfer in the single fiber fragmentation test. But the analysis is limited to carbon fiber-epoxy matrix composite.
Abstract: An improved micromechanics analysis is developed for the stress transfer in the single fibre fragmentation test. Considering the partially debonded interface as the most general case, Griffith's fracture mechanics approach is employed to derive a debond criterion at the fibre-matrix interface. An average fibre strength model from the Weibull statistics is used to determine the mean fibre fragment length as a function of applied stress. A parametric study for a carbon fibre-epoxy matrix composite shows that there is a critical applied stress below which no interfacial debonding takes place. The Poisson effect increases the interface shear stress at the debonded region towards the fibre ends, which in turn discourages further debond propagation. The mean fibre fragment length is the sum of the bonded and debonded lengths, and is substantially smaller for the composite containing fibres with a higher surface treatment level at a given applied stress greater than the critical level.

Journal ArticleDOI
TL;DR: In this paper, the authors examined parameters which are believed to control the strength of triaxially braided carbon/epoxy composites under planar biaxial loading.

T. E. Wilt1
01 Mar 1995
TL;DR: In this article, the Generalized Method of Cells (GMC) is implemented into the finite element code MARC using the user subroutine HYPELA, which provides comparable predictions of the composite behavior and requires significantly less CPU time as compared to a finite element analysis of the unit cell.
Abstract: The Generalized Method of Cells (GMC), a micromechanics based constitutive model, is implemented into the finite element code MARC using the user subroutine HYPELA. Comparisons in terms of transverse deformation response, micro stress and strain distributions, and required CPU time are presented for GMC and finite element models of fiber/matrix unit cell. GMC is shown to provide comparable predictions of the composite behavior and requires significantly less CPU time as compared to a finite element analysis of the unit cell. Details as to the organization of the HYPELA code are provided with the actual HYPELA code included in the appendix.

Journal ArticleDOI
TL;DR: In this paper, the effects of material property and fiber volume grading on the overall mechanical response of metal matrix composite tubes subjected to mechanical loadings are evaluated through the development of a fully elastic-plastic axisymmetric generalized plane strain tube model.

Journal ArticleDOI
TL;DR: In this article, the microstructure-macroproperty relation of electronic composites is studied by use of the Eshelby's method which has been extended to treat the inclusion problem of thermal and electromagnetic behavior.
Abstract: The microstructure-macroproperty relation of electronic composites is studied by use of the Eshelby's method which has been extended to treat the inclusion problem of thermal and electromagnetic behavior. Eshelby's model has further been extended to the case of coupling behavior such as piezoelectric or pyroelectric behavior. When fillers embedded in the matrix are overlapped, the Eshelby's model may not be applicable. Then one must use a percolation model, which is also discussed in this paper. Finally, the predictions based on these models are compared with experimental data to check the validity of the analytical modeling.

Journal ArticleDOI
TL;DR: In this article, the dependence of the positions of the R 1 and R 2 fluorescence lines upon fiber strain has been determined for the PRD-166 alumina-zirconia fiber.
Abstract: The dependence of the positions of the R 1 and R 2 fluorescence lines upon fibre strain has been determined for the PRD-166 alumina-zirconia fibre. It is found that the wavenumbers of both lines increase with increasing strain. The approximately linear relationship between line shift and fibre strain has been used to map the distribution of thermal residual strain along the fibres in Pyrex and soda-lime silicate (SLS) glass-matrix model single-fibre composites. It has been shown that the values of thermal strain in the fibres are close to those expected from theoretical analyses. The interfacial shear stress has been derived from the point-to-point variation of the fibre strain along the fibres. It has also been found that the distribution of strain along a fully embedded fibre is close to that predicted by conventional shear-lag analysis. It has been demonstrated that fluorescence spectroscopy is a powerful method of following the micromechanics of deformation in ceramic fibres and composites.