Sharif Digital Repository

The use of micromechanical models to study composite material's behavior leads to save time and cost. In this paper, bridging micromechanical models have been used in order to observe the behavior of unidirectional laminate composite under fatigue loading. In order to study the fatigue behavior, stiffness degradation has been studied as well as the strength degradation and a driftnet model has been proposed for each of them. The strength degradation has only been studied for the unidirectional fiber, while the stiffness degradation has been studied for the fibers with different fiber angle. The results are compared with macro-mechanical models and other methods in literature  

The aim of this paper is to investigate adhesion property between nano-layered filler and the polymer matrix using a combination of experimental and micromechanical models as well as the changes in yield strength and stiffness of a layered silicate-filled epoxy nanocomposite. The results indicate that addition of intercalated layered silicate particles increased Young's modulus and yield strength of the epoxy resin, although the increases in stiffness and yield strength are modest, 30% and 4%, respectively. In addition, experimental results were compared with predictive stiffening and strengthening models. The rule of mixtures provides an upper bound for the modulus in these materials, while... 

Based on the Eshelby's equivalent inclusion method (EIM) and Hill's theorem on discontinuities of elastic fields across the interfaces, a theory for the determination of the stress intensity factors (SIFs) of arbitrarily oriented interacting cracks under non-uniform far-field applied stress (strain) is developed. As shown in this investigation the EIM proposed by Moschovidis and Mura can be extended for treatment of such problems, but their formulations are quite cumbersome and computationally inefficient. An alternative analytical approach is proposed that is computationally more efficient, and unlike the method of Moschovidis and Mura can easily handle complex problems of interacting... 

The objective of the present study is to predict Young's modulus of polymer-layered silicate nanocomposites (PLSNs) containing fully intercalated structures. The particular contribution of this article is to consider the changes in structural parameters of different intercalated morphologies in vicinity of each other. These parameters include aspect ratio of intercalated stacks, number of silicate layers per stack, d-spacing between the layers, modulus of the gallery phase, and volume fraction of each intercalated morphology. To do this, the effective particle concept has been employed and combined with the Mori-Tanaka micromechanical model. It has been shown that the simultaneous effects of... 

Due to the necessity for methods that are able to handle complexities of systems, use of Method Engineering (ME) to construct more adaptable and flexible methods has become of importance. Assemblybased approach is the most well-known approach of ME that performs method construction by reusing and assembling different method fragments. This approach, like other approaches of ME, suffers from the lack of suitable guidelines. In this way, architecture-centric method engineering (ArCME) is a new approach which aims at performing ME processes in a more disciplined and cohesive way. In this paper, process of assemblybased ME is enhanced by ArCME. Furthermore, benefits of implementing the process... 

The evolution of the microstructure of an assembly of cohesionless granular materials with associated pores, which carry the overall applied stresses through frictional contacts is a complex phenomenon. The macroscopic flow of such materials take place by the virtue of the relative rolling and sliding of the grains on the micro-scale. A new discrete element method for biaxial compression simulations of random assemblies of oval particles with mixed sizes is introduced. During the course of deformation, the new positions of the grains are determined by employing the static equilibrium equations. A key aspect of the method is that, it is formulated for ellipse cross-sectional particles, hence... 

In this report, the time-dependent carrier concentration in electrolytic cells, due to some basic periodic shapes, has been studied. Exact analytical solutions for step, sinusoidal and periodic pulse reverse inputs are derived. The effect of frequency, forward and reverse amplitudes, and pulse modulation width are investigated. Analytical solution of the model is obtained as a Fourier series, using Laplace transformations applied to a one-dimensional model with linearized Butler-Volmer electrode kinetics. The results are applied to an acid-copper bath and discussed. It is shown that there exist optimal operation points or optimal current waveforms to obtain efficient and enhanced deposition... 

An analytical approach is proposed for studying the elastic-plastic behavior of short fiber reinforced metal matrix composites under tensile loading. In the proposed method, a micromechanical approach is employed, considering an axi-symmetric unit cell including one fiber and the surrounding matrix. First, the governing equations and the boundary conditions are derived and the elastic solution is obtained based on some shear lag type methods. A plastic deformation is considered for the matrix under each small tensile loading step. Then, applying the successive elastic solutions method, all the plastic strain terms are obtained for the matrix. Thereafter, the elastic-plastic stress transfer... 

In contrast to the traditional study of composites containing ellipsoidal inclusions, we highlight some calculated results for the effective moduli when the inclusion shape can be described by the superspherical equation, [image omitted], such that when p = 2 it reduces to a sphere and when p it becomes a perfect cube. We consider the cases of both aligned and randomly oriented superspherical inclusions with isotropic, cubic, and transversely isotropic properties, and show how the shape parameter, p, affects the overall moduli of the composites during the spherical to cuboidal transition  

A modified analytical model is developed for analysis of 3D elastic stress fields in short fiber composites subjected to an applied axial load. Two sets of exact displacement solutions for the matrix and fiber are derived based on the theory of elasticity. The superposition state of these solutions are then used to obtain the analytical expressions for the 3D stress field components over the entire composite system including the fiber end region, which is modeled by the use of imaginary fiber technique. The main difference with the previous works here is that the stress field is considered to be a function of both radial and axial directions. Such an assumption made it possible to calculate... 

The efficiency of fiber/matrix interface bonding in composites has an important influence on their overall performance. This article deals with the simulation of interface imperfection effect as it grows under fatigue loading. The relations have been derived based on the constituents' properties for the primary damage mode in unidirectional composites and boundary conditions defined for elements of the micromechanics model. Conformation of model stiffness predictions with the best described residual stiffness model indicates the way to find the remaining constants in the simulated relation. Finally through this relation, cyclic corrected stress components in constituents could be determined.... 

The overall mechanical properties of composite materials are dependent on the mechanical response of individual constituents and their interactions while they may be relatively easy to determine. This paper represents a simulation process by which the cyclic stresses and fatigue loadings on its constituents could be predicted for an under fatigue loading lamina. Hence, the unidirectional composites fatigue would be studied through its constituents. The proposed model introduces a new coupled stiffness/strength technique by relating lamina stiffness to the stress field in its constituents. Therefore, the stress field and strength considerations in its constituents could be studied when the... 

An analytical approach is proposed for studying the elastic–plastic behavior of short-fiber-reinforced metal matrix composites under tensile loading. In the proposed research, a micromechanical approach is employed, considering an axisymmetric unit cell including one fiber and the surrounding matrix. First, the governing equations and the boundary conditions are derived and the elastic solution is obtained based on some shear-lag-type methods. Since under normal loading conditions and according to the fiber material characteristics, the metal matrix undergoes plastic deformation, while the fiber remains within the elastic region, a plastic deformation is considered for the matrix under each... 

In this paper, a micromechanical study on rate-dependent behavior of connective tissues is performed. To this end, a hyper viscoelastic constitutive model consisting a hyperelastic part for modeling equilibrium response of tissues and a viscous part using a hereditary integral is proposed to capture the time-dependent behavior of the tissues. With regard to the hierarchical structure of the tissue, strain energy function are developed for modeling elastic response of the tissue constituents i.e. collagen fibers and ground matrix. The rate-dependency is incorporated into the model using a viscous element with rate-dependent relaxation time. The proposed constitutive model is implemented into... 

In this paper, a micromechanical model for connective soft tissues based on the available histological evidences is developed. The proposed model constituents i.e. collagen fibers and ground matrix are considered as hyperelastic materials. The matrix material is assumed to be isotropic Neo-Hookean while the collagen fibers are considered to be transversely isotropic hyperelastic. In order to take into account the effects of tissue structure in lower scales on the macroscopic behavior of tissue, a strain energy density function (SEDF) is developed for collagen fibers based on tissue hierarchical structure. Macroscopic response and properties of tissue are obtained using the numerical...