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    Electroelastic Analysis of Piezoelectric Composites Using Electro-Echanical Equivalent Inclusion Method:A Micromechanical Approach

    , Ph.D. Dissertation Sharif University of Technology Hashemi, Roohollah (Author) ; Kargarnovin, Mohammad Hassan (Supervisor) ; Mohammadi Shodja, Hossein (Supervisor)
    It is the main idea of present thesis to provide a micromechanical method as a general treatment for several fundamental problems of the piezoelectric inhomogeneities. For initial demonstration of pertinent methodology, a single piezoelectric inhomogeneity of ellipsoidal geometry, under non-uniform far-field loading is considered. Accordingly, it is taken equivalent to elastic and dielectric inclusion problems connected by proper eigenstrain-electric field. This approach is named the electro-mechanical equivalent inclusion method (EMEIM) and requires that the electroelastic fields of the inhomogeneity to be equal to fields of the equivalent inclusions. Afterwards, the complex problem of... 

    Calculation of Heterogenous Material Properties by Using of Eshelby based and BEM Methods

    , M.Sc. Thesis Sharif University of Technology Yazdanparast, Reza (Author) ; Hosseini Kordkheili, Ali (Supervisor)
    To days the heterogeneous material are used extensively in the engineering materials. Optimization ability is a key feature of these materials to reach desired properties. Heterogeneous materials are the materials that make up from the constituents of multiphase materials in lower length scale such as mesoscopic, microscopic or/and Nano scales. So the properties of these materials at each scale are depending on to several characteristics of heterogeneities such as geometry, material and packing. In these materials the effects of heterogeneities at the lower scales are very significant and the constitutive equations are different for each range of scale. The proper selection of this range... 

    Hierarchical Multi-scale Analysis using Nonlinear Finite Element & its Application to Porous Media

    , M.Sc. Thesis Sharif University of Technology Asgharzadeh, Mohammad Ali (Author) ; Naghdabadi, Reza (Supervisor) ; Sohrabpour, Saeed (Supervisor)
    Porous materials, with diverse applications in engineering branches, are categorized as multi-scale. A multi-scale material is one which shows different structure and/or behavior in two or more different length scales. There are physical models which can calculate the macroscopic properties of such materials by using both the properties and volume fractions of the ingredients. However, the number of such theories which can handle problems in the fields of elasticity and hydrodynamics is much less; the fields in which the tensor orders of the properties are more than one. Fortunately, in recent years, a new method named "Computational Multi-scale Homogenization" has been offered to homogenize... 

    A Micromechanical Progressive Damage Algorithm for Prediction of Failure in Composite Laminates

    , M.Sc. Thesis Sharif University of Technology Rajaeenezhad, Iman (Author) ; Hosseini Kordkheili, Ali (Supervisor)
    Macro models which are used to predict failure of composite structures in most cases predict ¬reasonable results; however, they are not able to consider micro level parameters such as micro cracks. Furthermore, these failure macro models need various empirical data. Considering micromechanical construction of composites; including fiber, matrix and their interfaces, using micromechanical models for predicting failures in these phases is more appropriate. The aim of this study is to represent a micro-mechanical algorithm in order to predict progressive failures of fiber-reinforced composites. The failure model which is used in this study is a micromechanical modeling of failure (MMF) model,... 

    A Self-Consistence Numerical Method to Estimate Effective Mechanical Properties of Fibrous Composites

    , M.Sc. Thesis Sharif University of Technology Vasheghani, Koorosh (Author) ; Hosseini Kordkhaili, Ali (Supervisor)
    One of the most widely used methods in the study of the mechanical behavior of fiber-reinforced polymers is modeling and simulation of a unit cell behavior. According to the arrangement of composite materials, the unit cell is selected in order to include and represent actual constructions of the material. In this study a numerical self-consistence method is proposed to estimate effective properties of Carbon-epoxy composite materials. In this method, in addition of two main phases i.e. matrix and fiber, a phase of composite properties is also considered surrounding the unit cell. First using analytical and semi-empirical methods, the properties are calculated and are converged after... 

    Behavioral Modeling and Homogenizing of Materials Containing Rough Crack

    , M.Sc. Thesis Sharif University of Technology Shaker Ardakani, Kamal (Author) ; Mofid, Masoud (Supervisor) ; Khezrzadeh, Hamed (Co-Advisor)
    The present paper proposes a micromechanical damage model for two and three dimensional Representative Volume Element (RVE) with randomly distributed cohesive rough slit-like and penny-shaped micro cracks (Barenblatt-Dugdale type). First, the influence of crack roughness on the crack opening under macro hydrostatic stress state is studied and then the energy release contribution to material damage process is estimated. Considering the fractality of the crack trajectories yields to lower values of the volume crack opening. This will result in lower energy release rate in RVE and higher levels of material resistance. Based on the energy release rate of RVE, the effective material properties... 

    Micro-Mechanical Analysis of Matrix Shear Deformation Effect on Energy Release Rate of Fiber/Matrix Interface Debond in Unidirectional Fiber-Reinforced Plastic Composites

    , M.Sc. Thesis Sharif University of Technology Bazargani, Mahsa (Author) ; Hosseini Kordkheili, Ali (Supervisor)
    The present thesis deals with the effect of matrix shear deformation on energy released due to debonding at fiber/matrix interface during fiber pull out test, which is modeled using two concentric cylinders representing fiber and matrix. Tensile on fiber causes a shear stress at the interface. When this stress exceeds the tensile strength of the interface, debonding occurs at the interface and grows as a crack along the interface. This debonding causes a relative axial displacement between fiber and matrix along the debonded interface, which varies along the debond crack. How fiber/matrix relative displacement changes along the debond region is not known. Thus, the fiber/matrix interface is... 

    A Multi-Scale Method for Modeling and Analysis of the Creep Behavior in Composite plates

    , M.Sc. Thesis Sharif University of Technology Barzegar, Mohsen (Author) ; Hosseini Kordkheili, Ali (Supervisor)
    Polymer matrix composites, which are composed of a wide variety of short or long fibers bound together by organic polymer matrix, have been widely utilized in many engineering aeras, particularly in aerospace engineering. Recently, studying and analyzing the mechanical behavior of composites was one of the major reaserch interests. Regarding the vast variety of data drived from experimental tests, a requirement of tools that could facilitate estimating creep properties of materials is an important concern for researchers. The present work at first, introduces some major creep models and then proposes a 3D creep Burgers model for implementing in abaqus which could be used in macro phase. This... 

    Inclusion Problem in Linear Viscoelastic Media

    , M.Sc. Thesis Sharif University of Technology Kheirkhah Gildeh, Mohammad (Author) ; Mohammad Shodja, Hossein (Supervisor)
    In this study, using the correspondence principle and Laplace transform, the results obtained in the elastic medium for the Eshelby inclusion problem are expanded into the linear viscoelastic medium. The simplicity and breadth of application of the correspondence principle is so great that it enables one to obtain closed-form solutions in Laplace domain for problems that have closed form solutions in elastic media. However, in complex problems, the long formulas lead the user to apply numerical methods to perform inverse Laplace transform. First, by taking advantage of Green’s function the strain and stress fields are obtained in Laplace domain for the points lying inside and outside of an...