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micromechanical-modeling
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Modeling of Moisture-Induced Damage in Asphalt Mixtures
, M.Sc. Thesis Sharif University of Technology ; Tabatabaee, Nader (Supervisor)
Abstract
The deleterious effect of moisture on the structural integrity of asphalt mixtures has been recognized as one of the main causes of early deterioration of asphalt pavements. This phenomenon, usually referred to as moisture damage, is defined as the progressive loss of structural integrity of the mixture. Moisture damage is associated with the development of different physical, mechanical and chemical processes occurring within the microstructure of the mixture at different intensities and rates. Although there have been important advancements in identifying and characterizing this phenomenon, there is still a lack of understanding of the damage mechanisms occurring at the...
New approach for fatigue life prediction of composite plates using micromechanical bridging model
, Article Journal of Composite Materials ; Volume 49, Issue 3 , February , 2015 , Pages 309-319 ; 00219983 (ISSN) ; Farsadi, M ; Koochi, A ; Khorashadizadeh, S. N ; Sharif University of Technology
SAGE Publications Ltd
2015
Abstract
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
Modeling of stiffening and strengthening in nano-layered silicate/epoxy
, Article International Journal of Engineering, Transactions A: Basics ; Volume 30, Issue 1 , 2017 , Pages 93-100 ; 17281431 (ISSN) ; Pearson, R. A ; Bagheri, R ; Sharif University of Technology
Abstract
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...
Micromechanical Modeling the Viscoelastic Performance of the Asphalt Concrete with Finite Element
, M.Sc. Thesis Sharif University of Technology ; Tabatabaee, Nader (Supervisor)
Abstract
Asphalt concrete is a composite mixture of three phases; aggregate, bitumen and air void. Stress and strain distributions obtained from macroscopic modeling yield different results due to distinctly different mechanical properties of the above-mentioned phases. In this study a more exact analysis of the stress and strain, were carried out by considering the mixture as a two-phase composite; aggregate and mastic phases. Asphalt concrete was considered a composite material consisted of sand mastic and aggregate. Aggregate and mastic phases were separated and response of the loaded asphalt mixture was investigated. Aggregates finer than 2.36 mm in diameter, filler and bitumen consist the...
Characterization of Mechanical Properties of Polymer Nanocomposites with Spherical Inhomogeneities
, M.Sc. Thesis Sharif University of Technology ; Naghdabadi, Reza (Supervisor) ; Bagheri, Reza (Supervisor)
Abstract
The improved properties of nanocomposites are not achievable with conventional composites. Scale effect is one the most important parameters in the physical and mechanical properties of polymeric nanocomposites. One of the physical phenomena, which can be related to the scale effect, is the very large interface between the nanoparticles and the polymeric matrices. Motional behavior and conformation of polymeric chains change near the nanoparticles surfaces. Due to high interface of the nanoparticles with the polymeric matrices the amount of these types of changes in the polymeric chains are so large that can change the physical and mechanical properties of polymeric nanocomposites. In this...
Investigation of Effective Parameters in Contact Mechanics of FGM Coated Half-Space through FEM Modeling
,
M.Sc. Thesis
Sharif University of Technology
;
Adib Nazari, Saeed
(Supervisor)
Abstract
In this research, the surface contact and lateral stress distribution due to the contact between a rigid flat punch and a FG coating is investigated through macro and micro mechanical modeling due to FEM. The effects of important parameters in modeling of contact mechanics, both macro mechanically and micromechanically investigated. Study of such parameters is important, especially in fracture mechanics point of view, since stress distribution of mechanical contacts can cause the crack nucleation and evolution and finally catastrophic failure. Investigating the effective parameters in FEM models and analyzing the result admittedly help to improve manufacturing methods in order to smooth the...
A Micromechanical Study of Implants via Eigenstrain Theory
, M.Sc. Thesis Sharif University of Technology ; Mohammadi Shodja, Hossein (Supervisor)
Abstract
In this thesis, concerning Eigenstrain Theory, the micromechanical formulation of dental implants has been derived for the first time in the fields of Mechanics and Medical Science. The proliferation of using dental implants as a prosthesis for the people who lost their teeth because of poor maintenance and smoking cigarette results in scientists think more about the design of these implants and their stress fields inside the mandible. It is crystal clear that these stress fields cause stress shielding, which is a phenomenon that brings about bone loss or decrement in the bone density. Hence, if we know the stress that is produced by the implants inside the mandible, we can optimize the...
Traumatic Brain Injury at Cellular Level by Using Multi-scale Modelling in Comparison with Clinical Data
, M.Sc. Thesis Sharif University of Technology ; Farahmand, Farzam (Supervisor) ; Ahmadian, Mohammad Taghi (Supervisor)
Abstract
This study aims to provide a multiscale model of traumatic brain injury including the three levels of macro, meso, and microscale information. In order to do this, a macroscale voxel-baed model of human head was constructed. The model was designed and generated to include mesoscale tissue information as well as a voxel-based approach to include voxel-based microscale data and to be coupled in a multiscale framework. Next, three different microscale models were constructed. The variations of fractional anisotropy within one standard deviation in the regions (including 60% to 70% of voxels) can change the stiffness of the tissue by up to the considerable amount of 40%. The microscale models...
Optimization of Load Distribution at the Bone-Implant Interface in Porous Coated Implants ''A Micromechanical Study Using FEM'
, M.Sc. Thesis Sharif University of Technology ; Katoozian, Hamid Reza (Supervisor) ; Ahmadian, Mohammad Reza (Supervisor) ; Zohoor, Hassan (Supervisor)
Abstract
Loosening and gap opening at the bone-implant interface depends on several physiological and mechanical factors such as bone remodeling, stress concentration, and variation in load transfer pathway. Since fracture of orthopedic material at the interface is one of the major failure mode of total joint implants, this study focused on the micromechanical behavior of the interface. Using a two-dimensional FE model, with pure compressive, tensile, and shearing forces applied on bone or cement, ratio of the stress at the interface to the applied stress has been calculated. Stress distribution was considered as a function of porosity,angle of bead contact to surface, as well as size of bead for two...
3-D FEM analysis of plastic behavior inside MMC composites considering damage theory
, Article 25th Congress of the International Council of the Aeronautical Sciences 2006, Hamburg, 3 September 2006 through 8 September 2006 ; Volume 3 , 2006 , Pages 1759-1768 ; Farahpour, H ; Sharif University of Technology
Curran Associates Inc
2006
Abstract
The delamination phenomenon has been studied in macroscopic scale by different approaches. Here, using micro-mechanical models, it is tried to find the possible relationship between the problem and the stress fields around a fiber. Using the ideas and the results on the free surface cracking of unidirectional composite, the FEM model is developed. The model verification is done by comparing the results by the results obtained in presence of damaged incorporated by the damage theory. Here, on the free surfaces fiber/matrix debonding is applied as a composite damage and the results show a good agreement with the available results
Predicting the Brain Injury Effects on Physical Arrangement of White Matter Neuronal Tracts using a Finite Element Head Model based on Tractography
, Ph.D. Dissertation Sharif University of Technology ; Farahmand, Farzam (Supervisor) ; Shamloo, Amir (Co-Supervisor) ; Oghabian, Mohammad Ali (Co-Supervisor)
Abstract
Diffuse tensor imaging or tractography is a useful method for tracking the axonal tracts pathways within the brain white matter by monitoring the movements of water molecules along the axons. The higher the level of the tissue anisotropy, the more accurate the pathways can be estimated. But in the swelling regions around an edematous tumor, the excess of watery fluid disrupts the directional movement of water molecules, and consequently, the diffuse tensor imaging is unable to track the pathways. This impairment should be resolved by predicting the axontal tracts arrangement in the blind regions of the images using the numerical modeling. To this end, a finite element model of the human...
Incorporating multiscale micromechanical approach into PLSNs with different intercalated morphologies
, Article Journal of Applied Polymer Science ; Volume 119, Issue 6 , September , 2011 , Pages 3347-3359 ; 00218995 (ISSN) ; Bagheri, R ; Kazeminezhad, M ; Heidarian, D ; Sharif University of Technology
2011
Abstract
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...
Parametric Analysis of Thermomechanical Stresses in Functionally Graded Materials Under in-phase and out-of-phase Loading
, M.Sc. Thesis Sharif University of Technology ; Abedian, Ali (Supervisor)
Abstract
Using Functionally Graded Materials (FGMs) in hot sections of aged aircrafts is one of the most important ways for life extending of Thermal Barrier Coatings (TBCs). Sudden variation of thermal stresses in interface of bond coat and ceramic coat layers could be changed to gradual variation with use of FGMs. The stress in FGMs has been the subject of several researches. Both macro and micromechanical modeling approaches have been used in these studies. In the macro mechanical approach, FGM is modeled as a multi-layer composite in which mechanical properties of each layer is found by averaging the properties and volume fraction of FGM constituents through the thickness of the layer. In this...
Analysis of Degradation for Laminated Notched Plate in Micromechanics by “Strain Energy Release Rate” Method and Illustrations the Results in Ansys
, M.Sc. Thesis Sharif University of Technology ; Hosseini Kordkheili, Ali (Supervisor)
Abstract
By developing composites, difficulties of modeling of degradation of properties as stiffness is most considered. The recent advances in the modeling of degradations in stratified composites have led to improved models on all scales. Macro scales methods are good to estimate fracture but not to estimate the failure in micro scale (as microcrack) and moreover, they need many experimental data. Therefore by considering a stratified structure which contains fiber, matrix and intermediate area, mesoscale modeling method is most suitable. In this research Micromechanical Progressive Algorithm (MPA) is used. The method employed is Micromechanic Method of Fracture (MMF). In this work by developing a...
Elastic-Plastic Behavior Analysis of Short Fiber Metal Matrix Composites under Thermal Loading
, Ph.D. Dissertation Sharif University of Technology ; Abedian, Ali (Supervisor) ; Mondali, Mahdi (Supervisor)
Abstract
The use of metal matrix composite materials (MMC) in aerospace structures and engine parts has become more frequent recently. These materials are composed of metal matrices reinforced by hard discontinuous ceramic fibers, usually oriented longitudinally within the matrix, and due to the stability of the mechanical properties, including the hardness and the strength at high working temperatures, have found various applications.Stress transfer from the matrix to the fiber is known as the most important mechanism governing the deformation and the fracture response of such MMCs. The stress transfer characteristic of fiber reinforced composite materials under various mechanical and thermal...
Micromechanic Failure Analysis of Carbon/Phenolic Composite Conic Structures under Thermal Loading
, M.Sc. Thesis Sharif University of Technology ; Hosseini Kordkheili, Ali (Supervisor)
Abstract
In this study, through explaining a micromechanical model of progressive damage, failure in a composite conical structure under mechanical and thermal loads with 36 layers of carbon/phenolic material have been studied. To this end, first, mechanical behaviors of composite layers in micro and macro scale and their properties via fiber and matrix characterizations are discussed. In the following, selection of a proper RVE along with different types of boundary conditions on RVE are discussed. Then stress reinforcement coefficients in order to convert the mechanical and thermal stresses from macro to micro scale for carbon / phenolic material are extracted through defining appropriate RVE for...
Characterization of reinforcing effect of alumina nanoparticles on the novolac phenolic resin
, Article Polymer Composites ; Vol. 35, Issue 7 , July , 2014 , pp. 1285-1293 ; ISSN: 02728397 ; Shojaei, A ; Sharif University of Technology
Abstract
Very fine alumina nanoparticles were loaded in novolac type phenolic resin (PF) using solution mixing method. The concentration of nanoalumina in PF was varied between 2.5 to 20 wt%. All the compounds were compression molded and then subjected to scanning electron microscopy (SEM), tensile, flexural, and dynamic mechanical analysis (DMA) tests. SEM analysis showed that the nanoalumina were dispersed uniformly at low concentrations, however, at high concentrations, dispersion was suppressed leading to agglomerates in the composites. Mechanical testing revealed that the nanoalumina had a great influence on the strength and stiffness of PF resin particularly at concentrations below 5 wt%....
An investigation on the structural characteristics and reinforcement of melt processed polyamide 66/multiwalled carbon nanotube composites
, Article Polymers for Advanced Technologies ; Vol. 25, issue. 4 , 2014 , pp. 406-417 ; ISSN: 10427147 ; Nourbakhsh, P ; Faghihi, M ; Sharif University of Technology
Abstract
Properties of melt processed polyamide 66 (PA66)/multiwalled carbon nanotube composite were first characterized experimentally. The experimental results exhibited the formation of crystalline layer around the nanotubes and a considerable enhancement in mechanical properties by incorporation of multiwalled carbon nanotube up to 1 wt%. Mechanical properties were analyzed in terms of structural parameters using micromechanical models proposed in this study. It was suggested that the mechanical properties were greatly dominated by crystalline layer and nanotube length. It was also deduced that the melt mixing process caused a significant nanotube breakage restricting further enhancement of...
Effect of lateral placement of ceramic and metal grains on thermal stress distribution throughout FGMS
, Article 28th Congress of the International Council of the Aeronautical Sciences 2012, ICAS 2012 ; Volume 3 , 2012 , Pages 1878-1884 ; 9781622767540 (ISBN) ; Abedian, A ; Sharif University of Technology
2012
Abstract
The properties of Functionally Graded Materials (FGM) are characterized by gradual variation of volume fraction of their constituents or phases over the thickness direction. They are normally ceramic in one side and metal in the other side. This kind of material has been employed as thermal barrier and also as coatings in many applications including turbine blades. Thermal stress behavior of FGMs is normally studied by simulating the material as a composite laminate where the properties ofeach layer are found by averaging the properties and volume fraction of FGM constituents through the thickness of the layer. However, it should be mentioned that the grains of FGM constituents are usually...
Progressive Flexural Fatigue Failure Analysis of Composites Through Layer Failure Determination
, Ph.D. Dissertation Sharif University of Technology ; Adibnazari, Saeed (Supervisor)
Abstract
Non-uniform damage growth of the composites under flexural fatigue loading condition makes it difficult to predict the fatigue behavior. In this thesis, A new modeling procedure is developed to introduce a progressive damage model. By using this model, it will be possible to define layer failure through its damage growth and layers constituents’ properties. On the other hand, an efficient micromechanics model must be utilized to relate the external loading to the constituents’ properties. Indeed the micromechanics model must be capable of including both constituent's properties and also fiber/matrix interface efficiency. For representing a complete description of the constituents’ properties...