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Dr. Abdalla M. A. Ahmed :: Theses : |
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| Title | Modeling of Open-Hole Fiber-Reinforced Polymer Composites Failure Under Tensile Loading |
| Type | PhD |
| Supervisors | |
| Year | 2014 |
| Abstract | Fiber-reinforced polymer composites (FRPCs) are increasingly being utilized in a wide variety of industrial sectors; such as aerospace, automotive, biomedical, civil infrastructure, renewable energy and marine. A detailed awareness of the mechanical properties of these composites is extremely important for their appropriate design and optimization. Experimental determination of these properties like strength and modulus is restrictively extravagant, as there are unlimited significant factors that contribute to the increase in experimental cost including materials, tooling, processing, machining, testing, and many others. A standout amongst the most significant, however most challenging, endeavors in composites design and analysis is modeling material and structural failure. More importantly, understanding how and when a structure fails is crucial to determining how its design could be optimized, and whether it would meet its requirements. In this thesis, progressive failure analysis was performed on open-hole (O-Hole) FRPCs under tensile loading. The effect of existence of central hole, varying fabric orientation (0, 45, or 90°]), and utilizing different types of fabrics (unidirectional or woven) on the behavior of FRPCs (load, stiffness, and progressive failure) were investigated. The commercial finite element platform ABAQUS/Standard V6.12 was used for the finite element simulations, and the commercial plug-in for ABAQUS, Autodesk Simulation Composite Analysis was employed. This plug-in utilizes the concept of Multi-Continuum Theory (MCT) to efficiently model progressive failure by extracting the average constituent (fibers and matrix) stresses and strains from the corresponding composite ones and applying the appropriate physics to the constituent materials individually in order to predict composite structure failure response. The woven model is validated according to a pre-published experimental work. It was found that the numerical model is in good correlation with the experimental work. |
| Keywords | Advanced Fiber-Reinforced Polymer Composites (FRPC); Synthesis of Carbon Nanotubes (CNT) by Plasma-Enhanced Chemical Vapor Deposition (PECVD); Finite Element Modeling (FEM); Progressive Failure Analysis (PFA); |
| University | Egypt-Japan University of Science and Technology |
| Country | Egypt |
| Full Paper | - |
| Title | Mechanics of Self-Healing Microcapsules-Based Composites |
| Type | PhD |
| Supervisors | |
| Year | 2017 |
| Abstract | Recently, self-healing microcapsules attract much attention as self-healing ability considerably improves the reliability of polymer matrix composites and extends their lifetime by repairing internal and external damages. However, the present self-healing microcapsules lack the mechanical strength and thus is critical to be used in practical applications. Recent investigations have focused on the theoretical evaluation of the effective mechanical properties of microcapsules-based composites by assuming the constituents mechanical properties. The aim of this study is to investigate, as a first brick, the effective elastic properties of self-healing microcapsules-based polymer composites theoretically and validate them experimentally. In order to build the theoretical models, the elastic properties of urea-formaldehyde microcapsules encapsulating dicyclopentadiene (UF/DCPD) and epoxy matrix constituents were determined experimentally. The elastic modulus of the matrix material was evaluated using dynamic mechanical analysis (DMA) of neat polymer. Furthermore, single-microcapsule compression by micromanipulation was performed accompanied by two-dimensional finite element modeling (FEM) to extract the elastic modulus of single-microcapsules. These determined constituents elastic properties were used in FEM and analytical modeling of self-healing microcapsules-based composites to predict their effective elastic properties. Microstructures having packing arrangement of simple cubic (SC), body-centered cubic (BCC), face-centered cubic (FCC), and random-monodispersed (RM) microcapsules were investigated using detailed three-dimensional finite element models (FEMs). The microcapsules size and shell wall thickness reflect the microstructural geometry at definite volume fractions. A proposed analytical model of three-constituent core-shell-matrix composites was developed to be suitable for a hierarchal approach for solving three-constituent composites. Dynamic mechanical analysis (DMA) was performed to determine the elastic modulus of prepared composites containing 5, 10, and 20 vol% of microcapsules. Experimental verification was obtained by comparing the experimental work with the FEM and analytical modeling results. Good agreement was achieved. It was found that the volume fraction and the packing arrangement of the self-healing microcapsules in the polymer were the only parameters that affect the composite effective elastic modulus, while the size and shell thickness of these microcapsules are not effective. This work is important for designers and researchers involved in designing of composite structures incorporating self-healing microcapsules. Moreover, this work creates a simple paradigm for future studies on verified multiscale modeling and progressive failure of self-healing microcapsules-based composites. The effect of variation of the microcapsules shell elastic modulus on the effective mechanical properties of the composite was studied. This variation of shell elastic properties was due to different microcapsules load-deformation response, diameter, and/or shell thickness. It was found that for self-healing healing microcapsules that are always characterized by low shell thickness to radius ratio, only one microcapsule testing is sufficient for verification of the theoretical results because the effect of this variation on the effective properties is not significant. Moreover, the dynamic mechanical properties of self-healing microcapsules-based composites at different microcapsules volume fractions and sizes were studied. It was found that the addition of microcapsules in polymers decreases the storage modulus. However, it increases the glass transition temperature at low volume fraction due to the higher glass transition temperature of the shell material and then increases again due to the increase of the core volume fraction which is a liquid phase basis. As smaller microcapsules show higher stiffness and higher shell thickness to radius ratio, the storage modulus and glass transition temperature of the composites containing smaller microcapsules were found to be higher than that containing larger ones. |
| Keywords | Microcapsules Systems; Single-Microcapsule Compression; Polymer Composites; Dynamic Mechanical Analysis (DMA); Finite Element Modeling (FEM); Micromechanics; |
| University | Egypt-Japan University of Science and Technology |
| Country | Egypt |
| Full Paper | - |
