Master Degree / Yüksek Lisans Tezleri
Permanent URI for this collectionhttps://hdl.handle.net/11147/3008
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Master Thesis Development of Fiber Reinforced Cylindrical Composite Structures by Filament Winding Technique(Izmir Institute of Technology, 2019) Aydın, Mustafa; Tanoğlu, MetinFiber reinforced composite structures with superior properties are used for cylindrical structure systems in many application areas nowadays. The major aim of this thesis is development of filament wound composite cylindrical structures with various fiber types on different ply sequence and investigate their mechanical properties. For this purpose, 4 layered glass, carbon and glass/carbon hybrid fiber reinforced cylindrical structures were manufactured with 55 degree winding angle by utilizing filament winding technique. Produced 6 different composite structures have 1 m length and 60 mm inner diameter. Glass/carbon fiber reinforced systems were developed to reduce the cost by reducing carbon fiber usage. Apparent hoop tensile strength and radial compression tests were applied to the manufactured composite structures. In addition to these studies, two different composite plate with glass fiber and carbon fiber reinforcements were produced by filament winding to investigate glass transition temperature. These plates were manufactured with 4 layered by using the same fiber and matrix as used in the previous tube production. Dynamic mechanical analysis was performed with samples which is sectioned from plates to obtain glass transition temperature. Consequently, apparent hoop tensile strength test results showed that hoop strength of glass fiber reinforced cylindrical structures can be improved significantly by hybridization. Based on the radial compression test results, deflection of the structures decreases by hybridizationMaster Thesis Fabrication of Colloidal Photonic Crystals Via Langmuir Blodgett Technique and Their Integration of Polymer Matrix(Izmir Institute of Technology, 2019) İnci, Ezgi; Demir, Mustafa Muammer; Varlıklı, CananColloidal films have potential uses in various fields such as photonics, electronics, sensors, membrane filters, and surface devices owing to their unique optical properties. Photonic crystals composed of uniform diameter colloidal silica particles have been arranged in a periodic structure by taking inspiration from nature. The periodic structure of silica particles has physical interaction with light in a visible range. This special interaction is known as structural coloration. The close-packed monolayers and multilayers of colloidal silica particles in large area can be produced by using Langmuir Blodgett method. The integration of these photonic films with transparent polymer matrices having an elastomer feature provides for their use in optical sensor applications. In this thesis, we examined the fabrication of mechano-sensitive nanostructured films based on colloidal particles. Silica colloidal particles were synthesized at different sizes by using Stöber Process. Langmuir-Blodgett deposition was used to create three-layer of photonic crystal films with different particle diameters. For this purpose, various substrates were examined for the Langmuir Blodgett deposition process before starting the coating. The coated silica particles on the glass substrate were then embedded in an elastomeric transparent matrix. The generation of structural coloration after stretching was examined in manufactured elastomer films. In accordance with this purpose, various polymers such as acrylates and siloxanes with elastomer properties have been used. The structural characterization of these composite films and their optical properties were summarized in this thesis.Master Thesis Synthesis of Ni and Zn Based Organic Frameworks as Photocatalyst(Izmir Institute of Technology, 2019) Dikmen, Merve; Çakıcıoğlu Özkan, Seher FehimeNickel (Ni) and zinc (Zn) based organic frameworks were synthesized on the synthetic zeolite (5A and 13X), natural zeolite mineral clinoptilolite, -Alumina. Initially the zeolite surface was modified or seeded with metal organic framework (MOF). MOF-zeolite composite materials were characterized with XRD, SEM and ATR-IR to understand whether surface processes was achieved successfully or not. Additionally, band gap energies were evaluated to understand these composite materials were used as photocatalyst. Surface modification with APTES was not affect surface of the zeolites. In spite of that seeding created a layer on the surface of zeolite. Nickel based organic framework was coated onto the surface of modified 5A surface. Hydrothermal ZIF8 (ZIF8(1)) and solvothermal ZIF8 (ZIF8(2)) were synthesized successfully as MOF crystals. Besides ZIF8(2) was coated onto the surface of natural zeolite. Additionally, ZIF8/CuBTC sample were synthesized, seeded and coated onto the surface of natural zeolite. Band gap energies of the MOFs and composite materials were calculated with Tauc plot. Results showed that UV light can be used as light source for photocatalytic reactions of these photocatalysts. Also increasing photocatalyst amount increased dye degredation under UV light.Master Thesis Stacking Sequence Optimization and Modeling of Laminated Composite Plates for Free Vibration(Izmir Institute of Technology, 2018) Hasanoğlu, Emre Azim; Artem, Hatice SeçilComposite materials, especially fiber reinforced composites, have been extensively used in various engineering fields such as automotive, aerospace, aircrafts, defense, marine and so on due to having their high specific strength to weight and stiffness to weight ratios. In these last years, vibration problem has become more and more important in the structures where thin plates are used. Therefore, free vibration characteristics of composite structures under the influence of dynamic forces should be determined in the design process. Accordingly, in this thesis, optimum designs, which maximize the natural frequencies of laminated composite plate, are investigated by using hybrid algorithm combining the genetic algorithm (GA) and generalized pattern search algorihm (GPSA). Composite plates made of graphite/epoxy have been considered and assumed to be symmetric with continuous fiber angles in the laminate sequences. The natural frequency of plates is obtained bu using the Rayleigh Ritz method analytically. Free vibration equation is taken as objective function and fiber orientation angles are chosen as design variables. The natural frequency is maximized for various boundary conditions, aspect ratios, number of ply and material properties. The optimum designs obtained are verified by finite element method, and mode shapes of laminated composite plates are presented. A comparison between continuous and conventional (laminate in which the orientation angles are limited to the conventional orientations) designs is performed in order to show the reliability of continuous plates. As a results, it is observed that material properties, boundary conditions and dimensions of composite plates play important role on vibration behavior of composite plates. On the other hand, the natural frequencies and the optimum fiber oriantation angles are not affected from the change of number of plies.Master Thesis Analysis and Implementation of Optical Fiber Sensors for Process Monitoring of Composite Materials(Izmir Institute of Technology, 2016) Yılmaz, Anıl; Yüksel Aldoğan, Kıvılcım; Yüksel Aldoğan, KıvılcımThe use of composite materials in many industrial applications and structures under high stress (airplane wings, unmanned air vehicles, wind turbines, etc.) has been exponentially growing thanks to their lightweight, superior strength, durability, and corrosion resistance. However, the unique mechanical properties of composite materials cannot be fully exploited without monitoring them when material is placed under constraints. It is essential to monitor their behavior not only in the field but also during manufacturing process to ensure the high quality of manufactured materials. For this purpose, the use of optical fiber sensing, particularly the embedding of fiber Bragg grating (FBG) sensors into composite materials has been gaining growing popularity thanks to various advantages of FBGs. In this context, the main purpose of this thesis is to demonstrate the feasibility of using optical fiber sensors for process monitoring (cure and resin flow) of fiber reinforced thermoset composite materials. The first sensor type studied in the thesis was based on Fresnel reflection. The capability of monitoring the curing profile of liquid matrix (mixture of resin and hardener) has been demonstrated by the way of Fresnel reflection sensor interrogated by Optical Time Domain Reflectometry (OTDR). Then, FBG sensors were embedded into composite plates to measure the temperature change during resin injection and cure cycle, as well as determining the residual strain inside the material. In spite of the popularity of using FBG sensors, most recent researches clearly prove that there is still a lack of technical maturity in real life applications in interrogating embedded FBGs for strain measurements. There is still room for new sensing approaches. In the last part of the thesis, we proposed a novel method to interrogate fiber cavity ring-down (CRD) loop by using OTDR which makes this sensing approach more practical and cheaper than the conventional techniques. Thanks to these advantages, our proposed interrogation method can be implemented for strain measurements inside the composite materials as an alternative to the FBG sensors.Master Thesis Integration of Red & Blue Tl Materials To Different Polymer End-Use(Izmir Institute of Technology, 2016) İncel, Anıl; Demir, Mustafa MuammerTriboluminescence (TL) is known as the emission of light upon the application of any mechanical force. In this master thesis, two organometallic-based TL crystals, which are EuD4TEA and Cu(NCS)(py)2(PPh3) were obtained and they were integrated in the transparent polymers: poly (methylmetacrylate) (PMMA), poly (styrene) (PS), poly (urethane) (PU) and polyvinylidene fluoride (PVDF) for different end-use. In the development of composites, two different processes were carried out: i) embedding (or blending) and ii) surface impregnation. The different end-use polymers were used as transparent polymer film, electrospun nanofibers, and nanobeads. TL performance of composites were investigated by using drop tower system which was specficically designed for this research. Atomic force microscopy (AFM), scanning electron microscopy (SEM) were used to characterize the topographic and morphologic properties of both polymers and composites. Additionally, fluorescence microscopy helped to understand the signal of emitted light by composites. Lastly, piezoelectric properties of composite materials were invetigated by oscilloscope. According to results, type of process, particle size of crystal, surface property and form of host material (polymer), the concentration of crystalline particles in composites were determined as the main parameters and the results were estimated with respect to these parameters. PU-based composite film and fiber show better stability towards mechnical stress rather than PMMA, PS, and PVDF due to the roughness surface of thin-film surface for film-based composites, smallest wickerwork formation of electrospun mats for fiber-based composite, and the chemical affinity of PU with TL crystals.Master Thesis Preparation of Natural Zeolite Supported Tio2 Composites for Removal of Terephthalic Acid(Izmir Institute of Technology, 2014) Deliismail, Özgün; Çakicioğlu Özkan, Seher Fehime; Helvacı, Şerife ŞerefThis study focuses on the preparation of natural zeolite supported TiO2 composites for the removal of model pollutant, terepththalic acid (TPA) via sorption. Natural zeolite was purified and used to prepare natural zeolite supported TiO2 adsorbents. Prior to sorption, the adsorbents were characterized by Scanning Electron Microscopy, Volumetric Adsorption Instrument, X-ray Diffractometer, Fourier Transformer Infrared, Induced Coupled Plasma Atomic Emmision Spectroscopy, and Thermal Gravimetric Analyzer. It was deduced that natural zeolite was clinoptilolite rich low (Ca) silicate. The sorption studies of TPA on adsorbents were applied in dark conditions at room temperature by altering adsorbent amount (0.2-1.5 g/l) and initial TPA concentration (20-60 ppm). It was observed that the amount of adsorbed TPA per unit mass of adsorbent decreased with increasing adsorbent amount, and sorption percent was unchanged (about 72%). This can be explained by the affinity of adsorbents to water molecules more than TPA molecules. Much more number of TPA molecules was allocated on the clinoptilolite than TiO2 composites. Sorption mechanism was identified by fitting the kinetic data to diffusion (Weber-Morris model, intraparticle/external diffusion) and reaction models (First order and pseudo second order model). First order reaction model was well correlated to experimental data for sorption process. Comparing pore size of the adsorbents to molecular size of TPA indicates that main contribution to intraparticle diffusion was the intercrystalline diffusion. Intraparticle diffusion was not the sole rate-limiting step due to the existence of external resistance. Biot and Weber-Morris calculations corroborated these results. In the future, photocatalytic performance of these adsorbents will also be tested.Master Thesis Minimum Weight Design of Carbon/Epoxy Laminated Composites for Maximum Buckling Load Using Simulated Annealing Algorithm(Izmir Institute of Technology, 2014) Gülmez, Erkut; Artem, Hatice SeçilComposite materials have been mostly used in engineering applications such as aerospace, automotive, sports equipment, marine because of their high specific strength-to-weight and stiffness-to-weight ratios. Weight reduction and buckling load capacity are critical issue for the engineering application. Accordingly, in this thesis, identification of optimum fiber orientations and laminate thicknesses of the composite plates resisting to buckling under given loading conditions and aspect ratios are investigated. Furthermore, a comparison study on continuous and conventional designs is performed to determine the effect of stacking sequence on weight. Symmetric and balanced N-layered carbon/epoxy composite plates are considered for optimization process. Critical buckling load factor is taken as objective function and fiber orientations which are considered continuous are taken as design variables. Simulated Annealing (SA) algorithm is specialized by using fmincon as hybrid function and this optimization method is used to obtain the optimum designs. Maximum critical buckling load factor and minimum thickness and hence minimum weight are achieved and shown in tables. As a result, it is observed that loading conditions and plate dimensions play an important role on stacking sequence optimization of lightweight composite laminates for maximum buckling load capacity.Master Thesis Stacking Sequence Optimization of the Anti-Buckled Graphite/Epoxy Laminated Composites for Minimum Weight Using Generalized Pattern Search Algorithm(Izmir Institute of Technology, 2014) Boyacı, Hakan; Artem, Hatice Seçil; Artem, Hatice SeçilComposite materials have been increasingly used during the last decades due to their properties such as low weight, high stiffness, superior fatigue and corrosion resistance. They have been used in aerospace, automobile, marine applications and etc. Composite materials being an expensive but efficient technology to get minimum weight structures, it is logical to make an attempt to find out how to design properly optimum laminated composite plates with no reduction in their strength. The aim of the thesis is to find the optimum stacking sequence to obtain the minimum thickness (weight) of laminated composite plates in different loadings and plate dimensions under buckling constraint. Moreover, a comparison study of conventional and continuous designs are performed to determine the effect of stacking sequence on weight. The objective function is the critical buckling load factor. Fiber angles of the composite plates are taken as continuous design variables and the plate is assumed to be balance and symmetric. Composite plates made of graphite/epoxy have been considered in this thesis. A combination of Generalized Pattern Search Algorithm (GPSA) and Genetic Algorithm (GA) has been considered as an optimization method. All the results show that the loading conditions and dimensions of composite plates are significant in stacking sequences optimization of laminated composite materials in terms of maximum critical buckling load factor and minimum thickness.Master Thesis Development of Carbon Black-Layered Clay/Epoxy Nanocomposites(Izmir Institute of Technology, 2008) Pekşen Özer, Bahar Başak; Tanoğlu, Metin; Tanoğlu, MetinIn this study, a novel epoxy nanocomposite with electrical conductivity and having improved mechanical and thermal properties was synthesized. Carbon black/ epoxy composites and carbon black-layered clay/epoxy nanocomposites were prepared by mixing via 3-roll mill. The first type of the composite was produced to determine the percolation threshold concentration (Vc). The second type with constant carbon black concentration, slightly over Vc, was synthesized to investigate the influence of clay content on the thermal, mechanical, electrical and structural properties of nanocomposites. Carbon black used in the study was extra conductive filler with 30 nm spherical particles. Layered clay was Na+ Montmorillonite treated with ditallow dimethlyamine to assure better intercalation within the epoxy resin. Vc value was determined to be 0.2 vol% and 0.25 vol% carbon black was added together with varying clay contents to the epoxy system to produce nanocomposites. Only the nanocomposites with 0.5 vol. % clay loading showed electrical conductivity. However, the composites with higher clay loadings showed insulating behaviour due to hindrance of carbon black network by clay layers. According to the XRD results, nanocomposites exhibited some extent of exfoliation. It was found that tensile modulus values of the epoxy increased;however flexural modulus values remained constant, with increasing clay content.Elastic modulus of neat epoxy (3.7 GPa) was increased about 28 % with 0.5 vol% clay addition. Thermomechanical analysis results revealed that the storage modulus, glass transition temperature and initial degradation temperature of epoxy was slightly enhanced due to clay loading.
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