Master Degree / Yüksek Lisans Tezleri
Permanent URI for this collectionhttps://hdl.handle.net/11147/3008
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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.Master Thesis Preparation and Physical Characterization of Clay/Epdm Nanocomposites(Izmir Institute of Technology, 2008) Karşal, Çiçek; Tanoğlu, MetinPolymer/clay nanocomposites have been extensively studied in recent years because they often exhibit improved properties different from their micro and macrocomposite counterparts. Addition of organophilic layered silicates to the polymer produces effective polymer nanocomposites by intercalation of macromolecules into the interlayer spaces. The performance of polymer/clay composites is not only related to the nature of the clay but also to the reinforcing mechanism of filler and the preparation conditions.In this study, the effects of mixing conditions and effect of aging on mechanical,physical and thermal properties of ethylene-propylene-diene rubber (EPDM)/Organo modified montmorillonite (OMMT) nanocomposites were studied at two different clay loadings 5 wt.% and 10 wt.%. EPDM/OMMT nanocomposites were prepared by melt blending method. The experimental results of X-ray diffraction (XRD) and scanning electron microscopy showed that the organically modified MMT existed in the form of an intercalated structure and that was exfoliated in EPDM matrix depending on the mixing conditions. XRD patterns showed that the interlayer distance of the organically modified clay was 30.9A, which was larger than those of the unmodified clay (14.6A).The mechanical evaluation of the nanocomposites was performed by tensile and tear testing. The mechanical tests showed that the properties of nanocomposites were significantly improved with addition of OMMT. The effects of the processing conditions were manifested in both the morphology and mechanical properties, which showed significant increase when optimized process conditions are applied. In addition, chemical test was performed on the nanocomposites to monitor the degradation of the mechanical properties. It was found that the reduction of the mechanical properties of nanocomposites after aging process is lower as compared to those of neat EPDM.Master Thesis Processing and Characterization of High Performance Piping Materials for Geothermal Applications(Izmir Institute of Technology, 2003) Toğulga, Murat; Tanoğlu, MetinPolymer composite based pipes are being recently utilized in transportation of geothermal fluids.The utilization of composites is due to their resistance to aggressive chemicals and hot-wet environment with relatively high specific strength and design flexibility.Exposure of materials to wide range of temperatures and humidity level, while under the action of load, may degrade them and cause to severe reduction in their properties and service life.Understanding the complex degradation mechanism of the composites exposed to a variety of temperature and fluid chemistry (including geothermal fluid) is essential to improve their durability.This research focuses on the investigation of interactions between geothermal fluid and composite piping materials made of various matrices and the mechanism of degradation in these composites.The matrix materials include polyester, epoxy and graphite particle added epoxy materials.In this study, E-glass fiber reinforced polymer composites were fabricated by employing filament winding and tube rolling techniques.Fabricated composites and neat polymers were exposed to dry environment, distilled water and geothermal fluid of Balçova geothermal field until the saturation of weight gains due to water uptakes.In addition, the specimens with neat polymers were prepared to simulate and follow the degradation of matrix materials under hot-wet environments.Once the saturation occurred, the specimens were subjected compressive mechanical testing.For both dry and wet specimens, the mechanical testing was performed to obtain stress-strain behavior, modulus of elasticity, strain at failure values and energy absorption during the loading.The results were compared to evaluate the degradation of the properties due to various exposures.Moreover, the thermal conductivity of the various composites fabricated in this research was measured to determine the heat losses and temperature distribution within the materials.The temperature distribution within the cross-section of the pipes for various materials was analyzed using a finite element-modeling tool, LUSAS for uninsulated pipes.The heat loss occurring during the transportation of hot geothermal fluid was calculated as a case study to compare composites and traditional metal piping.It was found that polyester composite pipes have higher mechanical performance under axial and radial compression as compared to the composite with epoxy matrices. For all the composite types, some considerable degradations were measured due to exposure to hot-wet environments.The extend of degradation was less for graphite particles added epoxy composite pipes that exhibited the lowest water uptake values. The graphite particles incorporated into the matrix affected the water uptake and thermal conductivity of the epoxy.The water uptake of polyester matrix composite pipes was the highest that might be related to the most extensive degradation of polyester based composite.Moreover, it was found that the thermal conductivity of the composites is much lower than traditional materials.The graphite particles cause reduction in thermal conductivity, simultaneously in heat loss for uninsulated pipes.However, if the isolation is used, heat loss is not sensitive to pipe material.Master Thesis Polyropylene - natural zeolite composite films(01. Izmir Institute of Technology, 1999) Özmıhçı, Filiz; Balköse, DevrimIn this project, preparation and characterization of polypropylene natural zeolite composites were studied. Three different series of preparation methods were performed, hot press, microscope slide, and extrusion. The composites are ranged between 0-10 wt%, 0-50 wt%, and 0-6 wt% zeolites, for hot press, microscope slide, and extrusion respectively.Polymer matrix composites are materials which contain polymers as matrix materials surrounding very small reinforcing fibers or fillers. Polymeric composites have great potential from a manufacturing standpoint and show advantages. Such as they are inexpensive, derive from natural sources, present lower density than mineral fillers, and increases the mechanical properties of the final product.In this research polypropylene was used as a matrix material and natural zeolite as a filler. Natural zeolite particles were modified with polyethylene glycol to break agglomerates and make a homogenous dispersion of natural zeolite in polypropylene matrix. These composites were characterized by using differential scanning calorimetry, thermal gravimetric analyzer, infrared spectrophotometer, optical microscopy, mechanical testing and by density measurement device. It has been found that, branched shaped air pockets existed in hot pressed and extruded composites. This causes low mechanical strength, and the densities of these films also indicate the presence of voids in the composite.Master Thesis Preparation and Characterization of Polypropylene Cellulose Composites(Izmir Institute of Technology, 2004) Atikler, Ulaş; Tıhmınlıoğlu, FundaIn recent years, much effort has been driven to replace glass fibers, which were used to reinforce thermoplastic composites, with natural fibers. In this study, three natural fibers, namely cellulose (CE), sawdust (SD) and wheat straw (WS) were employed as reinforcement to polypropylene (PP) polymer matrix. The most important problem encountered with natural fiber/PP composites is the inherent incompatibility between hydrophilic natural fibers and hydrophobic PP matrix, thus coupling agents were employed to alter incompatibility between fiber and matrix. Coupling agents enhance interfacial interactions by chemical and physical bonding between fiber and matrix. Surface treatment of natural fibers were carried out with two kinds of silanes;(3-aminopropyl)-triethoxysilane (AS) and methacriloxy propyl trimethoxy silane (MS), and maleic anhydride grafted polypropylene (MAPP). Silane coupling agents were agitated in aqueous ethanol solution in the presence of fibers at weight percents of 0.5, 1 and 2.5 with respect to fiber weight. MAPP was compounded during melt mixing of fiber and PP at weight percents of 2.5, 5 and 10 with respect to PP weight PP/fiber composites were prepared in a rheomixer equipped with two rotor blades and adjustable temperature, mixing rate and mixing time. Composites were prepared at 185 oC, 50 rpm mixing rate and 10 minutes mixing time. Torque values of each composite formulation were recorded with respect to time to determine changes in rheological properties of composites. It was found that increase in fiber loading increases stabilization torque of composites. Mechanical properties of PP/fiber composites were significantly enhanced byemployment of coupling agents and MAPP was found to be the most effective coupling agent. Mechanical properties of SD composites were found to exhibit the best performance compared to C and WS. Extent of interfacial interactions were evaluated with Pukanszky and Nielsen model and superior performance of MAPP in enhancing interfacial interactions was confirmed by these two models. Optimum conditions for coupling agents were found to be 1 wt % for silane coupling agents and 5 wt % for MAPP. It was found that water sorption and void fraction of the composites decreased with employment of coupling agents. Among the coupling agents, MAPP exhibited the best performance in decreasing water sorption and void fraction of composites confirming results of mechanical tests. Scanning electron micrographs (SEM) used to illustrate the effect of coupling agents on adhesion between fiber and matrix and fracture modes of the composites. In addition, FTIR analysis revealed the decrease in hydrophilicity of fibers with silane treatment and new bond formations with employment of MAPP.Master Thesis Development and Characterization of Light-Weight Armor Materials(Izmir Institute of Technology, 2005) Ünaler, Erol; Tanoğlu, MetinIn this study, E-glass/unsaturated polyester composite laminates using woven and non-crimp stitched fabrics and isophtalic and orthophthalic polyester resin were fabricated using RTM (Resin Transfer Molding) technique. In addition to composite laminates, multilayered sandwich laminates using aluminum (Al) plates and alumina (Al2O3) tiles were manufactured to improve the ballistic resistance of the composite structure. An experimental investigation was carried out to determine the mechanical and ballistic performance of E-glass/unsaturated polyester composite laminates with and without aluminum and alumina tiles. The mechanical properties of the composite laminates made with 0/90 woven fabrics and 0/90 and 0/-45/+45/90 non-crimp stitched fabrics and two resin systems were measured for comparison of fabric and resin types. The flexural strength and modulus, compressive strength and modulus through ply-lay up and in plane loading directions, mode I interlaminar fracture toughness and apparent interlaminar shear strength of the composites were measured to evaluate the effects of the fiber architecture on the mechanical properties of the composites. It was found that in general the mechanical properties of the composites made with 0/90 woven fabrics are higher than those of the composites made with multiaxial non-crimp stitched fabrics. Moreover, the composite plates with and without aluminum plates and alumina tiles were subjected to ballistic impact by AP (armor piercing), FSP (fragment simulating projectile) and ball (B) type projectiles with initial velocities in the range of 420-1173 m/s. The ballistic test results exhibit that the polymer composites have ballistic resistance against 7.62 mm fragment simulating projectiles (FSP) up to 1001 m/s projectile velocities. However, the composites without any support layer are not sufficient to stop AP projectiles. The sandwich panels containing ceramic tiles subjected to the ballistic impact by AP and FSP projectiles exhibited only partial penetrations at all the velocities applied within the study (446-1020 m/s with AP and 435-1173 m/s with FSP). The extensions of damages in the composites were evaluated after impact. It is concluded that the multilayered composite structures have capacity against the ballistic threats and potential to be used as lightweight armor materials.Master Thesis Crushing Behaviour of Aluminum Foam-Filled Composite Tubes(Izmir Institute of Technology, 2005) Yüksel, Sinan; Güden, MustafaAn experimental study has been conducted in order to determine the effect of Al-foam filling on the composite and hybrid (Al metal and composite) composite tubes.Tubes and fillers used in the experiments were prepared using the tube rolling and foaming from powder compacts methods, respectively. The composite was prepared using E-glass fiber fabric (2x2 twill fiber construction of 165 g/m2 areal density) and polyester matrix with a 45/45 fiber angle to the tube axis. The quasi-static crush tests were conducted axially on the empty, hybrid and foam filled tubes at 25 mm/min crosshead speed. The deformation sequences of the tubes were further recorded during the tests in order to identify the crushing modes of the tubes. Two failure mechanisms literally known as progressive crushing and catastrophic failure (compression shear) were observed during the crushing of empty composite tubes. The progressive crushing mode leaded to higher crushing loads hence Specific Absorbed Energies (SAE). The predominant progressive crushing mode of empty tubes of thinner wall section was attributed to the surface end defects introduced during sectioning of the tubes. In hybrid tubes, the deformation mode of Al tube was found to be a more complex form of the diamond mode of deformation, leading to higher SAE values than the sum of the SAEs of empty composite and empty metal tube. The increased load and SAE values ofhybrid tubes were attributed to the constraining effect of the composite to the metal tube folding. Results further showed that when the progressive crushing mode was taken into account hybrid tubes had lower SAE values than those of empty composite tubes. The foam filling of the composite tubes however showed two different results. It increased the foam filled tube crush loads over the sum of the crush loads of empty composite tube and foam. In the latter case it was not effective in increasing crush loads over the sum of the crush loads of empty composite tube and foam in the progressive crushing region. These two effects were discussed in terms of possible interactions between composite tube and foam.Master Thesis Preparation and Characterization of Ha Powders-Dense and Porous Ha Based Composite Materials(01. Izmir Institute of Technology, 2002) Şimşek, Deniz; Çiftçioğlu, Muhsin; Şimşek, Deniz; Çiftçioğlu, MuhsinThe synthesis of hydroxyapatite (HA) powers, whiskers and preparation of HA based ceramics have been investigated in this work. Commercial HA powders were used for comparion purposes. The powder and sintered ceramics were characterized by optical microscopy, SEM,XRD, particle size determination, dilatometry and mechanical testing.Ca-P powders were synthesized by using (NH4)2HPO4 and Ca(NO3)2. 4H2O by aprecipitation method in aqueous medium. Ca/P ratio was set to 1,5 and 1,667 that yield the mixture of Ca-P phases and HA powder respectively at pH 10, 60 C and 24hrs aging. Ca/P ratio was set to 1,667 and the effect of pH of the medium, aging temperature and aging time on the powder characteristics was investigated. pH was set to 4,6,8,9,10 and 11 while aging temperature and time kept constant at 60 C and 24 hrs.Formation of HA powder was observed over pH 8. Agglomerated Monetite-Brushite powder was obtained at pH.4. Monodispersed prismatic Brushite crystals were obtained at pH.6. Aging temperature investigation was performed at 30-90 C at pH.10 for 24 hrs aging. Increase in the aging temperature led to formation of more thermally stable HA phase. Precipitates were aged for 0, 0.5, 1, 24 and 48 hours at constant pH.10 and temperature 60 C. Thermally stable HA phase was obtained over 24hr aging. All of the oven-dried precipitates were heat treated at 400-1250 C range in order to investigate the thermal stability and phase structure development. Optimum conditions for the precipitation of thermally stable HA powder was determined as pH.10, 60 C aging temperature and 24 hrs aging time that yields equaxed HA powder with particle size about 40-60 nm.Molten salt synthesis (MSS) and hydrothermal synthesis (HDT) were used to prepare HA whiskers. XRD patterns of both whiskers have shown that HA was the dominant phase in whiskers and no other phases were detected. Hydrothermal whiskers had submicron diameters with an average aspect ratio of 20. The diameter of the MSS whiskers were in the 1-5 micron range and were mostly hexagonal with an average aspect ratio of 10.10, 20 and 30 vol% whisker containing composites were prepared. Sintering behavior and mechanical properties were investigated. 98% TD of HA ceramics (3.16 g/cm3) was obtained in the 1150-12500C range. 80-90% TD was obtained at above 1200 C for the MSS whisker composites with very little shinkages. Densities of the HDT whisker containing composites were higher than those of the MSS whisker composites. The highest hardness value was determined as 537 Hv for the HA ceramics 1250 C sintered. Hardness of the composites was lower than that of pure HA powder based ceramics due to the presence of relatively high porosity. 10vol% MSS whisker addition yields comparable compressive strength (460-470 MPa) and elastic modulus values (14-17 GPa) with that of natural bone tissues (170-193 MPa compressive strength, 14-18 GPa elastic modulus).Master Thesis Effects of Processing Parameters on the Mechanical Behavior of Continuous Glass Fiber/Polypropylene Composites(Izmir Institute of Technology, 2009) Merter, Nevres Emrah; Tanoğlu, MetinFiber reinforced polymeric composite materials have an increasing demand in industrial applications. Easy and rapid processing capability, high impact and delamination resistance, low moisture absorption and infinite shelf life of the raw materials are the attractive properties of continuous fiber reinforced thermoplastic composite materials. Therefore, thermoplastic based composites find in many application areas in automobile, aerospace, construction, defense, transportation and marine industries. In recent years, hybrid fabrics; composed of continuous glass fibers and polymer fibers such as polypropylene (PP), have been used to fabricate thermoplastic composite with higher fiber volume fraction and improved performance. In this study, hybrid fabrics were developed by commingling the continuous PP and glass fibers using air jet and direct twist hybrid yarn preparation techniques. The hybrid commingled fabrics obtained with 450 fiber orientation and non-crimp fabric pattern. Non-crimp fabrics were obtained various fiber sizing that are compatible and incompatible with PP matrix to investigate the effect of interfacial adhesion on the properties of the thermoplastic composites. Composite panels were produced from these fabrics via hot press compression method. Microstructural properties of the composites were investigated by matrix burn-out test and optical and scanning electron microscopy (SEM) analyzes. Tensile, compression, flexural and interlaminar peel tests were used to investigate the mechanical properties of the composites. Impact properties of the composites were examined by charpy impact test. Results showed that laminates of the fabrics fabricated by air jet hybrid yarn preparation technique exhibit superior properties to those fabricated by direct twist covering hybrid yarn preparation technique. The results also showed that the fabrics with polypropylene compatible sizing results with enhanced composite properties.