Phd Degree / Doktora
Permanent URI for this collectionhttps://hdl.handle.net/11147/2869
Browse
9 results
Search Results
Now showing 1 - 9 of 9
Doctoral Thesis Examination of Fatigue Behaviour of Carbon Fiber Reinforced Polymer Composites(Izmir Institute of Technology, 2021) Güneş, Mehmet Deniz; Tanoğlu, Metin; Tanoğlu, MetinThis PhD thesis aims to examine the fatigue behavior of sandwich panels fabricated from adhesively bonded aluminum honeycomb core and carbon fiber reinforced polymer composite face sheets. Initially, sandwich panels were manufactured with three different amounts of adhesive in their interface. Static flexural behavior was characterized with three-point bending tests. Load-displacement curves and static flexural failure modes were obtained and utilized to compare the static flexural behavior of fabricated sandwich. Fatigue behavior of sandwich panels were characterized with the three-point bending fatigue tests. Stiffness degradation curves were used to identify the failure cycles of sandwich panels. Fatigue failure modes and S-N curves were obtained to find out the effect of amount of adhesive on fatigue behavior of sandwich panels. The other study within this thesis was made to investigate the effect of core thickness on the fatigue behavior of the sandwich panels based on aluminum honeycomb core and carbon fiber reinforced polymer composite face sheets. Sandwich panels were fabricated by using three different aluminum honeycomb core thickness. Static flexural tests were carried out to determine the static flexural behavior of developed sandwich panels. Load-displacement curves and failure modes were obtained from flexural tests. In addition to this, core shear tests were performed to investigate the core shear strength of the honeycomb cores with different core thickness. Effect of core thickness on fatigue behavior of sandwich panels were characterized with fatigue failure modes and S-N curves. Stiffness degradation method was used to determine the fatigue failure cycles of the sandwich panels.Doctoral Thesis Development and Characterization of Innovative Fiber Reinforced Prepregs and Their Composites Containing Functional Fillers(Izmir Institute of Technology, 2021) Uz, Yusuf Can; Tanoğlu, MetinThis Ph.D. thesis aims to prepare laboratory-scale carbon fiber reinforced prepregs and improve the performance of their composites by incorporating functionalized single-wall carbon nanotubes (SWCNTs). The effect of nano-scale functional fillers on the characterization of prepregs and their composites was investigated to develop innovative materials for primary structures. To affect dispersion characteristics, SWCNTs were functionalized by oxidizing their surface with the carboxyl (-COOH) group using acid treatment. The modified resin system containing 0.05, 0.1, and 0.2 wt. % F-SWCNTs were developed with novel multi-step dispersion techniques. FTIR spectroscopy was performed to identify new bonding groups formed after the covalent functionalization. Unidirectional carbon fiber reinforced prepregs with/without F-SWCNTs were prepared using a drum-type winding technique by utilizing the solvent-dip (solution impregnation) process. The effect of F‐SWCNTs on the curing process and kinetic parameters of the carbon fiber/epoxy-based prepregs were investigated using non‐isothermal DSC. The activation energy of the curing reaction was calculated by the isoconversional methods. Also, the new numerical approach called GMN was developed to determine the activation energy of the thermosetting materials. For the fabrication of prepreg-based composite laminates, the vacuum bag-only (VBO) method was performed. The fiber volume fractions of the CFRP samples changed between 55.3% and 50.16%. The mechanical and thermomechanical properties of prepreg-based CFRP composites with/without F-SWCNTs were investigated. The optimum mechanical properties of F-SWCNTs filled CFRP composite was achieved at 0.05 wt.% of F-SWCNTs. However, mechanical properties were decreased due to the addition of higher content of F-SWCNTs, in comparison with neat CFRP.Doctoral Thesis Performance Improvement of Composite Materials Used as Hydrogen Storage Tanks by Microstructural Modifications(Izmir Institute of Technology, 2020) Ay, Zeynep; Tanoğlu, MetinThe goal of this Ph.D. thesis is to improve the performance of the cylindrical composites manufactured by filament winding method by using the toughened matrix resin with nano-sized filler (noncovalently functionalized with ethoxylated alcohol chemical-vapor-deposition-grown SWCNTs). The effect of SWCNT concentration on the mechanical performance of these composites was investigated and discussed. One of the main focus of this thesis is to examine the effect of nano-sized filler type and filler concentration on the performance of the epoxy-based composites. For this purpose, epoxy-based nanocomposites with different nano-sized filler types (SWCNT, TEGO, and HNT) at varying concentrations were developed by a calendaring (3-roll-mill) method. A series of mechanical tests were performed for reference composite and developed nanocomposites. The scanning electron microscopy (SEM) was used to reveal the morphology and toughening mechanisms by examining the fractured surface of nanocomposites. The rheological behaviors and contact angle measurements with glass fiber of the selected filler (SWCNT) incorporated epoxy suspensions were investigated to determine the suitability of suspensions for the filament winding process. The reference and SWCNT modified glass fiber (GF)-based cylindrical fiber-reinforced polymeric composites (CFRPCs) with an inner diameter of 60 and 275 mm were manufactured by the filament winding method. The split-disk and three-point bending tests were performed for GF-based CFRPCs. The double cantilever beam (DCB) test was also carried out for the reference and SWCNT modified GF-based CFRPCs to investigate the effect of SWCNT existence on the interlaminar fracture toughness of CFRPCs. The fractured surfaces after the DCB test were analyzed under the SEM to comprehend the toughening mechanisms, and micro-and nano-sized filler morphologies. Consequently, it was revealed that blending and hence toughening the epoxy resin with SWCNT improves the interlaminar properties of the GF-based composites.Doctoral Thesis Desing and Production of Light-Weight Pressure Resistant Composite Tank Materials and Systems for Hydrogen Storage(Izmir Institute of Technology, 2020) Kartav, Osman; Tanoğlu, MetinThis thesis focuses on the development of high-pressure resistant composite tanks for hydrogen storage. For this aim, composite tanks with aluminum liners were designed and manufactured by filament winding technique with various lay-up configurations and tested. The main objective of this study was to develop composite tanks with 700 bar working pressure and 1400 bar burst pressure. Furthermore, composite doily layers were incorporated into the filament winding technique and inserted at the front and end dome sections of the composite tanks to improve the burst pressure performance of the composite tanks and to develop the manufacturing process. Before the manufacturing process, the winding simulations were completed using CADWINDTM CAM software. The manufactured composite tanks were hydrostatically loaded with increasing internal pressure up to the burst pressure. During loading, the deformations over the composite tanks and liners were measured locally using strain gauges. Besides, composite plates were manufactured by filament winding technique to determine the mechanical and the thermo-mechanical properties, and the fiber mass fractions of composite sections were determined. Additionally, a preliminary study was carried out to investigate the effect of hybrid fiber usage on the burst pressure performance of steel liner based composite tanks. The effect of filament winding parameters on the burst pressure performance of composite tanks was investigated experimentally. The aimed burst pressure value of more than 1400 bar was obtained in this study for aluminum liner-based carbon fiber reinforced composite tanks. Also, a desired safe burst mode that is expected to occur in the mid-region of the composite tanks was successfully obtained. This study may be useful for the development of composite tanks for high-pressure hydrogen storage especially for the automotive industry and can be helpful to decrease the usage of fossil fuels.Doctoral Thesis Modeling, Simulation and Analysis of Type-Iii Composite Overwrapped Pressure Vessels for High-Pressure Gas Storage(Izmir Institute of Technology, 2019) Kangal, Serkan; Tanoğlu, MetinIn this thesis, multi-layered composite overwrapped pressure vessels (COPVs) for high-pressure gaseous storage were modeled by finite element (FE) method and manufactured by filament winding technique. Two liners with distinct geometries were utilized for containing gas and forming a basis for composite filament winding. 34CrMo4 steel as a load-sharing metallic liner was selected for investigation of hybridization effects. Glass and carbon filaments were overwrapped to the liner with a winding angle of [±11°/90°2]3 to obtain a fully overwrapped composite reinforced vessel with non-identical front and back dome endings. The other type of liner was made of Al 6061-T6 and chosen for containing high-pressure gas such as hydrogen and its better strength-to-weight ratio suitable for onboard applications. Doily layers were implemented to the structure for inducing safe burst modes and increasing the burst pressure of the aluminum-based COPVs. All vessels were hydrostatically loaded with increasing internal pressure up to the burst pressure. The mechanical performances of pressure vessels were investigated by both experimental and numerical approaches. In numerical approaches, FE analysis was performed featuring a simple progressive damage model available in ANSYS for composite section. The metal liners were modeled as elastic-plastic material with two different hardening approaches; bilinear and multilinear hardening. The results from steel based COPV indicate that the FE model provided a good correlation between experimental and numerical strain results for the vessels with indications that the composite interlayer hybridization has positive effects on radial deformation of the COPVs. The constructed model for aluminum-based COPVs was also able to predict experimental burst pressures within a range of 8%.Doctoral Thesis Toughening of Carbon Fiber Based Composites With Electrospun Fabric Layers(Izmir Institute of Technology, 2017) Beylergil, Bertan; Tanoğlu, Metin; Aktaş, EnginThe objective of this PhD thesis is to investigate interlaminar Mode-I fracture toughness of carbon fiber/epoxy composites interleaved by micro and/or nano scaled PA66 nonwoven veils. Also, the effects of electrospun PVA nanofibers on the mechanical performance of these composites were investigated. Additionally, this thesis also deals with the effects of aramid nonwoven veils on the mechanical properties of CF/EP composites. The produced nanofibers produced by electrospinning were directly deposited on carbon fiber fabrics. Then, reference and nano-modified laminates were manufactured by vacuum infusion method. A series of mechanical tests such as tensile, compression, three point bending, Charpy-impact, interlaminar shear strength and open hole tensile tests (OHT) were carried out on the prepared specimens. Double cantilever beam (DCB) tests were conducted on reference and interleaf-modified laminates. The effect of PA 66 nanofiber areal weight density was also evaluated with varying electrospinning time. Scanning electron microscopy (SEM) was used to investigate the fiber morphology and to understand the toughening mechanisms. Dynamic mechanic analysis (DMA) was used to investigate the thermo-mechanical behavior of reference and interleaf-modified composite specimens. Differential scanning calorimetry (DSC) was used to determine the thermal properties of micro and electrospun PA66 nonwoven veils. Comparing the mechanical test results, the most effective nonwoven interleaving system was determined in terms of higher delamination resistance and in-plane mechanical properties. Finite element method (FEM) was used to evaluate the effects of electrospun PA66 nonwoven veils on the CF/EP composites. Numerical simulations of Mode-I fracture toughness tests were carried out using ANSYS Workbench. The results showed that the most effective material was electrospun PA66 nonwovens considering the higher delamination resistance. Additionally, the electrospun PA 66 nonwovens also improved Charpy-impact and interlaminar shear strength of the reference CF/EP composites. Numerical results showed good agreement with the experimental ones.Doctoral Thesis Preparation of Nanosized Ceo2 Particles and Their Incorporation Into Transparent Acrylate Polymers(Izmir Institute of Technology, 2014) Tunusoğlu, Özge; Demir, Mustafa Muammer; Tanoğlu, MetinNanoparticles having a size smaller than 100 nm are important building blocks of nanomaterials. Organically functionalized CeO2 nanoparticles were prepared by colloidal synthesis in this work. The particles were nucleated by mixing aqueous solutions of Ce(NO3)3·6H2O and ammonia at room temperature. Different small organic molecules were chosen as capping agents and injected into the reaction medium at the beginning of the synthesis: 3- (mercaptopropyl) trimethoxy silane (MPS), hexadecyltrimethyl ammonium bromide (CTAB), 3-mercapto propionic acid (3-MPA), and thioglycolic acid (TGA). The resulting nanocrystals were quasi-spherical and has a narrow mean size distribution with an average size smaller than 10 nm. Polymerization of monomer/nanoparticle dispersion, namely in situ polymerization, has been frequently used for the fabrication of polymer nanocomposites. Both in situ and ex situ approaches were applied for surface functionalization. The particles were dispersed into methyl methacrylate and free radical polymerization was carried out. The process of nanocomposite formation was examined in terms of conversion, molecular weight, and molecular weight distribution. The polymerization responds merely to the in situ functionalized particles. Regardless of the capping agents used, the particles function as a retarder and inhibitor. Their interaction with polymerization medium shows many complexities such that molecular weight is found to be strongly dependent on the capping agent employed.Doctoral Thesis Development of Multi and Double Walled Carbon Nanotubes (cnts) / Vinylester Nanocomposites(Izmir Institute of Technology, 2008) Seyhan, Abdullah Tuğrul; Tanoğlu, MetinThis study focuses on development and characterization of thermosetting resin based nanocomposites containing multi and double walled carbon nanotubes with and without amine functional groups (MWCNT, DWCNTs, MWCNT-NH2 and DWCNTNH2).A novel 3-roll milling technique was conducted to prepare the resin suspensions with carbon nanotubes (CNTs). Rheological measurements performed on the resin suspensions showed that addition of very low contents (0.05, 0.1 and 0.3 wt. %) of MWCNTs and MWCNT-NH2 affected the flow characteristic of the resin, significantly.Further, the curing behavior of a vinylester-polyester hybrid resin suspensions containing 0.3 wt % of MWCNTs and MWCNT-NH2 was intensively studied. It was found that regardless of amine groups, presence of CNTs affected the polymerization of the hybrid matrix resin. Final individual fractional conversion rates of styrene and vinylester monomers were found to be vastly dependent on the type of CNTs. Glass transition temperature (Tg) values of the nanocomposites with MWCNTs and MWCNTNH2 were found to increase with filler content. Moreover, nanocomposites containing MWCNTs and MWCNT-NH2 were found to possess higher tensile strength, elastic modulus as well as fracture toughness and fracture energy as compared to the neat hybrid resin. On the other hand, electrical properties of the nanocomposites were also investigated and it was found that nanocomposites with MWCNTs exhibited the lowest percolation threshold value. In addition, nanocomposites with amino functionalized CNTs were found to exhibit lower electrical conductivity as compared to those with untreated CNTs. Nanocomposites with AC electric field induced aligned CNTs were also prepared. Finally, based on the findings obtained for CNT/ resin suspensions, as a case study, electrically conductive glass fiber reinforced composite laminates were successfully produced, using the CNT modified resin suspensions as matrix material, via Vacuum Assisted Resin Transfer Molding (VARTM) and Resin Transfer Molding (RTM) methods.Doctoral Thesis Development and Mechanical Characterization of Anti-Blast Sandwich Composites for Explosive Effect(Izmir Institute of Technology, 2011) Baştürk, Suat Bahar; Tanoğlu, MetinComposite sandwich structures have high potential to be used in anti-blast armour systems due to their lightweight and resistance to explosive effects. This study focuses on the production and mechanical characterization of sandwich structures with aluminium (Al) foams of various thicknesses in conjunction with skins composed of Al/GFPP fibre/metal laminates. The bonding between the components of the sandwich was achieved by various surface modification techniques such as silane surface treatment, polypropylene (PP) adhesive film addition and their combination. The Al sheet/Al foam sandwiches were also prepared to investigate the effect of GFPP addition on the performance of sandwich structures. The energy absorption capacities together with compressive and flexural behaviour of both Al foams and FML/Al foam sandwiches were evaluated by flatwise compression and three point bending tests. The samples with higher elastic modulus usually exhibited higher collapse strength for each thickness set of foam and foam based sandwiches. Also, the core thickness increase led to the increase of overall flexural collapse load and GFPP presence promoted the strength of the sandwiches and dissipated energy values. In order to investigate the blast response of the sandwich panels, the quasi-static sandwich panel analysis was related to dynamic blast loadings. For this purpose, the sandwich composites were subjected to compression loading with a specially designed loading fixture and the corresponding test method is called as “simulated blast test”. The sandwiches were assumed as single degree of freedom mass-spring systems to include the dynamic effect. The peak deflections and survivability of the panels under blast loading were predicted based on the formulations reported in the literature. To evaluate the blast response of the monolithic materials, composites and sandwich panels, blast testing was performed using specially designed blast test frame system and 0.5 to 6 kg TNT explosives. Test results revealed that composites such as GFPP exhibited successful results against blast explosions.