Master Degree / Yüksek Lisans Tezleri
Permanent URI for this collectionhttps://hdl.handle.net/11147/3008
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Master Thesis Improving Mechanical Properties of Adhesive Joints in Carbon Fiber Reinforced Polymer Composites by Incorporation of Graphene Added Electrospun Polymeric Nanofibers(01. Izmir Institute of Technology, 2023) Yeke, Melisa; Tanoğlu, MetinSince composites joined with mechanical fasteners cause severe delamination damage, stress concentration in the joint area, and weight increase, joining composite materials with innovative methods have recently gained more importance. These joining methods prevent delamination damage, provide a uniform distribution of stress, and do not cause considerable weight increases. However, modifying the surface of composite parts joined by innovative methods is critical. In this study, the bonding surface was modified by coating carbon/epoxy prepregs with electrospun nanofibers with 10% wt/v ratio of PA 66 and 1%, 2% and 3% wt/v ratio of rGO added. Composite parts were joined in the hot press by the secondary bonding method using 3 plies of FM 300K film adhesive. The morphological structure of nanofibers and the dispersion of rGO were analyzed by SEM. The thermal properties of nanofibers were analyzed by DSC. The contact angle measurement device was used to determine the hydrophilic and hydrophobic properties of the unmodified prepreg and nanofiber-modified prepreg surface. The most hydrophilic surface was observed on the nanofiber-coated surface with 2% rGO added. Single Lap Joints (SLJ), and Charpy Impact tests were performed to examine the mechanical properties of modified and unmodified composite plates. According to the SLJ and Charpy Impact results, an improvement of 17.89% and 30.59% was observed in carbon/epoxy composite plates whose surface was modified with 2% rGO, respectively.Master Thesis Investigating the Filament Wound Hybrid Cylindrical Structures With Enhanced Thermal Properties by Numerical Analysis(01. Izmir Institute of Technology, 2023) Özkan, Mert; Tanoğlu, MetinThe filament winding method is a composite production technique found at the beginning of the 20th century. The technique has been used in different fields since the day it was introduced in literature. Today, with the developments in the continuous fiber structure used in this technique and the development of carbon technology, filament-wound composites are widely used in the automotive, aerospace, and defense industries. In this study, the finite element method was used to model filament-wound composite cylinders. It was wanted to observe the matrix effect of the composite structure numerically and criticize experimentally produced composites. Even though the current studies work on a hybridized composite structure with respect to the fiber, this study tried to find the hybridized matrix effect by numerical analysis. For this purpose, in this study, the finite element program ANSYS was used. In order to make realistic calculations with ANSYS, material data were observed from composite plates. Finite element models created with the obtained data were compared with the experimental results. The analysis results were observed with the help of the first-ply failure theory. In addition, since the pattern representations from the winding poles cannot be displayed in ANSYS, the pattern effect was ignored, and comparison were made with the assumption of a full layer at given angles. As a result of all this study, although there were differences between experimental and finite element methods' models in homogeneity and pattern, methods' comparisons gave consistent and close results.Master Thesis Analysis of Adhesively Bonded Composite Aerospace Structures Developed by Laser Surface Treatment(01. Izmir Institute of Technology, 2023) Nuhoğlu, Kaan; Tanoğlu, MetinAmong the various joining techniques, adhesive bonding is a feasible alternative to mechanical fasteners to prevent incisions and discontinuity on aerospace structures. The performance of the bonded structures highly depends on the adhesion strength, which is directly related to the condition of the bonding surface. It is for this that laser surface treatment, a recently developing technique to improve bonding performance, has become suited for CFRP structures. Yet, predicting the failure strength and mechanism is vital for designing primary aircraft structures involving adhesively bonded composite structures. The scope of this paper consists of the validation and evaluation of adhesive bonding behavior in the case of joining between laser surface-treated CFRP structures, in particular, components of an aircraft wing box. To this end, both the experiment and numerical investigations of the secondary bonded coupons were examined. This study, in other words, includes experimentally revealing the bonding behavior through coupon and element-level mechanical test setups, as well as the simulation of those structures in the computer environment by performing FEA to predict the failure load and damage growth. In this regard, besides observing the effects of the laser surface treatment on the pure and mix-mode behaviors by means of the DCB, ENF, SLJ, and SSJ tests, identical specimens were numerically analyzed by utilizing macro-scale 2D and 3D models, employing the CZM technique. Meanwhile, a novel characterization study and the resulting TSL parameter identification method were achieved for an accurate numerical analysis. Eventually, in addition to the application methodology, the capabilities and appropriateness of the presented FEA method were discussed, comparing experimental and numerical results.Master Thesis Development and Experimental Characterization of Filament Wound Hybrid Cylindrical Structures With Enhanced Thermal Properties(01. Izmir Institute of Technology, 2023) Özarslan, Dora; Tanoğlu, MetinComposite tube components have key roles in many industrial applications, such as pipelines, drive shafts, airplane fuselages, and offshore construction components. Filament winding technology has enabled precise tailoring and manufacturing processes, allowing for a variety of applications to be manufactured with advanced machinery. In this study, the aim was to enhance the thermal properties without any significant change in the mechanical properties. Therefore, the samples were manufactured as carbon fiber composite tubes with different resin layer configurations by utilizing filament winding technology. The fiber orientation was set to a 55° winding angle with a 5/3 pattern to wrap over a 58.8 mm diameter mandrel as a 5-layer stacking. Due to difficulties in manufacturing different stacked groups of phenolin resin layers, only two groups (one with a 5-layer carbon epoxy resin group and one with a 4-layer carbon epoxy resin with 1 outer layer of carbon phenolin resin group) were successfully manufactured and thus tested. For each group, with dimensions of ±62.7 mm outer diameter and ±1.95 mm thickness with an 800 mm length, two composite tubes were manufactured. Before the test procedures, the homogeneity and quality of the groups were analyzed. For the observation of properties, mechanical and thermal tests were conducted: Apparent hoop tensile, radial compression, 3-point bending, Flammability, Thermogravimetric analysis, Differential scanning calorimeter, Thermal conductivity. The tests were proceeded according to their standards. The results and failure behaviors demonstrate that, with the replacement of the outer layer with phenolin resin, no significant improvement or drawback was observed compared to its fully epoxy resin counterpart.Master Thesis Development of Joining Techniques for Carbon Fiber Based Polymer Matrix Composites(Izmir Institute of Technology, 2020) İplikçi, Hande; Tanoğlu, MetinIn recent years, adhesive bonding has been a promising joining technology for CFRP composites. An appropriate treatment of surfaces for adhesive bonding is one of the effective factors for obtaining a high-quality adhesion strength. However, the adhesion strength is decreased by contaminants, like release agents, as well as an excess of matrix in the top layer. The contact of the adhesive with the reinforcing element is critical. Therefore, it is necessary to make a pre-preparation process on the adherent surface. One of the surface treatments preferred due to the advantages it provides is laser processing. The joint area strength of CFRP (carbon fiber reinforced polymer) composite can be enhanced with laser surface treatment. In this work, the carbon fiber/epoxy composites surface treatment by a nanosecond (1064nm wavelength) laser has been investigated. The polymer layer (epoxy matrix) on the CFRP (carbon fiber reinforced polymer) composite surface was selectively removed by laser treatment to expose carbon fibers. In order to remove the epoxy from the surface sufficiently, laser surface modification parameters were investigated and their effects were examined. These parameters are laser power, frequency, scanning speed and offset distance, respectively. Epoxy removal and fibers damage was analyzed by optical microscope and SEM (scanning electron microscope). Contact angle tests were carried out to analyzed wettability effect on the laser parameters. Lap shear, charpy impact and double cantilever beam (DCB) tests were performed to examine the effect of laser surface modification on mechanical performance.Master Thesis Improving Joining Performance of Composites by Electro-Spinning of Nano Fibers(01. Izmir Institute of Technology, 2021) Esenoğlu, Gözde; Tanoğlu, MetinMechanical joints traditionally used in composite materials (screws, rivets, etc.) not only increase weight but also act as a stress collector, causing serious delamination problems. At the same time, the development of alternative joining techniques has become an important issue in the composite industry due to its sensitivity to corrosion, electromagnetic properties/radar absorption properties, labor cost and adverse effects on the manufacturing process. In this master's thesis, the effects on the mechanical properties of two different prepreg composites (UD and woven) coated with polyamide 66 (PA 66) nanofibers in the joint region were investigated. In addition, the fiber structures of the produced PA66 nanofibers were investigated. The produced nanofibers were directly coated on the bond zone layer (top surface) of the carbon prepregs. The reference and nanofiber doped prepregs were cured by the hot press method, and then they were combined with the secondary bonding method using FM300K film adhesive in the hot press. Tensile, compression, bending, shear, Charpy-impact and double cantilever beam (DCB) tests were performed on the produced samples. The effect of homogeneity and areal weight density (AWD) of PA66 nanofibers on mechanical performance was investigated. The morphology and post-test deformations of the nanofibers were investigated by scanning electron microscopy (SEM). The thermal properties of PA66 nanofibers were investigated by the differential scanning calorimetry (DSC) method. By comparing the SEM images and the lap shear test results, the most efficient parameters for the mechanical performance of the composites were determined. The results showed that PA66 nanofibers produced with a 10% wt solution ratio and 10 min coating time were the most efficient on composites. The addition of PA66 nanofibers to the junction region with the electro-spinning technique has been proven to increase the junction region performance of the materials and outputs have been obtained.Master Thesis Enhancement of Ballistic Properties by Hybridization Method of Multi-Layered Composite Panels(01. Izmir Institute of Technology, 2020) Üstün, Hikmet Sinan; Tanoğlu, MetinHigh performance fiber reinforced composite structures are used for ballistic applications in recent years due to several advantages lightweight, high strength and high energy absorbing capability. In this regard, it is aimed to enhance ballistic performance of fiber reinforced composites by hybridization method in this thesis. Two of most used fiber types were selected as reinforcement which are E-Glass and Aramid fibers. As matrix epoxy resin was used. Homogeneous and hybrid structures were manufactured. In hybrid structures configuration was arranged as E-Glass layers are at the front and Aramid layers are at the back. Two different hybrid composites were manufactured with 50:50 and 70:30 Aramid and E-Glass layers. The effect of volume fraction of fabric layers on ballistic properties was investigated. Since there is a linear relationship between V50 and thickness, composite structures were manufactured with two different thicknesses and by the equation derived V50 values for different thicknesses could be determined. Mechanical and ballistic tests were carried out in the study. Tensile, 3-Point bending and short beam strength tests were applied as mechanical tests and a V50 test was carried out as ballistic test. Composite structures were compared with each other based on test results. Consequently, it was found that hybridization method increased mechanical and ballistic properties. Mass efficiency of hybrid structures were found to be higher than 1 (E-Glass composite was used as reference). It was also found that presence of E-Glass layers assists aramid structures to experience more delamination during impact and therefore increased energy absorbing capability.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 Investigation of Mechanical Properties and Fatigue Performance of Carbon-Glass Fiber Reinforced Epxy Hybrid Composites(Izmir Institute of Technology, 2019) Sandallı, Hatice; Tanoğlu, MetinRecently, hybrid composites have known as high performance engineering materials and they have been used broadly in engineering applications where high strength to weight ratio, reasonable cost and ease of fabrication are requested. Since these composites offer combination of benefits of different kinds of fibers, their usage is increasing day after day. The objective of this thesis is to examine the mechanical properties of carbonglass fiber reinforced epoxy hybrid composites in two different configurations. Also, the fatigue performance under bending tests of these composites were investigated. The hybrid composites were manufactured by using vacuum infusion technique at ambient temperature. To examine the mechanical properties of manufactured composites, a series of mechanical tests such as compression, tensile and three-point bending tests were performed on the samples which were prepared in accordance with the relevant ASTM standards. Load-controlled three-point bending fatigue tests were also carried out to investigate the performance of manufactured composites under fatigue. The fatigue tests were performed at different stress levels varied from 30 percent to 90 percent of average ultimate flexural strength of the samples which were determined from static three-point bending tests. Subsequently stiffness loss and Wöhler curves were constructed using a specific failure criterion.Master Thesis Development of Adhesively Bonded Glass Fiber Reinforced Polypropylene/Aluminum Based Fiber Metal Laminates (fmls)(Izmir Institute of Technology, 2019) Türkdoğan, Ceren; Tanoğlu, MetinOne of the most important steps during the production of adhesively bonded fiber metal laminates (FMLs) is adhesive bonding. In glass fiber reinforced polypropylene/aluminum laminates, it is very difficult to provide good bond strength. In order to solve this problem, applying various surface pre-treatments to the bonding surfaces prior to adhesively bonded is very important for good performance properties. In the present study, glass fiber reinforced polypropylene (GFPP) composite plates were manufactured from (±450) fabrics using hot press compression method. Tensile, Charpy impact and flexural tests were performed to investigate the mechanical properties of the composites. The produced GFPP plate and Al were used as the adherends and polyurethane-based film as adhesive in FMLs. While manufacturing FMLs, various surface modification techniques (silane and sandblasting pre-treatment) were applied to aluminum for good adhesion of GFPP and Al interface and their effect on the adhesive properties of GFPP/Al laminates were presented. The mechanical properties lap shear, and flexural strength and Mode-I fracture toughness of the adhesively bonded Al/GFPP laminates were investigated to evaluate the effects of surface treatments. Scanning electron microscope (SEM) was used to examine the fracture surfaces. Single lap shear test showed that the adhesion of the GFPP/Al was improved by treatments of aluminum surfaces with silane and sandblasting. According to Mode-I fracture toughness values, silane treated specimens gave the best results. Based on the flexural test results, no significant change was observed in the flexural strength values of treated specimens compared to non-treated specimens.