Master Degree / Yüksek Lisans Tezleri

Permanent URI for this collectionhttps://hdl.handle.net/11147/3008

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Subject: search.filters.subject.Fibrous composites

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Now showing 1 - 6 of 6
  • Master Thesis
    Experimental Analysis and Modeling of Shear Strength of Adhesive-Bonded Single-Lap Glass Fiber Reinforced Composites
    (01. Izmir Institute of Technology, 2024) Artem, Hatice Seçil; Serbest, Sertaç; Artem, Hatice Seçil
    Composite materials are being used in many fields of industry day by day. With this increasing interest in composites, the methods of joining composites have also become the focus of attention. Mechanical fasteners cause damage to the composite, increase in weight, and stress accumulation in the joint area. Recently, joining composites with adhesives has attracted the attention of researchers. In this study, glass fiber reinforced polymer composites were combined with two paste adhesive thicknesses, using two brands of paste adhesives as fast-curing and slow curing, and three different peel plies and the effects of these three different parameters on the bonding strength were investigated both experimental and numerical analyses. In the experimental part of the thesis, glass fiber reinforced polymer composites were produced by the vacuum infusion method. The surfaces modified with different peel plies were combined with two different paste adhesives. A single-impact shear test was performed to examine the bond strength. As a result, it was observed that the fast-curing paste adhesive showed better performance in bond strength. At the same time, it has been experimentally demonstrated that the paste adhesive thickness of 0.6 mm has a positive effect compared to the paste adhesive with a thickness of 0.4 mm. It has been observed that the different peel plies used did not make a critical difference in the bond strength. In the numerical part of the thesis, six different regression models were used to model the shear strength of adhesive-bonded composites and then an optimization study was carried out by selecting the two best regression models that accurately express the physical model. Using the stochastic optimization methods, Differential Evolution and Nelder Mead algorithms, the optimum shear strength values possible with the existing parameters were found. This thesis contributes to determination of the bonded samples with the highest shear stress value by determining the optimum parameters.
  • Master Thesis
    Joining and Interfacial Properties of Aluminum/Glass Fiber Reinforced Polypropylene Sandwich Composites
    (Izmir Institute of Technology, 2009) Guruşçu, Aslı; Tanoğlu, Metin
    The joining of separate components using a suitable technique is a critical step in the manufacture of composite structures. For good property performance of aluminum/glass fiber reinforced polypropylene (Al/GFPP) laminates, one of the most important problems is to obtain good adhesive bond strength.In the present study, Al/GFPP laminates have been manufactured with various surface pretreatment techniques. Adhesion at the composite/metal interface has been achieved by surface pretreatment of Al with amino based silane coupling agent, incorporation of polyolefin based adhesive film and modification with PP based film containing 20 wt. % a maleic anhydride modified polypropylene (PP-g-MA). The mechanical properties shear, peel and bending strength of the adhesively bonded Al/GFPP laminates were investigated to evaluate the effects of those various surface treatments. In addition, peel strengths of Al foam/GFPP laminates with various surface treatments were measured. The fracture surfaces have been examined by scanning electron microscope (SEM). Results showed that the adhesion of the laminated Al/GFPP systems were improved by treatment of aluminum surfaces with amino-based silane coupling agent. Based on peel and bending strength results, Al/GFPP laminates with incorporation of polyolefin based adhesive films exhibited significant increase on the adhesive behaviour. Modification of Al/GFPP interfaces with PP-g-MA layer leads to highest improvement on the adhesion properties.
  • Master Thesis
    Seismic Behavior of Steel I-Beams Modified by a Welded Haunch and Reinforced With Glass Fiber Reinforced Polymers
    (Izmir Institute of Technology, 2009) Özdemir, Timur; Eğilmez, Oğuz Özgür
    Flange and web local buckling in beam plastic hinge regions of welded steel moment frames (SMF) can prevent beam-column connections to achieve adequate plastic rotations under earthquake-induced forces. As the use of fiber reinforced polymers (FRP) have increased in strengthening and repair of steel members in recent years, using FRPs in stabilizing local instabilities have also attracted attention. Generally, high modulus carbon FRP (CFRP) laminates, with elastic modulus similar to that of steel, are preferred in strengthening applications. On the other hand, glass FRP (GFRP) has a much smaller modulus than that of steel, typically one order of magnitude less, which limits its use in strengthening applications. However, this modulus mismatch is an asset when the primary goal is to stabilize inelastic local buckling with the least possible strength increase in the section. In a steel-GFRP hybrid system, while the low modulus of GFRP will not allow a significant strength increase in the beam, the flexural strength of GFRP can provide bracing to the underlying steel, which is flowing plastically. In this research study, the cyclic behavior of steel beams modified by a triangular haunch welded to the beam bottom flange only and reinforced with GFRP laminates at beam flanges have been investigated by finite element analysis (FEA). Cantilever I-sections with flange-web slenderness ratios higher then those stipulated in current seismic design specifications are analyzed under reversed cyclic loading. Both bare beam sections and sections reinforced with GFRP are investigated. The effects of GFRP thickness, width, and length on stabilizing local buckling are investigated. The flexural resistance of the beams at column face, interlaminar shear stresses in GFRP strips, and shear stresses at beam-GFRP binding surface are examined. The results reveal that the plastic rotation capacity of steel beams can be enhanced by the use of GFRP strips.
  • Master Thesis
    Quasi-Static and High Strain-Rate Mechanical Behavior of Fp™ (α-Alumina) Long Fiber Reinforced Magnesium and Aluminum Metal Matrix Composites
    (Izmir Institute of Technology, 2004) Akil, Övünç; Güden, Mustafa
    The mechanical response of an FP long fiber (35%) Mg composite has been determined in the transverse and longitudinal directions in compression. Results were also compared with those of a similar composite of Al matrix. It was found that the composite in the transverse direction exhibited strain rate sensitivity of the flow stress and maximum stress within the studied strain rate range (10-4 to 1x103s-1). However the increase in strain rate decreased the failure strain. Microscopic observations on the failed samples have shown that the composite failed predominantly by shear banding. Near to the fracture surface DRX grains were observed within the shear band and it was proposedthat the lower ductility of the composite at increasing strain rates was due to the early DRX grain formation which softened thecomposite and resulted in lower ductility. Although twinning was observed in the deformed cross-sections of the samples at all strain rates particularly near the shear band region, it was proposed that the main deformation mechanism was slip which was evidenced by the slip lines on the fracture surface. The strain rate sensitivity in fracture stress of the composite in transverse direction was also found to be similar to that of the Al composite tested in the same direction. In the longitudinal direction, the composite failed by kink formation at quasi-static strain rates, while kinking and splitting at high strain rates. The maximum stress in the axial direction was however foundto be strain rate insensitive. In this direction similar to transverse direction DRXgrain formation was observed in the kink region. The lack of strain rate sensitivity in this direction was attributed to DRX grain formation at high strain rates combined with adiabatic heating and the brittle nature of the composite leading to fluctuatitonin the compressive strength.
  • Master Thesis
    Preparation of Electrospun Composite Fibers Based on Ps-pi-ps/Cdsxse1-x Nanoparticles
    (Izmir Institute of Technology, 2011) Aşkın, Görkem; Demir, Mustafa Muammer; Özçelik, Serdar
    Polymeric fibrous films were prepared based on polystyrene-b-polyisoprene-bpolystyrene triblock copolymer (SIS) and CdSxSe1-x nanoparticles by electrospinning process. SIS with 14 wt % Styrene (14% PS-SIS) and 22 wt % Styrene (22% PS-SIS) triblock copolymers were employed. Both of them undergo microphase separation. While the former shows cylinder-like morphology, the latter exhibits the lamellae one. CdSxSe1-x partciles were stabilized by two different surfactant molecules: i) n-trioctylphosphine oxide (TOPO) and ii) oleic acid (OA). When the particles were blended with 22% PS-SIS, particles capped with TOPO preferentially filled to PS domain whereas particles capped with OA loaded into the PI domain. Composite electrospun fibers were prepared with a diameter of 1.5 mm on average. Electrospinning parameters (potential difference, solution concentration, flow rate) were investigated on fiber morphology. The films are colorless under day light and have strong green emission under UV light.
  • 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, Metin
    Fiber 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.