WoS İndeksli Yayınlar Koleksiyonu
Permanent URI for this collectionhttps://hdl.handle.net/20.500.12416/8653
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Article Random Vibration Analysis of Nuclear Power Plant Structures(Elsevier Science Sa, 2026) Dal, Gizem Caglar; Soyluk, Kurtulus; Çağlar Dal, GizemIn this study, random vibration analysis of a nuclear power plant building under earthquake loading is performed based on a large-magnitude earthquake of Kobe 1995. A typical nuclear power plant structure widely used in China is selected as a numerical model and modeled as a 3D system. Within the scope of the study, random vibration and deterministic analyses were performed on firm, medium, and soft soils to determine the effects of earthquake motions on nuclear power plant systems. In the study, the theory of random vibration analysis based on the filtered white noise (FWN) ground motion model was utilized and it was intended to determine to what extent the FWN model reflects the real earthquake motion. In addition to soil type, the considered power plant system is analyzed for the ground motions showing near-fault and far-fault characteristics. As a result of the study, it is concluded that the FWN ground motion model used to model earthquake ground motion can be used to consider the effect of real earthquakes. It is also underlined that differences in soil type, fault type and analysis methods affect the results for the considered nuclear power plant structure.Article Citation - WoS: 10Citation - Scopus: 12Influence of the Heat Treatment on the Microstructure, Mechanical and High-Temperature Oxidation Behavior of Hastelloy X Alloy Fabricated Via Laser Powder Bed Fusion(Elsevier Science Sa, 2025) Ozer, Seren; Yalcin, Mustafa Alp; Bilgin, Gueney Mert; Davut, Kemal; Esen, Ziya; Dericioglu, Arcan F.The effect of building direction and heat treatment on the microstructure, mechanical properties, and high- temperature oxidation behavior of Hastelloy X (HX) alloy fabricated by the laser powder bed fusion (L-PBF) method was studied. Electron backscatter diffraction analyses revealed that the development of textured columnar grains with varying average grain sizes, boundary fractions, and dislocation densities induced the mechanical anisotropy observed in both horizontally and vertically fabricated samples. The yield strength (YS) values of the horizontally and vertically as-fabricated samples were determined as 605.7 +/- 15.9 MPa and 552.3 +/- 8.5 MPa, respectively. The post-processing heat treatment increased the ductility remarkably and reduced YS value down to similar to 445 MPa for all samples by the elimination of microstructural anisotropy and increased grain size subsequent to recrystallization. Oxidation tests conducted at 900 degrees C up to 100 h on as- fabricated samples exhibited severe intergranular oxidation, which was accompanied by the formation of large voids and microcracks as well as spallation of the oxide layer. In contrast, the heat-treatment improved the oxidation resistance of the alloy possibly due to the formation of uniform and dense Cr2O3 layer on the substrate surface.Article Citation - WoS: 3Citation - Scopus: 3Nanomechanical Properties of Al-Tb Marginal Metallic Glass(Elsevier Science Sa, 2023) Okuyucu, Can; Ulucan, Tolga Han; Abboud, Mohammad; Motallebzadeh, Amir; Ozerinc, Sezer; Kalay, Ilkay; Kalay, Yunus ErenAl-Rare Earth (RE) metallic glasses provide an effective model system to study the effect of nanocrystallites in an amorphous matrix on nanomechanical behavior. In this work, we achieved a series of Al-Tb metallic glasscrystalline composites with systematically varying crystalline content through annealing. The nanomechanical properties were characterized using micropillar compression tests and nanoindentation for as-quenched amorphous and annealed amorphous/nanocrystalline composite specimens. The promising hardness increases after annealing from 3.0 GPa to 4.6 GPa and elastic modulus increment from 68 GPa to 92 GPa were discussed in detail, considering the structural features of Al-RE marginal metallic glass formers. The increase in elastic modulus is associated with the nucleated fcc-Al nanocrystals that divide the amorphous matrix, leading to the branching of the shear bands. The correlation between the fcc-Al nanocrystals and the behavior of shear bands was discussed in detail.Article Citation - WoS: 41Citation - Scopus: 44Effect of Post Fabrication Aging Treatment on the Microstructure, Crystallographic Texture and Elevated Temperature Mechanical Properties of In718 Alloy Fabricated by Selective Laser Melting(Elsevier Science Sa, 2022) Bilgin, Guney Mert; Davut, Kemal; Esen, Ziya; Dericioglu, Arcan F.; Ozer, SerenThe effect of building direction and post fabrication aging treatment on the microstructure, crystallographic texture and high temperature mechanical properties of Inconel 718 (IN718) alloy fabricated by selective laser melting (SLM) method was investigated. After aging, arc-shaped structures seen in as-fabricated samples dis-appeared and converted into a mixture of columnar and equiaxed grains. Nano-sized gamma '' and/or gamma' precipitates were formed upon aging; however, MC type carbides and Laves phase encountered in as-fabricated samples were not dissolved completely after aging. Moreover, aging did not alter the texture ((001)//building direction (BD)) of as-fabricated samples. Mechanical properties of the alloys under tension were influenced by the build direction, aging time and test temperature. As-fabricated samples produced in vertical direction exhibited higher room temperature strengths with lower ductility due to orientation of overlapped prior melt pools. Room temperature tensile test results revealed that peak aging caused a significant improvement in ultimate tensile strength (UTS), from 1066.5 MPa and 998.4 MPa to 1408.5 MPa and 1330.4 MPa whereas elongation values decreased from 27.5% and 32.2% to 19.6% and 23.7% in vertically and horizontally built samples, respectively. Peak-aged samples (aged at 700 degrees C for 8 h) tested at 600 degrees C displayed serrated regions in their stress-strain curves due to dynamic strain aging (DSA). Although strength values of the samples displayed an expected decrease by temperature, ductility of the samples reduced to minimum at temperatures around 700-800 degrees C, which was attributed to intermediate temperature embrittlement.Article Citation - WoS: 4Citation - Scopus: 4Temperature-Dependent Absorption Edge and Photoconductivity of Tl2in2s3se Layered Single Crystals(Elsevier Science Sa, 2013) Ambrico, M.; Ligonzo, T.; Gasanly, N. M.; Guler, I.Temperature variation of indirect band gap of Tl2In2S3Se layered single crystals were obtained by means of absorption and photoconductivity measurements. The temperature coefficient of -7.1 x 10(-4) eV/K from absorption measurements in the temperature range of 10-300 K in the wavelength range of 520-1100 nm and -5.0 x 10(-4) eV/K from PC measurements in the temperature range of 132-291 K in the wavelength range of 443-620 nm upon supplying voltage V = 80 V were obtained. From the analysis of dark conductivity measurements in the temperature range of 150-300 K, conductivity activation energy was obtained as 0.51 eV above 242 K. The degree of the disorder, the density of localized states near Fermi level, the average hopping distance and average hopping energy of Tl2In2S3Se crystals were found as, 1.9 x 10(5) K, Nf = 4 x 10(20) cm(-3)eV(-1), 29.1 angstrom and 24.2 meV in the temperature range of 171-237 K, respectively. Activation energy of hopping conductivity at T = 171 K was obtained as 41.3 meV and the concentration of trapping states was found as 1.6 x 10(19) cm(-3). (C) 2012 Elsevier B.V. All rights reserved.Article Citation - WoS: 8Citation - Scopus: 8Design of Quantum Sensor To Duplicate European Robins Navigational System(Elsevier Science Sa, 2021) Salmanogli, Ahmad; Gokcen, DincerIn this article, we design a quantum device to duplicate the European Robins procedure to precisely deter-mine the migratory route. In the mentioned procedure, the important issue is the geomagnetic field effect on the magnetic momentum of the created radical pairs (triplet-singlet states) dancing with a special fre-quency. To duplicate the procedure, a quantum sensor consisting of two coincident tripartite systems is designed. Each tripartite system is independently excited with the entangled photons (signal and idler). The interesting point is that by manipulation of the system in the right condition, the microwave cavities modes separately affected by the entangled photons can be entangled. The entangled microwave photons play the same role as the triplet-singlet states present in the bird's navigational system. The key point in the design of the quantum sensor is that the entanglement between microwave photons can be strongly affected by the external magnetic field. In fact, this is the criterion employed by the quantum sensor to sense the magnetic field intensity and the direction. To analyze the system, the canonical quantization (or microscopic) method is used to determine the sensor's Hamiltonian, and also the system dynamics equations of motions are analytically derived using Heisenberg-Langevin equations. (c) 2021 Elsevier B.V. All rights reserved.Article Citation - WoS: 5Citation - Scopus: 7Structural and Optical Properties of Thermally Annealed Thallium Indium Disulfide Thin Films(Elsevier Science Sa, 2020) Gasanly, N.; Guler, IStructural and optical properties of thallium indium disulfide (TlInS2) thin films, deposited by thermal evaporation technique and thermally annealed at different temperatures, were analyzed. Crystallite size, dislocation density and lattice strain of the thin films were found from X-ray diffraction experiments. The atomic compositions of the films were determined from energy dispersive spectroscopy analysis. Surface morphology of the films was analyzed using atomic force microscopy. From room temperature transmittance spectrum, the band gap energies of the films were identified. The decrease in band gap energies of the films with the annealing temperature up to 300 degrees C was observed due to increase in crystallite size and decrease in lattice strain. From Raman measurements, it was observed that the Raman shifts of the films were well correlated with those of TlInS2 bulk crystal.Article Citation - WoS: 62Citation - Scopus: 69Titanium-Magnesium Based Composites: Mechanical Properties and In-Vitro Corrosion Response in Ringer's Solution(Elsevier Science Sa, 2013) Esen, Ziya; Dikici, Burak; Duygulu, Ozgur; Dericioglu, Arcan F.Ti-Mg composite rods exhibiting both bioinert and biodegradable characteristics have been manufactured by hot rotary swaging from elemental powders of titanium and magnesium. As a result of processing, spherical magnesium powders elongated in the direction of deformation and the dendritic structure in starting magnesium powders transformed into highly equiaxed grains. Magnesium particles in the outer layer of the composites were decorated by thin layer of MgO while the interior parts were free from oxides. As expected, Young's moduli, yield and peak strengths of the composites were observed to decrease with an increase in the magnesium content, while ductility of composites was enhanced by decreasing the amount of titanium. Composites fractured at an angle 45 to the loading axis along the titanium particle boundaries and through the magnesium particles via transgranular type of fracture with the accumulation of twins near the fracture surface of magnesium. Mechanical properties of the composites were observed to be comparable to that of bone and the composites exhibited biodegradable and bioinert character upon testing in Ringer's solution such that magnesium was selectively corroded and pores were formed at prior magnesium powder sites while titanium preserved its starting skeleton structure. In addition, it was found that volume ratio of titanium and magnesium, and continuous MgO layer are the most important parameters which should be considered in designing biodegradable magnesium alloys with an appropriate corrosion rate. (C) 2013 Elsevier B.V. All rights reserved.Article Citation - WoS: 66Citation - Scopus: 66Comparison of the Short and Long-Term Degradation Behaviors of As-Cast Pure Mg, Az91 and We43 Alloys(Elsevier Science Sa, 2020) Esen, Ziya; Aydinol, Kadri; Dericioglu, Arcan F.; Ocal, Ezgi Butev; Bütev Öcal, EzgiThe corrosion behaviors of pure magnesium, AZ91, and WE43 alloys have been evaluated by weight loss, hydrogen evolution rate, pH change measurements and potentiodynamic polarization as well as electrochemical impedance spectroscopy (EIS) methods. Main corrosion product formed on the surface of Mg/Mg-alloys after immersion of 24 h was Mg(OH)(2) on the other hand, at the end of the 20 days additional CaCO3 which was found to display a critical role in degradation characteristics of the samples, was found. Examination in the cross section of the polished surfaces revealed that protective layers became thicker and corrosion rate of the samples decreased possibly due to increased protective abilities of the surfaces. Intermetallics in AZ91 and WE43 alloys acted as cathodic centers and induced micro galvanic corrosion. Undermining of intermetallics in WE43 alloy intensified the corrosion rate. AZ91 alloy exhibited the lowest corrosion rate among the samples when tested in simulated body fluid (SBF).Article Citation - WoS: 96Citation - Scopus: 96Fractional Frequency Flexible Fourier Form To Approximate Smooth Breaks in Unit Root Testing(Elsevier Science Sa, 2015) Omay, TolgaIn this study, a Fractional Frequency Flexible Fourier Form DF-type unit root test is proposed. The small sample properties of the proposed test are found to be better than that of the integer frequency counterpart. (C) 2015 Elsevier B.V. All rights reserved.
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