Scopus İndeksli Yayınlar Koleksiyonu / Scopus Indexed Publications Collection

Permanent URI for this collectionhttps://hdl.handle.net/11147/7148

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Now showing 1 - 10 of 15
  • Conference Object
    Citation - WoS: 3
    Citation - Scopus: 3
    Halloysite Nanotube Loaded Polyamide Nanocomposites: Structural, Morphological, Mechanical, Thermal and Processing Behaviors
    (American Institute of Physics, 2023) Akar, Alinda Öykü; Yıldız, Ümit Hakan; Tayfun, Ümit
    In this study, the polyamide 6 (PA) matrix was reinforced with the purified, fine ground and amino-silane treated halloysite nanotubes (HNT) at different concentrations. The preparation of composites was carried out using a lab-scale twin-screw micro-compounder with loading ratios at 0.5, 1, 3, and 20% by weight, and the test samples were prepared by the injection-molding process. According to mechanical test results, additions of HNT to the PA matrix caused slight improvements in tensile strength and Youngs' modulus parameters. The optimum concentrations for all of the additives used were estimated by comparison of mechanical test data. The addition of aminosilane-modified HNT resulted in a higher impact performance at high loading levels up to 3% concentrations. Further addition of HNT caused a reduction in the mechanical parameters of composites. Thermal studies revealed that the glass transition temperature of PA shifted to higher values after HNT mineral inclusions. Thermo-mechanical results showed that storage moduli of PA exhibited improvement with an increase in HNT content. The distributions of HNT clay into the PA phase were visualized with SEM images. Based on these observations, a high level of dispersion homogeneity was achieved for lower filling ratios. According to melt-flow and force measurements, composites filled with 20% of HNT displayed a remarkable increase in exerted force during melt-blending. © 2023 Author(s).
  • Conference Object
    Structural and Thermal Characterization of Ti+o Ion Implanted Ultrahigh Molecular Weight Polyethylene (uhmwpe)
    (American Institute of Physics, 2009) Öztarhan, Ahmet; Urkaç Sokullu, Şadiye Emel; Tıhmınlıoğlu, Funda; Kaya, N.; Ila, Daryush; Budak, S.; Nikolaev, A.
    In this work, Metal-Gas Hybrid Ion Implantation technique was used as a tool for the surface modification of Ultra High Molecular Weight Polyethylene (UHMWPE). Samples were Ti + O ion implanted by using Metal-Vapour Vacuum Arc (MEVVA) ion implanter to a fluence of 5x10(16) ion/cm(2) for each species and extraction voltage of 30 kV. Untreated and surface treated samples were investigated by Rutherford Back Scattering (RBS) Spectrometry, Attenuated Total Reflectance - Fourier Transform Infrared (ATR-FTIR) Spectroscopy, Thermo Gravimetric Analysis (TGA) and Differential Scanning Calorimetry (DSC). Results indicate that Ti + O ion implantation can be applied on UHMWPE surfaces successfully. ATR-FTIR spectra indicate that the C-H concentration on the surface decreased after Ti + O implantation. Thermal characterization with TGA and DSC shows that polymeric decomposition temperature is shifted after ion implantation.
  • Conference Object
    Citation - WoS: 3
    Citation - Scopus: 4
    Properties of Roman Lime Mortars in Ancient Lycia Region
    (American Institute of Physics, 2018) Taşcı, Burcu; Böke, Hasan
    In this study, the characteristics of mortars used in some ancient Roman buildings located Xanthos (Antalya), Patara (Antalya) and Tlos (Mugla) in Southern Turkey were determined in order to define the properties of the new mortars to be used in the conservation works of the buildings. For this purpose, their basic physical properties, raw material compositions, mineralogical and microstructural properties were determined by X-Ray Diffraction, Fourier Transform Infrared Spectroscopy, Scanning Electron Microscopy coupled with X-Ray Energy Dispersive Spectroscopy. Analysis results indicated that the binder of the mortars composed of lime and fine aggregates have compact and uniform structure. The mortars are of low density and high porosity were produced from high calcium lime containing magnesium and natural aggregates. The lime and aggregate ratios were between 3/4 - 5/2 by weight and the aggregates with particle sizes greater than 1mm. composed the largest fraction of the aggregates. Lime composed of small size of micritic crystals due to use of aged lime puny. Aggregates were natural and mainly composed of quartz, albite, diopside and amorphous silica that may derived from the use of volcanic ash as pozzolans.
  • Conference Object
    Citation - WoS: 1
    Citation - Scopus: 2
    Three Dimensional Grain Boundary Modeling in Polycrystalline Plasticity
    (American Institute of Physics, 2018) Yalçınkaya, Tuncay; Özdemir, İzzet; Fırat, Ali Osman
    At grain scale, polycrystalline materials develop heterogeneous plastic deformation fields, localizations and stress concentrations due to variation of grain orientations, geometries and defects. Development of inter-granular stresses due to misorientation are crucial for a range of grain boundary (GB) related failure mechanisms, such as stress corrosion cracking (SCC) and fatigue cracking. Local crystal plasticity finite element modelling of polycrystalline metals at micron scale results in stress jumps at the grain boundaries. Moreover, the concepts such as the transmission of dislocations between grains and strength of the grain boundaries are not included in the modelling. The higher order strain gradient crystal plasticity modelling approaches offer the possibility of defining grain boundary conditions. However, these conditions are mostly not dependent on misorientation of grains and can define only extreme cases. For a proper definition of grain boundary behavior in plasticity, a model for grain boundary behavior should be incorporated into the plasticity framework. In this context, a particular grain boundary model ([l]) is incorporated into a strain gradient crystal plasticity framework ([2]). In a 3-D setting, both bulk and grain boundary models are implemented as user-defined elements in Abaqus. The strain gradient crystal plasticity model works in the bulk elements and considers displacements and plastic slips as degree of freedoms. Interface elements model the plastic slip behavior, yet they do not possess any kind of mechanical cohesive behavior. The physical aspects of grain boundaries and the performance of the model are addressed through numerical examples.
  • Conference Object
    Kahve Laboratory Rf Circulator and Transmission Line Project
    (American Institute of Physics, 2018) Çetinkaya, Hakan; Çağlar, Aslıhan; Çicek, Cihan; Özbey, Aydın; Sunar, Ezgi; Türemen, Görkem; Yıldız, Hüseyin; Yüncü, Alperen; Özcan, Erkcan; Ünel, Gökhan; Yaman, Fatih
    An 800 MHz RF circulator and transmission line project has recently started at the newly commissioned Kandilli Detector, Accelerator and Instrumentation (KAHVE) Laboratory at the Boǧaziçi University. The aims are to design, build and construct an RF circulator and transmission line in Turkey for high power and high frequency applications. The project consists of 8 transmission line elements: 800 MHz RF generator with 60 kW power (klystron), klystron to waveguide converter, waveguides, E and H bends, 3-port circulator and waveguide to coaxial converter to transmit RF power to a pillbox RF cavity. Design studies and details of the ongoing project will be presented.
  • Conference Object
    Citation - WoS: 1
    Citation - Scopus: 1
    Intrinsic and Statistical Size Effects in Microforming
    (American Institute of Physics, 2017) Yalçınkaya, Tuncay; Demirci, Aytekin; Simonovski, Igor; Özdemir, İzzet
    This paper analyzes the intrinsic (grain size dependent) and the statistical (grain number and orientation distribution dependent) size effects of micron level polycrystalline metallic specimens under plastic deformation through a strain gradient crystal plasticity framework. The macroscopic and local behavior of specimens from very limited number of grains to high number of grains are studied and the results are discussed in detail taking into account different boundary conditions.
  • Conference Object
    Citation - WoS: 1
    Citation - Scopus: 1
    Strain Gradient Polycrystal Plasticity for Micro-Forming
    (American Institute of Physics, 2016) Yalçınkaya, Tuncay; Simonovski, Igor; Özdemir, İzzet
    The developments in the micro-device industry has produced a substantial demand for the miniaturized metallic components with ultra-thin sheet materials that have thickness dimensions on the order of 50-500 μm which are produced through micro-forming processes. It is essential to have predictive tools to simulate the constitutive behavior of the materials at this length scale taking into account the physical and statistical size effect. Recent studies have shown that on the scale of several micrometers and below, crystalline materials behave differently from their bulk equivalent due to micro-structural effects (e.g. grain size, lattice defects and impurities), gradient effects (e.g. lattice curvature due to a non-uniform deformation field) and surface constraints (e.g. hard coatings or free interfaces). These effects could lead to stronger or weaker material response depending on the size and unique micro-structural features of the material. In this paper a plastic slip based strain gradient crystal plasticity model is used to address the effect of microstructural features (e.g. grain size, orientation and the number of grains) on the macroscopic constitutive response and the local behavior of polycrystalline materials.
  • Conference Object
    Evolution of Binaries Towards Hmxbs and Lmxbs
    (American Institute of Physics, 2011) Kalomeni, Belinda
    In this study we investigate the evolution of binary systems towards low mass x-ray binaries and high mass x-ray binaries using Eggleton's binary star evolution code. © 2011 American Institute of Physics.
  • Conference Object
    Magnetic Cataclysmic Variables
    (American Institute of Physics, 2010) Kalomeni, Belinda
    We present a study on magnetic cataclysmic variables (polars) using the collected data from the literature. These parameters (mass, radius, magnetic field intensity, mass transfer rate, etc.) and the relations between them are important to understand their nature, to explain the observed properties of them and to test the current evolutionary models. © 2010 American Institute of Physics.
  • Conference Object
    Resolutions in Cotorsion Theories
    (American Institute of Physics, 2010) Akıncı, Karen; Alizade, Rafail
    We consider the λ- (μ-) and λ̄- (μ̄-) dimensions of modules taken under a cotorsion theory (F, C) satisfying the Hereditary Condition, and establish some inequalities between the dimensions of the modules of a short exact sequence, not necessarily Hom (F, -) exact. We investigate the question of whether the property of having a (special) F- or C-resolution of length n is resolving, closed under extensions or coresolving and establish some inequalities connecting the λ- (μ-) and λ̄- (μ̄-) dimensions of modules in a short exact sequence. © 2010 American Institute of Physics.