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Öğe High Temperature Mechanical Behavior of MgAl2O4-YAG Eutectic Ceramic In Situ Composites by Float Zone Method(Walter De Gruyter Gmbh, 2017) Abalı, SerkanThe directionally solidified eutectic MgAl2O4-Y3Al5O12 crystal was prepared at a pressure of 0.4 MPa of ambient nitrogen gas by the high frequency induction heated floating zone furnace. In order to determine the high temperature characteristics, directionally solidified MgAl2O4-Y3Al5O12 eutectic phase has been analyzed with creep test, tensile strength, young modulus and fracture toughness at the various temperatures and the microstructural variations have been studied according to the analysis results. It has been seen that directionally solidified with zone melting MgAl2O4-YAG eutectic ceramic which has given the value of 168 MPa below 10(-6)/s strain rate at 1,700 degrees C temperature has revealed minimum stress.Öğe Effect of calcination and sintering temperature on porosity and microstructure of porcelain tiles(Walter De Gruyter Gmbh, 2022) Durgun, Ramazan; Abalı, SerkanPorcelain tiles are prepared from kaolin, silica sand, feldspar, clay raw materials, and various additives. Ceramic powders are calcined at different temperatures after grinding, drying, and sieving. After the powders are formed and dried, they are sintered at different temperatures. Firing shrinkage (FS), water absorption (WA), and three-point flexure tests of the samples are compared. The mineralogical definitions are completed by performing a phase analysis via X-ray diffraction (XRD). After the microstructural investigations, pore-sizes and distributions are examined by the Barrett-Joyner-Halenda (BJH) method. The powder sintering process increases the crystallization of the compact material. Low porosity and high strength structures are obtained for the samples with powder calcination temperatures of 800 and 900 degrees C and a compact sintering temperature of 1200 degrees C. The pore volume increases by increasing the powder calcination temperature in samples compact-sintered at 1200 degrees C. When the powder calcination temperature of these samples is increased to 1000 degrees C, the flexural strength decreases. Therefore, the powder sintering temperature of 900 degrees C is the critical value.Öğe Significantly improved shear, dynamic-mechanical, and mode II fracture performance of seawater aged basalt/epoxy composites: The impact of halloysite nanotube reinforcement(Elsevier B.V., 2021) Ulus, Hasan; Kaybal, Halil Burak; Eskizeybek, Volkan; Avcı, AhmetThe primary concern of fiber-reinforced polymers (FRPs) subjected to seawater environment is losing their initial mechanical performance since water can diffuse into the composite and deteriorates the fiber-matrix interface. Recent studies related to aging performance in the seawater environment have shown that introducing halloysite nanotubes (HNTs) into the polymer matrix offers a combination of an efficient barrier effect and an improved fiber-matrix interface. Hereupon, the principal objective of this study was to experimentally investigate the impact of HNTs on shear and mode II fracture performances of the seawater aged basalt fiber (BF) reinforced epoxy (EP) composites. After six months of aging in seawater, the findings indicated that HNTs reinforced multi-scale composites exhibited 34 and 46% higher shear strength and mode II delamination toughness compared to the neat specimens. Moreover, according to the dynamic-mechanical analysis, higher glass transition temperatures (8%) were obtained for the multi-scale composites. The reduction in mechanical performances induced by fiber-matrix interfacial degradation was also confirmed by scanning electron microscopy analysis. Chemical deterioration of the polymer matrix was explored by Raman spectroscopy to reveal the efficiency of HNTs induced barrier effect. As a result of these investigations, HNT modified BF/EP multi-scale composites were offered for future advanced engineering applications.Öğe An experimental study on low velocity impact performance of bolted composite joints-part 2: Influence of long-term seawater aging(Elsevier Ltd, 2021) Kaybal, Halil Burak; Ulus, Hasan; Eskizeybek, Volkan; Avcı, AhmetIn the first part of this two-part paper (Part 1), the low-velocity impact (LVI) response of bolted fiber-reinforced polymer joints was investigated considering with two scenarios based on the localized impact damage as the impactor hit on the top of the bolt (ToB) and the side of the washer (SoW). Moreover, the influence of halloysite nanotubes (HNTs) reinforcement of the epoxy matrix on the impact performance was also evaluated. As the second part of the research, this paper represents the effects of seawater aging on the LVI response of FRPs. For this, the composite joints were submerged in an artificial seawater environment for six months to accelerate aging. Afterward, as following the systematic experimental path exhibited in Part 1, LVI tests were conducted by dropping the impactor on ToB and SoW regions. The test results showed that the seawater aging impaired almost 30% of the composite joints' impact resistance, where HNTs reinforced multi-scale composite joints exhibited a 13% higher impact loading performance. The ToB impact scenario was considered as visually and quantitatively more detrimental than the SoW tests. The detrimental impact of seawater aging was validated by tracking the elemental evolution in the seawater environment. Based on the mechanical, morphological, and structural analyses, a novel damage mechanism was introduced to address seawater aging's progress, including the role of nanoreinforcements.Öğe An experimental study on low velocity impact performance of bolted composite joints part 1: Influence of halloysite nanotubes on dynamic loading response(Elsevier Ltd, 2021) Kaybal, Halil Burak; Ulus, Hasan; Eskizeybek, Volkan; Avcı, AhmetMechanical joints are a widely utilized to assembly fiber reinforced polymer composites in marine applications. Impact is one of the most encountered unpredictable loading types which significantly diminishes the mechanical properties of structures. The goal of this study is to investigate the dynamic loading response of bolted basalt-epoxy composite laminates under different impact energies. Unlike the existing low velocity impact tests of bolted composite joints, to reveal the effect of localized impact damage, the low-velocity impact tests were conducted on two different regions as the top of bolt (ToB) and the side of washer (SoW). In addition, the effects of HNTs reinforcement on the impact response and the damage propagation were also evaluated. It was obtained that ToB damage was comparatively severe for the composite joints due to the propagation of the damage through the hole center. Moreover, HNTs improved the impact resistance about %15, especially at lower impact energies. However, the nanoreinforcement efficiency diminished with increasing impact energy levels. The obtained results were further supported with macro-size images and scanning electron microscopy (SEM). Together with Part II, this study reports an extensive work of impact tests of bolted composite joints utilized in the marine industry.Öğe GaN/ZnO hybrid nanostructures for improved photocatalytic performance: One-step synthesis(TUBITAK, 2023) Üstün, Tugay; Haspulat Taymaz, Bircan; Eskizeybek, Volkan; Kamış, Handan; Avcı, AhmetNanostructured semiconductor materials are considered potential candidates for the degradation of textile wastewater via the photocatalytic process. This study aims to produce hexagonal gallium nitride (GaN) nanoplates and zinc oxide (ZnO) nanoparticles in a deionized water environment utilizing a one-step arc discharge process. Detailed characterization of samples has been completed via scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and UV visible spectroscopy methods. The hybrid nanostructure morphologies consist of nanoplates and nanorods of different sizes. The photoperformance of GaN/ZnO hybrid nanostructures was assessed via the malachite green (MG) dye degradation under UV exposure. Under UV exposure, the degradation yield reached 98% in 60 min. Compared to individual ZnO and GaN nanoparticles, the photocatalytic reaction rate of the GaN/ZnO photocatalyst is 2.2 and 3.6 times faster, respectively. Besides, the GaN/ZnO hybrid nanostructures show excellent photocatalytic stability. The energy consumption of the photocatalytic degradation in the presence of GaN/ZnO hybrid nanostructures was 1.688 kWhL–1. These results demonstrate that the GaN/ZnO hybrid nanostructures with improved photocatalytic activity are a reasonable option for the decomposition of textile wastewater under UV light exposure.Öğe Combined effect of fiber hybridization and matrix modification on mechanical properties of polymer composites(SAGE Publications Ltd, 2023) Demir, Okan; Yar, Adem; Eskizeybek, Volkan; Avcı, AhmetGlass/carbon fiber reinforced hybrid composites are great candidates for wind turbine blade manufacturers to make larger blades. Variation of stacking sequences ensures design freedom to the composite engineers to optimize the composite structure's mechanical performance. On the other hand, matrix modification of polymer composites with nanoparticles is also of interest to introduce multifunctional properties. This research aims to scrutinize the influence of simultaneous fiber hybridization and matrix modification on polymer composites’ tensile, flexural, and low-velocity impact properties. Hybrid glass/carbon epoxy composites and hybrid glass/carbon/multi-walled carbon nanotube (MWCNT) multiscale polymer composites of stacking sequences [GCGCGC]S, [CGCGCG]S, and [G6C6] were manufactured. Fiber hybridization dramatically improved tensile strength between 51% and 76% compared to glass fiber composite. Depending on the stacking sequence, the flexural strength of the hybrid composites was improved between 10% and 16% concerning carbon fiber composite. With the introduction of MWCNTs, a slight increase in the tensile strength for unsymmetrical hybrid composites by around 5% and decreases by 7% for symmetrical ones were observed. Similar behavior was seen for bending characteristics. Additionally, low-velocity impact tests showed that it is achievable to bring greater impact peak forces up to 70% for hybrid composites than carbon fiber epoxy composites. MWCNTs modification of the matrix restrained the impact damage propagation, as proved by C-scan analysis.Öğe Coating graphene nanoplatelets onto carbon fabric with controlled thickness for improved mechanical performance and EMI shielding effectiveness of carbon/epoxy composites(Elsevier Ltd, 2023) Mutlu, Gökhan; Yıldırım, Ferhat; Ulus, Hasan; Eskizeybek, VolkanCoating nanostructures on fiber reinforcement is a facile and scalable technique to manufacture next-generation fiber-reinforced polymer composites with tailored physical properties. Optimizing the nanomaterial coating thickness on fibers is vital in tailoring the multifunctionality of fiber-reinforced composites without sacrificing the mechanical performance since it relies on the fiber–matrix interface, where interlaminar and other physical properties are governed. This paper investigates the impact of graphene nanoparticle (GNP) coating thickness on the mechanical properties, fracture behavior, thermo-mechanical, and electromagnetic interference (EMI) shielding effectiveness (SE) of composite structures. We grafted GNPs on carbon fabrics using a solution coating method with various thicknesses (10, 20, and 30 µm), and GNPs grafted fabrics were impregnated with an epoxy resin. The 20 µm GNPs coating thickness exhibited the highest mechanical performance, increasing the tensile and interlaminar shear strength by 32% and 26%, respectively, compared to pristine samples. Storage modulus and transition (Tg) temperature values increased by 18.6% and 13.6% for 20 µm coating thickness, respectively. Besides, the unstable crack growth at the fiber–matrix interface was stabilized when the GNPs coating thickness reached 20 µm according to delamination toughness tests. While mode-I fracture toughness increased up to 22%, an improvement of 13.5% was obtained in mode-II fracture toughness. The underlying toughening mechanisms at the interfacial region were identified using scanning electron microscopy. The EMI-SE was slightly increased by the GNPs grafting, whereas thinner GNPs coatings exhibited higher shielding efficiency.Öğe Effect of High-Chromium Ferrous-Based TiC Composite Coating on Microstructural and Corrosion Properties of Steels(Springer, 2023) Buytoz, Soner; Demirören, Hülya; Kaya, EsadCoatings are generally one of the surface protection methods used to prevent corrosion damage. However, coatings with a lean chemical content usually perform low corrosion resistance. Additive carbides could be added to enhance the corrosion resistance of the coatings. Hence, the current study focuses on the effect of TiC addition on FeCrC powder, which is frequently used as a coating material. Different proportions of TiC powder were added to FeCrC powder. 42CrMo4 steel plate was used as substrate. A gas tungsten arc (GTA) welding device was used as the energy source in the coating process. Corrosion tests were performed via a standard three-electrode system. TiC improved the corrosion resistance of FeCrC coating. The corrosion rate was observed to have an inverse proportion of TiC amount in the coating. The sample with the highest TiC powder concentration has the lowest calculated corrosion rate (25 wt %) as 2 × 10–6 (A/mm2).Öğe Possible optical counterparts of ULXs in NGC 1672(John Wiley and Sons Inc, 2023) Allak, Sinan; Akyüz, Aysun; Sonbaş, Eda; Dhuga, Kalvir S.In this study, we use archival data from Hubble Space Telescope (HST), Chandra, XMM-Newton, and Swift-XRT, to probe the nature of 9 (X1-X9) candidate ultraluminous X-ray sources (ULXs) in NGC 1672. Our study focuses on using the precise source positions obtained via improved astrometry based on Chandra and HST observations to search for and identify optical counterparts for these ULXs. Unique optical counterparts are identified for X2 and X6; two potential counterparts were determined for X1, X5, and X7 within the respective error radii while no optical counterparts were found for the remaining four sources. Based on spectral energy distributions, X-ray, and optical temporal analyses, some evidences about the nature of X1 and X2 were obtained.Öğe An experimental implication of long-term hot-wet-aged carbon fiber/polyether ketone ketone composites: The impact of automated fiber placement process parameters and process-induced defects(John Wiley and Sons Inc, 2023) Şükür, Emine Feyza; Elmas, Sinem; Eskizeybek, Volkan; Sas, Hatice S.; Yıldız, MehmetDuring the service life of aerospace-grade composites, process parameters and process-induced defects may become crucial. Most studies in this field have mainly focused on the relationship between process-induced defects and mechanical performance. However, the potential impact of process parameters and process-induced defects on the service life of composites serving under severe service conditions has received little attention. In this work, the effects of hydrothermal conditioning on the mechanical performance of carbon fiber/polyether ketone ketone (CF/PEKK) composites are examined, along with the correlation between automated fiber placement (AFP) process parameters and process-induced defects. For this, gap and overlap defects integrated CF/PEKK laminates were exposed to a long-term (90 days) hot-wet aging environment to simulate the actual service conditions. Defect-induced composite samples reached saturation point at the end of 30 days with a mass gain of 0.2 wt%. The aging process resulted in an increase in the degree of crystallization by almost 14% without a change in the chemical structure, indicating the postcrystallization of the PEKK matrix. Even though the thermo-mechanical performance diminished (~25%) with the aging process, storage modulus was slightly affected by process parameters and process-induced defects. Considering the flexural and shear test results after the aging process, the impact of gap and overlap defects on the service life of AFP composites can be minimized with higher compaction forces (600 N) and lower lay-up speeds (0.1 m/s).Öğe Effects of sintering temperature on the microstructural properties of Al2O3-Y2O3 powder mixtures(Walter de Gruyter GmbH, 2021) Abalı, Serkan; Kılıç, SongülIn this study, YAlO3 (YAP) was produced at low temperatures by a powder sintering process. Al2O3-Y2O3 powder mixtures were subjected to heat treatment at different temperatures. The relationship between the sintering temperature and the emergence of new phases was investigated via X-ray diffraction, and supported by energy dispersive X-ray spectroscopy. The crystallization of the monoclinic yttrium aluminum oxide (Y4Al2O9) occurred at 1 000 °C, whereas the yttrium aluminum perovskite (YAlO3) crystallization occurred at 1 100°C. Energy dispersive X-ray spectroscopy analysis showed yttrium content in the sample containing Al2O3-YAlO3 powder sintered at 1100 °C, associated with the YAlO3 phase formed at this temperature. Brunauer-Emmett-Teller surface analysis showed a significant decrease in the pore volume of the sample sintered at 1 100°C.Öğe Selectively Reinforced Functionally Graded Composite-like Glass/Carbon Polymer Nanocomposites: Designed for Efficient Bending and Impact Performance(Korean Fiber Society, 2022) Demir, Okan; Tatar, Ahmet Caner; Eskizeybek, Volkan; Avcı, AhmetOffshore wind turbine blades (OWTBs) are exposed to various types of loadings during their service life. Moreover, due to their tremendous size, huge investment costs are established, including advanced engineering materials and production process solutions. To decrease their investment cost without sacrificing their mechanical performances, advanced engineering solutions in the view of material selection and design should be implemented. With this motivation, we aimed to develop a novel laminated composite design considering reducing investment costs without compromising the bending and impact resistance of an OWTB. For this, an efficient and cost-effective design of a functionally graded composite (FGM)-like glass/carbon fibers reinforced hybrid polymer composite with a specific stacking sequence was presented. To evaluate mechanical performance of the composite structure, tensile, flexural, and to simulate environmental conditions, low-velocity impact tests were conducted. Furthermore, multi-walled carbon nanotubes (MWCNTs) were also introduced into the polymer matrix to evaluate their effectiveness in the hybridized composite. Drastic improvements in the bending strength (55.8 %) and strain (39.7 %) were obtained compared to the neat carbon fiber reinforced epoxy composites (CFs), especially with the aid of MWCNTs. According to impact tests, it was pointed out that it is possible to obtain higher impact peak forces (around 15 %) compared to neat CFs. However, MWCNTs contributed with slight increments in impact resistance but effectively restricted the impact damage propagation. This study reveals it is possible to tune the bending performance, the absorbed energy, and the damage extension by utilizing glass and carbon fiber laminates in an FGM-like structure.Öğe In-situ measurement of aligning intensity and rotational temperature in field-free molecular alignment via white light generation(Elsevier GmbH, 2021) Kaya, Necati; Kaya, Gamze; Boran, Yakup; Kolomenski, Alexandre; Schuessler, Hans A.We determine the aligning intensity and rotational temperature in field-free molecular alignment measured via white light signal. Relying on temporal dependencies of the time-resolved alignment signature obtained via white-light generation by femtosecond laser pulses in N2 molecules, we derived the aligning pump intensity and rotational temperature using the occurrence times of the local alignment and anti-alignment around the half and full revivals. Results proved that the aligning intensity and rotational temperature can be obtained simultaneously by any two reverse local alignment extrema in the evolution of field-free molecular alignment.Öğe Energy and angular distributions of electrons from sodium atoms photo-ionized with femtosecond laser pulses(IOP Publishing Ltd, 2021) Boran, Y.; Hart, N.; Kaya, Necati; Zhou, J.; Kolomenskii, A. A.; Schuessler, H. A.We studied photoelectron angular distributions (PADs) and energy spectra of sodium atoms photo-ionized with intense short laser pulses in the near-infrared region. Energy spectra of photoelectrons due to multistep ionization of sodium atoms through intermediate levels 5p, 6p, 7p, and 4f were observed in above threshold ionization (ATI) at laser intensities of 2 × 1013 W cm−2 and 1 × 1013 W cm−2. The PADs from the 5p(4f) state for zero, first, second and third order ATI peaks were measured. We observed that for the two selected laser intensities the angular distribution of photoelectrons showed only slight variations. The PADs exhibit main lobes within ∼60◦ degrees from the laser polarization and additional lobes that become more pronounced with the increasing ATI peak number. Besides a general analytical representation of the observed angular dependences, the experimental PADs for each ATI peak were fitted with Legendre polynomials accounting for different ionization channels. The good agreement between the experimental data and fitting functions allowed to evaluate the contributions of the ionization channels to the observed ATI orders. The calculations of the photoelectron spectra by numerically solving the time-dependent Schrödinger equation in a single active electron approximation produced agreement with the experiment in the main features of the spectra, while differences in more subtle details were observed.Öğe Effectiveness of different packaging films and trays on mushrooms (Agaricus bisporus) subjected to simulated transportation conditions at different vibration frequencies(Wiley Periodicals LLC., 2021) Özturk, Mehmet; Yakar, Emin; Temizkan, Rıza; Aday, Mehmet SeçkinThis study aimed to determine the different vibration frequencies (4, 8, 12, and 16 Hz) and packaging trays and films (Polypropylene trays + microperforated films (MP) and Polystyrene foam trays + polyvinyl chloride stretch films (PVC)) effects on mushroom quality. The quality of the mushrooms in MP was reduced with the increment in the frequency, whereas the effect of the frequency was only detrimental in the mushrooms packaged with PVC at 16 Hz. Oxygen concentration reached the equilibrium state at the level of 15% in PVC and 9% in MP groups. The whiteness index of mushrooms in MP was between 25 and 40, whereas it was around 20-30 in PVC films. However, changes in electrolyte leakage, pH, and hardness were minimal in the mushrooms packaged with PVC. As a result, PVC stretch films reduced the effect of transport frequencies, however, the optimal gas concentrations for mushrooms were only achieved using MP films. Practical applications In this study, effects of different packaging films, and trays were studied on mushrooms (Agaricus bisporus) which were subjected to simulated transportation conditions at different vibration frequencies. Foam trays with PVC films reduced the effect of transportation damage. Transportation damage in MP packages observed to be increased with the rise in the frequency. MP films helped to achieve the desired gas composition inside the packages.Öğe Diffractive multifocal lenses by computer-generated holograms(SPIE (Society of Photo-optical Instrumentation Engineers), 2021) Kaya, Necati; Kaya, Gamze; Strohaber, James; Zhou, Junfeng; Kolomenskii, Alexandre A.; Schuessler, Hans A.The dynamics of rotational wave packets of laser-aligned linear molecules were studied with femtosecond laser-driven strong-field ionization (SFI). The dynamics were observed as a function of the delay between a femtosecond probe pulse and a linearly polarized aligning pump pulse. The induced nonadiabatic molecular alignment was directly monitored by the total SFI yield. The measured revival signatures were compared to the calculated degree of molecular alignment taking into account the effects of electronic structure and symmetry of the molecules. By fitting the calculated alignment parameter to the measured experimental data, we also determined the molecular rotational constants of N2, CO, O2, and C2H2 gas molecules.Öğe An overwiew on corrosion behavior of steels in factory(L.N. Gumilyov Eurasian National University, 2021) Demirören, HülyaIn this study, corrosion behaviors of diffuser unit solution by which raw sugar is produced from minced sugar beets in sugar factories on St-37 low alloy steel and AISI 304, 304L, 316 austenitic stainless steel types were examined. Moreover, influence of heat treatment on corrosion resistance was investigated. Corrosion tests were performed using mass loss method. SEM-EDX, X-rays Diffraction, microhardness and surface hardness analyses of samples were carried out. As a result, it was determined that AISI 304L and 316 steels have better corrosive resistance and heat treatment improves corrosion resistance.Öğe Facile synthesis and electrochemical properties of Prussian Blue/MWCNT and PB/WO3 films(Bulgarska Akademiya na Naukite, 2021) Yakar, EminIn this study, Prussian Blue (PB)/MWCNTs and PB/WO3 nanocomposite films were deposited onto In-SnO2 (ITO) substrates by a simple chemical bath deposition method. The structural, morphological, and electrochemical properties of PB/MWCNTs films were systematically investigated in detail. Removing influence of ITO, it was evident that both of the patterns could be indexed in the cubic PB phase, from X-ray diffraction analysis. While intense tubular carbon and agglomerative formations were detected in PB/MWCNTs films, cubic PB and spherical WO3 forms were depicted in PB/WO3 films. Average particle sizes (D) of MWCNTs (5.8 nm) were smaller than WO3 (10.5 nm) due to improved particle growth process as shown in this work. Raman analysis proved the production of PB structures. Typical Prussian Blue ν(CN) and stretching vibration of Fe-C at 2159 cm-1 and 507 cm-1 were observed, respectively. Improved electrochemical performance of PB/MWCNTs electrodes was indicated compared to PB/WO3 electrodes.Öğe An electrochemical approach to evaluating surface coatings(Inderscience, 2021) Demirören, Hülya; Buytoz, SonerIn order to understand the influence of metal carbides and niobium carbides on electrochemical behaviour of Fe-based composite powder and FeNb powder coatings were added. Above mentioned composite layer was prepared on a medium carbon steel surface by using GTAW coating technique. The morphology of the coatings' surface was analysed by optical microscope, scanning electron microscope (SEM) equipped with an energy-dispersive spectroscopy (EDS) and X-ray diffractometer (XRD). Then the samples were exposed to seawater. Electrochemical impedance spectroscopy (EIS) method with triple electrode system was used in order to obtain Bode and Nyquist diagrams. Ag/AgCl electrode is used as reference electrode, and platin plate is counter electode in this system. As a result, adding NbC has harmful effect on the electrochemical behaviour of FeCrC coating powder.
