Makine Mühendisliği Bölümü Koleksiyonu
Permanent URI for this collectionhttps://hdl.handle.net/20.500.11779/1944
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Article Room-Temperature Synthesis of Refractory Borides: a Case Study on Mechanochemistry and Characterization of Mo-Borides and W-Borides(Elsevier Sci Ltd, 2025) Süzer, İlayda; Akbari, Amir; Kaya, Faruk; Mertdinç Ülküseven, Sıddıka; Derin, Bora; Öveçoğlu, M. Lütfi; Ağaoğulları, Duygu; Mertdinc-Ulkuseven, SiddikaMo-boride and W-boride powders were produced from native boron oxide, magnesium, and related metal oxide starting materials by mechanochemical synthesis (MCS) followed by an purification treatment. The reaction formation mechanisms and the products were predicted with the FactSageTM thermochemical simulation program. Different conditions were tested to determine the optimum synthesis parameters. MCS was conducted at stoichiometric ratios and different milling durations, using excess reactant amounts over the determined optimum time. After MCS, unwanted phases were removed by HCl acid leaching. Detailed phase analyses of the final powders were obtained by X-ray diffractometer (XRD), whereas detailed microstructure characterization was conducted by scanning electron microscope/energy dispersion spectrometer (SEM/EDS), transmission electron microscope (TEM) and particle size analyzer. Among the utilized parameters, the ideal composition chosen for Mo boride synthesis was 6 h milled and leached MoO3-100 wt% B2O3-50 wt% Mg (1.41 mu m), including alpha-MoB, beta-MoB, MoB2, Mo2B, Mo2B5, and Mo phases. For the synthesis of W boride, the proper composition was found as WO3-100 wt% B2O3-50 wt% Mg (0.37 mu m) containing W2B5, WB, beta-WB, WB4, W2B, and W phases after milling for 20 h and leaching. Besides, as a result of the oxidation resistance measurements at 700 and 800 degrees C, phases belonging to MoO2 and WO2 were found along with boride phases.Article Nbmovta Refractory High-Entropy Alloy Incorporated Wni Matrix Composite as a Future Plasma-Facing Material: Evaluation of Mechanical Properties and Helium Ion Irradiation Behavior(Elsevier Sci Ltd, 2025) Boztemur, Burcak; Filiz, Kaan; Karaguney, Zahide; Gokaydin, Eyupcan; Bozkurt, Yasin; Ozbasmaci, Ceren; Ovecoglu, M. LutfiRefractory high-entropy alloys (RHEAs) have gained attention in the last decades with their high mechanical strength, self-healing mechanism, and high irradiation resistance. These materials are evaluated to have a high potential as plasma-facing materials for fusion reactors. In this study, helium ion irradiation and mechanical behaviors of the RHEA-reinforced WNi matrix composites were investigated based on this perspective. Equimolar molybdenum, niobium, tantalum and vanadium powders were mechanically alloyed for 6 h to produce NbMoVTa RHEA with a single BCC phase. Then, different amounts (10, 20, 30, and 40 wt%) of RHEA were added into the W1Ni (containing 99 wt% W and 1 wt% Ni) matrix by planetary ball milling for 72 h. Consolidation was conducted by spark plasma sintering technique (1410 degrees C, 1 min). X-ray diffraction, scanning electron microscopy coupled with energy dispersion spectroscopy, and Archimedes' density analyses were performed on the composites. Moreover, wear and hardness properties of the composites were examined, and the lowest specific wear rate (0.59 mm3/N.m x 10- 5) and the highest hardness value (10.10 GPa) were found for the W1Ni-40RHEA composite. Helium irradiation was exposed to the composites to observe their irradiation resistance. It was observed that the lowest increment and the least deformation were obtained with the SPS'ed W1Ni-40RHEA composite. With the analysis of He+ irradiation, it was determined that the effect of radiation on mechanical properties is irrelevant. Also, it was observed that the addition of RHEA into the W matrix can create a high potential for using plasma-facing material. Moreover, it decreased the problems of tungsten against He+ irradiation.Article Citation - WoS: 3Citation - Scopus: 3Powder metallurgy processing of seven/eight component multi-phase (HfTiZr-Mn/Mo/W/Cr/Ta)B<sub>2</sub> high entropy diboride ceramics(Elsevier, 2024) Suzer, Ilayda; Akbari, Amir; Ates, Semih; Bayrak, Kuebra Gurcan; Mertdinc-Ulkuseven, Siddika; Arisoy, C. Fahir; Agaogullari, Duygu; Öveçoğlu, M. LutfiThis study aims to show the possibility of synthesizing seven- and eight-component high entropy diboride (HEB) ceramics using high energy ball milling-assisted spark plasma sintering (SPS). Metal boride powders, synthesized in laboratory conditions from metal oxide-boron oxide-magnesium powder blends, were combined equimolarly as seven and eight components containing systems. Afterwards, hybridized powders were mechanically alloyed (MA) for 6 h and subjected to spark plasma sintering (SPS) at 2000 degrees C and under 30 MPa. Detailed phase analysis and physical, microstructural, and mechanical characterization of the samples were performed. in the sintered products, the main phase belongs to the HEB, and also low amounts of Hf/Zr oxides and secondary phases (W or Ti-rich) occurred. The highest hardness was observed at the (HfTiZrMoWCrTa)B-2 with 25 GPa, and the lowest hardness was seen at the (HfTiZrMnCrMoWTa)B2 with 17 GPa. Also, the highest wear resistance was calculated for the (HfTiZrMnCrMoTa)B-2 as 6.05 x 10(-7) mm(3)/Nm. Additionally, (HfTiZrMnMoWTa)B-2 and (HfTiZrMnMoCrTa)B-2 have the highest and lowest Archimedes' densities, with 7.94 g/cm(3) and 6.91 g/cm(3), respectively.Article Citation - WoS: 4Citation - Scopus: 4Vibration of Locally Cracked Pre-Loaded Parabolic Arches(Academic Press, 2022) Tüfekci, Ekrem; Eroğlu, Uğurcan; Giuseppe, Ruta; Ruta, GiuseppeWe study linear dynamics of an initially parabolic arch deformed by a uniform ‘dead’ load. The arch is seen as a fully deformable one-dimensional continuum with rigid cross-sections, one of which suffers from a small local crack at its boundary. The crack is simulated by springs, the stiffnesses of which are evaluated via stress intensity factors. By two first-order perturbations we investigate a non-trivial equilibrium adjacent to the reference configuration and small vibration superposed on it. The modulation of the initial load on the natural angular frequencies and its consequences on damage detection is described and commented. It turns out that neglecting the initial load, recalling for actual ‘dead’ structural actions, can be misleading in damage identification, while its inclusion leads to better results.Article Citation - WoS: 6Citation - Scopus: 6Propulsive Performance of Plunging Airfoils in Biplane Configuration(American Institute of Physics Inc., 2022) Yücel, S. Banu; Şahin, Mehmet; Ünal, Mehmet FevziBiplane configuration of pure plunging airfoils is investigated in terms of vortex dynamics both experimentally and numerically by utilizing particle image velocimetry and unstructured finite volume solver of incompressible unsteady Navier-Stokes equations. Experiments are carried out to disclose the vortex shedding and interaction mechanisms for various values of frequency and amplitude of the plunging motion. For the non-dimensional plunge amplitude with respect to the chord of airfoil h = 0.2, the effect of the reduced circular frequency based on chord length and the free stream velocity k = 1 and 10 are considered, whereas for h = 0.3, k = 2, 4, 8, and 10 cases are examined. Influence of the plunge amplitude is studied for h = 0.25 at k = 2.5 and for h = 0.0875, 0.15, and 0.3 at k = 4. Numerical simulations are performed to investigate the effect of phase difference on vortex structures and propulsive characteristics, such as thrust and Froude efficiency. Two cases having the highest thrust and efficiency values k = 2.5, h = 0.25, and k = 4, h = 0.15 value couples are selected for the phase angle of φ = 0 °, φ = 90 °, φ = 180 °, and φ = 270 °. Opposed plunge, φ = 180 °, was found as the most efficient amongst all phase angles that were investigated, where φ = 90 ° is beneficial in lift production. Additionally, three-dimensional simulations indicate no significant three dimensionalities for the parameters used herein.Article Citation - WoS: 8Citation - Scopus: 10Identification of the Viscoelastic Properties of Soft Materials Using a Convenient Dynamic Indentation System and Procedure(Elsevier, 2022) Körük, Hasan,; Beşli, Ayça,; Koç, Ömer Hayati,; Yurdaer, Berk Salih,; Yurdaer, Salih Berk; Koc, Hayati OmerThe responses of soft structures such as tissue depend on their viscoelastic properties. Therefore, the knowledge of the elastic and damping properties of soft materials is of great interest. This paper presents the identification of the viscoelastic properties of soft materials using a convenient dynamic indentation system and procedure. Using an electromagnet, a force is applied to a rigid sphere located at the soft-material interface and the dynamic response of the sphere is recorded using a high-speed camera. The recorded video is processed to identify the displacement of the sphere as a function of time. The dynamic response of the sphere located at the soft-material interface is predicted using an analytical model that considers the shear modulus and density of the soft sample, the radiation damping due to shear waves, and the radius and density of the sphere. By matching the measured and predicted steady-state displacements of the sphere, the shear modulus of the soft sample is determined. The viscous damping ratio of the soft sample is identified by using an equivalent viscous damping ratio for the soft sample in the analytical model and matching the measured and predicted oscillation amplitudes of the sphere. Experiments and analyzes are performed using gelation phantoms with different mechanical properties, spheres of different materials and sizes, and different force levels to verify the system and procedure. Three experiments are performed for each gelation phantom, sphere, and external force, and the repeatability of the results is presented. The results show that the dynamic indentation system and procedure presented in this study can be conveniently used to determine the viscoelastic properties of soft materials in practical applications.Article Citation - WoS: 6Citation - Scopus: 8Development of an Improved Mathematical Model for the Dynamic Response of a Sphere Located at a Viscoelastic Medium Interface(IOP, 2021) Körük, HasanA comprehensive investigation on the static and dynamic responses of a sphere located at elastic and viscoelastic medium interfaces is performed in this study. First, the mathematical models commonly used for predicting the static displacement of a sphere located at an elastic medium interface are presented and their performances are compared. After that, based on the finite element analyses, an accurate mathematical model to predict the static displacement of a sphere located at an elastic medium interface valid for different Poisson's ratios of the medium and small and large sphere displacements is proposed. Then, an improved mathematical model for the dynamic response of a sphere located at a viscoelastic medium interface is developed. In addition to the Young's modulus of the medium and the radius of the sphere, the model takes into account the density, Poisson's ratio and viscosity of the medium, the mass of the sphere and the radiation damping. The effects of the radiation damping, the Young's modulus, density and viscosity of the medium and the density of the sphere on the dynamic response of the sphere located at a viscoelastic medium interface are explored. The developed model can be used to understand the dynamic responses of spherical objects located at viscoelastic medium interfaces in practical applications. Furthermore, the proposed model is a significant tool for graduate students and researchers in the fields of engineering, materials science and physics to gain insight into the dynamic responses of spheres located at viscoelastic medium interfaces.Article Citation - WoS: 34Citation - Scopus: 37Development of a New Solar, Gasification and Fuel Cell Based Integrated Plant(Elsevier, 2021) Dinçer, İbrahim; Karapekmez, ArasDespite its shortcomings, fossil-based fuels are still utilized as the main energy source, accounting for about 80% of the world's total energy supply with about one-third of which comes from coal. However, conventional coal-fired power plants emit relatively higher amounts of greenhouse gases, and the derivatives of air pollutants, which necessitates the integration of environmentally benign technologies into the conventional power plants. In the current study, a H2–CO synthesis gas fueled solid oxide fuel cell (SOFC) is integrated to the coal-fired combined cycle along with a concentrated solar energy system for the purpose of promoting the cleaner energy applications in the fossil fuel-based power plants. The underlying motivation of the present study is to propose a novel design for a conventional coal-fired combined cycle without altering its main infrastructure to make its environmentally hazardous nature more ecofriendly. The proposed SOFC integrated coal-fired combined cycle is modeled thermodynamically for different types of coals, namely pet coke, Powder River Basin (PRB) coal, lignite and anthracite using the Engineering Equation Solver (EES) and the Ebsilon software packages. The current results show that the designed hybrid energy system provide higher performance with higher energy and exergy efficiencies ranging from 70.6% to 72.7% energetically and from 35.5% to 43.8% exergetically. In addition, carbon dioxide emissions are reduced varying between 18.31 kg/s and 30.09 kg/s depending on the selected coal type, under the assumption of 10 kg per second fuel inlet.Article Citation - WoS: 44Citation - Scopus: 45Development of a Multigenerational Energy System for Clean Hydrogen Generation(Elsevier Ltd, 2021) Dinçer, İbrahim; Karapekmez, ArasThe existing fueling options for many power plants are still dependent primarily on fossil fuel resources, which in return cause serious local and global environmental problems. Therefore, in order to reduce the detrimental effects of greenhouse gas emissions, the use of cleaner production methods has been accelerated to develop and implement environmentally- friendly energy systems. In this regard, the combination of renewable energy systems and hydrogen production methods will definitely play a crucial role in the energy sector’s transition to a carbon-free production. In order to make the use of geothermal energy cleaner and more sustainable, some obstacles need to be eliminated. Most importantly, the hydrogen sulfide emissions may cause serious concerns in public acceptance of geothermal power plants. In the current study, solar, wind and geothermal energy resources are integrated to develop an integrated renewable-based energy system with a key objective of higher environmental and system performance. The underlying motivation is to propose a model which consists of a hydrogen sulfide abatement unit and an electrolyzer to produce hydrogen from hydrogen sulfide and hence eliminites the hydrogen sulfide emissions. A detailed thermodynamic analysis is carried out using Engineering Equation solver (EES) software. In addition, the effects of key design parameters and operating conditions (such as wind inlet speed and average hourly solar radiation) are analyzed, and their effects on the system overall performance are investigated. When 60 kg/s of geothermal fluid is supplied to the designed system, assuming that the NCG composition is equal to 15%, 0.7388 kg hydrogen sulfide will be emitted and 0.0433 kg hydrogen will be produced per second. The first-law (energy) and second-law (exergy) efficiencies are found to be 52.97% and 55.69% respectively.Article Citation - WoS: 28Citation - Scopus: 29Development of a New Integrated Energy System With Compressed Air and Heat Storage Options(Elsevier, 2020) Javania, Nader; Dinçer, İbrahim; Karapekmez, Aras; Javani, NaderThe present study investigates a biomass driven power plant integrated with compressed air and thermal energy storage subsystems. Compressed air energy storage system exploits the pressurized air at non-peak periods to be used in peak times when there is a need for extra energy. Thermal energy storage systems including phase change material, allow the solar subsystem to operate independently in order to produce hot air when solar irradiation is insufficient. The energy stored in the present system is then supplied to both the gasifier and combustion chamber in order to achieve a higher combustion efficiency. Three different phase change materials (PCMs) are investigated and their efficiencies are comparatively evaluated. Among the considered PCMs, LiNO3 is the most suitable material for the considered system with 82% energy efficiency and 84% exergy efficiency. The current study also aims at designing a renewable energy based power plant which operates continuously through using storage subsystems and is more environmental benign compared to fossil fuel based conventional systems. In this regard, wet wood (CH1.46O0.64N0.002) with 15% moisture content is selected as a fuel instead of fossil-based fuels in order to reduce the greenhouse gas emissions and eliminate the dep endency on fossil fuels. A comprehensive thermodynamic analysis is conducted to evaluate the entropy generations, exergy destructions, and energy and exergy efficiencies. The highest overall energy and exergy efficiencies are obtained as 28.58% and 24.08% in the discharging period, respectively.