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    Finite Element Analyses of Stresses Developed in Oil Separator Composite Tank Used in Screw Type Compressor Systems
    (2022) Gezginci, Volkan; Boğa, Cem; Seyedzavvar, Mirsadegh
    Pressure vessels are geometrically cylindrical, spherical or conical work equipment used for the storage and transportation of pressurized fluid. In the case of design and/or manufacturing deficiency, or for the case of improper applications of such vessels due to working conditions, the damages that may occur can cause serious harm to the environment and employees. The aim of this study is to estimate the performance of a typical oil separator pressure vessel used in screw compressor systems, exposed to high pressure and temperature, using finite element method. Here, the aim is to estimate performance of this tank after modifications in design and to compare the results with that of pressure vessel designed using conventional materials. The inner liner of the separator tank is metal material and the other layers are wrapped with three different composite materials, including carbon fiber/epoxy, glass fiber/epoxy and kevlar fiber/epoxy, at different angles, and then were exposed to high pressures in the environment of finite element simulation software. As a result of the study, stress and deformation values were examined and the most suitable material and orientation angle for the composite pressure vessel were decided. According to the results, it was observed that the lowest first-ply equivalent stress value was obtained in glass fiber/epoxy coated separator tanks at 11.25 bar pressure and 45 degree winding angle. In addition, it was observed that the lowest total deformation value was obtained in kevlar fiber/epoxy coated separator tanks at 11.25 bar pressure and 45 degree winding angle.
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    INVESTIGATION OF MECHANICAL AND METALLOGRAPHIC PROPERTIES OF TWO DIFFERENT ALUMINUM ALLOYS JOINED WITH FRICTION STIR WELDING METHOD USING DIFFERENT WELDING PARAMETERS
    (Yildiz Technical University, 2020) Öcalir, Şeref; Eşme, Uğur; Boğa, Cem; Külekci, Mustafa Kemal
    In this study two aluminum alloy materials of EN AW-5083-H111 and EN AW-6082-T651 were joined with Friction Stir Welding considering the parameters as the tool shoulder diameter, spindle speed and feed rate. The mechanical properties of the weld joints such as yield strength, tensile strength and micro-hardness and metallographic properties were investigated comparatively with the use of these welding parameters. The yield strength of the weld joints were determined to be between 136-217 MPa while the tensile strengths were between 159-230 MPa and the percent elongations were between 2.28-5.44 %. The hardness values measured in weld areas were higher in the EN AW-6082 base metal side compared with EN AW-5083 base metal side. © 2020 Yildiz Technical University.
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    Molecular dynamic approach to predict thermo-mechanical properties of poly(butylene terephthalate)/CaCO3 nanocomposites
    (Elsevier Ltd, 2021) Seyedzavvar, Mirsadegh; Boğa, Cem; Akar, Samet; Pashmforoush, Farzad
    Thermo-mechanical properties of poly(butylene terephthalate) polymer reinforced with carbonate calcium nanoparticles have been investigated using molecular dynamics simulations. Detailed analyses have been conducted on the effects of nanofiller content, at concentration levels of 0–7 wt%, on the mechanical properties of PBT, i.e. Young's modulus, Poisson's ratio and shear modulus. Thermal properties, including thermal conductivity and glass transition temperature, have been determined using Perl scripts developed based on nonequilibrium molecular dynamics and a high temperature annealing procedure, respectively. Experiments have been performed to verify the accuracy of the results of MD simulations. The CaCO3/PBT nanocomposites were synthesized using melt blending and mold injection techniques. The uniaxial tensile test, thermal conductivity, differential scanning calorimetry and x-ray diffraction spectroscopy measurements were conducted to quantify the thermo-mechanical properties of such nanocomposites experimentally. The results showed significant improvements in the mechanical properties by addition of CaCO3 nanoparticles due to strong binding between rigid particles and PBT polymer and high nucleation effects of nanoparticles on the matrix. Thermal conductivity and glass transition temperature of nanocomposites represented a consistent increase with the ratio of CaCO3 nanoparticles up to 5 wt% with an enhancement of 38% and 36% with respect to that of pure PBT, respectively. © 2021 Elsevier Ltd
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    Multi Response Optimization of Friction Stir Spot Welding Process
    (2021) Er, Onur; Külekci, Mustafa Kemal; Eşme, Uğur; Boğa, Cem
    Friction stir spot welding (FSSW) is a solid state welding method mainly used to join non-ferrous metalsand their alloys. When opposed to other welding processes, FSSW has the benefits of being pollution-freeand having no filler material. In this study an attempt was made for multi response optimization offriction stir spot welded EN AW 5005 aluminum alloy using Taguchi method and Grey relational analysis(GRA). Pin height (h, mm), tool rotation (S, rpm), and welding time (t, s) were used as input parameterswhile tensile shear strength (TSS, MPa) and joint efficiency (JE, %) were used as multi responseparameters. Therefore, Taguchi’s L8 orthogonal design matrix was used in order to plan the experiments.GRA was then applied to determine the optimum condition which gives the higher grey relational degree.Analysis of Variance method (ANOVA) was also carried out in order to show the most significantparameter. Finally, confirmation test was applied to confirm the results and determine the improvement ingrey relational grade throughout this method. The best results were obtained with parameters such as2.6 mm pin height, 1500 rpm tool rotation and 10 s welding time with 122.16 MPa TSS and 111.05 JE. Asignificant improvement of 0.310 was obtained in the optimal parameter in grey relation grade.
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    Optimization of the Effect of Processing Parameters on Surface Roughness and Cutting Energy in CNC Milling of Al-7075 Material
    (2020) Pınarbaşı, Ali Talip; Külekçi, Mustafa Kemal; Eşme, Uğur; Boğa, Cem
    In this study, it is intended to determine the most suitable process parameters for surface roughness and cutting energy of the 7075 series aluminum material in dry environment conditions by using Taguchi method in CNC milling. The process parameters were determined as, cutting speed, feed rate and cutting depth and the effects of these parameters on surface roughness, current flow through the grid and the energy consumed were examined. As a result, optimum process parameters were determined and the results were analyzed by graphs. It was observed that the most effective parameter on the surface roughness was the feed rate, while the most effective parameter on the current drawn from the network was the cutting depth. As a result of the experiments, the best surface roughness value was found to be 0.39 ?m and the lowest current value was 0.9 A. In addition, considering the determined current amount and processing time, the lowest energy amount consumed was calculated as 7089.28 J.
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    Stress analysis of functionally graded beams due to thermal loading
    (Taylor's University, 2020) Boğa, Cem; Selek, Onur
    In this paper, axial stress analysis of a functionally graded beam (FGB) was performed analytically and numerically under thermal loading. In these analyses, three different FGBs were used. Material properties of these FGBs are varied depending on the power law function along the z axis while Poisson ratio was assumed to be constant along the z-axis. Analytical formulas were given for axial stress analysis along z axis. FGBs were analysed numerically using the ANSYS program. Analytical and numerical results of axial stresses were compared and observed to be in consistence with each other. Then, the effect of different FGB types on axial stress was investigated under thermal loading. After analytical and numerical calculations, it was concluded that the FGM type consisting of Ti-6Al4V / Al2O3 metal ceramic pair had the lowest axial stress values. The results are given in graphs. © School of Engineering, Taylor’s University.