Master Degree / Yüksek Lisans Tezleri

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Author: search.filters.author.Artem, Hatice SeçilPublisher: search.filters.publisher.Izmir Institute of Technology

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Now showing 1 - 10 of 13
  • Master Thesis
    Stacking Sequences Optimization of Laminated Composites for Maximum Buckling Strength by Stochastic Search Methods
    (Izmir Institute of Technology, 2020) Artem, Hatice Seçil; Adabaşı, Gökay; Artem, Hatice Seçil; 01. Izmir Institute of Technology; 03.10. Department of Mechanical Engineering; 03. Faculty of Engineering
    Based on materials developed and made available by humans, there are materials that will serve their purpose. Using lighter materials, especially in the field of aviation and space, significantly reduces the costs. However, lightness is not the only feature required in materials. In addition, the physical and mechanical properties of the materials must be at the desired level. Knowing the buckling load capacity of composite materials, which are widely used, is also very important in determining the material properties. Accordingly, an important focus of this thesis is to examine the behavior of different materials against the same loading; the other is to examine the increase in the critical buckling load factor although they have the same geometric structure. Critical buckling load factor is considered when performing the buckling analysis. The mechanical behavior of composite materials used by considering the factors of critical buckling load factor has been investigated and discussed. Different optimization methods have been used while making the optimum design of different composite materials with 48 and 64 layers in total. The verification of mechanical properties of materials was made with the help of coding. Subsequently, the referenced articles were verified to prove the accuracy of this code. Optimization was carried out by using material properties information from reference articles and verifying the code. As a result, considering the buckling strength of different layered composite materials, it has been found that the optimum designs depend on the load, load ratio, and plate aspect ratio.
  • Master Thesis
    Optimization of Weld Bead Geometric Parameters in a Tig Welding Process
    (Izmir Institute of Technology, 2019) Dilsiz, Kadriye Çağla; Artem, Hatice Seçil; Artem, Hatice Seçil; 03.10. Department of Mechanical Engineering; 03. Faculty of Engineering; 01. Izmir Institute of Technology
    Welding is a process that widely used in many areas of industry. Tungsten Inert Gas (TIG) welding process in several types of welding is often preferred in space and aircraft industry, defense industry, and automotive. The welding should be at the required limits and quality when working under pressure. Visual and physical welding quality determined by welding bead geometric parameters. Weld bead dimensions response variables as front height (FH), front width (FW), back height (BH), and back width (BW). In this thesis, Neuro-regression approach which is hybrid study of conventional regression analysis and artificial neural network. Third order polynomial function is used to design front width response itself. The differences between neuro-regression approach and conventional regression analysis while modeling the weld bead geometric dimensions are examined. Welding speed, wire feed rate, percentage of cleaning, gap, and welding current are taken as input variables of the system during modeling. Effects of welding speed, wire feed rate, percentage of cleaning, gap, and welding current on front height, front width, back height, and back width are expressed. Optimization of weld bead geometric parameters in TIG welding process were carried out by using Differential Evolution, Nelder Mead, Simulated Annealing and Random Search stochastic optimization algorithms. Two different problems of front width are studied. Differential Evolution is selected as stochastic search method to have minimum value of front width as a result of the study. All mathematical calculations are carried in Wolfram Mathematica.
  • Master Thesis
    Optimization of Surface Roughness on a Milling Process Using Stochastic Methods
    (Izmir Institute of Technology, 2019) Dinç, Özcan; Artem, Hatice Seçil; Artem, Hatice Seçil; 03.10. Department of Mechanical Engineering; 03. Faculty of Engineering; 01. Izmir Institute of Technology
    Nowadays, milling process is one of the most widely used metal processing methods in many fields from space and aircraft to automotive industry. The surface roughness values of the workpiece in milling process vary depending on the thermal, chemical and abrasive loads that occur during cutting. Spindle speed, depth of cut and feed rate are the cutting parameters affecting the surface roughness. Hence, these parameters at the time of machining constitute an important issue. Accordingly, in this thesis optimization of surface roughness has been performed using the stochastic search methods. First, using experimental data obtained in the milling process, it was aimed to establish a regression model to determine average surface roughness equation as an objective function. The cutting parameters and average surface roughness value were considered as input and output in regression analysis, respectively. In this study, seven different mathematical models have been established and examined to carry out regression analysis. The reliability and stability of the mathematical models were investigated. The most appropriate mathematical model has been constructed and then used as an objective function for optimization. Nelder-Mead, Random-Search, Simulated Annealing, and Differential Evolution were the stochastic search algorithms to perform the optimization in the present study. In conclusion, it was found that the minimum average surface roughness value depends on spindle speed, depth of cut and feed parameters.
  • Master Thesis
    Optimum Design of Composite Hydrogen Pressure Vessels by Stochastic Search Methods
    (Izmir Institute of Technology, 2018) Sayı, Abdülmecit Harun; Artem, Hatice Seçil; Artem, Hatice Seçil; 03.10. Department of Mechanical Engineering; 03. Faculty of Engineering; 01. Izmir Institute of Technology
    Fiber-reinforced composite materials are extensively used in many engineering applications such as aircraft wings and frames, vehicle drive shafts, sport equipment, and pressure storage vessels. One of the reasons for the extensive use of laminated composite materials is their tailorable nature, which allows them to satisfy specific design objectives in an application. As an application, hydrogen-powered fuel cell vehicles require high amount of hydrogen to increase distance range. Hence, hydrogen is pressurized at elevated rates. Since, it is hard to satisfy safety and weight regulations for high pressure gas, composite storage vessels offering high strength with low weight are preferred. Optimization techniques are applied to the design of composite pressure vessels to maximize strength with comprising weight restrictions. In the thesis, first-ply failure optimizations of stacking sequence design of cylindrical composite pressure vessels with metal liner having 700-bar working pressure and safety factor of 2.0, have been performed using stochastic search algorithms which are Differential Evolution and Nelder Mead. Three separately categorized failure theories; Tsai-Wu, Maximum Stress and Hashin-Rotem criteria have been incorporated to failure analysis of the vessel designs. In addition, the effects of volume on the stacking sequence design have been investigated. Hence, four volumetrically separated pressure vessel designs have been considered. Change in volume has been provided by inner radius. Single objective optimization has been set to minimize failure criteria index which incorporates into classical lamination theory. Fiber orientation angles and number of plies are design variables. CPU time has been calculated to compare the workloads of algorithms. In conclusion, optimized pressure vessels have provided design targets and the difference in volume has caused variable fiber angle orientations, number of plies and CPU time.
  • Master Thesis
    Design and Mechanical Behaviour of Brazed Plate Heat Exchangers
    (Izmir Institute of Technology, 2018) Gürler, Yiğit; Artem, Hatice Seçil; Artem, Hatice Seçil; 03.10. Department of Mechanical Engineering; 03. Faculty of Engineering; 01. Izmir Institute of Technology
    In recent years, the developments in clean, renewable and efficient energy policies have been enabled to design new and innovative heat exchangers. The plate heat exchangers have crucial importance among these innovative products due to compact size and thermally efficient behaviour. There are many studies dealing with the thermo-fluidic behaviour of brazed plate heat exchangers. However, since the usage of these products often includes relatively high pressure and toxic fluids, the examination of structural stability of these products is cruical from the point of scientific perspective view. There are very few studies of plate heat exchangers regarding to mechanical aspects. Accordingly, in this thesis it is intended to investigate structural behaviour of brazed plate heat exchangers by numerical methods. For this purpose, the material properties of brazing interface of plate heat exchangers have been determined by experimental methods. The tensile and stress based fatigue experiments are carried out and the material models have been obtained. The validation of material model which is used in numerical analysis has been carried out by explicit method using maximum displacement as a boundary condition. The mechanical behaviour of chevron type brazed plate heat exchangers has been investigated by considering effect of chevron angle under different pressure conditions. The results have been obtained numerically in two stages; static structural analysis results and fatigue analysis. The numerical results show that the chevron angle has a significant effect on the formation of brazing points of plate heat exchangers. The dimensions of brazing points directly affects the overall structural behaviour of plate heat exchanger. It is observed that the single brazing point surface area and homogeneous distribution of brazing points on the plates are more critical than the total surface area. Finally, it is thought that the developed numerical methodology will lead to the structural design of brazed plate heat exchangers before the production of protoype molding and experimental testing. Eventually, it will be advantageous in terms of mold costs and time spent for experimental testing.
  • Master Thesis
    Stacking Sequence Optimization and Modeling of Laminated Composite Plates for Free Vibration
    (Izmir Institute of Technology, 2018) Hasanoğlu, Emre Azim; Artem, Hatice Seçil; Artem, Hatice Seçil; 03.10. Department of Mechanical Engineering; 03. Faculty of Engineering; 01. Izmir Institute of Technology
    Composite materials, especially fiber reinforced composites, have been extensively used in various engineering fields such as automotive, aerospace, aircrafts, defense, marine and so on due to having their high specific strength to weight and stiffness to weight ratios. In these last years, vibration problem has become more and more important in the structures where thin plates are used. Therefore, free vibration characteristics of composite structures under the influence of dynamic forces should be determined in the design process. Accordingly, in this thesis, optimum designs, which maximize the natural frequencies of laminated composite plate, are investigated by using hybrid algorithm combining the genetic algorithm (GA) and generalized pattern search algorihm (GPSA). Composite plates made of graphite/epoxy have been considered and assumed to be symmetric with continuous fiber angles in the laminate sequences. The natural frequency of plates is obtained bu using the Rayleigh Ritz method analytically. Free vibration equation is taken as objective function and fiber orientation angles are chosen as design variables. The natural frequency is maximized for various boundary conditions, aspect ratios, number of ply and material properties. The optimum designs obtained are verified by finite element method, and mode shapes of laminated composite plates are presented. A comparison between continuous and conventional (laminate in which the orientation angles are limited to the conventional orientations) designs is performed in order to show the reliability of continuous plates. As a results, it is observed that material properties, boundary conditions and dimensions of composite plates play important role on vibration behavior of composite plates. On the other hand, the natural frequencies and the optimum fiber oriantation angles are not affected from the change of number of plies.
  • Master Thesis
    Minimum Weight Design of Carbon/Epoxy Laminated Composites for Maximum Buckling Load Using Simulated Annealing Algorithm
    (Izmir Institute of Technology, 2014) Gülmez, Erkut; Artem, Hatice Seçil; Artem, Hatice Seçil; 03.10. Department of Mechanical Engineering; 03. Faculty of Engineering; 01. Izmir Institute of Technology
    Composite materials have been mostly used in engineering applications such as aerospace, automotive, sports equipment, marine because of their high specific strength-to-weight and stiffness-to-weight ratios. Weight reduction and buckling load capacity are critical issue for the engineering application. Accordingly, in this thesis, identification of optimum fiber orientations and laminate thicknesses of the composite plates resisting to buckling under given loading conditions and aspect ratios are investigated. Furthermore, a comparison study on continuous and conventional designs is performed to determine the effect of stacking sequence on weight. Symmetric and balanced N-layered carbon/epoxy composite plates are considered for optimization process. Critical buckling load factor is taken as objective function and fiber orientations which are considered continuous are taken as design variables. Simulated Annealing (SA) algorithm is specialized by using fmincon as hybrid function and this optimization method is used to obtain the optimum designs. Maximum critical buckling load factor and minimum thickness and hence minimum weight are achieved and shown in tables. As a result, it is observed that loading conditions and plate dimensions play an important role on stacking sequence optimization of lightweight composite laminates for maximum buckling load capacity.
  • Master Thesis
    Stacking Sequence Optimization of the Anti-Buckled Graphite/Epoxy Laminated Composites for Minimum Weight Using Generalized Pattern Search Algorithm
    (Izmir Institute of Technology, 2014) Boyacı, Hakan; Artem, Hatice Seçil; Artem, Hatice Seçil; 03.10. Department of Mechanical Engineering; 03. Faculty of Engineering; 01. Izmir Institute of Technology
    Composite materials have been increasingly used during the last decades due to their properties such as low weight, high stiffness, superior fatigue and corrosion resistance. They have been used in aerospace, automobile, marine applications and etc. Composite materials being an expensive but efficient technology to get minimum weight structures, it is logical to make an attempt to find out how to design properly optimum laminated composite plates with no reduction in their strength. The aim of the thesis is to find the optimum stacking sequence to obtain the minimum thickness (weight) of laminated composite plates in different loadings and plate dimensions under buckling constraint. Moreover, a comparison study of conventional and continuous designs are performed to determine the effect of stacking sequence on weight. The objective function is the critical buckling load factor. Fiber angles of the composite plates are taken as continuous design variables and the plate is assumed to be balance and symmetric. Composite plates made of graphite/epoxy have been considered in this thesis. A combination of Generalized Pattern Search Algorithm (GPSA) and Genetic Algorithm (GA) has been considered as an optimization method. All the results show that the loading conditions and dimensions of composite plates are significant in stacking sequences optimization of laminated composite materials in terms of maximum critical buckling load factor and minimum thickness.
  • Master Thesis
    Analysis of the Carcked Infinite Hollow Cylinder With Loading on Crack Surfaces
    (Izmir Institute of Technology, 2009) Avcı, Fatih; Artem, Hatice Seçil; Artem, Hatice Seçil; 03.10. Department of Mechanical Engineering; 03. Faculty of Engineering; 01. Izmir Institute of Technology
    In this study, the cracked infinite hollow cylinder with an axisymmetric crack of width (b-a) is considered. The ring-shaped crack is located at the symmetry plane. Surfaces of the crack are subjected to the distributed compressive loads. The outer surface of the cylinder is rigid and the inner one is stress free. The material of the cylinder is assumed to be linearly elastic and isotropic. Integral transform techniques are used for the solution of the field equations. The resultant singular integral equation in terms of crack surface displacement derivative is converted to a system of linear algebraic equations by using Gauss-Lobatto, Gauss-Jacobi and Gauss-Laguerre integration formulas. The stress intensity factors at the tips of the crack are numerically calculated for uniform and linear load distributions on crack surfaces. Some results are presented in graphical and tabular forms.
  • Master Thesis
    Evaluation of Strees Intensity Factor for an Infinite Hollow Cylinder Containing a Crack and Two Rigid Inclusions by Finite Element Analysis
    (Izmir Institute of Technology, 2002) Öterkuş, Ertan; Artem, Hatice Seçil; Artem, Hatice Seçil; 03.10. Department of Mechanical Engineering; 03. Faculty of Engineering; 01. Izmir Institute of Technology
    A numerical implementation based on the finite element method for the infinite cracked hollow cylinder under the action of axisymmetric tensile loads at infinity is considered in this study. The infinite cylinder contains a ring-shaped crack of width (b . a) at the symmetry plane z . 0, and two rigid inclusions of width (d . c) located symmetrically on both sides of the crack. Material of the cylinder is assumed to be linearly elastic and isotropic.The proposed model uses efficiently the capabilities of a commercially available finite element analysis program, ANSYS, to determine the stress intensity factors at the crack tips. In the finite element analysis, six-noded triangular elements were used to model the square-root stress singularity at the crack tips. In order to get the stress intensity factors, the displacement extrapolation method was used.The numerical results for various crack and inclusion configurations are obtained and compared with the analytical results in order to verify Artem.s study. When the inclusions are far away from the crack, the interaction among them vanishes. In this case, the numerical and analytical results are in good agreement. On the other hand, when the inclusions get closer to the crack, a discrepancy has been occurred within the acceptable limits.