Master Degree / Yüksek Lisans Tezleri
Permanent URI for this collectionhttps://hdl.handle.net/11147/3008
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Master Thesis Process Parameter Optimization of Additively Manufactured Maraging Steel(01. Izmir Institute of Technology, 2024) Sivri, Burak; Artem, Hatice SeçilBu çalışmada lazer toz yatak füzyonu ile üretilen maraşlama çeliği parçaların üretim parametleri araştırılmaktadır. Lazer toz yatak füzyonu, hafif ve mukavim parçaların hızlı üretilmesini sağlar ancak lazer gücü, tarama hızı ve katman kalınlığı gibi proses parametrelerinin hassas bir şekilde kalibre edilmesi gerekmektedir. Üretim yönteminin karmaşıklığı ve maliyetleri nedeniyle parametreler arası uyumun ve parça kalitesinin öngörülebilir olması kritiktir. Maraşlama çeliği yüksek mukavemet, sertlik ve süneklik gibi mekanik özelliklere sahiptir. Maraşlama çeliği, metal eklemeli imalat esnasında gerçekleşen katmanlı üretim nedeniyle peş peşe ısınma ve soğuma döngülerine maruz kalır ve süreç boyunca östenit ve martenzit fazları arasında geçiş yapar. Bu çalışma, içerisinde faz dönüşümü bilgisi içeren bir maraşlame çeliği malzeme modelini kullanmayı, lazer toz yatağı füzyonunun sonlu elemanlar analizini oluşturmayı, analize yapay faktörler ekleyerek analiz modelini literatürden alınan fiziksel test sonuçlarıyla uyumlu çıktılar verecek şekilde direkt optimizasyon metotlarıyla kalibre etmeyi içermektedir. Sonrasında ise simülasyon ve literatür çıktıları ile optimum öngörü sağlayacak bir metamodel oluşturulmaktadır. Stokastik optimizasyon metotları incelendikten sonra evrimsel bir algoritma metamodel verisi ile eğitilmekte, üretim parametreleri arası uyum ve ideal eklemeli imalat parametreleri elde edilmektedir. Bu araştırmada üretim sebebiyle oluşan deformasyon başlıca optimizasyon problemi olarak belirlenmiştir ve bu etkinin minimuma indirgenmesi hedeflenmiştir. Araştırmada elde edilen bulgular, maraşlama çeliğinin simülasyon ve optimizasyon metotları sayesinde sıfıra yakın deformasyon ile üretilebileceğini göstermektedir. Bu çalışmada maraşlama çeliği eklemeli imalatının doğruluğunu ve verimliliğini artırmak adına bir yöntem önerilmekte olup, bu doğrultuda sonlu elemanlar analizi ve optimizasyon yöntemlerinin faydaları vurgulanmaktadır.Master Thesis Semi-Analytical Finite Element Modeling for Dispersion Analysis of Multilayered Structures(Izmir Institute of Technology, 2017) Akyol, Çağrı Gökhan; Özkol, Ünver; Önen, OnursalUltrasonic guided waves are frequently employed for Non-destructive tests (NDT), and Structural Health Monitoring (SHM) applications in the industry. Several analytical and numerical approaches have been developed in order to investigate guided wave behavior on multilayered structures. In this thesis, guided waves were investigated using the Semi-Analytical Finite Element (SAFE) approach on planar (plate like) structures. The guided wave theory and dispersive behavior in bounded structure were presented for Lamb waves for isotropic elastic plate model first. The numerical method to solve the SAFE problem was developed using the Matlab 2014b in order to obtain dispersion curves. The curves were compared with the Disperse Software, which utilizes global matrix approach for analytical solution of the same problem. Good agreement was achieved on obtained dispersion curves. As a second part of this study, dispersion analysis was carried out in a multilayer plate model consisting of elastic and viscoelastic materials. The semi-analytical finite element method was solved by adapting the hysteretic damping model so that it can also be applied in a damped plate model. Phase velocity and attenuation dispersion curves were illustrated and the effect of the viscoelastic layer thickness is also discussed. The obtained attenuation dispersion curves in this damped plate configuration are examined for wave modes with low-attenuation. The dispersion curve results obtained using the SAFE method was also compared with the results of studies available in literature.Master Thesis Out-Of Plane Displacements of Curved Beams With Variable Curvature(Izmir Institute of Technology, 2016) Uyar, Ahmet Serhend; Yardımoğlu, BülentThe differential equations of out-of-plane displacements of curved beams with variable curvature have variable coefficients. Selection of the solution method is based on the curvature function of the curved beam. In this study, Differential Quadrature Method (DQM) and Finite Element Method (FEM) are used to find the out-of-plane displacements of curved beams with variable radius of curvature. Since the parabola is very famous and known curve, it is selected as the form of curved beam. To test and validate the computer codes developed based on DQM in Matlab and based on FEM by APDL (ANSYS Parametric Design Language) in ANSYS, some typical examples are considered. As first step, convergence studies are performed to determine the number of sampling points in DQM and number of elements in FEM. After having information about aforementioned modeling parameters, comparisons between DQM and FEM results are given. The effects of variable curvature parameter of the curved beam on out-of-plane displacements are obtained. The practical application of the present model is discussed.Master Thesis In Plane Vibrations of Curved Timoshenko Beams With Variable Curvature(Izmir Institute of Technology, 2016) Cin, Uğur; Yardımoğlu, BülentIn this study, in-plane vibrations of curved Timoshenko beams with variable curvature is studied by Finite Element Method. In the selected method, it is known that generalized differential eigenvalue problem are solved by reducing the equations from continuous to discrete domain. Catenary form is used as the axis of curved beam. An APDL (ANSYS Parametric Design Language) code is developed for the geometric and finite element models of the curved beam. The computer code is validated by the data available in the literature. After validation of developed computer code, the effects of parameters, which are related to shape of the curved beam, on the natural frequencies and mode shapes are studied.Master Thesis Design of Acoustic Meta-Material Sound Absorbers by Finite Element Method(Izmir Institute of Technology, 2016) Manoğlu, Kaya; Önen, OnursalAcoustic meta-materials are widely known with their extra-ordinary sound properties like transmission, absorption and orientation which are not available in natural materials. These features are provided by their repeating constructions and various configurations. Sound absorbers are used in a wide variety of applications such as sound treatment in buildings, vehicles, concert halls and any place noise control and/or desirable acoustic properties are required. Traditional sound absorbers are long-known to be inefficient in the low frequency ranges. In this study, to overcome the absorption problem in low frequencies, absorption characteristics of foam based porous structures are analyzed with the addition of locally resonant blocks. Elements embedded in the absorber material with various shapes and properties are investigated by finite elements method to improve sound absorption, especially in the low frequency range. The results showed that embedding air cavities enclosed by thin solid shells to the absorber improves sound absorption in the low frequencies without significant deterioration in the high frequencies.Master Thesis Displacement Analysis of Non-Circular Planar Curved Beams Under In-Plane Impulsive Load(Izmir Institute of Technology, 2015) Çelik, Ahmet; Yardımoğlu, BülentIn this study, time response of a planar curved beam with variable curvatures under in-plane impact load is analyzed by two numerical methods which are Finite Difference and Finite Element Methods. The solution procedures in both methods are based on solution of eigenvalue and time response problems. Catenary form is selected as the axis of curved beam. A computer program is developed in Mathematica for the solution with Finite Difference Method. Moreover, a computer code is written for the geometric and finite element models of curved beam with variable curvature in ANSYS by using APDL (ANSYS Parametric Design Language). Solutions of the two methods are compared in each other and then good agreement is observed. The effects of impuls and damping properties on the time response are investigated.Master Thesis Static and Dynamic Deformation Behavior of Combined Geometry Aisi 304l Stainless Stell Shells(Izmir Institute of Technology, 2015) Şahin, Selim; Taşdemirci, Alper; Güden, MustafaIn this study, the static and dynamic crushing behavior of combined geometry shells consisting of hemi-spherical and cylindrical segments were studied both experimentally and numerically. The proposed geometries were manufactured by deep drawing. Due to the nature of the deep drawing process, specimens inherited significant amount of residual stress/strain and thickness variation along the cross-section was observed. Thus, the manufacturing process was also numerically modeled explicitly. Quasi-static compression and dynamic drop weight tests were conducted both experimentally and numerically. The plastic deformation of the combined geometry shells started with the inward dimpling of the hemi-spherical segment and progressively continued deforming with the asymmetric or axisymmetric folding in cylindrical segment depending on the radius to thickness ratios and strain rates. The failure/fracture was observed in the thicker specimens at dynamic strain rates and that caused decreases in specific absorbing energy (SAE) levels. In addition, the energy partitions between the hemi-spherical segments increased at higher loading rates. Furthermore, the inertia and rate sensitivity influenced the crushing response of cylindrical segment more than that of hemi-spherical segment and inertia effect was more pronounced than the rate sensitivity at higher loading rates. Considering the thermal effects in the crushing behavior of the combined geometry shells, it was shown that the mean crushing load lowered as the temperature increased. Additionally, the percentages of increase in the crushing load were limited at lower temperatures for varying loading rates. It was shown that as the absolute temperature increased the percentage of increase in crushing load was significantly increased due to the change in deformation mode.Master Thesis Modelling and Simulation of Metal Cutting by Finite Element Method(Izmir Institute of Technology, 2009) Kılıçaslan, Cenk; Yardımoğlu, BülentMetal cutting is one of the most widely used manufacturing techniques in the industry and there are lots of studies to investigate this complex process in both academic and industrial world. Predictions of important process variables such as temperature, cutting forces and stress distributions play significant role on designing tool geometries and optimising cutting conditions. Researchers find these variables by using experimental techniques which makes the investigation very time consuming and expensive. At this point, finite element modelling and simulation becomes main tool. These important cutting variables can be predicted without doing any experiment with finite element method. This thesis covers a study on modelling and simulation of orthogonal metal cutting by finite element method. For this purpose, orthogonal cutting simulations of AISI 1045 steel are performed and model used in simulations is validated. At first step, effects of work piece flow stress and friction models on cutting variables such as cutting forces, chip geometry and temperature are investigated by comparing simulation results with experimental results available in the literature. Then, mechanical and thermal analyses are performed. Lastly, effects of rake angle and tool tip radius on strain, temperature and stress distributions are investigated.Master Thesis Vibration Analysis of Pre-Twisted Rotating Beams(Izmir Institute of Technology, 2003) Yıldırım, Tolga; Yardımoğlu, BülentA new linearly pretwisted rotating Timoshenko beam element, which has two nodes and four degrees of freedom per node, is developed and subsequently used for vibration analysis of pretwisted beams with uniform rectangular cross-section. First, displacement functions based on two coupled displacement fields (the polynomial coefficients are coupled through consideration of the differential equations of equilibrium) are derived for pretwisted beams. Next, the stiffness and mass matrices of the finite element model are obtained by using the energy expressions. Finally, the natural frequencies of pretwisted rotating Timoshenko beams are obtained and compared with previously published both theoretical and experimental results to confirm the accuracy and efficiency of the present model. The new pretwisted Timoshenko beam element has good convergence characteristics and excellent agreement is found with the previous studies.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 SeçilA 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.