Department of Manufacturing Engineering
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Item A COMBINED EXPERIMENTAL-NUMERICAL INVESTIGATION ON ALUMINIUM EXTRUSION(2011-04-27) KALKAN, Hakan; ÖZDEMİR, İzzet; BARANOĞLU, BesimThis study focuses on an industrial size aluminum extrusion process and consists of both experimental and computational parts. On the basis of process parameters and die geometry supplied by ASAŞ Aluminum Company, full scale computational models of the process have been constructed by using different commercial Finite Element and Finite Volume software packages. The necessary material characterization has been done by compression tests for which a new uni-axial compression test set-up suitable for high temperatures has been designed and manufactured. The measured load-displacement diagrams and exit temperatures are compared with the computational results. In addition to that, Finite Element and Finite Volume results are also compared. These results indicate that reasonable good agreement between the measured data and computational results can be achieved provided that the Finite Element Method is used and proper material characterization is conducted.Item THERMOELASTIC ANALYSIS OF HEAT GENERATING MULTI-LAYERED COMPOSITE CYLINDERS AND TUBES(2012-04-18) YILDIRIM, Murat; ARGEŞO, HakanA computational method is developed for the thermoelastic analysis of internally heat generating multi-layered composite cylinders and tubes having temperature dependent physical properties. The composite assembly is considered to be infinitely long and have axially constrained ends. In the formulations, small deformation theory is used. The layers that form the composite assembly are isotropic and have uniform heat generation. The thermal and mechanical problems are uncoupled and axisymmetric. The thermal problem is steady state and the mechanical problem is a plane strain problem. The computational model is based shooting algorithm. Both the thermal and mechanical problems are solved with the use of shooting algorithm. The computational model is first verified through the use of some benchmark problems that have analytical solutions in which the physical properties are considered to be temperature independent. The computational method is then used to solve some composite cylinder/tube assemblies that have temperature dependent physical properties.Item EXPERIMENTAL INVESTIGATION OF INFLUENCE PARAMETERS ON FORMING LIMIT DIAGRAMS OF ALUMINUM ALLOY-AL 2024(2013-04-22) ÇELİK, Gökhan; KAFTANOĞLU, Bilgin; KARADOĞAN, CelalettinSheet metal forming is the key word for aerospace, automobile and aeronautics industry. To fulfill the customer expectations, safety requirements and market competitions, sheet metal forming processes must be well analyzed before production. At this stage, importance of material characterization and finite element (FE) simulations arise. This study is focused on combination of material characterization and FEA (Finite Element Analyses) of sheet metals to be able to make improvements of sheet metal while considering cost and quality. On the material characterization parts of the study, simple tension tests, hydraulic bulge tests (HBT) and forming limit diagrams are determined for Al2024 aluminum alloy. HBT is obtained using a new specialized code and compared to the simple tension tests. High accuracy mechanical extensometers are used to obtain instantaneous deformation during tensile test and similarly high accuracy CCD cameras are used to obtain material deformation during determination of FLDs and flow curves from HBT. FE studies are performed to validate experimental studies and to determine coefficient of frictions of different lubricants. Analyses are carried out using a commercial FE package, Marc Mentat 2007® . Material inputs are supplied from experimental uniaxial and hydraulic bulge tests. Flow curve validations are performed comparing HBT and uniaxial tensile tests up to 0.15 strains. Experiments revealed that initial material thickness and lubrication has a significant effect on formability window of aluminum sheets and speed of punch has no great effect on limits of aluminum formability since Al2024 is a strain rate independent material. Beside these, higher strains than uniaxial tensile test are obtained in HBT with new developed code.Item A COMBINED NUMERICAL-EXPERIMENTAL INVESTIGATION ON MICRO-EXTRUSION(2013-06-14) MURAT, Levent; ÖZDEMİR, İzzet; ŞENGÖNÜL, MerihIn this work, to develop an understanding on micro forming processes, a combined experimental-numerical investigation on micro forming is presented. On the experi mental side, in order to demonstrate the statistical size effect, an experimental set-up for micro-extrusion has been designed and micro-extrusion test with copper billets of different average grain size, has been conducted successfully. On the modelling side, due to large displacement and large strains developing during the forming process, a geometrically non-linear continuum mechanics description is preferred. Since a grain level description is necessary for micro forming operations, crystal plasticity is used to model the mechanical response of each grain. To this end, the crystal plasticity framework has been coded as a user defined material model and integrated into the commercial FE software Abaqus as a UMAT subroutine. With this tool, a numerical investigation on the influence of grain orientations on frictional response at small scales is carried out.Item EXPERIMENTAL AND NUMERICAL STUDY ON STRETCH FORMING PROCESS(2013-06-20) ALKAŞ, Celal Onur; KARADOĞAN, Celalettin; ŞİMŞİR, CanerStretch forming process is commonly used in the aircraft industry for the manufacturing of large sheet panels. The success of this process is highly dependent on the process parameters like mechanical properties of sheet material, the friction condition between tools-part interfaces and relative motions between tool and jaws. Determining the best parameters by trial - error procedure is quite difficult and costly, so that finite element analysis is needed. The scope of this study is to establish finite element model (FEM) for stretch forming process. For this purpose, accurate material and reliable friction modeling are required. Material characterization tests of mostly used aluminum alloys are conducted to prepare input to the model. Standard tensile, stack compression, hydraulic bulge test (HBT) and forming limit diagram (FLD) tests are performed in order to identify deformation behavior and anisotropy properties of aluminum sheet materials. High accuracy CCD cameras are used to obtain material deformation during determination of FLDs and flow curves from HBT. Also, friction coefficients are determined for various lubrication conditions encountered in stretch forming processes using inverse based analysis. Using these inputs, numerical model of the process is established by FEM for three basic stretching tool motions, which are; stretching the sheet by jaw, stretching the sheet by form die and finally stretching the sheet material by synchronized motion of both tools. In order to improve the model and validate the analyses results, experimental work is also performed in which the deformation of the sheet is measured optically using GOM-Argus® 3- D deformation measurement device. Then, three selected aerospace sheet parts were analyzed and success of the model for industrial applications is proved.Item ENHANCED CHARACTERIZATION and DIE DESIGN for SHEET METAL FORMING in AUTOMOTIVE INDUSTRY(2014-03-10) GÜRBÜZ, İsmail; KARADOĞAN, CelalettinLast several decades, existing global competition are going on among automotive companies because of increasing customer expectations, safety requirements, the manufacturing time and cost. These requirements play most significant role for automotive companies to continue one’s existence in automotive market. Many automotive companies manage to develop their capabilities and techniques as mechanically, trial-error and virtually to manufacture high quality car components. Since the trial-error method is quite difficult and costly, finite element method (FEM) must be used. Tryout is the validation process of dies for a robust mass production. Each company has its own tryout strategy and the crucial know-how is usually not publicised. Being the major player in automotive industry in Turkey, TOFAŞ aims to catch up with the global actors, and hence intends to further develop its own tryout strategy utilizing virtual tools. In this study, one of the major milestones towards this success is introduced. Concerning the material properties, friction coefficients, elastic properties of dies and compensation strategies, the basic know-how and necessary information is created for further automatization of the virtual tryout practice. Material characterization plays most significant role in order to prepare input the virtual model. In this study, several material characterization tests are performed. Standard tensile tests are performed to obtain early stage of the yield curves and anisotropy parameters of sheet materials. The plastic behavior of the sheet metal under biaxial stress state is usually obtained by HBT. Hydraulic Bulge Test (HBT) is performed using high quality optical measurement system (GOM Aramis). Nakajima test is used to obtain Forming Limit Curve (FLC). The optical measurement system GOM Aramis is used to obtain sheet metal deformation during prediction of FLC and yield loci and flow curves from HBT. Furthermore, friction coefficient is an important parameter in order to obtain accurate results from virtual model. Basically there are two approaches in determining the friction coefficient: direct approaches provide the friction coefficient without inverse analysis through simulations and indirect ones requires inverse simulative evaluation. Elastic modulus, which is also a significant parameter to get accurate results from virtual models, is determined using several testing methods such as, tensile testing, ultrasonic measurement, Resonant Frequency and Damping Analysis (RFDA). Moreover, several testing method (Three Point Bending, Four Point Bending and Frictionless Stretch Drawing) and finite element method are used to verify obtained elastic modulus values. Finally, a new approach is proposed for the compensation of die and press deflection.Item ANALYSIS OF COLD EXTRUSION(2014-06-09) DURAN, Deniz; KARADOĞAN, Celalettin; ÖZDEMİR, İzzetCold extrusion is a cold forging process where product of smaller cross sectional area is obtained by compressing a billet through an aperture in the die. In this study, different facets of cold extrusion processes are investigated experimentally and numerically to a certain extent that seem to be overlooked in the existing studies. Proper material characterization that is necessary to analyse cold extrusion processes is addressed. A method for reconstruction of isothermal flow curves based on the flawed test data is proposed. An unexpected instability is observed for 16MnCr5 steel in the process range of 200-400°C, where material exhibits negative strain rate sensitivity. This instability is associated with dynamic strain aging phenomenon. The importance of the proposed method is presented for a forward rod extrusion case. The pitfall existing for a common friction identification test, namely, the double cup extrusion test, is emphasized when insufficient material data is used in the inverse analysis. Treatment of surface enlargement, a crucial tribological parameter, within FEA framework under arbitrary deformations is discussed and an alternative calculation scheme is developed. An experimental method for surface enlargement measurement is developed to verify the numerical predictions. A recently proposed, surface evolution based friction model is investigated and possible improvements are addressed. Forward rod extrusion process with multiple area reductions is examined as the proof of concept study. Following, the simulated surface roughness predictions are compared with the experimental surface topography measurements for a forward rod extrusion process.Item INVESTIGATION OF BORON NITRIDE COATINGS(2014-06-09) DÖKMETAŞ, Nihan; KAFTANOĞLU, Bilgin; ŞİMŞİR, CanerThis thesis presents detailed characterization studies on Boron Nitride (BN) coatings. In this study, BN coatings are obtained with the method of Radio Frequency (RF) magnetron sputtering technique, in a Physical Vapor Deposition (PVD) system, from target to substrate. BN coating formation on different substrates are investigated on varies substrates such as AISI D2 Steel, 316 L steel, optical glasses, Ti implants. Also, using different deposition parameters, the effect of parameters are researched. All coating results are investigated by using XRD, SEM, CaloTest®, Filmetrics F20 Thin-Film Analyzer Device ®, step profilometer, Scratch tester, Tribometer tester, Nanoindentation tester, FTIR, AFM and profilometer. Compositional, structural and mechanical measurements and analysis are performed for the characterization of BN coating. According to our investigations, it is observed that BN coatings obtained in different phases such as a--BN, e-BN, r-BN, w-BN, t-BN and h-BN structures besides c-BN structures. The effects of chemical and microstructural constitution on the tribological properties were investigated. Generally, it is found that there is good adhesion and lower friction because of more than one structure. In some cases hardness is found to increase. On the other hand, some difficulties are encountered in measurements because the coating thickness is generally 1 μm or lower. A statistically significant change could not be determined in roughness for 3 and 6 hours coating compared to substrate roughness.Item ENHANCED CHARACTERIZATION and DIE DESIGN for SHEET METAL FORMING in AUTOMOTIVE INDUSTRY(2015-01-30) GÜRBÜZ, İsmail; KARADOĞAN, CelalettinLast several decades, existing global competition are going on among automotive companies because of increasing customer expectations, safety requirements, the manufacturing time and cost. These requirements play most significant role for automotive companies to continue one’s existence in automotive market. Many automotive companies manage to develop their capabilities and techniques as mechanically, trial-error and virtually to manufacture high quality car components. Since the trial-error method is quite difficult and costly, finite element method (FEM) must be used. Tryout is the validation process of dies for a robust mass production. Each company has its own tryout strategy and the crucial know-how is usually not publicised. Being the major player in automotive industry in Turkey, TOFAŞ aims to catch up with the global actors, and hence intends to further develop its own tryout strategy utilizing virtual tools. In this study, one of the major milestones towards this success is introduced. Concerning the material properties, friction coefficients, elastic properties of dies and compensation strategies, the basic know-how and necessary information is created for further automatization of the virtual tryout practice. Material characterization plays most significant role in order to prepare input the virtual model. In this study, several material characterization tests are performed. Standard tensile tests are performed to obtain early stage of the yield curves and anisotropy parameters of sheet materials. The plastic behavior of the sheet metal under biaxial stress state is usually obtained by HBT. Hydraulic Bulge Test (HBT) is performed using high quality optical measurement system (GOM Aramis). Nakajima test is used to obtain Forming Limit Curve (FLC). The optical measurement system GOM Aramis is used to obtain sheet metal deformation during prediction of FLC and yield loci and flow curves from HBT. Furthermore, friction coefficient is an important parameter in order to obtain accurate results from virtual model. Basically there are two approaches in determining the friction coefficient: direct approaches provide the friction coefficient without inverse analysis through simulations and indirect ones requires inverse simulative evaluation. Elastic modulus, which is also a significant parameter to get accurate results from virtual models, is determined using several testing methods such as, tensile testing, ultrasonic measurement, Resonant Frequency and Damping Analysis (RFDA). Moreover, several testing method (Three Point Bending, Four Point Bending and Frictionless Stretch Drawing) and finite element method are used to verify obtained elastic modulus values. Finally, a new approach is proposed for the compensation of die and press deflection.Item ANALYSIS OF ELASTIC-PLASTIC INTERFERENCE FIT JOINTS(2015-10-23) IŞIK, Hatice Hava; MUSIC, Omer; KARADOĞAN, CelalettinIn automotive industry, increasing product complexity has driven the development of new joining processes for mechanical parts. Typical examples are welding, adhesive bonding and mechanical fastening used to join components in a product assembly. Joining by interference fits belongs to a wider group of mechanical joining processes, some examples of which are self-pierce rivets, mechanical clinches, pin joints and threaded connections. In interference-fit joints, interference of two mating parts leads to contact pressure at the interface. This contact pressure holds the two parts together through friction, providing a mechanical joint. Strength of this joint depends mainly on the coefficient of friction, contact pressure and contact area. Such joints are used in a wide variety of applications, ranging from automobile to aerospace industry. This study focuses on analysis of elastic-plastic interference fit joints formed by fitting the filter pin into the cylindrical hole in the injector body. This process has been studied in detail, however a review of literature reveals that analytical and numerical models have been developed for relatively simple geometries, and the number of publications for complex, asymmetric, three-dimensional geometries is limited. This study presents a detailed examination of the elastic-plastic interference fit joints for both simple and complex geometries. The mechanics of the process is studied in detail through physical trials, analytical and numerical models. Both trials and modelling are done for two-dimensional and three-dimensional geometries. The effects of geometrical properties, material properties and cylinder-tube, grooved geometry and actual process are investigated. Developed numerical models are applied to an industrial problem; analysis of an asymmetric, three-dimensional interference fit joints used in high pressure diesel injection systems, specifically the joint between the fuel filter and the injector body of an injection system. Strength of this joint is one of the key parameters determining the performance of the fuel injection system as a whole and as such is studied in detail. A detailed investigation of the joining process shows that the joint strength can be improved through careful selection of filter and body materials, geometry and other parameters that affect the joining process.Item MODELLING AND ANALYSIS OF TUBE SPINNING(2017-04-02) Çizmeci, Kerem; Şimşir, CanerThis thesis investigates the process of tube spinning. The investigation is based on numerical simulations by commercial finite element software Transvalor Forge. Two dimensional and three dimensional numerical analysis models have been developed. Parameter optimization has been performed to find the variables of numerical analysis. The proposed numerical model was compared with the related works in the literature. Using the developed models, analysis of tube spinning process has been performed.Item PREDICTION OF CREEP MODEL PARAMETERS OF A LOW MELTING POINT ALLOY BY USING HARDNESS TEST(2022-01-20) Ben Saoud, Farij Abduljali; Şengönül, Cemal Merih; Şimşir, CanerThe tensile test is a method frequently used to determine the mechanical properties of materials. However, this method needs bulky instruments, which can be costly to attain and maintain. Besides tedious sample preparation processes and sometimes complicated test protocols that necessitate trained personnel to run, which makes this type of test time and money consumed. Therefore, it is convenient to utilize more practical and simple instrumentation that can provide sought material properties with tolerable deviation compared to the tensile test. Such an approach will be well received, particularly by manufacturing facilities. Since there is a strong correlation between hardness and tensile strength of the material, researchers look for ways to substitute tensile test measurements by hardness for some groups of materials. In this study, we took a further step in this endeavor by developing a technique to predict the strength properties of a low melting point alloy Sn-Bi eutectic at elevated temperatures via hardness test. We established an analytical relationship that predicts creep exponent (n) and the strength coefficient (A) values, also the strain rate sensitivity index (m) and the constant (C) values of the eutectic Sn-Bi alloy. Creep parameters were determined in the tensile test by applying stresses of 10, 15, and 20 MPa, which iv are less than the yield strength of Sn-Bi eutectic alloy at temperatures 25, 45, and 65 °C respectively. Also, the strain rate sensitivity (SRS) tests were performed at similar temperatures by applying strain rates of 10−3 , 10−2 , and 10−1 s -1 to calculate the SRS parameters. Similarly, Vickers hardness measurements were performed under the same conditions. As a result, we determined a strong correlation between the uniaxial tensile mechanical properties and the hot hardness measurements of the Sn-Bi alloy, and the obtained numeric model predicted most of the mechanical properties with a high statistical significance.Item PERFORMANCE EVALUATION OF A SINGLE CYLINDER HBO ENGINE(2022-01-25) Fendal, Metin; Jafari, Rahim; Bayka, DemirThe development of 2 and 4 stroke cycle prototype spark ignition engines using gasoline, manufactured by Minisan A.Ş., is intended in this study. The engines, designed to operate with carburetors and conventional ignition system, functioned successfully. The first designed engine was manufactured with a similar cylinder head, valve configuration, spark plug location and equal cylinder diameter and piston stroke with the ACME model engine, for comparison. The geometry of the connecting rod was altered. The center of the crankshaft shifted approximately 40 – 70 mm from the center of the cylinder. The specific fuel consumption of the new engine was lower and a decision was made to develop it. After the first 340 cc prototype, 2 cylinder, air and water cooled prototype engines were manufactured. A 340 cc engine was also developed within the scope of this thesis. Appropriate combustion chamber geometry and valve configuration for the thermodynamic cycle of these engines were not included in this study. Within the scope of the thesis, commercial electronic fuel injection and ignition systems were acquired and adapted to the engines. These systems were operated by electronic control units (ECU) which were acquired. Theoretical simulation and experimental performance and mapping work were done on the engines for programming the ECU. Two dimensional tables were constructed for the injectors and igniton systems to follow according to the working modes of the engines and were uploaded to the ECU’s. Performance tests were conducted with the upgraded electronic injection and ignition system of the engines. In comparison to the operation of the engines with carburetors and conventional ignition system, for same engine speed ranges and loads up to 20 percent increase was observed for the excess air coefficient and up to 30 percent decrease was observed for the brake specific fuel consumption.Item AN INVESTIGATIONS INTO THE MICRO WIRE ELECTRICAL DISCHARGE MACHINING OF SHAPE MEMORY ALLOY(2022-01-26) Meshri, Hassan Ali; Akar, Samet; Kılıç, Sadık EnginRecently, the use of nitinol as a shape memory alloy (SMA) has become significant in vital industries, such as the medical and aerospace industries, due to its distinctive characteristics of pseudoelasticity and shape memory effect. Due to its high hardness, high fracture toughness, strain hardening and issued such as rapid tool wear the use of conventional machining processes has become difficult when producing complex shapes from nitinol. Therefore, non traditional machining processes, especially wire electro-discharge machining (WEDM) has become the dominant method of machining nitinol alloy. However, WEWD faces some challenges, especially in terms of surface integrity of the workpiece which requires an in-depth investigation. In this study, the effect of µ-WEDM process on nitinol alloy was studied. 100 µm diameter brass wire was used for the cutting in addition to a set of µ-WEDM adjustable input cutting parameters, such as peak current (Ip), servo voltage (Sv), pulse on time (Ton), and pulse off time (Toff) are selected. The experiments were designed based on L27 Taguchi orthogonal array to reduce the number of experiments. Multi-regression analysis was applied based on the surface response methodology (RSM) to determine the effect of µ-WEDM process parameters on the surface integrity of the nitinol alloy. The aim of surface integrity studies was to minimizing Kerf width variation, minimizing white layer thickness (WLT), maximizing metal removal rate (MRR), minimizing surface roughness (Ra), and minimizing µ-hardness. Optimization studies were performed using two algorithms, the gradient algorithm (GA) and the particle swarm optimization algorithm (PSO) to determine the best µ-WEDM cutting parameters set for each output parameter individually according to the target that was specified. Moreover, a combined multi-response optimization analysis was performed to find the best set of µ-WEDM process parameters to achieve the best surface integrity of the nitinol alloy sample that satisfies the goal of all output responses’ simultaneously.Item PREDICTION OF SHEAR LOCALIZATION ONSET IN MACHINING OF Ti-6Al-4V(2022-01-26) Yılmaz, Okan Deniz; Oliaei, Samad Nadimi Bavil; Kılıç, Sadık EnginApplication of lightweight and energy-saving materials plays a significant role in different industries including automotive, aerospace and biomedical, to name a few. One important lightweight material is Ti-6Al-4V titanium alloy known as the working horse of the titanium industry, because of its excellent chemical and mechanical properties. In spite of its widespread applications, Ti-6Al-4V is known as a difficult to-cut material because of its low thermal conductivity, its high chemical affinity with most cutting tool materials, low modulus of elasticity and the formation of shear localized (serrated) chips during machining. The latter is of paramount importance, because of the fact that the consequences of the emergence of serrated chip formation in machining are fluctuations in the machining forces, accelerated tool wear, deterioration of the surface quality, reduced accuracy and out-of-tolerance machined components. The prediction of the onset of shear localization is one of the most challenging problems in the field of machining, i.e. determining the conditions in which the chip morphology is changing from continuous to a periodically varying. The issues associated with shear localized chips were the main driving force in the literature for the development of several material models for the simulation of shear localization during machining of Ti-6Al-4V titanium alloy. However, the accuracy and capability of the developed models for the prediction of the onset of serrated chip formation during machining Ti-6Al-4V have not been investigated. The aim of this thesis is to evaluate the accuracy of different material models to predict the onset of serrated chip formation during the machining of Ti-6Al-4V. The results of the finite element models are compared with the results of the experiments in terms of machining forces and chip morphology. Ploughing forces are obtained by varying uncut chip thickness at different cutting speeds by using the extrapolation method, and are used to correct cutting and thrust forces. Corrected cutting and thrust forces are used to calculate the Coulomb friction coefficient. Both explicit and implicit finite element codes are used with different material models with/without damage, with/without strain softening. The weakness and strength of each material model have been investigated for the prediction of the critical cutting speed, chip morphology and machining forces. The results of this study revealed that a modified Johnson-Cook material model which includes temperature softening and strain softening in the form of the hyperbolic tangent function is able to give acceptable predictions for the onset of shear-localization during machining of Ti-6Al-4V.Item AN EXPERIMENTAL INVESTIGATION ON ENHANCING THE MACHINABILITY OF DIFFICULT TO CUT MATERIALS USING ULTRASONIC ASSISTED MILLING PROCESS(2022-01-26) Namlu, Ramazan Hakkı; Sadigh, Bahram Lotfi; Kılıç, S. EnginTi-6Al-4V has unique material properties such as high strength-to-weight ratio, good corrosion resistance, and excellent fracture toughness. Therefore, it’s widely used in aerospace, medical and automotive industries where machining is an essential process. However, machining of Ti-6Al-4V is highly challenging due to its wear resistance and low thermal conductivity. Ultrasonic assisted machining is quite recent a method in metal cutting applications and it has numerous advantages over conventional machining processes such as reduced cutting forces, increased surface quality and lowered tool wear. In addition, minimum quantity lubrication (MQL) is an alternative type of cooling that is being used instead of conventional cooling systems in machining because of its several improvements on process efficiency. Cutting forces are one of the most important outputs that measure cutting performance of a machining process. Another important output for machining is the surface roughness due to its direct impact on the quality of the workpart. However, there is not much work to compare the changes in cutting forces and surface roughness in ultrasonic assisted machining with the use of minimum quantity lubrication. In this study the changes in cutting forces and surface roughness during the machining of Ti-6AL-4V material were investigated by using ultrasonic assisted milling with ultrasonic vibrations applied to cutting tool on Z axis with the use of MQL. This is believed to be the first time done in literature. Experimental work conducted in the thesis showed that the ultrasonic assisted milling with MQL cooling is capable of significantly enhancing the cutting performance in terms of the cutting forces and the surface quality if the cutting conditions are properly selected.Item OPTIMIZATION OF ROLL FORMED BEAMS USED IN CEILING CONSTRUCTION(2022-02-14) Altunsaray, Tunç Safa; Kaftanoğlu, BilginIn this thesis, the deflections of the C and U beams manufactured by using roll forming of strip material and used in present ceiling constructions in cantilever and simple support modes are calculated by using finite element method. Also, a testing laboratory is developed to check the calculations and to be able to make the real-life measurements and experiments on the profiles. First the elastic deflections of the existing C and U profiles are calculated in the simply supported and cantilever modes. Then experiments are conducted in the developed laboratory to check the theoretical results. Later, new C and U profiles have been developed using thinner material with a more complex design giving deflections not more than the original C and U beams. New designs have been manufactured by roll forming and testing in the simply supported and cantilever modes have been completed. This way, the thicknesses of C and U beams have been reduced by approximately 0.05 mm, resulting in deflections not more than the original designs. Hence, material saving is obtained with an optimal design also saving cost and energy.Item MULTISTAGE LAUNCH VEHICLE DESIGN(2022-02-15) Hamzah Alghadeer, Noor; Inger, ErkIn this thesis, we designed a multistage launch vehicle. In the first stage, it uses a liquid propellant in a booster with five solid rocket propellants to reach about 42 km. In the second stage, after rejecting the five solid rocket propellants to reduce the weight and used liquid propellant only to reach the low earth orbit (LEO) at 925 Km altitude in order to transfer satellite for science study. After finishing the design, three case studies for this design. The first case studied the effect of a number of solid rockets with a velocity of the rocket. A second case study is dealing with an altitude of the rocket and the number of the solid rocket. The last case was dealing with an altitude of the rocket and the orbit velocity at the same altitude.Item DESIGN, MANUFACTURING AND TESTING OF HIGH TEMPERATURE PEM FUEL CELL STACK(2022-02-15) Budak, Yağmur; Devrim, YılserIn recent years, the need for energy has been increasing with the developing of technology and population. The proton exchange membrane fuel cell (PEMFC) considered to be the preferred alternative energy technology in recent years due to its high efficiency, low emission, high power density, quiet operation and short start-up period. High Temperature PEMFC (HT-PEMFC) type PEMFC provide easy water management and high carbon monoxide (CO) tolerance thanks to over 100 oC of operation temperature. PEMFC must have high CO tolerances for PEMFC commercialization and usage of reformed gases obtained from a short process of gases such as natural gas and methane, which are frequently used today. In this thesis, the design, manufacturing and testing of a nominal 300 W HT-PEMFC stack which has 150 cm2 active area and 12 cells were performed. The materials chosen to manufacture this stack are composite graphite bipolar plates, eloxal coated aluminum plates, Gold-coated copper plate current collectors, stainless steel connections, Viton® gasket, Pt/C coated carbon paper gas diffusion layer and PBI membranes. In the scope of the thesis, the current test station was upgraded in order to test HT PEMFC stack by reformate gas mixture. Firstly, a single HT-PEMFC performance test was performed with Hydrogen (H2) gas and reformate gas mixture supply at 160oC in order to obtain the design parameters of the stack would be produced. The current density value at 0.6 V was obtained as 0.33 A/cm2 with H2 supply, and 0.28 A/cm2 was obtained with reformate gas mixture supply. Then, according to single HT-PEMFC test result, the stack of HT-PEMFC was designed. After the design of the stack, the pressure drop on the bipolar plate was analyzed for 3 different gas flow rates using Solid Works® Flow Simulation program. The pressure losses were determined maximum 83.5 Pa for H2 at 0.5 slpm and 129.83 Pa to reformate gas mixture (H2/CO2/CO;75/22/3) at 0.56 slpm. After that, the performance of stack produced were tested by pure H2 and reformate gas mixture supply. The stack power with pure H2 feed was 320 W at 7.2 V operation voltage, it was 218 W at 7.2 V for reformate gas mixture. In addition, with the H2 supply, the total efficiency of the stack was 79 %, while this efficiency decreases to 76 % with its reformate gas mixture supply. These losses can be ignored considering the advantages of reformate gas mixture use and the importance of fuel cell for commercialization.Item APPLICATION OF THE CONTOUR METHOD IN COLD ROLLED ALUMINUM PLATES(2022-02-16) Mutlu, Mert; Şimşir, CanerThe recently popular contour method can measure residual stresses through cross section of any part. The contour method can give 2D stress map without any inverse calculation as other techniques do. It is cheap, simple and has many applications. Moreover, measurement depth is not limited by contrast with other techniques such as hole drilling and neutron diffraction. This study presents an application of the contour method on a cold rolled aluminum plate. In this thesis, two AA 5083 specimens were used to determine the residual stresses by the contour method. The specimens were cut in two by using wire-Electric Discharge Machining (w-EDM) and then, the contours from the cut surfaces were measured by an optical surface profiler using the focus variation technique. The obtained data were processed by MATLAB software. After data processing, inverse of the measured contours were applied to a FE model and a 2D map of the residual stress was attained. The stress distribution profiles were compared to the results obtained from Slitting and Ring Core methods for verification and a good agreement with Slitting Method was achieved. Also, the stress distribution profile from the Contour Method was according to the expected stress distribution after a cold rolling process. Although there were some differences with Ring Core Method, similar trends were observed.