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2D-axisymmetrical modeling and experimental study of hydrogen absorption in copper coated metal hydride
(Pergamon-Elsevier Science Ltd, 2023) Atalmis, Gamze; Toros, Serkan; Timurkutluk, Bora; Kaplan, Yuksel
The storage of hydrogen in metal hydride reactors is examined experimentally and numerically in this paper. In this respect, as-received LaNi5 powders are coated with different amounts of copper by using copper sulphate solution to accelerate the hydrogen charging processes. The thermal conductivity of the copper-coated storage material is found to reach up to 8 times of the uncoated powders. A two-dimensional axisymmetric model regarding complex heat and mass transfer occurring during hydrogen charging process in metal hydride reactors is numerically solved at macro level. The developed model is validated by using experimental data related to the amount of hydrogen stored and the reactor temperatures. In accordance with the experimental results, the simulation results show that more homogenous temperature distribution in the reactor can be obtained with the copper coating due to improved thermal properties. Moreover, charging time is also improved by the copper coating. However, since the reactor is loaded with coated/uncoated LaNi5 powders at the same weight of 65 g, the total amount of hydrogen stored decreases with the copper coating due to reduced amount of LaNi5. (c) 2023 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.
A novel approach to enhance formability in Ti-6Al-4V alloy: Experimental investigations and microstructural analysis of pulsating tensile test
(Elsevier, 2024) Korkmaz, Habip Gokay; Yapan, Yusuf Furkan; Toros, Serkan; Turkoz, Mevlut
Ti-6Al-4V alloy, widely utilized in aerospace, medical industries, and specialized applications, boasts exceptional properties. However, its limited formability poses challenges in manufacturing processes. The pulsating loading method emerges as a promising solution to enhance formability in such materials. This study delves into the impact of stress relaxation and loading-unloading tests on the formability of Ti-6Al-4V alloy, conducting tensile tests on sheets of two different thicknesses: 0.5 mm and 2.65 mm. Investigating parameters such as pulse starting strain, relaxation time, and strain increment in stress relaxation experiments, as well as unloading ratio and strain increment in loading-unloading experiments, enabled a comprehensive comparison of the two pulsating loading methods across different sheet thicknesses. Results indicate a notable increase in material formability, up to approximately 20 % for the 2.65 mm thickness and up to 50 % for the 0.5 mm thickness compared to monotonic loading. Stress relaxation time emerged as the most influential parameter for both thicknesses. Additionally, XRD analysis was employed to elucidate the microstructural reasons behind the observed formability enhancement, while SEM imaging provided insights into the fracture surface morphology. This systematic approach sheds light on the microstructural mechanisms underlying the effect of pulsating loading on material behavior.
Alüminyum-magnezyum (Al-Mg) alaşımlarının farklı sıcaklık ve hızlardaki mekanik davranışlarının modellenmesi
(Niğde Üniversitesi, 2009) Toros, Serkan; Öztürk, Fahrettin
Bu tez çalışmasında otomotiv endüstrisinde yaygın kullanıma sahip alüminyummagnezyum(Al-Mg) alaşımlarından 5083-H111 ve 5754-O'nun akma eğrilerininsıcaklık ve deformasyon hızına bağlı matematiksel modeli geliştirilmiştir. Geliştirilenmodel hem geliştirilmiş Nadai model hem de deneysel verilerle bire birkarşılaştırılmıştır. Geliştirilen yeni model alaşımların yüksek sıcaklıklardaki yumuşamadavranışını tahmin edebilme kabiliyetine sahiptir. Bu özellik diğer modellerdebulunmamaktadır. Ayrıca malzemenin farklı sıcaklık ve hızlardaki davranışları içinyapay sinir ağları modeli oluşturulmuş ve analizler yapılmıştır. Sonuç olarak yapay sinirağları modelinin diğer modellere göre daha basit, hızlı ve doğru sonuç verdiği tespitedilmiştir.
ANALYSIS OF THE FRACTURE BEHAVIOUR OF DUAL-PHASE STEELS USING THE GISSMO AND JOHNSON-COOK MODELS
(Univ Zagreb Fac Mechanical Engineering & Naval Architecture, 2023) Topilla, Labinot; Toros, Serkan
This research explores an extended method of fracture mechanics to determine the parameters of the Johnson Cook and GISSMO models. The primary objective of the optimization process and iterative finite element method (FEM) was to identify optimised modelling parameters suitable for specimens with different shapes to predict the failure behaviour of dual-phase steels (DP), specifically DP600 and DP800 steels. Numerous experimental tests were conducted on these DP steels, which mainly consist of ferrite and martensite phases. The specimens underwent deformation at three different tensile velocities. To determine the flow curves, a Simplified Johnson-Cook model (MAT_SJC_098) was employed, while the Johnson-Cook model (MAT_JC_015) was used to identify failure, and a combined JC-GISSMO model was used to determine damage. The numerical simulation results were then compared with the experimental results. In conclusion, all modelling methods used in this research yielded the desired results.
Characterization of heating elements of different dimensions used in resistance welding of thermoplastic matrix composite materials
(2023) Öztürkmen, Hakan; Usta, Yusuf; Toros, Serkan; Öztürk, Fahrettin
Resistance welding is one of the most useful methods for joining of thermoplastic composite materials. In this method, the joining process between two thermoplastic composite materials by passing a current through a stainless-steel heating element under pressure for a certain period. Within the scope of this study, meshes with a width of 12.7, 25.4, 38.1, 50.8, 63.5, 76.2 mm and a length of 160 mm were used to characterize the joule heating performance. These meshes have a mesh range of 33, 45, 61, 91, 109 and 154 microns. The temperature values on the heating elements were observed with a thermal camera by giving different current values to the relevant elements. Results reveal that the 12.7 x 160 mm heating element with 33-micron mesh spacing reached 349 °C under 10 A current, and the temperature value increased with current. In addition, it was determined that the resistance values of the heating elements with different widths were determined by the relevant system and the resistance properties changed non-linearly with the width.
COMPARISON OF (G '/G)-METHODS FOR FINDING EXACT SOLUTIONS OF THE DRINFELD-SOKOLOV SYSTEM
(WALTER DE GRUYTER GMBH, 2015) Daghan, Durmus; Yildiz, Ozlem; Toros, Serkan
Nonlinear Drinfeld-Sokolov system is studied analytically by using four different methods (G'/G)-expansion, direct algebraic, different form of the (G'/G)-expansion methods, and direct integration) and the results are found numerically. New exact and numeric solutions are given and the comparison of the results obtained from these different methods, methods themselves and numerical results are discussed in detail. It is found that the (G'/G)-expansion and different form of the (G'/G)-expansion methods are really coincide and effective methods in the view of finding different solutions that cannot be obtained by using the direct integration for Drinfel-Sokolov system.
Contribution of functionally graded material modelling on finite element simulation of rod end parts in automotive steering system
(KOREAN SOC MECHANICAL ENGINEERS, 2016) Toros, Serkan; Altinel, Kayhan
One of the most important manufacturing steps of the rod end materials is the induction process by which the both hardness of the surfaces and the toughness of the part can be adjusted at the same time. In the study, rod end materials which are inducted and non-inducted are simulated in the view of the fatigue life properties. In the simulations, the rod end parts are defined as functionally graded materials where the mechanical properties of the materials are varying with the dimensions. Additionally, the noninducted material properties or fully strengthened material properties are defined for the geometry in order to comprehend the contribution of the definitions on the congruity of the finite element simulation results with the experiments. When the materials properties of the rod end part are defined as functional graded, the simulation results are found to be much more close to the experimental results.
Determination of optimum ejector operating pressures for anodic recirculation in SOFC systems
(Pergamon-Elsevier Science Ltd, 2017) Genc, Omer; Toros, Serkan; Timurkutluk, Bora
In this study, a numerical analysis of an ejector for micro combined heat and power system based on 18 kW Solid Oxide Fuel Cell (SOFC) using methane as fuel is presented. An ejector design, which reflects the real system conditions in the view of the flow characteristics, is provided and the ejector performance is numerically investigated for various methane pressure to exhaust pressure ratios and methane inlet temperatures. The results show that the fuel inlet temperature and the pressure ratio of the methane to exhaust significantly affect the steam to carbon ratio (STCR) and entrainment ratio. The higher pressure ratio and methane temperature allow a high entrainment ratio and STCR, but as pressure ratio and methane temperature increase, STCR and entrainment ratio remain unchanged after a specific value. 1140 different scenarios related with the inlet and outlet pressures of the ejector and methane temperature are created to determine the optimum operating conditions. The simulations show that the optimum methane inlet pressure is 7 bar and exhaust pressure is 1.159 bar for the ejector geometry of the interest. The entrainment ratio and STCR are determined as 2.05 and 0.92, respectively at this optimum scenario. (C) 2017 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.
Effect of expanded natural graphite addition and copper coating on reaction kinetics and hydrogen storage characteristics of metal hydride reactors
(Pergamon-Elsevier Science Ltd, 2024) Atalmis, Gamze; Toros, Serkan; Timurkutluk, Bora; Kaplan, Yuksel
Experimental and numerical studies are carried out to determine the effects of copper coating and/or ENG (expanded natural graphite) addition on the hydrogen storage performance of ground LaNi5. The amounts of copper coating and/or ENG addition are also investigated. The results reveal that the thermal conductivity of ground LaNi5 can be improved by up to similar to 6 and similar to 12 times with copper coating and ENG addition, respectively. This results in enhanced hydrogen absorption kinetics thereby significantly reduced hydrogen charging times, compared to those determined for LaNi5 without any addition. On the other hand, the amount of hydrogen stored shows a decreasing trend with increasing copper coating and ENG addition since the weight of storage material loaded to the reactor is kept the same. Nevertheless, the optimum copper and ENG contents are determined regarding the amount of stored hydrogen and the corresponding charging time. Similar H/M values are obtained with the optimized powders with additives compared to that of ground LaNi5. Based on these results, various new samples are also prepared by mixing the decided copper coated LaNi5 and ENG added LaNi5 powders and examined to optimize the composition of these blended powders.
EFFECT OF PRE-STRAINING ON THE SPRINGBACK BEHAVIOR OF THE AA5754-0 ALLOY
(INST ZA KOVINSKE MATERIALE I IN TEHNOLOGIE, 2011) Toros, Serkan; Alkan, Mahmut; Ece, Remzi Ecmel; Ozturk, Fahrettin
This study presents the effect of pre-straining on the springback behavior of the AA5754-0 aluminum-magnesium (Al-Mg) alloy sheet under V bending by an experimental and finite-element simulation studies. Pre-straining ranges from 0 To to 11 % were applied to the samples, which were bent on a 60 degrees V-shaped die for the springback evaluation. Commercially available finite-element software, ETA/Dynaform, was used to simulate the 60 degrees V-die bending process. The dynamic explicit finite-element method for pressing and the static implicit finite-element method for the unloading phase were used for the simulations. The results from both the experiment and the simulation indicate that the pre-straining has no positive effect on the springback compensation.
Effect of pre-straining on the springback behavior of the AA5754-0 alloy
(2011) Toros, Serkan; Alkan, Mahmut; Ece, Remzi Ecmel; Ozturk, Fahrettin
This study presents the effect of pre-straining on the springback behavior of the AA5754-0 aluminum-magnesium (Al-Mg) alloy sheet under V bending by an experimental and finite-element simulation studies. Pre-straining ranges from 0 % to 11 % were applied to the samples, which were bent on a 60°V-shaped die for the springback evaluation. Commercially available finite-element software, ETA/Dynaform, was used to simulate the 60°V-die bending process. The dynamic explicit finite-element method for pressing and the static implicit finite-element method for the unloading phase were used for the simulations. The results from both the experiment and the simulation indicate that the pre-straining has no positive effect on the springback compensation.
Effects of aging parameters on formability of 6061-O alloy
(ELSEVIER SCI LTD, 2010) Ozturk, Fahrettin; Esener, Emre; Toros, Serkan; Picu, Catalin R.
6XXX series aluminum-magnesium-silicon (Al-Mg-Si) alloys are medium strength alloys widely used as automotive body materials. The mechanical properties of these alloys are adjusted by performing age hardening heat treatments. In this research, the effect of aging time on formability of 6061-O alloy is investigated. The formability of the material is evaluated by tensile. Erichsen, and hole expansion tests. Results reveal that formability decreases with increasing aging time. The evolution of the anisotropy, r, with the aging time depends on the direction of probing relative to the texture direction. Yield surfaces predicted using the Hill-90 and Barlat-89 models are plotted using experimental r values for several aging times. Since r changes, these surfaces deform slightly and expand with increasing aging time. (C) 2010 Elsevier Ltd. All rights reserved.
Effects of anisotropic yield functions on prediction of forming limit diagrams of DP600 advanced high strength steel
(ELSEVIER SCIENCE BV, 2014) Ozturk, Fahrettin; Toros, Serkan; Kilic, Suleyman; Ishikawa, T; Mori, KI
In recent years, numerous researchers have reported that the predicted forming limit diagrams strongly depend on the method of determining the material parameters used in the yield functions and the corresponding the shape of the yield surface. In this study, the capability of different yield functions to predict the forming limit diagram of DP600 advanced high strength steel sheet is investigated. Additionally, the effects of determination method of the anisotropic parameters on the forming limit diagram are studied. The yield functions proposed by Hill-48, Barlat-89, and YLD2000-2d are considered and the forming limit diagrams are constructed using the Marciniak Kuczynski model. Results reveal that predictions using different yield functions are lower than the experimental forming limits. In terms of shape and tendency, the YLD2000-2d curve is best suited for representing experimental curve. (C) 2014 Published by Elsevier Ltd.
Effects of different optimization methods on the predictions of YLD2000 yield criterion coefficients
(Niğde Ömer Halisdemir Üniversitesi, 2019) Kılıç, Süleyman; Kacar, İlyas; Öztürk, Fahrettin; Toros, Serkan
The improved yield criteria are generally used in the finite element simulations of plastic deformation processes. Calculation accuracies of these criteria coefficients result successful simulation outcomes. In this study, the coefficients of the YLD2000 yield criterion are calculated by three most widely used optimization methods in literature, namely the least squares, nonlinear conditional optimization, and genetic algorithm methods. Two different aluminum alloys, AA7003-T6 and AA6063-T6 are selected to verify the prediction results. Results reveal that the nonlinear conditional optimization and genetic algorithm methods are very dependent on the initial values. Therefore, different result is determined for each different case. For this reason, it has been concluded that the least squares method should be preferred to calculate the coefficients of the yield criterion by using optimizing method.
EFFECTS OF DIFFERENT OPTIMIZATION METHODS ON THE PREDICTIONS OF YLD2000 YIELD CRITERION COEFFICIENTS
(2019) Kılıç, Süleyman; Kacar, İlyas; Öztürk, Fahrettin; Toros, Serkan
The improved yield criteria are generally used in the finite element simulations of plastic deformationprocesses. Calculation accuracies of these criteria coefficients result successful simulation outcomes. In thisstudy, the coefficients of the YLD2000 yield criterion are calculated by three most widely used optimizationmethods in literature, namely the least squares, nonlinear conditional optimization, and genetic algorithmmethods. Two different aluminum alloys, AA7003-T6 and AA6063-T6 are selected to verify the predictionresults. Results reveal that the nonlinear conditional optimization and genetic algorithm methods are verydependent on the initial values. Therefore, different result is determined for each different case. For this reason,it has been concluded that the least squares method should be preferred to calculate the coefficients of the yieldcriterion by using optimizing method.
Effects of electrolyte pattern on mechanical and electrochemical properties of solid oxide fuel cells
(ELSEVIER SCI LTD, 2012) Timurkutluk, Bora; Celik, Selahattin; Toros, Serkan; Timurkutluk, Cigdem; Mat, Mahmut D.; Kaplan, Yuksel
In order to enhance the electrochemical performance and reduce the operation temperature of a conventional electrolyte supported solid oxide fuel cell (SOFC), a three layered electrolyte with various geometry is designed and fabricated. Novel three layered electrolytes comprise a dense and thin scandia alumina stabilized zirconia (ScAlSZ) electrolyte layer sandwiched between two hallow ScAlSZ electrolyte layers each having the same thickness as the support but machined into a filter like architecture in the active region with circular, rectangular and triangular cut off patterns. The percent of thin electrolyte layer in the active region is kept constant as 30% for all designs in order to investigate the effect of pattern geometry on the mechanical properties and the performance of the electrolytes. Single cells based on novel electrolytes are manufactured and electrochemical properties are evaluated. A standard electrolyte and electrolyte supported cell are also fabricated as a base case for comparison. Although the electrolyte having triangular patterns has the highest peak power at all operation temperatures considered, it exhibits the lowest flexural strength. (c) 2012 Elsevier Ltd and Techna Group S.r.l. All rights reserved.
Engineering solid oxide fuel cell electrode microstructure by a micro-modeling tool based on estimation of TPB length
(Pergamon-Elsevier Science Ltd, 2021) Timurkutluk, Bora; Altan, Tolga; Toros, Serkan; Genc, Omer; Celik, Selahattin; Korkmaz, Habip Gokay
In this study, a typical solid oxide fuel cell (SOFC) electrode microstructure is numerically optimized in terms of the volume fraction of the catalyst, electrolyte and pore phases via a novel tool based on Dream.3D for the synthetic microstructure reconstruction and COM-SOL Multiphysics (R) Modeling for visualizing and computing three/triple phase boundaries (TPBs). First, the properties of the representative volume element are studied by a parameter independence analysis based on the average particle size. The results indicate that the size of the representative volume element should be at least 10 times greater than the largest average particle size in the microstructure, while the number of mesh elements should be selected such that the smallest average particle size in the system is divided into at least 5. The method is then validated with the available studies in the literature and seems to agree well. Therefore, numerical reconstruction of SOFC electrodes by the pro-posed method is found to be a very useful tool in the viewpoints of accuracy, flexibility and cost. Finally, SOFC electrode microstructures having the same particle size distribution of an average particle size of 0.5 mm for each phase but with various phase volume fractions are generated and the resultant TPBs are computed similarly. It is found out that the volume fraction of each phase should be close to each other as much as possible to maximize the active TPB density and among the cases considered, the highest active TPB density of 9.53 mm/mm(3) is achieved for an SOFC electrode including 35 vol% catalyst, 35 vol % electrolyte and 30 vol% porosity. The active TPB density is also found to be around 93% of the total TPB density. (C) 2021 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.
Estimation of microscale redox tolerance for Ni-based solid oxide fuel cell anodes via three-dimensional finite element modeling
(Pergamon-Elsevier Science Ltd, 2023) Altan, Tolga; Celik, Selahattin; Toros, Serkan; Korkmaz, Habip Gokay; Timurkutluk, Bora
Reduction-oxidation (redox) cycles of Ni-based anodes in solid oxide fuel cells (SOFCs) directly affect the cell performance due to breaking anode three/triple phase boundary (TPB) networks at microscale. Furthermore, these microcracks accumulate with the number of redox cycles leading to mechanical damage in the cell as a result of continuous volumetric changes during the inevitable cyclic reduction and oxidation of the nickel oxide and nickel, threatening the service life of SOFC systems. Therefore, the redox process needs to be investigated as a phenomenon at microscale to understand and minimize its effects. In this regard, we suggest a microscale approach for the redox process of Ni-based SOFC anodes in this study. For this purpose, SOFC anode microstructures with different compositions and porosities are synthetically generated by Dream.3D software and me-chanical damages due to the redox cycle are investigated via element deletion through LS-DYNA for the first time in the literature. The anodes are characterized by computing the redox tolerance based on the resultant damage and the anode composition showing the highest redox tolerance is determined among the cases considered.(c) 2022 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.
EVALUATION OF TENSILE PROPERTIES OF HIGH STRENGTH STEELS AT WARM TEMPERATURES AND VARIOUS STRAIN RATES
(VERLAG STAHLEISEN MBH, 2008) Ozturk, Fahrettin; Toros, Serkan; Bas, M. Hakan; Kilic, Suleyman
The use of advanced high strength steels in automotive industry has been increased recently. Dual-phase (DP) high-strength steel, which is an advanced high strength steel, has gained great attention due to its high strength and good formability. In this study, uniaxial tensile deformation of DP600 and DP800 advanced high strength steels were studied at temperatures between room temperature (RT) and 300 degrees C and at strain rates between 0.008 s(-1) and 0.16 s(-1). Results indicate that the formability of the materials is lower after the testing at 200 degrees C and 300 degrees C than the testing at RT. Moreover, the formability decreases with the increasing strain rate. Finally, the forming should be done at RT and low strain rates to get good formability.
Evaluation of tensile properties of high strength steels at warm temperatures and various strain rates
(Wiley-VCH Verlag, 2008) Ozturk, Fahrettin; Toros, Serkan; Hakan Bas, M.; Kilic, Suleyman
The use of advanced high strength steels in automotive industry has been increased recently. Dual-phase (DP) high-strength steel, which is an advanced high strength steel, has gained great attention due to its high strength and good formability. In this study, uniaxial tensile deformation of DP600 and DP800 advanced high strength steels were studied at temperatures between room temperature (RT) and 300 °C and at strain rates between 0.008 s-1and 0.16 s-1. Results indicate that the formability of the materials is lower after the testing at 200 °C and 300 °C than the testing at RT. Moreover, the formability decreases with the increasing strain rate. Finally, the forming should be done at RT and low strain rates to get good formability. © 2008 Verlag Stahleisen GmbH, Düsseldorf.

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