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Öğe 3D microstructural finite element simulation of martensitic transformation of TRIP steels(Brazilian Association of Computational Mechanics, 2018) Toros S.; Öztürk F.In this paper the effects of deformation modes on martensitic transformation for TRIP steels which are composed of Ferrite, Bainite and Retained austenite are investigated in the view of the microstructural level. For this porpose the simulations are run for a synthetically generated microstructure which have 55% Ferrit, 35% Bainite and 10% Retained austenite. In the simulations tensile, biaxial and shear type deformation modes are considered. The results reveal that biaxially loaded microstructure has the maximum amounts of martensite phases at the end of the given deformation and the less martensite is occurred in the shear type loading condition. © 2018 Brazilian Association of Computational Mechanics. All rights reserved.Öğe Determination of formability characteristics of Crofer 22 APU sheets as interconnector for solid oxide fuel cells(Elsevier Ltd, 2018) Timurkutluk B.; Toros S.; Onbilgin S.; Korkmaz H.G.In this study, the general formability characteristics of Crofer® 22 APU sheets of different thicknesses (0.2 mm–1.0 mm) are experimentally investigated via tensile, out of plane, Erichsen, cupping and springback tests for a possible application for solid oxide fuel cells in sheet form unlike the conventional bulk form. Holloman equation is also used to fit the experimental stress-strain curves and the anisotropic behavior of the material is considered by determining Lankford parameters. The tensile test results show that the formability is about 0.29 mm/mm for 0.2 mm thick sheets, indicating the suitability of these sheets for the fabrication of interconnectors by a stamping process with desired channel geometry having dimensions similar to conventional channel dimensions. In addition, for a specific combination of process parameters such as blank holder force and lubrication, the formability can be enhanced as proven by Erichsen and cupping test results. Moreover, the formability is found to increase with increasing the sheet thickness and highly anisotropic behavior is observed. In three point bending tests, the negative springback behavior, namely spring-in, is surprisingly observed for a relatively narrow shoulder distance at all thicknesses and set angle values (? = 90°–120°). © 2018 Hydrogen Energy Publications LLCÖğe Evaluation of anisotropy by two different tests for TRIP800 steel(Trans Tech Publications Ltd, 2014) Ozturk F.; Toros S.; Kilic S.; Kacar I.For the process modeling, material properties such as anisotropy values at different orientation are very important. The most commonly used method for the determining of the anisotropy values is the tensile test that is performed for samples are prepared at different orientation. Besides the tensile test, the anisotropy parameters of TRIP 800 steel are measured with the hole-expansion test. The effects of the test methods on the yield surfaces are determined for using two different anisotropic yield criteria are Hill-48 and Barlat-89. Results illustrated that a significant difference is observed in the yield surfaces for the two test methods. The material under biaxial deformation is deformed plastically faster than the uniaxial deformation mode. © (2014) Trans Tech Publications, Switzerland.Öğe Experimental Research and Mathematical Modeling of Parameters Effecting on Cutting Force and SurfaceRoughness in CNC Turning Process(Institute of Physics Publishing, 2018) Zeqiri F.; Alkan M.; Kaya B.; Toros S.In this paper, the effects of cutting parameters on cutting forces and surface roughness based on Taguchi experimental design method are determined. Taguchi L9 orthogonal array is used to investigate the effects of machining parameters. Optimal cutting conditions are determined using the signal/noise (S/N) ratio which is calculated by average surface roughness and cutting force. Using results of analysis, effects of parameters on both average surface roughness and cutting forces are calculated on Minitab 17 using ANOVA method. The material that was investigated is Inconel 625 steel for two cases with heat treatment and without heat treatment. The predicted and calculated values with measurement are very close to each other. Confirmation test of results showed that the Taguchi method was very successful in the optimization of machining parameters for maximum surface roughness and cutting forces in the CNC turning process. © Published under licence by IOP Publishing Ltd.Öğe Geometric optimization of an ejector for a 4 kW SOFC system with anode off-gas recycle(Elsevier Ltd, 2018) Genc O.; Toros S.; Timurkutluk B.One of the important energy saving tools used in solid oxide fuel cell (SOFC) system is the anode off-gas recycling (AGR) via an ejector which allows the recirculation of the unused fuels in the anode exhaust gas including hot steam which is essential for the elimination of the carbon deposition and the initiation of the reactions in the reformer. In an ejector system developed for the SOFCs, the steam to carbon ratio (STCR) and entrainment ratio are the crucial parameters for the determination of the ejector performance. These parameters can be engineered by modifying the geometric dimensions and operation conditions. This study focuses on the determination of the maximum STCR value and entrainment ratio via numerical geometric analyses for a micro combined heat and power (µ-CHP) system based on 4 kW SOFC, utilizing methane. A detailed numerical procedure for designing an ejector is provided and the ejector performance is investigated for different critical dimensions (throat diameter, nozzle exit angle and nozzle position etc.). The results show that the nozzle position and the nozzle exit angle significantly affect STCR and the entrainment ratio. When the nozzle position increases and nozzle exit angle decreases, the entrainment ratio and STCR is found to increase. The entrainment ratio and STCR are determined as around 7.3 and 2.7, respectively for a specific design created in the study. © 2018 Hydrogen Energy Publications LLCÖğe Influence of sintering support design on the properties of NiO-YSZ anode support micro-tubes(Elsevier Ltd, 2018) Timurkutluk B.; Timurkutluk C.; Toros S.; Kaplan Y.The effects of the sintering support design on the microstructural and mechanical properties of NiO/YSZ anode support micro-tubes are investigated in this study. For this purpose, a number of micro-tubes of the same geometrical properties are fabricated via extrusion method from the same extrusion paste. The micro-tubes are then sintered at the same temperature on sintering plates with different C- and V-type sintering channels designed. The micro-tubes after sintering are found to have similar geometric properties. However, the microstructural investigations and three point bending tests indicate that the microstructural properties of the micro-tubes are strongly influenced by the sintering plate design. As a result, the flexural strength of the micro-tubes are found to be different. Among the cases considered, the micro-tubes of V2 (half of the micro-tube is initially in the V-type channel) and V4 (whole micro-tube is initially in the V-type channel) design provide relatively fine microstructure and thus relatively higher flexural strength values at a reliability of 80%. The flexural strengths of these micro-tubes are also found to be more consistent. © 2017 Elsevier Ltd and Techna Group S.r.l.Öğe Investigation of Hydro-piercing Method for Stainless Steels by Finite Element Method(EDP Sciences, 2018) Gökay Korkmaz H.; Toros S.; Halkaci M.; Halkaci H.S.Researches and studies on hydroforming process, which is a method that is getting more and more popular every day thanks to its many advantages in application, are ongoing. It is possible to pierce-the holes on a tube or sheet hydroformed part using hydropiercing method after the forming operation. In this study, hydropiercing process of a 304 stainless steel is simulated via the LS-Dyna in 2D axial symmetry model. In the simulations two types of punch movement was investigated to determine the contribution to the burr formation. In the simulations, Jonson-Cook hardening and damage model were used to determine the initiation of the crack on the samples. As a result, the burr formation can be eliminated by the two step movement of the punch through the piercing operation. © The Authors, published by EDP Sciences, 2018.Öğe Numerical optimization of channel to land width ratio for PEM fuel cell(Elsevier Ltd, 2018) Chowdhury M.Z.; Genc O.; Toros S.Flow field plays a vital role in proton exchange membrane (PEM) fuel cell where channel geometry being the primary factor. Most of the channel geometry analyses were limited to few number of case studies, whereas in this study total 73 case studies were analyzed for the optimization of channel and land width. A three dimensional isothermal single phase flow mathematical model is developed and further validated with experimental study to optimize the channel and land width through parametric sweep function for a staggering 73 number of case studies. The optimization analyses are carried out for a straight channel geometry considering a fixed operating voltage of 0.4 V and channel depth of 1.0 mm. Due to the large number of case studies, the analyzed performance parameters i.e. current density and pressure drop are easily understandable for the change in different channel and land width. The numerical results predicted that the pressure drop is more dependent on channel width compare to the land width and anode pressure drop is less significant than cathode pressure drop. However, both channel and land width have an equal importance on the cell current density. Considering channel pressure drop and current density, the optimization analyses showed that the channel to land width of 1.0 mm/1.0 mm would be best suitable for PEMFC channel geometry. © 2017 Hydrogen Energy Publications LLCÖğe Springback evaluation of 5052-H32 aluminum-magnesium alloy(Hanrimwon Publishing Co., 2008) Alkan M.; Ozturk F.; Toros S.; Kilic S.Springback is one of the most common problems in sheet metal forming operation. It causes improper fit which creates serious problems during assembly of the parts. Based on material strength, a considerable elastic recovery during unloading can be observed. In the present study, the springback evaluation of 5052-H32 aluminum magnesium alloy sheets with a thickness of 1.5 mm was investigated using 60o angle V-shape die at several temperatures range of room to 300°C and strain rate range of 25-625 mm/min. Although the springback of the material was increased with increasing the temperature up to 200°C, it was decreased for all deformation speeds at 300°C. Bending force of the material was not changed with deformation speeds except for 300°C. The bending force was obtained at 625 mm/min is higher than the other deformation speeds. The best bending condition of this material was obtained at 300°C and 25 mm/min.Öğe Strain rate sensitivity and strain hardening response of DP1000 dual phase steel(EDP Sciences, 2018) Çavusoglu O.; Gürün H.; Toros S.; Güral A.In this study, strain hardening and strain rate sensitivity behavior of commercial DP1000 dual phase steel have been examined in detail at temperatures of 25 °C, 100 °C, 200 °C and 300 °C, at strain rates of 0.0016 s -1 and 0.16 s -1 . As the strain rate has increased, the yield strength has increased but no significant change in tensile strength and strain hardening coefficient has been observed. As the temperature has increased, the yield and tensile strength has decreased in between 25 and 200 °C but it has showed an increase at 300 °C. The strain hardening coefficient has increased in parallel with temperature increase. It has been seen that the strain rate sensitivity has not been affected by temperature. No significant difference in the hardening rate has appeared in between 25 and 200 °C, but the highest value has been calculated at 300 °C. It has been determined that the fracture behavior has occurred earlier and load carrying capacity on necking has reduced with the increase of strain rate and not significantly affected by temperature. © 2018 EDP Sciences.Öğe The effects of temperature and strain rate on yielding and springback behaviour of DP1000 dual phase steel(Institute of Physics Publishing, 2019) Çavuşoglu O.; Toros S.; Gürün H.This study aims to investigate the effects of the temperature and strain rate on the yielding and springback behavior of DP1000 advanced high strength steel. For this purpose, material properties were defined using tensile tests at several temperatures (25 °C, 100 °C, 200 °C) and strain rates (0.0083 s -1 , 0.16 s -1 ). Yield loci were estimated by using Barlat-89 yield criteria. Springback behavior is specified by performing V bending tests. No significant effect was observed in the assessment of the effect of temperature on the yield locus and springback. Moreover, it was found that the increase in strain rate increased dramatically the yield locus and springback. © 2018 IOP Publishing Ltd.
