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Article Strain Hardening Behavior Characterization of Dual Phase Steels(2018) Davut, Kemal; Şimşir, Caner; Çetin, BarişThe requirements for higher passenger safety, improved fuel economy and weight reductionin automobile industry necessitates the usage of advanced high strength steel (AHSS)grades. Dual phase (DP) steels are the most widely used one among AHSS. DP steels becomeincreasingly popular, since they provide a combination of sufficient formability at room temperatureand tensile strength over 1000 MPa. The current standards for DP steels only specifiesyield and tensile strength. Steels from various producers have considerably different compositionand microstructure; however they still have the same grade name. Combined withthe inherited heterogeneous microstructure, those steels exhibit different strain hardeningbehavior. The aim of this study is to evaluate the strain hardening behavior of DP800 steels,obtained from different vendors and thus having different compositions and microstructures.The strain hardening behavior was characterized with tensile tests performed along rollingand transverse directions. The microstructure has been characterized with optical andscanning electron microscopes. The martensite fraction, grain size of ferrite and chemicalcomposition has been correlated to the strain hardening behavior. The results show thatthe steel with more micro-alloying addition has finer ferritic grain size, which cause higherinitial strain hardening rate. The steel with higher Mn and Cr has higher martensite fraction,which cause strain hardening rate to be higher at higher strain levels.Article Production of 20 Mm Thick Api Psl 2 X60 and X70 Grade Plates From a Nb-Ti Microalloyed Steel(2020) Konca, ErkanThis study was undertaken to determine the controlled rolling and cooling conditions for the production of 20 mm thick American Petroleum Institute (API) X60 and X70 grade steel plates. Nb-Ti microalloyed steel slabs of 200 mm thickness were rolled at fourdifferent finish rolling temperatures (conventional, 950°C, 850°C and 800°C). In some trials, a water table was employed to provide accelerated cooling just after finish rolling. Mechanical tests (tensile, impact and drop weight tear-DWTT) and microstructural examinations were performed on the samples taken from the trial production plates. Fine grainedand essentially ferritic microstructures with strength values satisfying the minimum yieldstrength requirement of 415 MPa for the API X60 grade were easily obtained in all rollingconditions. However, the minimum yield strength requirement of 485 MPa for the APIX70 grade was reached only when accelerated cooling was applied after finish rolling. Theminimum 85% shear fracture required by the DWTT of the API PSL 2 specification couldbe met when the finish rolling temperature was lowered or when accelerated cooling wasapplied regardless of the finish rolling temperature.Article Design and Manufacturing of a Pin on Disk Tribometer(2024) Küçüköztaş, Korcan; Nassar, Mohammed; Kaftanoğlu, Bilgin; Talay, İlker; Çalışkan, Fatih; Elsakka, Mustafa A.A.This paper presents the design and manufacturing of a pin on disk tribometer aimed at performing friction and wear testing as accurate as a professional tribometer at a lower cost. Since friction is an important part of our lives and its application varies greatly in size, environment and other factors, testing can be expensive. Tribometers are instruments where these conditions can be simulated experimentally. They are manufactured by various companies abroad and are imported to Turkey. For this reason, the cost of these instruments is very high. The design of the manufactured tribometer prioritizes portability and low cost of manufacturing. The manufacturing process of the various parts are discussed in detail. The tribometer was manufactured in the ATILIM University manufacturing laboratories within a tight budget using CNC machining. The instrument has the full capability to adjust the load, testing radius, motor speed, and the duration of the test before starting the experiments. To handle the electronics and data gathering within the instrument, Arduino boards and software are utilized. Real-time data streaming is made possible for data analysis tasks both during and after the experiments. The paper also provides the results of experiments that are obtained from the newly developed tribometer and comparisons with a mass produced, professional tribometer. The experiments are conducted with the same type of samples and with the same parameters. The manufactured tribometer provides researchers with easily accessible friction data that is within close range to what they would get from a professional tribometer.Article Kristal Plastisite Modellemesi ile Inconel 718 Alaşımının İşlenmesinde Artık Gerilmelerin Doğru Tahmini(2023) Kesriklioğlu, Sinan; Kapçı, Mehmet Fazıl; Buyukcapar, Ridvan; Çetin, Barış; Yılmaz, Okan Deniz; Bal, BurakArtık gerilmelerin belirlenmesi ve değerlendirilmesi, savunma, havacılık ve otomotiv endüstrilerinde kullanılan bileşenlerin arızalanmasını önlemede çok önemlidir. Bu çalışmanın amacı, Inconel 718'in işlenmesi sırasında oluşan artık gerilmeleri doğru bir şekilde tahmin etmek için bir malzeme modeli sunmaktır. Ortogonal talaşlı imalat testleri, çeşitli kesme ve ilerleme hızlarında gerçekleştirilerek, Inconel 718'in işlenmesinden sonraki artık gerilmeler, X-Ray ışın kırınımı ile karakterize edildi. Bu süper alaşımın mikroyapısal girdilerini ticari olarak temin edilebilen bir sonlu eleman yazılımına (Deform 2D) aktarmak için bir viskoplastik kendi içinde tutarlı kristal plastisite modeli geliştirildi. Ayrıca simülasyonlar klasik Johnson - Cook malzeme modeli ile aynı işleme parametrelerinde yapıldı. Bu çalışmada elde edilen simülasyon ve deneysel sonuçlar, kristal plastisite tabanlı çok ölçekli ve çok ölçekli malzeme modelinin, mevcut modele kıyasla Inconel 718'in işleme kaynaklı kalıntı gerilmelerinin tahmin doğruluğunu önemli ölçüde geliştirdiğini ve yüzey kusurlarını en aza indirmek için kullanılabileceğini göstermiştir. Geliştirilen bu model, kesilmesi zor malzemelerin işlenmesinde yüzey kusurlarını ve üretim denemelerinin maliyetini en aza indirmek için kullanılabilir.Article Microstructural Analysis of Austempered Ductile Iron Castings(2016) Çetin, Barış; Meco, Halim; Davut, Kemal; Arslan, Ebru; Uzun?, Mustafa CanAustempered ductile iron (ADI) castings have a wide range of application areas in engineering designs due to their promising mechanical properties and lower cost. ADI has very good strength and toughness values at the same time its ductility is relatively high compared to most of the other cast irons. These promising mechanical properties originate from combination of specific graphite and matrix microstructure. The size, shape and fraction of graphite as well as the matrix microstructure influences the mechanical properties. In this paper the efforts regarding to a localization project of ADI is presented. In a more detailed manner, the first locally produced ADI which cannot satisfy the mechanical properties stated in ISO 17804 is compared with the original sample which is conform with the standard. The two pieces are inspected by mechanically and microstructurally by means of which necessary actions are detected for the local production. In other words the relation between the macro mechanical properties and the microstructural conditions are tried to be clarified.
