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Öğe Corrosion response of ultra-high strength steels used for automotive applications(Iop Publishing Ltd, 2019) Gerengi, Hüsnü; Şen, Nuri; Uygur, İlyas; Solomon, Moses M.The corrosion resistance properties of two ultra-high strength steels, Docol 1200 and 1400 were studied in 3.5 wt% NaCl solution using chemical and electrochemical techniques supported by surface characterization techniques namely scanning electron microscope (SEM), energy dispersive spectroscopy (EDX), atomic force microscope (AFM), and optical profilometer. The mechanical properties of both Docol 1200 and Docol 1400 uncorroded and corroded were determined by tensile test. Results obtained reveal that the two alloys exhibit similar mechanical properties. Corrosion has effect on the mechanical properties of the alloys. Corrosion studies reveal that both Docol 1200 and 1400 are prone to corrosion in NaCl environment. A corrosion rate of 30.6 mpy and 49.6 mpy was recorded for a Docol 1200 at 25 degrees C and 60 degrees C, respectively. For Docol 1400, the corrosion rate obtained at 25 degrees C and 60 degrees C was 32.7 mpy and 52.4 mpy, respectively. Docol 1200 is adjudged to exhibit superior corrosion resistance property than Docol 1400. The optical profilometric results disclose that Docol 1200 and Docol 1400 suffered pitting corrosion in NaCl solution. Pitting corrosion was more severe with Docol 1400 than 1200.Öğe Development of car wishbone using sheet metal tearing process via the theory of inventive problem-solving (TRIZ) method(Springer Heidelberg, 2019) Şen, Nuri; Baykal, YakupIn the automotive industry, sheet metal forming process design is of great importance. The cold forming process in particular is the most widely preferred of these methods. In the production of car parts in complex forms, forming problems such as tearing, wrinkling, back spring and unwanted thinning can appear. Recently, numerical analysis technology and software tools have been widely used in process design and metal forming. Elimination of these problems without the use of analysis programs means the use of the trial and error method, which results in much wasted time and huge costs. In addition to the use of analysis programs, resolving problems without mold process and design knowledge is also problematic. In this study, the theory of inventive problem-solving (TRIZ) approach was utilized to reach an analytical solution. In this methodology, the improving and worsening features were determined and a TRIZ 39 x 39 contradiction matrix was created which led to the solutions. Virtual experiments were carried out on a wishbone mold model designed via the Siemens NX 12 CAD program using the Autoform R7 analysis program. Real environment experiments were then performed, and the problem of tearing during the forming process was eliminated. The measured thickness value of this area, which was formed without tearing, was measured as 2.7 mm in the virtual environment experiments and 2.9 mm in the real environment experiments. In addition, the wishbone was subjected to two-axis (x and z) dynamic testing, with acceptable values reached at 500,000 cycles.Öğe DP600 Çeliğine Uygulanan Kesme ve Hassas Kesme İşleminin Sonlu Elemanlar Yöntemi Kullanılarak İncelenmesi(2020) Helimergin, Fatih; Şen, NuriOtomotiv sanayii başta olmak üzere, metal şekillendirme işlemlerinin yapıldığı sektörlerde kesme işlemi yoğunbir şekilde kullanılmaktadır. Kesme işleminden sonra gerçekleştirilen form verme işleminde istenmeyenyırtılmalar oluşmaktadır. Bu oluşumlar kesme işlemi tamamlandıktan sonra oluşan ve istenmeyen mikro ve makrodüzeyde çatlaklardan kaynaklanmaktadır. Bu çalışmada, kesme işleminde oluşan çatlakları minumum seviyeyeindirmeye çalışılmıştır. Soğuk şekillendirme esnasında malzemede oluşan mikro ve makro boyuttaki çatlaklarıönlemek için her geçen gün kullanımı artan hassas kesme yönteminin önemini simufact forming V16 sonluelemanlar yöntemi (SEY) programı kullanılarak sanal ortamda hem kesme hem de hassas kesme yöntemi deneylerigerçekleştirilmiştir. Deneylerde, yüksek mukavemetli çeliklerden olan 1 mm kalınlığındaki çift fazlı DP600 sacmalzeme kullanılmıştır. Sanal ortam deneylerinde kullanılan malzemeye ait akma noktası, çekme dayanımı, %uzama değerleri çekme testlerinden elde edilmiştir. Çalışmada ayyıldız figürlü kalıp tasarlanmış ve sanal ortamdeneyleri gerçekleştirilmiştir. Deneyler sonucunda kesme yönteminin ve hassas kesme yönteminde kullanılanfarklı yükseklikteki v çentikli baskı bileziğinin malzemede meydana getirdiği gerilme, kavislenme genişliği vederinliği, çapak yüksekliği değerleri incelenmiştir. Ayrıca v çentikli baskı bileziği hassas kesmedeki önemi ortayakonmuştur.Öğe DP600 Malzemenin Şekillendirilmesinde Değişken Baskı Plakası Kuvveti Etkisinin Sonlu Elemanlar Yöntemiyle Araştırılması(2018) Şen, NuriOtomotiv üreticileri hem ağırlık/dayanım oranının düşürülmesinde hem de çarpışma anında daha mukavemetliaraçları üretmek için ultra yüksek mukavemetli malzemelerin kullanım oranını gittikçe artırmaktadır. Buçalışmada, ultra yüksek mukavemetli DP600 malzemesi için sonlu elemanlar yöntemi kullanılarakşekillendirebilirlik analizi yapılmıştır. Kalıp tasarımı yapılarak belirli bir geometride ve başlangıçta 1 mmkalınlığındaki sac malzeme için sanal ortamda hem sabit hem de değişken baskı plakası kuvvetlerinde derinçekme işlemi uygulanarak malzemenin oda şartlarında her iki farklı yöntem için sınır çekme oranı belirlenmiştir.Derin çekme analizleri sonucunda değişken baskı plakası kuvveti kullanılarak sınır çekme oranı 2,07’den2,12’ye yükseldiği tespit edilmiştir.Öğe Effect of Different Conical Punch Angle Geometries and the Initial Hole Diameters on the Hole Expansion Ratio of DP steels(Society of Automotive Engineers Turkey, 2022) Şen, Nuri; Civek, Tolgahan; Bektaş, N.In the recent decade, advanced high strength steels (AHSS) have gained a great popularity in the automotive manufacturing industries due to their high strength to weight ratio, which significantly improves the safely of the manufactured automobiles while reducing the weight and thus, enabling to improve the fuel efficiency. However, it is known that some types of AHSSs, especially DP steels, are highly susceptible to edge cracking behaviour during the forming operations. Edge cracking behaviour is generally investigated with a 600 conical punch as suggested by the ISO 16630 standard. However, in mis study, to observe the behaviour of edge cracking ability of DP steels under different conical punch angles for different initial hole diameters, hole expansion tests have been performed with conical punches with three different angles (300 ,600 and 900) for three different initial hole diameters (14, 16 and 18 mm). The results have shown that the hole expansion ratio (HER) does not differ considerably with the variation of the conical punch angle and the initial hole diameter due to low fracture strain of DP steels observed after hole expansion tests. The major factor for the edge stretching ability of DP steels have been observed to be microstructure rather than geometrical factors such as conical punch angles. © 2023. Multidisciplinary Science Journal. All rights reserved.Öğe Experimental research on warm deep drawing of HC420LA grade sheet material(Springer London Ltd, 2016) Şen, Nuri; Karaağaç, İbrahim; Kurgan, NaciThe use of high-strength sheet material applications in the automotive industry has become widespread due to their high strength/weight ratios. The formability, however, of these high-strength sheet materials is limited at room temperatures (RTs). In this study, the first of its kind to be conducted, experimental research was performed on the formability of HC420LA grade sheet material using the warm deep drawing (WDD) method. Temperature control is the most important parameter in WDD. In this method, a new temperature control system was designed and manufactured to increase the formability of HC420LA grade sheet material. The limiting drawing ratio (LDR) for a 1.2-mm sheet thickness of HC420LA grade sheet material, which is 2.14 at RT, increased to 2.47 after applying this method. For a 1.5-mm sheet thickness of HC420LA, LDR, which is 2.15 at RT, increased to 2.59 after applying this method. Percent increases of the drawing ratios for 1.2 and 1.5 mm thicknesses were 15.42 and 20.45 %, respectively. A maximum reduction of 15 % in thickness was obtained in formed cups. Lastly, the microstructures of the warm cup's punch corner region and wall and bottom regions were investigated under an optical microscope. The results showed whether any changes occurred in the microstructures and mechanical properties.Öğe Geri Dönüşümü Yapılmış PP ve ABS Prototip Malzemelerin Bazı Mekanik ve Termal Özelliklerinin İncelenmesi(2020) Şen, Nuri; Şengül, Ömer; Uygur, İlyasPolimer malzemelerden üretilen ürünlerin tüketim miktarları ve tüketim artış hızları gün geçtikçe artmaktadır. Buplastik malzemeler, uzun süre doğada çözünemeyeceğinden dolayı çeşitli kirlilikleri de beraberinde getirmektedir.Ayrıca hemen hemen tüm polimer esaslı ürünler sınırlı kaynak olan petrolden üretilmektedir. Bu nedenle plastikmalzemelerin geri dönüşümü ve geri dönüşümü yapılmış malzemelerin özelliklerinin tespit edilmesi büyük önemarz etmektedir. Bu çalışmada birincil geri kazanım yöntemi kullanılarak atık plastiklerden ve orijinal polimermalzemelerden elde edilebilecek ürüne yakın eş değerde ürün elde etmek amaçlanmıştır. Bu çalışmada, orijinalpolipropilen (PP) ve Akrilonitril Bütadin Stiren (ABS) malzemesinden MA/G serisi enjeksiyon makinesi ile üçkez geri dönüşümü yapılmış (PP) ve ABS malzeme üretimleri gerçekleştirilmiştir. Üretimi yapılan prototipmalzemeler üzerinde; Isı Deformasyon testi (HDT), Eriyik akış endeksi (MFI), Izod Darbe Testi, Çekme Testi veSertlik (Shore-D) testleri yapılarak termal ve mekanik özelliklerindeki değişmeler deneysel olarak incelenmiştir.Sonuç olarak, geri dönüşümü yapılmış PP ve ABS numunelerin termal özelliklerinde yaklaşık %30 iyileşme,mekanik özelliklerde yaklaşık %50 azalma gözlenmiştir.Öğe Investigation of deep drawing of square cups using high-strength DP600 and DP800 sheets(2021) Şen, Nuri; Taşdemir, Vedat; Çolakoğlu, İsaThis study investigated the deep drawing of square cups using high-strength du-al phase DP600 and DP800 sheets via both experimental and finite element meth-ods. The limiting drawing ratio (LDR) and wall thickness distribution were exam-ined. The initial thickness of the materials used in the study was equal to 1-mm. The experiments were carried out at room temperature using both Teflon film and graphite spray lubricants at the same time. In terms of LDR, both experimental and numerical results corresponded with each other. A ratio of 1.97 LDR was reached for the DP600 steel and 1.92 LDR for the DP800. Given that the thick-ness distribution between the experimental and numerical results, an accord of over 90% was noticed. For the DP600 steel, the lowest experimental thickness value was 0.864 mm and the lowest numerical value was 0.87 mm. For the DP800 steel, the lowest experimental thickness value was measured to be 0.89 mm while the lowest numerical value was found to be 0.88 mm. In the conclusion, the pre-sent paper proves that the experimental results in the deep drawing of square cups can be achieved with very satisfying results by using numerical methods.Öğe Investigation of formability of HC380LA material via the TPIF-RL incremental forming method(Taylor & Francis Ltd, 2019) Şen, Nuri; Taşdemir, Vedat; Seçgin, ÖmerPrototype parts can be produced rapidly and at low cost using the incremental forming method. The most important problem with this method is that it causes undesirable variations in wall thickness. Various methods have been developed to improve the wall thickness distribution of the part resulting from forming. One of these techniques, the rolling blank holder (TPIF-RL) method, was used in this study to form 1 mm-thick HC380LA sheet. The Taguchi experimental design was used to determine optimum levels of each of the parameters (forming force, surface roughness and wall thickness) separately via signal/noise analysis. Gray Relational Analysis was then performed to determine the parameters that optimize surface roughness and wall thickness together. In the study, it was determined that the use of low pressing force increases the wall thickness. As a result, a 6% increase in wall thickness was achieved by using the optimum parameters.Öğe Kayar baskı plakalı artımlı sac şekillendirme yöntemiyle şekillendirilen Erdemir 7136 sacının geri esneme davranışının araştırılması(2021) Taşdemir, Vedat; Şen, Nuri; Seçgin, ÖmerArtımlı şekillendirme yöntemi ile kalıp imalatına ihtiyaç duyulmadanhızlı ve düşük maliyetli prototip parça üretimi yapılabilmektedir. Ancakbu yöntemdeki en önemli sorunlardan bir tanesi üretilen parçalarıngeometrik doğruluğudur. Geometriksel hatanın en büyük kaynağı isegeri esneme olayıdır. Bu çalışmada, kayar baskı plakalı artımlı sacşekillendirme metodu kullanılarak 1 mm kalınlığındaki Erdemir 7136sacı şekillendirilmiştir. Klemp sıkma (sacı tutma) basıncı, artım miktarı,form takım çapı ve ilerleme hızı parametrelerinin geri esnemeye olanetkileri araştırılmıştır. Araştırma neticesinde geri esneme açısınıntakım çapı arttıkça büyüdüğü, ilerleme hızı ve artım miktarının artmasıile düştüğü tespit edilmiştir. Çalışma kapsamında optimum parametredeğerleri 5.8776 bar klemp sıkma basıncı, 1500 mm/dk. ilerleme hızı,0.75 mm artım miktarı ve 5 mm takım çapı olarak belirlenmiştir.Öğe Mechanical properties of ultra-high-strength steels at elevated temperatures(Taylor & Francis Ltd, 2019) Şen, Nuri; Durucan, Gökhan; Elkoca, Oktay; Uygur, İlyasThis paper presents an experimental study on the mechanical properties of ultra-high-strength steels at elevated temperatures. Tensile tests were carried out at 300-600 degrees C on Docol 1200M and Docol 1400M steel samples. The results indicate that as the temperature increases Young's Modulus, yield strength (YS) and ultimate tensile strength (UTS) display a decrease. YS/UTS ratios at 300 degrees C are lower than those at room temperature, they make peaks at 400 and 500 degrees C for Docol 1400M and Docol 1200M, respectively, and then decrease again beyond those temperatures. While total elongation continuously increases, uniform elongation slightly decreases with increasing temperature. Present carbides in tempered matrix continue to grow and new carbides are observed at the grain boundaries. Considering all roll forming parameters, 300 degrees C seems the most convenient temperature for warm forming. In this sense, the warm roll forming has a potential for forming complex-shaped parts by reconciling strength with formability.Öğe A review on devulcanization of waste tire rubber(International University of Sarajevo, 2018) Gürsel, Ali; Akça, Enes; Şen, NuriRubber has become an indispensable material for the technological development of civilization, including simple balloon and complex rocket propellant. Rubber Industry worldwide is using on an average 50% of raw materials. These materials were mostly petroleum-based, except natural rubber (NR), steel cord and bead wire. Using of these petroleum-based raw materials not only depletes natural resources, but also produces more extreme environmental hazards. The waste tire rubber problem is of great magnitude and has far reaching environmental and economic implications. There are some ways for recycling of rubber, such as reclaiming technology, surface treatment, grinding and pulverization technology, devulcanization technology. Methods of devulcanizing rubber (or elastomers) have been researched almost since the time of the discovery of the rubber/sulfur vulcanization process. By devulcanization process the cross-links in the structure of rubber are broken and devulcanized rubber can be revulcanized into a raw material for rubber industry, which is a highly valued form of waste rubber. This study provides a review of the recent advances in understanding of methods of recycling rubber and claims that the capacity of thermomechanical and mechanochemical devulcanization methods of recycling waste tire rubber can be improved in future studies. © 2018 International University of Sarajevo.
