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3. Corrosion behavior of SiC and FeCrC reinforced AISI 304 components fabricated by plasma wire arc additive manufacturing (P-WAAM).

Author

Bayar, İsmail, Öteyaka, Mustafa Özgür, Çakir, Ersin, and Ulutan, Mustafa

Abstract

Wire arc additive manufacturing (WAAM) has recently been widely used to produce different materials. The present study fabricated AISI 304 stainless steel parts using the Plasma-WAAM (P-WAAM) method. FeCrC and SiC microparticles were added to enhance the corrosion properties of additive-manufactured (AM) AISI 304. The corrosion behaviors of the samples were studied in the 3.5 wt.% NaCl solution using electrochemical techniques. The results show that additively manufactured AISI 304 sample microstructure consisted of austenitic and δ-ferrite phases in the form of lathy and skeletal. The electrochemical results showed that the 304-WAAM sample open circuit potential (Eocp) was −180 mV and slightly more cathodic than the 304-NT sample. The Eocp decreased by 69 and 145 mV in the 304-FeCr and 304-SiC samples, respectively, compared to the 304-WAAM sample. The polarization resistance of the WAAM sample was triple compared to the reinforced with microparticles WAAM sample due to lower galvanic activity. In addition, the corrosion resistance was investigated by impedance technique, and it was found that the WAAM 304 without reinforcement had a better protective film with a larger semi-circle capacitive loop. [ABSTRACT FROM AUTHOR]

Published
2024
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4. Dolgu desenlerinin ve oranlarının ergiyik biriktirme modellemede PLA malzemesinin mekanik performansına olan etkisi.

Author

Kaya, Esad, Bayar, İsmail, and Akpınar, Ali Fuat

Abstract

In this study, the effect of Polylactic Acid (PLA) filament material and different filling ratios and filling patterns on its mechanical properties on tensile, compression and bending deformation behavior was investigated using the three-dimensional melt fused deposition modeling (FDM) method. In the research, parts were produced using triangular and triple-hexagonal patterns at 25%, 50%, 75% and 100% infilling ratios. The mechanical properties of the produced parts were evaluated by tensile, compression and three-point bending tests. The results show that mechanical properties increase in all test types with increasing infilling ratio. Optimum processes were determined by considering the mechanical properties of the selected production patterns and filling ratios. The results of mechanical tests were used to determine the best filling patterns and ratios. Samples produced with a triangular pattern and a 50% infilling ratio are predicted to exhibit optimal specific tensile strength; samples produced with a triple hexagonal pattern and a 50% infilling ratio are predicted to exhibit ideal specific compressive strength; and samples produced with a triple hexagonal pattern and a 75% infilling ratio are predicted to exhibit optimal specific bending strength. [ABSTRACT FROM AUTHOR]

Published
2024
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7. Detecting spam tweets using machine learning and effective preprocessing

Author

Alhajj R., Özyer T., Bayar, İsmail Erdem, Kardaş B., Alhajj R., Özyer T., Bayar, İsmail Erdem, and Kardaş B.

Abstract

ACM Special Interest Group on Knowledge Discovery in Data (SIGKDD);Elsevier;IEEE Computer Society;IEEE TCDE;Springer, 13th IEEE/ACM International Conference on Advances in Social Networks Analysis and Mining, ASONAM 2021 -- 8 November 2021 -- 176732, Nowadays, with the rapid increase in popularity of online social networks (OSNs), these platforms are realized as ideal places for spammers. Unfortunately, these spammers can easily publish malicious content, advertise phishing scams by taking advantage of OSNs. Therefore, effective identification and filtering of spam tweets will be beneficial to both OSNs and users. However, it is becoming increasingly difficult to check and eliminate spam tweets due to this great flow of posts. Motivated by these observations, in this paper we propose an approach for the detection of spam tweets using machine learning and effective preprocessing techniques. The approach proposes the advantages of the preprocessing and which of these preprocessing techniques are the most effective. To compare these techniques UtkML Twitter spam dataset is used in testing. After the most effective methods determined, the detection accuracy of the spam tweets will be better optimized by combining them. We have evaluated our solution with four different machine learning algorithms namely - Naïve Bayes Classifier, Neural Network, Logistic Regression and Support Vector Machine. With SVM Classifier, we are able to achieve an accuracy of 93.02%. Experimental results show that our approach can improve the performance of spam tweet classification effectively. © 2021 ACM.

Published
2022

9. Plazma tek ark katmanlı imalat yöntemi ile malzeme üretimi ve mekanik özelliklerinin araştırılması

Author

Bayar, İsmail, Ulutan, Mustafa, and ESOGÜ, Mühendislik Mimarlık Fakültesi, Makine Mühendisliği Anabilim Dalı

Subjects
Mikroyapı, Plazma Tel Ark Katmanlı İmalat, Wear, Malzeme Üretimi, Mekanik Özellikler, Aşınma, Mechanical Properties, Plasma Wire Ark Additive Manufacturing, Material Production, Microstructure
Abstract

Bu çalışma kapsamında plazma tel ark katmanlı imalat yöntemi (P-TAKİ) ve toz takviyesi ile oluşturulan özlü teller kullanılarak yeni bir uygulama ile kompozit malzeme üretimi gerçekleştirilmiştir. AISI 304 paslanmaz çelik ince borulara bor karbür, silisyum karbür ve ferrokrom karbür tozları takviye edilerek ve sade AISI 304 paslanmaz çelik tel kullanılarak malzeme üretimi gerçekleştirilmiştir. Bu malzemelerin mekanik özellikleri birbiri ile karşılaştırılmıştır. Toz takviyesinin mikroyapısı, çekme dayanımı, aşınma davranışı ve sertlik üzerine etkisi araştırılmıştır. Deneysel çalışmalarda sade AISI 304 tel malzeme, SiC ve FeCrC toz takviyeli teller kullanılarak P-TAKİ yöntemi ile düz duvar şeklinde kompozit malzemeler başarılı bir şekilde üretilmiştir. Üretilen bu malzemelerin mikroyapıları incelendiğinde boşluk, porozite ve çatlak görülmemiştir. B4C takviyeli malzeme üretiminde ise ilk katmanlarda makro çatlaklar oluştuğu için çalışmaya devam edilmemiştir. Deney sonuçlarına göre toz takviyesi sertlik ve aşınma direncini arttırmıştır, fakat SiC takviyeli malzemede çekme dayanımı istenildiği ölçüde iyileştirilememiştir. FeCrC takviyeli malzemede çekme dayanımı, sertlik ve aşınma direnci özelliklerinde sade AISI 304 P-TAKİ malzemesine göre oldukça iyi sonuçlar elde edilmiştir. Üretilen AISI 304 P-TAKİ malzemesinin çekme dayanımı, sertlik, aşınma direnci ve tokluk değerleri döküm AISI 304 malzemesine göre gelişme göstermiştir. En iyi çekme dayanımı 978,7±45 MPa değeri ile FeCrC takviyeli yatay numunesinde elde edilmiştir. En iyi aşınma direnci ve sertlik değeri ise SiC takviyeli malzemelerde elde edilmiştir. SiC takviyeli malzemenin aşınma direnci sade AISI 304 P-TAKİ malzemesine göre 25,2 kat daha iyidir In this study, the composite material was produced with a new application using the plasma wire arc additive manufacturing method (P-WAAM) and powder-reinforced flux-cored wires. The materials were produced by reinforcing AISI 304 stainless steel thin pipes with boron carbide, silicon carbide, and ferrochromium carbide powders and using only AISI 304 stainless steel wire. The mechanical properties of these materials have been compared with each other. The effect of powder reinforcement on microstructure characteristics, tensile strength, wear resistance, and microhardness have been investigated. In experimental studies, using the AISI 304, the SiC reinforced, and the FeCrC reinforced wires were successfully produced the composite materials in the form of walls. When the microstructures of these produced materials were examined, no voids, porosity, and cracks were observed. In the production of the B4C reinforced material, work was not continued as macro cracks occurred in the first layers. According to the results, the powder reinforcement increased the hardness and wear resistance, but the tensile strength of the SiC reinforced material was not improved enough. In the FeCrC reinforced material, very good results were obtained in tensile strength, hardness, and wear resistance properties compared to the AISI304 P-WAAM material. The tensile strength, microhardness, wear resistance, and toughness values of the AISI 304 P-WAAM material have improved compared to the cast AISI 304 material. The highest tensile strength was obtained with the value of 978.7 ± 45 MPa in the FeCrC reinforced horizontal sample. The greatest wear resistance and hardness values were obtained in SiC reinforced materials. The wear resistance of the SiC reinforced material is 25,2 times better than AISI 304 P-WAAM material

Published
2021

10. Plazma kaynak metodu ile özellikleri geliştirilmiş plazma püskürtme kaplamaların tribolojik davranışlarının incelenmesi

Author

Bayar, İsmail, Ulutan, Mustafa, and Makine Mühendisliği Anabilim Dalı

Subjects
Wear, Mechanical Engineering, Makine Mühendisliği
Abstract

Bu çalışmada, WC-Co, Cr3C2-NiCr ve Mo tozları AISI 8620 sementasyon çeliğinin yüzeyine atmosferik plazma püskürtme (APS) yöntemi ile kaplanmıştır. APS ile kaplanan numuneler daha sonra plazma transferli ark (PTA) kaynak yöntemi ile farklı akımlarda ergitilerek yüzey özellikleri geliştirilmiştir. APS yöntemi ve PTA ile üretilen numunelerin mikroyapı, aşınma ve sertlik değişimleri incelenmiştir. Deneysel çalışmalarda optik mikroskop (OM), taramalı elektron mikroskobu (SEM), enerji dağılım x-ışını spektrometresi (EDS), X ışını kırınım analizi (XRD) ve mikrosertlik testi kullanılmıştır. Deneysel çalışmalar sonunda APS ile birlikte PTA uygulanan numunelerin alt malzeme ile iyi bir metalürjik bağ oluşturduğu ve mikroyapının değiştiği belirlenmiştir. APS yöntemi ile oluşan boşluk ve gözenek hataları PTA ile giderilmiştir. En yüksek aşınma direnci ve sertlik PTA 80 A akım değerinde yüzey özellikleri geliştirilen WC-Co kaplamada elde edilmiştir. Bu numunede sertlik değeri 980 HV0,1'e ulaşmıştır. In this study, AISI 8620 cementation steel substrates were coated with WC–Co, Cr3C2-NiCr, and Mo by using atmospheric plasma-sprayed (APS) method. The coated specimens were then subjected to surface melting with different current value by using plasma transferred arc (PTA) method. Microstructure, hardness, and wear properties of as-sprayed and surface-melted specimens were investigated. In experimental studies OM, SEM, XRD, and Microhardness tester were used.As a result of this study combination of APS coating and plasma welding is a very effective method for change and improve the surface quality and substrate. Microstructure of APS coated surface had some void crack. These microstructure defects were eliminated by PTA welding process. The highest wear resistance and hardness were obtained in WC-Co coatings which was improved surface properties with PTA at 80 A current value. The hardness of the melted layer reached to the values as high as 980 HV0,1 on this specimen. 71

Published
2016

11. Yükümlülük karşılama yeterliliği II ve bir uygulama

Author

Bayar, İsmail Emre, Sucu, Meral, and Aktüerya Bilimleri Anabilim Dalı

Subjects
Insurance, Aktüerya Bilimleri, Actuarial Sciences, Ability to pay, Cost of capital, Sigortacılık
Abstract

Sigortacılığın bir risk işi olmasına rağmen, tahmin edilemeyen risklerin ortaya çıkması durumunda; sigorta şirketlerinin varlıkları yükümlülüklerini karşılamada yetersiz kalabilmektedir. Bu nedenle, sigortalıların menfaatlerinin ve finans sisteminin korunması amacıyla, sigorta şirketlerinin mali yapılarının güçlü olması gereklidir. Sigorta ve reasürans şirketlerinin mali yeterliliklerinin sağlanması için çeşitli kontrol mekanizmaları geliştirilmektedir.Bu çalışmada, mali yeterlilik kavramı, Avrupa Birliği'nde yürürlükte olan Solvency I sistemi, Türkiye'de uygulanmakta olan yükümlülük karşılama yeterliliği ve 2012 yılında Avrupa Birliği'nde yürürlüğe girecek olan Solvency II sistemi ele alınmıştır. Ayrıca, bir hayat sigortası şirketi için mali yeterlilik seviyesi gelecekte yürürlüğe girecek olan Solvency II projesi esaslarına göre hesaplanmış ve Türkiye'deki mevcut sisteme göre hesaplanmış yükümlülük karşılama yeterliliği ile karşılaştırılması yapılmıştır. Sigorta şirketlerimizin Solvency II projesine dahil olması durumunda karşılaşacakları sermaye yeterlilik ihtiyaçları incelenmekte ve sektörün Solvency II projesine geçiş sürecindeki ihtiyaçları irdelenmiştir. Although insurance is a business of risks, the possessions of insurance companies might fail to satisfy the liabilities in the event of occurrence of unexpected risks. Therefore, the financial structures of insurance companies should be strong in order to protect the interests of the insured and the financial system. Various control mechanism are being developed for the purpose of ensuring the solvency of insurance and reinsurance companies.In this study, the concept of solvency, the Solvency I system; which is in force in European Union, the solvency; which is in practice in Turkey and the Solvency II system; which is going to be in force in 2012 in European Union have been handled. Moreover, solvency of a life insurance company have been calculated according to the principals of Solvency II system, which is going to be in force in the future and have been compared to the solvency, which has been calculated according to the current system in Turkey. The solvency needs of our insurance companies, which will be confronted in the event of getting involved in the Solvency II project, and the needs of the market during the transition period have been examined. 100

Published
2010

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