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Öğe Çekme bölgesi lifli beton olan cam fiber takviyeli polimer (GFRP) ve çelik donatılı etriyesiz kirişlerin eğilme etkisi altındaki davranışı ve hasar analizi(Selçuk Üniversitesi Mühendislik Fakültesi, 2018) Gemi, Lokman; Köroğlu, Mehmet AlpaslanDonatı çeliğinde meydana gelen korozyon, yapı elemanlarının önemli problemlerinden biri haline gelmiştir. Bu yüzden son yıllarda, Elyaf Takviyeli Polimerler (FRP), korozyon dayanımı yüksek olması sebebiyle, çelik donatılara alternatif olarak kullanılmaya başlanmıştır. Ayrıca, FRP donatıların yüksek dayanımı, hafif olması ve kimyasal etkilere karşı dayanımı özellikle endüstriyel alandaki kullanımını arttırmıştır. Bu çalışmada, çekme bölgesinde 5 cm yüksekliğinde polipropilen lif katkılı betonun kullanıldığı çelik ve Cam Elyaf Takviyeli Polimer (GFRP) donatılı etriyesiz kirişlerin eğilme etkisi altındaki davranışı deneysel olarak incelenmiş ve devamında hasar analizleri yapılmıştır. Bu amaçla geleneksel çelik ve GFRP donatılı etriyesiz kirişler üretilmiş ve üç noktalı eğilme testleri yapılmıştır. Eğilme testleri sonrasında eğilme dayanımları hesaplanarak yük-deplasman grafikleri oluşturulmuş, malzeme davranışındaki farklılıklar incelenmiştir. Deneylerden sonra GFRP donatılarda oluşan hasarlar incelenmiş ve hangi hasar modları olduğu tespit edilmiştir. Çalışmalar sonucunda GFRP donatılı kirişlerin eğilme performanslarının büyük oranda arttığı görülmüştür.Öğe Comparison of stability of titanium and absorbable plate and screw fixation for mandibular angle fractures(MOSBY-ELSEVIER, 2008) Esen, Alparslan; Ataoglu, Hanife; Gemi, LokmanObjective. The purpose of this experimental study was to compare the stability of titanium and absorbable plate and screw fixation systems for mandibular angle fractures. Study design. Twenty-one sheep hemimandibles were used to evaluate 3 different plating techniques. The groups were fixated with a single titanium plate, a single absorbable plate and double absorbable plates. A cantilever bending biomechanical test model was used for the samples. Each group was tested with vertical forces by a servohydraulic testing unit. The displacement values in each group at each 10 N stage up to 100 N were compared using the 2-way analysis of variance test. Results. The displacement values for the 3 groups differed significantly (P < .05). The variance analyses showed that titanium plate placement had more favorable biomechanical behavior than others. In addition, the 2 absorbable plates group had more favorable biomechanical behavior than a single absorbable plate group but it was not significantly different at 10 to 40 N. Conclusion. The study demonstrated that titanium plate and screw fixation system had greater resistance to occlusal loads than absorbable plate and screw systems. In addition, a second absorbable plate orientation provides a more favorable biomechanical behavior than a single absorbable plate placement. (Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2008; 106: 806-811)Öğe Correlation Between Machinability and Chip Morphology of Austempered Ductile Iron(AMER SOC TESTING MATERIALS, 2018) Yazman, Şakir; Gemi, Lokman; Uludağ, Muhammet; Akdemir, Ahmet; Uyaner, Mesut; Dışpınar, DeryaIn this work, macrostructure, microstructure, and work hardening of as-cast and austempered ductile iron chips produced by different cutting speeds were investigated. Cutting forces, surface roughness, and tool wear were also studied. After austenitizing at 900 degrees C for 90 min, samples were austempered in a salt bath at 360 degrees C for 90 min. Machinability tests were conducted with uncoated cemented carbide tools on a CNC lathe. The tests were carried out without using any lubricant. In these tests, the cutting speed was varied in the range 50-200 m/min, while the feed rate (0.12 mm/rev) and depth of cut (2 mm) were kept constant. The tangential, feed, and radial cutting force components acting on the tool holder were measured with a three-component dynamometer. The chips obtained during machining were polished by embedding into epoxy resin, examined with optical microscope and micrographs were taken. The microhardness values were measured on each chip sample. As the cutting speed was increased, deformation strengthening of the microstructure was increased, which decreased the tool life. It was also detected that during the machining, with the effect of cutting forces and stress, spheroidal graphites were broken off in the chip and lost their sphericity, so the chip became fragile and unstable and the graphite displayed a lubricant feature. At low cutting speed, a built-up edge was observed. However, as the cutting speed was increased because of heating, built-up edges were unstable.Öğe Cryogenic machining of carbon fiber reinforced plastic (CFRP) composites and the effects of cryogenic treatment on tensile properties: A comparative study(ELSEVIER SCI LTD, 2018) Morkavuk, Sezer; Koklu, Ugur; Bagci, Mehmet; Gemi, LokmanCarbon fiber reinforced plastics (CFRPs) are prone to damage locally during machining due to the applied cutting forced and generated heat. Cryogenic machining can reduce the heat generated damages of CFRPs by utilizing cryogenic liquids instead of conventional cutting fluids. The goal of this study is to investigate milling performance of CFRPs in cryogenic medium. For this, a new cryogenic machining approach was adopted to slot milling of CFRPs by submerging the workpiece within a cryogenic liquid. The CFRPs were fabricated via vacuum assisted resin transfer method by using woven carbon fiber fabric as a reinforcement and epoxy as a matrix. Machining performance was evaluated based on the resulting cutting force, delamination factor, surface roughness, and surface damage. Moreover, the influences of cryogenic coolant on the tensile properties, fracture surface microstructure, and machined surface of the CFRP laminates were analyzed with scanning electron microscopy (SEM). SEM analysis revealed that combination of different damage modes such as debonding, micro matrix crack, fiber pull out, and bundle pull out, delamination, and fiber breakage were observed. The results showed that cryogenic machining approach provided less damage formation on the machined surface, reduced delamination factor and surface roughness but increased resulting cutting force during machining of the CFRPs. On the other hand, there was a slight improvement (about 3%) of the tensile properties for the CFRPs exposed to cryogenic coolant due to matrix hardening and increasing in the fiber strength and shear strength.Öğe Düşük hızlı darbe hasarlı filaman sarım hibrid boruların iç basınç altında yorulma davranışı(Selçuk Üniversitesi Fen Bilimleri Enstitüsü, 2014-01-30) Gemi, Lokman; Akdemir, Ahmet; Uyaner, MesutFilaman sarım kompozit borular yüksek basınçta kimyasal madde içeren akışkanların iletilmesinde, endüstriyel atıkların uzaklaştırılmasında, petrol ve doğalgaz iletim hatlarında kullanılmaktadır. Kullanım sırasında kompozit boruların uğrayacağı düşük hızlı darbeler; matris çatlakları, elyaf kopmaları ve özellikle tabakalar arası ayrılma gibi gözle zor tespit edilebilecek hasarlara yol açarlar. Oluşan bu hasarlar borularda hem mukavemet kaybına hem de yorulma ömründe düşüşe neden olabilirler. Bu amaçla cam/karbon/cam sıralaması kullanılarak [±75g°/±55c°/±45g°] konfigürasyona sahip hibrit kompozit borular üretilmiştir. ANSI/AWWA C950 standardında ön görülen çalışma koşulları esas alınarak CTP borular basınç sınıflarına ayrılmış ve boruların işletme basınç değerleri 3, 6, 12, 18, 24, 30, 36, 42 ve 48 MPa teğetsel ön gerilmeler olacak şekilde test koşulları belirlenmiştir. Düşük hızlı darbe hasarının etkisinin incelenmesi amacıyla, yukarıda belirtilen ön gerilmeler altında çalışan borular üzerine 20J enerjiyle düşük hızlı darbe uygulanmış ve ön hasar oluşturulmuştur. Düşük hızlı darbe sırasında boruların dinamik davranışları ve oluşan hasar incelenmiştir. Yapılan çalışma neticesinde 24 MPa ön gerilme değerinden daha yüksek gerilmeler altında, darbe ön hasarının, boruların yorulma davranışına etkisi olmadığı tespit edilmiştir. Bu aşamadan sonra, ANSI/AWWA C950 standardına ön görülen işletme basıncı kategorilerinden 6-12-18 MPa ön gerilme değerleri esas alınarak deney parametreleri belirlenmiştir. Darbe hasarlı hibrit borular, ASTM D 1599-99 standardına göre statik iç basınç testine tabi tutulmuştur. Boruların patlama mukavemetleri belirlenmiştir ve oluşan hasarlar incelenmiştir. Darbe hasarlı ve hasarsız boruların yorulma davranışlarının belirlenmesi amacıyla ASTM-D 2992-06 standardına uygun olarak (R=0.05 gerilme oranı ve f=0.42 Hz frekansta) yorulma testleri gerçekleştirilmiştir. Bu amaçla, 6, 12 ve 18 MPa teğetsel ön gerilme altında darbeye maruz kalmış numuneler, hasarsız numunelerin patlama mukavemetinin %30 ila %55'ı arasında değiştirilen gerilme değerlerinde yorulmaya tabi tutulmuştur. Elde edilen sonuçlar, hasarsız numunelerin davranışlarıyla kıyaslanmıştır..Yorulma deneyleri sırasında gelişen hasarlar detaylı bir biçimde incelenmiş ve üç önemli hasar aşaması belirlenmiştir. Bu hasarlar; terleme veya damlacık şeklinde ilk sızıntı, yoğun sızıntının (su jeti) başlaması ve sonuç hasarıdır. Sonuç hasarın oluştuğu çevrim sayıları kayıt edilerek S-N eğrisi elde edilmiştir. Yorulma sonrası numunede oluşan hasar bölgeleri incelenmiştir. Bu çalışmalar neticesinde uygulanan ön gerilme değeri arttıkça darbe ön hasarının azaldığı, statik patlatma mukavemetinin ve yorulma ömrünün arttığı tespit edilmiştir.Öğe The effect of nonwoven electrospun PAN nanofiber mat on mechanical and thermal properties of epoxy composites(2018) Erdal, Mehmet Okan; Yazman, Şakir; Gemi, Lokman; Yapıcı, AhmetIn this study mechanical and thermal properties of epoxy resin reinforced withdifferent numbers of nanofiber layers which produced with electrospinning method wasinvestigated. Solution of 10 wt% of polyacrylonitrile (PAN) in N,N-dimethylformamide(DMF) was used for electrospinning. The diameters of the obtained nanofibers were in therange of 380-420 nm. The average thickness of the produced nanofiber layer was about200 ?m. The special molds were prepared to produce the laminated composite plates. Thetensile tests show that the using of nanofiber PAN layers increase the tensile force 34.54%and decrease the elongation 8.87% in comparison with neat epoxy. The fracture surfaces ofthe specimens were inspected by using optical and scanning electron microscopy (SEM).The thermal properties of the nanofiber layered composites were determined by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) analysis. It wasobserved that the glass transition temperature increased parallel to this as the number ofPAN layers increased and rose up to 86?C, while the thermal stability did not show mucheffect of PAN layers.Öğe THE EFFECT OF SR MODIFICATION AND HOLDING TIME ON Si MORPHOLOGY AND MECHANICAL PROPERTIES OF ETIAL 195 ALLOY(PAMUKKALE UNIV, 2015) Uludag, Muhammet; Gemi, Lokman; Eryilmaz, Muhammed Rasit; Dispinar, DeryaHypereutectic Al-Si alloys are typically used in applications where wear resistance is required. The primary factor that determines the wear properties is the morphology of Si in these types of alloys. Pouring temperature is one of the ways to control Si size and shape. On the other hand, bifilm defects that may be present in the liquid can significantly alter the morphology of Si acting as a heterogeneous nucleant. Therefore in this work, castings were made at 800 degrees C with varying holding time and the effects of bifilm on the Si morphology was studied. Bifilm content was measured by Reduced Pressure Test and image analysis was used to characterize Si morphology. In addition, tensile tests were carried out to correlate Si morphology with mechanical properties.Öğe ETİAL 195 ALAŞIMINDA Sr MODİFİKASYONU VE TUTMA SÜRESİNİN Si MORFOLOJİSİ VE MEKANİK ÖZELLİKLERE ETKİSİ(2015) Uludağ, Muhammet; Gemi, Lokman; Eryılmaz, Muhammed Raşit; Dışpınar, DeryaÖtektik üstü Si içeren Al-Si alaşımları tipik olarak aşınmaya karşı direnç arzu edilen parçalarda uygulama alanı bulmaktadır. Aşınma direncini arttıran en temel parametre, Si morfolojisidir. Ötektik üstü alaşımlarda, Si yapısı döküm sıcaklığından etkin bir şekilde etkilenmektedir. Ancak, döküm sırasında oluşabilecek bifilm hataları Si için potansiyel heterojen çekirdek kaynağı olabilmektedirler. Bu doğrultuda bu çalışmada, 800 C ergitme sıcaklığın farklı bekleme süreleri sonrasında dökümler yapılarak, sıvı metal içerisinde var olabilecek bifilmlerin Si morfolojisi üzerine etkisi incelenmiştir. Bifilm miktarı, sıvı metalden alınan vakum altında katılaşma testi sonrasında elde edilen numunelerin kesit alanındaki görüntü analizi ile tespit edilmiştir. Üretilen numunelerin mikroyapıları üzerinde de görüntü analizi yapılarak Si morfolojisindeki değişim incelenmiştir. Aynı zamanda her parametre için çekme testi yapılarak Si morfolojisi ile mekanik özellikler arası ilişki ortaya çıkartılmıştırÖğe Experimental and statistical analysis of low velocity impact response of filament wound composite pipes(ELSEVIER SCI LTD, 2018) Gemi, Lokman; Kayrici, Mehmet; Uludag, Muhammet; Gemi, Dilek Soylu; Sahin, Omer SinanNowadays, filament wound composite pipes (GRP) are used as a structural element in many applications such as natural gas and oil transmission lines, and portable bridge constructions for military purposes. GRP pipes can expose to impact loading from various causes. This loading can cause an invisible level of damage. Thus, the detection and evaluation of such damages are of great importance. In this study, the low velocity impact response of (+/- 55 degrees)(3) filament wound E-glass/epoxy composite pipes has been studied. The pipes have been subjected to drop weight impact loading with various impact energies. The force-time and force-displacement relations have been examined. The impact damage formation was also evaluated. It is concluded that the damage development in the pipes is controlled by displacement trough radial direction. The obtained results were evaluated statistically by means of Weibull approach. Microscopy analysis of impacted region revealed that debonding, radial cracks, transfer cracks and delamination damage modes are the main observed damage modes.Öğe Experimental investigation of fatigue damage formation of hybrid pipes subjected to impact loading under internal pre-stress(ELSEVIER SCI LTD, 2017) Gemi, Lokman; Sahin, Omer Sinan; Akdemir, AhmetIn this study, the effect of impact loading upon fatigue behavior of hybrid composite pipes has been investigated. The composite pipes were subjected to tangential pre-stress as 3-48 MPa according to ANSI/AWWA C950 standard than, subjected to low velocity impact at 20 J. The impact pre-damaged pipes then subjected to cyclic loading at 50% sigma ult in accordance with ASTM D 2992-06. It is also observed that increasing the tangential pre-stress decreases impact damage area and increases fatigue life of the pipe. It is also showed that impact pre-damage are not effective on the fatigue life of the pipe at the pre-stress level of 24 MPa. (C) 2017 Elsevier Ltd. All rights reserved.Öğe Experimental investigation of shear capacity and damage analysis of thinned end prefabricated concrete purlins strengthened by CFRP composite(ELSEVIER SCI LTD, 2019) Gemi, Lokman; Aksoylu, Ceyhun; Yazman, Şakir; Özkılıç, Yasin Onuralp; Arslan, Musa HakanPrefabricated structures supported with purlins are exposed to numerous damages due to the excessive snow loadings as vertical loadings. The thinned regions of the purlins are responsible with the failure of the structure since the shear cracks usually initiate at these regions and propagate along with the purlins, and as a result, a total collapse may occur. In this study, carbon fiber reinforced polymer (CFRP) composites with four different configurations (P-2-P-5) were employed for strengthening prefabricated purlins in order to increase the strength of the purlin against shear damage generated under vertical loading. The load carrying capacities and damage patterns of the purlins were compared. The failure of the reference purlin (P-1) was occurred as a shear damage at the thinned regions before reaching its bending capacity. However, the failure characteristic of the CFRP reinforced purlins was dominated by the bending damage and the vertical loading capacity of the purlins were increased up to 59% depends on the CFRP wrapping. Damage analysis of the CFRP composite was also performed. Various damage modes of the structure such as cover separation, air voids, delamination, debonding, fiber bundles breakage, matrix cracks, fiber bundles debonding, fiber breakage and buckling were observed and explained thoroughly.Öğe Fatigue Crack Growth Behavior of Filament Wound Composite Pipes in Corrosive Environment(SAGE PUBLICATIONS LTD, 2009) Sahin, Oemer Sinan; Akdemir, Ahmet; Avci, Ahmet; Gemi, LokmanThe stress corrosion crack growth behavior of +/- 45 degrees, +/- 55 degrees, and +/- 75 degrees filament wound composite pipes with surface crack subjected to 0.6 M HCl acid under alternating internal pressure was investigated. E-glass/epoxy pipes consist of six layers with stacking sequences of (+45/-45)(3), (+55/-55)(3), and (+75/-75)(3). Dilute (0.6M) HCl acid was applied to the surface crack region by a corrosion cell mounted on the outer surface of the pipe. The specimens were tested at room temperature and exposed to open-ended fatigue tests in which the pipes can deform freely in the axial direction. The tests were performed in accordance with the ASTM D-2992 standard. The surface notches with different a/t and a/c forms were cut on the outer surface of the pipe parallel to the pipe axis. The internal pressure was generated by conventional hydraulic oil for fatigue loading. The low cycle tests were applied with 0.42 Hz frequency and R = 0.05 stress ratio. After the corrosion fatigue test, the fracture surfaces were examined and observed damage mechanisms discussed.Öğe Fiber takviyeli termoplastik kompozit levhalarda farklı delik çaplarına göre elasto-plastik gerilmelerin analizi(Selçuk Üniversitesi Teknik Bilimler Meslek Yüksekokulu, 2005) Önal, Gürol; Yapıcı, Ahmet; Gemi, LokmanBu çalışmada fiber takviyeli termoplastik kompozit delikli bir levhanın tek yönde çekmeye maruz kalması durumunda delik çapına bağlı olarak levhalarda meydana gelen elasto-plastik gerilmeler incelenmiştir. Delik tipi daire olarak ele alınmıştır. Çözüm tekniği olarak sonlu elemanlar metodu kullanılmıştır. Çözümlerde delik çapı D=10, 30, 50 mm ve tabakalar ([30, -30]2) şeklinde alınarak çözümler yapılmış, sonuçlar tablo ve plastik bölge dağılımını gösteren şekillerde verilmiştir.Öğe Low velocity impact response of prestressed functionally graded hybrid pipes(ELSEVIER SCI LTD, 2016) Gemi, Lokman; Kara, Memduh; Avci, AhmetFilament wound hybrid composite pipes are frequently used for the transmission of high pressured chemical fluids, disposal of industrial wastes, oil and natural gas transmission lines. In this study, low velocity impact behavior of the glass/carbon functionally graded filament wound composite pipes with 55 winding angle was experimentally investigated. The hybrid composite pipes were graded with a fixed layer configuration from inside to outside as glass-glass/glass-carbon/carbon-glass/carbon-carbon. The functionally graded hybrid pipes were subjected to different internal pressure values (4, 16 and 32 bar), and impact response and energy absorption capacity of the hybrid composite pipes were investigated by using weight drop test method with impact energies of 5, 10, 15 and 20 J. The impact force and displacement versus interaction time were measured. The impulsive force, energy absorption capability, and damage formation were also investigated. Delamination, radial and surface Matrix crack formations were observed as the main failure mechanisms at the outer surface of the hybrid pipes. Moreover, the effect of impact damage decreased with the increasing internal pressure of the prestressed hybrid composite pipes. The impact damaged composite pipes were subsequently subjected to burst tests according to ASTM D1599-99 standards to calculate burst strengths of the damaged composite pipes. The hybrid composite pipes subjected to 32 bar internal pressure before impact loading were exhibited highest burst strengths for the same impact energy levels. (C) 2016 Elsevier Ltd. All rights reserved.Öğe Progressive fatigue failure behavior of glass/epoxy (+/- 75)(2) filament-wound pipes under pure internal pressure(ELSEVIER SCI LTD, 2009) Gemi, Lokman; Tarakcioglu, Necmettin; Akdemir, Ahmet; Sahin, Oeer SinanFatigue failure behaviors of filament-wound composite pipes under pure internal pressure were investigated. The filament-wound pipes are made of E-glass/epoxy and have four layers which have +/-75 degrees winding angle. The fatigue tests have been done in accordance with ASTM D-2992, which stipulate 0.42 Hz frequency and R = 0.05 stress ratio. Tests have been performed at different load levels from 30% to 70% of ultimate tangential strength of the pipe, the damage progression such as whitening, leakage and final failure have been observed, and S-N curves of these damages were obtained. (C) 2009 Elsevier Ltd. All rights reserved.
