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Öğe ALUMINIUM OXIDE (Al2O3)-FEW LAYER GRAPHENE (FLG) REINFORCED ALUMINIUM HYBRID COMPOSITES(POLISH SOC COMPOSITE MATERIALS, 2022) Kaykılarlı, Cantekin; Altinisik, Zehra; Kilic, E. Can; Uzunsoy, Deniz; Yeprem, H. AygulThe present study investigates the microstructural and mechanical properties of few layer graphene (FLG, 0.1 to 5 wt.%) and aluminium oxide (Al2O3, 4 to 20 wt.%) reinforced Al6061 matrix composites prepared via mechanical alloying (MA), uniaxial pressing and pressureless sintering. The effects of the amounts of Al2O3 and FLG were studied. MA was carried out at 300 rpm for 3 h in a planetary ball mill in argon atmosphere. The mechanically alloyed (MAed) powders were compacted via uniaxial pressing (400 MPa) and sintering (620 degrees C, 2 h). The microstructural and mechanical properties of the Al-xAl(2)O(3)-yFLG powders and bulk samples were investigated via X-ray diffraction (XRD), light microscopy (LM), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), the Archimedes' method and a hardness test. In the XRD analysis, the aluminium carbide (Al4C3) phase was not detected. The SEM, LM micrographs and EDS results show that the produced composites have a homogeneous structure. Based on the Archimedes' method, the densification rates of the rein-forced samples were higher than the unreinforced sample. The Al-20Al(2)O(3)-3FLG sample exhibited the highest relative density, 99.25%. According to the hardness measurements, the highest hardness value was 87.28 HV for the Al-20Al(2)O(3)-1FLG composite and increased twofold compared to Al6061.Öğe Boron and nitrogen doping in graphene: an experimental and density functional theory (DFT) study(IOP Publishing, 2020) Kaykılarlı, Cantekin; Uzunsoy, Deniz; Şam Parmak, Ebru Devrim; Fellah, Mehmet Ferdi; Çakır, Özgen ÇolakBoron (B) and Nitrogen (N) doped few layer graphene (BNG) is directly synthesized via electric arc discharge (EAD) method. NH3 and BCl3 gas mixtures are used in the synthesis atmosphere. Raman spectroscopy is used to determine graphene's purity and number of layers. The investigation of structure and morphology of pristine graphene and BNG are carried out via Transmission Electron Microscopy (TEM). The presence of B and N in the structure of graphene is detected by Energy Dispersive X-ray Spectroscopy (EDS) analysis. Elemental mapping show that N and B are distributed homogeneously in the graphene structure. It is observed that doping process did not affect the positions of the D, G and 2D bands in the Raman spectroscopy. The effect of doping on the number of layers of graphene is found negligible. TEM results exhibit that pristine graphene and BNG have 5 to 6 layers. Besides, the theoretical calculations based on Density Functional Theory (DFT) are employed to support experimental studies. Theoretical results based on DFT showed that bonding of B and N is favorable.Öğe A comparison and identification study of dry sliding wear behaviour of Al/B4CP and Mg/B4CP composites for automobile disk brakes(SAE International, 2014) Isin, O.; Istif, I.; Uzunsoy, Deniz; Guleryuz, F.The brake friction materials in an automotive brake system play an important role in the overall braking performance of a vehicle. Metal Matrix Composites (MMCs) have been widely investigated and applied due to their advantages of improved strength, stiffness and increased wear resistance over the monolithic alloys in automobile industries. In this paper, Al/B 4CP and Mg/B4CP composites were compared to find a suitable candidate material for automotive disk brake application, in terms of wear behavior results of the materials. In addition, the experimental data was also used to model this behavior by identification. The measured tangential force was considered as the input parameter, whereas the weight loss as the output parameter. Preliminary results of this work showed that B4CP addition improved wear resistance of both aluminum and magnesium matrix composites. Additionally, the study pointed out that identified models provide a reliable and cost effective tool for wear prediction. Copyright © 2014 SAE International.Öğe Comparison of fatigue crack growth rate of selective laser sintered Rapid Steel via computational fracture mechanics(Carl Hanser Verlag, 2014) Okyar, Ali Fethi; Uzunsoy, Deniz; Qzsoy, BurakThe fatigue-crack growth behavior of materials manufactured by means of selective laser sintering was studied. In the process, specimens were prepared from metal powders (316 steel) into the desired shape by additive manufacturing technology, followed by sintering and infiltration in a suitable molten metal. The latter process was aimed at eliminating the inherent porosity associated with powder metallurgy. Porosity is known to adversely affect the fatigue-crack growth rate behavior of powder metallurgy components. Carefully conducted fatigue-crack growth rate tests (single-edge-notch four-point bending type) were carried out on RapidSteel (TM) and the results were compared with data of infiltrated low carbon steel in the literature. Finite element analysis was carried out as an intermediate step in order to validate the geometry factor calculations provided by empirical formulae. It was found that the fracture resistance of Rapid Steel was higher compared with low-carbon copper infiltrated steel tempered at 177 degrees C and 428 degrees C, and same as that tempered at 704 degrees C.Öğe Development of High Purity, Few-Layer Graphene Synthesis by Electric Arc Discharge Technique(Polish Acad Sciences Inst Physics, 2018) Çotul, Uğur; Şam Parmak, Ebru Devrim; Kaykilarli, C.; Saray, O.; Colak, O.; Uzunsoy, DenizIn this study, high purity graphene nanoflakes (GNF) were synthesized by electric arc discharge technique. The arc discharge method is more advantageous than other graphene synthesis methods for producing cheap and good-quality graphene with minimum defects and not including dangerous chemicals. Because of this advantages, the arc discharge method is one step ahead of all graphene synthesis methods. In order to synthesize GNF, a DC electric arc discharge reactor was designed by our team. Electric arc discharge method based on a principle that provides a constant current between two high purity graphite electrodes to vaporize. After the arc discharge, nanoparticles accumulate on the inner surface of the reactor. The voltage stabilizer DC power source is used to create a current in the environment and the discharge usually occurs in a range 20-60 V. This current can be adjusted depending on the diameter of electrodes, the distance between electrodes and arc current varies between 100 and 150 A. Different characterization techniques such as the Raman spectroscopy, scanning electron microscope and transmission electron microscope were used to characterize the graphene layers synthesized by the arc discharge method. The L-D / L-G ratio was calculated as 0.66 while the L-G / L-2D was determined as 1.31. These values show that the purity of the synthesized graphene is compatible to that of commercially supplied graphene. Besides, the synthesized graphene has fewer layer than commercially supplied one. Transmission electron microscope observations confirmed the typical wrinkled feature of graphene.Öğe Experimental investigation of oligo cyclic compression behavior of pure epoxy and graphene-epoxy nanocomposites(Springer, 2021) Colak, Ozgen U.; Uzunsoy, Deniz; Bahlouli, Nadia; Francart, CharlesThe loading-unloading compression behavior and the oligo cyclic behavior of pure epoxy and graphene-epoxy nanocomposites are investigated since the systematic evaluation of the mechanical behavior under cyclic loading is of great importance in the development of damage characterization and fatigue models for polymer composites. High purity graphene nanoflakes (GNF) are synthesized by electric arc discharge method, and the manufacturing of graphene epoxy nanocomposites is done using solution blending. The structural characterizations of produced GNF are performed using several techniques such as transmission electron microscopy (TEM), Raman spectroscopy and Brunauer-Emmett-Teller (BET). Oligo quasi-static strain-controlled cyclic tests are performed at the elastic (or viscoelastic) region, around yield and after softening at the viscoplastic region. Comparing the behavior under compression, loading-unloading and oligo (repeated) cycled reveals that prehistory does not have much effect on the subsequent behavior. The change in the elasticity modulus during repeated cyclic compression is determined. It is observed that elasticity modulus decreases initially, and then, it progressively increases with the increase in applied maximum strain. Compared to epoxy, the yield stresses of graphene-epoxy decrease in both strain rates and a small increase in the elasticity modulus of graphene-epoxy is observed at low strain rate (1.E-4 /s).Öğe High strain rate behavior of graphene-epoxy nanocomposites(Elsevier Sci Ltd, 2020) Colak, Ozgen U.; Bahlouli, Nadia; Uzunsoy, Deniz; Francart, CharlesThis work consists of the synthesis of high purity graphene nanoflakes (GNF), the manufacturing of GNF-epoxy nanocomposites and the mechanical characterization of the nanocomposite at high and quasi static strain rates, (2750/s - 1.E 5/s). GNF were synthesized by using the electric arc discharge technique. Thermogravimetry/ Differential Thermal Analysis (TG/DTA) of synthesized graphene reveals high purity and high crystallinity. Raman spectra and the broad Brunauer-Emmet-Teller (BET) specific surface area indicate that the synthesized graphene has several layers. Following the solution mixing manufacturing process of GNF-epoxy nanocomposites, the influences of strain rate on the mechanical behaviors are investigated under quasi static and dynamic loadings. High strain rate uniaxial compression tests (1270-2750/s) using Split Hopkinson Pressure Bar (SHPB) and quasi static compression tests (1.E-3 and 1.E-5/s) of GNF-epoxy with two graphene contents (0.1 and 0.5 wt %) are performed at room temperature. The maximum elasticity modulus achieved by the GNF-epoxy with 0.5 wt% at the strain rate of 2350/s corresponds to a 68% increase compared to the neat epoxy. The yield strength of the material is doubled under dynamic loading conditions compared to the quasi static loading.Öğe Investigation of Mechanical Properties of Graphene and Reduced Graphene Oxide Reinforced Epoxy Matrix Composites(Amer Soc Testing Materials, 2016) Topal, Emre; Şam Parmak, Ebru Devrim; Uzunsoy, Deniz; Cakir, O. ColakGraphene has generated great excitement in the scientific community due its unique mechanical and electronic properties, and also the availability of bulk quantities of graphene as both colloidal dispersion and powder. With the development of relatively high yield and defect-free synthesis methods, this exciting material is ready for practical application in the preparation of polymer nanocomposites. Here, we reported on the mechanical performances of epoxy nanocomposites which have been reinforced with exfoliated graphene nano platelet (GNP) and reduced graphene oxide (RGO) at a loading of 0 to 0.5 wt. %. A soft molding method was used for the preparation of epoxy nanocomposites. The reinforcing effects of GNP and RGO on epoxy resin were examined by tensile testing and dynamic mechanical analysis (DMA). The morphology of the epoxy/GO and epoxy/RGO nanocomposites were investigated using a scanning electron microscope (SEM). A significant improvement on mechanical properties of epoxy/GO and epoxy/RGO nanocomposites was observed at low GNP and RGO loading. Contrary to the literature, the ultimate tensile strength values have mainly decreased, although the Young's modulus has improved. Dynamic mechanical analysis has shown that with the addition of both GNP and RGO, storage modulus was significantly enhanced at 40 degrees C. The loss factor was almost not affected by both RGO and GNP loading. SEM investigation of the fractured surface indicates that GNP and RGO fillers are dispersed uniformly in the epoxy matrix.Öğe Investigation of microstructural, mechanical and corrosion properties of graphene nanoplatelets reinforced Al matrix composites(Iop Publishing Ltd, 2019) Akçamlı, Nazlı; Küçükelyas, Burak; Kaykilarli, Cantekin; Uzunsoy, DenizGraphene nanoplatelets (GNP) were utilized as reinforcement for Al matrix with the aim of exploiting its extremely high mechanical properties. GNP reinforced composites were prepared via powder metallurgical processing route based on mechanical alloying, cold pressing and pressureless sintering. 0.5 to 2 wt% of GNP were incorporated into the aluminum via mechanical alloying up to 8 h in a high-energy ball mill. The mechanically milled powders were compacted by two different methods as uniaxial cold pressing and cold isostatic pressing. The prepared powders and bulk samples were characterized by differential thermal calorimetry (DSC), X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive X-ray spectrometry (EDX), optical microscopy (OM), and Archimedes density, microhardness and dry sliding wear tests. Additionally, corrosion properties of the Al-GNP composites were determined by the Tafel exploration method. The results showed that the optimum GNP amount could be expected as 0.5 wt%, which enhanced the microhardness and wear resistance values of the Al from 84.5;;1.98 HV and 0.7384 mm(3) to 199.4;;1.88 HV and 0.4476 mm(3), respectively. However, this amount of graphene addition tended to slightly deteriorate the corrosion resistance of Al.Öğe Investigation of Wear Behavior of Aluminum Alloy Reinforced with Carbon Nanotubes(2014) Uzunsoy, Deniz; Peng, T.; Chang, I.; Istif, I.The material demands for advanced technologies have led to development of new generation, light-weight, and multi-functional materials. Aluminum matrix composites (AMCs) have captured considerable attention in aviation, space and automotive industries in recent years. Carbon nanotubes (CNT) are one of the most promising candidate of reinforcements used to improve mechanical strength and hardness of metal matrix composites (MMCs). In this study, dry sliding wear behavior of aluminum (Al) matrix (MMCs) reinforced with different amounts (0, 0.5, 1 and 2 wt%) of CNTs were prepared through ball milling, the process was followed by compaction at room temperature and pressureless sintering at 630 °C under argon atmosphere for 1hr. Wear tests were performed on a pin-on-disk tribometer against SAE 1040 steel counter body under constant load and sliding speed at room temperature. Worn surfaces of composites were characterized by scanning electron microscopy (SEM) technique in order to identify dominant wear mechanism of the as-produced composite materials. Preliminary result of this study showed that the composite displayed lower wear rate and friction coefficient under mild wear conditions comparing to aluminum alloy without reinforcement. © 2014 SAE International.Öğe Prediction of wear behavior of aluminum alloy reinforced with carbon nanotubes using nonlinear identification(SAE International, 2014) Istif, I.; Isin, O.; Uzunsoy, Deniz; Peng, T.; Chang, I.Aluminum metal matrix composites reinforced with particulates have attracted much attention in the automotive industry, due to their improved wear resistance in comparison to aluminum alloys, in recent years. The wear behavior is the critical factor influencing the product life and performance in engineering components. Carbon nanotubes (CNT) are one of the most promising candidates of reinforcements used to improve mechanical strength such as wear in metal matrix composites (MMCs). However, in industrial applications, wear tests are relatively expensive and prolonged. As a result, for several years, research has been increasingly concentrated on development of wear prediction models. In this study, prediction of wear behavior of aluminum (Al) matrix (MMCs) reinforced with different amounts (0, 0.5, 1 and 2 wt%) of CNTs was investigated. A nonlinear autoregressive exogenous (NARX) model structure was chosen for the modeling. The wear load was considered as the input parameter, whereas the wear rate and friction coefficient as the output parameters. Simulations using the identified models were compared with experimental results and it was found that the modeling of wear process was satisfactory. Copyright © 2014 SAE International.Öğe Processing and characterization of graphene nano-platelet (GNP) reinforced aluminum matrix composites(Carl Hanser Verlag, 2016) Akçamlı, Nazlı; Gokce, Hasan; Uzunsoy, DenizAluminum matrix composites containing graphene nanoplatelets (GNPs) as reinforcement additive were fabricated by a two-step process consisting of mechanical alloying and pressureless sintering. The effects of graphene nano-platelets amounts and mechanical alloying duration on the microstructural and mechanical properties of aluminum were investigated. The characterization studies were performed by X-ray diffractometry, Raman spectroscopy, scanning electron microscopy/energy dispersive spectrometry, particle size analysis, differential scanning calorimetry, Archimedes' density and microhardness test method. The microhardness of composites increased gradually by the addition of 0.5 and 1 wt.-% GNP, whereas an adverse effect was observed by the increment of the GNP amount to 2 wt.-%.Öğe Structural characterization of graphene nanostructures produced via arc discharge method(Elsevier Sci Ltd, 2021) Borand, Gökce; Akçamlı, Nazlı; Uzunsoy, DenizFew-layered graphene (FLG) was produced via substrate-free direct current arc discharge between pure graphite electrodes in an originally designed reactor chamber. Previously, parameters influencing the synthesis condition and properties of graphene-like discharge density, precursor composition, electrode diameter/length, reactor design and type and pressure of buffer gases were optimized. In this study, it was observed that carbon structures with different properties deposited in the different regions of the DC arc reactor. The mechanism of graphene formation by the arc discharge method was investigated in terms of the collection side and distance to the arc region. Variations in the distance to arc region result in dissimilar temperature gradients in the reactor chamber, thereby the deposition mechanism of carbon clusters differs with regard to reactor zones. The products collected from the different regions of the reactor were characterized via Raman Spectroscopy and integrated intensity ratio (I-D/I-G and I-G/I-2D), full width half at maximum (FWHM), crystallite size (L-a), defect density (eta(D)) values were examined. The crystallite size (L-002) and average number of graphene layers (N) were determined by X-Ray diffraction (XRD) analyses. In addition, their morphological properties were investigated with scanning electron microscopy (SEM) and transmission electron microscope (TEM). As a result, the carbon nanostructures with high purity and few-layered morphology collected on the anode region of the reactor. While, the purity of few-layered graphene decreased as moving away from the anode region of the chamber. Therefore, it was determined that the properties of graphene were influenced greatly by the temperature distribution and its gradient around the arc plasma.Öğe Suggestion of an Indicator to Evaluate Material Deposition in Resistance Spot Welding: Weld-Surface Interaction Index(Springer, 2018) Kinagu, Hasan Melih; Gokcedaglioglu, Mehmet; Ates, Fatih; Küçükelyas, Burak; Mutlu, Mustafa; Uzunsoy, DenizResistance spot welding (RSW) is still leading joining process in the automotive industry due to the simplicity and speed of the process. On the other hand, galvanized steel sheets provide improvement in corrosion resistance of the auto body. Material deposition has an influence on the corrosion resistance and weld strength; however, in the literature very little effort has been made to identify any weld-surface interaction numerically. In this study, a numerical approach called Weld-Surface Interaction Index (I-WSI) has been introduced to investigate the effect of material deposition on the corrosion sensitivity of the welding zone and its periphery. A systematic investigation was carried out to better understand the effects of an electrode cap-galvanized steel sheet interface on the corrosion resistance of spot-welded steel. The chemical composition of DP600 steel sheet and Z-Trode electrode cap was analyzed by using a spectrometer. The specimens were then joined by using same caps up to 1200 welds. SEM-EDS analysis was also performed on the chosen specimens to determine the weight percentages (wt.%) of Fe, Zn and Cu. EDS analysis results and coefficient of variation wt.% of Fe, Zn and Cu were used to compose I-WSI formula. In the proposed formula, wt.% of Zn represented resistivity of the cover to corrosion, while wt.% of Fe represents the vulnerability.Öğe Synthesis and characterization of graphene-epoxy nanocomposites(Carl Hanser Verlag, 2015) Acar, A.; Çolak, O.U.; Uzunsoy, DenizGraphene, a monolayer of carbon atoms arranged in a two dimensional lattice, has attracted great attention in recent years due to its extra ordinary properties and potential applications. One obvious application of graphene is in the field of nano-composites. In this work, graphene platelets (GPL) reinforced with epoxy nano-composites were fabricated by using soft molding technique in two different ratios with two different solvents. Raman spectroscopy and scanning electron microscopy (SEM) were used to investigate the structure of graphene and graphene reinforced composites. Tensile and dynamic mechanical analysis (DMA) in three point bending mode were used to investigate the mechanical properties of the composites. The tensile strength and strain to failure of nanocomposites of GPL reinforced epoxy nanocomposite were enhanced by 9.31 % and 34.78 %, respectively, while small improvement is observed in the elasticity modulus. Dynamic mechanical analysis has shown that with the addition of 0.1 and 0.5 wt.-% graphene nanoplatelets, storage modulus has increased by 20 and 46 % on the glassy region, respectively. The glass transition temperature is not affected with addition of graphene. © Carl Hanser Verlag, München.
