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Öğe Effect of Aging Time at High Temperature on the Shear Strength of Adhesively Bonded Aluminum Composite Foam Joints(Taylor & Francis Ltd, 2019) Taskin, Nilhan Urkmez; Sahin, AnilIn this study, the shear strength behavior of adhesively bonded joints, made of aluminum composite foams subjected to high-temperature processes, has been investigated. Aluminum composite foam and solid aluminum blocks were used to form single lap joints and as the binder, a methacrylate-based structural adhesive has been selected. Foam-foam and solid-foam joints were formed and cured at room temperature for 24 hours. After curing process, aging at 200 C-o was performed on the samples for 15, 30, 45, 60 minutes. The aged samples were subjected to lap shear testing for adhesively bonded metals and the influences of aging duration on joint strength and failure type were investigated. As a result, lower strengths were obtained in all samples that aged under high temperature compared to non-aged samples. After the application of short-term (15-30 min) aging processes on samples, it is observed that they have joint strength values about 50% of the joint strength of non-aged samples. However, strength values of short-term aged joints (15, 30 min) remain higher than the strength values of the foam materials used in the tests. These results show that methacrylate-based adhesives subjected to short-term thermal loads up to 200 degrees C can be used in constructions.Öğe Effect of etching duration on roughness and wettability of different carbon steel substrates(Elsevier Science Sa, 2021) Taskin, Nilhan Urkmez; Ordu, FatihSurface chemistry and morphology play a significant role in affecting the wettability of engineering surfaces. To create functional surfaces that are hydrophobic or superhydrophobic, these properties must be understood and controllable. The purpose of this study is to understand the relationship between surface roughness and contact wettability. For this purpose, samples were prepared by using different steel alloys and etched at different etching durations in a mixed solution. The mixed solution for roughening process was prepared by keeping the molar ratio of nitric acid and hydrogen peroxide constant at 1:1, 1:2 respectively. The steel substrates were then immersed in another mixed solution of stearic acid and N, N'-dicyclohexylcarbodiimide in n-hexane (5 mmol/L) for 24 h to lower the surface energy of steel alloy surfaces after roughening step. The effects of the duration of chemical etching on surface roughness were evaluated by using profilometer and surface contact angles were measured using the sessile drop method. Surfaces were analyzed using scanning electron microscopy. Steel surfaces were changed from hydrophilic to hydrophobic/superhydrophobic. The obtained maximum contact angle was 168.36 degrees for CK40 samples, 161.99 degrees for CK22 samples, and 166.35 degrees for 5t37 steel samples. The results of this study showed that the surface contact angle was very sensitive to the change of surface roughness, and wettability could be controlled by changing the surface roughness. In addition, the surface roughness values of steel substrates that exhibit superhydrophobic behavior varied according to the steel type.Öğe The Morphologies and Wetting Properties of CK40 and AA2024 Surfaces Produced by Chemical Etching and Stearic Acid Modification(Maik Nauka/Interperiodica/Springer, 2023) Taskin, Nilhan Urkmez; Beji, Cigdem Ovaci; Ordu, Fatih; Taskin, VedatBy applying surface modification after chemical etching, superhydrophobic aluminum and steel surfaces were obtained. With different etching times, from all surfaces, different surface roughness values (Ra) were obtained. The effect of Ra's on surface contact angles (CA) was determined by applying surface modification with stearic acid (STA) to all surfaces under the same conditions. With increased etching time, the surface roughness of both aluminum and steel has increased. Thus, in the current study, wettability seems to be affected only by the changes in surface roughness values. Although the etching reactive and the modification procedure are being same, higher contact angles were obtained on steel surfaces in shorter etching durations compared to aluminum surfaces. The maximum contact angles measured were 125.35 +/- 8.32 degrees on aluminum surfaces and 164.68 +/- 3.62 degrees on steel surfaces. With the current etching method, the minimum etching times required to reach the hydrophobic/superhydrophobic structure for the CK40 and the AA2024 samples were determined. Furthermore, optimum etching times under 10 min for CK40 and under 30 min for AA2024 were determined achieve the maximum contact angle.Öğe New Processing Route for the Production of Functionally Graded 7075 Al/SiCp Composites via a Combination of Semisolid Stirring and Sequential Squeeze Casting(Mdpi, 2024) Genc, Serhan Karaman; Taskin, Nilhan UrkmezAdvanced processing techniques are required to produce functionally graded metal matrix composites due to the metallurgical conditions required during production. In this study, we developed a novel approach for this task by using a combination of two different methods to produce functionally graded 7075 Al/SiCp (5-20 wt.%) composites. The first process was direct semisolid stirring, which was used to prevent particle agglomeration, brittle reaction products, floating or settling of the reinforcements, and poor wettability. The second process was sequential squeeze casting, which enabled liquid diffusion between the two composite layers that were used to produce a functionally graded aluminum matrix composite. Thus, a method was developed to eliminate the problems encountered in the production of particle-reinforced metal matrix composite materials using liquid stirring methods and to produce composite materials with the desired functionally graded structure. The resulting functionally graded material was subjected to spectrometer analyses, density measurements, and metallographic examinations to determine the characteristics of its layers and interfacial zones, as well as to assess the formation of the graded structure. The results indicate the potential of using this new combined manufacturing method, which is efficient and controllable, to produce functionally graded metal matrix composites.Öğe PRODUCTION OF FG-AL-MMC BY SEMI-SOLID STIRRING AND SEQUENTIAL SQUEEZE CASTING METHODS(Tanger Ltd, 2020) Taskin, Nilhan Urkmez; Genc, Serhan KaramanIn this study, manufacturing of functionally graded ceramic reinforced aluminum matrix composite materials (FG-Al-MMC) by using direct semi-solid stirring and sequential squeeze casting method has been investigated. As a matrix material Al-7075 and as a reinforcement material SiC ceramic particles have been chosen for composite materials of FGM layers. Aluminum composite mixtures with different reinforcement ratios have been prepared by mechanically mixing SiCp reinforcements into semi-solid aluminum alloy and, FG-Al-MMC's have been produced by pouring the composite mixtures into a mold on top of each other in liquid form where each layer has been solidified under pressure. The partial melting of the previous layer due to the added liquid layer and the applied pressure cause bonding between layers with a transition region. This process has been repeated sequentially until a structure with the desired thickness and features were obtained. The structure formed between the layers with this manufacturing method was investigated by taking samples from different layers and transition regions of FG-Al-MMC. Density analyses, spectrometric analyses and optical analyses were carried out to determine the properties of FG-Al-MMC material. As a result, it is observed that successful production of functionally graded aluminum composite materials by the direct semi-solid stirring and sequential squeeze casting methods is possible.
