Browsing by Author "Celik S."

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Analysis of indentation size effect (ISE) behavior in low-load Vickers microhardness testing of (Sm123) 1-x (Nd123) x superconductor system
(2013-01-01) Celik S.; Ozturk O.; Coşkun E.; Sarıhan M.; Asikuzun E.; Ozturk K.; Terzioglu C.
Indentation size effect (ISE) for (Sm123) 1-x (Nd123) x superconducting samples which were fabricated by the solid state reaction technique for values of x = 0.00, 0.05, 0.10, 0.20, and 0.30 was investigated by analyzing the theoretical models. When the experimental data of a number of single crystals which have the different crystal structure and different chemical bonding inside the polycrystallined samples were analyzed with the ISE models, the sample encountering with resistance and elastic deformation was observed as well as plastic deformation. The microhardness values on different surfaces of materials were calculated by using Meyer Law, proportional specimen resistance model, modified proportional specimen resistance model, elastic/plastic deformation model and the Hays-Kendall (HK) approach. The results showed that the HK approach was determined as the most successful model. Furthermore, X-ray powder diffraction and scanning electron microscope measurements were analyzed for superconducting properties of (Sm123) 1-x (Nd123) x superconductor system. The results showed that microhardness values at the minimum load and averaged plateau region of load increased with increase of Nd123 concentration. Nd123 content can be used as to be estimated the microhardness value of (Sm123) 1-x (Nd123) x superconducting sample in the range of 0.878-2.717 GPa. The control of the microhardness value by using Nd123 content in (Sm123) 1-x (Nd123) x superconducting structure can be useful in technological applications in superconductivity industry. © 2013 Springer Science+Business Media New York.
Investigation of structural, superconducting and mechanical properties of Co/Cu substituted YBCO-358 ceramic composites
(2019-01-01) Ozturk O.; Arebat R.; Nefrow A.; Bulut F.; Guducu G.; Asikuzun E.; Celik S.
In this study, we have examined the structural, superconducting and mechanical properties of Y 3 Ba 5 Cu 8−x Co x O 18 − δ system (x = 0, 0.05, 0.1, 0.15, 0.2 and 0.5), which is produced by conventional solid-state reaction method. Produced samples have been examined using X-ray diffraction (XRD), Scanning electron microscopy (SEM), Energy dispersive X-ray spectroscopy (EDS), Vicker’s hardness (H v ) and electrical resistance measurement (R–T). According to the XRD patterns, we have obtained that the Co nanopowder doping has been caused some changes on the average grain size, characteristic peak intensities and lattice parameters of the Y 3 Ba 5 Cu 8 O 18 − δ crystal system. Furthermore, according to the electrical resistance measurements, the critical temperature (T c ) values of all the samples have tended to decrease constantly with the increment in the doping ratio in the Y358 crystal structure. As for the variation in the microhardness parameters of superconducting materials, the H v parameters and other related computations (Young’s modulus and yield strengths) have been found to increase regularly with the Co/Cu substitution level. Besides, the characteristic H v curves have confirmed that the whole bulk of Bi-2212 samples showed untypical reverse indentation size effect (RISE) behavior.
Throughfall, stemflow, and interception characteristics of coniferous forest ecosystems in the western black sea region of Turkey (Daday example)
(2018-05-01) Aydın M.; Güneş Şen S.; Celik S.
This study aims to identify precipitation, throughfall, stemflow, precipitation, and interception processes in pure black pine, pure Scots pine, and mixed black pine–Scots pine forest ecosystems and present the precipitation partitioning according to different stand types. Throughfall and stemflow measurements were performed using five standard precipitation gauges in a pilot area established to represent pure black pine, pure Scots pine, and mixed black pine–Scots pine stands in the Bezirgan Basin. The total precipitation was measured in an open field close to the study area. Throughfall values were calculated as the percentage of precipitation measured in an open field. According to the results of the study, the throughfall values were 69.8% in black pine, 73.9% in Scots pine, and 77.7% in the mixed black pine–Scots pine stands; the stemflow values were 2.6% in black pine, 5.9% in Scots pine, and 3.1% in the mixed black pine–Scots pine stands; the amounts of precipitation reaching the forest floor were 72.3% in black pine, 79.8% in Scots pine, and 80.7% in the mixed black pine–Scots pine stands; and the interception values were found to be 27.7% in black pine, 20.2% in Scots pine, and 19.2% in the mixed black pine–Scots pine stands.