Browsing by Author "Köksal, NS"
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Item Mechanical properties of magnesia and magnesia-chromite refractory materialsKöksal, NS; Toparli, M; Altun, IAIn this study, modulus of rupture, elastic modulus and fracture toughness values were investigated at elevated temperature for magnesia and magnesia-chromite content of chromite between 6% and 20%. Modulus of rupture and elastic modulus values were calculated by three point bending test at temperatures 400, 600, 800 and 1400 degreesC. Modulus of rupture and Young's modulus values decreased when temperature and content of chromite increased. Modulus of rupture and Young's modulus values at room temperature were compared to the values at 400, 600, 800 and 1400 degreesC. Young's modulus values decreased to about 40% and modulus of rupture values decreased to about 25% of the values at room temperature. The samples were notched as a/h = 0.3 by cutting tool of 0.2 mm thickness. Fracture toughness values were calculated at each temperature. Fracture toughness value at room temperature was compared to the values at 400, 600, 800 and 1400 degreesC. It was seen that fracture toughness values had decreased by the increase at temperature.Item Production and Characterization of Wall Plaster with Borax and Paper Wastes and Perlite AdditivesBatar, T; Köksal, NS; Yersel, SEIn this study, a new wall plaster product was generated using 0-5% perlite, 0-2.5% waste paper and 3.5-17.7% waste calcined borax. The optimum ratios for the additives were 3% perlite, 1.5% waste paper and 7.1% waste calcined borax. The new plaster was subjected to mechanical strength and thermal transmittance measurements using TS 825 and TS 12808-3 Turkish standards. Under optimal mixing ratios, the plaster had a thermal conductivity of 0.17 W/m(2)K and a mechanical strength (bending) of 61.44 kg/cm(2) 2K. V. The required standards by TSE 825 are 0.13 W/m(2)K the new product was compared with the existing plasters in the market, it was observed that thermal transmittance and mechanical strength were both increased by 26% and 31%, respectively. Thus, a new environmental-friendly wall plaster product was produced.Item Calculation of temperature and thermal stress in refractory materials quenched in water using finite element methodsKöksal, NS; Toparli, MIn this study, temperature and thermal stress distribution calculated using a finite element method for magnesia and magnesia-chromite content of chromite between 6% and 15%. The thermal and mechanical properties of the materials were measured using standard laboratory procedure. The samples were dried at 110 degreesC and then transferred into electric furnace at 400, 600 and NOT and held there for 30 min. Samples were then moved into water and left there for 3 minutes. A quenching simulation was made for three different temperatures (400, 600 and 800 degreesC) using ANSYS 6.0 package. The finite element study was carried out using two-dimensional models. The refractory material was assumed to be homogenous and isotropic. Time dependence of temperature and thermal stress were calculated in surface and center of the plate specimen subjected to the thermal shock by quenching in water.Item Nonlinear stress analysis of unidirectionally reinforced symmetric aluminum metal-matrix laminated beams under a bending momentSayman, O; Çallioglu, H; Atas, C; Köksal, NSThis study deals with elastic-plastic behavior of aluminum metal-matrix laminated cantilever beam subjected to a bending moment at the free end. The Bernoulli-Euler theory is utilized in the solution and small plastic deformations are considered. The beam consists of four layers and its material is assumed to be linearly hardening. A few ply arrangements such as [90degrees/0degrees]s, [30degrees/-30degrees]s, [45degrees/-45degrees]s and [60degrees/-60degrees]s are taken into consideration for such an analysis. The moment values that initiate plastic flow at any point of the beam are carried out for diverse stacking sequences. The variation of the elastic, elastic-plastic and residual stress components versus increasing plastic zone spread are given in tables and figures.Item Tribological properties of polymer-based journal bearingsÜnlüe, BS; Atik, E; Köksal, NSPolymer-based materials are widely used due to their good corrosion resistance, self lubrication, and wear resistance properties at low speeds and but are not suitable for lubrication in journal bearings. High performance engineering polymers ensure desired properties for journal bearings and give good tribological results. In this study, tribological behaviors of polymer-based PE, PA, POM, PTFE, and Bakelite bearings have been investigated and evaluated. As a result, the highest wear resistance has occurred in PA and POM bearings. (C) 2008 Published by Elsevier Ltd.Item INVESTIGATION OF TRIBOLOGICAL PROPERTIES CuSn10 BEARING MATERIALÜnlü, BS; Köksal, NS; Atik, E; Meriç, CBronzes which copper based alloys is widely used because of properties physical, thermal and tribological as journal bearing material. This material that has tribological performance good conclusions gives at journal bearings. In this study, CuSn10 bronze that were manufactured journal bearings friction and wear properties has been examined and compared. SAE 1050 steel shaft has been used as counter abrader. Experiments have been carried out 10 N and 20 N loads, 750 and 1500 rpm, dry and lubricated conditions by using radial journal bearing wear test rig. As a results, high friction coefficient and weigh loss have been obtained at dry condition more than lubricated condition.Item The determination of element diffusion in connecting SAE 1040/WC material by brazingUzkut, M; Köksal, NS; Ünlü, BSThis paper examines the element diffusions that take place in material when SAE 1040-WC materials are connected by brazing. During the brazing process, oxyacetylene fire was used and connected parts were cooled in air. On the connection zone, microhardness measurements and microprobe analyses were made. The hardness distribution in microhardness measurements on this zone shows the existence of element diffusion. Having performed line and surface micro probe analyses of various zones, postbrazing diffusions of Co and Ni elements were determined. (c) 2005 Published by Elsevier B.V.Item Investigation of mechanical and metallurgical properties of titanium alloys by using laser and GTA weldingKilerci, I; Köksal, NSTitanium alloys are widely used in many fields such as the automotive, aerospace and chemical industries. In some applications, titanium alloys are needed for use with particular welding methods. These are GTAW, GMAW and laser welding. In this study, Titanium Grade-2 (Cp-Ti) plates were welded using laser welding and GTAW. Tensile and flexural tests were applied to the welded samples. The microstructure and SEM images of main material and welded regions were studied and microhardness measurements were performed. Tensile and flexural strengths of laser welded samples were higher than those of GTA welded samples. The microhardness values of the weld-zone of laser welded samples were lower than those of the GTA welded samples welding zone. In microstructure and SEM investigations, the oxide structures and splashes of molten metal appearing like drops were identified. The width of the weld-zone in laser welding was in a narrow range.Item INVESTIGATION OF THE GEOMETRICAL ACCURACY AND THICKNESS DISTRIBUTION USING 3D LASER SCANNING OF AA2024-T3 SHEETS FORMED BY SPIFBayram, H; Köksal, NSIncremental sheet forming (ISF) is developed in order to meet the increasing demand for sheet metal forming and because it is a more economical method. First of all, this method gains attention become it is a die-less method. Furthermore, process flexibility and higher formability are other advantages of this method. In this study, AA2024-T3 sheets with a determined geometry and parameters were formed using the ISF method. Among the forming process parameters, tool path, step size and lubrication parameters were changed. The tool diameter, feed rate, spindle speed, angle of the wall and the tool coating parameters were kept constant. The thickness distributions and geometrical accuracy of the processed samples with the three-dimensional laser scanning method were examined accurately. It is clear from the results that the tool path that spirals and always keeps in touch is more successful than the tool path that makes it an incremental process. ISF is preferable to die production for limited production runs because it is more economic and the processing time is short.