Browsing by Author "Köksal N.S."
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Item Investigation of joining steel hard metal tips used in boring machines; [Sondaj matkaplarinda kullanilan sert metal uç-çeli̇k çi̇fti̇ni̇n bi̇rleşebi̇li̇rli̇ǧi̇ni̇n i̇ncelenmesi̇](1999) Uzkut M.; Köksal N.S.; Şahin S.The use of boring machines under highly varying working conditions for long periods requires a successful joining of material couples. If the joining is not performed successfully, hard metal tips will shorten the life of the boring machine by breaking off from the steel body. In addition, these broken hard metal tips deposited in the bore will affect later boring work negatively. For this reason, the quality of joining has a great significance from the economy and efficiency point of view. In this study, joining by brazing of 0.4% C steel with 9% Co bonder mixed wolfram carbide based hard metal tip used in boring machines is investigated. Joining by brazing of wolfram carbide based hard metal tip with 0.4% C steel is made under suitable temperature and pressure using suitable dekapan. The microhardness and metalographic investigation of steel, braze, and hard metal tip has been done in the joining region. In the metalographic investigations, it has been observed that, in the internal structure and hardness values of solder, diffusion from steel to solder and from solder to steel occurs. Also element diffusion from hard metal tip to solder layer takes place.Item Nonlinear stress analysis of unidirectionally reinforced symmetric aluminum metal-matrix laminated beams under a bending moment(2002) Sayman O.; Çallioǧlu H.; Ataş C.; Köksal N.S.This 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 [90°/0°]s, [30°/-30°]s, [45°/-45°]s and [60°/-60°]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 Calculation of temperature and thermal stress in refractory materials quenched in water using finite element methods(Trans Tech Publications Ltd, 2004) Köksal N.S.; Toparli M.In 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°C and then transferred into electric furnace at 400, 600 and 800°C 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°C) 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 Mechanical properties of magnesia and magnesia-chromite refractory materials(Trans Tech Publications Ltd, 2004) Köksal N.S.; Toparli M.; Altun I.A.In 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°C. 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°C. 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°C. It was seen that fracture toughness values had decreased by the increase at temperature.Item Elastic-plastic stress analysis of thermoplastic matrix laminated composite beams(2004) Çallioǧlu H.; Köksal N.S.; Ataberk N.; Kaynak I.This study deals with an elastic-plastic behavior of woven steel fibers reinforced thermoplastic matrix laminated composite beam subjected to a bending moment. The beam consists of symmetric four orthotropic layers and its material is assumed to be strain hardening. The Tsai-Hill theory is used as a yield criterion in the solution. The Bernoulli-Euler hypotheses are utilized for small plastic deformations. The beam lay-up sequences are chosen as [0°]4, [15°/-15°]s, [30°/-30°] s and [45°/45°]s. The bending moment values that begin plastic flow at the upper and lower surfaces of the beam are carried out for various stacking sequences. The variations of the elastic, elastic-plastic and residual stress components versus increasing plastic region spread are given in tables and figures. The transverse displacement is obtained at the free end, numerically.Item The determination of element diffusion in connecting SAE 1040/WC material by brazing(2005) Uzkut M.; Köksal N.S.; Ünlü B.S.This 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. © 2005 Published by Elsevier B.V.Item Production and characterization of wall plaster with borax and paper wastes and perlite additives; [Atık bor, atık kâǧıt ve perlit katkılı sıva: Malzemesinin üretimi ve karakterizasyonu](Ekoloji, 2009) Batar T.; Köksal N.S.; Yersel Ş.E.In 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 .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/m2K and a mechanical strength (bending) of 61.44 kg/cm2. The required standards by TSE 825 are 0.13 W/m2K. When 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 Stress analysis in al based composites depending on joining quality(Association for Scientific Research, 2011) Köksal N.S.; Alkan M.It is essential that joints in the design of aluminium based materials be safe and at the desired strength. Specific methods are to be used in welding of these materials. Brazing, that assures joining without changing the material properties, is widely used for this purpose. In this method, quality joining can be achieved, provided the parameters are set up accurately. In this study, joining characteristics of aluminium based composite materials widely used in automotive industry are investigated in detail. Solid models of the parts manufactured by brazing are created using Solidworks software. Hydrostatic loading similar to the real working conditions is applied to these models and stress analysis is performed using ANSYS software. In the samples, joining regions are 2 mm and 2,83 mm in length; and stress distributions are investigated in three groups assuming full, 70% and 50% joining. Stresses arising from loading in the model are below the damage inducing level, but the shape and the length of the joining region are observed to be significant in stress development. © Association for Scientific Research.Item Investigation of mechanical and metallurgical properties of titanium alloys by using laser and GTA welding(2013) Kilerci I.; Köksal N.S.Titanium 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 mechanical and metallurgical properties of titanium alloys by using laser and GTA welding(Institute of Materials and Machine Mechanics, Slovak Academy of Sciences, 2013) Kilerci I.; Köksal N.S.Titanium 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. © 2013 Institute of Materials and Machine Mechanics, Slovak Academy of Sciences. All rights reserved.Item Investigation of the geometrical accuracy and thickness distribution using 3D laser scanning of AA2024-T3 sheets formed by SPIF(Institute of Metals Technology, 2017) Bayram H.; Köksal N.S.Incremental 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.