Browsing by Author "Toparli M."
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Item Calculation of temperature distribution on a crown tooth by using three-dimensional finite element method(Assoc Sci Res, 1999) Aykul H.; Toparli M.; Koksal N.S.The finite element was used to temperature changes with time to Au-AgPd alloy and porcelain crowns in three dimensional models of average maxillary second premolar. Temperature changes some critical nodes were calculated as a result of hot/cold liquid. Calculation programs were prepared by authors using FORTRAN 77. The tooth was assumed isotropic, homogenous, elastic and unsymmetric.Item The Three-Dimensional Finite Element Analysis of Fixed Bridge Restoration Supported by the Combination of Teeth and Osseointegrated Implants(Lippincott Williams and Wilkins, 2002) Dalkiz M.; Zor M.; Aykul H.; Toparli M.; Aksoy S.This study investigated the designs of osseointegrated prostheses in cases of free-end partial edentulism using comparative stress interpreted with the three-dimensional finite element method. Three free-end fixed osseointegrated prostheses models with various connection designs (ie, rigidly connected to an abutment tooth and an implant, rigidly connected to an implant and two abutment teeth, and rigidly connected to an implant and three abutment teeth) were studied. The stress values of the three models loaded with vertical, buccolingual, and linguobuccal directions at 30 ° angled to vertical axis forces were analyzed. When the fixed partial denture was connected to the three natural abutment teeth and an implant, the lowest levels of stress in the bone were noted.Item A calculation of stress distribution in metal-porcelain crowns by using three-dimensional finite element method(2002) Aykul H.; Toparli M.; Dalkiz M.The objective of this study was to calculate stress distribution in a maxillary second premolar tooth which occurred by the mastication force. The tooth model was crowned with Au-Pd alloy, Ni-Cr alloy and porcelain. A load of 450 N, at an angle of 45° to the longitudinal axis was applied on the occlusal margin of the crown tooth. The tooth was assumed isotropic, homogenous, elastic and unsymmetrical. This numerical study was carried out using three-dimensional finite element models and calculation programs were prepared by the authors using FORTRAN 77. The distribution of compressive, tensile and shear stress were plotted for the dentine, dentine-metal and metal-porcelain interfaces. The highest stress values were observed when Ni-Cr alloy and porcelain was used. © 2002 Blackwell Science Ltd.Item Residual thermal stress analysis in cylindrical steel bars using finite element method and artificial neural networks(2002) Toparli M.; Sahin S.; Ozkaya E.; Sasaki S.In this study, it was proposed that the residual stresses within steel bars after quenching in water from 600 °C could be calculated by using the finite element method (FEM) and an artificial neural network (ANN) algorithm. Three modelled cylindrical specimens of AISI 1020 steel were heated and then quenched in water. Using FEM, temperature distribution with time and thermal residual stress values in the samples were calculated after cooling. The analysis was extended to elastic-plastic deformation during the quenching of steel cylinders of various diameters. The calculated temperature and thermal residual stress values were used in training a multi-layer, feed forward, back propagation ANN algorithm. The results obtained via the ANN algorithm method have been compared with the FEM results. Comparison showed good agreement. © 2002 Elsevier Science Ltd. All rights reserved.Item Modelled and measured residual stresses in a bimaterial joint(2003) Sahin S.; Toparli M.; Ozdemir I.; Sasaki S.A finite element technique has been used to predict residual and thermal stresses due to welding. For this purpose, a steel-brass material couple was chosen and thin plates of the materials were hard brazed. The finite element study was carried out using two-dimensional models. After the temperature distributions as a result of welding were calculated, thermal and residual stress values obtained. Thermo-elasto-plastic formulations using a von-Mises yield criterion with linear isotropic-hardening were employed. For this deformation, the initial stress method was used and the kinematical Bauschinger effect was considered. The authors prepared all calculation programs using FORTRAN 77. To obtain residual stresses that occur during the welding, the hole-drilling strain-gage method was chosen and conducted in accordance with the ASTM Standard E 837-99. The agreement between the calculated results and the experimental data shows that the finite element analysis method is reliable. © 2002 Elsevier Science B.V. All rights reserved.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 Hardness and yield strength of dentin from simulated nano-indentation tests(2005) Toparli M.; Koksal N.S.The finite element method (FEM) is applied for studying the hardness (H) and yield strength (Y) of dentin subjected to a nano-indentation process. The nano-indentation experiments were simulated with the ABAQUS finite element software package. This test, performed with a spherical indenter, was simulated by axisymmetric finite element analysis. The load versus displacement was calculated during loading-unloading sequence for different elastic modulus (E) and yield strength. Hardness and maximum principal compressive and tensile stresses were plotted for different elastic modulus depending on yield strength. The dentin was assumed to be isotropic, homogenous and elasto-plastic. The theoretical results outlined in this study were compared with the experimental works reported in the literature and then hardness and yield strength of dentin was estimated. © 2004 Elsevier Ireland Ltd. All rights reserved.Item The evaluation of thermal stresses in thermoplastic laminated composites with different square holes(Association for Scientific Research, 2007) Şen F.; Toparli M.; Sinan Köksal N.In this study, a thermal stress analysis was evaluated on symmetric angle-ply laminated thermoplastic composite plates that were having different square hole dimensions. The temperature loading was selected uniformly. Besides, it was applied with various values that were chosen as 50, 60, 70, 80, 90, 100°C, because of the fact that the effect of increasing uniform temperature on thermal stresses was examined. The width plate-to-the width square hole, a/b, ratios were changed as 2, and 4. Thermoplastic laminated composite plates were assumed to be simple supported. Laminated plates were composed of four orthotropic layers oriented with angle-ply in symmetric manner. The solution was carried out by using ANSYS finite element program. The results were showed in figures depending on applied temperatures, orientations and dimensions of square hole. © Association for Scientific Research.Item Characterization and determination of FexB layers' mechanical properties(2008) Culha O.; Toparli M.; Sahin S.; Aksoy T.The aim of this study is to obtain microstructural characteristics and investigate the mechanical properties such as hardness, Young's modulus and fracture toughness of the boride layer depending on process time and temperature. The produced double layers (FeB and Fe2B) were extensively analyzed with respect to X-ray diffraction (XRD) and scanning electron microscopy (SEM). The XRD pattern of the boride layers, which were formed on SAE 1020 and 1040 quality steel at 900 °C for 2 h, 4 h and 6 h, include only FeB phase on surface with (1 1 1), (2 1 0), (1 0 1) and (1 1 1) planes. SEM cross-sectional investigations show that double-phase boride layer existence from surface to inside of substrate. The structural compositions of layers consist of boron rich phase (FeB) and iron rich phase (Fe2B), respectively. Surface roughness value of samples is important parameter for micro-indentation test with Dynamic Ultra Micro Hardness Tester. After diffusion controlled boriding process, material surface roughness can be high for micro-indentation test. So, surface polishing process is applied for decreasing roughness of FeB layers. Surface roughness values of 2 h, 4 h and 6 h borided SAE 1020 and SAE 1040 quality steel were decreased from 0.9 μm to 0.05 μm by polishing process. Mechanical properties of layers were examined by Shimadzu Dynamic Ultra-microhardness test machine for estimating Young's modulus due to load-unload sensing analysis and in addition to mechanical investigation hardness-depth curves of the layer were obtained for estimating indentation depth and load dependency of mechanical properties. Load depended elastic modulus (125-624 GPa) and hardness (17-33 GPa) were obtained at 80 mN, 160 mN, 320 mN and 640 mN applied peak loads depending on boriding process time. Fracture toughness properties of FeB surface layers were calculated by Vickers Fracture Toughness method for 1 N applied peak load with measuring crack length after loading stage was finished. © 2007 Elsevier B.V. All rights reserved.Item Characterization and determination of mechanical properties of ybco superconducting thin films with manganese using the tfa-mod method(2013) Culha O.; Birlik I.; Toparli M.; Celik E.; Engel S.; Holzapfel B.The aim of this study is to determine the microstructure, superconducting and mechanical properties of YBa2Cu3O6.56 (YBCO) and YBCO thin films with a manganese (Mn) addition. All the YBCO superconducting films (undoped and Mn-doped) were dip-coated onto (001) SrTiO3 (STO) single-crystal substrates with a metalorganic deposition using the trifluoroacetate (TFA-MOD) technique. The phase analysis, microstructure, surface morphologies and critical temperature (Tc) of the superconducting thin films were determined with an X-ray diffractometer (XRD), a scanning electron microscope (SEM), an atomic force microscope (AFM) and an inductive Tc measurement system. Since the main issue of this study is to determine the mechanical-property variations of the superconducting thin films with/without a Mn addition, the adhesion strength of these films on a STO substrate was tested with a Shimadzu scratch tester. Depending on the Mn addition, the critical forces of pure films increase from 56.23 mN, 58.63 mN and 60.11 mN for pure YBCO, YBCO with 0.05 g and 0.10 g of Mn. Furthermore, Young's modulus and the hardness of the undoped and Mn-doped YBCO thin films were measured with a CSM Berkovich nanoindenter using the load-unload sensing analysis under a 0.3 mN applied load.Item Heat treatment effects on mechanical properties of atmospheric plasma sprayed FexB coatings on Al substrate(2014) Culha O.; Sahin S.; Ozdemir I.; Toparli M.In this work, we draw attention to determination of heat-treatment effects on mechanical properties of atmospheric plasma sprayed (APS) FexB coatings on aluminum substrates by micro-indentation technique. With this regard, iron boride powders of Fe-18.8B-0.2C-0.5Si-0.8Al (wt.%) were deposited onto Al substrates by APS in order to improve the mechanical properties of Al surface. As-sprayed coatings are composed of mainly FexB and iron matrix supersaturated with boron owing to the rapid solidification of molten droplets flattened on a substrate. It was observed that APS coatings exhibited characteristic wavy layered structure having porosity, inclusions, and semi-melted particles. The postfurnace treatment of APS coatings was carried out at temperatures ranged from 450 to 550°C in an argon atmosphere. The post-treatment applied for APS deposits led to increase in hardness of 40% without showing cracks. Furthermore, micro-mechanical properties of Fe xB coatings were examined by Shimadzu Dynamic Ultra-Microhardness Tester for estimating Young's modulus and hardness due to load-unload sensing analysis by applying different loads such as 160, 320, and 640 mN to determine load and indentation depth dependency of APS FexB on Al substrate for each samples, in details. © 2011, Society for Experimental Mechanics.Item Fabrication and characterization of nanostructured anatase TiO2 films prepared by electrochemical anodization and their photocatalytic properties(Elsevier Ltd, 2015) Yurddaskal M.; Dikici T.; Yildirim S.; Yurddaskal M.; Toparli M.; Celik E.In this study, nanostructured anatase titanium dioxide (TiO2) films were fabricated by electrochemical anodization of titanium first, and then annealed at 500 °C for 2 h. Effect of electrolyte concentration, anodization time and electrolyte temperature on the surface morphology of the resulting TiO2 thin films were investigated. The phase structures, surface morphology and chemical composition were analyzed using X-ray diffraction (XRD), scanning electron microscope (SEM), atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). The photocatalytic activity tests of the samples were evaluated by the degradation of aqueous methylene blue (MB) solutions under UV light illumination for different periods of time. The results showed that the structure of nanostructured TiO2 films depended strongly on the anodization parameters. It was found that there were micro-scale pores (<10 μm) and nano-scale pores (diameter in the range from 40 to 70 nm) on the anodized titanium surfaces. This study indicated that structures, surface morphology, and surface area of the nanostructured anatase TiO2 films played an important role on their photocatalytic performance. The results clearly proved that nanostructured anatase TiO2 film prepared with optimum process parameters resulted in enhancement of the photocatalytic activity. © 2015 Elsevier B.V.Item Synthesis and characterization of Ag doped TiO 2 heterojunction films and their photocatalytic performances(Elsevier B.V., 2016) Demirci S.; Dikici T.; Yurddaskal M.; Gultekin S.; Toparli M.; Celik E.In this study, undoped and silver (Ag) doped titanium dioxide (TiO 2 ) films were successfully synthesized by sol-gel spin coating technique on the Si substrates. Photocatalytic activities of the TiO 2 films with different Ag content were investigated for the degradation of methylene blue (MB) under UV light irradiation. The crystal phase structure, surface morphology, chemical and optical properties of Ag-doped TiO 2 films were characterized using an X-ray diffractometer (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), UV–vis spectrophotometer, and FTIR spectrophotometer. The results showed that the Ag-doped TiO 2 films calcined at 500 °C had the crystalline anatase phases and the surface morphologies with some cracks. Ag substitution into TiO 2 matrix enhanced the photocatalytic activity of TiO 2 films under UV light irradiation as compared to the undoped TiO 2 film. Furthermore, the results indicated that the 0.7% Ag doped TiO 2 film exhibited a superior photocatalytic activity than that of undoped and other Ag-doped TiO 2 films. This study demonstrated the potential of an application of Ag doped films to efficiently treat dissolved organic contaminants in water. © 2016 Elsevier B.V.