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Citation - WoS: 8
Citation - Scopus: 8
Experimental Investigation of Friction in Deep Drawing
(Springer London Ltd, 2017) Kalkan, Hakan; Hacaloglu, Tugce; Kaftanoglu, Bilgin
Investigation of friction is carried out in the radial drawing region between the die and blank holder and also in the stretching zone over the punch in deep drawing. Two methods are developed to calculate the coefficient of friction in each zone using the experimentally determined data such as punch force diagrams and strain distributions obtained by an optical scanning system. The current methods differ from the existing techniques which are obtained in simulative tests. The proposed methods can be applied in room temperature and at elevated temperatures. Comparisons of friction coefficients are made with those obtained by other techniques.
Citation - WoS: 8
Citation - Scopus: 9
Development of Hard, Anti-Reflective Coating for Mid Wave Infrared Region
(Elsevier, 2021) Ozhan, Alp Eren Sinan; Hacaloglu, Tugce; Kaftanoglu, Bilgin
In the 3-5 mu m Mid Wave Infrared (MWIR) thermal imaging region, the number of alternative transparent optical substrate materials are quite limited. Silicon (Si) and germanium (Ge) are among the common optical materials used in the MWIR region. However, these materials and the thin film coatings on them, suffer from low hardness and brittleness hence need to be protected against scratches and hard flying particles like sand, dust, etc.. In industry, a single layer amorphous Diamond Like Carbon (DLC) coating is used to protect the outer layer while transmitting MWIR energy. This paper suggests single layer Boron Nitride (BN) and Boron Carbide (B4C) coatings as alternatives to commercial DLC coating, providing the necessary protection and transmission efficiency with anti-reflective properties. The proposed boron-contained coatings also have an advantage of greater temperature resistance over DLC. Finally, a two-layer anti-reflective coating containing Boron Carbide layer as an outer protective coating is demonstrated.
Citation - WoS: 12
Citation - Scopus: 14
Coating of Titanium Implants With Boron Nitride by Rf-Magnetron Sputtering
(indian Acad Sciences, 2016) Gokmenoglu, Ceren; Ozmeric, Nurdan; Cakal, Gaye; Dokmetas, Nihan; Ergene, Cansu; Kaftanoglu, Bilgin
Surface modification is necessary for titanium implants since it is unable to induce bone apposition. The beneficial effects of boron on bone formation, composition and physical properties make it suitable as a coating material. In the present study, surface properties of boron nitride (BN) coating on titanium implants were evaluated. Twenty-four implants and 12 abutments were coated with BN by RF-magnetron sputtering system. ATR-FTIR measurements were conducted to assess surface chemistry and morphology of BN-coated implants. Adhesion tests were performed by CSM nanoscratch test device to determine adhesion of BN to titanium surface. Surface profilometry and atomic force microscopy (AFM) was used to evaluate surface roughness. Mean roughness values were calculated. Contact angle measurements were done for evaluation of wettability. Surface characterization of coated implants was repeated after RF power of the system was increased and voltage values were changed to evaluate if these settings have an impact on coating quality. Three different voltage values were used for this purpose. Hexagonal-BN was determined in FTIR spectra. RF-coating technique provided adequate adherence of BN coatings to the titanium surface. A uniform BN coating layer was formed on the titanium implants with no deformation on the titanium surface. Similar roughness values were maintained after BN coating procedure. Before coating, the contact angles of the implants were in between 63(ay) and 79(ay), whereas BN coated implants' contact angles ranged between 46(ay) and 67(ay). BN-coated implant surfaces still have hydrophilic characteristics. The change in voltage values seemed to affect the surface coating characteristics. Especially, the phase of the BN coating was different when different voltages were used. According to our results, BN coating can be sufficiently performed on pretreated implant surfaces and the characteristics of BN coated surfaces can be changed with the change in parameters of RF-magnetron sputtering system.
Citation - WoS: 7
Citation - Scopus: 7
Effect of Hardening Models on Different Ductile Fracture Criteria in Sheet Metal Forming
(Springer France, 2016) Dizaji, Shahram Abbasnejad; Darendeliler, Haluk; Kaftanoglu, Bilgin
Prediction of the fracture is one of the challenging issues which gains attention in sheet metal forming as numerical analyses are being extensively used to simulate the process. To have better results in predicting the sheet metal fracture, appropriate ductile fracture criterion (DFC), yield criterion and hardening rule should be chosen. In this study, the effects of different hardening models namely isotropic, kinematic and combined hardening rules on the various uncoupled ductile fracture criteria are investigated using experimental and numerical methods. Five different ductile fracture criteria are implemented to a finite element code by the user subroutines. The criterion constants of DFCs are obtained by the related experimental tests. The in-plane principle strains obtained by the finite element analyses for different DFCs are compared with the experimental results. Also, the experimental results are used to evaluate the principle strain values calculated by the finite element analysis for different combinations of DFCs and hardening rules. It is shown that some DFCs give better predictions if the appropriate hardening model is employed.
Theoretical Modelling of Magnetron Sputtering of Boron Nitride Coating
(Springer Heidelberg, 2023) Rake, Nakka; Kaftanoglu, Bilgin; Hacaloglu, Tugce; Aydogan, Asude
The fundamentals of the magnetron sputtering (MS) technique are simple. However, the complex interplay of various physical and chemical sub-processes lies in its simplicity. The direct simulation Monte Carlo (DSMC) method is used to model the MS of the Boron Nitride (BN) coating. The Lorentz force, which is created by an electric field, magnetic field and particle collision, is utilised to model the BN coating. Three distinct bias voltages are used to generate three different BN-coating models under the same conditions. The modelling of BN coatings reveals that the deposition rate decreases as the substrate voltage increases.
Citation - WoS: 5
Measurement of Solar Radiation in Ankara, Turkey
(Turkish Soc thermal Sciences Technology, 2013) Caglar, Ahmet; Yamali, Cemil; Baker, Derek K.; Kaftanoglu, Bilgin
The solar energy potential of Ankara, Turkey, (39.89 degrees N, 32.78 degrees E) has been investigated using the measurements of global and beam radiation over the period May 2008 to May 2009. Surface air temperature was also measured and variation in clearness index evaluated over this period. Global and beam radiations have been analyzed using hourly, daily and monthly averages obtained from 1-minute averages of recorded data. Results show that annual average daily global and beam radiations were 17.04 and 15.72 MJ/m(2)/day, respectively, for this period. The results are compared with the data available for several other cities in Turkey. The study shows that Ankara has a large solar potential. The consistency of these data with that from the State Meteorological Service (SMS) weather station in Ankara was analyzed. Significant differences between these 2 stations were found and are attributed to measurement error at the SMS station. New radiation-measurement stations should be established to create a better national radiation database for Turkey.
Citation - WoS: 58
Citation - Scopus: 66
Experimental Investigation of a Natural Zeolite-Water Adsorption Cooling Unit
(Elsevier Sci Ltd, 2011) Solmus, Ismail; Kaftanoglu, Bilgin; Yamali, Cemil; Baker, Derek
In this study, a thermally driven adsorption cooling unit using natural zeolite-water as the adsorbent-refrigerant pair has been built and its performance investigated experimentally at various evaporator temperatures. The primary components of the cooling unit are a shell and tube adsorbent bed, an evaporator, a condenser, heating and cooling baths, measurement instruments and supplementary system components. The adsorbent bed is considered to enhance the bed's heat and mass transfer characteristics; the bed consists of an inner vacuum tube filled with zeolite (zeolite tube) inserted into a larger tubular shell. Under the experimental conditions of 45 degrees C adsorption, 150 degrees C desorption, 30 degrees C condenser and 22.5 degrees C, 15 degrees C and 10 degrees C evaporator temperatures, the COP of the adsorption cooling unit is approximately 0.25 and the maximum average volumetric cooling power density (SCR,) and mass specific cooling power density per kg adsorbent (SCP) of the cooling unit are 5.2 kW/m(3) and 7 W/kg, respectively. (C) 2011 Elsevier Ltd. All rights reserved.
Antibacterial Activity of Cubic Boron Nitride (cbn) Coatings on Stainless Steel Grade 316 (316l)
(Amer Chemical Soc, 2010) Uzunoglu, Emel; Sengonul, Merih; Derici, Kursat; Biriken, Derya; Kaftanoglu, Bilgin; Sengonul, Merih
[No Abstract Available]
Citation - WoS: 38
Citation - Scopus: 48
Focus Variation Measurement and Prediction of Surface Texture Parameters Using Machine Learning in Laser Powder Bed Fusion
(Asme, 2020) Ozel, Tugrul; Altay, Ayca; Kaftanoglu, Bilgin; Leach, Richard; Senin, Nicola; Donmez, Alkan
The powder bed fusion-based additive manufacturing process uses a laser to melt and fuse powder metal material together and creates parts with intricate surface topography that are often influenced by laser path, layer-to-layer scanning strategies, and energy density. Surface topography investigations of as-built, nickel alloy (625) surfaces were performed by obtaining areal height maps using focus variation microscopy for samples produced at various energy density settings and two different scan strategies. Surface areal height maps and measured surface texture parameters revealed the highly irregular nature of surface topography created by laser powder bed fusion (LPBF). Effects of process parameters and energy density on the areal surface texture have been identified. Machine learning methods were applied to measured data to establish input and output relationships between process parameters and measured surface texture parameters with predictive capabilities. The advantages of utilizing such predictive models for process planning purposes are highlighted.
Citation - WoS: 17
Citation - Scopus: 20
Prediction of forming limit curve at fracture for sheet metal using new ductile fracture criterion
(Elsevier Science Bv, 2018) Dizaji, Shahram Abbasnejad; Darendeliler, Haluk; Kaftanoglu, Bilgin
The application of ductile fracture criteria (DFCs) in numerical analysis of sheet metal forming processes can lead to the accurate determination of the fracture initiation. In this study, a new uncoupled ductile fracture criterion (DFC) has been developed which considers the effects of material parameters on the forming limit curves (FLCs) and can be easily implemented in the finite element codes. Two different constitutive models have been employed with the new DFC in order to evaluate the results obtained for fracture prediction. Various experimental tests have been utilized to validate the new criterion and its results are also compared with other well-known uncoupled DFCs. It is observed that the new criterion predicts the ductile fracture for all aluminum, steel and stainless steel materials better than the former criteria.

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