Browsing by Author "Kaftanoglu, Bilgin"
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Article Citation Count: 73Adsorption properties of a natural zeolite-water pair for use in adsorption cooling cycles(Elsevier Sci Ltd, 2010) Kaftanoğlu, Bilgin; Yamali, Cemil; Kaftanoglu, Bilgin; Baker, Derek; Caglar, Ahmet; Manufacturing EngineeringThe equilibrium adsorption capacity of water on a natural zeolite has been experimentally determined at different zeolite temperatures and water vapor pressures for use in an adsorption cooling system. The Dubinin-Astakhov adsorption equilibrium model is fitted to experimental data with an acceptable error limit. Separate correlations are obtained for adsorption and desorption processes as well as a single correlation to model both processes. The isosteric heat of adsorption of water on zeolite has been calculated using the Clausius-Clapeyron equation as a function of adsorption capacity. The cyclic adsorption capacity swing for different condenser, evaporator and adsorbent temperatures is compared with that for the following adsorbent-refrigerant pairs: activated carbon-methanol; silica gel-water; and, zeolite 13X-water. Experimental results show that the maximum adsorption capacity of natural zeolite is nearly 0.12 kg(w)/kg(ad) for zeolite temperatures and water vapor pressures in the range 40-150 degrees C and 0.87-738 kPa. (C) 2009 Elsevier Ltd. All rights reserved.Article Citation Count: 12Coating of titanium implants with boron nitride by RF-magnetron sputtering(indian Acad Sciences, 2016) Kaftanoğlu, Bilgin; Ozmeric, Nurdan; Ergene, Cansu; Dokmetas, Nihan; Ergene, Cansu; Kaftanoglu, Bilgin; Manufacturing EngineeringSurface 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.Article Citation Count: 15COP trends for ideal thermal wave adsorption cooling cycles with enhancements(Elsevier Sci Ltd, 2012) Kaftanoğlu, Bilgin; Baker, Derek K.; Kaftanoglu, Bilgin; Manufacturing EngineeringModels are presented for ideal thermal wave adsorption cooling cycles without mass recovery, with adiabatic mass recovery and with isothermal mass recovery. Coefficient of performance (COP) values obtained from simulations are compared with the results of a reversible cycle and previously developed models for a simple cycle and heat recovery cycle with two spatially isothermal beds (2SIB). The effects of maximum and minimum bed temperatures, bed's dead mass, and condensation and evaporation temperatures on COP were investigated. The thermal wave cycle has significantly higher COP's than the simple and 2SIB cycles. For the conditions investigated, adding mass recovery to the thermal wave cycle does not affect its COP significantly. The COP of the thermal wave cycle increases with increasing maximum bed and evaporation temperatures and decreasing minimum bed and condensation temperatures. Unlike for the simple and 2SIB cycles, variations in the bed's dead mass have minimal impact on COP. (C) 2010 Elsevier Ltd and IIR. All rights reserved.Article Citation Count: 8Development of hard, anti-reflective coating for mid wave infrared region(Elsevier, 2021) Kaftanoğlu, Bilgin; Hacaloglu, Tugce; Kaftanoglu, Bilgin; Manufacturing EngineeringIn 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.Conference Object Citation Count: 6Effect of hardening models on different ductile fracture criteria in sheet metal forming(Springer France, 2016) Kaftanoğlu, Bilgin; Darendeliler, Haluk; Kaftanoglu, Bilgin; Manufacturing EngineeringPrediction 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.Article Citation Count: 57Experimental investigation of a natural zeolite-water adsorption cooling unit(Elsevier Sci Ltd, 2011) Kaftanoğlu, Bilgin; Kaftanoglu, Bilgin; Yamali, Cemil; Baker, Derek; Manufacturing EngineeringIn 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.Article Citation Count: 7Experimental investigation of friction in deep drawing(Springer London Ltd, 2017) Kalkan, Hakan; Kaftanoğlu, Bilgin; Kaftanoglu, Bilgin; Manufacturing EngineeringInvestigation 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.Article Citation Count: 7Experimental investigation of non-isothermal deep drawing of DP600 steel(Springer London Ltd, 2018) Kaftanoğlu, Bilgin; Kaftanoglu, Bilgin; Kayhan, Erdem; Manufacturing Engineering; Airframe and Powerplant MaintenanceTo increase the limiting drawing ratio (LDR) in deep drawing, experiments are conducted on DP600, IF, and HSLA steels. The flange region of blank is heated up to temperatures in the warm range by inductance heating. During heating, the central portion of blank is cooled by water to prevent the reduction of the strength of the material in the central region. The temperature increase of flange region is observed by two infrared sensors focusing on two different points, one on the blank rim and the other near the die radius. An intensive cooling by cold water is applied to the bottom side of a blank during deep drawing. Increases up to 25.58% on LDR are obtained. There is no significant change in the microstructure of the material due to warm forming. Material characterization is obtained by a Gleeble 3800 thermo-mechanical testing machine for the temperature range 150-300 degrees C.Article Citation Count: 23Focus Variation Measurement and Prediction of Surface Texture Parameters Using Machine Learning in Laser Powder Bed Fusion(Asme, 2020) Kaftanoğlu, Bilgin; Altay, Ayca; Kaftanoglu, Bilgin; Leach, Richard; Senin, Nicola; Donmez, Alkan; Manufacturing EngineeringThe 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.Article Citation Count: 3Histomorphometric and biomechanical evaluation of the osseointegration around micro- and nano-level boron-nitride coated titanium dental implants(Elsevier, 2022) Kaftanoğlu, Bilgin; Cakal, Gaye Ozgur; Gokmenoglu, Ceren; Ozmeric, Ahmet; Oduncuoglu, Bahar Fusun; Hacaloglu, Tugce; Kaftanoglu, Bilgin; Manufacturing EngineeringIntroduction: Titanium dental implants has been coated with different materials such as polymers and biomi-metic agents, bone morphogenetic protein, calcium phosphate to enhance surface properties of the titanium implants for osseointegration. The aim of this study was to evaluate the bone tissue healing around Boron Nitride-coated (BN-coated) titanium implants histomorphometrically and biomechanically and also observe the effect of different coating thicknesses on osseointegration. Materials and methods: BN was coated on dental titanium implants with two different coating thicknesses by using RF magnetron sputtering system. Totally fifty-four implants were inserted into the tibias' of 12 New Zealand rabbits bilaterally under general anesthesia. All animals were sacrificed after 4-weeks. Bone-implant contact (BIC) and new bone area/total area ratios (BATA) were calculated. Also, the removal torque (RT) test was performed. Results: The highest new bone area in the medullary cavity was around the nano-BN-coated surface with 15.70%. In micro-BN-coated surface and control group, this ratio was determined as 10.48% and 8.23%, respectively. The BIC ratios in upper-side of implants and cortical-associated BIC ratios in lower-side were found significantly higher in control and micro-BN-coated group than nano-BN-coated group (p > 0.05). Sim-ilar BIC values were observed between control and micro-BN-coated groups (p > 0.05). BATA values did not show statistically significant differences between all three groups (p > 0.05). The RT values measured in all groups were found comparable and no statistically significant differences were found (p > 0.05). Conclusion: No inflammatory reaction developed around any implant. Relatively more new bone formation around nano-BN-coated titanium implants indicates the promising osseoinductive effect of BN coating. BN-coated implants showed similar biomechanical and histomorphometrical outcomes to that of the conven-tional titanium implants through a 4-week evaluation period. (c) 2022 Elsevier Masson SAS. All rights reserved.Article Citation Count: 13Intramedullary implants coated with cubic boron nitride enhance bone fracture healing in a rat model(Elsevier Gmbh, 2020) Kaftanoğlu, Bilgin; Tanoglu, Oguzhan; Ocak, Mert; Celik, Hakan Hamdi; Firat, Aysegul; Kaymaz, Fevziye Figen; Kaftanoglu, Bilgin; Manufacturing EngineeringBackground: Boron nitride is a biocompatible and an osteo-inductive material for orthopedic applications. The aim of this study was to evaluate the effects of two different allotrope boron nitride coated implants, cubic boron nitride and hexagonal boron nitride, on fracture healing. Methods: In this experimental study, a total of 24 rats were divided into three groups. Group A was the control group with Kirschner wire without coating, while the wires were coated dominantly by cubic boron nitride in Group B and hexagonal boron nitride in Group C. Then a mid-third femoral fracture was created. The fracture healing was examined in terms of new bone formation with micro-CT analysis and histopathological examination, quantitative measurement of bone turnover metabolites and scintigraphic examination of osteoblastic activity on 28th day post fracture. Results: Micro-CT measurement results revealed a statistically significant increase in bone volume/tissue volume ratio and bone surface values in group B compared to group A. Cortex diameter and osteoblast counts were statistically higher in group B compared to group A. Inflammatory response was increased in group C compared to groups A and B. Biochemical test results showed significantly increased alkaline phosphatase levels and decreased osteocalcin levels in group B compared to group A. The increase in serum phosphorus and decrease in serum calcium levels was statistically significant in group C compared to Group A. Conclusion: Both types of boron nitride coating had superior fracture healing features compared to control group. Therefore, c-BN coating can accelerate the fracture healing and could lead to shorten of union time.Conference Object Citation Count: 0Investigation of Influence Parameters on Forming Limit Diagrams of Aluminum Alloy-AA2024(Trans Tech Publications Ltd, 2011) Kaftanoğlu, Bilgin; Kaftanoglu, Bilgin; Karadoğan, Celalettin; Manufacturing EngineeringSheet metal forming technology is the keyword for many industries such as aerospace, aeronautics and automobile industries. Customer expectations, quality and safety requirements and market competitions require sheet metal forming operations to be well analyzed before the process to fulfill all these requirements. In this study, combination of FEA (finite element analysis) and mechanical material characterization were used in order to improve sheet metal forming operations while considering cost and quality. On the material characterization side of the studies, simple uniaxial tensile tests were conducted to obtain anisotropy parameters and yield points along different directions and hydraulic bulge test (HBT) was performed to obtain plastic behavior of the material up to 0.7 strains. Deformation measurements were conducted using optical measurement system GOM-ARAMIS while a 60-ton hydraulic press; Zwick/Roell BUP600 was used to deform the sheet part AA2024-0 aluminum alloy. Effects of process parameters, which are initial material thickness, lubrication and punch speed, on sheet metal formability and forming limit diagrams (FLDs) were investigated. On the study of thickness effects, sheet metals those having 0.81mm, 1.27mm and 1.60mm thickness were tested. Punch velocities of 250mm/min, 500mm/min and 750mm/min were used to investigate effect of punch speed on formability of sheet metals. Finally, PTFE (Polytetrafluoroethylene), paraffin lubricated and dry conditions were presented to obtain friction effects. FE analyses were performed to simulate experiments and to obtain friction coefficients of different lubricants. Good correlations were observed between numerical simulations and experimental results.Article Citation Count: 42Investigations on microstructural changes in machining of Inconel 100 alloy using face turning experiments and 3D finite element simulations(Pergamon-elsevier Science Ltd, 2016) Kaftanoğlu, Bilgin; Guo, Changsheng; Kaftanoglu, Bilgin; Oezel, Tugrul; Manufacturing EngineeringNickel-base IN100 alloy is a choice of material for components requiring high strength at elevated temperatures. Machining processes applied to these components affect the microstructure, grain size, and microhardness of the finished surface. This research investigates the effects of tool micro-geometry, coating, and cutting speed on the microstructural changes during machining. 3D customized finite element simulations have been performed to predict the average grain size by implementing modified temperature dependent flow softening based material and Johnson-Mehl-Avrami-Kolmogorov crystallization models. Simulation predictions on the average grain sizes, phase fractions, and resultant microhardness are compared against experimental measurements revealing good agreements. (C) 2016 Elsevier Ltd. All rights reserved.Article Citation Count: 59A mechanistic approach to investigate drilling of UD-CFRP laminates with PCD drills(Elsevier, 2014) Kaftanoğlu, Bilgin; Bahtiyar, O.; Deger, B.; Kaftanoglu, Bilgin; Manufacturing EngineeringCarbon fiber reinforced plastics (CFRPs) possess desirable material properties that satisfy the aerospace industry's high strength to weight ratio objective. Therefore, CFRPs are commonly used in structural parts, either alone or together with aluminum and titanium alloys. Drilling of CFRPs has been studied extensively in the literature in recent years, with special emphasis on process parameters and delamination. This study identifies mechanical properties of uni-directional CFRPs through drilling tests. Drilling of uni-directional CFRP plates with and without pilot holes has been performed, and cutting and edge force coefficients are identified. A polycrystalline diamond (PCD) drill was used in tests since this type of drill is commonly used in practice. Finally, validation tests on multi directional CFRP laminates have been performed and good results have been obtained. (C) 2014 CIRP.Article Citation Count: 1Normalized Thermodynamic Model for Intermittent Energy Systems and Application to Solar-Powered Adsorption Cooling Systems(int Center Applied thermodynamics, 2011) Kaftanoğlu, Bilgin; Baker, Derek K.; Kaftanoglu, Bilgin; Manufacturing EngineeringA new normalized model is developed to quantify and explore trends in coincidence of supply and demand in generic intermittent energy systems as key design and operating parameters are varied. This novel model is applied to seasonal-transient simulations for a solar-thermal powered adsorption system with and without heat recovery to investigate the coincidence between the solar-supplied cooling power and cooling load in terms of seasonal solar and loss fractions. Additionally, the system's basic performance trends are investigated as a number of parameters are varied. Results for the conditions explored include the following. The solar fraction increases and the loss fraction decreases with increases in storage capacity, and both fractions decrease with increases in maximum bed temperature. The required evacuated tube collector area is smaller than the flat plate collector area while the required mass of adsorbent is independent of collector and adsorption cycle types. Simulation results also show the effects of operating conditions and several design parameters on the system's COP.Article Citation Count: 41Numerical investigation of coupled heat and mass transfer inside the adsorbent bed of an adsorption cooling unit(Elsevier Sci Ltd, 2012) Kaftanoğlu, Bilgin; Rees, D. Andrew S.; Yamali, Cemil; Baker, Derek; Kaftanoglu, Bilgin; Manufacturing EngineeringIn this study, the influence of several design parameters on the transient distributions of temperature, pressure and amount adsorbed in the radial direction of a cylindrical adsorbent bed of an adsorption cooling unit using silica gel/water have been investigated numerically. For this purpose, a transient one-dimensional local thermal non-equilibrium model that accounts for both internal and external mass transfer resistances has been developed using the local volume averaging method. For the conditions investigated, the validity of the local thermal equilibrium and spatially isobaric bed assumptions have been confirmed. To improve the performance of the bed considered, efforts should be focused on reducing heat transfer resistances and intra-particle (interior) mass transfer resistances but not inter-particle (exterior) mass transfer resistances. (C) 2011 Elsevier Ltd and IIR. All rights reserved.Article Citation Count: 15Prediction of forming limit curve at fracture for sheet metal using new ductile fracture criterion(Elsevier Science Bv, 2018) Kaftanoğlu, Bilgin; Darendeliler, Haluk; Kaftanoglu, Bilgin; Manufacturing EngineeringThe 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.Letter Citation Count: 0Theoretical modelling of magnetron sputtering of boron nitride coating(Springer Heidelberg, 2023) Kaftanoğlu, Bilgin; Kaftanoglu, Bilgin; Hacaloglu, Tugce; Aydogan, Asude; Manufacturing EngineeringThe 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.