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Article Citation - WoS: 38Citation - Scopus: 47Focus 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, AlkanThe 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.Conference Object Citation - WoS: 7Citation - Scopus: 7Effect of Hardening Models on Different Ductile Fracture Criteria in Sheet Metal Forming(Springer France, 2016) Dizaji, Shahram Abbasnejad; Darendeliler, Haluk; Kaftanoglu, BilginPrediction 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 - WoS: 7Citation - Scopus: 13Experimental Investigation of Non-Isothermal Deep Drawing of Dp600 Steel(Springer London Ltd, 2018) Kayhan, Erdem; Kaftanoglu, BilginTo 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 - WoS: 8Citation - Scopus: 8Experimental Investigation of Friction in Deep Drawing(Springer London Ltd, 2017) Kalkan, Hakan; Hacaloglu, Tugce; Kaftanoglu, BilginInvestigation 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 - WoS: 8Citation - Scopus: 9Development of Hard, Anti-Reflective Coating for Mid Wave Infrared Region(Elsevier, 2021) Ozhan, Alp Eren Sinan; Hacaloglu, Tugce; Kaftanoglu, BilginIn 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.Article Citation - WoS: 13Citation - Scopus: 16Intramedullary Implants Coated With Cubic Boron Nitride Enhance Bone Fracture Healing in a Rat Model(Elsevier Gmbh, 2020) Ozmeric, Ahmet; Tanoglu, Oguzhan; Ocak, Mert; Celik, Hakan Hamdi; Firat, Aysegul; Kaymaz, Fevziye Figen; Kaftanoglu, BilginBackground: 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.Article Citation - WoS: 7Citation - Scopus: 9Histomorphometric and Biomechanical Evaluation of the Osseointegration Around Micro- and Nano-Level Boron-Nitride Coated Titanium Dental Implants(Elsevier, 2022) Ozmeric, Nurdan; Cakal, Gaye Ozgur; Gokmenoglu, Ceren; Ozmeric, Ahmet; Oduncuoglu, Bahar Fusun; Hacaloglu, Tugce; Kaftanoglu, BilginIntroduction: 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.
