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Öğe Bending performance of the AuxOcta multi-cellular beam structure(Elsevier Science Ltd, 2023) Kahraman, Mehmet Fatih; Genel, KenanAuxetic cellular tubes are potential candidates for several engineering applications requiring resistance to bending due to the enormous demand for lightweight and high mechanical performance. Interestingly, we found that the preferential buckling mode can change the direction of deformation in the beam cross-section by applying negative Poisson's ratio cells in the lateral direction and is an effective modifying region. The bending response and energy absorption of multi-cellular tube with auxetic cells (Aux) and novel design tubes with auxetic and octagonal cells (AuxOcta) have been investigated with numerical and experimental systematically. These unique auxetic structures are produced by direct metal laser sintering (DMLS) with 316L stainless steel. The bending results show that the Aux tube indicates gradual local deformation in the loading region, while the cells of the AuxOcta tube beam are homogeneously deformed in the loading region. Moreover, AuxOcta structure is optimized to improve load-carrying and energy-absorbing capacities. This optimized AuxOcta structure (AuxOcta-G) offers superior bending performance from the test results. Compared to the Aux structure, the improvement in the specific load carrying (SLC) capacity of the AuxOcta-G structure above is 15% for 5 mm displacement, while the improvement in the specific energy absorption (SEA) approximately reaches 16%. The Finite Element Method (FEM) results showed that AuxOcta and AuxOcta-G structures offer a preferred behavior with a wide displacement range. This study provides a baseline for future investigation of hybrid beam design with a negative Poisson cross-section.Öğe Comparative failure behavior of metal honeycomb structures under bending: A finite element-based study(Pergamon-Elsevier Science Ltd, 2024) Kahraman, Mehmet Fatih; İriç, Sedat; Genel, KenanIn recent years, metallic honeycomb structures have been popularly researched due to their significant influence on structural strength and rigidity. In this study, the bending response of multi-cellular beam structures with four (hollow tube (HT), square (Squ), hexagonal (Hex) and octagonal (Octa) and Re-entrant honeycomb (ReH)) cross-sections are numerically investigated. Furthermore, using the nonlinear finite element codes LS-DYNA, a comparative study of the energy absorption characteristics between structures with auxetic and non-auxetic beam crosssections was carried out. The ReH specimen used in the finite element (FE) validation study was manufactured using the Direct metal laser sintering (DMLS) additive manufacturing method to accommodate the complex geometries. FE method analysis are carried out to systematically investigate the influence of the geometrical configuration and identify the failure mechanism on the bending performance. The results show that in the HT structure, an upper corner fracture occurred because of folding in the contact area of the indenter. For Squ, Hex and Octa beam structures, failure occurs due to localized stress caused by buckling in the cell walls. On the other hand, the cross-sectional area of ReH structure tends to shrink under the bending load. Thus, the influence of the local buckling effect could be minimized despite the high displacements. This situation has ensured that the reduction in the moment of inertia of the crosssection remains limited. Furthermore, the specific energy absorption (SEA) capacity of the ReH beam significantly performed 11.3, 3.76 and 1.77 times better than the multi-cellular beam with Hex, Squ and Octa honeycomb beams, respectively. Accordingly, it was understood that the failure of the re-entrant cross-section under severe deformation was more limited than the others. This study is expected to contribute to evaluating the load-bearing capacity of metallic honeycomb structures, including understanding the failure process.Öğe Degeneration of mechanical characteristics and performances with Zr nanoparticles inserted in Bi-2223 superconducting matrix and increment in dislocation movement and cracks propagation(Springer, 2016) Akdemir, Ertuğrul; Pakdil, Murat; Bilge, Habibullah; Kahraman, Mehmet Fatih; Bekiroğlu, Erdal; Yıldırım, Gürcan; Öz, MuhammedThis study explains the role of Zr concentration level on mechanical characteristics and performance belonging to the bulk Bi-2223 superconducting materials by means of standard Vickers microhardness (H-v) measurements at different applied loads in the range of 0.245-2.940 N and evaluated theoretical calculations. The experimental measurement results obtained display that the mechanical performances regress with the increment of the Zr addition level due to the increased artificial disorders/damages/breaks/voids/cracks and irregular grain orientation distribution. In other words, the Zr addition accelerates both the dislocation movement and especially the cracks/voids propagation of as a consequence of the decrement in the Griffith critical crack length, being one of the most striking points deduced from this work. These vital findings are also favored by the extracted parameters of Young's modulus, yield strength, fracture toughness and brittleness index. Nevertheless, it is found that every sample studied exhibit typical indentation size effect (ISE) behavior due to the production of the elastic and plastic deformations simultaneously in the system. Moreover, the load dependent microhardness values are theoretically analyzed with the aid of six available models such as six available approaches: Meyer's law, proportional sample resistance model, modified proportional sample resistance model, elastic/plastic deformation, Hays-Kendall (HK) and indentation-induced cracking model for the first time. The results obtained show that the HK approach exhibits perfectly performance on the analysis of the mechanical characteristics of the superconducting materials exhibiting ISE behavior whereas the other models are inadequate to explain the load independent mechanical characteristics of the Bi-2223 system added by the Zr nanoparticles.Öğe Effect of angle and thickness of cell wall on bending behavior of auxetic beam(Elsevier, 2024) Kahraman, Mehmet Fatih; Genel, KenanAuxetic (Aux) structures, which exhibit unique mechanical properties due to the tunability of negative Poisson's ratio (NPR), have become great attention in recent years. In this work, the bending response and energy absorption behavior of beam structure in which the auxetic cells are oriented along the beam axis under bending are systematically investigated for various thicknesses and angles (55-85 degree) of walls experimentally and numerically. The beam structure was manufactured from AISI 316 L stainless steel by Powder Bed Fusion (PBF) additive manufacturing method, and three-point bending test was employed to determine the mechanical properties. The results revealed that the auxetic cross-section subjected to loading shrinks relating to NPR, orienting the outer wall inward thus reducing local buckling effect causing the main damage mechanism. It was also found that increasing the cell wall angle with the same relative density (rho = 0.485) owing to the change in the negative Poisson's ratio of the cross-section was beneficial in improving the load carrying and energy absorption capacity of Aux beam. However, increasing the cell wall angle up to a certain value (75 degrees) provides a significant benefit in the bending performance of the beam. The cell wall angle takes larger values resulting in a negligible increase in performance, whereas damage occurs at lower displacements. Moreover, the performance of the Aux beam can be improved by functionally graded thickness of the auxetic cell wall, increasing the specific load carrying (SLC) and specific energy absorption (SEA) capacity. By grading the cell wall thickness of the structure with the best mechanical performance according to the cell angle 75 degrees, it is understood that SLC and SEA values can be increased by 19.4% and 25.4%, respectively. This research is estimated to ensure a valuable reference for improving the bending response of the auxetic cross-section beams.Öğe Effect of Ni diffusion annealing temperature on crucial characterization of Bi-2223 superconducting system(Amer Inst Physics, 2016) Sarıtekin, Namık Kemal; Kahraman, Mehmet Fatih; Bilge, Habibullah; Zalaoğlu, Yusuf; Pakdil, Murat; Doğruer, Musa; Yıldırım, Gürcan; Öz, MuhammedIn this current work, influence of diffusion annealing temperature (650-850 degrees C) on the electrical, superconducting and structural characterizations of pure and Ni diffused Bi-2223 materials produced by conventional solid-state reaction route is surveyed by dc electrical resistivity (rho-T), transport critical current density (J(c)) and powder X-ray diffraction (XRD) measurements. All the experimental findings indicate that the curial characteristics, being responsible for the novel and feasible applications, improve significantly with the enhancement of the diffusion annealing temperature up to the certain value of 700 degrees C after which they degrade dramatically, meaning that the properties initially get better and better as a consequence of the penetration of more and more Ni concentrations into the superconducting grains or over grain boundaries in the Bi-2223 crystal matrix. From the diffusion annealing temperature value of 700 degrees C onwards, the excess penetration of the Ni nanoparticles along with consecutively stacked layers in the Bi-2223 crystal structure is, however, unfavorable for the attractive and feasible applications due to new induced disorders, local structural distortions and artificial dislocations.Öğe Experimental study of newly structural design grinding wheel considering response surface optimization and Monte Carlo simulation(Elsevier Sci Ltd, 2019) Kahraman, Mehmet Fatih; Öztürk, SabriThe grinding process has a great advantage during machining structures in brittle and hard materials. Under this circumstance, the new grinding wheel - cutting surface of grinding - was structurally redesigned, which enables to produce and apply any size of grinding tools. With this new designed grinding wheel, the influence of grit size, grit concentration, and type of bond as well as operation parameters on the material removal mechanisms was analyzed during the grinding of hard-brittle materials. So, it becomes a necessity that the grinding operation with its parameters must be optimized correctly to have good control over the productivity, quality, and cost aspect of the operation. Furthermore, to demonstrate the modeling and optimization of the grinding process using three approaches. First, multi non-linear regression (MNLR) based on Box-Behnken design (BBD) was used to determine the process model based on surface roughness. Then the grinding parameters were optimized considering response surface methodology (RSM). Finally, Monte Carlo simulations were found quite effective for identification of the uncertainties in surface roughness that could not be possible to be captured by deterministic ways. (C) 2019 Elsevier Ltd. All rights reserved.Öğe Gerçek zamanlı görüntüleme sistemi vasıtasıyla sertlestırilmiş aısı 4340 çeliğinin farklı kesme parametreleri kullanılarak işlenmesinde CBN kesici takımların aşınma davranışlarının incelenmesi(Bolu Abant İzzet Baysal Üniversitesi, 2015) Kahraman, Mehmet Fatih; Çakan, AhmetKesici takım kenar aşınmasında, malzemenin işlenebilirliği hakkında değerlendirilmesi için önemli bir kriterdir. Bu çalışmada, CBN (kübik born nitrür) kesici takım ile sertleştirilmiş AISI 4340 (51-53 HRC) düşük alaşımlı çelik malzeme üzerinden sert malzemelerin tornalanması işlemiyle (HT) talaş kaldırma işlemi sırasında kesici uç aşınmasının, kesme hızı ve ilerleme hızı gibi faktörlerin etkilerini geliştirmek üzere araştırımalar yapılmıştır. Kesici takım uç aşınması, kesici takım ömrünü dolayısıyla, üretim zamanını etkilemektedir. On-line izleme yönteminden dolayı kesici takım uç aşınması ölçümü deneyi durdurmadan ölçüm yapma imkanı sunarmaktadır. Ayrıca görüntüleme sistemi düşük maliyetli sensör kullanımıyla gerçekleştirilmiştir. Bu deneyler, 180 ve 250 m/dak kesme hızında, 0.04, 0.08, 0.12 mm/dev ilerleme hızında ve 0.2 mm kesme derinliğinde gerçekleştirilmiştir. En önemli kesme parametresi Varyans analiz (ANOVA) yöntemiyle kullanılarak gerçekleştirilmiştir. Kesici uç aşınmasını çoğunlukla kesme hızı parametresi etkilemektedir.Öğe Improvement of mechanical characteristics and performances with Ni diffusion mechanism throughout Bi-2223 superconducting matrix(Amer Inst Physics, 2016) Sarıtekin, Namık Kemal; Bilge, Habibullah; Kahraman, Mehmet Fatih; Zalaoğlu, Yusuf; Pakdil, Murat; Doğruer, Musa; Yıldırım, Gürcan; Öz, MuhammedThis study is interested in the role of diffusion annealing temperature (650-850 degrees C) on the mechanical characteristics and performance of pure and Ni diffused Bi-2223 superconducting materials by means of standard compression tests and Vickers hardness measurements at performed different applied loads in the range of 0.245-2.940N and theoretical calculations. Based on the experimental findings, the mechanical performances improve with increasing annealing temperature up to 700 degrees C beyond which they degrade drastically due to the increased artificial disorders, cracks and irregular grain orientation distribution. In other words, the penetration of excess Ni inclusions accelerates both the dislocation movement and especially the cracks and voids propagation as a result of the decrement in the Griffith critical crack length. Further, it is to be mentioned here that all the sample exhibit typical indentation size effect (ISE) behavior. In this respect, both the plastic (irreversible) and elastic (reversible) deformations have dominant role on the superconducting structures as a result of the enhancement in the elastic recovery. At the same time elastic modulus, yield strength and fracture toughness parameters are theoretically extracted from the microhardness values. Moreover, the elastic modulus parameters are compared with the experimental values. It is found that the differentiation between the comparison results enhances hastily with the increment in the applied indentation test loads due to the existence of the increased permanent disorders, lattice defects and strains in the stacked layers. Namely, the error level increases away from the actual crystal structure. Additionally, the microhardness values are theoretically analyzed for the change of the mechanical behaviors with the aid of Meyer's law, elastic/plastic deformation and Hays-Kendall approaches for the first time.Öğe Modeling and optimization of machining parameters during grinding of flat glass using response surface methodology and probabilistic uncertainty analysis based on Monte Carlo simulation(Elsevier Sci Ltd, 2019) Öztürk, Sabri; Kahraman, Mehmet FatihIn this paper, the performance of diamond grinding wheels was investigated. The industrial diamond crystals with a size of 140/170 mesh were utilized. The microstructure of the grinding tool was observed using a Scanning Electron Microscope (SEM) and Energy Dispersive X-ray Analysis Device (EDX). The experiments were designed using Box-Behnken method and optimum grinding parameters for glass were analytically determined. Experimental studies were carried out on a surface grinding machine in a flat glass factory. Grinding characteristics were examined with respect to surface roughness. The effects of grinding parameter on output responses were studied using analysis of variance (ANOVA). Probabilistic uncertainty analysis depends on Monte Carlo simulation was applied. Moreover, after the experiments using the optimized cutting parameters, the microstructure of the grinding wheels was analyzed. From results, the established model and optimization method could be employed for predicting surface roughness and this work is reliable and suitable for solving the problems encountered in machining operations. The lifetime of Cu-based grinding discs can be increased by adding Zn and Fe to the matrix material.Öğe A novel tilt and acceleration measurement system based on hall-effect sensors using neural networks(Hindawi Ltd, 2022) Nour, Majid; Daldal, Nihat; Kahraman, Mehmet Fatih; Sindi, Hatem; Alhudhaif, Adi; Polat, KemalA tilt sensor is a device used to measure the tilt on many axes of a reference point. Tilt sensors measure the bending position according to gravity and are used in many applications. Slope sensors allow easy detection of direction or slope in the air. These tilt gauges have become increasingly popular and are being adapted for a growing number of high-end applications. As an example of practical application, the tilt sensor provides valuable information about an aircraft's vertical and horizontal tilt. This information also helps the pilot understand how to deal with obstacles during flight. In this paper, Hall-effect effective inclination and acceleration sensor design, which makes a real-time measurement, have been realized. 6 Hall-effect sensors with analog output (UGN-3503) have been used in the sensor structure. These sensors are placed in a machine, and the hall sensor outputs are continuously read according to the movement speed and direction of the sphere magnet placed in the assembly. Hall sensor outputs produce 0-5 Volt analog voltage according to the position of the magnet sphere to the sensor. It is clear that the sphere magnet moves according to the inclination of the mechanism when the mechanism is moved angularly, and the speed of movement from one point to the other changes according to the movement speed. Here, the sphere magnet moves between the hall sensors in the setup according to the ambient inclination and motion acceleration. Each sensor produces analog output values in the range of 0-5 V instantaneous according to the position of the spheroid. Generally defined, according to the sphere magnet position and movement speed, the data received from the hall sensors by the microcontroller have been sent to the computer or microcomputer unit as UART. In the next stage, the actual sensor has been removed. The angle and acceleration values have been continuously produced according to the mechanism's movement and output as UART. Thanks to the fact that the magnet is not left idle and is fixed with springs, problems such as vibration noises and wrong movements and the magnet leaning to the very edge and being out of position even at a slight inclination are prevented. In addition, the Hall-effect sensor outputs are given to an artificial neural network (ANN), and the slope and acceleration information is estimated in the ANN by training with the data obtained from the real-time slope and accelerometer sensor.Öğe Uncertainty analysis of cutting parameters during grinding based on RSM optimization and Monte Carlo simulation(Carl Hanser Verlag, 2019) Kahraman, Mehmet Fatih; Öztürk, SabriDue to the importance of high surface quality of machined parts, regarding its functional requirements, it is necessary to determine an appropriate set of grinding parameters. According to the uncertainty of the machining process, the statistical techniques have recently been used to set up an experimental-based model for estimating the performance of machining parameters and optimizing them. The purpose of this study is to demonstrate the modeling and optimization of the grinding process using three approaches. First, multi non-linear regression (MNLR) based on central composite design (CCD) was used to determine the process model. Then the grinding parameters were optimized considering response surface methodology (RSM). Finally, the probabilistic uncertainty analysis was applied by using Monte Carlo simulation as a function of wheel speed and feed rate.. The surface roughness value, which was named the response variable, was estimated by fitting the MNLR model with a predicted regression coefficient (R-pred(2)) of 84.69 %. Wheel speed of 4205.6 rpm and feed rate of 2.969 mm x min(-1) were calculated as RSM-optimized conditions with a surface roughness of 2.26326 mu m. The verification experiments were performed with three replications to verify the predicted surface roughness value obtained with the derived model, and 2.263 +/- 2 % mu m of surface roughness was calculated using RSM optimized conditions. Monte Carlo simulations were found to be quite effective for identification of the uncertainties in surface roughness that could not be identified by deterministic ways.
