Browsing by Author "Çulha O."

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    Computer aided design, analysis and manufacturing of hot rolled bulb flat steel profiles; [Sıcak haddelenmiş çelik hollanda profillerinin bilgisayar destekli tasarımı, analizi ve imalatı]
    (TUBITAK, 2020) Akkaş M.; Onder B.; Sevgi E.; Çulha O.
    In this study, roll-pass designs were designed and controlled rolling simulations were realized by using of Simufact Forming simulation tool based on finite element method for acquiring an asymmetrical profile with low carbon-micro alloyed steel used in ship buildings. Simulation aided manufacturing studies have been realized for eliminating the manufacturing defects and obtaining stress-strain curves, forces acting on the rollers and torque requirements at the inlets and the outlets of the rolling stands. Optimization studies of the production parameters to improve the final product mechanical properties. Mechanical tests and metallurgical tests have been applied to the production samples obtained by ensuring that the production parameters obtained in simulated support activities are used in prototype productions and the improvement of the mechanical properties of the profile with asymmetric section is provided. © 2020, TUBITAK. All rights reserved.
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    An investigation on the reasons of emerging iron oxides in different colors than normal in alloyed steel profiles produced by hot rolling; [Sıcak haddeleme ile üretilen alaşımlı çelik profillerde normalden farklı renkte oluşan demir oksitlerin ortaya çıkış sebeplerinin incelenmesi]
    (TUBITAK, 2020) Akkaş M.; Çulha O.
    The red scale formation in hot rolled steel profiles is a chemical iron oxide reaction that disrupts the natural color of the surface of the steel. Tempering temperature, atmosphere, time and rolling temperature, silicon content in the chemical composition of the raw material affect this formation. In this study, red scale formation on the surface, which is a very rare case in steel profiles produced by hot rolling method, was investigated. Samples were taken from a production which appeared in the forms I and U in the produced profile types. The profiles in which red scale formation is observed are as follows; visual inspection, spectral analysis, XRD analysis and microstructure analysis. According to the findings of the analysis and literature, it was found that the red scale formed in this case has no correlation with the ratio of silicon element. It has been found that the red scale formation of different density in I and U profiles depends on the accumulation of water depending on the rolling position of the profile during rolling. In general, it has been found that hematite scales cause red scales due to cooling effect. © 2020, TUBITAK. All rights reserved.
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    Aluminum Alloy Development for Wheel Production by Low Pressure Die Casting with New Generation Computational Materials Engineering Approaches
    (Polska Akademia Nauk, 2021) Yaǧci T.; Cöcen Ü.; Çulha O.
    Computational Materials Engineering (CME) is a high technological approach used to design and develop new materials including the physical, thermal and mechanical properties by combining materials models at multiple techniques. With the recent advances in technology, the importance of microstructural design in CME environments and the contribution that such an approach can make in the estimation of material properties in simulations are frequently discussed in scientific, academic, and industrial platforms. Determination of the raw material characteristics that can be modeled in a virtual environment at an atomic scale by means of simulation programs plays a big role in combining experimental and virtual worlds and creating digital twins of the production chain and the products. In this study, a new generation, alternative and effective approach that could be used to the development of Al-Si based wheel casting alloys is proposed. This approach is based on the procedure of optimizing the physical and thermodynamic alloy properties developed in a computer environment with the CME technique before the casting phase. This article demonstrates the applicability of this approach in alloy development studies to produce Al-Si alloy wheels using the low pressure die casting (LPDC) method. With this study, an alternative and economical way is presented to the alloy development studies by trial and error in the aluminum casting industry. In other respects, since the study is directly related to the automotive industry, the reduction in fuel consumption in vehicles is an expected effect, as the new alloy aims to reduce the weight of the wheels. In addition to conserving energy, reducing carbon emissions also highlights the environmental aspects of this study. © 2021 Polish Academy of Sciences. All rights reserved.
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    Investigation of metallurgical properties of Al-Si-Mg casting alloys with integrated computational materials engineering for wheel production; [Investigación de las propiedades metalúrgicas de las aleaciones coladas Al-Si-Mg para la producción de llantas utilizando ingeniería de materiales computacional integrada]
    (CSIC Consejo Superior de Investigaciones Cientificas, 2023) Yağcı T.; Cöcen Ü.; Çulha O.; Armakan E.
    In this study, integrated computational materials engineering, which is one of the new generation approaches in materials science, was used in the production of aluminum alloy wheels by low pressure die casting method. In casting alloys, the efficiency of grain refinement provided by master alloys added to the melt decreases with increasing silicon content of the alloy. In this context, as-cast properties of silicon reduced (Si: 5.0 wt.%) alloys with different Mg ratios (Mg: 3.0, 5.0, 7.0 wt.%) are discussed using integrated computational materials engineering approaches. It has been evaluated whether the examined alloys can be an alternative to the AlSi7Mg0.3 alloy, which is currently used traditionally in the production of aluminum-based wheels, with their microstructural and mechanical properties. The study consists of three stages which are computer-aided production, pilot production, testing and characterization studies. In computer-aided production, original sub-eutectic compositions were determined in types and amounts of alloying elements, alloy designs were realized and a database was created with a computational materials engineering software. Then, low pressure die casting analysis were performed in a virtual environment by transferring these data directly to the casting simulation software. Thus, the microstructural and mechanical properties of the wheel were obtained computationally on the basis of the varying alloy composition. In the second stage, the virtually designed alloy compositions were prepared and sample wheels were manufactured by the low pressure die casting method on an industrial scale. In the testing and characterization phase, spectral analyses, macro and microstructural examinations, hardness measurements and tensile tests were carried out. As a result of this study, it was determined that the studied alloys could be used in the production of wheels by the low pressure die casting method considering the metallurgical properties expected from the wheel. In addition, it is thought that the mathematical design of the material with integrated computational materials engineering approaches before casting simulations will play an active role in the competitiveness and sustainability of the aluminum industry in technological conditions. © 2023 CSIC.
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    Failure analysis of cardan shaft’s flange yoke fracture occurred during torsional fatigue test; [Torsiyonel yorulma testi sırasında kırılan kardan miline ait çatallı flanş parçasının hasar analizi]
    (Gazi Universitesi, 2023) Akkaş O.; Işık E.; Çulha O.
    In this study, the analysis and characterization of the failure that occurred during the torsional fatigue test of the flange yoke unit part of the cardan shaft used in heavy commercial vehicles were carried out. In order to determine the root cause of the failure according to the production, structure, property and performance relationship in materials science, chemical analysis of the steel raw material used in the production of flange yoke, hardness measurement, grain size analysis, decarburization measurement, inclusion analysis and raw material characterization by scanning electron microscopy (SEM) were carried out. As a result of the studies, it was determined that the values obtained for 41Cr4 steel raw material were conformant according to the TS EN ISO 683-2 standard, but in the SEM examination and EDS analysis, elongated MnS inclusions in the microstructure and cracks were detected at the interface of the metal matrix and MnS inclusions. In this context, as a result of the characterization of the flange yoke unit part, it was determined that the MnS ratio was 2-4 μm x 898-1.181 μm according to the ASTM E45 standard, at the same level as the raw material and equivalent to the A-type value of 3.0-3.5. It was determined that MnS inclusion formations in the subsurface region formed crack propagation zones. © 2023 Gazi Universitesi Muhendislik-Mimarlik. All rights reserved.
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    Effect of the substrate surface and coating powder hardness on the formation of a cold sprayed composite layer
    (Walter de Gruyter GmbH, 2023) Kahraman A.D.; Kahraman F.; Çulha O.; Yaǧcl T.
    In this study, the powder hardness and substrate surface hardness on the coating formation in the cold spray process was investigated. The AA6082 aluminum alloy hardened by the shot-peening process was used as the base material. Two different metallic powders and a ceramic particle powder were used as powder materials with different hardness. Thus, the powder particles from different materials were sprayed onto the surface under the same spraying process conditions. In order to obtain a workpiece surface with different hardness values, shot-peening treatment was applied to the substrate material at different treatment times. According to the microstructural examination, the harder metallic coating powder has accumulated more and the lower hardness metallic coating powder has accumulated less when the substrate material hardness increases. Al2O3 particles in the layer formed were distributed close to homogeneous. Furthermore, the size of Al2O3 particles near the contact surface has become much finer especially in the long-term shot peened samples due to their higher hardness. From the indentation experiments, the elastic behavior and recovery amount of the composite coating layer increased due to the increase of the substrate surface hardness, and the stress distributions were performed less after the load was removed. © 2022 Walter de Gruyter GmbH, Berlin/Boston.
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    Investigation of microstructural and mechanical properties of hot forged 31Mn4 dual phase steel with computer-aided simulations
    (Taylor and Francis Ltd., 2023) Kilerci İ.; Çulha O.; Yağcı T.
    In this study, it is aimed to realise the hot forging process design and prototype production of the steel yielding support connection clamp, the critical safety element of underground mining ground support systems, by using 31Mn4 dual phase steel. In this context, at the end of the forging and deburring processes, air cooling was designed, simulated and cooling rates were obtained. The cooling curve was integrated into the continuous cooling transformation diagram and phase formation was predicted. The distribution of pearlitic, ferritic, bainitic structures and formation rates, hardness distributions, strength data were also obtained. The hardness and tensile strength calculations, microstructural examinations and SEM analysis were carried out for validation. It has been determined that pearlitic-ferritic microstructures are formed in regions where the cooling rate is slow. In thinner sections where the cooling rate is around 1.2°C/sec, ferritic structures become smaller and bainite phase was observed. As a result, the average tensile strength in 1st and 2nd regions were recorded as 684.5, 690 MPa in simulation, while these values were recorded as 688.45 and 694.15 MPa in tensile tests. It has been determined that this result corresponds to the 99.4% accuracy rate of the prototype obtained by simulation-supported and real productions. © 2022 Canadian Institute of Mining, Metallurgy and Petroleum.
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    Optimization of T6 Heat Treatments for AlSi5Mgx Alloys via Computational Materials Engineering and Experimental Validation for Automotive Applications
    (Springer, 2024) Korkmaz A.; Yağcı T.; Çulha O.
    In this study, T6 heat treatments were applied to AlSi5Mgx (x: 0.3, 0.5, 0.7 wt.%) alloys, fabricated through the low pressure die casting technique. Optimization of these treatments was conducted utilizing computational materials engineering (CME) methodologies, simulation techniques, and design of experiment studies. The objective is to position the investigated alloys as potential substitutes for the heat-treated AlSi7Mg0.3 alloy commonly employed within the automotive sector, with a focus on enhancing microstructural and mechanical characteristics. A comparative analysis was conducted between virtual and empirical data through laboratory-scale experimental investigations. Utilizing the Taguchi experimental design methodology, heat treatments were administered to the spoke region of the wheels, employing three distinct parameters: solution treatment, aging temperature, and time. The analysis outcomes underwent assessment employing the Taguchi method, analysis of variance, and regression analyses, facilitating an exploration into the effects of heat treatment conditions on the physical and mechanical attributes of the alloys. The AlSi5Mg0.5 alloy exhibited optimal mechanical properties when subjected to a solution treatment temperature of 550 °C, an aging temperature of 180 °C, and an aging time of 4 h. Furthermore, a notable similarity was observed between the analysis outcomes derived from CME methodologies and experimental studies. This concurrence lends credence to the accuracy and reliability of the employed software. © ASM International 2024.