Makine Mühendisliği Bölümü Koleksiyonu

Permanent URI for this collectionhttps://hdl.handle.net/20.500.12573/206

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An accurate investigation of the mechanical response and damage model of aluminum 7068
(Abdullah Gül Üniversitesi, 2018) Karaveli, Kadir Kaan; AGÜ, Mühendislik Fakültesi, Makine Mühendisliği Bölümü; Karaveli, Kadir Kaan
The promising combination of high strength, high toughness, low density and corrosion resistivity have made aluminium (Al) alloys the material of choice in various applications, from buildings to aerospace, for decades. Especially, Al 7068 alloy is one of the recently developed materials used mostly in defence and automobile industries due to their exceptional mechanical properties. In this master thesis, the mechanical response and Johnson-Cook damage model of Al 7068-T651 alloy was investigated. Specifically, different Johnson-Cook damage parameters were determined for different application areas considering the maximum, minimum and average results. These damage parameters can be used for accurate Finite Element Analysis simulations. To determine these damage parameters tensile tests were conducted on notched and smooth specimen son both rolling direction and perpendicular to the rolling direction. The notch radius were selected as smooth, 0.4 mm, 0.8 mm and 2 mm to provide different stress triaxiality values and observe the mechanical response at these triaxiality values. Tensile tests were repeated seven times to obtain the accurate results. The final cross-sectional areas of fractured specimens were calculated through optical microscopy. The effects of stress triaxiality factor and rolling direction on the mechanical properties of Al 7068-T651 alloy were successfully investigated. All damage parameters were calculated via LevenbergMarquardt optimization method. Overall, three different Johnson-Cook damage parameters based on minimum, average and maximum equivalent strain values were calculated. These Johnson-Cook ii damage parameters can be utilized for the accurate damage simulations of different applications in Finite Element Analysis, which is a computational technique and is used to obtain approximate solution of several engineering problems
Accurate Prediction of Residual Stresses in Machining of Inconel 718 Alloy through Crystal Plasticity Modelling
(Afyon Kocatepe Üniversitesi, 2023) Kesriklioglu, Sinan; Kapci, Mehmet Fazil; Büyükçapar,Rıdvan; Çetin , Barış; Yılmaz, Okan Deniz; Bal, Burak; 0000-0002-2914-808X; 0000-0003-3297-5307; 0000-0002-2550-7911; 0000-0002-7389-9155; AGÜ, Mühendislik Fakültesi, Makine Mühendisliği Bölümü; Kesriklioglu, Sinan; Kapci, Mehmet Fazil; Büyükçapar, Rıdvan; Bal, Burak
Determination and assessment of residual stresses are crucial to prevent the failure of the components used in defense, aerospace and automotive industries. The objective of this study is to present a material method to accurately predict the residual stresses induced during machining of Inconel 718. Orthogonal cutting tests were performed at various cutting speeds and feeds, and the residual stresses after machining of Inconel 718 were characterized by X-ray diffraction. A viscoplastic self-consistent crystal plasticity model was developed to import the microstructural inputs of this superalloy into a commercially available finite element software (Deform 2D). In addition, same simulations were carried out with classical Johnson - Cook material model. The simulation and experimental results showed that the crystal plasticity based multi-scale and multi-axial material model significantly improved the prediction accuracy of machining induced residual stresses of Inconel 718 when compared to the existing model, and it can be used to minimize the surface defects and cost of production trials in machining of difficult-to-cut materials.
Anhydrous proton conducting poly(vinyl alcohol) (PVA)/ poly(2-acrylamido-2-methylpropane sulfonic acid) (PAMPS)/1,2,4-triazole composite membrane
(Elsevier Ltd, 2016) Erkartal, Mustafa; Aslan, Ayse; Erkilic, Ufuk; Dadi, Seyma; Yazaydin, Ozgur; Usta, Hakan; Sen, Unal; 0000-0002-9772-128X; 0000-0003-1849-9180; 0000-0001-8562-723X; 0000-0002-0618-1979; 0000-0003-3736-5049; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü; Erkartal, Mustafa; Erkılıç, Ufuk; Dadı, Şeyma; Usta, Hakan; Şen, Ünal
The design and fabrication of anhydrous proton exchange membranes are critically important for high temperature proton exchange membrane fuel cell (HT-PEMFC) operating between 100 and 200 °C. Herein, we demonstrate a novel proton conducting membrane consisting of poly(vinyl alcohol) (PVA), poly (2-acrylamido-2-methylpropane sulfonic acid) (PAMPS) and 1,2,4-triazole, which was fabricated by physical blending, casting and solvent evaporation techniques. The in-situ chemical cross-linking was performed by glutaraldehyde (GA) to improve the water management of the membranes. The molecular structure of the membranes and intermolecular interactions between the constituents were confirmed by Fourier-transform infrared spectroscopy (FT-IR). The surface and cross-section morphologies of the membranes were observed by scanning electron microscopy (SEM). The thermal stability performance of the membranes was studied with thermogravimetric analysis (TGA). In order to determine the physico-chemical properties of the membranes, water uptake (WU), dimensional change and ion exchange capacity (IEC) tests were carried out. The proton conductivities of composite membranes increase with the temperature and the temperature dependencies exhibit an Arrhenius behavior. Proton conductivity measurements revealed an optimum ratio between PAMPS and 1,2,4-triazole content to achieve higher proton conductivity. In anhydrous state at 150 °C, the highest proton conductivity measured was 0.002 S/cm for PVA:PAMPS:1,2,4-triazole (1:1:1) composition. Overall, our investigation showed that 1,2,4-triazole is a promising proton carrier reagent above 100 °C when it is embedded into appropriate host polymers.
Application of Classical Lamination Theory to Fused Deposition Method 3-D Printed Plastics and Full Field Surface Strain Mapping
(Afyon Kocatepe Üniversitesi, 2022) Yılmaz, Çağatay; ALI, Hafiz Qasim; Yıldız, Mehmet; 0000-0002-8063-151X; 0000-0001-8288-2737; 0000-0003-1626-5858; AGÜ, Mühendislik Fakültesi, Makine Mühendisliği Bölümü; Yılmaz, Çağatay
In this study, five differently oriented sets of 3D-printed tensile samples are produced using the Fused Deposition Method (FDM). Among these five sets, three are used to determine the elastic constant to be used in Classical Lamination Theory (CLT), which is generally used to model fiber-reinforced polymers (FRP). Based on the obtained results, CLT is further applied to the remaining two sets of unreinforced 3D-printed polymer samples where the deposition direction varies in each layer. The stress and strain calculated with CLT are then compared with experimental results obtained through tensile testing. The comparison depicts that experimental and CLT results are in good agreement at lower strain levels. In contrast, the stress calculated with CLT deviates from the experimental result at the higher strain levels.Thereafter, a full-field surface strain mapping is applied by using Digital Image Correlation (DIC) Techniques to reveal the damage progression and failure of Fused Deposition Method 3-D Printed Plastics.
APPLICATION OF HOOKE’S LAW TO ANGLE PLY LAMINA
(ESKİŞEHİR TEKNİK ÜNİVERSİTESİ, 2022) Yılmaz, Çağatay; Ali, Hafiz Qasim; Yıldız, Mehmet; 0000-0002-8063-151X; AGÜ, Mühendislik Fakültesi, Makine Mühendisliği Bölümü; Yılmaz, Çağatay
Aerospace-grade carbon fiber reinforced polymer composite plates with four different fiber orientations 0º, 30º, 45ºand 60º is produced with the autoclave curing method and subjected to tensile testing. The stress-strain curves of the composite specimens are compared with Hooke’s law. It is observed that Hooke’s law coincides precisely with the experimental results for samples containing fibers parallel to the loading direction. However, it does not coincide with samples where the fibers make a certain angle with the applied load direction. Moreover, it is reported that Hooke’s law converges the experimental results for small strain values but diverges significantly from the experimental results at higher strain values.
An atomistic study on the HELP mechanism of hydrogen embrittlement in pure metal Fe
(PERGAMON-ELSEVIER SCIENCE LTD, 2024) Hasan, Md Shahrier; Kapci, Mehmet Fazil; Bal, Burak; Koyama, Motomichi; Bayat, Hadia; Xu, Wenwu; 0000-0002-7389-9155; AGÜ, Mühendislik Fakültesi, Makine Mühendisliği Bölümü; Kapci, Mehmet Fazil; Bal, Burak
The Hydrogen Enhanced Localized Plasticity (HELP) mechanism is one of the most important theories explaining Hydrogen Embrittlement in metallic materials. While much research has focused on hydrogen's impact on dislocation core structure and dislocation mobility, its effect on local dislocation density and plasticity remains less explored. This study examines both aspects using two distinct atomistic simulations: one for a single edge dislocation under shear and another for a bulk model under cyclic loading, both across varying hydrogen concentrations. We find that hydrogen stabilizes the edge dislocation and exhibits a dual impact on dislocation mobility. Specifically, mobility increases below a shear load of 900 MPa but progressively decreases above this threshold. Furthermore, dislocation accumulation is notably suppressed at around 1 % hydrogen concentration. These findings offer key insights for future research on Hydrogen Embrittlement, particularly in fatigue scenarios.
Basalt Fiber Reinforced Polymers: A Recent Approach to Electromagnetic Interference (EMI) Shielding
(WILEY Online Library, 2025) Fareez, Umar Naseef Mohamed; Loudiy, Aymen; Erkartal, Mustafa; Yilmaz, Cagatay; 0000-0001-9763-6598; 0000-0002-9772-128X; 0000-0002-8063-151X; AGÜ, Mühendislik Fakültesi, Makine Mühendisliği Bölümü; Fareez, Umar Naseef Mohamed; Loudiy, Aymen; Yilmaz, Cagatay
Electromagnetic wave (EMW) radiation pollution is getting more severe as result of the advancement of electronic technology. Researching shielding materials with superior EMI (electromagnetic interference) shielding characteristics is therefore crucial. Basalt fibers (BFs) have been an emerging candidate in the fiber-reinforced polymer (FRP) category due to their favorable mechanical and chemical properties, along with being favorites in sustainability and having low production costs. Therefore, due to the rising need for cheaper and efficient alternatives in the EMI shielding industry, the EMI shielding is covered in terms of BF composite materials and their properties in this review, starting with the EMI shielding mechanism and followed by how BF composites affect the EMI properties. This review then covers the post-treatments of BF composites and, finally, the factors of the composites that affect the EMI properties. Moreover, the EMI shielding applications in which BFRPs are used are comprehensively discussed as well. This review aspires to bridge an understanding between EMI shielding as a material property and the BF composites that are developed to aid in the EMI shielding application.
Çok Ölçekli Malzeme Modellemesi Yoluyla Talaşlı İmalat Çıktılarının Daha Kapsamlı Ve Doğru Analizi
(TUBİTAK, 2020) Bal, Burak; LAYEGH KHAVIDAKI, SEYD EHSAN; 0000-0002-7389-9155; AGÜ, Mühendislik Fakültesi, Makine Mühendisliği Bölümü; Bal, Burak; LAYEGH KHAVIDAKI, SEYD EHSAN
İnconel 718 savunma sanayi, uzay-havacılık ve otomotiv için kullanılan ve ileride kullanım alanı daha da genişleyebilecek olan süper alaşımdır. Bu projede Inconel 718 süper alaşımının talaşlı imalat sonucunda yüzeyinde oluşan kalıntı gerilimler, sertlik değişimleri ve kesici takımda oluşan aşınmalar gözlenmiştir. Talaşlı imalat simülasyonları için kullanılan Deform 2D programına, klasik Johnson-Cook malzeme modeli yerine, kristal plastisite tabanlı çok ölçekli malzeme davranışı tanıtılarak daha kapsamlı ve deneysel veriye daha yakın analizler yapılmıştır. Bu konunun seçilme nedeni, gerçek deneysel sonuçlara daha yakın sonuçlar elde edilip beklenmedik üretim hataları ve denemeleri en aza indirebilecek bir yöntem geliştirmektir. Bugüne kadar gerçekleştirilen talaşlı imalat simülasyonlarında malzeme davranışı genellikle tek ölçekli gerinim pekleşmesi, gerinim hızı pekleşmesi ve sıcaklık yumuşamasını kapsayan Johnson-Cook malzeme modelleri ile gerçekleştirilmiştir ve bu modeller malzemelerin mikroyapısal girdilerini içermemektedir. Bu projede ise Johnson-Cook malzeme modeli ile ve karşılaştırmalı olarak çok ölçekli kristal plastisite tabanlı malzeme modeli ile 2D deform programında farklı kesme hızlarında ve farklı ilerleme hızlarında simülasyonlar gerçekleştirilmiştir. Bu projede ilk olarak, Inconel 718 malzemesinin talaşlı imalat deneylerini yapılarak sonuçları gözlenmiştir. Daha sonra Johnson-Cook malzeme modellemesiyle gerçekleştirilen simülasyon sonuçları gözlenmiştir. Son olarak da Inconel 718 süper alaşımının kristal plastisite modelinin yapılması ve mikroyapı girdileri ile elde edilen kristal plastisite modeli ile çıkarılan çok ölçekli ve çok eksenli malzeme davranışının Deform 2D simülasyonlarına tanıtılarak simülasyonu gerçekleştirip, elde edilen sonuçlar gözlenmiştir. Yapılan simülasyonlar ve deney sonucunda, iki farklı malzeme modelin deneysel sonuçlarla karşılaştırılması yapılmıştır. Mikroyapı girdileri ile elde edilen kristal plastisite modeli ile çıkarılan çok ölçekli ve çok eksenli malzeme davranışının, tek ölçekli malzeme davranışı ile karşılaştırıldığında deneysel sonuçlara daha yakın sonuçlar verdiği gözlemlenmiştir. Böylelikle çok ölçekli malzeme modellemesiyle gerçekleştirilen simülasyonların daha gerçekçi ve güvenilir sonuçlar gösterdiği kanıtlanmıştır.
A Comparison of Ensemble and Base Learner Algorithms for the Prediction of Machining Induced Residual Stresses in the Turning of Aerospace Materials
(Bitlis Eren Üniversitesi, 2022) Buyrukoğlu, Selim; Kesriklioglu, Sinan; 0000-0002-2914-808X; AGÜ, Mühendislik Fakültesi, Makine Mühendisliği Bölümü; Kesriklioglu, Sinan
The estimation of residual stresses is essential to prevent the catastrophic failures of the components used in the aerospace industry. The objective of this work is to predict the machining induced residual stresses with bagging, boosting, and single-based machine learning models based on the design and cutting parameters used in the turning of Inconel 718 and Ti6Al4V alloys. Experimentally measured residual stress data of these two materials was compiled from the literature, including the surface material of the cutting tools, cooling conditions, rake angles, as well as the cutting speed, feed, and width of cut to show the robustness of the models. These variables were also grouped into different combinations to clearly show the contribution and necessity of each element. Various predictive models in machine learning (AdaBoost, Random Forest, Artificial Neural Network, K-Neighbors Regressor, Linear Regressor) were then applied to estimate the residual stresses on the machined surfaces for the classified groups using the generated data. It was found that the AdaBoost algorithm was able to predict the machining induced residual stresses with a mean absolute error of 18.1 MPa for the IN718 alloy and 31.3 MPa for Ti6Al4V by taking into account all the variables, while the artificial neural network provides the lowest mean absolute errors for the Ti6Al4V alloy. On the other hand, the linear regression model gives poor agreement with the experimental data. All the analyses showed that AdaBoost (boosting) ensemble learning and artificial neural network models can be used for the prediction of the machining induced residual stresses with the small datasets of the IN718 and Ti6Al4V materials.
Computational Fluid Dynamics (CFD) Analysis of Bioprinting
(John Wiley and Sons Inc, 2024) Fareez, Umar Naseef Mohamed; Naqvi, Syed Ali Arsal; Mahmud, Makame; Temirel, Mikail; 0000-0002-8199-0100; AGÜ, Mühendislik Fakültesi, Makine Mühendisliği Bölümü; Fareez, Umar Naseef Mohamed; Naqvi, Syed Ali Arsal; Mahmud, Makame; Temirel, Mikail
Regenerative medicine has evolved with the rise of tissue engineering due to advancements in healthcare and technology. In recent years, bioprinting has been an upcoming approach to traditional tissue engineering practices, through the fabrication of functional tissue by its layer-by-layer deposition process. This overcomes challenges such as irregular cell distribution and limited cell density, and it can potentially address organ shortages, increasing transplant options. Bioprinting fully functional organs is a long stretch but the advancement is rapidly growing due to its precision and compatibility with complex geometries. Computational Fluid Dynamics (CFD), a carestone of computer-aided engineering, has been instrumental in assisting bioprinting research and development by cutting costs and saving time. CFD optimizes bioprinting by testing parameters such as shear stress, diffusivity, and cell viability, reducing repetitive experiments and aiding in material selection and bioprinter nozzle design. This review discusses the current application of CFD in bioprinting and its potential to enhance the technology that can contribute to the evolution of regenerative medicine.
Computational fluid dynamics for the optimization of internal bioprinting parameters and mixing conditions
(WHIOCE PUBL PTE LTD, 2023) Ates, Gokhan; Bartolo, Paulo; AGÜ, Mühendislik Fakültesi, Makine Mühendisliği Bölümü; Ates, Gokhan
Tissue engineering requires the fabrication of three- dimensional (3D) multimaterial structures in complex geometries mimicking the hierarchical structure of biological tissues. To increase the mechanical and biological integrity of the tissue engineered structures, continuous printing of multiple materials through a printing head consisting of a single nozzle is crucial. In this work, numerical analysis was carried out to investigate the extrusion process of two different shear-thinning biomaterial solutions (alginate and gelatin) inside a novel single-nozzle dispensing system consisting of cartridges and a static mixer for varying input pressures, needle geometries, and outlet diameters. Systematic analysis of the dispensing process was conducted to describe the flow rate, velocity field, pressure drop, and shear stress distribution throughout the printing head. The spatial distribution of the biopolymer solutions along the mixing chamber was quantitatively analyzed and the simulation results were validated by comparing the pressure drop values with empirical correlations. The simulation results showed that the proposed dispensing system enables to fabricate homogenous material distribution across the nozzle outlet. The predicted shear stress along the proposed printing head model is lower than the critical shear values which correspond to negligible cell damage, suggesting that the proposed dispensing system can be used to print cell-laden tissue engineering constructs.
Convenient Site Selection of a Floating PV Power Plant in Türkiye by using GIS-Fuzzy Analytical Hierarchy Process
(SPRINGER, 2024) Karipoğlu, Fatih; Koca, Kemal; İlbahar, Esra; 0000-0003-2464-6466; AGÜ, Mühendislik Fakültesi, Makine Mühendisliği Bölümü; Koca, Kemal
Floating photovoltaics (FPVs) are appearing as a promising and an alternative renewable energy opinion in which PV panels are mounted on foating platforms in order to produce electricity from renewable energy on water such as seas, dams, rivers, oceans, canals, fsh farms, and reservoirs. So far, such studies related to the body knowledge on fnancial, technical, and environmental aspects of installation of FPV have not been performed in Turkey while expanding steadily in other countries. In this study, suitable site selection for installation of FPV power plants on three lakes in Turkey was studied by performing geographic information system (GIS) and the fuzzy analytic hierarchy process (FAHP) as multi-criteria decision-making (MCDM) method. This detailed study revealed that the criterion of global horizontal irradiance (GHI) was determined as the most crucial criterion for the installation of FPV on Beysehir Lake, Lake of Tuz, and Van Lake. Additionally, it was clearly seen that the Beysehir Lake had the highest value approximately 52% among other lakes for installation, that is why Beysehir Lake is selected as the best option for installation of an FPV system with this multi-criteria approach.
Data-driven discovery and DFT modeling of Fe4H on the atomistic level
(ELSEVIER, 2024) Zagorac, Dejan; Zagorac, Jelena; Djukic, Milos B.; Bal, Burak; Schön, J. Christian; 0000-0002-7389-9155; AGÜ, Mühendislik Fakültesi, Makine Mühendisliği Bölümü; Bal, Burak
Since their discovery, iron and hydrogen have been two of the most interesting elements in scientific research, with a variety of known and postulated compounds and applications. Of special interest in materials engineering is the stability of such materials, where hydrogen embrittlement has gained particular importance in recent years. Here, we present the results for the Fe-H system. In the past, most of the work on iron hydrides has been focused on hydrogen-rich compounds since they have a variety of interesting properties at extreme conditions (e.g. superconductivity). However, we present the first atomistic study of an iron-rich Fe4H compound which has been predicted using a combination of data mining and quantum mechanical calculations. Novel structures have been discovered in the Fe4H chemical system for possible experimental synthesis at the atomistic level.
DETERMINATION OF MATERIAL RESPONSE AND OPTIMIZATION OF JOHNSON-COOK DAMAGE PARAMETERS OF ALUMINIUM 7075 ALLOY
(Selçuk Üniversitesi, 2018) Bal, Burak; 0000-0002-7389-9155; AGÜ, Mühendislik Fakültesi, Makine Mühendisliği Bölümü; Bal, Burak
The effects of rolling direction and notch radius on the mechanical response of aluminium7075-T651 alloy were investigated and the Johnson-Cook damage parameters of aluminium 7075-T651alloy on both rolling directions were determined. Specifically, mechanical responses of aluminium 7075-T651 along the rolling direction and perpendicular to the rolling direction were obtained frommonotonic tensile tests. 56 tensile tests in total were performed on notched specimens with 3 differentnotch radiuses and smooth specimens. Tensile tests were repeated 7 times for each case to ensure theconsistency and to obtain the closest mechanical response to the real mechanical response withminimum error. Experimental findings revealed that being perpendicular to the rolling directiondeteriorates the elongation at failure dramatically but can increase the mechanical properties in elasticregion. The final areas of the fractured samples, used for the calculation of Johnson-Cook damageparameters, were measured by an optical microscope. The Johnson-Cook damage parameters ofaluminium 7075-T651 alloy for different applications were computed by Levenberg-Marquardtoptimization method. Collectively, this study opens the venue for accurate damage simulations ofaluminium 7075-T651 along the rolling direction and perpendicular to the rolling direction for differentapplications.
The effect of different tabbing methods on the damage progression and failure of carbon fiber reinforced composite material under tensile loading
(ELSEVIER SCI LTD, 2022) Yılmaz, Çağatay; Ali, Hafiz Qasim; Yıldız, Mehmet; 0000-0003-1626-5858; AGÜ, Mühendislik Fakültesi, Makine Mühendisliği Bölümü; Yılmaz, Çağatay
Composites are well-known and widely used materials due to their anisotropic nature and high strength-to-weight ratio; therefore, the mechanical performance of these materials is crucial. Precise tensile testing is essential to obtain material properties that are crucial for the design stage of composite structures. This study is an effort to investigate the effect of adhesive materials used for tabbing process, which is necessary for the tensile testing procedure. Araldite and AF 163-2k film are used as the adhesive film, whereas in the case of AF 163-2k, tabbing is done through two different procedures (Jig and corner holes method). Apart from the tensile performance, strain distribution and damage progression are monitored simultaneously using digital image correlation (DIC) and acoustic emission (AE) analysis. It is observed that there is no significant difference in the ultimate tensile strength of these composites tabbed with different adhesives and procedures. Nevertheless, the first major failure strength is much higher in Araldite tabbed specimens compared to AF 163-2k film (the first major failure activity is defined as a point at which material loses its integrity, especially when considering structural or aerospace applications). Also, strain distribution throughout the gauge length recorded via DIC is appreciably different, which is attributed to damage accumulation and progression monitored by AE analysis. The frequency-based analysis of AE data is performed to classify the damage, and cumulative energy is correlated with the DIC to navigate the failure activity at different times and stress levels.
Effect of Geometry Modifications on the Vectoring Performance of a Controlled Jet
(ISFAHAN UNIV TECHNOLOGY, MECHANICAL ENGINEEING DEPT, JAFM OFFICE, ISFAHAN, 84156-83111, IRAN, 2017) Tomac, Mehmet N.; AGÜ, Mühendislik Fakültesi, Makine Mühendisliği Bölümü; Tomac, Mehmet N.
Jet vectoring performances of ten different designs with various depths and geometrical outlines were quantified through constant temperature anemometry measurements for a Reynolds number range from 10,000 to 30,000 by using passive and active flow control methods at cold flow. The reference design was based on NASA's double throat nozzle concept and a self-injection double throat nozzle design that uses similar flow control concept as the reference design, were also tested for performance comparison. Furthermore, jet vectoring performance of a single throat design, utilizing Coanda effect for jet vectoring, was also quantified. Results indicated jet vectoring angles starting from 2 degrees up to 47 degrees for a control jet flow rate range from 1% up to 10% with respect to the primary jet flow rate in the investigated Re range. Maximum jet vectoring angle was achieved with a single throat design which incorporates small step geometry before the Coanda surface for more effective flow attachment and these results were compared with the vectoring performance of the double throat nozzle designs.
Effect of strain rate on hydrogen embrittlement susceptibility of twinning-induced plasticity steel pre-charged with high-pressure hydrogen gas
(PERGAMON-ELSEVIER SCIENCE LTD, THE BOULEVARD, LANGFORD LANE, KIDLINGTON, OXFORD OX5 1GB, ENGLAND, 2016) Bal, Burak; Koyama, Motonnchi; Gerstein, Gregory; Maier, Hans Juergen; Tsuzaki, Kaneaki; AGÜ, Mühendislik Fakültesi, Makine Mühendisliği Bölümü;
The effects of tensile strain rate on the hydrogen-induced mechanical and microstructural features of a twinning-induced plasticity (TWIP) steel were investigated using a Fe-23Mn-0.5C steel with a saturated amount of hydrogen. To obtain a homogeneous hydrogen distribution, high-pressure hydrogen gas pre-charging was performed at 423 K. Similar to previous studies on hydrogen embrittlement, the deterioration in the tensile properties became distinct when the strain rate was decreased from 0.6 x 10(-3) to 0.6 x 10(-4) s(-1). In terms of microstructural features, hydrogen-precharging decreased the thickness of deformation twin plates, and it localized dislocation slip. Moreover, facets of the hydrogen induced quasi-cleavage feature on the fracture surface became smoother with decreasing strain rate. In this study, we proposed that a combined effect of hydrogen segregation, slip localization, and thinning of twin plates causes the hydrogen embrittlement of TWIP steels, particularly at a low strain rate. (C) 2016 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.
Experimental and statistical damage analysis in milling of S2-glass fiber/epoxy and basalt fiber/epoxy composites
(John Wiley and Sons Inc, 2024) Sayin, Ahmed Cagri; Danisman, Sengul; Ersoy, Emin; Yilmaz, Cagatay; Kesriklioglu, Sinan; 0000-0002-8063-151X; 0000-0002-2914-808X; 0009-0008-8666-7995; AGÜ, Mühendislik Fakültesi, Makine Mühendisliği Bölümü; Sayin, Ahmed Cagri; Yilmaz, Cagatay; Kesriklioglu, Sinan
S2-glass fiber reinforced plastics (S2-GFRP) and basalt fiber reinforced plastics (BFRP) have emerged as crucial materials due to their exceptional mechanical properties, and milling of composite materials plays an important role in achieving desired properties. However, they have proven challenges due to relative inhomogeneity compared with metals, resulting unpredictability in quality of milling operations. The objective of this work is to investigate the effect of cutting parameters, tool geometry and tool surface materials on the surface quality of composites using burrs as a metric. S2-GFRP and BFRP composites were produced by the vacuum infusion method. Helical and straight flute end mills were manufactured from high-speed steel (HSS) and carbide rounds, and half of them were coated with titanium nitride using reactive magnetron sputtering technique. Taguchi L18 orthogonal array is used to determine the effect of tool material, tool angle, coating, cutting direction, spindle speed, and feed rate on the machining quality of S2-GFRPs and BFRPs with respect to burr formations. Milling experiments were conducted under dry conditions and then the burrs were imaged to calculate the total area and length. Statistical analysis was also performed to optimize the machining parameters and tool type for ensuring the structural integrity and performance of the final composite parts. The results showed that the selection of tool material has the most significant impact on the burr area and length of the machined surface. The novel image analysis allows to analyze the extent of the burr size with a desirable operation speed for industrial applications. Highlights: Aerospace grade S2-Glass (S2-GFRP) and basalt fiber reinforced plastics (BFRP) were manufactured. Carbide and HSS end mills were fabricated and coated with titanium nitride protective layer. FRPs were machined at various process parameters designed by Taguchi method. Distinctive image processing was firstly used to compute milling induced Burr area and length. Statistical analysis was performed to quantify the contribution of parameters and optimize milling.
Farklı Mikroyapısal Değişkenlerin Yüksek Manganlı Fe-%33Mn Çeliğinin Pekleşme Davranışına Etkilerinin Araştırılması
(TUBİTAK, 2019) Bal, Burak; 0000-0002-7389-9155; AGÜ, Mühendislik Fakültesi, Makine Mühendisliği Bölümü; Bal, Burak
İleri yüksek mukavemetli çelikler sahip olmuş oldukları yüksek mukavemet, yüksek süneklik ve yüksek pekleşme kabiliyeti gibi üstün özellikler sayesinde otomotiv, demiryolu, savunma sanayi uygulamalarında ve yapı endüstrisi gibi pek çok farklı alanda tercih edilmektedir. Bu projede yeni nesil yüksek mukavemetli çelikler sınıfından olan yüksek manganlı çeliklerin pekleşme davranışına etki eden farklı mikroyapısal değişkenlerin etkisi kristal plastisite modellemesi yoluyla araştırılmıştır. Öncelikle östenitik Fe-33Mn çeliğinin 1x10-4 s -1 gerinim hızındaki malzeme davranışının, tane sayısı gibi faktörleri girdi olarak kullanarak kristal plastisite modellemesi yapılmıştır ve pekleşme sabitleri bulunmuştur. Daha sonra bulunan pekleşme sabitleri sabit tutularak, malzeme dokusu, hız gradyanı, gerinim artışı ve etkileşim tensörü cinsi gibi tek bir mikroyapısal girdi değiştirilerek bu girdilerin malzemenin toplam pekleşme davranışına etkisi açığa çıkarılmıştır. Spesifik olarak, proje önerisinin üzerine konularak farklı karbon konsantrasyonlarının pekleşme sabitlerine olan etkisi de hesaplanmıştır. Bahsi geçen çeliğin oda sıcaklığında ve düşük gerinim hızındaki malzeme davranışı proje yürütücüsünün daha önceki çalışmalarında çekme testi yardımı ile makro ölçekte gözlemlenmiştir. Fe-33Mn çeliğinin seçilme nedeni, yüksek mangalı östenitik çeliklerinin sahip olduğu çok yüksek pekleşme kapasitesi ile birlikte yüksek süneklik değerleri ve aşınma direnci sayesinde uzay-havacılık, otomotiv, savunma sanayi gibi öncül sektörlerde yer alması ve önümüzdeki yıllarda çok daha fazla miktarda yer alacağına inanılmasıdır. Bu konunun seçilme nedeni ise, bugüne kadar yapılan kristal plastisite çalışmalarında deneysel davranışı modelleyebilmek için genelde tek tip malzeme dokusu, hız gradyanı, gerinim artışı ve etkileşim tensörü kullanılmıştır. Bu doğru bir yaklaşım olmasına rağmen bu girdilerin toplam malzeme pekleşme davranışına etkisi bilinmemektedir. Bu kapsamda kristal plastisite modellemeleri Visco-Plastic Self-Consistent (VPSC) algoritması yardımı ile gerçekleştirilmiştir. Fe-33Mn çeliğinin düşük gerinim hızındaki tek eksenli deformasyon davranışı voce tipi pekleşme teorisi ile modellenmiştir ve bulunan Voce parametreleri bütün simülasyonlarda aynı kalmıştır. Böylelikle değişik mikroyapısal değişkenlerin Fe-33Mn çeliğinin pekleşme davranışına etkileri aynı pekleşme teorisi ile açığa çıkarılmıştır.
Flow properties of an Ahmed Body with different passive flow control methods
(Gazi Üniversitesi, 2024) Koca, Kemal; Özden, Mustafa; 0000-0003-2464-6466; AGÜ, Mühendislik Fakültesi, Makine Mühendisliği Bölümü; Koca, Kemal
A numerical simulation by utilizing the FloEFD software was carried out in order to investigate the flow topology formed on slant surface and wake region of an Ahmed Body with and without passive flow control techniques. The effects of those flow controllers on flow at the slant surface and wake region by influencing the flow topology as well as aerodynamic drag coefficient examined carefully. The numerical findings clearly revealed that the best performance in terms of providing the drag reduction obtained when sphere and hemispherical shape flow control techniques were applied at the rear part of slant surface of Ahmed Body. Sphere and hemispherical shape flow controllers positioned at the rear part of slant surface led to have drag reduction of 6% and 7%, respectively. Besides, the results of current study compared with the results obtained from published studies in the literature. It was clearly observed that they are consistent with each other even though they were found by different software.

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