Mekatronik Mühendisliği Bölümü Koleksiyonu

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https://hdl.handle.net/20.500.12846/481

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New additions to the guitar family: Lego and automatic microtonal guitars
(2022) Acet, Ruşen Can; Çoğulu, Tolgahan; Italia, Tony; Başar, Batuhan; Çoğulu, Atlas; Keser, Selçuk
One of the modern classical guitar’s biggest strengths is also one of its biggest weaknesses. The instrument depends on an equal temperament fretboard system that has lent itself to brilliant repertoire and ease of production, yet this same fretboard system does not lend itself to perfectly tuned notes and tuning systems not found in Eurocentric classical music. Many guitarists and luthiers have sought a fretboard system that marries the benefits of equal temperament with the rich possibilities of just intonation and other tuning systems. This paper presents two new fretboard designs and discuss their role in the history of guitar fretboard construction. Our first design is a fully functional fretboard made from the popular toy ‘Legos’ and solves many of the problems that previous designs had, including ease of use and production, affordability, and versatility. Our second design is a onestring prototype for an automatic (automated) fretboard that would allow performers to switch tuning systems instantly at the press of a button.
Farklı dispersiyon tekniklerinin elektroeğirilmiş karbon nanotüp/ termoplastik poliüretan nanokompozitlerin elektromekanik özelliklerine etkisinin deneysel incelenmesi
(2022) Şanlı, Abdulkadir
In this study, a detailed investigation on the influence of different dispersion methods that are magnetic stirring (MK), ultrasonic bath (UB), and ultrasonication (S) of the electrospun CNTs/ TPU nanocomposite on their morphological and electromechanical properties was conducted. Obtained results suggest that the dispersion method of the CNTs plays a significant role in their physical electromechanical and sensory properties tremendously. Microscopic investigations show that ultrasonicated samples give better dispersed fibrous structures owing to the positive effect of the ultrasonic force. It is also seen that especially for the S-samples, by addition of CNTs to the TPU solution conductivity increases almost 10 times which is attributed to the better dispersion of the fibrous structure. From the mechanical tests, it was observed that the elongation at break in S-samples increased by 31.6%, and the tensile strength increased by approximately 56% compared to MK-samples. Subsequently, from the tensile strain test, it is observed that all probes give strain-sensitive responses in two linear regions and S-samples are the most sensitive among others that are due to higher total amount of nanofiber networks. All the results prove that the importance of good CNTs dispersion that affects not only physical properties but also their electromechanical and sensory properties. Results obtained from this study can shed a light on the importance of controlling the dispersion of the CNTs for fabricating highly sensitive, flexible strain sensors through electrospinning technology.
2-D microstructure modeling based on micrographs of laser powder bed fusion melted specimens
(2024) Kaya, Ali Can
Optik mikrograflara dayalı 2 boyutlu mikroyapısal modelleme başarıyla gerçekleştirildi. Füzyon sınırları ve fazlar gibi mikroyapısal özellikleri içeren gerçekçi bir mikroyapısal modelin oluşturulmasıyla mikroyapı ve özellik arasındaki ilişkinin analiz edilmesi mümkün olmuştur. Bu yöntemi 316 paslanmaz çelik (SS) lazer toz yataklı füzyon ile sinterlenmiş numunelere uyguladık. Optik mikrograflara mesh atıldı ve sonlu elemanlar (FE) yazılımına aktarıldı. Sonuçlara göre, füzyon sınırlarının yönelimi, 3d yazıcı ile üretilmiş parçaların mekanik özelliklerini önemli ölçüde etkilemektedir. Füzyon sınırları yükleme eksenine paralel olduğunda önemli bir gerilim lokalizasyonu oluşmuştur. Füzyon sınırları yükleme doğrultusuna dik olduğunda ise durum faklıdır. Bu durumda büyük miktarda ve boyuttaki füzyon sınırları, homojen olarak dağılmış bir şekil değiştirme ile önemli bir süneklik göstermiştir.
Influence of anisotropy on the deformation behaviour in microtensile 316L steel specimens fabricated by laser powder bed fusion (PBF-LB/M)
(2023) Kaya, Ali Can; Fleck, Claudia; Salamci, Metin U.
Laser powder bed fusion of metals (PBF LB/M) allows fabrication of intricate structures without any need of tools and moulds. In this process the building orientation becomes a significant issue for the complex structures. Here we fabricated small size 316L steel tensile specimens aligned with their loading axis perpendicular and parallel to the building direction by PBF LB/M. Microstructure and mechanical properties were characterized by colour etching, in-situ tensile testing in a scanning electron microscope, nanoindentation and digital image correlation. The orientation of the melt pools has a significant impact on the deformation behaviour of the PBF LB/M specimens. In parallel specimens (polar angle = 90o ) the semi-circular melt pools are aligned perpendicular to the loading axis resulting in an accommodation of larger amount of plasticity as compared to the perpendicular specimens (polar angle = 0o ). While strain is localized in the case of perpendicular specimens because primary slip lines are aligned perpendicular to the loading axis, strain is homogenously distributed along the longitudinal axis of the parallel specimens because primary slip lines are aligned parallel to the loading axis. Twin-inducedplasticity and transformation induced plasticity are the deformation mechanisms observed on the fractured specimens. Strain hardening rate in stage IV extended to a higher stress value for the perpendicular specimens as compared to parallel specimens because cross slip is confined in the fusion boundaries. The building direction has shown significant influence on the deformation mechanisms of the PBF LB/M steels which may be a significant issue to overcome for the complex shape specimens.
Analyzing the influence of the investment casting process parameters on microstructure and mechanical properties of open-pore Al–7Si foams
(2023) Firoozbakht, Mahan; Blond, Aurelien; Zimmermann, Golo; Kaya, Ali Can; Fleck, Claudia; Bührig-Polaczek, Andreas
Aluminum alloy foams with high specific compressive strength and good energy absorption capacity are widely used as structural materials and shock absorbers. The investment casting process offers an interesting opportunity for the production of open-pore aluminum foams. However, foam casting differs from casting of solid parts, and there is a lack of practical knowledge about the microstructure tuning of the ultra-thin cast struts. Our study focuses on the influences of the casting conditions such as mold temperature on the microstructure and consequently on the mechanical properties of aluminum-silicon alloy foams. We investigated microstructural features using various metallography techniques and defined mechanical properties under uniaxial compression test. Here, we observed improvements in the strut microstructure together with decrease of the mold filling by reduction of the mold temperature. Microstructure improvements involve transformation of a single dendritic aluminum grain in each strut to globular grains along with a more homogeneous distribution of the silicon particles across the strut cross-section. These changes bring higher ductility and energy absorption efficiency to the foams, which are evident from the smoother plateau of the stress-strain curves. Decline of the mold filling, on the other hand, has negative effect on the overall mechanical properties.
Mechanical performance of reverse-engineered resin foam structures developed by image processing on the computed tomography data: A revisit
(2023) Kaya, Ali Can; Rastanawi, Nouh; Korucu, A.
Using digital design methods, additive manufacturing processes enable us to create novel complex structures. In the current study, 3 and 10 ppi, density-graded, and merged foams (digitally joined 3 and 10 ppi) were reproduced from computed tomography data of the commercially available steel foams using MSLA (masked stereolithography). The mechanical performance of the foams has been characterized by quasi-static compression testing. Density grading increases the slope of the plateau regime and reduces the densification strain. Merged foams at high relative densities (?rel~35 %) showed the highest energy absorption capacity, specific strength, and densification strain. 3,10 and density-graded foams deform by bending of struts. In the case of merged foams, the bending-dominated structure has been transformed into a stretch-dominated structure. The power exponent (n = 0.72) delivers the deformation mode of the strut, revealing stretch-dominated behavior. Moreover, additively manufactured resin foams have a lower scattering in mechanical properties than conventionally manufactured metal foams because structures can be remanufactured with the same cell/strut dimensions and imperfections.
Influence of additional strut elements in 3D Re-Entrant auxetic unit cells on the damage and energy absorption properties
(2024) Kaya, Ali Can; Boğoçlu, M.; Korucu, A.
Background Geometric parameter optimization, novel design, and mechanism modeling of auxetic materials have been widely studied. However, manipulating the topology of the 3d printed auxetic unit cells and its influence on the damage have yet to be explored. Objective This study aims to characterize the energy absorption properties and damage mechanisms of the modified auxetic unit cells. Methods In the current study, bending-dominated re-entrant auxetic unit cells (Cell0), torsion-dominated auxetic unit cells with cross elements (CellX), buckling-dominated auxetic unit cells with vertical elements (CellB), and bending-dominated auxetic unit cells with panels (CellW) have been fabricated by FDM (Fused deposition modeling). Uniaxial compression testing of the PLA (Polylactic acid) unit cells has been carried out, and a camera has observed their deformation behavior. SR- µCT (Synchrotron radiation microtomography) and an SEM (Secondary electron microscope) accomplished further damage analysis of the struts. Results Adding additional struts hinders the lateral shrinking of the re-entrant auxetics, and re-entrant auxetic unit cells with cross elements have shown higher energy absorption capacity and efficiency than others. The struts’ damage has been governed by building direction, printed material, and strut dimensions. Intra-layer and interlayer fracture of the layers and rupture in the circumferential direction of the PLA struts have been observed in the SR- µCT slices. Conclusions By additional struts, it is possible to fabricate complex auxetic structures with enhanced energy absorption properties, but their inherent characteristics dominate the damage of the struts in the auxetic unit cells.
Relation between Tensile Strut and Compressive Foam Deformation Behaviour: Failure Mechanisms and the Influence of Dendritic Versus Globular Grain Structure in an AlSi7Mg0.3 (A356) Precision?Cast Open?Cell Foam
(2024) Kaya, Ali Can; Blond, Aurelien; Firoozbakht, Mahan; Bührig-Polaczek, Andreas; Fleck, Claudia
Open-cell aluminum foams are gaining importance for the design of lightweightstructures and as electrodes in lithium-ion batteries. AlSi7Mg0.3 foams areproduced by a modi?ed investment casting process. By tuning the mold tem-perature, a change from the usual nearly monocrystalline dendritic to a poly-crystalline globular grain structure is achieved. Tension and compression tests onsingle struts and foam specimens, respectively, are combined with digital imagecorrelation, scanning electron microscopy, and phase contrast-enhancedmicrocomputed tomography in a synchrotron facility to correlate the mechanicalproperties and the failure mechanisms with the microstructure. The “globular”foams exhibit a lower strength and a less pronounced subsequent stress dropthan the “dendritic” foams and the deformation mechanism changes from shearband-dominated failure to a layer-by-layer collapse, because of the lower strengthand higher ductility of the “globular” struts. The “dendritic” struts have a morehomogeneous microstructure, while the “globular” struts often contain siliconagglomerates in their central region. Accordingly, the latter struts exhibit a higherdegree of scatter for the fracture strain. Thus, the arrangement of the siliconparticles and the eutectic determines the mechanical properties on the strut leveland thereby the failure behavior on the foam level.
Fatigue and corrosion-fatigue behavior of the ?-metastableTi-5Al-5Mo-5V-3Cr alloy processed by laser powder bedfusion
(2024) Kaya, Ali Can; Alcântara, Erika Gabriele Alves; Meinke, Reinhard; Selve, Sören; Fleck, Claudia
We performed rotating bending tests and axial (tension-compression) loadincrease and constant amplitude high-cycle fatigue tests in air and Hanks' balanced salt solution (HBSS) on the ?-metastable titanium alloy Ti-5Al-5Mo-5V3Cr, processed by laser powder bed fusion (LPBF-M), solution-treated and aged, and shot-peened. Rotating bending loading in air revealed a strong influence of process-induced flaws on fatigue endurance. Especially in the highcycle fatigue range and the transition region, the stochastic distribution of the flaws and flaw sizes led to a high scatter of the number of cycles to failure. The axial load-increase tests yielded a good fatigue life estimation, with a negligible difference between air and HBSS. The cyclic deformation behavior in HBSS was also strongly influenced by the local microstructure and defect distribution, and, thus, by crack formation and propagation. Plastic deformation and microcrack growth interact, and their relative amount resulted in different progressions of the plastic strain amplitude over the number of cycles for different specimens. Changes in the free corrosion potential and the corrosion current were highly sensitive indicators for fatigue-induced damage on the rough surfaces, which was correlated to the microscopic examination, fracture surface features, and the fatigue crack development.
Modification of open-cell cast aluminum-silicon foams with strontium
(2024) Kaya, Ali Can; Firoozbakh, Mahan; Buehrig-Polaczek, Andreas; Blond, Aurelien; Fleck, Claudia
The mechanical properties of open-cell aluminum foams can be influenced by enhancing the microstructure of the struts. The foams produced by investment casting face slow cooling rates, which makes it challenging to improve the morphology of the phases. In the case of aluminum silicon cast foams, the silicon phase accumulates on the surface of the struts, which leads to brittle fractures. In the present study, we successfully modified the silicon phase in open-cell AlSi7Mg and AlSi10Mg cast foams by adding strontium and investigated the influence of the strontium content on the microstructure and mechanical properties at the foam and strut levels. Despite the cooling rates of less than 0.5 ?C/s during solidification, the strontium addition of 200–800 ppm effectively decreased the size of the silicon particles and improved their distribution in the micrometer-sized struts. Improvements in the compressive properties of the foams and the tensile properties of the struts only occurred at the strontium levels of 200 and 400 ppm. The effective modification in this casting condition is due to the limited solidification space, which favors the formation of the atomic clusters responsible for the modification
Micro and nano damage observations of martensitic and austenitic open cell cast foams
(Elsevier Science, 2022) Kaya, Ali Can; Fromert, Jan; Jost, Norbert; Fleck, Claudia
In current study a detailed investigation of the 304 austenitic and 420 martensitic foams damage has been carried out at all hierarchical levels. In-situ compression testing of foams and microtensile testing of single struts have been conducted in scanning electron microscope (SEM). Strain field analysis has been carried out by Digital image correlation (DIC) method. Nano damage has been applied by Nanoindentation on the unloaded and compressed foams. 304 foams depicted a ductile failure at each scale, while 420 foams failed with a tremendous brittleness, such that no real plateau regime has been observed. At microscale 420 struts ruptured with an intergranular cracking, while 304 struts underwent transformation induced plasticity (TRIP) effect with signif-icant ductility. Although 304 steel struts have higher strength, 420 steel foams exhibited a higher strength due to their high hardness. Since there is not a plastic bending of the 420 struts, load is distributed homogenously to all struts. For this reason, it was concluded that the hardness and ductility of struts are the dominating factors in the foam deformation.
Experimental study of the impact of electrospinning parameters on the electromechanical properties of strain sensitive electrospun multiwalled carbon nanotubes/ thermoplastic polyurethane nanofibers
(Taylor & Francis, 2021) Şanlı, Abdulkadir
Flexible strain sensitive electrospun fibrous layers have attracted widespread attention of researchers owing to their large surface area and exceptional flexibility. Herein, a detailed research on the impact of electrospinning parameters on the morphological and electromechanical properties of electrospun multiwalled carbon nanotubes (MWCNTs)/thermoplastic polyurethane (TPU) nanofibers is conducted. Besides the MWCNTs concentrations, electrospinning parameters have a significant effect on the morphology, electromechanical and sensory properties of electrospun MWCNTs/TPU nanofibrous membrane. Results show that at lower collector speeds, tip to collector distances, and higher electrospinning time lead to the formation of more homogeneously dispersed fibrous structures, which result in enhanced conductivity and strain sensitivity. Consequently, from the repeatability tests, all samples show quite similar linear responses under strain, indicating a highly repeatable fabrication process. Obtained results can help to gain a deeper understanding of the importance of controlling the electrospinning parameters, especially in the production of flexible strain sensors.
Stewart platform based robot design and control for passive exercises in ankle and knee rehabilitation
(Gazı University Faculty Engineering Architecture, 2021) Budaklı, Merve Teke; Yılmaz, Cüneyt
Nowadays, usage of robots in industry and daily life is increasing, additionally, different robot designs are developed in order to fulfill the applications optimally by means of robots. Parallel robots have a restricted workspace due to their closed chain kinematic structure. However, this kinematic structure provides the robot high positioning accuracy and rigidity. Precise positioning and rigidity are most important key aspects for rehabilitation robots, therefore parallel robots are very suitable for rehabilitation applications. However, the limited workspace of the parallel robot creates a limitation in joint range of motion. In this study, a new rehabilitation robot was designed with the addition of Stewart Platform structure, 7th linear actuator and mechanical part, thus extending the workspace and providing rehabilitation to ankle and knee joints. The robot is configured by combining mechanical design, electronic hardware, mathematical model based on the Newton-Raphson method for forward kinematics as well as vectorial approach for inverse kinematics, and PID position control. Experiments were performed on human leg; ankle and knee range of motion and positioning results are evaluated and compared with literature. According to experimental measurements, the time delay in trajectory tracking was less than 0.5 seconds and the maximum angle deviation was 1.2 degrees.
Modeling of complex gray cast iron open-cell foams revealing insights on failure and deformation on different hierarchical length-scales
(Wiley-VCH, 2021) Kaya, Ali Can; Zaslansky, Paul; Fleck, Claudia
Open-cell gray cast iron foams are a class of porous materials of increasing interest, with great potential to be used in energy damping applications and for sound isolation. We created finite element (FE) models from 3D reconstructed data of foams and of isolated struts imaged with resolutions spanning from 0.65 to 10.5 mu m. Representative volume elements (RVE) are loaded in tension to simulate and analyze foam mechanical behavior. A ductile damage model is used for tensile testing of single struts and compression testing of foams. RVEs loaded along three axes demonstrate important effects of orientation of graphite particles in the microstructure. Only simulation results that take failure into consideration are consistent with experimental findings. Strut fracture initiation strongly depends on the cross-sectional area and its circularity and foam simulation results are heavily influenced by damage modeling. The complexity of the open-cell foam behavior is revealed at several hierarchical levels. Simulations in which material properties are assigned excluding damage overestimate the experimental results of the foam; conversely, a very good agreement is observed if damage is considered. The models exhibiting anisotropic mechanical properties fully reproducing large fluctuations in the mechanical properties of the struts are observed in in situ experiments.
Performance analysis of HQAM based spatial modulation over Nakagami-m Fading Channels
(Institute of Electrical and Electronics Engineers, 2020) Çögen, Fatih; Aydın, Erdoğan
In this study, the performance analysis of the recently proposed Hexagonal Square Amplitude Modulation Spatial Modulation (HQAM-SM) system on Nakagami-m fading channels is presented. Performance analysis was performed considering the most general state of the Nakagami-m channel distribution phase for the phase without uniform-distribution. HQAM optimizes the assignment of code words to points in the form of a hexagonal constellation to minimize the average Hamming distance. This arrangement always uses energy more effectively than conventional quadrature amplitude modulation (QAM) and performs almost the same performance as QAM at higher SNRs. In this study, a more energy-efficient system was proposed for Nakagami-m fading channels compared to conventional SM, where SM will carry data with HQAM instead of carrying data with conventional modulated symbols in addition to the antenna index. Performance analysis of the proposed system was carried out in Nakagami-m fading channels.
Performance analysis of Hexagonal QAM constellations on quadrature spatial modulation with perfect and imperfect channel estimation
(Elsevier, 2021) Çögen, Fatih; Aydın, Erdoğan
In this study, the quadrature spatial modulation (QSM) technique, which is a rational multiple-input multiple-output (MIMO) transmission technique and frequently encountered in recent studies in the literature, and the hexagonal quadrature amplitude modulation (HQAM) constellation technique, which combines symbols in an "optimum" way are combined. This new MIMO scheme has been named by the authors as HQAM-QSM. Also, the impact of imperfect channel knowledge on the performance of the proposed scheme is examined. The HQAM constellation technique is a technique that provides better results under the same power assumption than the conventional QAM constellation in terms of symbol separation and is more often encountered when it comes to energy-efficiency. Due to the nature of HQAM symbols, error-floor occurs when the QSM system is applied. Hence, the optimum angle is obtained by rotating the HQAM symbols. With this optimum angle, it has been seen that the error-floor disappeared and the performance of the system is improved. Besides, the HQAM technique performs similar bit error rates (BER) to QAM at high signal-to-noise ratio (SNR) values. From this point forth, in our study, the rational HQAM-QSM technique, which uses energy-efficient HQAM symbols instead of traditional modulated QAM symbols and also carries information effectively on two active antennas, is proposed. Performance analysis of the HQAM-QSM technique is performed on Rayleigh fading channels. (C) 2021 Elsevier B.V. All rights reserved.
Generalized code index modulation and spatial modulation for high rate and energy-efficient MIMO systems on rayleigh block-fading channel
(IEEE, 2021) Çögen, Fatih; Aydın, Erdoğan; Kabaoğlu, Nihat; Başar, Ertuğrul; İlhan, Hacı
In this article, a high data rate and energy-efficient multiple-input multiple-output transmission scheme is considered by combining two popular and rational modulation techniques: spatial modulation (SM) and code index modulation-spread spectrum (CIM-SS). Since in the considered system, called generalized CIM-SM (GCIM-SM), incoming information bits determine modulated symbols, activated transmit antenna indices as well as their corresponding spreading code indices, data bits are conveyed not only by modulated symbols but also by the indices of the active antenna and spreading codes. Hence, a GCIM-SM scheme accommodates faster data rates while spending less transmission power and possessing better error performance compared to the conventional direct sequence spread spectrum (DS-SS), SM, quadrature SM (QSM), and CIM-SS systems. The mathematical expressions of the GCIM-SM system for bit error rate, throughput, energy efficiency, and the system complexity are derived to analyze the overall system performance. Besides, it has been shown via computer simulations that the GCIM-SM system has lower transmission energy, faster data transmission rate, and better error performance than DS-SS, SM, QSM, and CIM-SS systems. Performance analysis of the considered
Differential chaos shift keying assisted media-based modulation
(İstanbul Üniversitesi, 2021) Önal, Beyza; Aydın, Erdoğan; Çögen, Fatih
This study proposes a new energy-efficient and high data-rated communication technique by combining media-based modulation (MBM) and differential chaos shift keying technique (DCSK), called DCSK–MBM. The MBM technique, which forms the infrastructure of this proposed system, is one of the newest members of the index modulation family, while DCSK offers considerable performance improvements for fading channels. Communication comprises two stages in the DCSK system. In the first stage, only the reference symbol is transmitted to the receiver side, whereas in the second stage, information is carried along with the reference symbol. The negative aspect of this method is that it reduces both transmission data rate and spectral efficiency. The MBM technique provides a significant increase in both spectral efficiency and data rate because it performs index modulation with reconfigurable antennas and transmits extra information bits. To minimize the disadvantages of the DCSK technique and create a more energy-efficient and high data-rated technique, the MBM technique is combined with the DCSK technique. Thus, considerable progress is made. All performance analyses are performed over Rayleigh fading channels for M-ary phase shift keying/quadrature amplitude modulation.
Two-way code index modulation
(Institute of Electrical and Electronics Engineers Inc., 2019) Aydın, Erdoğan; Çögen, Fatih
In this study, a new code index modulation (CIM) aided two-way network coded (TW-CIM) scheme with high energy-efficiency, high data speed and good error performance is proposed. In the proposed system model, unlike conventional decode-and-forward (DF) cooperative network coded communication techniques that perform three time-interval communications, only two time-intervals are used for communication since the spreading codes used are orthogonal to each other. In the proposed system structure, as well as the transmitted modulated symbol data, the spreading code indices carry data. In the TWCIM system, two different users communicate via a half-duplex relay based on the CIM technique. The considered TW-CIM system has been compared with the cooperative TW-DF system at different data rates. The theoretical error analysis of the proposed system is performed and the average bit error probability is achieved. Performance analyzes have been performed on Rayleigh fading channels for BPSK modulation. © 2019 IEEE.
Drilling process and resulting surface properties of Inconel 718 alloy fabricated by selective laser melting additive manufacturing
(Elsevier B.V., 2020) Karabulut, Yusuf; Kaynak, Yusuf
One of the challenges is to produce holes with expected dimensional accuracy in metal additive manufacturing. Although post-processing is usually carried out for the additively manufactured components but improving the quality of the holes produced through additive manufacturing seems to be requirement. Otherwise, it is difficult to obtain expected quality for the holes in metal components. Therefore, this study focuses on drilling operation of Inconel 718 alloy fabricated by selective laser melting additive manufacturing. Specimens fabricated by selective laser melting (SLM) were drilled using carbide drill bit under various drilling conditions including cutting speed and feed values. The measured outputs were surface quality of drilled hole, surface topography, surface and subsurface microhardness, and microstructure. Obtained results were compared with the results from wrought Inconel 718. This study showed that drilling process helps to improve the surface quality of additively manufactured Inconel 718 by reducing the surface roughness. Besides, increased feed rate results in work hardening effect on the hole surface and eventually microhardness of surface and subsurface increases notably. © 2020 The Author(s).

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