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YAPICI, Güney Güven

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Güney Güven

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    A comparative study on the high-temperature forming and constitutive modeling of Ti-6Al-4V
    (Springer, 2022-09-28) Uz, M. M.; Hazar Yoruç, A. B.; Aydoğan, C. S.; Yapıcı, Güney Güven; Mechanical Engineering; YAPICI, Güney Güven
    Ti-6Al-4V alloy is often preferred for high-performance components such as aerospace components due to its superior material properties and thermal resistance. In order to produce these components in the desired geometry, it is very important to determine the high-temperature thermomechanical properties of Ti-6Al-4V. In order to define these properties, uniaxial tensile tests at strain rates of 0.001, 0.01 and 0.1 s−1 at 700, 750 and 800 °C were applied in this study. In tests performed at a strain rate of 0.001 s−1 at 800 °C, an elongation at break above 0.8 representing a dominant ductile behavior is observed. It is clearly demonstrated that the initial 17.32% β phase reaches 31.02% at 800 °C, and the α grain size increases with temperature. Existence of dimples and voids in the fracture surfaces are an indicator of increased ductility behavior. In addition to the Modified Johnson–Cook model, which is widely used for modeling flow stress, the use of the extended Ludwik equation is suggested in this study. According to the correlation coefficient (R), it is claimed that the Extended Ludwik model is a more suitable approach for modeling the mechanical behavior for the studied forming temperature range.
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    Conference paperPublicationMetadata only
    Influence of warm rolling and aging on the microstructural evolution and mechanical behavior of AZ31 magnesium alloy
    (American Institute of Physics Inc., 2019) Mısırlı, Mustafa; Ghobadlou, Ali Hosseinzadeh; Yapıcı, Güney Güven; Mechanical Engineering; YAPICI, Güney Güven; Mısırlı, Mustafa; Ghobadlou, Ali Hosseinzadeh
    The microstructural evolution and tensile properties of AZ31 after warm rolling and different aging methods and conditions were investigated. The warm rolling was conducted on the as-received AZ31 after homogenization at 400°C for 3h. The rolled slabs were artificially aged at different temperature of 120°C, 180°C and for various durations. As an alternative approach, stress aging was applied on the samples. The results of tensile tests illustrated that the ultimate tensile strength of the as- received AZ31 after 24h aging at 120°C increased up to 300 MPa with the expense of 5% reduction in elongation. While the ductility of the sample aged at 180°C and 48h increased to 14% with the UTS of 285MPa. Also, the stress aging at 120 °C for only 1h increased the yield strength of as-received sample to over 240 MPa. This points to almost 50% increase in strength thermo-mechanical processing. Microstructural observations revealed that the grain growth firstly decreased the strength of rolled samples while improving the ductility. This is followed by the nucleation of recrystallized grains during ageing enhanced the strength with decent ductility as compared to the rolled samples.
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    On the low-cycle fatigue behavior of a multi-phase high entropy alloy with enhanced plasticity
    (Elsevier, 2023-08) Radi, Amin; Sajadifar, S.; Seyedmohammadi, Seyedveghar; Krochmal, M.; Bolender, A.; Wegener, T.; Niendorf, T.; Yapıcı, Güney Güven; Mechanical Engineering; YAPICI, Güney Güven; Radi, Amin; Seyedmohammadi, Seyedveghar
    A multi-phase non-equiatomic FeCrNiMnCo high entropy alloy (HEA) was fabricated using vacuum induction melting. Thermo-mechanical treatments consisting of cold rolling and annealing at 750 °C and 850 °C were employed to improve the mechanical properties of the HEA in focus. Tensile experiments revealed that yield strength and ultimate tensile strength levels can be enhanced significantly after thermo-mechanical processing (TMP). At the same time, ductility remains at an adequate level. Strain-controlled low-cycle fatigue (LCF) experiments were carried out in order to assess the mechanical properties of this HEA under cyclic loading conditions. At the same strain amplitude, the stress levels of the processed samples were considerably higher than that of the as-received counterpart. Similarly, fatigue lives of the former could surpass the base condition at the strain amplitudes of 0.2% and 0.4%; however, at the higher strain amplitudes, cyclic softening was observed. Electron backscatter diffraction (EBSD) and X-ray diffraction (XRD) results revealed that phase transformation from face-centered cubic (FCC) to body-centered cubic (BCC/B2) took place at a higher occurrence with increasing strain amplitude (0.2% to 0.6%). Furthermore, transmission electron microscopy (TEM) studies confirm that upon tensile deformation additional plasticity mechanisms, i.e., deformation twinning and phase transformation, contribute to the overall mechanical behavior of the multi-phase HEA.
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    On the mechanical behavior of cold deformed aluminum 7075 alloy at elevated temperatures
    (Elsevier, 2016-07-18) Shojaei, Kambiz; Sajadifar, Seyed Vahid; Yapıcı, Güney Güven; Mechanical Engineering; YAPICI, Güney Güven; Shojaei, Kambiz; Sajadifar, Seyed Vahid
    In the present study, elevated temperature deformation behavior and microstructural evolution of 7075 aluminum alloy at annealed and cold rolled conditions were examined. Isothermal uniaxial tensile tests at a temperature range of 200–350 °C and at a strain rate range of 0.001–0.1 s−1 were conducted to investigate the effects of deformation parameters on the mechanical behavior. High temperature flow was noticeably strain rate sensitive especially for the rolled condition. Cold work was shown to have a remarkable influence on increasing the peak stress up to 250 °C. At and above this temperature the rolled microstructure enabled higher ductility reaching over 50% accompanied by a stress plateau. The ductility drop at 350 °C at the slowest deformation rate was attributed to impurity rich regions with possible formation of secondary phases due to dynamic precipitation.
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    High temperature deformation behavior of 4340 steel: activation energy calculation and modeling of flow
    (Elsevier, 2013-12) Sajadifar, Seyed Vahid; Yapıcı, Güney Güven; Ketabchi, M.; Bemanizadeh, B.; Mechanical Engineering; YAPICI, Güney Güven; Sajadifar, Seyed Vahid
    The 4340 steel is extensively utilized in several industries including automotive and aerospace for manufacturing a large number of structural components. Due to the importance of thermo-mechanical processing in the production of steels, the dynamic recrystallization (DRX) characteristics of 4340 steel were investigated. Namely, hot compression tests on 4340 steel have been performed in a temperature range of 900–1200 °C and a strain rate range of 0. 01–1 s−1 and the strain of up to 0. 9. The resulting flow stress curves show the occurrence of dynamic recrystallization. The flow stress values decrease with the increase of deformation temperature and the decrease of strain rate. The microstructure of 4340 steel after deformation has been studied and it is suggested that the evolution of DRX grain structures can be accompanied by considerable migration of grain boundaries. The constitutive equations were developed to model the hot deformation behavior. Finally based on the classical stress-dislocation relations and the kinematics of the dynamic recrystallization; the flow stress constitutive equations for the dynamic recovery period and dynamic recrystallization period were derived for 4340 steel, respectively. The validity of the model was demonstrated by demonstrating the experimental data with the numerical results with reasonable agreement.
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    Design and development of a durable series elastic actuator with an optimized spring topology
    (Sage, 2021-12) Yıldırım, M. C.; Şendur, Polat; Kansızoğlu, Mehmet Taha; Uras, U.; Bilgin, Onur; Emre, Sinan; Yapıcı, Güney Güven; Arık, Mehmet; Uğurlu, Regaip Barkan; Mechanical Engineering; ŞENDUR, Polat; YAPICI, Güney Güven; ARIK, Mehmet; UĞURLU, Regaip Barkan; Kansızoğlu, Mehmet Taha; Bilgin, Onur; Emre, Sinan
    This paper aims to present the integrated design, development, and testing procedures for a state-of-the-art torsion-based series elastic actuator that could be reliably employed for long-term use in force-controlled robot applications. The main objective in designing the actuator was to meet weight and dimensional requirements whilst improving the long-term durability, ensuring high torque output, and containing its total weight. A four-fold design approach was implemented: (i) following recursive design-and-test procedures, an optimal torsional spring topology was unveiled with the help of SIMP (Solid Isotropic Material with Penalization) topology optimization method, (ii) the proposed spring was manufactured and multiple specimens were experimentally tested via a torsional test machine to validate linearity, loading rate response, and mechanical limits, (iii) the actuator’s thermal response was experimentally scrutinized to ensure that the generated heat was dissipated for long-term use, and (iv) the fatigue life of the spring was computed with the help of real-life experiment data. Having concluded the development and verification procedures, two different versions of the actuator were built, and preliminary torque control experiments were conducted. In conclusion, favorable torque tracking with a bandwidth of 19 Hz was achieved while peak-to-peak torque input was 20 Nm.
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    Conference paperPublicationMetadata only
    Discrete-time integral sliding mode control of a smart joint for minimally invasive surgeries
    (IEEE, 2016) Jabeen, Saher; Yeganeh, Ali Vahid; Şimsek, Görkem Muttalip; Yapıcı, Güney Güven; Abidi, K.; Bebek, Özkan; Mechanical Engineering; BEBEK, Özkan; YAPICI, Güney Güven; Jabeen, Saher; Yeganeh, Ali Vahid; Şimsek, Görkem Muttalip
    In this work, a shape memory alloy(SMA) actuator based joint (smart joint) is controlled using a discrete-time integral sliding mode (DISM) control to guide the motion of an active catheter. Controller is designed on the base of a simplified physical model of a single SMA actuator which eliminates the necessity of obtaining an accurate model. SMAs are nonlinear actuators and for this reason, a disturbance observer (DOB) is integrated in to the controller to compensate the model uncertainties and external disturbances to the system. A linearized model is used to design the controller. Bandwidth of SMA actuator is small (response frequency is less than 0.1Hz) and hardware communication frequency is 20Hz. Due to high sampling time (τ= 50ms) it is idealized to design a discrete-time controller, as switching frequency of the controller variable is then limited by τ-1. An experimental setup is designed to test the proposed controller with position feedback. In experimental results, DISM controller with DOB is shown to be robust against system model uncertainties and external disturbances. Different frequency responses are compared and it is shown that the response of 0.04 Hz can be achieved with rms tracking error of 0.0112 radians.
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    Optimization of the intermediate layer friction stir spot welding process
    (Springer Nature, 2019-09) Bajilane, Isam Jabbar Ibrahim; Yapıcı, Güney Güven; Mechanical Engineering; YAPICI, Güney Güven; Bajilane, Isam Jabbar Ibrahim
    Friction stir spot welding was performed for joining sheets of 2024 and 6061 aluminum alloys, which is otherwise difficult using conventional welding techniques. The presented approach utilizes an intermediate layer to avoid the keyhole problem. Design of experiment analysis was carried out to evaluate the influence of process parameters. The optimized set of parameters led to the fabrication of sound joints with strength properties exceeding twice the applicable standard requirements as discussed with the evidence of branched hook formations with extensive penetration. Tool rotational speed was determined to be the most significant parameter influencing the mechanical performance. The failure mode revealed itself as sheet tearing-nugget pull out in the joints produced under optimum conditions with various sized dimples apparent on the fracture surface.
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    ArticlePublicationOpen Access
    Effect of build parameters on the compressive behavior of additive manufactured CoCrMo lattice parts based on experimental design
    (MDPI, 2022-07) Gülcan, O.; Simsek, U.; Çokgünlü, Okan; Özdemir, Mirhan; Şendur, Polat; Yapıcı, Güney Güven; Mechanical Engineering; ŞENDUR, Polat; YAPICI, Güney Güven; Çokgünlü, Okan; Özdemir, Mirhan
    Due to their high specific strength, toughness, and corrosion and wear resistance characteristics, CoCrMo alloys are widely used in different industries and applications: wind turbines and jet-engine components, orthopedic implants, dental crowns, etc. The aim of this paper is to investigate the effect of lattice parameters on the compressive behavior of laser powder bed fusion (LPBF) parts from CoCrMo material. Build orientation, volume fraction, and lattice type are chosen as input parameters or control factors, and compressive yield strength (σy), elastic modulus (E), and specific energy absorption are chosen as the output or performance parameters for optimization. The Taguchi experimental design method is used in the arrangement of lattice parameters during experimental studies. The level of importance of the lattice parameters on σy, E, and specific energy absorption is determined by using analysis of variance (ANOVA). At the same material volume fractions, Diamond specimens showed higher σy and specific energy absorption than Gyroid and Primitive specimens, except σy at 0.4 volume fraction, where a Gyroid specimen showed the best result. The experimental and statistical results revealed that volume fraction and build orientation were found to be the major and minor effective factors, respectively, for all performance parameters (σy, E, and specific energy absorption). The effect of volume fraction on σy, E, and specific energy absorption was found to be 85.11%, 91.83%, and 57.71%, respectively. Lattice type was found to be the second-ranking factor, affecting σy, E, and specific energy absorption with contributions of 11.04%, 6.98%, and 39.40%, respectively. Multi objective optimization based on grey relation analysis showed that a Diamond specimen with 0.4 volume fraction and 45◦ build orientation was the best parameter set for the investigated performance outputs.
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    Book ChapterPublicationMetadata only
    Application of friction stir spot welding on additive manufactured carbon fiber composite
    (Trans Tech Publications Ltd, 2022) Raza, Muhammad Farhan; Yapıcı, Güney Güven; Mechanical Engineering; YAPICI, Güney Güven; Raza, Muhammad Farhan
    Friction stir spot welding as a solid state processing technique is used to join dissimilar and similar metals, composites and polymers. This study illustrates the implementation of friction stir spot welding (FSSW) on additive manufactured nylon-based composites with chopped carbon fibre reinforcements. The purpose of this study is to employ FSSW technique for joining additive manufactured carbon fibre composites. The utilization of pinless tool serves a crucial function in the formation of sound welded joints. The joining process consists of two mechanisms: the piercing and melting of the sheets and the adhesive bonding during the re-solidification. As a result of the FSSW process, the joints indicate a decent mechanical performance with a lap shear failure force (LSFF) of about 250N.