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YAPICI, Güney Güven

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Güney Güven

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Now showing 1 - 10 of 67
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    Conference ObjectPublicationMetadata 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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    ArticlePublicationMetadata only
    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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    ArticlePublicationMetadata only
    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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    Book PartPublicationMetadata 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.
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    Book PartPublicationMetadata only
    Solid state routes for composite materials production
    (Elsevier, 2021) Heidarzadeh, A.; Radi, Amin; Ghobadlou, Ali Hosseinzadeh; Yapıcı, Güney Güven; Brabazon, D.; Mechanical Engineering; YAPICI, Güney Güven; Radi, Amin; Ghobadlou, Ali Hosseinzadeh
    Solid-state methods are frequently used to fabricate metal matrix composites, which usually lead to superior mechanical properties compared to liquid state routes. In this article, different solid-state routes including powder metallurgy, diffusion bonding, forging, accumulative roll bonding, extrusion, explosive bonding, and friction stir processing are elucidated for the production of metal matrix composites. For this aim, the different stages and capabilities of each of these processes are presented. This is an area in which both research and commercial activity is expected to grow significantly in the coming years.
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    ArticlePublicationMetadata only
    High temperature characteristics of Al2024/SiC metal matrix composite fabricated by friction stir processing
    (Elsevier, 2018-07-25) Ghobadlou, Ali Hosseinzadeh; Yapıcı, Güney Güven; Mechanical Engineering; YAPICI, Güney Güven; Ghobadlou, Ali Hosseinzadeh
    In the present study, friction stir processing (FSP) is used for the synthesis of an aluminum metal matrix composite (MMC) reinforced by SiC particles. MMC specimens with reinforced microstructures exhibited significant improvement in hardness (near 50%). Isothermal uniaxial tensile tests were employed for the as-received, friction stir processed and composite microstructures at ambient and high temperatures under strain rates ranging from 10−2 to 10−4 s−1 to investigate the effect of deformation rate on the mechanical behavior. At ambient temperature, notable improvement of the yield strength was observed reaching about 240% of the as-received samples while the ductility was reduced near to 4%. Elevated temperature flow curves were perceptibly sensitive to strain rate, especially for FSPed and MMC samples. Fracture surface observations hinted at the distribution of second phase particles along with possible damage mechanisms.
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    Elevated temperature mechanical behavior of severely deformed titanium
    (Springer Nature, 2014-05) Sajadifar, Seyed Vahid; Yapıcı, Güney Güven; Mechanical Engineering; YAPICI, Güney Güven; Sajadifar, Seyed Vahid
    In this investigation, compression tests were performed at a strain rate of 0.001-0.1 s(-1) in the range of 600-900 degrees C to study the high temperature deformation behavior and flow stress model of commercial purity (CP) titanium after severe plastic deformation (SPD). It was observed that SPD via equal channel angular extrusion can considerably enhance the flow strength of CP titanium deformed at 600 and 700 degrees C. Post-compression microstructures showed that, a fine grained structure can be retained at a deformation temperature of 600 degrees C. Based on the kinematics of dynamic recovery and recrystallization, the flow stress constitutive equations were established. The validity of the model was demonstrated with reasonable agreement by comparing the experimental data with the numerical results. The error values were less than 5% at all deformation temperatures except 600 degrees C.
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    ArticlePublicationMetadata only
    On the high-temperature flow response of friction stir processed magnesium metal matrix composites
    (ASME, 2021-01-01) Ghobadlou, Alı Hosseınzadeh; Yapıcı, Güney Güven; Mechanical Engineering; YAPICI, Güney Güven; Ghobadlou, Alı Hosseınzadeh
    In the current work, multi-pass friction stir processing (FSP) was utilized to fabricate samples of fine-grained aluminum-zinc (AZ) magnesium alloy and its metal matrix composite (MMC). The microstructure and high-temperature tensile behavior of friction stir processed (FSPed) AZ31 and AZ31/SiC MMC at various strain rates in the range of 10(-2) to 10(-4) s(-1) were investigated, and the fracture mechanisms of each condition were analyzed. The results verified that MMC samples exhibited a remarkable enhancement in microhardness. The evolution of inclined basal texture was observed after processing for both FSPed and MMC samples. The ambient temperature stress-strain response revealed that the formability of AZ31 has improved after friction stir processing, whereas high-temperature flow curves were discernibly sensitive to strain rate. Equiaxed deep dimples were detected on the fracture surfaces of FSPed samples, but decreased strain rate led to an increase in the number of dimples as attributed to the recrystallization of new grains.