Researcher:
Gümüş, Berkay

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PhD Student

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Berkay

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Gümüş

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Gümüş, Berkay

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2015 - 20166

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Researcher Of Publications: search.filters.isAuthorOfPublication.f510e5e8-fdb2-4ca3-9061-dbb48dc7e359

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Now showing 1 - 6 of 6
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    Twinning activity in high-manganese austenitic steels under high velocity loading
    (Taylor & Francis Ltd, 2016) Gerstein, G.; Maier, H. J.; N/A; N/A; Department of Mechanical Engineering; Gümüş, Berkay; Bal, Burak; Canadinç, Demircan; PhD Student; PhD Student; Faculty Member; Department of Mechanical Engineering; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; College of Engineering; N/A; N/A; 23433
    Deformation temperature and manganese content dependencies of twinning activity in two types of high Mn austenitic steels were investigated upon high velocity tensile loading. It was observed that nanotwin formation within previously formed twins dominates at subzero temperatures and significantly contributes to work hardening.
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    On the micro-deformation mechanisms active in high-manganese austenitic steels under impact loading
    (Elsevier Science Sa, 2015) Gerstein, G.; Maier, H. J; N/A; N/A; Department of Mechanical Engineering; Bal, Burak; Gümüş, Berkay; Canadinç, Demircan; PhD Student; PhD Student; Faculty Member; Department of Mechanical Engineering; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; College of Engineering; N/A; N/A; 23433
    The composition and temperature dependencies of deformation response of TWIP and XIP steels were investigated under high-velocity impact loading with a focus on micro-scale deformation mechanisms. The promotion of twinning deformation under high-velocity loading over the slip-twin interactions usually observed in low-velocity loading conditions was comprehensively examined with scanning electron microscopy and transmission electron microscopy. In addition, thermal analyses of plastic deformation were carried out by in situ thermal imaging. The current findings demonstrate that the deformation of TWIP steel is dictated by two major twin systems at elevated temperatures, while nano-twin formation within one primary twin system dominates at subzero temperatures. The XIP steel, on the other hand, deforms mainly by slip at elevated temperatures, while competing slip and twin activities, and eventually nano-twin formation within primary twins dominates as the temperature decreases. Overall, the current findings shed light on the complicated work hardening mechanisms prevalent in high-manganese austenitic steels utilizing high-velocity deformation experiments. (C) 2015 Elsevier B.V. All rights reserved.
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    Micro-scale cyclic bending response of NiTi shape memory alloy
    (Japan Inst Metals & Materials, 2016) Aksoy, Bekir; Gerstein, Gregory; Maier, Hans Jurgen; N/A; N/A; Department of Mechanical Engineering; Department of Mechanical Engineering; Önal, Orkun; Gümüş, Berkay; Alaca, Burhanettin Erdem; Canadinç, Demircan; PhD Student; PhD Student; Faculty Member; Faculty Member; Department of Mechanical Engineering; Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; College of Engineering; College of Engineering; N/A; N/A; 115108; 23433
    Fatigue performance of micro-scale pseudoelastic nickel-titanium (NiTi) wires was investigated under cyclic bending loading. The current findings demonstrated that the change from macroscopic to microscopic scale promotes the formation of the B19' phase and significantly hinders stabilization of the R-phase.
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    Incorporation of dynamic strain aging Into a viscoplastic self-consistent model for predicting the negative strain rate sensitivity of hadfield steel
    (Asme, 2016) N/A; N/A; Department of Mechanical Engineering; Bal, Burak; Gümüş, Berkay; Canadinç, Demircan; PhD Student; PhD Student; Faculty Member; Department of Mechanical Engineering; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; College of Engineering; N/A; N/A; 23433
    A new multiscale modeling approach is proposed to predict the contributions of dynamic strain aging (DSA) and the resulting negative strain rate sensitivity (NSRS) on the unusual strain-hardening response of Hadfield steel (HS). Mechanical response of HS was obtained from monotonic and strain rate jump experiments under uniaxial tensile loading within the 10(-4) to 10(-1) s(-1) strain rate range. Specifically, a unique strain-hardening model was proposed that incorporates the atomic-level local instabilities imposed upon by the pinning of dislocations by diffusing carbon atoms to the classical Voce hardening. The novelty of the current approach is the computation of the shear stress contribution imposed on arrested dislocations leading to DSA at the atomic level, which is then implemented to the overall strain-hardening rule at the microscopic level. The new model not only successfully predicts the role of DSA and the resulting NSRS on the macroscopic deformation response of HS but also opens the venue for accurately predicting the deformation response of rate-sensitive metallic materials under any given loading condition.
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    Twinning activities in high-mn austenitic steels under high-velocity compressive loading
    (2015) Gerstein, G.; Maier, H. J.; Güner, F.; Elmadağlı, M.; N/A; N/A; Department of Mechanical Engineering; Gümüş, Berkay; Bal, Burak; Canadinç, Demircan; PhD Student; PhD Student; Faculty Member; Department of Mechanical Engineering; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; College of Engineering; N/A; N/A; 23433
    High-velocity compression tests were carried out on three different types of high-manganese (Mn) austenitic steels, namely Hadfield, TWIP and XIP steels, with the purpose of favoring twinning over slip. The experiments were conducted at three temperatures: -170 degrees C, room temperature and 200 degrees C, in order to cover both ductile and brittle deformation ranges. Various mechanisms such as slip, formation of more than one twin variant, nano-twins inside primary twins and voids were activated in Hadfield steel, while the deformation was twin-dominated in TWIP steel at all temperatures, which stems from the increase in stacking fault energy (SFE) due to the higher Mn content. The XIP steel with the highest SFE, on the other hand, deformed mostly by slip at elevated temperatures, even though extensive twin and nano-twin formation was prevalent in the microstructure as the temperature decreased to room temperature, and then to -170 degrees C, respectively. The current set of results lay out the roles of temperature, deformation velocity and alloy content on the microstructure evolution of high-Mn steels, which altogether can be tailored to improve the work hardening capacity of this class of materials.
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    PublicationOpen Access
    A critical approach to the biocompatibility testing of NiTi orthodontic archwires
    (Vibgyor Online Publishers, 2016) Şahbazoğlu, D.; Toker, S. M.; Saher, D.; Department of Mechanical Engineering; Canadinç, Demircan; Gümüş, Berkay; Uzer, Benay; Yıldırım, Cansu; Polat-Altıntaş, Sevgi; Faculty Member; Department of Mechanical Engineering; College of Engineering; 23433; N/A; N/A; N/A; N/A
    The biocompatibility of Nickel-Titanium (NiTi) archwires was investigated by simulating actual contact state of archwires around brackets, which enabled incorporation of realistic mechanical conditions into ex situ experiments. Specifically, archwires (undeformed, and bound to brackets on acrylic dental molds) were statically immersed in artificial saliva (AS) for 31 days. Following the immersion, the archwires and the immersion solutions were analyzed with the aid of variouselectron-optical techniques, and it was observed that carbon-rich corrosion products formed on both archwire sets upon immersion. The corrosion products preferentially formed at the archwire–bracket contact zones, which is promoted by the high energy of these regions and the micro-cracks brought about by stress assisted corrosion. Moreover, it is suggested that these corrosion products prevented significant Ni or Ti ion release by blocking the micro-cracks, which, otherwise, would have led to enhanced ion release during immersion. The current findings demonstrate the need for incorporating both realistic chemical and mechanical conditions into the ex situ biocompatibility experiments of orthodontic archwires, including the archwire-bracket contact.