Researcher:
Toker, Sıdıka Mine

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PhD Student

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Sıdıka Mine

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Toker

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Toker, Sıdıka Mine

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2012 - 20167

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Researcher Of Publications: search.filters.isAuthorOfPublication.e630057d-69be-442a-a668-9959d4e14924

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Now showing 1 - 7 of 7
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    Incorporating the grain boundary misorientation effects on slip activity into crystal plasticity
    (Taylor & Francis Inc, 2016) N/A; N/A; Department of Mechanical Engineering; Bıyıklı, Emre; Toker, Sıdıka Mine; Canadinç, Demircan; Master 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; 255504; 23433
    The role of grain boundary misorientation angle (GBMA) distribution on slip activity in a high-manganese austenitic steel was investigated through experiments and simulations. Crystal plasticity simulations incorporating the GBMA distribution and the corresponding dislocation-grain boundary interactions were conducted. The computational analysis revealed that the number of active slip systems decreased when GBMA distribution was taken into account owing to the larger volume of grain boundary-dislocation interactions. The current results demonstrate that the dislocation-grain boundary interactions significantly contribute to the overall hardening, and the GBMA distribution constitutes a key parameter dictating the slip activity.
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    On the role of slip-twin interactions on the impact behavior of high-manganese austenitic steels
    (Elsevier Science Sa, 2014) Taube, Alexander; Gerstein, Gregory; Maier, Hans Jürgen; N/A; Department of Mechanical Engineering; Toker, Sıdıka Mine; Canadinç, Demircan; PhD Student; Faculty Member; Department of Mechanical Engineering; Graduate School of Sciences and Engineering; College of Engineering; 255504; 23433
    The temperature-dependent relative contributions of slip, twinning, and slip-twin interactions to the deformation response of a high-manganese austenitic steel were investigated under impact loading. Thorough transmission electron microscopy and scanning electron microscopy showed that either twinning or slip dictates the deformation response under impact loading, as opposed to the slip-twin interactions typically observed in high-manganese austenitic steels under tensile or compressive loading. Specifically, slip dominates at elevated temperatures, whereas slip activity is restricted by enhanced twinning at low temperatures, and the parameters, such as twin volume fraction, twin thickness and length, or glide dislocation density, show a strong temperature-dependence. The enhanced activity of only one mechanism rather than the slip-twin interaction is associated with the high-strain rate deformation taking place under impact loading, which does not allow for significant interaction of the two mechanisms.
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    An exploration of plastic deformation dependence of cell viability and adhesion in metallic implant materials
    (Elsevier, 2016) Gerstein, G.; Maier, H. J.; N/A; N/A; N/A; N/A; Department of Mechanical Engineering; Uzer, Benay; Toker, Sıdıka Mine; Cingöz, Ahmet; Önder, Tuğba Bağcı; Canadinç, Demircan; Researcher; PhD Student; Researcher; Faculty Member; Faculty Member; Department of Mechanical Engineering; N/A; Graduate School of Sciences and Engineering; Graduate School of Health Sciences; School of Medicine; College of Engineering; N/A; 255504; N/A; 184359; 23433
    The relationship between cell viability and adhesion behavior, and micro-deformation mechanisms was investigated on austenitic 316L stainless steel samples, which were subjected to different amounts of plastic strains (5%, 15%, 25%, 35% and 60%) to promote a variety in the slip and twin activities in the microstructure. Confocal laser scanning microscopy (CLSM) and field emission scanning electron microscopy (FESEM) revealed that cells most favored the samples with the largest plastic deformation, such that they spread more and formed significant filopodial extensions. Specifically, brain tumor cells seeded on the 35% deformed samples exhibited the best adhesion performance, where a significant slip activity was prevalent, accompanied by considerable slip-twin interactions. Furthermore, maximum viability was exhibited by the cells seeded on the 60% deformed samples, which were particularly designed in a specific geometry that could endure greater strain values. Overall, the current findings open a new venue for the production of metallic implants with enhanced biocompatibility, such that the adhesion and viability of the cells surrounding an implant can be optimized by tailoring the surface relief of the material, which is dictated by the micro-deformation mechanism activities facilitated by plastic deformation imposed by machining.
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    Microstructure-based modeling of the impact response of a biomedical niobium-zirconium alloy
    (Cambridge University Press (CUP), 2014) Maier, Hans J.; N/A; N/A; N/A; N/A; Department of Mechanical Engineering; Önal, Orkun; Bal, Burak; Toker, Sıdıka Mine; Mirzajanzadeh, Morad; Canadinç, Demircan; PhD Student; PhD Student; PhD Student; PhD Student; Faculty Member; Department of Mechanical Engineering; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; College of Engineering; N/A; N/A; 255504; N/A; 23433
    This article presents a new multiscale modeling approach proposed to predict the impact response of a biomedical niobium-zirconium alloy by incorporating both geometric and microstructural aspects. Specifically, the roles of both anisotropy and geometry-based distribution of stresses and strains upon loading were successfully taken into account by incorporating a proper multiaxial material flow rule obtained from crystal plasticity simulations into the finite element (FE) analysis. The simulation results demonstrate that the current approach, which defines a hardening rule based on the location-dependent equivalent stresses and strains, yields more reliable results as compared with the classical FE approach, where the hardening rule is based on the experimental uniaxial deformation response of the material. This emphasizes the need for proper coupling of crystal plasticity and FE analysis for the sake of reliable predictions, and the approach presented herein constitutes an efficient guideline for the design process of dental and orthopedic implants that are subject to impact loading in service.
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    Anisotropy of ultrafine-grained alloys under impact loading: the case of biomedical niobium-zirconium
    (Pergamon-Elsevier Science Ltd, 2012) Rubitschek, F.; Niendorf, T.; Maier, H. J.; N/A; Department of Mechanical Engineering; Toker, Sıdıka Mine; Canadinç, Demircan; PhD Student; Faculty Member; Department of Mechanical Engineering; Graduate School of Sciences and Engineering; College of Engineering; 255504; 23433
    The anisotropy-impact response relationship of a biocompatible niobium zirconium (NbZr) alloy with an ultrafine-grained microstructure was investigated. The current findings not only shed light on the micromechanisms dictating the impact response in the microstructures studied, but are also encouraging with respect to the use of NbZr in orthopedic and dental implants.
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    Evaluation of passive oxide layer formation–biocompatibility relationship in NiTi shape memory alloys: geometry and body location dependency
    (Elsevier, 2014) Maier, H. J.; N/A; Department of Mechanical Engineering; N/A; Toker, Sıdıka Mine; Canadinç, Demircan; Birer, Özgür; PhD Student; Faculty Member; Researcher; 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; College of Engineering; N/A; 255504; 23433; N/A
    A systematic set of ex-situ experiments were carried out on Nickel-Titanium (NiTi) shape memory alloy (SMA) in order to identify the dependence of its biocompatibility on sample geometry and body location. NiTi samples with three different geometries were immersed into three different fluids simulating different body parts. The changes observed in alloy surface and chemical content of fluids upon immersion experiments designed for four different time periods were analyzed in terms of ion release, oxide layer formation, and chemical composition of the surface layer. The results indicate that both sample geometry and immersion fluid significantly affect the alloy biocompatibility, as evidenced by the passive oxide layer formation on the alloy surface and ion release from the samples. Upon a 30 day immersion period, all three types of NiTi samples exhibited lower ion release than the critical value for clinic applications. However; a significant amount of ion release was detected in the case of gastric fluid, warranting a thorough investigation prior to utility of NiTi in gastrointestinal treatments involving long-time contact with tissue. Furthermore, certain geometries appear to be safer than the others for each fluid, providing a new set of guidelines to follow while designing implants making use of NiTi SMAs to be employed in treatments targeting specific body parts.
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    Evaluation of the biocompatibility of niti dental wires: A comparison of laboratory experiments and clinical conditions
    (Elsevier, 2014) N/A; N/A; Department of Mechanical Engineering; Toker, Sıdıka Mine; Canadinç, Demircan; PhD Student; Faculty Member; Department of Mechanical Engineering; Graduate School of Sciences and Engineering; College of Engineering; 255504; 23433
    Effects of intraoral environment on the surface degradation of nickel-titanium (NiTi) shape memory alloy orthodontic wires was simulated through ex situ static immersion experiments in artificial saliva. The tested wires were compared to companion wires retrieved from patients in terms of chemical changes and formation of new structures on the surface. Results of the ex situ experiments revealed that the acidic erosion effective at the earlier stages of immersion led to the formation of new structures as the immersion period approached 30 days. Moreover, comparison of these results with the analysis of wires utilized in clinical treatment evidenced that ex situ experiments are reliable in terms predicting C-rich structure formation on the wire surfaces. However, the formation of C pileups at the contact sites of arch wires and brackets could not be simulated with the aid of static immersion experiments, warranting the simulation of the intraoral environment in terms of both chemical and physical conditions, including mechanical loading, when evaluating the biocompatibility of NiTi orthodontic arch wires.