Researcher:
Önal, Orkun

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PhD Student

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Orkun

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Önal

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Önal, Orkun

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2012 - 20165

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Researcher Of Publications: search.filters.isAuthorOfPublication.dd87b038-4f23-4830-954f-2b6fb95595fd

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    Experimental and numerical evaluation of thickness reduction in steel pate heat exchangers
    (Asme, 2015) Akdari, E.; N/A; N/A; Department of Mechanical Engineering; Önal, Orkun; 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
    A multiscale modeling approach was utilized to predict thickness reduction in steel plate heat exchangers (PHEs) utilized in combi boilers. The roles of texture and microstructure were successfully accounted for by properly coupling crystal plasticity and finite element analysis (FEA). In particular, crystal plasticity was employed to determine the proper multiaxial hardening rule to describe the material flow during the forming of PHEs, which was then implemented into the finite element (FE) metal-forming simulations. The current findings show that reliable thickness distribution predictions can be made with appropriate coupling of crystal plasticity and FEA in metal forming. Furthermore, the multiscale modeling approach presented herein constitutes an important guideline for the design of new PHEs with improved thermomechanical performance and reduced manufacturing costs.
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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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    Investigation of rolling contact crack initiation in bainitic and pearlitic rail steels
    (Wiley, 2012) Sehitoglu, H.; Verzal, K.; Jiang, Y.; N/A; Department of Mechanical Engineering; Önal, Orkun; Canadinç, Demircan; PhD Student; Faculty Member; Department of Mechanical Engineering; Graduate School of Sciences and Engineering; College of Engineering; N/A; 23433
    The stress-strain history and the crack initiation lives of bainitic and head-hardened pearlitic rail steels were determined under rolling contact loading by implementing the semi-analytical Jiang-Sehitoglu rolling contact model that incorporates both ratchetting and multiaxial fatigue damage. The calculations revealed that the bainitic steel withstands higher loads than the pearlitic steel at low shear tractions, however; both materials behave in an increasingly similar manner as the shear tractions increase. Furthermore, maximum damage occurs in both steels when ratchetting and fatigue damage coincide on the surface. In addition to shedding light on the rolling contact fatigue (RCF) performance of bainitic and pearlitic rail steels, the current work also establishes a methodology for the realistic prediction of crack initiation under RCF.
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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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    PublicationOpen Access
    Multi-scale modeling of the impact response of a strain-rate sensitive high-manganese austenitic steel
    (Frontiers, 2014) Department of Mechanical Engineering; Canadinç, Demircan; Önal, Orkun; Özmenci, Cemre; Faculty Member; Department of Mechanical Engineering; College of Engineering; 23433; N/A; N/A
    A multi-scale modeling approach was applied to predict the impact response of a strain rate sensitive high-manganese austenitic steel. The roles of texture, geometry, and strain rate sensitivity were successfully taken into account all at once by coupling crystal plasticity and finite element (FE) analysis. Specifically, crystal plasticity was utilized to obtain the multi-axial flow rule at different strain rates based on the experimental deformation response under uniaxial tensile loading. The equivalent stress – equivalent strain response was then incorporated into the FE model for the sake of a more representative hardening rule under impact loading. The current results demonstrate that reliable predictions can be obtained by proper coupling of crystal plasticity and FE analysis even if the experimental flow rule of the material is acquired under uniaxial loading and at moderate strain rates that are significantly slower than those attained during impact loading. Furthermore, the current findings also demonstrate the need for an experiment-based multi-scale modeling approach for the sake of reliable predictions of the impact response.