WoS İndeksli Yayınlar Koleksiyonu
Permanent URI for this collectionhttps://hdl.handle.net/20.500.12573/394
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Article Citation - WoS: 40Citation - Scopus: 43The Role of Hydrogen in the Edge Dislocation Mobility and Grain Boundary-Dislocation Interaction in Α-Fe(Pergamon-Elsevier Science Ltd, 2021-09) Kapci, Mehmet Fazil; Schoen, J. Christian; Bal, Burak; Schön, J. ChristianThe atomistic mechanisms of dislocation mobility depending on the presence of hydrogen were investigated for two edge dislocation systems that are active in the plasticity of alpha-Fe, specifically 1/2<111>{110} and 1/2<111>{112}. In particular, the glide of the dislocation pile-ups through a single crystal, as well as transmission of the pile-ups across the grain boundary were evaluated in bcc iron crystals that contain hydrogen concentrations in different amounts. Additionally, the uniaxial tensile response under a constant strain rate was analyzed for the aforementioned structures. The results reveal that the presence of hydrogen decreases the velocity of the dislocations -in contrast to the commonly invoked HELP (Hydrogen-enhanced localized plasticity) mechanism-, although some localization was observed near the grain boundary where dislocations were pinned by elastic stress fields. In the presence of pre-exisiting dislocations, hydrogen-induced hardening was observed as a consequence of the restriction of the dislocation mobility under uniaxial tension. Furthermore, it was observed that hydrogen accumulation in the grain boundary suppresses the formation of new grains that leads to a hardening response in the stress-strain behaviour which can initiate brittle fracture points. (C) 2021 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.Article Citation - WoS: 23Citation - Scopus: 24Strain Rate and Hydrogen Effects on Crack Growth From a Notch in a Fe-High Steel Containing 1.1 Wt% Solute Carbon(Pergamon-Elsevier Science Ltd, 2020-01) Najam, Hina; Koyama, Motomichi; Bal, Burak; Akiyama, Eiji; Tsuzaki, KaneakiEffects of strain rate and hydrogen on crack propagation from a notch were investigated using a Fe-33Mn-1.1C steel by tension tests conducted at a cross head displacement speeds of 10(-2) and 10(-4) mm/s. Decreasing cross head displacement speed reduced the elongation by promoting intergranular crack initiation at the notch tip, whereas the crack propagation path was unaffected by the strain rate. Intergranular cracking in the studied steel was mainly caused by plasticity-driven mechanism of dynamic strain aging (DSA) and plasticity-driven damage along grain boundaries. With the introduction of hydrogen, decrease in yield strength due to cracking at the notch tip before yielding as well as reduction in elongation were observed. Coexistence of several hydrogen embrittlement mechanisms, such as hydrogen enhanced decohesion (HEDE) and hydrogen enhanced localized plasticity (HELP) were observed at and further away from the notch tip resulting in hydrogen assisted intergranular fracture and cracking which was the key reason behind the ductility reduction. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.Article Citation - WoS: 21Citation - Scopus: 27High-Concentration Carbon Assists Plasticity-Driven Hydrogen Embrittlement in a Fe-High Mn Steel With a Relatively High Stacking Fault Energy(Elsevier Science SA, 2018-02) Tugluca, Ibrahim Burkay; Koyama, Motomichi; Bal, Burak; Canadinc, Demircan; Akiyama, Eiji; Tsuzaki, KaneakiWe investigated the effects of electrochemical hydrogen charging on the mechanical properties of a Fe-33Mn-1.1C austenitic steel with high carbon concentration and relatively high stacking fault energy. Hydrogen pre charging increased the yield strength and degraded the elongation and work-hardening capability. The increase in yield strength is a result of the solution hardening of hydrogen. A reduction in the cross-sectional area by subcrack formation is the primary factor causing reduction in work-hardening ability. Fracture modes were detected to be both intergranular and transgranular regionally. Neither intergranular nor transgranular cracking modes are related to deformation twinning or simple decohesion in contrast to conventional Fe-Mn-C twinning induced plasticity steels. The hydrogen-assisted crack initiation and subsequent propagation are attributed to plasticity-dominated mechanisms associated with strain localization. The occurrence of dynamic strain aging by the high carbon content and ease of cross slip owing to the high stacking fault energy can cause strain/damage localization, which assists hydrogen embrittlement associated with the hydrogen-enhanced localized plasticity mechanism.Article Citation - WoS: 17Citation - Scopus: 21Finite Element Analysis of the Stress Distribution Associated With Different Implant Designs for Different Bone Densities(Wiley, 2022-06-06) Kurtulus, Ikbal Leblebicioglu; Kilic, Kerem; Bal, Burak; Kilavuz, Ahmet; Leblebicioğlu Kurtuluş, IkbalPurpose The main objective of this study was to investigate the influence of implant design, bone type, and abutment angulation on stress distribution around dental implants. Materials and methods Two implant designs with different thread designs, but with the same length and brand were used. The three-dimensional geometry of the bone was simulated with four different bone types, for two different abutment angulations. A 30 degrees oblique load of 200 N was applied to the implant abutments. Maximum principal stress and minimum principal stresses were obtained for bone and Von misses stresses were obtained for dental implants. Results The distribution of the load was concentrated at the coronal portion of the bone and implants. The stress distributions to the D4 type bone were higher for implant models. Increased bone density and increased cortical bone thickness cause less stress on bone and implants. All implants showed a good distribution of forces for non-axial loads, with higher stresses concentrated at the crestal region of the bone-implant interface. In implant types using straight abutments there was a decrease in stress as the bone density decreased. The change in the abutment angle also caused an increase in stress. Conclusions The use of different implant threads and angled abutments affects the stress on the surrounding bone and implant. In addition, it was observed that a decrease in density in trabecular bone and a decrease in cortical bone thickness increased stress.Article Citation - WoS: 13Citation - Scopus: 17Effect of Hydrogen on Fracture Locus of Fe-16Mn Twip Steel(Pergamon-Elsevier Science Ltd, 2020-11) Bal, Burak; Cetin, Baris; Bayram, Ferdi Caner; Billur, ErenEffect of hydrogen on the mechanical response and fracture locus of commercial TWIP steel was investigated comprehensively by tensile testing TWIP steel samples at room temperature and quasi-static regime. 5 different sample geometries were utilized to ensure different specific stress states and a digital image correlation (DIC) system was used during tensile tests. Electrochemical charging method was utilized for hydrogen charging and microstructural characterizations were carried out by scanning electron microscope. Stress triaxiality factors were calculated throughout the plastic deformation via finite element analysis (FEA) based simulations and average values were calculated at the most critical node. A specific Python script was developed to determine the equivalent fracture strain. Based on the experimental and numerical results, the relation between the equivalent fracture strain and stress triaxiality was determined and the effect of hydrogen on the corresponding fracture locus was quantified. The deterioration in the mechanical response due to hydrogen was observed regardless of the sample geometry and hydrogen changed the fracture mode from ductile to brittle. Moreover, hydrogen affected the fracture locus of TWIP steel by lowering the equivalent failure strains at given stress triaxiality levels. In this study, a modified Johnson-Cook failure mode was proposed and effect of hydrogen on damage constants were quantified. (C) 2020 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.Article Citation - WoS: 12Citation - Scopus: 12Edge Dislocation Depinning From Hydrogen Atmosphere in Α-Iron(Pergamon-Elsevier Science Ltd, 2024-07) Kapci, Mehmet Fazil; Yu, Ping; Marian, Jaime; Liu, Guisen; Shen, Yao; Li, Yang; Bal, BurakUnderstanding the dislocation motion in hydrogen atmosphere is essential for revealing the hydrogen-related degradation in metallic materials. Atomic simulations were adopted to investigate the interaction between dislocations and hydrogen atoms, where the realistic hydrogen distribution in the vicinity of the dislocation core was emulated from the Grand Canonical Monte Carlo computations. The depinning of edge dislocations in alpha-Fe at different temperatures and hydrogen concentrations was then studied using Molecular Dynamics simulations. The results revealed that an increase in bulk hydrogen concentration increases the flow stress due to the pinning effect of solute hydrogen. The depinning stress was found to decrease due to the thermal activation of the edge dislocation at higher temperatures. In addition, prediction of the obtained results was performed by an elastic model that can correlate the bulk hydrogen concentration to depinning stress.Article Citation - WoS: 34Citation - Scopus: 35An Atomistic Study on the Help Mechanism of Hydrogen Embrittlement in Pure Metal Fe(Pergamon-Elsevier Science Ltd, 2024-02) Hasan, Md Shahrier; Kapci, Mehmet Fazil; Bal, Burak; Koyama, Motomichi; Bayat, Hadia; Xu, WenwuThe Hydrogen Enhanced Localized Plasticity (HELP) mechanism is one of the most important theories explaining Hydrogen Embrittlement in metallic materials. While much research has focused on hydrogen's impact on dislocation core structure and dislocation mobility, its effect on local dislocation density and plasticity remains less explored. This study examines both aspects using two distinct atomistic simulations: one for a single edge dislocation under shear and another for a bulk model under cyclic loading, both across varying hydrogen concentrations. We find that hydrogen stabilizes the edge dislocation and exhibits a dual impact on dislocation mobility. Specifically, mobility increases below a shear load of 900 MPa but progressively decreases above this threshold. Furthermore, dislocation accumulation is notably suppressed at around 1 % hydrogen concentration. These findings offer key insights for future research on Hydrogen Embrittlement, particularly in fatigue scenarios.Article Citation - WoS: 4Citation - Scopus: 4A Phenomenological Hydrogen Induced Edge Dislocation Mobility Law for Bcc Fe Obtained by Molecular Dynamics(Pergamon-Elsevier Science Ltd, 2024-10) Baltacioglu, Mehmet Furkan; Kapci, Mehmet Fazil; Schoen, J. Christian; Marian, Jaime; Bal, Burak; Schön, J. ChristianInvestigating the interaction between hydrogen and dislocations is essential for understanding the origin of hydrogen-related fractures, specifically hydrogen embrittlement (HE). This study investigates the effect of hydrogen on the mobility of 1/2<111>{110} and 1/2<111>{112} edge dislocations in body-centered cubic (BCC) iron (Fe). Specifically, molecular dynamics (MD) simulations are conducted at various stress levels and temperatures for hydrogen-free and hydrogen-containing lattices. The results show that hydrogen significantly reduces dislocation velocities due to the pinning effect. Based on the results of MD simulations, phenomenological mobility laws for both types of dislocations as a function of stress, temperature and hydrogen concentration are proposed. Current findings provide a comprehensive model for predicting dislocation behavior in hydrogencontaining BCC lattices, thus enhancing the understanding of HE. Additionally, the mobility laws can be utilized in dislocation dynamics simulations to investigate hydrogen-dislocation interactions on a larger scale, aiding in the design of HE-resilient materials for industrial applications.Article Citation - WoS: 32Citation - Scopus: 32A Detailed Investigation of the Effect of Hydrogen on the Mechanical Response and Microstructure of Al 7075 Alloy Under Medium Strain Rate Impact Loading(Pergamon-Elsevier Science Ltd, 2020-09) Bal, Burak; Okdem, Bilge; Bayram, Ferdi Caner; Aydin, MuratEffects of hydrogen and temperature on impact response and corresponding microstructure of aluminum (Al) 7075 alloy were investigated under medium strain rate impact loading. The specimens were subjected to impact energy of 12 J and 25 J, corresponding to impact velocities of 2.13 m/s and 3.08 m/s, respectively. These energy levels were decided after a couple of impact tests with different impact energy values, such as 6 J, 10 J, 12 J, 25 J. The experiments were conducted at five different temperatures. Electrochemical charging method was used for hydrogen charging. Microstructural observations of hydrogen uncharged and hydrogen charged specimens were carried out by scanning electron microscope. Hydrogen changed the crack propagation behavior of Al 7075 alloy depending on the temperature. Coexistence of several hydrogen embrittlement mechanisms, such as hydrogen enhanced decohesion (HEDE) and hydrogen enhanced localized plasticity (HELP) were observed under impact loading. The impact response of Al 7075 was significantly deteriorated by the hydrogen charging and changing temperature affected the absorbed energy of hydrogen-charged specimens. In addition, molecular dynamics simulations were conducted to uncover the atomistic origin of hydrogen embrittlement mechanisms under impact loading. In particular, hydrogen decreased the cohesive energy and enhanced the average dislocation mobility. Therefore, the experimental results presented herein constitute an efficient guideline for the usage of Al alloys that are subject to impact loading in service in a wide range of temperatures. (C) 2020 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.