Scopus İndeksli Yayınlar Koleksiyonu
Permanent URI for this collectionhttps://hdl.handle.net/20.500.12573/395
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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: 13Citation - Scopus: 14The Effect of Strain Rate on the Hydrogen Embrittlement Susceptibility of Aluminum 7075(ASME, 2022-11-22) Baltacioglu, Mehmet Furkan; Cetin, Baris; Bal, BurakThe effects of changing the strain rate regime from quasi-static to medium on hydrogen susceptibility of aluminum (Al) 7075 were investigated using tensile tests. Strain rates were selected as 1 s(-1) and 10(-3) s(-1) and tensile tests were conducted on both hydrogen uncharged and hydrogen charged specimens at room temperature. Electrochemical hydrogen charging method was utilized and the diffusion length of hydrogen inside Al 7075 was modeled. Material characterizations were carried out by X-ray diffraction (XRD) and energy dispersive X-ray spectroscopy (EDX) and microstructural observations of hydrogen uncharged and hydrogen charged specimens were performed by scanning electron microscope (SEM). As opposed to earlier studies, hydrogen embrittlement (HE) was more pronounced at high strain rate cases. Moreover, hydrogen enhanced localized plasticity (HELP) was the more dominant hydrogen embrittlement mechanism at slower strain rate but coexistence of hydrogen enhanced localized plasticity and hydrogen enhanced decohesion was observed at a medium strain rate. Overall, the current findings shed light on the complicated hydrogen embrittlement behavior of Al 7075 and constitute an efficient guideline for the usage of Al 7075 that can be subject to different strain rate loadings in service.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.Book Part Citation - Scopus: 2Potential Effects of Short-Range Order on Hydrogen Embrittlement of Stable Austenitic Steels—A Review(Springer Science and Business Media Deutschland GmbH, 2021) Koyama, Motomichi; Bal, Burak; Canadinc, Demircan; Habib, Kishan; Tsuchiyama, Toshihiro; Tsuzaki, Kaneaki; Akiyama, EijiHere, we present a review of the hydrogen embrittlement behavior of face-centered cubic (FCC) alloys with short-range order (SRO) of solute atoms. In this paper, three types of FCC alloys are introduced: Fe–Mn–C austenitic steels, high-nitrogen steels, and CoCrFeMnNi high-entropy alloys. The Fe–Mn–C austenitic steels show dynamic strain aging associated with Mn–C SRO, which causes deformation localization and acceleration of premature fracture even without hydrogen effects. The disadvantageous effect of dynamic strain aging on ductility, which is associated with the deformation localization, amplify plasticity-assisted hydrogen embrittlement. Cr–N and Co–Cr–Ni SRO effects in high-nitrogen austenitic steels and high-entropy alloys enhance the dislocation planarity, which causes stress concentration in the grain interior and near the grain boundaries. The stress concentration coupled with hydrogen effects causes quasi-cleavage and intergranular fractures. © 2021 Elsevier B.V., All rights reserved.Conference Object Parameter Analysis of a Biomass Based SOFC-Engine Polygeneration System for Cooling, Heating and Power Production(Scanditale AB, 2020) Zhu, Pengfei; Guo, Leilei; Yao, Jing; Ren, Jianwei; Kapci, Mehmet Fazil; Bal, Burak; Zhang, Z. X.In order to meet the demand of clean and efficient energy conversion technology, a novel combined cooling, heating and power (CCHP) system fueled by biomass is proposed. This system is consists of biomass gasification unit, solid oxide fuel cell, IC engine unit and absorption refrigeration chiller. Thermodynamic model of the CCHP system are developed and then parameter analysis is adopted to optimize the performance of this system. The effect of air equivalent ratio (ER), steam biomass ratio (S/B) and the fuel utilization factor of SOFC (μ) on the performance of the entire system are studied. The results show that increase of S/B and μ will prompt the electrical efficiency, while the increase of ER has a negative effect on electrical efficiency. The exergy analysis shows that the exergy destruction of biomass gasification process and engine is larger, which is 454.5 kW and 207.2 kW respectively. On the contrary, exergy destruction of SOFC and absorption refrigeration chiller are 15.9 kW and 52.8 kW, respectively. © 2024 Elsevier B.V., All rights reserved.Article Citation - WoS: 11Citation - Scopus: 13On the Detailed Mechanical Response Investigation of PHBV/PCL and PHBV/PLGA Electrospun Mats(IOP Publishing Ltd, 2019-03-29) Bal, Burak; Tugluca, Ibrahim Burkay; Koc, Nuray; Isoglu, Ismail AlperIn this study, electrospun mats of pristine poly(epsilon-caprolactone) (PCL), Poly(D, L-lactide-co-glycolide) (PLGA), poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), as well as PHBV/PCL blends and PHBV/PLGA blends in different ratios (80:20, 75:25, 50:50, 25:75, 20:80, 10:90, 5:95%, w/w) and Centella Asiatica (CA) loaded (1, 5, 10%, w/v) PHBV/PCL and PHBV/PLGA polyester blends were prepared. Electrospun mats were characterized by scanning electron microscopy (SEM) in order to show uniform and bead and defect-free fiber structure with average diameter. The blend ratio and strain rate dependencies of mechanical behavior of these electrospun membranes were investigated under tensile loading. The tensile tests were conducted at an initial strain rates of 10(-1) s(-1), 10(-2) s(-1), 10(-3) s(-1) and 10(-4) s(-1) at room temperature and the best and worst combinations of PHBV/PLGA, PHBV/PCL blend ratios for both stress and ductility required applications were specified for each strain rate. The effects of blend ratios on the tensile strength and Young's modulus were also investigated. Moreover, the effects of Centella Asiatica on the electrospun membranes' mechanical behavior were demonstrated at different strain rates. Consequently, this study constitutes an important guideline for the selection and usage of the aforementioned electrospun membranes as a wound dressing material in terms of mechanical response at different loading scenarios.Conference Object Numerical Study of Magnesium-Based Metal Hydride Reactor Incorporating Multi-Phase Heat Exchanger for Thermal Energy Storage System(Scanditale AB, 2021-03-02) Yao, Jing; Zhu, Pengfei; Ren, Jianwei; Kapci, Mehmet Fazil; Bal, Burak; Kurko, Sandra V.; Zhang, Z. X.Metal hydride based thermal energy storage system is regarded as a promising method due to its good reversibility, low cost, and no by-product. Multi-phase heat exchange has much higher heat transfer coefficient than single-phase fluid heat exchange, thus facilitating the steam generation. In this study, a two-dimensional model of the metal hydride reactor using multi-phase heat exchange is proposed to estimate the performance and its feasibility of application in the concentrated solar power system. The results show that the velocity of the heat transfer fluid should match well with the thermal conductivity of the metal hydride bed to maintain the heat flux at a relatively constant value. The match of thermal conductivity of 3 or 5 W/(m·K) and fluid velocity of 0.0050 m/s results in the heat flux up to about 19 kW/m2, which is increased by 3 orders of magnitude than single-phase heat exchange. This study helps to facilitate the widespread application of metal hydride based thermal energy storage system in the concentrated solar power system. © 2024 Elsevier B.V., All rights reserved.Article Citation - WoS: 2Citation - Scopus: 2Numerical Investigation of the Role of Volumetric Transformation Strain on the Relaxation Stress and the Corresponding Hydrogen Interstitial Concentration in Niobium Matrix(Hindawi Ltd, 2017) Bal, BurakThe effects of relaxation stress on the hydrogen concentration in Niobium-(Nb-) H media were investigated by iterative numerical modeling approach. To calculate the transformation strain, relaxation stress, and corresponding relaxed hydrogen concentration around an edge dislocation, a new third-order polynomial formulation was utilized in the model. With the aid of this polynomial, hydrogen induced relaxation stress never exceeds the dislocation stress, which indicates that the total stress field never turns to compressive state and diverges the results. The current model calculates the hydrogen concentration not only in the vicinity of an edge dislocation but also far away from the dislocation. Furthermore, the effect of relaxation stress on the interaction energy was also captured in the model. Overall, the current findings shed light on the complicated hydrogen embrittlement mechanisms of metallic materials by demonstrating that hydrogen induced relaxation has a significant effect on the hydrogen atom concentration and the interaction energy between the existing internal stress field and the solute hydrogen atom.Article Citation - WoS: 14Citation - Scopus: 16Lowering Strain Rate Simultaneously Enhances Carbon- and Hydrogen-Induced Mechanical Degradation in an Fe-33Mn Steel(Springer, 2019-01-02) Tugluca, Ibrahim Burkay; Koyama, Motomichi; Shimomura, Yusaku; Bal, Burak; Canadinc, Demircan; Akiyama, Eiji; Tsuzaki, KaneakiWe investigated the strain rate dependency of the hydrogen-induced mechanical degradation of Fe-33Mn-1.1C steel at 303K within the strain rate range of 10(-2) to 10(-5)s(-1). In the presence of hydrogen, lowering the strain rate monotonically decreased the work hardening rate, elongation, and tensile strength and increased the yield strength. Lowering the strain rate simultaneously enhanced the plasticity-related effects of hydrogen and carbon, leading to the observed degradation of the ductility.Article Citation - WoS: 14Citation - Scopus: 15Lateral Angular Co-Extrusion: Geometrical and Mechanical Properties of Compound Profiles(MDPI, 2020-08-28) Thuerer, Susanne Elisabeth; Peddinghaus, Julius; Heimes, Norman; Bayram, Ferdi Caner; Bal, Burak; Uhe, Johanna; Klose, Christian; Thürer, Susanne ElisabethA novel co-extrusion process for the production of coaxially reinforced hollow profiles has been developed. Using this process, hybrid hollow profiles made of the aluminum alloy EN AW-6082 and the case-hardening steel 20MnCr5 (AISI 5120) were produced, which can be forged into hybrid bearing bushings by subsequent die forging. For the purpose of co-extrusion, a modular tooling concept was developed where steel tubes made of 20MnCr5 are fed laterally into the tool. This LACE (lateral angular co-extrusion) process allows for a variation of the volume fraction of the reinforcement by using steel tubes with different wall thicknesses, which enabled the production of compound profiles having reinforcement contents of either 14 vol.% or 34 vol.%. The shear strength of the bonding area of these samples was determined in push-out tests. Additionally, mechanical testing of segments of the hybrid profiles using shear compression tests was employed to provide information about the influence of different bonding mechanisms on the strength of the composite zone.
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