WoS İndeksli Yayınlar Koleksiyonu
Permanent URI for this collectionhttps://hdl.handle.net/20.500.12573/394
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Article Citation - WoS: 3Citation - Scopus: 4The Experimental Determination of Thermophysical Properties of Intermetallic CuAl2 Phase in Equilibrium With (Al Plus Cu Plus Si) Liquid(Academic Press Ltd- Elsevier Science Ltd, 2016-06) Altintas, Yemliha; Aksoz, Sezen; Keslioglu, Kazim; Marasli, Necmettin; Keşlioʇlu, KâzImThe equilibrated grain boundary groove shapes of solid CuAl2 in equilibrium with (Al + Cu + Si) eutectic liquid were observed from a quenched sample by using a radial heat flow apparatus. The Gibbs-Thomson coefficient, (solid + liquid) interfacial energy and grain boundary energy of the solid CuAl2 were determined from these observed shapes. The thermal conductivity of the eutectic solid and the thermal conductivity ratio of eutectic liquid to the eutectic solid in the (Al + 26.82 wt.% Cu + 5.27 wt.% Si) eutectic alloy at its eutectic melting temperature were also measured with a radial heat flow apparatus and a Bridgman-type growth apparatus, respectively. The three phases of (Al + Cu + Si) alloy have detected as Al solution, Si and theta (CuAl2) phases with EDX composition analysis and the microstructure of these phases were photographed by SEM. (C) 2016 Elsevier Ltd. All rights reserved.Article Structural Behavior of Geopolymer Reinforced Concrete Beams: Experimental, Numerical, and Code-Based Assessment(Springer, 2025-08-11) Ozbayrak, Ahmet; Kucukgoncu, HurmetThis study experimentally investigates the flexural performance of heat-cured low-calcium fly ash-based geopolymer concrete (GPC) beams reinforced with ribbed steel bars, focusing on the effects of reinforcement ratio, alkaline activator concentration (SS/SH), and curing regime. Fifteen full-scale beams, including twelve GPC and three OPC specimens, were tested under four-point loading to evaluate load-deflection and moment-curvature behavior. Despite a lower compressive elastic modulus, the results showed that GPC beams exhibited comparable or superior cracking and ultimate moment capacities relative to OPC beams. Increasing the reinforcement ratio enhanced load capacity but reduced ductility in both systems, with GPC beams showing more brittle post-yield behavior. Numerical models based on OPC parameters were developed in SAP2000 to compare with experimental GPC moment-curvature data, revealing good agreement in the linear range but notable differences in post-yield response. The study also examined the microstructure of failed GPC beams via SEM, XRD, and EDX analyses to correlate matrix morphology with mechanical behavior. Finally, moment capacities calculated according to ACI 318 and TS 500 provided conservative estimates, supporting the safe applicability of current design codes to heat-cured GPC beams. These findings demonstrate that GPC, when properly proportioned and cured, is a viable structural alternative to OPC for reinforced concrete members.Article Citation - WoS: 3Citation - Scopus: 4On the Utility of Crystal Plasticity Modeling to Uncover the Individual Roles of Microdeformation Mechanisms on the Work Hardening Response of Fe-23Mn TWIP Steel in the Presence of Hydrogen(ASME, 2018-02-08) Bal, B.; Koyama, M.; Canadinc, D.; Gerstein, G.; Maier, H. J.; Tsuzaki, K.This paper presents a combined experimental and theoretical analysis focusing on the individual roles of microdeformation mechanisms that are simultaneously active during the deformation of twinning-induced plasticity (TWIP) steels in the presence of hydrogen. Deformation responses of hydrogen-free and hydrogen-charged TWIP steels were examined with the aid of thorough electron microscopy. Specifically, hydrogen charging promoted twinning over slip-twin interactions and reduced ductility. Based on the experimental findings, a mechanism-based microscale fracture model was proposed, and incorporated into a visco-plastic self-consistent (VPSC) model to account for the stress-strain response in the presence of hydrogen. In addition, slip-twin and slip-grain boundary interactions in TWIP steels were also incorporated into VPSC, in order to capture the deformation response of the material in the presence of hydrogen. The simulation results not only verify the success of the proposed hydrogen embrittlement (HE) mechanism for TWIP steels, but also open a venue for the utility of these superior materials in the presence of hydrogen.Article Citation - WoS: 22Citation - Scopus: 26Microstructure and Mechanical Properties of Dense Si3N4 Ceramics Prepared by Direct Coagulation Casting and Cold Isostatic Pressing(Elsevier Science SA, 2022-09) Marulcuoglu, Hande; Kara, FerhatComplex shaped dense Si3N4 ceramics were produced by using direct coagulation casting technique via dispersant reaction method of Si3N4 suspension, followed by gas pressure sintering. The effects of solid content of the suspension, additional cold isostatic pressing of the cast parts, and sintering behaviour and on the mechanical reliability of silicon nitride ceramics were investigated. It was observed that all slurries exhibited rheological properties suitable for casting in the range of 44-50 vol.% solid concentrations. Nevertheless, higher solid concentration suspensions resulted in smaller floc size and thus better green microstructures. Parts shaped by direct coagulation casting at all the solid loadings had relatively low strength and reliability after sintering. However, application of additional cold isostatic pressing to the cast parts increased the strength and, particularly, reliability. Dense Si3N4 ceramics with relative density above 99.5%, average bending strength 760 +/- 39 MPa and Weibull module 23.5 had been obtained with 50 vol.% solids content after DCC + CIP process.Article Citation - WoS: 4Citation - Scopus: 4Investigations of Electrical Resistivity and Thermal Conductivity Dependences on Growth Rate in the Al-Cu Eutectic Alloy(Springer/plenum Publishers, 2021-05-03) Marasli, Necmettin; Bayram, UmitDirectional solidification of Al-Cu-Ti (Al-33wt%Cu-0.1wt%Ti) eutectic alloy was done with a growth rate range (V = 8.58 to 2038.65 mu m.s(-1)) at a temperature gradient of 6.45 K.mm(-1) using Bridgman-type directional solidification furnace. The measurements of thermal conductivity (K) and electrical resistivity (rho) for the Al-Cu-Ti alloy solidified with the different values of V were made by the longitudinal heat flow method (LHFM) and DC four-point probe technique (FPPT). While the highest values of K and rho were determined to be 236.04 W.K-1.m(-1) and 5.91 x 10(-8) omega m, respectively, at 8.58 mu m.s(-1), the lowest values of K and rho were obtained to be 199.82 W.K-1.m(-1) and 12.11 x 10(-8) omega m, respectively, at 2038.65 mu m.s(-1). The K and rho dependences on V were obtained to be K=259.96xV(-0.032) and rho=4.47x10(-8)V(0.13) from linear regression analysis. The fusion enthalpy ( increment H) and specific heat difference between solid and liquid ( increment C-P) for the Al-Cu-Ti were also determined to be 222.69 J.g(-1) and 0.266 Jg(-1).K-1, respectively, by means of differential scanning calorimetry (DSC).Article Hydrogen Susceptibility of Al 5083 Under Ultra-High Strain Rate Ballistic Loading(Walter de Gruyter Gmbh, 2024-09-25) Baltacioglu, Mehmet Furkan; Mozafari, Farzin; Aydin, Murat; Cetin, Baris; Oktan, Aynur Didem; Teoman, Atanur; Bal, BurakThe effect of hydrogen on the ballistic performance of aluminum (Al) 5083H131 was examined both experimentally and numerically in this study. Ballistics tests were conducted at a 30 degrees obliquity in accordance with the ballistic test standard MIL-DTL-46027 K. The strike velocities of projectiles were ranged from 240 m s-1 to 500 m s-1 level in the room temperature. Electrochemical hydrogen charging method was utilized to introduce hydrogen into material. Chemical composition of material was analyzed using energy dispersive X-ray (EDX) analysis. Instant camera pictures were captured using high-speed camera to compare H-uncharged and H-charged specimen ballistics tests. The volume loss in partially penetrated specimens were assessed using the 3D laser scanning method. Microstructural examinations were conducted utilizing scanning electron microscopy (SEM). It was observed that with the increased deformation rate, the dominance of the HEDE mechanism over HELP became evident. Furthermore, the experimental findings were corroborated through numerical methods employing finite element analysis (FEM) along with the Johnson-Cook plasticity model and failure criteria. Inverse optimization technique was employed to implement and fine-tune the Johnson-Cook parameters for H-charged conditions. Upon comparing the experimental and numerical outcomes, a high degree of consistency was observed, indicating the effective performance of the model.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: 9Citation - Scopus: 11Evaluation of Diatomite Substitute With Thermal Power Plant Waste Fly Ash in Sustainable Geopolymer Through Life Cycle Assessment(Springer, 2025-02-28) Ilkentapar, Serhan; Orklemez, Ezgi; Durak, Ugur; Gulcimen, Sedat; Bayram, Savas; Uzal, Nigmet; Atis, Cengiz DuranThis research demonstrates the potential of diatomite as a fly ash replacement to improve mechanical properties and environmental sustainability and presents it as a viable alternative for sustainable construction. Additionally, a life cycle assessment (LCA) was conducted on the produced mortars to quantitatively compare their environmental impacts using a cradle-to-gate approach. In mixtures, it was used by replacing the diatomite in the ratios of 1%, 2%, 3%, 4%, and 5% by weight of the fly ash. Workability, unit weight, flexural and compressive strength, abrasion resistance, elevated temperature resistance and microstructure analysis were carried out. The results indicated that replacing 1%, 2%, and 3% diatomite increased the compressive and flexural strength of mortars due to their higher specific surface area. Two percent replacement of diatomite provided the best results. FESEM results of 3% diatomite inclusion showed more intense and compact microstructure of geopolymer. Diatomite inclusion increased the abrasion resistance of geopolymer. Since 2% diatomite replacement was found to be optimum, the LCA results showed that geopolymer mortar with 2% diatomite has 25% lower impacts in terms of global warming potential and 10% lower impacts in terms of terrestrial ecotoxicity than conventional Portland cement mortar.Article Citation - WoS: 28Citation - Scopus: 30Effect of Construction and Demolition Waste on the Long-Term Geo-Environmental Behaviour of Cemented Paste Backfill(Springer, 2021-05-05) Yilmaz, T.; Ercikdi, B.The construction and demolition waste (CDW) could be used as backfill material to fill the voids created during the ore production in underground mining. However, there is a need to clarify the impact of CDW on groundwater pollution when it is used as backfill material in cemented paste backfill (CPB) of sulphide-rich tailings (S-rT). This study presents the influence of CDW on the long-term geo-environmental behaviour of CPB samples (CPBs) when used as replacement (10 wt.%) to S-rT. For this reason, the dynamic-tank leaching test was conducted on CPBs and pH, conductivity (Ec), sulphate (SO42-) and heavy metals (HMs) analyses were executed for leachates over 30-360 days of leaching period. The effects of mineralogy and microstructure on the geo-environmental behaviour of CPBs were also analysed via X-ray fluorescence (XRD) and mercury intrusion porosimeter (MIP). The utilisation of CDW in CPB mixtures was found to reduce the SO42- release (up to 13.89%), neutralise the acid generated and lower the Ec (up to 22.16%). Furthermore, the HMs releases (except As, Cu and Zn) were prevented (Ni and Cr) or reduced up to 92%, which is compatible with the improved CPB microstructure. Only the release of arsenic (As) exceeded the limit value for groundwater in CPB of CDW leachate. These findings suggest that not only the cost, strength and stability but also the impact on groundwater pollution should be considered when disposing of CDW as CPB material in underground voids.Article Citation - WoS: 32Citation - Scopus: 35A New Parameter Influencing the Reaction Kinetics and Properties of Fly Ash Based Geopolymers: A Pre-Rest Period Before Heat Curing(Elsevier, 2021-03) Durak, Ugur; Ilkentapar, Serhan; Karahan, Okan; Uzal, Burak; Atis, Cengiz DuranIn this study, the influence of a pre-rest period before heat curing (as a new parameter), on the physical properties, flexural and compressive strength, and microstructure of geopolymer mortars and pastes produced with alkali activation of fly ash were investigated. In this context, geopolymer mortar and paste samples were prepared and pre-rested under laboratory conditions for 0, 1, 2, 3, 7, 14, and 28 days before heat curing. After the pre-rest period, the samples were subjected to heat curing at 75 degrees C in an oven, for 2 days. Mortar and paste samples exposed to a pre-rest period while in the fresh state before heat curing were compared with control samples without pre-resting. Water absorption, porosity, specific gravity, capillarity, flexural strength, compressive strength, and abrasion resistance tests were conducted on the geopolymer mortar samples. A reaction kinetics study using an isothermal calorimeter, XRD, and SEM analyses were performed on the geopolymer paste samples for microstructural investigations. Based on the results obtained, it was observed that the mechanical strength of the samples subjected to the pre-rest period before heat curing increased considerably compared to the reference (without pre-resting) samples. In addition, because of pre-resting, the capillarity coefficient, water permeability, and porosity of the samples decreased compared to the reference samples, and it was concluded that pre-resting improves durability-related properties. Moreover, the reaction kinetics and SEM analysis results, supporting the above findings, showed that a pre-resting period increases the geopolymeric reaction products and causes a denser microstructure.