Scopus İndeksli Yayınlar Koleksiyonu / Scopus Indexed Publications Collection
Permanent URI for this collectionhttps://hdl.handle.net/11147/7148
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Article Citation - WoS: 22Citation - Scopus: 27Micromechanical Modeling of Intrinsic and Specimen Size Effects in Microforming(Springer Verlag, 2018) Yalçınkaya, Tuncay; Özdemir, İzzet; Simonovski, IgorSize effect is a crucial phenomenon in the microforming processes of metallic alloys involving only limited amount of grains. At this scale intrinsic size effect arises due to the size of the grains and the specimen/statistical size effect occurs due to the number of grains where the properties of individual grains become decisive on the mechanical behavior of the material. This paper deals with the micromechanical modeling of the size dependent plastic response of polycrystalline metallic materials at micron scale through a strain gradient crystal plasticity framework. The model is implemented into a Finite Element software as a coupled implicit user element subroutine where the plastic slip and displacement fields are taken as global variables. Uniaxial tensile tests are conducted for microstructures having different number of grains with random orientations in plane strain setting. The influence of the grain size and number on both local and macroscopic behavior of the material is investigated. The attention is focussed on the effect of the grain boundary conditions, deformation rate and the grain size on the mechanical behavior of micron sized specimens. The model is intrinsically capable of capturing both experimentally observed phenomena thanks to the incorporated internal length scale and the crystallographic orientation definition of each grain.Article Citation - WoS: 4Citation - Scopus: 5Quantification of Peg40st Squeeze Out From Dspc/Peg40st Monolayers at Higher Molar Ratios(Elsevier Ltd., 2018) Kılıç, SevgiMixtures of 1,2 Distearoyl-sn-glycero-3-phosphocholine (DSPC) and polyoxyethylene-40-stearate (PEG40St) were prepared at different molar ratios and their miscibility were investigated using Langmuir isotherms. Pure DSPC monolayer exhibited a liquid-condensed (LC) phase whereas PEG40St monolayer exhibited liquid-expanded (LE) phase at the air-water interface at 22 ± 2 °C. At the collapse pressure of 33 mN/m, the PEG40St mean molecular area was calculated to be 28 Å2/molecule for 9:1 composition and 50 Å2/molecule for 5:5 composition, showing an increasing trend with the emulsifier content. A quantification method was developed to estimate the squeeze out amount of PEG40St from Langmuir isotherms of the DSPC/PEG40St mixtures at different molar ratios. Almost 93%, 82%, and 53% of PEG40St displaced for the 9:1, 7:3, and 5:5 mixtures, respectively, at the end of the first collapse plateau and showed a decreasing trend with the PEG40St content. Remaining PEG40St squeezed out at the end of the second collapse plateau, where 20% of PEG40St still contained within the 5:5 composition. It was concluded that increasing PEG40St content would be advantageous to design more stable lipid based microbubbles.Article Citation - WoS: 21Citation - Scopus: 23Activated Carbon Adsorption of Fuel Oxygenates Mtbe and Etbe From Water(Springer Verlag, 2009) İnal, Fikret; Yetgin, Senem; Aksu, Gülsüm T.; Şimşek, Selvi; Sofuoğlu, Aysun; Sofuoğlu, Sait CemilThe aqueous phase adsorption of fuel oxygenates methyl tertiary butyl ether (MTBE) and ethyl tertiary butyl ether (ETBE) onto commercially available granular activated carbon (GAC; Norit GAC 1240) was investigated in a batch system at 27°C. The oxygenate concentrations were determined by headspace gas chromatography/mass spectrometry analyses. The experimental data were used with four two-parameter isotherm models (Langmuir, Freundlich, Temkin, and Dubinin-Radushkevich) and two kinetic models (pseudo first-order and pseudo second-order) to determine equilibrium and kinetic parameters. Considering the correlation coefficient and root mean square error, Dubinin-Radushkevich isotherm showed better fit with the equilibrium data for MTBE. However, the performances of Langmuir and Dubinin-Radushkevich models were comparable for ETBE. The adsorption capacities were calculated as 5.50 and 6.92 mg/g for MTBE and ETBE, respectively, at an equilibrium solution concentration of 1 mg/L using Dubinin-Radushkevich isotherm. The differences between the model predictions and experimental data were similar for the pseudo first-order and pseudo second-order kinetic models. Gibbs free-energy changes of adsorption were found to be -22.59 and -28.55 kJ/mol for MTBE-GAC and ETBE-GAC systems, respectively, under the experimental conditions studied.