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Article Citation - WoS: 139Citation - Scopus: 140CaXH3 (X = Mn, Fe, Co) perovskite-type hydrides for hydrogen storage applications(Wiley, 2020) Surucu, Gokhan; Gencer, Aysenur; Candan, Abdullah; Gullu, Hasan H.; Isik, MehmetHydrogen storage is one of the attractive research interests in recent years due to the advantages of hydrogen to be used as energy source. The studies on hydrogen storage applications focus mainly on investigation of hydrogen storage capabilities of newly introduced compounds. The present paper aims at characterization of CaXH3 (X: Mn, Fe, or Co) perovskite-type hydrides for the first time to understand their potential contribution to the hydrogen storage applications. CaXH3 compounds have been investigated by density functional theory studies to reveal their various characteristics and hydrogen storage properties. CaXH3 compounds have been optimized in cubic crystal structure and the lattice constants of studied compounds have been obtained as 3.60, 3.50, and 3.48 angstrom for X: Mn, Fe, and Co compounds, respectively. The optimized structures have negative formation enthalpies pointing out that studied compounds are thermodynamically stable and could be synthesized experimentally. The gravimetric hydrogen storage densities of X: Mn, Fe, and Co compounds were found in as 3.09, 3.06, and 2.97 wt%, respectively. The revealed values for hydrogen storage densities indicate that CaXH3 compounds may be potential candidates for hydrogen storage applications. Moreover, various mechanical parameters of interest compounds like elastic constants, bulk modulus, and Poisson's ratio have been reported throughout the study. These compounds were found mechanically stable with satisfying Born stability criteria. Further analyses based on Cauchy pressure and Pugh criterion, showed that they have brittleness nature and relatively hard materials. In addition, the electronic characteristics, band structures, and associated partial density of states of CaXH3 hydrides have been revealed. The dynamic stability behavior of them was verified based on the phonon dispersion curves.Article Citation - WoS: 9Citation - Scopus: 10Synthesis and Characterization of Novel High Temperature Structural Adhesives Based on Nadic End Capped Mda-Btda Copolyimide(Iop Publishing Ltd, 2018) Acar, Oktay; Varis, Serhat; Isik, Tugba; Tirkes, Seha; Demir, Mustafa M.A series of novel copolyimide structural adhesives were synthesized using 4,4'-diaminodiphenyl-methane (MDA), 3,4'-oxydianiline (ODA) and 3,3',4,4'-benzophenonetetracarboxylic acid dianhy-dride (BTDA) as co-monomers, and nadic anhydride as an end cap reagent. The adhesives with different MDA and ODA contents were examined in terms of their structure, thermal stability, mechanical properties, and adhesive performance. They have glass transition temperatures (T-g) about 400 degrees C, with thermal stability up to 500 degrees C. The effect of diamine monomer compositions on adhesion performance and processability of the copolyimides were studied. The copolyimides exhibited adhesion strength up to 16.3 MPa at room temperature. Nadic end capped MDA-BTDA-ODA copolyimide resins gained adjustable and controllable processability with the addition of ether bridged aromatic segments. The copolyimide adhesive with equimolar composition of MDA: ODA is distinguished form the both commercial PMR-15 and LARC RP-46 polyimides in terms of its better processability and mechanical performance.Article Citation - WoS: 31Citation - Scopus: 34Mechanical, Thermo-Mechanical and Morphological Characterization of Abs Based Composites Loaded With Perlite Mineral(Iop Publishing Ltd, 2020) Alghadi, Aiah Mohamed; Tirkes, Seha; Tayfun, UmitAcrylonitrile-butadiene-styrene (ABS) copolymer was filled with perlite mineral (PER) at four different loading level of 2.5%, 5%, 10% and 15%. ABS/PER composites were produced using lab-scale micro-compounder followed by injection molding process. Mechanical, thermo-mechanical, melt-flow and morphological properties of composites were reported by tensile and impact tests, dynamic mechanical analysis (DMA), melt flow index (MFI) test and scanning electron microscopy (SEM), respectively. Mechanical characterizations revealed that tensile strength, elongation and Youngs? modulus of ABS were improved by PER inclusions. However, impact strength of ABS reduced with increase of PER concentration. Glass transition temperature of ABS displayed increasing trend for %5 concentration of PER. MFI test implied that PER addition caused slight decreasing for MFI value of unfilled ABS. Homogeneous dispersion of PER particles into ABS matrix for their lower loading level was obtained from SEM micrographs of composites. According to findings, 5% PER containing sample exhibited the best performance and it was remarked as the most suitable candidate among fabricated ABS based composites.Article Citation - WoS: 4Citation - Scopus: 5Assessing Cast Aluminum Alloys With Computed Tomography Defect Metrics: a Gurson Porous Plasticity Approach(Mdpi, 2023) Gul, Armagan; Aslan, Ozgur; Kayali, Eyuep Sabri; Bayraktar, EminAluminum alloys have inherent tendencies to produce casting defects caused by alloying or metal melt flow inside the mold. The traditional detection method for these defects includes reduced pressure tests, which assess metal quality in a destructive manner. This leaves a gap between metal quality assessments and tensile test correlations. Computed tomography (CT) scans offer crucial assistance in evaluating the internal quality of castings without damaging the structure. This provides a valuable opportunity to couple mechanical tests with numerical methods such as finite element analysis to predict the mechanical performance of the alloy. The present study aims to evaluate the internal quality of cast aluminum alloys using CT scans and to correlate the defect metrics obtained from CT scans with mechanical test results. The Gurson-type material model and finite element methodology have been used to validate the correlation studies. Therefore, we propose a more holistic approach to predicting the behavior of metals by coupling damage models with CT scans and mechanical tests. The study investigates several CT metrics such as the defect volume, total defect surface, biggest defect surface, and projected area of defects. The conclusion reveals that CT scans provide crucial assistance in evaluating the internal quality of castings, and CT defect metrics can be used to build correlations between mechanical tests and CT evaluations. The study also suggests that the concept of adjusted representative material yield parameter (ARMY) or computed representative material yield parameter (CRMY) can be used to correlate CT metrics with mechanical strength in cast materials and parts for a given aluminum alloy. Overall, the study proposes a more comprehensive methodology to assess the quality of cast aluminum alloys and couple the quality to mechanical performance.
