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  • Küçük Resim
    Öğe
    Analysis of data on indentation load against penetration depth for bulk MgB2 crystal using indentation work and Oliver-Pharr approaches
    (Elsevier Science Sa, 2008) Uzun, O.; Guclu, N.; Kolemen, U.; Sahin, O.
    Vickers microindentation tests were carried out on a bulk MgB2 superconductor with the load of ranging from 300 to 1500 mN at a room temperature. The load-penetration depth curves and the energy data (the absolute, the total, the plastic, and the elastic energy) were analyzed to evaluate the mechanical properties. Hardness and elastic modulus values were calculated by the Oliver-Pharr method and the work of indentation approach. The work of indentation hardness and elastic modulus were calculated directly from the energy of indentation without the need for estimating displacement, areas or volumes, which can be time consuming and inaccurate. It was found that the hardness and elastic modulus increased with decreasing load (i.e. indentation size effect). In addition, the hardness and elastic modulus calculated from the work of indentation approach seem to correlate very well with Oliver-Pharr method at high peak load. Some specific material constant describing the properties of materials were also calculated as total energy, plastic energy, elastic energy, elastic-total energy, plastic-total energy and elastic-plastic energy constants. (C) 2008 Elsevier B.V. All rights reserved.
  • Küçük Resim
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    Effects of ZnO addition on mechanical properties of Bi1.84Pb0.34Sr1.91Ca2.03Cu3.06O10 prepared by a wet technique
    (Elsevier Science Sa, 2009) Karaca, I.; Uzun, O.; Koelemen, U.; Yilmaz, F.; Sahin, O.
    In this study, ZnO molar wt% 0, 5,10,20,30, and 50 added Bi1.84Pb0.34Sr1.91Ca2.03Cu3.06O10 superconductors were prepared by wet technique. The experimental works consist of powder X-ray diffraction (XRD) for phase analyses and c-axes parameters, scanning electron microscopy (SEM) for microstructure examination, and microhardness measurements for mechanical properties. These measurements showed that Zn-added material, in comparison with the pure sample, had increased c-axes parameters and decreased grain size. In addition, the experimental results of microhardness measurements were analyzed using Oliver-Pharr model. It was observed that the change of indentation hardness (H-rr) and reduced elastic modulus (E-r) values showed an increasing trend with ZnO addition and exhibited peak load dependence (i.e., indentation size effect (ISE)). (C) 2008 Elsevier B.V. All rights reserved.
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    Öğe
    Preparation of Fine-Grained Silicon-Nitride Ceramics and their Characterization by Depth-Sensing Indentation Tests
    (Polish Acad Sciences Inst Physics, 2015) Sahin, O.; Guder, H. S.; Uzun, O.; Sahin, E.; Sopicka-Lizer, M.; Gocmez, H.; Artunc, E.
    Both pressureless-sintered and dense, fine-grained silicon nitride ceramics were produced from mechanochemically activated nitride-based precursors. Scanning Electron Microscopy (SEM), Transmition Electron Microscopy (TEM), X-Ray Diffraction (XRD) and an ultra-low load microhardness tester were used to characterize these ceramics. Depth-sensing indentation (DSI) tests in the range of 200-1800 mN were performed on the silicon nitride ceramic to determine dynamic hardness (H-d) and reduced elastic modulus (E-r) values. These values were deduced by analyzing the unloading segments of the DSI curves. It was found that both H-d and E-r exhibits a significant indentation load dependence. Nix-Gao (NG) model was used to analyze the dynamic hardness data in the calculation of the load independent hardness value.