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991.
Hyunjo Jeong Seung-Hoon Nahm Kyung-Young Jhang Young-Hyun Nam 《Journal of Mechanical Science and Technology》2002,16(2):147-154
The objective of this paper is to develop a nondestructive method for estimating the fracture toughness (K IC) of CrMoV steels used as the rotor material of steam turbines in power plants. To achieve this objective, a number of CrMoV steel samples were heat-treated, and the fracture appearance transition temperature (FATT) was determined as a function of aging time. Nonlinear ultrasonics was employed as the theoretical basis to explain the harmonic generation in a damaged material, and the nonlinearity parameter of the second harmonic wave was the experimental measure used to be correlated to the fracture toughness of the rotor steel. The nondestructive procedure for estimating theK IC consists of two steps. First, the correlations between the nonlinearity parameter and the FATT are sought. The FATT values are then used to estimateK IC, using theK IC versus excess temperature (i.e.,T-FATT) correlation that is available in the literature for CrMoV rotor steel. 相似文献
992.
Kook?Nam?ParkEmail author Chuel?Muu?Sim Chang?Oong?Choi Chang?Hee?Lee Jong?Hark?Park 《Journal of Mechanical Science and Technology》2002,16(7):927-934
The HANARO (High-flux Advanced Neutron Application Reactor) has been operated since 1995. The Cold Neutron (CN) hole was implanted
in the reflector tank from the design stage. Before a vacuum chamber and a moderator cell for the cold neutron source are
installed into the CN hole, it is necessary to measure exactly the size of the inside diameter and thickness of the CN hole
to prevent the interference problem. Due to inaccessibility and high radiation field in the CN hole, a mechanical measurement
method is not permitted. The immersed ultrasonic technique is considered as the best way to measure the thickness and the
diameter of the CN hole. The 4-Axis manipulator was designed and fabricated for locating the ultrasonic sensors. The transducer
of an ultrasonic sensor having 10 MHz frequency leads to high resolution as much as 0.03mm. The inside diameter and thickness
of 550 points of the CN hole were measured using 2 channel ultrasonic sensors. The results show that the thickness and inside
diameter of the CN hole is in the range of 3.3 - 6.7mm and 0 156-165mm, respectively. This data will be a good reference for
the design of the cold neutron source facility. 相似文献
993.
Yul-Hwan SeongJongok Won Sang-Kyung KimKidon Nam Soo-Kil KimDong-Won Kim 《International Journal of Hydrogen Energy》2011,36(14):8492-8498
A series of sulfonated poly(fluorenyl ether nitrile oxynaphthalate) (SPFENO) copolymers with different degree of sulfonation (DS) are synthesized via nucleophilic polycondensation reactions with commercially available monomers. Incorporation of the naphthalanesulfonate group into the copolymers and their copolymer structures are confirmed by 1H NMR spectroscopy. Thermal stability, mechanical properties, water uptake, swelling behavior, proton conductivity and methanol permeability of the SPFENO membranes are investigated with respect to their structures. The electrochemical performance of a direct methanol fuel cell (DMFC) assembled with the SPFENO membrane was evaluated and compared to a DMFC with a Nafion 117 membrane. The DMFC assembled with the SPFENO membrane of proper DS exhibits better electrochemical performance compared to the Nafion 117-based cell. 相似文献
994.
Seong-Hyeon HongJong-Soo Bae Sung Nam KwonMyoung Youp Song 《International Journal of Hydrogen Energy》2011,36(3):2170-2176
A Mg-23.5wt%Ni-5wt%Cu alloy was synthesized by the gravity casting method in a large quantity (7.5 kg). From this alloy, Mg-23.5wt%Ni-xwt%Cu (x = 2.5, 5 and 7.5) samples for hydrogen storage were prepared by melt spinning and crystallization heat treatment. The samples were ground under H2 in order to obtain a fine powder. These alloys contained crystalline Mg and Mg2Ni phases. The Mg-23.5Ni-2.5Cu alloy had the highest hydriding and dehydriding rates after activation among these alloys. The dehydriding curve under 1.0 bar H2 at 573 K exhibits two stages; the dehydriding rate is high for about 2.5 min (the decomposition of Mg2Ni hydride and Mg hydride in small particles), and then it becomes lower (the decomposition of Mg hydride). 相似文献
995.
Nguyen Huy Tuan Danh Hua Quoc Nam Thi Minh Nhat Vo 《Computers & Mathematics with Applications》2019,77(1):15-33
We study for the first time the backward problem for nonlocal nonlinear boundary value problem of Kirchhoff’s model of parabolic type. First, we show that the problem is severely ill-posed in the sense of Hadamard. We propose two methods: the Fourier truncation method for stabilizing the problem with homogeneous source and the quasi-reversibility method for regularizing the problem with nonlinear source. Under some priori assumptions on the exact solution, we establish some stability estimates in the norm. 相似文献
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