• Transactions of the Korean Society of Mechanical Engineers A
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• v.23 no.11 s.170
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• pp.2022-2032
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• 1999

In recent years, the subject of remaining life assessment has drawn considerable attention in the power generation industry. In power generation systems a variety of structural components, such as steam pipes, turbine rotors, and superheater headers, typically operate at high temperatures and high pressures. Thus a life prediction methodology accounting for fracture and rupture is increasingly needed for these components. For accurate failure assessment, in addition to the single parameter such as K or J-integral used in traditional fracture mechanics, the second parameter like T-stress describing the constraint is needed. The most critical defects in such structures are generally found in the form of semi-elliptical surface cracks in the welded piping-joints. In this work, selecting the structures of surface-cracked plate and straight pipe, we first perform line-spring finite element modeling, and accompanying elastic-plastic finite element analyses. We then present a framework for including constraint effects (T-stress effects) in the R6 failure assessment diagram approach for fracture assessment.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.33 no.11
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• pp.1187-1194
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• 2009

During the last decade, possibility of flaw occurrences has been rapidly increased world-widely as the increase of operating times of petro-chemical facilities. For instance, from a recent in-service inspection, three different sized surface cracks were detected in welding parts of a spherical oxygen holder in Korea. While API579 code provides corresponding engineering assessment procedures to determine crack driving forces, in the present work, numerical analyses are carried out for the cracked oxygen holder to investigate effects of complex geometry, analysis model and residual stress. With regard to the detailed finite element analysis, stress intensity factors are determined from both the full three-dimensional model and equivalent plate model. Also, as an alternative, stress intensity factors are calculated for equivalent plate model by employing the noted influence stress function technique. Finally, parametric structural integrity evaluation of the cracked oxygen holder is conducted in use of failure assessment diagram method, J/T method and DPFAD method. Effects of the geometry and so forth are examined and key findings from the simulations are fully discussed, which enables to determine practical safety margins of spherical components containing a defect.

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.11
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• pp.2860-2870
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• 1994

When crack are detected in aged turbine rotors of power plants, information on fracture resistance of the aged material at operating temperature is needed for determination of critical loading condition and residual life of the turbine. In this study, fracture toughness (J$_lc$) and tearing modulus(T$_mat$) of virgin and thermally degraded 1Cr-1Mo-0.25V steel, which is one of the most widely used rotor steels, were measured at 538.deg. C according to ASTM E813 and ASTM E1152, respectively. Five kinds of specimen with different degradation levels were prepared by isothermal aging heat treatment at $630^{\circ}C.$ It was observed that J$_lc$ and T$_mat$ value decreased as the degradation level increased. Analysis of microstructures using a scanning electron microscope showed that the decrement of J$_lc$ is related to segregation of impurities at grain boundaries. It was also verified that the DC electric potential drop method is accurate and reliable for crack length monitoring at elevated temperature.

• Proceedings of the KIEE Conference
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• 2002.07b
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• pp.915-916
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• 2002

최근 산업체 및 국가교정검사기관에서 교정용 표준기급으로 많이 사용하고 있는 Digital Multimeter(HP 3458A)의 수동교정과 불확도 평가후 성적서 발급까지 5시간 정도가 소요된다. 이러한 교정시간을 단축시키고 객관적인 양질의 교정data를 얻을수 있는 교정자동화 프로그램을 개발하였다. 이 프로그램은 Labview를 이용하여 작성하였고 교정부터 불확도평가후 성적서 발급까지 자동적으로 1시간내에 수행이 된다. 또한 기존의 수동교정에 의한 결과와 비교했을 때 불화도 범위 내에서 동일한 결과를 얻었다.

• Proceedings of the KIEE Conference
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• 2007.07a
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• pp.571-573
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• 2007

본 논문에서는 전력계통의 신뢰도를 확률적인 관점에서 접근하고 평가 할 수 있는 신뢰도평가 시스템의 기본 개념과 설계를 소개한다． 확률기반 신뢰도 평가시스템은 Enumeration 기반，Cumulant 기반， Monte-Carlo 시뮬레이션 기반의 세 가지 기법을 사용하여 신뢰도를 평가하도록 설계하였다．

• Computational Structural Engineering
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• v.24 no.3
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• pp.33-40
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• 2011

• Journal of the Korean Institute of Gas
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• v.15 no.4
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• pp.21-26
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• 2011

Type-3 cylinder liner has a limitation of machining the standard specimen for fracture toughness test because it has approximately 5 mm in thickness as well as a curvature. Hence, it needs to be employed a miniature specimen test technique to evaluate fracture toughness of the cylinder liner. In this study, small punch (SP) test method was employed to evaluate fracture toughness of the cylinder liner. Load-displacement curve result measured from the SP test showed that the liner material was failed during membrane stretching in the general SP load-displacement curve. Additionally, it was shown that liner material was isotropic although the amount of plastic deformation was different depending on the direction due to manufacturing process characteristics. Fracture toughness, $J_{Ic}$, was evaluated using the SP test data. The value of fracture toughness obtained was $13.0kJ/m^2$. This value was similar to that of the same kind of materials. Therefore, the fracture toughness evaluated using the SP test data was reasonable.

• Electronics and Telecommunications Trends
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• v.35 no.6
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• pp.119-128
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• 2020

ISO/TC 268, IEC Systems Committee on Smart Cities, ISO/IEC JTC 1/WG 11, and ITU-T SG 20 have been developing smart city-related standards since 2013. ISO/TC 268 and ITU-T SG 20 have provided various and lots of smart city standards relatively. In this paper, the status of the standardization activities of ITU-T SG 20, the IEC Systems Committee on Smart Cities, ISO/TC 268, and ISO/IEC JTC 1/WG 11 is reviewed.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2012.05a
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• pp.889-890
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• 2012

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2010.05a
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• pp.795-796
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• 2010