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Dislocation mechanisms of radius effect on displacement bursts during spherical nanoindentations
Shin, Chansun,Shim, Sanghoon Cambridge University Press (Materials Research Soc 2012 Journal of materials research Vol.27 No.16
<▼1><B>Abstract</B><P/></▼1><▼2><P>Indentation load-displacement curves for Mo (100) single crystals reveal clear displacement bursts from spherical indenters with various radii from ∼0.1 to ∼130 μm. There are two different size-dependent mechanisms for dislocation evolution involved during the displacement bursts. It has been postulated that these bursts are triggered by the nucleation of dislocations for a small indenter radius and the activation of preexisting dislocations for a large indenter radius. We present a simple model with which the displacement bursts from a larger indenter radius can be rationalized. This model relates the load and the excursion length during the first displacement burst. The correspondence between the model and experimental data indicates that the displacement bursts are initiated by the activation of preexisting dislocations and the model can accurately describe the mechanism for the displacement bursts from large indenters.</P></▼2>
Lim, Sangyeob,Shin, Chansun,Heo, Jungwoo,Kim, Sangeun,Jin, Hyung-Ha,Kwon, Junhyun,Guim, Hwanuk,Jang, Dongchan Elsevier 2018 JOURNAL OF NUCLEAR MATERIALS Vol.503 No.-
<P><B>Abstract</B></P> <P>HT9, a ferritic/martensitic steel, is a candidate structural material for next-generation advanced reactors. Its microstructure is a typical tempered martensite showing a hierarchical lath-block-and-packet structure. We investigate the specimen size effect and strengthening contribution of various microstructural boundaries manifested in the compression tests of micropillars with diameters ranging from 0.5 to 17 μm. It is observed that micropillars with diameters larger than 3 μm show uniform deformation and plastic flow curves comparable to the bulk flow curve. Localized deformation by a few pronounced slip bands occurs in micropillars with diameters smaller than 1 μm, and the yield strength is reduced. Careful examination of the sizes of the microstructural features and cross-sections of the micropillars shows that the block boundaries are the most effective strengthening boundaries in tempered martensitic microstructure. The bulk mechanical properties of HT9 can be evaluated from a micropillar with diameter as low as 3 μm.</P>
메탄계 가스의 Two-Phase Flow 현상에 따른 가스 익스팬더 성능 및 유동 특성 분석
신봉근(Bong Gun Shin),조연화(Yeonhwa Cho),임찬선(Chansun Lim) 대한기계학회 2018 대한기계학회 춘추학술대회 Vol.2018 No.12
In recent, the use of expander at a re-liquefaction system installed at LNG Ships is continuously increasing in order to improve the system performance. Expander used at the reliquefaction system can drop the temperature of the working fluid at the system exit to a lower level than JT valve and can reduce the power consumption of the system by using the energy generated during expansion process. The performance of the re-liquefaction system improves as the expander expansion ratio increases, which results in a two phase flow of working gas inside the expander. This working gas two phase flow reduces the expander’s aerodynamic performance and deteriorates the structure / dynamic characteristics. Therefore, it is very important to analyze the influence of the two phase flow on flow and performance characteristics of the expander. However, it is very difficult to investigate the effect by using previous the numerical methodologies due to complicated numerical models and high computation costs. In this study, the influence of the two phase flow on the flow and performance characteristics of expander using methane-based mixed gas as working gas were analyzed. Next, the new numerical methodology was suggested in order to reduce the computational cost and to improve the accuracy.
Seulki Hwang,Daesup Hwang,Hani Baek,Chansun Shin 대한금속·재료학회 2021 METALS AND MATERIALS International Vol.27 No.7
A spring beam in a miniature electrical switch enables the two electrical contacts to either close or separate and suppliesboth current and necessary contact pressure between the contacts. Arc erosion and material transfer between the contactsoccur, and those aspects depend on various parameters including the kinematics of the contacts. Therefore, the mechanicalproperties of the spring beam will affect the arc erosion and material transfer, but this topic has not been well studied. In thisstudy, the material transfer phenomena between two AgCu contacts attached to a spring beam made of three different copperbasedstrip alloys were investigated after 30,000 switching operations under 12 V and 9 A in a direct-current resistive loadcircuit. For spring beams made of beryllium copper (BeCu) and titanium copper (TiCu) alloy, the material transfer occurredfrom the cathode to the anode. However, an opposite material transfer occurred for a spring beam made of Corson-type(CuNiSi) alloy. The make- and break-arc voltage waveforms were analyzed, and the results showed that the changes in arcingbehaviors depend on the spring beam material. The properties of the spring beam materials responsible for the changedarcing behaviors are discussed and their relationship with the observed contact arc erosion and material transfer is analyzed.