• 한국압력기기공학회 논문집
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• 제11권1호
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• pp.1-11
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• 2015

Feedwater Heaters are important components in a nuclear power plant. As the age of heater increases, the maintenance cost required for continuous operation also increases. Most heaters have the carbon steel shells, tube support plates and flow baffles. The carbon steel is susceptible to flow-accelerated corrosion. This is especially true if the flow has a two-phase mixture of steam and condensate. The wall thinning around the wet steam entrance area of the shell is inevitable during some long term operation. The structural integrity of the feedwater heater shell affects the safe operation of the nuclear power plant. Therefore, it is needed for the thinned shell to be repaired. The maintenance method for preventing failure of the shell should be determined by investigating various factors including the stress distribution of thinned area. The stress analysis of the shell including the steam entrance region is studied in this paper. The results of thinned shell is compared with that of intact shell.

• 열처리공학회지
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• 제4권3호
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• pp.1-6
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• 1991

In this study, intermediate thermo-mechanical treated Al-2.0 wt%Li, and Al-2.0 wt%Li-1.2 wt%Cu-1.0 wt%Mg-0.12 wt%Zr alloys were tested in tension at $10^{\circ}C$ and elevated temperature(100, 200 and $300^{\circ}C$). The results are follows : The tensile strength of Al-Li-Cu-Mg-Zr alloy is the highest but the elongation of Al-Li alloy is the highest(106%) among the all alloys in tension at $300^{\circ}C$. The Portervin-LeChartlier effect is showed in AI-Li-Cu-Mg-Zr alloy at 10 and $100^{\circ}C$, because of tangled dislocation by Mg and Cu. In the true stress-strain curves of all alloy, the peaks of stress at $300^{\circ}C$ are showed at the strain less than 0.1. In the binary alloy, the dynamic restoration process at 200 and $300^{\circ}C$ is nearly similar to dynamic recovery type. The hot deformation stress is decreased with increase of dynamic recovery degree, but the elongation is increased. When the strain the strain rate are constant, the temperature dependence of hot deformation stress is increased with increase of deformation temperature. The elongation and degree of dynamic recovery are decreased with increase of hot deformation activation energy, but the deformation stresses slightly increased.

• Journal of Microbiology and Biotechnology
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• 제23권2호
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• pp.149-155
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• 2013

Heterologous expression of a putative $K^+/H^+$ antiporter of Streptomyces coelicolor A3(2) (designated as sha4) in E. coli and Streptomyces hygroscopicus JCM4427 showed enhanced tolerance to $K^+$ stress, acidic-pH shock, and/or geldanamycin production under $K^+$ stress. In a series of $K^+$ extrusion experiments with sha4-carrying E. coli deficient in the $K^+/H^+$ antiporter, a restoration of impaired $K^+$ extrusion activity was observed. Based on this, it was concluded that sha4 was a true $K^+/H^+$ antiporter. In different sets of experiments, the sha4-carrying E. coli showed significantly improved tolerances to $K^+$ stresses and acidic-pH shock, whereas sha4-carrying S. hygroscopicus showed an improvement in $K^+$ stress tolerance only. The sha4-carrying S. hygroscopicus showed much higher geldanamycin productivity than the control under $K^+$ stress condition. In another set of experiments with a production medium, the secretion of geldanamycin was also significantly enhanced by the expression of sha4.

• Geomechanics and Engineering
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• 제11권5호
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• pp.639-655
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• 2016

The effect of particle breakage and intermediate principal stress ratio on the behaviour of crushable granular assemblies under true triaxial stress conditions is studied using the discrete element method. Numerical results show that the increase of intermediate principal stress ratio $b(b=({\sigma}_2-{\sigma}_3)/({\sigma}_1-{\sigma}_3))$ results in the increase of dilatancy at low confining pressures but the decrease of dilatancy at high confining pressures, which stems from the distinct increasing compaction caused by breakage with b. The influence of b on the evolution of the peak apparent friction angle is also weakened by particle breakage. For low relative breakage, the relationship between the peak apparent friction angle and b is close to the Lade-Duncan failure model, whereas it conforms to the Matsuoka-Nakai failure model for high relative breakage. In addition, the increasing tendency of relative breakage, calculated based on a fractal particle size distribution with the fractal dimension being 2.5, declines with the increasing confining pressure and axial strain, which implies the existence of an ultimate graduation. Finally, the relationship between particle breakage and plastic work is found to conform to a unique hyperbolic correlation regardless of the test conditions.

• 대한기계학회논문집A
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• 제27권9호
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• pp.1571-1578
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• 2003

This paper proposes a robust method for the Ramberg-Osgood(R-O)fit to accurately estimate elastic-plastic J from engineering fracture mechanics analysis based on deformation plasticity. The proposal is based on engineering stress-strain data to determine the R-O parameters, instead of true stress-strain data. Moreover, for practical applications, the method is given not only for the case when full stress-strain data are available but also for the case when only yield and tensile strengths are available. Reliability of the proposed method for the R-O fit is validated against detailed 3-D Finite Element (FE) analyses for circumferential through-wall cracked pipes under global bending using five different materials, three stainless steels and two ferritic steels. Taking the FE J results based on incremental plasticity using actual stress-strain data as reference, the FE J results based on deformation plasticity using various R-O fits are compared with reference J values. Comparisons show that the proposed R-O fit provides more accurate J values for all cases, compared to existing methods for the R-O fit. Advantages of the proposed R-O fit in practical applications are discussed, together with its accuracy.

• 농업과학연구
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• 제45권1호
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• pp.74-83
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• 2018

Four early-fattening Hanwoo steers weighing $247{\pm}13.5kg$ were used within a $4{\times}4$ Latin square design to establish a nutrient requirement for maintenance and to investigate nutritional changes in the steers under heat stress condition. The steers were fed four different energy level diets: 100% (control) and 100%, 115% and 130% of total digestible nutrients (TDN) requirement of the early-fattening Hanwoo steers for maintenance based on the Korean Feeding Standard for Hanwoo. The steers in the control were housed with no stress (temperature $24^{\circ}C$ and humidity 60%), whereas the steers in the other groups were under heat stress (temperature $30^{\circ}C$ and humidity 70%). True digestibilities of dry matter (DM) and other nutrients were not significantly (p > 0.05) affected by heat stress (i.e., control vs T100). This may be the result of a lower DM intake than that of the Korean feeding standard due to the establishment of the nutrients requirement under heat stress. Heat stress and different energy intake levels did not affect the blood metabolite concentrations. Average daily gain (ADG) for T100 (-69.6 g) was lower than that of the control (-44.6 g, numerically), T115 (44.6 g, p < 0.05) and T130 (83.3 g, p < 0.05), respectively. Based on the ADG and TDN intake, the equation (Y = 0.1814X + 111.5) for the TDN requirement of the early fattening Hanwoo steers for maintenance was calculated, indicating that 11.5% of TDN requirement for maintenance under heat stress may be additionally supplied.

• 터널과지하공간
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• 제17권4호
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• pp.311-321
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• 2007

경암 내 암반구조물의 파괴는 현지응력의 크기, 무결암의 강도 그리고 암반 내에 존재하는 불연속면의 상태에 의해 결정되며, 특히 높은 현지응력이 작용하는 경우 유도응력에 의해 취성파괴가 발생할 수 있다. 취성 파괴의 특성은 파괴수준, 파괴개시시점, 파괴범위와 파괴심도 등으로 구분할 수 있으며, 암반구조물의 안정성을 확보하기 위해서는 응력조건에 따른 취성파괴의 특성을 규명하여야 한다. 본 연구에서는 취성파괴가 발생한 상태에서 응력조건에 따른 파괴범위와 파괴심도를 평가하고자 하였다. 이를 위해 진삼축 압축응력조건에서 모형실험을 수행하였으며, 취성파괴가 발생한 모형실험체에 대하여 육안관찰과 컴퓨터단층촬영을 수행하여 파괴심도와 파괴범위를 결정하였다. 파괴심도는 터널단면에 작용하는 축차응력의 크기에 영향을 받으나 파괴범위의 경우 응력조건에 따른 뚜렷한 경향성을 보이지 않는 것으로 나타났다.

• 한국지구과학회지
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• 제25권1호
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• pp.22-31
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• 2004

Laboratory experiments were conducted in order to find effects of the intermediate principal stress of ${\sigma}_{2}$ on rock fractures and faults. Polyaxial tests were carried out under the most generalized compressive stress conditions, in which different magnitudes of the least and intermediate principal stresses ${\sigma}_{3}$ and ${\sigma}_{2}$ were maintained constant, and the maximum stress ${\sigma}_{1}$, was increased to failure. Two crystalline rocks (Westerly granite and KTB amphibolite) exhibited similar mechanical behavior, much of which is neglected in conventional triaxial compression tests in which ${\sigma}_{2}$ = ${\sigma}_{3}$. Compressive rock failure took the form of a main shear fracture, or fault, steeply dipping in ${\sigma}_{3}$ direction with its strike aligned with ${\sigma}_{2}$ direction. Rock strength rose significantly with the magnitude of ${\sigma}_{2}$, suggesting that the commonly used Mohr-type failure criteria, which ignore the ${\sigma}_{2}$ effect, predict only the lower limit of rock strength for a given ${\sigma}_{3}$ level. The true triaxial failure criterion for each of the crystalline rocks can be expressed as the octahedral shear stress at failure as a function of the mean normal stress acting on the fault plane. It is found that the onset of dilatancy increases considerably for higher ${\sigma}_{2}$. Thus, ${\sigma}_{2}$ extends the elastic range for a given ${\sigma}_{3}$ and, hence, retards the onset of the failure process. SEM inspection of the micromechanics leading to specimen failure showed a multitude of stress-induced microcracks localized on both sides of the through-going fault. Microcracks gradually align themselves with the ${\sigma}_{1}$-${\sigma}_{2}$ plane as the magnitude of ${\sigma}_{2}$ is raised.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 추계학술대회
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• pp.388-393
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• 2004

Creep behavior of Ti had been studied in a stress from 9.8 to 29.4 MPa and temperature rang from 873K to 973K with a special reference to tertiary creep. It was found that stress exponent of Ti was larger than that of the general pure metal and the compound metal. The relationship between true strain and strain rate in tertiary creep was appeared as the equation, $ln{\dot{e}}$ = $ln{\dot{e}}_{0}$ + ${\Omega}$ e Also, Apparent activation energy of was appeared as 274.92kJ/mol by using the equation ${\dot{\varepsilon}}_{0}$ = A ${\sigma }_{0}^{\ast_0}$ exp$(-Q_{0}/RT)$

• 한국소음진동공학회논문집
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• 제24권6호
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• pp.452-461
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• 2014

Two stroke low speed diesel engines that have many advantages such as high thermal efficiency and durability have been widely used for marine engine. However, it is also true that many problems have occurred due to the high explosion pressure and severe operating environment. Especially problems of shaft damage etc. intensively occurred due to the phenomenon of crankshaft exceeding the allowable stress, including the shaft vibration of the engine model in the early stage. In this study, the crankshaft fracture phenomenon of early engine model was evaluated and analyzed by using up-to-date torsional vibration calculation program and measurement instrument. And this was numerically shown.