• Archives of Metallurgy and Materials
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• 제67권4호
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• pp.1497-1501
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• 2022

In-situ observation of the transformation behavior of acicular ferrite in high-strength low-alloy steel using confocal laser scanning microscopy was discussed in terms of nucleation and growth. It is found that acicular ferrite nucleated at dislocations and slip bands in deformed austenite grains introduced by hot deformation in the non-recrystallization austenite region, and then proceeded to grow into an austenite grain boundary. According to an ex-situ EBSD analysis, acicular ferrite had an irregular shape morphology, finer grains with sub-grain boundaries, and higher strain values than those of polygonal ferrite. The fraction of acicular ferrite was affected by the deformation condition and increased with increasing the amount of hot deformation in the non-recrystallization austenite region.

• Corrosion Science and Technology
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• 제23권2호
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• pp.113-120
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• 2024

An attempt was made to apply digital image correlation (DIC) strain analysis to in-situ scanning electron microscopy (SEM) observations of bending deformation to quantify local strain distribution inside a ZnMgAl-alloy coating in deformation. Interstitial-free steel sheets were hot-dipped in a Zn-3Mg-6Al (mass%) alloy melt at 400 ℃ for 2 s. The specimens were deformed using a miniature-sized 4-point bending test machine inside the SEM chamber. The observed in situ SEM images were used for DIC strain analysis. The hot-dip ZnMgAl-alloy coating exhibited a solidification microstructure composed of a three-phase eutectic of fine Al (fcc), Zn (hcp), and Zn2Mg phases surrounding the primary solidified Al phases. The relatively coarsened Zn₂Mg phases were locally observed inside the ZnMgAl-alloy coating. The DIC strain analysis revealed that the strain was localized in the primary solidified Al phases and fine eutectic microstructure around the Zn₂Mg phase. The results indicated high deformability of the multi-phase microstructure of the ZnMgAl-alloy coating.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 1996년도 가을 학술발표회 논문집
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• pp.61-70
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• 1996

• Geomechanics and Engineering
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• 제19권2호
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• pp.141-151
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• 2019

A novel theoretical solution is presented for created (zero initial radius) cavity expansion problem based on CamClay model and considers the effect of initial anisotropic in-situ stress and drained conditions. Here the strain of this theoretical solution is small deformation in elastic region and large deformation in plastic region. The works for cylindrical and spherical cavities expanding in drained condition from zero initial radius are investigated. Most of the conventional solutions were based on the isotropic and undrained condition, however, the initial stress state of natural soil mass is anisotropy by soil deposition history, and drained cavity expansion calculation is closer to actual engineering in permeable soil mass. Finally, the parametric study is presented in order to the engineering significance of this work.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 1998년도 터널.암반역학위원회 박사학위 논문집
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• pp.83-114
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• 1998

The most widely accepted method for understanding the deformation mechanism of rock is from the use of computer simulation. However, if the changes in rock properties after excavation are significant this will prevent the computer simulation kent predicting the deformation with acceptable accuracy. If the deformations are, however, carefully measured in situ, the resulting data can be more useful far predicting the deformational behavior of underground openings, since the effect of the parameters which influence the deformational behavior are included in the measurement. In this study, extensive data analyses were carried out using the deformation measurements from the Waste Isolation Pilot Plant (WIPP), which is a permanent nuclear waste repository The results from computer simulations were compared with field measurements to evaluate the assumptions used in the computer simulations, For better description of the deformational behavior around underground excavations, several techniques were developed, namely: (a) the calculation of the zero strain boundary; (b) the evaluation of the influence of adjacent excavations on the deformational behavior of pre-excavated openings; (c) the description of the deformational behavior using in situ measurements; (d) the calculation of the shear stress distribution; and (e) the application of a Neural Network for the prediction of opening deformation.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2000년도 가을 학술발표회 논문집
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• pp.3-14
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• 2000

Anisotropic consolidation, shear, a transportational component during or after deposition each may produce anisotropic fabrics, which result in the anisotropic properties of soils. Nevertheless, the isotropically consolidated compression triaxial tests are commonly used in practice to determine the strength of the anisotropically consolidated soils because of their practicality and simplicity. In this paper the effects of anisotropic consolidation on the strength properties of soils are discussed. For the sandy soils consolidated under a constant vertical consolidation pressure, the deformation modulus decreases with decreasing consolidation pressure ratio($\sigma$$\sub$3c/'/$\sigma$ sub 1c/'), but the liquefaction resistance increases. For the saturated cohesive soils, both the undrained shear strength and undrained creep strength decrese with decreasing the consolidation pressure ratio. When the in-situ strength properties of the anisotropically and normally consolidated soils are determined by the isotropically consolidated tests, the undrained shear strength and creep strength of saturated cohesive soils as well as the deformation modulus of sandy soils are measured to be higher than the rear in-situ values. This, therefore, could lead to a dangerous judgement in stability analysis

• Nuclear Engineering and Technology
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• 제53권7호
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• pp.2312-2322
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• 2021

In recent studies, the creep rate of Zircaloy-4, one of the basic property parameters of the nuclear fuel code, has been commonly used with the axial creep model proposed by Rosinger et al. However, in order to calculate the circumferential deformation of the fuel cladding, there is a limitation that a difference occurs depending on the anisotropic coefficients used in deriving the circumferential creep equation by using the axial creep equation. Therefore, in this study, the existing axial creep law and the derived circumferential creep results were analyzed through a circumferential creep test by the internal pressurization method in the isothermal conditions. The circumferential creep deformation was measured through the optical image analysis method, and the results of the experiment were investigated through constructed IDECA (In-situ DEformation Calculation Algorithm based on creep) code. First, preliminary tests were performed in the isotropic β-phase. Subsequently in the anisotropic α-phase, the correlations obtained from a series of circumferential creep tests were compared with the axial creep equation, and optimized anisotropic coefficients were proposed based on the performed circumferential creep results. Finally, the IDECA prediction results using optimized anisotropic coefficients based on creep tests were validated through tube burst tests in transient conditions.

• 터널과지하공간
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• 제18권2호
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• pp.134-148
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• 2008

암반의 초기응력 상태는 방사성 폐기물 지층 처분장의 적합성을 판단하는데 중요한 요소이다. 본 연구에서는 3차원 개별요소법을 이용하여 스웨덴 방사성 폐기물 처분장 후보지 중 하나인 오스카샴 지역에서 대규모 변형대가 초기응력에 미치는 영향을 살펴보았다. 수치해석에서는 부지조사 과정에서 확인된 변형대를 모델에 포함시켰으며 원거리 지각응력을 경계조건으로 사용하였다. 현지 암반에서 관찰되는 초기응력값의 변화 양상이 수치해석에서도 재현이 됨으로써 수치해석이 암반의 초기응력상태를 이해하는데 유용하게 쓰일 수 있음을 확인하였다. 수치해석을 통한 예측값과 초기응력 측정값과의 차이는 측정된 자료의 양호한 정도, 지질모델 및 변형대의 물성치의 불확실성 등에 기인하는 것으로 생각된다.

• 한국지반공학회논문집
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• 제19권5호
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• pp.335-342
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• 2003

지반 변형계수를 측정하는 방법중에서 원위치 시험법은 반력으로 대형 장비가 필요하고 많은 측정시간이 소요되므로 시험횟수가 제한되는 단점이 있다. 최근에는 이런 문제점을 보완하고 보다 신속하게 측정할 수 있는 장비들이 개발되어 적용되고 있다. 즉, Falling Weight Deflectometer(FWD), Light Drop Weight Tester(LDWT), Geogauge등이 있다. 이중에서 Light Drop Weight Tester(LDWT)는 경부 고속철도 공사에 ‘철도공사를 위한 경량 낙하 시험기’라는 명칭으로 적용된 이래로 여러 기관에 도입되어 노반의 품질관리 및 성토관리용으로 국내 조건에 맞는 기준을 정립하기 위한 연구가 진행중이다. 본 연구에서는 현장에서 지반변형계수를 쉽게 측정하는 방안을 제안하기 위해 독일 Stendal의 동적 평판 재하시험 장비(Light Drop Weight Tester(LDWT))인 ZFG 02를 이용하여 현장과 토조에서 동적변형계수를 측정하였다. 동일한 지반에서 실시한 평판재하시험 결과에 의한 정적 변형계수와의 상관성을 분석하였다.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2003년도 봄 학술발표회 논문집
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• pp.95-102
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• 2003

Corestone rock mass has complex characters because it is made up of stronger and stiffer corestone in a weaker and softer matrix. Physical model corestone rock mass made up of stiffer corestone in weaker matrix were tested in uniaxial compression and numercal modelling analysis The result of the uniaxial compression tests showed that increasing the corestone proportion generally increased the modulus of deformation. And the strength decreased in the lower corestone proportion, but it increased in the higher proportion(45%, 65% corestone by volume). The strength and the modulus of deformation were not affected by different size coretone on the same proportion. The result of the numerical modelling analysis showed similar trend compared with the result of the result of the uniaxial compression test. But though the result of th uniaxial compression test is similar to the result of the numerical modelling analysis, it's unreasonalble to apply the results of this paper to in situ corestone rock mass. So mere laboratory tests including triaxial test and the other numerical program analyses are necessary to apply the results to in situ corestone mass