• 터널과지하공간
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• 제6권1호
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• pp.19-29
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• 1996

Back analysis model, capable of calculating the mechanical properties and the in-situ stresses of jointed rock mass, was developed based on the inverse method using a continuum theory. Constitutive equation for the behavior of jointed rock contains two unknown parameters, elastic modulus of intact rock and stiffness of joint, hence algorithm which determines both parameters simultaneously cannot be established. To avoid algebraic difficulties elastic modulus of intact rock was assumed to be known, since the representative value of which would be quite easily determined. Then, the ratio ($\beta$) of joint stiffness to elastic modulus of intact rock was assigned and back analysis for the behavior of jointed rock was carried-out. The value $\beta$ was repeatedly modified until the elastic modulus from back analysis became very comparable to the predetermined value. The joint stiffness could be calculated by multipling the ratio $\beta$ to the final result of elastic modulus. Accuracy and reliability of back analysis procedure was successfully testified using a sample model simulating the underground opening in the jointed rock mass. Applicability of back analysis model for the underground excavation in practice was also verified by analyzing the mechanical properties of jointed rock in which underground oil storage cavern were under construction.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2004년도 춘계학술발표회
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• pp.815-822
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• 2004

A knowledge of in situ stress state is important to design various engineering structures such as dams, tunnels and so on. There are about three wellknown indicators that is, borehole will breakouts, hydraulic fracturing, ellipsoidal cross section of borehole that have been attributed to the state of stress in the vicinity of borehole. Fortunately, Televiewer traveltime image can be used as a caliper log with 144 or 288 arms, which allows to determine the borehole shape. Televiewer amplitude image will give detailed information about the distribution and character of breakouts and hydraulic fracturing as well. For investigation purposes, a series of boreholes(total 195 boreholes: 12.239m) that have been logged all over the country during past 10 years are analyzed. The primary objective of this paper are to examnine the ability of a Televiewer to determine the shape of borehole, to present data inferred by stress indicators, to indicate their possible relationship with the anisotropic horizontal stresses. It is shown that in most cases the fracture orientation statistically estimated from observed fractures denotes an excellent correlation with the orientations inferred by stress indicators. Many intervals of breakouts are terminated at the intersection of oblique fracture with the borehole. The results from Televiewer data are further compared with those of hydraulic fracturing techniques.

• Computers and Concrete
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• 제14권1호
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• pp.91-107
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• 2014

Using the principle of damage mechanics, zero-thickness pore pressure cohesive elements (PPCE) are used to simulate the casing-cement interface (CCI) and cement-rock interface (CRI). The traction-separation law describes the emergence and propagation of the PPCE. Mohr-coulomb criteria determines the elastic and plastic condition of cement sheath and rock. The finite element model (FEM) of delamination fractures emergence and propagation along the casing-cement-rock (CCR) interfaces during hydraulic fracturing is established, and the emergence and propagation of fractures along the wellbore axial and circumferential direction are simulated. Regadless of the perforation angle (the angle between the perforation and the max. horizontal principle stress), mirco-annulus will be produced alonge the wellbore circumferential direction when the cementation strength of the CCI and the CRI is less than the rock tensile strength; the delamination fractures are hard to propagate along the horizontal wellbore axial direction; emergence and propagation of delamination fractures are most likely produced on the shallow formation when the in-situ stresses are lower; the failure mode of cement sheath in the deep well is mainly interfaces seperation and body damange caused by cement expansion and contraction, or pressure testing and well shut-in operations.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2008년도 춘계학술대회 논문집
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• pp.1712-1723
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• 2008

In the trackbed design using an elastic multi-layer model, the stress-dependent resilient modulus is the key input parameter, which reflects substructure performance under repeated traffic loading. The prediction models of resilient modulus of crushed stone and weathered granite soil were developed from nonlinear dynamic stiffness, which can be combined by in-situ and laboratory seismic measurements. The models accommodate the variation with the deviatoric and/or bulk stresses. To investigate the performance of the prediction models proposed, the elastic response of the test trackbed near PyeongTaek, Korea was evaluated using a 3-D nonlinear elastic computer program (GEOTRACK) and compared with measured elastic vertical displacement caused by the passages of freight and passenger trains. The material types of the test sub-ballasts are crushed stone and weathered granite soil, respectively. The calculated vertical displacements within the sub-ballasts are within the order of 1mm, and agree well with measured values with the reasonable margin. The prediction models are thus concluded to work properly in the preliminary investigation.

• 한국자동차공학회논문집
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• 제13권5호
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• pp.171-180
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• 2005

Bending performances of aluminum square tube beams reinforced by aluminum plates under three point bending loads have been evaluated using experimental tests combined with theoretical and finite element analyses. A finite element simulation for the three-point bending test was performed. Basic properties of aluminum materials used for initial input data of the finite element simulation were obtained from the true stress-true strain curves of specimens which had been extracted from the Al tube beams. True stresses were determined from applied loads and cross-sectional area records of a tensile specimen with a rectangular cross-section by real-time photographing, and true strains were obtained from in-situ local elongation measurements of the specimen gage portion by the multi-point scanning laser extensometer. Six kinds of aluminum tube beam specimens adhered by aluminum plates were employed fur the bending test. The bending deformation behaviors up to the maximum load described by the numerical simulation were in good agreement with experimental ones. After passing the maximum load, reinforcing plate was debonded from the aluminum tube beam. An aluminum tube beam strengthened by aluminum plate on the upper web showed an excellent bending capability.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2007년도 춘계학술대회A
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• pp.60-65
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• 2007

Local buckling behaviors of aluminum square tube beams reinforced by aluminum plates under three point bending loads have been analyzed using experimental tests combined with theoretical and finite element analyses. For this analysis true stresses were determined from applied loads and cross-sectional area records of a tensile specimen with a rectangular cross-section by real-time photographing. True strains were also obtained from in-situ local elongation measurements of the specimen gage portion by the multi-point scanning laser extensometer. Six kinds of aluminum tube beam specimens reinforced by aluminum plates were employed for the bending test. The bending deformation behaviors up to the maximum load analyzed by the numerical simulation agreed well with experimental ones. After passing the maximum load, reinforcing plate hindering the local buckling of the tube beam was debonded from the aluminum tube beam. An aluminum tube beam strengthened by aluminum plate on the upper web showed the most excellent bending capacity, which could be explained on the basis of the neutral axis shift and the local buckling deformation range.

• 방사성폐기물학회지
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• 제20권2호
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• pp.161-170
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• 2022

The effect of oxidation time on the characteristics and mechanical properties of spent nuclear fuel cladding was investigated using Raman spectroscopy, tube rupture test, and tensile test. As oxidation time increased, the Raman peak associated with the tetragonal zirconium oxide phase diminished and merged with the Raman peak associated with the monoclinic zirconium oxide phase near 333 cm^-1. Additionally, the other tetragonal zirconium oxide phase peak at 380 cm^-1 decreased after 100 d of oxidation, whereas the zirconium monoclinic oxide peak became the dominant peak. The oxidation time had no effect on the tube rupture pressure of the oxidized zirconium alloy tube. However, the yield and tensile stresses of the oxidized nuclear fuel cladding tube decreased after 100 d of oxidation. The results of the scanning electron microscopy and transmission electron microscopy were represented with the in-situ Raman analysis result for the oxide characteristics generated on the cladding of spent nuclear fuel.

• 터널과지하공간
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• 제10권4호
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• pp.526-532
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• 2000

전단면터널 굴착장비에 의한 터널굴착을 설계할 때 일반적으로 적용되는 암반의 강도는 80-250 MPa로 알려져 있으나 설계단계에서 암반의 특성을 완전히 파악하지 못한 채 설계하고 수행하는 경우가 있다. 본 연구는 60% 이상 구간의 단축압축강도가 260 MPa이상이며, RMR값이 70이상의 암반에서 TBM으로 굴착된 약 5.3km 연장의 밀양댐계통 광역상수도 도수로터널 TBM 굴착구간의 암반특성을 규명하고 이로써 이론적 굴착속도를 분석하여, 실제의 순굴착속도와 비교분석한 것이다. 노르웨이 NTH에 의하여 제안된 이론적 굴착속도는 현장에서 수행된 순굴착속도의 평균값과 2∼20%의 오차를 갖는 것으로 평가되어, 극경암에서의 굴착속도 설계는 일본이나 미국에서 제안된 해석법에 비하여 NTH해석법이 가장 접근된 설계방법이라 할 수 있다. 현지암반을 펑가하여 순굴착속도와의 상관관계를 규명한 결과, 극경암에서의 순굴착속도는 슈미트 해머에 의한 반발경도와 RMR 값에 반비례하는 것으로 나타났는데, 이의 상관계수는 각각 0.705 및 0.777이었다. 이로써 반발경도와 RMR의 크기는 순굴착속도를 예측할 수 있는 요소가 될 수 있음을 알 수 있다. 또한 극경암에서의 순굴착속도는 현지암반의 지압의 크기에 크게 영향을 받고 있는 것으로 평가되어 TBM 굴착설계에서 지압상태는 중요한 설계요소의 하나로서 고려되어야 할 것이다.

• 공업화학
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• 제10권7호
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• pp.1014-1019
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• 1999

Dianhydride로서 1,2,4,5-benzenetetracarboxylic dianhydried(PMDA)와 2,2'-bis(3,4-dicarboxyphenyl) hexafluoropropane dianhydride(6FDA)를, diamine으로서 1,4-phenylenediamine(PDA)을 사용하여 homopolyimides인 PMDA-PDA, 6FDA-PDA와 다른 당량비의 copolyimides를 각각의 ploy(amic acid)로부터 제조하였다. 이들 박막에 대하여, thin film stress analyzer(TFSA)를 이용하여 공중합체 폴리이미드 박막의 잔류 응력거동을 공정온도 ($25{\sim}400^{\circ}C$)하에서 전구체의 열적 이미드화에 따라 in-situ로 측정하였고, WAXD분석을 통해 모폴로지 변화를 알아보았다. 다른 단량비로 이루어진 공중합체 폴리이미드 박막의 잔류 응력 결과는 PMDA 분율이 증가함에 따라 잔류 응력이 큰 폭으로 감소하였고 순수 PMDA-PDA 폴리이미드에서는 압축모드로 5 MPa로 나타났다. 본 연구에서는 PMDA-PDA의 높은 $T_g$로 인한 공정상의 어려움과 6FDA-PDA의 상대적으로 높은 응력을 서로 보완해 기계적 물성이 좋은 저응력의 폴리이미드를 만들 수 있음을 보였다. 즉, random한 PMDA/6FDA-PDA 공중합체 폴리이미드 합성을 이용하여 사슬 내에 벌키한 di(trifluoromethyl)기와 같은 관절기로 인한 상대적으로 높은 응력을 보이는 6FDA-PDA 폴리이미드 사슬 내에 강직한 사슬 구조를 가진 PMDA-PDA 폴리이미드의 사슬 구조를 적당량 첨가함으로써 우수한 기계적 물성을 갖는 저응력 폴리이미드를 만들 수 있었다. 특히, PMDA/6FDA-PDA (0.9:0.1:1.0) 폴리이미드가 저유전 상수 층간 절연막으로서의 우수한 기계적 물성과 낮은 응력 수준을 보여주고 있다.

• 한국지반공학회논문집
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• 제19권5호
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• pp.211-221
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• 2003

스웨덴$\"{A}"{s}"{p}"{o}$지하실험실에서는 방사성폐기물 처분공 사이 암반에서의 파쇄 및 안정성을 예측할 수 있는 능력을 평가하기 위해 $\"{A}"{s}"{p}"{o}$ 암주 안정성 실험 (APSE)이라고 하는 현지 가열 실험이 준비되고 있다. 계획된 시험 조건하의 암주에서의 균열 진전 과정을 합리적으로 예측하기 위해 경계요소 수치해석 코드인 FRACOD가 적용되었다. 암석경계와 무결암석 내에서의 균열 진전을 모사하기 위해 코드를 개선하였다. 또한 굴착 및 열하중에 의해 발생하는 응력분포를 FRACOD모델에 적용하기 위해 새로운 경계요소를 이용한 역해법을 개발하였다. 이 글은 계획된 시험조건에 대한 예측 모델링 결과를 제시한다. 굴착에 의한 응력분포는 암주 벽면에 약간의 균열을 발생시켰다. 120일 동안의 가열에 의해 암주 벽면 중앙부에서 전형적인 전단 균열들의 개시 및 전파가 일어났지만, 전반적으로 암주 내부는 고려되는 조건하에서 안정한 상태를 유지하였다. 기존 절리들의 존재와 균열 물성에 따른 영향이 또한 논의되었다. 해석 결과를 통해 FRACOD가 심부 터널 및 보어홀에서 취성 암반의 균열 진전 현상을 적절히 모델링할 수 있음을 알 수 있다. 취성 암반의 균열 진전 현상을 적절히 모델링할 수 있음을 알 수 있다.