• 한국지반공학회논문집
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• 제18권6호
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• pp.17-24
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• 2002

본 연구에서는 초음파실험을 통하여 카올린 점토 시료의 초음파 전파 속도와 감쇠특성을 조사하였다. 슬러리 압밀 방법을 이용하여 이산구조와 면모구조를 갖는 두 종류의 카올린 점토를 인공적으로 제작하였다. 초음파를 이용하여 각 구조를 가진 점토의 압축파 속도 및 감쇠 거동을 측정하였다. 측정시 가진 주파수, 시료 길이, 측정 방향 등을 변화시키며 그에 대한 영향을 조사하였다. 실험 결과 전파속도는 같은 압축 응력 조건에서 제작된 본 시료의 경우 미세구조의 영향이 크지 않았으나 감쇠 특성은 미세구조의 영향이 큰 것으로 나타났다.

• E2M - 전기 전자와 첨단 소재
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• 제7권1호
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• pp.42-48
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• 1994

The preventive diagnosis technique for power system is being highlighted as a research area for deterioration of insulation in machinery because of high-voltage power system. We make efforts to develop not only diagnosis of aging state but also detection of defects in the initial stage from preventive diagnosis technique. Especially, partial discharge is actively studied as a non-destructive diagnosis technique and very useful because partial discharge measurement reduces damage than conventional diagnosis technique. The loaded stress during this test is smaller than that of other diagnosis techniques. But the continuous research for various complicated analysis method is required because partial discharge has very small signals and its signals have complex forms. In this paper, the measurement of partial discharge was investigated and studied on many specimens with void. We made samples having artificial voids and measured partial discharge. In order to use as a practical diagnosis technique, we studied ways of measurement, measured illustrations and types of partial discharge which could be used in order to diagnose defects of power machinery.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1988년도 전기.전자공학 학술대회 논문집
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• pp.810-812
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• 1988

This paper is to investigate dielectric properties and new fabrication method of Glass-Cloth/Epoxy composite materials. According to the results of this paper, gelling point temperature is affected significantly on the ambient temperature. And Tan${\delta}$ characteristics of Glass-Colth/Epoxy composite materials is also affected significantly on the state of interior void of glass cloth and interface coupling between epoxy resin and glass cloth.

• Advances in Computational Design
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• 제3권2호
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• pp.133-146
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• 2018

The paper discusses numerical analysis of tensile notched specimens with the use of Gurson - Tvergaard - Needleman (GTN) material model. The analysis concerned S235JR and S355J2G3 steel grades, subjected to medium stress state triaxiality ratio, amounting 0.739. A complete procedure for FEM model preparation was described, paying special attention to the issue of determining material constants in the GTN model. An example of critical void volume fraction ($f_c$) experimental determination procedure was presented. Finally, the results of numerical analyses were discussed, indicating the differences between steel grades under investigation.

• Geomechanics and Engineering
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• 제25권4호
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• pp.283-294
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• 2021

This paper presents a rigorous solution for spherical cavity expansion in unsaturated soils under constant suction condition. The hydraulic behavior that describes the saturation-suction relationship is modeled by a void ratio-dependent soil-water characteristic curve, which allows the hydraulic behavior to fully couple with the mechanical behavior that is described by an extended critical state soil model for unsaturated soil through the specific volume. Considering the boundary condition and introducing an auxiliary coordinate, the problem is formulated to a system of first-order differential equations with three principal stress components and suction as basic unknowns, which is solved as an initial value problem. Parameter analyses are conducted to investigate the effects of suction and the overconsolidation ratio on the overall expansion responses, including the pressure-expansion response, the distribution of the stress components around the cavity, and the stress path of the soil during cavity expansion. The results reveal that the expansion pressures and the distribution of the stress components in unsaturated soils are generally higher than those in saturated soils due to the existence of suction.

• Geomechanics and Engineering
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• 제34권4호
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• pp.461-472
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• 2023

A box scale affects the shear behavior of soils in the direct shear test. The purpose of this study is to investigate the scale effect on the shear behavior of dilative granular materials by testing specimens of different heights placed in a type C shear box. Experimental tests were performed on specimens composed of glass beads with different heights and equal initial void ratios. Results showed that the peak friction and dilation angles linearly increased with the specimen height; however, the residual friction angle remained relatively constant. Similarly, the shear stiffness increased with the specimen height, rapidly reaching its peak state. Height does not have a significant effect on the total volume changes; nevertheless, a high aspect ratio can be assumed to result in global and homogeneous failure. The results and interpretations may be used as reference for recommending shear box scale in direct shear tests.

• 한국전기전자재료학회논문지
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• 제35권6호
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• pp.603-609
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• 2022

Passivation quality is mainly governed by epitaxial growth of crystalline silicon wafer surface. Void-rich intrinsic a-Si:H interfacial layer could offer higher resistivity of the c-Si surface and hence a better device efficiency as well. To reduce the resistivity of the contact area, a modification of void-rich intrinsic layer of a-Si:H towards more ordered state with a higher density is adopted by adapting its thickness and reducing its series resistance significantly, but it slightly decreases passivation quality. Higher resistance is not dominated by asymmetric effects like different band offsets for electrons or holes. In this study, multilayer of intrinsic a-Si:H layers were used. The first one with a void-rich was a-Si:H(I₁) and the next one a-SiO_x:H(I₂) were used, where a-SiO_x:H(I₂) had relatively larger band gap of ~2.07 eV than that of a-Si:H (I₁). Using a-SiO_x:H as I₂ layer was expected to increase transparency, which could lead to an easy carrier transport. Also, higher implied voltage than the conventional structure was expected. This means that the a-SiO_x:H could be a promising material for a high-quality passivation of c-Si. In addition, the i-a-SiO_x:H microstructure can help the carrier transportation through tunneling and thermal emission.

• 한국지반공학회논문집
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• 제23권4호
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• pp.91-100
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• 2007

대부분의 지반설계에 있어서 지반은 모래나 점토로 구분하며 각 지반의 거동에 따른 적절한 설계가 이루어지고 있다. 예를 들면, 사질토의 거동은 상대밀도로 나타내며, 점토의 거동은 연경도 등을 이용하여 나타낸다. 그러나 모래-점토 혼합토는 전형적으로 중간토로 구분되며 간단히 모래나 점토로 구분되지 않으므로 세립분 함유율이 낮은 사질토부터 세립분 함유율이 높은 점토에 대한 전이영역에서의 흙의 거동에 대하여 합리적인 해석이 필요하다. 본 연구에서는 활성을 가지고 있는 자연점토와 모래를 혼합하여 모래만으로 구성된 구조부터 세립분만의 구조에 이르기까지 다양한 세립분 함유율을 갖는 공시체를 제작하였다. 모래-점토 혼합토에 대한 세립분 함유율의 증가에 따른 전단특성을 명확하게 하기 위해 골격간극비에 착안하여 등방 및 이방압밀상태에서 전단실험을 수행하였다. 실험결과에서 모래-점토 혼합토의 정적전단강도는 골격간극비에 크게 의존하는 것으로 나타났다.

• 한국지반환경공학회 논문집
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• 제11권8호
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• pp.5-14
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• 2010

최근의 자갈질 지반에 대한 연구는 주로 상대밀도 혹은 자갈함유량에 바탕을 둔 연구로써 자갈질 지반의 액상화거동에 대하여 일부 연구자들은 상대밀도, 다른 연구자들은 자갈함유량에 상관성을 가지고 있음을 발표하였다. 그러나 자갈질 지반의 상대밀도는 자갈함유량에 따라 달라지게 되며 상대밀도만으로 자갈질 흙의 거동을 충분히 표현하기에는 어려운 점이 있다. 따라서 본 연구에서는 밀도와 구속압을 동시에 고려할 수 있는 상태정수를 도입하고 비배수 삼축압축시험을 통하여 자갈혼합율에 따른 정상상태선(Steady State Line, SSL)을 결정하고 상태정수에 따른 비배수 응력 거동을 고찰하였다. 연구 결과 정상상태선의 위치는 간극비에 의존하여 자갈 함유율이 증가할수록 상대적으로 아래쪽에 위치한다는 것을 알 수 있었다. 또한 같은 상대밀도라 할지라도 구속압에 따라 조밀하거나 혹은 느슨한 거동을 보였다. 특히 상대밀도가 80% 이상인 조밀한 시료일지라도 큰 구속압 아래에선 느슨한 거동을 하였다. 그러나 유사한 상태정수를 갖는 자갈질 흙은 비슷한 응력거동을 나타내었다. 이로서 흙의 거동은 상대밀도보다는 상태정수에 근거해야 함을 알 수 있었다. 또한 상태정수와 비배수전단강도는 좋은 상관 관계를 나타내었다.

• 산업기술연구
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• 제22권A호
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• pp.153-159
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• 2002

This paper is an experimental work of estimating friction angle of very coarse grained soil such as rubble mound by performing laboratory experiments. Two crushed rocks of rubble mound were used for tests. Triaxial compression tests with drained conditions were performed to measure friction angles of soils prepared by mixing the crushed soil having an identical coefficient of uniformity with different maximum grain size distribution. Centrifuge model experiments with those soils were also performed to measure angle of repose and to estimate friction angle of soil from measuring the slope of slip line in the active stress state. Model tests were carried out by changing the G-levels of 1G and 50G. From triaxial compression tests, the measured value of friction angle of soil is in the range of $41{\sim}57^{\circ}$. The measured value of repose angle is in the range of $32{\sim}35^{\circ}$. The values of friction angle are found not so sensitive to the maximum grain size of soil as long as the coefficient of uniformity is identical. Estimated value of friction angle from measuring the slope of slip line in the active stress state is in the range of $30{\sim}46^{\circ}$. Thus, the estimated angle of friction are found to be greater in the order of the measured angle of repose, the estimated value from the slope of active state, and triaxial compression test results. On the other hand, the measured values of friction angle from triaxial tests were compared with empirical equations, based on the relation between friction angle and void ratio. Equations proposed by Helenelund(l966) and Hansen(1967) found to be relatively reliable to estimate friction angles of soil.