• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1999.05a
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• pp.454-458
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• 1999

절연재료의 성능 개선과 전력계통의 신뢰성을 확보하기 위해 고분자 재료가 많이 사용되고 있다. 고분자 절연재료는 절연저항 및 절연파괴 강도가 우수하며, 유전손실이 낮고 기계적 강도가 우수하며 대량생산 및 제조가 용이하고, 경량이며 유지비용이 절감되는 등의 장점이 있으나 연구의 역사가 짧고 운전 실적이 적어 불분명한 점이 많으며, 내열성 및 내트랙킹성이 비교적 약하며 표면에 오손이 축적되어 열화가 발생, 진행되거나 수분침투에 의한 파괴사고가 발생하는 단점이 있다. 따라서, 고분자 절연재료의 기본적인 화학적 구조 및 인공적 인 오손 환경을 만들어, 오손 환경의 농도 및 시간대별로 오손환경하에서 우수한 특성을 보이는 샘플을 이용하여 LDPE전체에 대한 실험을 진행했다. 또한 측정법으로서는 화학적인 구조 및 함량을 측정하기 위하여 FT-lR, DSC, TGA를 이용했고, 전기적인 측정으로서는 각각의 조건별로 전도도 및 부분방전특성을 평가하였다.

• 전기의세계
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• v.16 no.4
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• pp.11-16
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• 1967

A physical analysis is applied to the measured phenomena of aromatic organic compounds under the uniform electric field of 0.1MV/cm through 1.5MV/cm, when they are irradiated or non-irradiated respectively. Upon the observations about irradiation effects, space charge effects and their temperature dependance, the conditions of lattice defects act conspicuously on electric conductrivity, photo conductivity and dielectric breakdown. Although the qualitative agreement with Frohlich's high energy criterion theory for the above mechanisms is poor, it is concluded that the phenomena of aromatic compounds may possibly be due to the effect of lattice defects or impurity centers generated by .gamma.-ray irradiations.

• Journal of the Korean Society for Precision Engineering
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• v.26 no.1
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• pp.105-111
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• 2009

Dielectric breakdown in piezoelectric ceramics is analyzed by using the three dimensional J integral. The J integral is shown to be a path-independent surface integral for a conductive tubular channel in a piezoelectric material. J integrals are also numerically calculated for conductive defects and tubular channels in piezoelectric ceramics through finite element analysis.

• Journal of Conservation Science
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• v.37 no.5
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• pp.505-515
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• 2021

In this study, we evaluated the slope stability of the Pohang Daljeon-ri columnar joint (Natural Monuments # 415) and calculated the maximum energy, jumping height and moving distance of rockfalls using a simulation. Based on the results, we established the range of rockfall risk. The slopes of the Pohang Daljeon-ri columnar joint have dip directions of 93.79°, 131.99°, 165.54° and 259.84° from left (SW) to right (NE). Furthermore, they have a fan-like shape. The Pohang Daljeon-ri columnar joints are divided into four sections depending on the dip direction. The measurement results of the discontinuous face show that zone 1 is 125, zone 2 is 261, zone 3 is 262, zone 4 is 43. The results of slope stability analyses for each section using a stereographic projection method correspond to the range of planar and toppling failure. Although it is difficult to diagnose the type of failure, risk evaluation of currently falling rocks requires further focus. The maximum movement distance of a rockfall in the simulation was approximately 66 m and the rockfall risk range was the entire area under slope. In addition, it is difficult to forecast where a rock will fall as it rolls in various directions due to topographic factors. Thus, the installation of measures to prevent falling is suggested to secure the stability based on the results of the rockfall simulations and its probabilistic analysis.

• Korean Journal of Materials Research
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• v.9 no.4
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• pp.398-403
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• 1999

Studies on the electrical treeing deterioration and dielectric breakdown phenomena in the polymeric insulator of polyethylene and epoxy resin were carried out. Block type samples with needle-plane electrode geometry were electrically stressed and the tree pattern from the needle tip was observed. In LDPE the density of electrical tree was very high and its pattern was bush type. For the case of XLPE, branched tree was observed. As temperature and SN content increased, the dielectric breakdown voltage decreased and the treeing phenomena became more complicated. Fan type cracks were observed around the conducting tree path in the brittle DGEBA/MDA system.

• Journal of the Korean Geotechnical Society
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• v.28 no.6
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• pp.5-17
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• 2012

The moment responses of electric pole foundations for a railway were investigated using real-scale load tests. Large overturning moments were applied to two circular rigid piles with a 0.75 m diameter and a 2.5 m embedded depth; the circular rigid piles were installed in an actual railway embankment fill. Two different loading directions-toward the fill slope and toward the track -were applied to evaluate the influence of the fill slope on the moment capacities of the foundations. It was found that the failure of the foundations that were constructed according to Korean railway practices exhibited a sudden overturning pattern without any significant pre-failure displacement. The moment capacity toward the fill slope was less than the moment capacity toward the track by 30%. From the test results, the geometry factor (K), which accounted for the reduction of the moment capacity, due to the fill slope, was 0.7. Moment capacities determined from the load tests were compared with those predicted from three existing design methods, and their applicability was discussed.

• Economic and Environmental Geology
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• v.38 no.3 s.172
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• pp.305-317
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• 2005

This study addresses the preliminary results of rock slope stability analyses including hazard assessments for slope failure conducted on the selected sections of rural road cut slope which are about 4 km long. The study area is located in the Mt. Chuntae northeast of Busan and mainly composed of Cretaceous rhyolitic ash-flow tuff', fallout tuff, rhyolitc and andesite. The volcanic rock mass in the area has a number of discontinuities that produce a potentially unstable slope, as the present cut slope is more than 70 degrees in most of the slope sections. Discontinuity geometry data were collected at selected 8 scanline sections and analyzed to estimate important discontinuity geometry parameters to perform rock slope kinematic and block theory analyses. Kinematic analysis for plane sliding has resulted in maximum safe slope angles greater than $65^{\circ}$ for most of the discontinuities. For most of the wedges, maximum safe cut slope angles greater than $45^{\circ}$ were obtained. Maximum safe slope angles greater than 80" were obtained fur most of the discontinuities in the toppling case. The block theory analysis resulted in the identification of potential key blocks (type II) in the SL4, SL5, SL6 and SL8 sections. The chance of sliding taking place through a type ll block under a combined gravitational and external loading is quite high in the investigated area. The results support in-field observations of a potentially unstable slope that could become hazardous under external forces. The results obtained through limit equilibrium slope stability analyses show how a stable slope can become an unstable slope as the water pressure acting on joints increases and how a stable slope under Barton's shear strength criterion can fail as the worst case scenario of using Mohr-Coulomb criterion.

• Journal of the Korean Geotechnical Society
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• v.33 no.8
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• pp.5-16
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• 2017

When a lateral load is applied to a short pile whose embedded depth is relatively smaller than its diameter, an overturning failure occurs. To investigate the behavior of laterally loaded short piles, several model tests in laboratory scales had been carried out, however the behavior of large moment carrying piles for electric poles, traffic sign and road lamp, etc. have not been revealed yet. This paper deals with the real-scale load tests for 750 mm diameter short piles. To simulate the actual loading condition, very large moment was mobilized by applying lateral loads to the location 8 m away from the pile head. Three load tests changing the pile embedded lengths to 2.0 m, 2.5 m, and 3.0 m were carried out. The test piles overturned abruptly with very small displacement and rotation before the failures. These brittle failures are in contrast with the ductile failures shown in the former model tests with the relatively smaller moment to lateral load ratio. Comparisons of the test results with three existing methods for the estimation of the ultimate lateral capacity show that the method assuming the rotation point at pile tip matches well when the embedded depth is small, however, as the embedded depth increases the other two methods assuming the inversion of soil pressure with respect to rotation points in pile length match better.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.8 no.1
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• pp.145-150
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• 1998

The electrical and mechanical properties of the 8 mol% yittria-stabilized zirconia and alumina composites have been examined as a function of the alumina content. The 3-point bending strength and fracture toughness of the composites increased with increasing alumina content up to 20 wt%. The average grain size of the composites decreased with increasing alumina content up to 20 wt%. The composite with 5 wt% $Al_2O_3$ showed a 3-point bending strength of 310 MPa and fracture toughness about $7.8MPa\cdot\textrm m^{1/2}$. The electrical conductivity of the composites at $1000^{\circ}C$ increased slightly with increasing alumina content up to 10 wt% and decreased monotonically with alumina content. The conductivity of the TZ-8YS with 5 wt% alumina was 0.4 S/cm at $1000^{\circ}C$.

• Proceedings of the Korea Water Resources Association Conference
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• 2017.05a
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• pp.513-513
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• 2017

홍수 시 하천을 따라 유하되는 유송잡물은 구조물에 집적을 통해 유수의 흐름을 방해하고 구조물 주변의 지반을 약화시키거나 월류로 인한 심각한 피해를 야기 시킨다. 교량의 경우 유송잡물의 집적은 교각의 항력을 증가시켜 전도파괴를 유발시킬 수 있으며, 교각주변 흐름교란을 통한 하상 세굴로 인해 기초부를 파괴시키기도 한다. 또한 통수단면적 증가로 인해 높아진 수위는 제방월류로 인해 재산 및 인명피해를 유발하기도 한다. 본 연구는 이러한 유송잡물의 집적을 억제시키는 저감시설물을 대상으로 연구를 수행하고자 한다. 유송잡물 저감시설 중 우회말뚝을 대상으로 수리모형실험을 수행하고 실규모 실험을 통해 저감효과를 검토하였다. 우회말뚝은 교각 전면부에 상류방향으로 이격되어 설치되는 말뚝형태의 구조물로 유송잡물의 우회를 통해 교각에 집적을 저감하는 목적으로 설치된다. 본 연구에서는 수리실험 및 실규모실험을 통해 우회말뚝의 저감능력 검토를 수행하였으며, 1개의 말뚝을 대상으로 교각과의 이격거리와의 관계를 검토하고자 하였다. 수리모형실험의 결과 유송잡물의 길이가 경간장의 100% 일 경우 저감시설이 없을 경우 교각에 87.6% 집적이 발생하였으나 말뚝이 설치되었을 경우 교각에 직접적으로 집적되는 유송잡물은 없으며 31.7% 유송잡물은 우회말뚝에 집적되는 것으로 나타났다. 실규모 실험의 경우 우회말뚝이 없는 경우 집적률은 60%의 집적이 이루어졌으나 우회말뚝을 설치한 경우 10%의 집적률로 나타났다. 우회 말뚝설치에 따른 저감효과는 발생하였으나 이격거리에 대한 저감능력의 차이는 없는 것으로 나타났다. 그러나 우회말뚝의 이격거리가 길어질수록 말뚝주변에서 회전되어진 유송잡물이 교각에 간헐적으로 집적되는 현상이 관측되었다. 따라서 말뚝의 위치를 선정하기 위해서는 유송잡물의 길이를 고려하여 설치하는 것이 유리할 것으로 판단된다.