• 한국지반환경공학회 논문집
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• 제16권6호
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• pp.23-30
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• 2015

본 연구는 국내의 대표적인 연약지반인 남해안 광양지역과 양산지역의 피스톤 샘플러와 대형블록시료로 수행된 실내시험 시료를 이용하여 교란도 분석을 시행하고 교란에 따른 실내시험 압축지수 특성을 평가하기 위하여 계측침하량 분석에 의한 역해석 압축지수와 비교 분석하였다. 본 연구대상지역의 피스톤 시료에 의한 실내시험 결과로 시료교란도 분석을 수행한 결과 대부분 시료가 품질이 불량한 것으로 평가되어 실내시험결과로 산정된 압축지수를 이용한 설계 예측침하량이 과소평가되었음을 알 수 있었다. 인근지역에서 수행된 시험자료에 대한 교란도 분석결과 대형블록시료가 피스톤 시료보다 교란도가 작은 것으로 분석되었다. 계측침하량을 이용한 장래침하량 예측기법인 쌍곡선법, Hoshino법, Asaoka법, ${\sqrt{S}}$법으로 예측한 결과 일부 측점의 예측자료를 제외하고는 예측기법별 신뢰도는 동일한 것으로 분석되었다. 피스톤 시료의 압축지수에 대한 교란영향을 보정하기 위하여 Schmertmann의 수정 압축지수와 계측침하량 분석에 의한 역해석 압축지수를 이용하여 피스톤 시료의 압축지수를 추정하는 새로운 보정식을 제시하였다.

• 한국농공학회논문집
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• 제55권2호
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• pp.77-85
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• 2013

The aim of this study is to investigate strength and water purification characteristics of effective microorganism-applied volcanic ash block using flexural strength test and water quality analysis. The specimens were prepared with volcanic ash from Mt. Baekdusan and Mt. Hallasan, and cement as the ratios of 3.5:1, 4.0:1, 4.5:1, 5.0:1 with and without metakaolin. Flexural strength degraded with increasing of the amount of volcanic ash, and increased with addition of metakaolin as a binder. Based on these results, the optimal ratio for fabricating volcanic ash-cement mixture block is determined as 3.5:1 with metakaolin. Furthermore, from water quality analysis on contaminated water, removal ability of effective microorganism-applied volcanic ash-cement mixture block and caged volcanic ash block against T-N, T-P and SS was highly evaluated because of adsorption due to the large specific surface area of volcanic ash. Hence, volcanic ash-cement mixture block and caged volcanic ash block possibly contribute to water purification.

• Applied Microscopy
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• 제41권3호
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• pp.147-154
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• 2011

후방산란전자(BSE)는 입사전자빔이 시료와 충돌하면서 발생한다. BSE 이미징은 시료의 화학적 특성을 구분할 수 있는 조성대비를 제공한다. 집속이온빔장치(FIB)는 전계방사형 주사전자현미경(FESEM)과 결합할 수 있으므로 이중빔 체계(FIB-FESEM)가 구현된다. 갈륨(Ga) 이온빔으로 10~100 nm 두께로 시료를 절삭할 수 있으므로 FIB-FESEM은 플라스틱으로 포매된 블록의 면을 z축 고해상도를 유지하며 연속적으로 이미징할 수 있다. BSE이미지의 대비를 반전시키면 투과전자현미경의 이미지와 유사하다. 연속블록면 이미징의 또 다른 방안으로써 특수한 초박절편기가 FESEM 내부에 장착된 것이 $3View^{(R)}$로 상용화되어 있다. 이로써 플라스틱으로 포매된 시료의 내부 구조를 넓은 면적을 연속적으로 이미징 할 수 있으므로 3차원 재구성도 용이하게 된다. 이러한 FESEM에 기반한 두 가지 방식은 복잡한 생물계의 총체적인 이해를 위하여 세포 및 세포 수준 이하의 구조물 간의 공간적 연관성을 규명하는 데 활용될 수 있다.

• 한국세라믹학회지
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• 제29권4호
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• pp.312-318
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• 1992

Two kinds of alumina specimens with different grain size (1 and 51 $\mu\textrm{m}$) but same density were prepared by hot-pressing. Fracture strength and fracture toughness of these specimens at low strain rate, sonic velocity, and elastic property were evaluated. Ballistic performance against Cal. 50 AP projectile was characterized by thick-backing method by using A16061-T6 reference block. Mechanical properties measured at low strain rate showed that the specimen with samll grain (SG) were better than specimen with large grain (LG). Fracture strength and fracture toughness of LG specimen were 131 MPa and 3.01 MPa{{{{ SQRT { m} }}, but those of SG specimen were 349 and 4.23, respectively. Sonic velocity and elastic properties of these specimen were similar, but bulk velocity and bulk modulus were different at amount of 4 and 9%. The tendency of ballistic performance was not consistent with the mechnaical properties at low strain rate. The ballistic performance based on quantitative efficiency revealed that the LG specimen (5.13) was ballistically better than the SG specimen (4.00) in spite of their lower mechanical properties.

• Journal of the Korean Wood Science and Technology
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• 제47권5호
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• pp.655-662
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• 2019

This study evaluated the multi-bonding performances of timbers as well as those of reinforcement and timber to obtain data for preparing guidelines regarding the use of timbers as large structural members. For the multi-bonding performances of timbers, four types of bonding surfaces were prepared according to the pith position. For the bonding performances of FRP (fiber-reinforced plastic)/steel plate and timber, a total of 11 types of specimens were produced for the selection of the appropriate adhesive. The bonding performances of the produced specimens were evaluated through a water soaking delamination test, a water boiling delamination test, and a block shear strength test. The test results showed that the bonding strength of the bonding surface according to the pith position was highest in the specimen for which the two sections with the pith at the center of the cross-section on timber and between the bonding surfaces (the tangential and radial sections were mixed) were bonded. Furthermore, the specimens for which the section (radial section) with the pith on the bonding surface of the timber was bonded showed a high delamination percentage. The results of the block shear strength test showed that the bonding section did not have a significant effect on the shear strength, and that the measured wood failure percentage was higher than the KS standard value. The PVAc adhesive showed the highest bonding strength between larix timber and GFRP (glass FRP). Furthermore, the epoxy and polyurethane adhesives showed good bonding strength for CFRP (carbon FRP) and structure steel, respectively.

• International Journal of Naval Architecture and Ocean Engineering
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• 제6권2호
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• pp.459-470
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• 2014

During ship design, welding-induced distortions are roughly estimated as a function of the size of the component as well as the welding process and residual stresses are assumed to be locally in the range of the yield stress. Existing welding simulation methods are very complex and time-consuming and therefore not applicable to large structures like ships. Simplified methods for the estimation of welding effects were and still are subject of several research projects, but mostly concerning smaller structures. The main goal of this paper is the application of a multi-layer welding simulation to the block joint of a ship structure. When welding block joints, high constraints occur due to the ship structure which are assumed to result in accordingly high residual stresses. Constraints measured during construction were realized in a test plant for small-scale welding specimens in order to investigate their and other effects on the residual stresses. Associated welding simulations were successfully performed with fine-mesh finite element models. Further analyses showed that a courser mesh was also able to reproduce the welding-induced reaction forces and hence the residual stresses after some calibration. Based on the coarse modeling it was possible to perform the welding simulation at a block joint in order to investigate the influence of the resulting residual stresses on the behavior of the real structure, showing quite interesting stress distributions. Finally it is discussed whether smaller and idealized models of definite areas of the block joint can be used to achieve the same results offering possibilities to consider residual stresses in the design process.

• Structural Engineering and Mechanics
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• 제76권5호
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• pp.663-674
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• 2020

In this study, partially restrained beam-column moment joints in the weak-axis direction were examined using three large-scale specimens subject to cyclic loading in order to assess the seismic resistance of the joints of low-rise steel structures and to propose joint details based on the test results. The influence of different number of bolts on the moment joints was thoroughly investigated. It was found that the flexural capacity of the joints in the direction of weak axis was highly dependent on the number of high-tension bolts. In addition, even though the flexural connections subjected to cyclic loading was perfectly designed in accordance with current design codes, severe failure mode such as block shear failure could occur at beam flange. Therefore, to prevent excessive deformation at bolt holes under cyclic loading conditions, the holes in beam flange need to have larger bearing capacity than the required tensile force. In particular, if the thickness of the connecting plate is larger than that of the beam flange, the bearing capacity of the flange should be checked for structural safety.

• 터널과지하공간
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• 제20권6호
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• pp.455-464
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• 2010

평면이방성 암석의 특성을 실험적으로 규명하기 위하여 이방성각도에 따른 일축압축강도 및 변형률, 탄성상수의 변화를 분석하였다. 실험에는 유상구조가 뚜렷한 유문암의 7개의 서로 다른 각도를 갖는 총 35개 시험편을 사용하였다. 본 연구의 제 1보에서는 시험자료의 각도에 따라 개별적인 분석을 주로 논의하였으며, 제 2보에서는 이들 자료를 종합적으로 검토할 것이다. 수평 및 수직시료에서는 가정식을 적용하지 않고 4개의 탄성상수를 얻을 수 있기 때문에 이들의 크기는 참값이라 결정할 수 있다. 변형률 측정에서 각도에 따라 자료의 분산 정도가 달라지는데, 작은 각도에서는 큰 각도보다 분산이 크게 나타났다. 겉보기 탄성계수의 변화는 각도에 따라 M자 또는 U자 형태로 측정되었다. 낮은 각도에서는 겉보기 탄성계수의 변화가 단조증가의 경향을 보이지 않으므로 Saint-Venant 식을 적용될 수 없으며, E1의 크기는 참값범위에 포함되는 값을 얻을 수 없다. 75도 각도의 시료는 변형률과 강도의 측정 편차가 가장 작게 나타났으며, 해석된 4개의 모든 탄성상수가 참값의 범위에 포함되었다. 따라서 만약 한 개의 시험편에서 평면이방성의 탄성상수를 얻고자하는 경우에, 이방성각도가 75도 근처의 시험편을 선정하는 것이 바람직하다.

• Structural Monitoring and Maintenance
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• 제10권1호
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• pp.1-23
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• 2023

Various efforts have been made to reduce the weight of concrete slabs while preserving their flexural strength. This will result in reducing deflection and allows the utilization of longer spans. The top zone of the slab requires concrete to create the compression block for flexural strength, and the tension zone needs concrete to join with reinforcing for flexural strength. Also, the top and bottom slab faces must be linked to transmit stresses. Voided slab systems were and are still used to make long-span slab buildings lighter. Eight slab specimens of (1000^*1000 (1000^*1000 mm²) were cast and tested as two-way simply supported slabs in this research. The tested specimens consist of one solid slab and seven voided slabs with the following variables (type of slab solid and voided), thickness of slab (100 and 125 mm), presence of steel fibers (0% and 1%), and the number of GFRP layers). The voids in slabs were made using high-density polystyrene of dimensions (200^*200^*50 mm) with a central hole of dimensions (50^*50^*50 mm) at the ineffective concrete zones to give a reduction in weight by (34% to 38%). The slabs were tested as simply supported slabs under partial uniform loading. The results of specimens subjected to monotonic loading show that the combined strengthening by steel fibers and GFRP sheets of the concrete specimen (V-125-2GF-1%) shows the least deflection, deflection (4.6 mm), good ultimate loading capacity (192 MPa), large stiffness at cracking and at ultimate (57 and 41.74) respectively, more ductility (1.44), and high energy absorption (1344.83 kN.mm); so it's the best specimen that can be used as a voided slab under this type of loading.

• 한국음향학회지
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• 제15권6호
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• pp.81-89
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• 1996

원전의 1차 계통 건전성 확보를 위한 일환으로서 초음파 검사 방법은 매우 중요하다. 그러나, 초음파는 검사 대상제의 내부 구조 및 형상에 따라 검사의 제한을 받으므로 결정립이 큰 재질에서 후방 산란 잡음 즉 시 불변성(time invariant) 잡음이 발생한다. 이로 인하여 수신 신호는 낮은 신호 대 잡음비의 결과로 나타나게 된다. 주파수 대역 분할 방식(split spectrum processing:SSP) 기술은 이와 같은 잡음을 억제하는데 효율적이다. 그러나, 종래의 SSP 기술은 minization, PT 알고리즘중 한 알고리즘만 적용하였으나 본 논문에서는 이두 가지 알고리즘을 동시에 처리하는 MPO(minimization and polarity threshold)알고리즘을 적용하고, 주파수 대 대역폭비가 일정한 FIR 여파기로서 새로운 constant-Q SSP를 수행하여 신호처리 시간을 단축하였다. 현장 검사 요건과 동일하게 종파와 횡파에도 일부 적용하였다. 한편, 이러한 새로운 SSP 기술을 적용할 수 있도록 초음파 탐상기를 설계 제작하였고, 시험편들의 준비는 원전 모재 대비시험편, 모재와 동일한 재질의 스테인레스 스틸 및 구리 시험편들이며, 이들 시험편으로 부터 초음파 신호를 수집하여 본 신호 처리를 적용한 결고 신호 대 잡음비가 향상됨을 알 수 있었다.