• Composites Research
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• v.30 no.5
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• pp.310-315
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• 2017

In this study, we have investigated microstructure, mechanical properties and wear characteristic of aluminum metal matrix composites with a high volume fraction and uniformly dispersed SiC particles which produced by a liquid pressing process. The volume fraction of bimodal SiC/Al7075 composite was 12% higher than that of the monomodal SiC/Al7075 composite and a compressive strength is increased about 200 MPa. As a result of the abrasion test, the wear width and depth of the bimodal SiC/Al7075 composite were $285.1{\mu}m$ and $0.45{\mu}m$, respectively. The coefficient of friction of bimodal SiC/Al7075 was 0.16.

• Journal of the Korean Geotechnical Society
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• v.17 no.4
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• pp.259-267
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• 2001

실내시험으로 구한 점토의 공학적 성질은 샘플링, 운반, 저장, 그리고 성형과정 동안에 발생하는 시료의 교란으로 인해 원지반의 성질과 다르게 측정된다. 본 연구에서는 양산점토에 대한 삼축압축시험($CK_{o}$ UC) 결과를 이용하여 샘플링 방법에 따른 교란의 정도를 평가하였다. 실험에 사용된 시료는 76mm 튜브샘플러, 76mm 피스톤샘플러, 블록샘플러로 채취되었으며, 시료의 교란정도를 평가하기 위해 각 시료에서 측정된 체적변형률, 비배수 전단강도, Secant Youngs modulus, 그리고 파괴시 간극수압계수를 비교하였다. 시료의 교란정도를 평가하는 것 이외에도 SHANSEP 방법을 이용하여 수행한 $CK_{o}$ U 삼축압축시험 결과를 이용하여 양산점토에 대한 정규화 전단강도($C_{u}$ /$\sigma$$_{vc}$ )와 OCR 관계를 규명하였다. 또, 피에조콘 관입시험, 딜라토메타 시험, 그리고 현장 베인시험결과를 이용하여 구한 양산점토의 비배수 전단강도를 삼축압축시험 결과와 비교하였다.

• Journal of the Korean Society of Propulsion Engineers
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• v.11 no.4
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• pp.19-25
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• 2007

A LNG safety valve functions to control a constant pressure inside the LNG line of transportation, and the flow through it accompanies with noise and vibration which affect adversely on the system. The present study aims at understanding the flow physics of LNG safety valve for a practical design of LNG safety valve. A computational work using the two-dimensional, axisymmetric, compressible, Navier-Stokes equations is carried out to simulate the gas flow through the LNG safety valve, and compared with the theoretical results. It is found that the shape of valve sheet and the gap size are the key parameters in determining the gas dynamic forces on the valve sheet, and there exists a distance between nozzle exit and valve sheet in which the thrust coefficient at the valve sheet increases abruptly.

• Journal of the Korean GEO-environmental Society
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• v.6 no.3
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• pp.5-15
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• 2005

A large diameter sampler that can take undisturbed samples from soft ground was developed by KICT. In order to compare the quality of samples taken by the sampler with those of the traditional piston sampler, a series of laboratory tests were performed. Samples were taken at different sites such as Incheon, Gimhae, Yangsan and Busan. The results showed that the values of unconfined compression strength, secant modulus, pre-consolidation pressure, undrained shear strength, and shear modulus exhibited higher in samples taken by the large scale sampler. Strains at shear failure and volumetric strains were low for the new sampler. It was proved from the comparison that better quality samples could be obtained by the KICT sampler.

• Proceeding of EDISON Challenge
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• 2014.03a
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• pp.574-578
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• 2014

본 연구에서는 인접 구조물의 상호 간섭에 의한 풍압 변화에 대한 분석을 수행하였다. 두 개의 구조물 사이의 거리 및 위치를 변경하여 비교 해석하는 것으로써 사각형 구조물 구현을 위해 EDISON_CFD를 이용하여 수치해석을 하였고, 유한 체적 법(Finite Volume Method, FVM) 기반의 범용 비압축성 유동 해석을 위해 2D_Incomp-P_2.1 해석자를 사용하였다. 이 연구를 통하여 인접한 구조물의 영향을 분석하여 상호 간 거리와 위치를 결정할 수 있는 근거자료를 확보하였다.

• Journal of the Korean Geotechnical Society
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• v.21 no.5
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• pp.45-50
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• 2005

Sand pile method, such as sand drain method and sand compaction pile method, has been popularly used as an improved method for soft clay grounds. The effect of accelerating consolidation of soft clay grounds has been evaluated with Barren's solution. The consolidation behavior of soft clay ground with sand piles strongly depends on both the nonlinear mechanical interaction between sand piles and surrounding clays and the degradation permeability of clays. In this paper a method of determining consolidation parameters of soft clay ground with sand drains by using Barren's solution was proposed through a series of numerical simulations. Through the method, the change in both volume compressibility and permeability during consolidation was reasonably evaluated.

• Journal of Advanced Marine Engineering and Technology
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• v.21 no.4
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• pp.331-355
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• 1997

본 연구에서는 에어챔버가 설치된 펌프관로계에서 수격현상에 대한 현장실험을 실시하고, 에어챔버의 입력변수 및 설계인자가 수격현상에 어떠한 영향을 미치는지 수치계산과 실험을 통하여 조사한 후 다음과 같은 결론을 얻었다. (1) 수치계산에 사용된 입력변수중 폴리트로프지수, 오리피스 유량계수, 압력파 전파속도순으로 수격현상에 대한 영향이 크게 나타났으며, 수치계산은 이 변수값이 각각 1.3, 0.7, 1,050m/s일 때 측정된 압력변동 및 공기체적변화를 가장 잘 모사하였다. (2) 에어챔버내 초기공기체적이 증가하면 압축공기의 압력변화율이 작아지기 때문에 수격현상의 주기는 길어지고, 관로내 압력변화는 감소하였다. 측관에 설치한 오리피스 내경을 줄임으로써 상승압은 상당히 완화되었으며, 시간이 지남에 따라 수격작용도 보다 빨리 감쇄되었다. 수치계산결과는 수격현상의 1-2주기까지 측정값과 비교적 잘 일치하였으며, 펌프관로계에 작용하는 최대.최소압력 및 그 발생시간도 합리적으로 예측되었다. (3) 수치계산은 측정된 과도특성 값들을 약 5%이내의 오차로 예측하였으며, 개발된 전산프로그램은 실제 펌프관로계에 대한 수격완화장치를 설계하는데 매우 유용하게 사용될 것으로 판단된다.

• The Journal of Engineering Geology
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• v.20 no.1
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• pp.89-100
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• 2010

Although various methods for determination of damage threshold in rock have been suggested, clear damage thresholds were determined by some methods, but different thresholds were measured by other methods. We determined the damage thresholds in Hangdeung granite using all the methods suggested, and investigated the best methods, applicability and errors of each method. The crack initiation threshold and the crack damage threshold which are important in investigation of characteristics of crack development and failure were verified by field strength ratio method and long-term constant load test. The crack closure stress and the crack initiation stress were 57.5 MPa and 77.6 MPa, and the most exact values were yielded by crack volumetric strain. The secondary crack initiation stress was 90.6 MPa and AE event count and AE event count rate were the effective methods. The volumetric stiffness, AE event count and AE event count rate were the most effective methods for determination of crack coalescence threshold and crack coalescence stress was 110.3 MPa. The crack damage stress was 127.5 MPa and was measured correctly by volumetric stiffness and AE event count rate. The ratio between crack initiation stress and uniaxial compressive strength was 0.47 which was very similar with the FSR value of 0.46. The ratio between crack damage stress and uniaxial compressive strength was almost the same as the ratio between long-term strength and uniaxial compressive strength, indicating that the crack initiation stress and the crack damage stress measured were correct.

• Composites Research
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• v.15 no.6
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• pp.30-37
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• 2002

A stiffness model has been proposed to predict elastic constants of twisted yam composites. The model is based upon the unit cell structure, the coordinate transformation, and the volume averaging of compliance constants for constituent materials. For the correlation of analytic results with experiments, composite samples of various yam twist angles were tested, and strength and Young's modulus under tensile, compressive, and shear loading have been obtained. The sample was fabricated by the RTM process using glass yarns and epoxy resin. The correlations of elastic constants showed relatively good agreements. The model provides the predictions of the three-dimensional engineering constants, which are valuable input data for the analytic characterization of textile composites made of twisted yam.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.34 no.2
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• pp.515-527
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• 2014

This study conducted experiment for understanding engineering characteristics of domestic sands by examining standard sand and sand from Yokji Island and Nakdong River in terms of confining pressure, $K_0$, over consolidation and relative density factors through triaxial compression test. The test showed that deviator stress by strain positively changed as confining pressure and relative density grow while $K_0$ and over consolidation factors do not directly correlated with it. Angle of internal friction decreases as confining pressure increases which strengthens contact force between particles, and declines as relative density drops, whereas $K_0$ and over consolidation factors hardly affect the results. When it comes to volumetric strain, volume expansion decreases as confining pressure increase due to crushability and rearrangement of particles while $K_0$ and over consolidation shows same movement unconditionally, and relative density appears compressed as it grows at the beginning however it expands as axial strain increases. Modulus of elasticity ($E_{sec}$) by strain has tendency into convergence resulting in initial secant modulus of elasticity ($E_{ini}$) > secant modulus of elasticity($E_{sec}$) > tangent modulus of elasticity ($E_{tan}$). On the other hand, it grows as confining pressure and relative density increase while indicating similar modulus of elasticity ($E_{sec}$) regarding on $K_0$ and over consolidation. Slope of critical line (M) tended to decrease as confining pressure increases, follow same line according to $K_0$, confining pressure and relative density, and increase as relative density grows.