• Geomechanics and Engineering
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• 제14권6호
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• pp.563-570
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• 2018

Ballast layer has an important role in vertical stiffness and stability of railway track. In most of the Middle East countries and some of the Asian ones, significant parts of railway lines pass through desert areas where the track (particularly ballast layer) is contaminated with sands. Despite considerable number of derailments reported in the sand contaminated tracks, there is a lack of sufficient studies on the influences of sand contamination on the ballast vertical stiffness as the main indicator of track stability. Addressing this limitation, the effects of sand contamination on the mechanical behavior of ballast were experimentally investigated. For this purpose, laboratory tests (plate load test) on ballast samples with different levels of sand contamination were carried out. The results obtained were analyzed leading to derive mathematical expressions for the strain modulus ($E_V$) as a function of the ballast level of contamination. The $E_V$ was used as an index for evaluation of the load-deformation characteristics and bearing capacity of track substructure. The critical limit of sand contamination, after which the $E_V$ of the ballast reduces drastically, was obtained. It was shown that the obtained research results improve the current track maintenance approach by providing key guides for the optimization of ballast maintenance planning (the timing of ballast cleaning or renewal).

• 대한치과보철학회지
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• 제40권1호
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• pp.68-78
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• 2002

The post core system has been used for reconstructon of severely damaged crown by caries or trauma. But problems such as crown exfoliation, post core fracture and root fracture have been reported. Ideal mechanical properies of the post require high fracture strength, high elastic limit and high resistance against fatigue and corrosion Modulus of elasticity of the post should be similar with that of dentine. Low hardness is also required for the convenience of post removal in failure. Furthermore, the post itself must be translucent for the esthetical purpose. Several types of the post have been developed to satisfy the criteria above mentioned. The purpose of this study was to find out the mechanical properties of quartz fiber post by comparing with those of gold post and zirconia post. The results of this study were as follows : 1. Maximal fracture strength and stiffness of quartz fiber post were similar with those of gold post and zirconia post. 2. Young's modulus and hardness of quartz fiber post were lower than those of gold post and zirconia post. Mechanical property of quartz fiber post against post fracture was similar with that of gold post and zirconia post. Mechanical property of quartz fiber post against root fracture was higher than that of gold post and zirconia post. Quartz fiber post could be removed easily due to low hardness.

• 한국분말재료학회지
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• 제28권3호
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• pp.253-258
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• 2021

There is increasing demand for the development of a new material with high strength, high stiffness, and good electrical conductivity that can be used for high-voltage direct current cables. In this study, we develop aluminum-based composites containing C₆₀ fullerenes, carbon nanotubes, or graphene using a powder metallurgical route and evaluate their strength, stiffness, coefficient of thermal expansion, and electrical conductivity. By optimizing the process conditions, a material with a tensile strength of 800 MPa, an elastic modulus of 90 GPa, and an electrical conductivity of 40% IACS is obtained, which may replace iron-core cables. Furthermore, by designing the type and volume fraction of the reinforcement, a material with a tensile strength of 380 MPa, elastic modulus of 80 GPa, and electrical conductivity of 54% IACS is obtained, which may compete with AA 6201 aluminum alloys for use in all-aluminum conductor cables.

• 한국철도학회논문집
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• 제18권1호
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• pp.53-62
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• 2015

동평판재하시험기(LWDT)는 궤도노반 등의 다짐강성 측정을 위하여 개발된 시험기이며 낙하추를 자유낙하시킬 때 가속도계를 이용하여 다짐표면의 처짐량을 측정, 반무한 탄성체로 가정된 노반의 동탄성계수를 결정한다. 본 연구에서는 LWDT시험기의 구성과 구동 메커니즘 및 동탄성계수 추출공식의 유효성을 상세히 분석하였다. 특히, 2층구조 노반 위에서 LWDT 시험시 상부층의 강성평가 유효깊이를 유한요소해석으로부터 결정하였다. 또한, LWDT 시험시 노반의 강성 차이를 고려하여 사용할 수 있는 동탄성계수 추출공식 수정계수를 제시하였다.

• The Korean Journal of Ceramics
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• 제6권1호
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• pp.37-42
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• 2000

To reduce shrinkage and the possibility of fracture during ambient pressure drying, it is of great importance to increase the strength and stiffness of the wet gels. In this paper is presented the strengthening and stiffening of wet silica gels prepared from sodium silicate (water glass) as well as properties of the corresponding xerogels. By washing gels containing different initial silica contents in water solutions at elevated pH, a maximum in shear modulus of ~4 MPa was obtained. The maximum stiffness enabled xerogels with bulk density of 0.28g/$\textrm{cm}^3$ to be made regardless of silica content and washing conditions. However, by aging the wet gels in a solution providing fresh monomers to the gel network, a shear modulus of 20 MPa was obtained after 27h. By this method monolithic xerogels with a density down to ~0.2g/$\textrm{cm}^3$ was prepared. The results are compared to alkoxide based gels.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2009년도 춘계 학술발표회
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• pp.102-107
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• 2009

Recently, the use of barrette pile is remarkably increased specially for high-rise building and bridge foundations. However, on the contrary, very few studies have been made for analyzing barrette pile behavior considering interface behavior between pile and soils around. Therefore, in this paper, these effects are evaluated by using the 3-dimensional non-linear finite element method with the results of full-scale pile load test from the fields. In addition to that, the selection of proper stiffness modulus on the pile interface is discussed.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2009년도 춘계 학술발표회
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• pp.326-330
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• 2009

In this study, coarse-grained geomaterials were mixed with cementing binder. To do that, typical soils from road construction sites were selected to assess the strength and stiffness characteristics of cemented geomaterials mixed with cement and recycled fly ash. Mechanistic evaluation on these samples was performed depending on the various binder contents. Increasing cementing content tend to increase the resilient modulus under repeated loadings and unconfined strength respectively. In addition, the toughness of cemented geomaterials was also estimated in order to check the ability to resisting fatigue failure.

• 한국철도학회논문집
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• 제19권2호
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• pp.204-212
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• 2016

국내 궤도 흙노반재료의 선정기준은 기초물성 값(입경, 200번체 통과량($P_{200}$), 4번체 통과량($P_4$), 균등계수($C_u$), 곡률계수($C_c$)등)을 이용하는 통일분류법에 의존하고 있으며, 선정된 궤도노반의 현장 다짐도는 들밀도 시험 및 반복평판재하시험 결과 $E_{v2}$에 의해 파악한다. 그러나 궤도노반의 변형 및 안정성에 미치는 가장 큰 영향요소는 강성(Stiffness)이므로, 노반재료의 분류특성은 기초물성 값 자체 보다는 다짐 후 변형계수를 활용하는 것이 보다 정확하다고 할 수 있다. 본 연구에서는 궤도노반에 사용되는 국내 대표적인 흙 재료의 기초물성과 현장시험에 의한 변형계수($E_{v2}$, $E_{vd}$)와의 상관식을 도출하였다. 이와 같은 상관특성은 성능설계를 위한 국내 고유의 철도궤도용 전용흙분류기준수립을 위한 근거로 사용될 수 있다.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2008년도 추계 학술발표회 제20권2호
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• pp.145-148
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• 2008

현행 AISC-LRFD, ACI 318과 국내의 설계지침에서는 CFT 기둥의 탄성계수와 항복강도 산정 시구속효과에 의한 축 강성의 증가를 반영하고 있지 않고 있다. 또한 AISC-LRFD와 ACI 318의 제시된 탄성계수와 항복강도의 산정방법으로 계산된 값이 차이가 큰 문제점이 있다. 본 연구에서는 CFT(Rectangular) 기둥을 강관의 두께 및 충진 콘크리트의 강도에 따른 시험체를 9개 제작하여, 실험을 통하여 AISC-LRFD, ACI 318과 국내의 설계지침과 비교하였다. 본 연구에서의 실험결과 현행 AISC-LRFD, ACI 318과 국내의 설계지침의 CFT 기둥의 항복강도는 실제 CFT 기둥의 항복강도와는 큰 차이가 있는 것으로 나타났다.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2005년도 춘계 학술발표회 논문집
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• pp.33-40
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• 2005

Impact-echo test, a kind of simple and economical method to evaluate the integrity of drilled piles has some limitations to use because the stress wave can be generated only on the head of a pile and the wave propagation in the pile with surrounding soils are very complicated. Numerical analyses and model tests in the laboratory have shown that both the ratio of length to diameter of a pile and the stiffness ratio of pile to soil have influence on the resolution of testing results. Full scale testing piles which have artificial defects were used to verify the capability of impact-echo technique as a tool for the pile integrity evaluation. Behaviour of the reflected signal of stress wave was investigated according to the type of defects. Elastic modulus of the pile was calculated using the wave velocity in the pile and the unconfined strength of concrete specimen. Influences of the stiffness difference between the pile and the ground on the characteristics of a wave signal were also examined.