• Geomechanics and Engineering
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• v.14 no.2
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• pp.203-209
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• 2018

Reliable estimation of compressive as well as tensile in-situ stresses is critical in the design and analysis of underground structures and openings in rocks. Kaiser effect technique, which uses acoustic emission from rock specimens under cyclic load, is well established for the estimation of in-situ compressive stresses. This paper investigates the Kaiser effect on marble specimens under cyclic uniaxial compressive as well as cyclic uniaxial tensile conditions. The tensile behavior was studied by means of Brazilian tests. Each specimen was tested by applying the load in four loading cycles having magnitudes of 40%, 60%, 80% and 100% of the peak stress. The experimental results confirm the presence of Kaiser effect in marble specimens under both compressive and tensile loading conditions. Kaiser effect was found to be more dominant in the first two loading cycles and started disappearing as the applied stress approached the peak stress, where felicity effect became dominant instead. This behavior was observed to be consistent under both compressive and tensile loading conditions and can be applied for the estimation of in-situ rock stresses as a function of peak rock stress. At a micromechanical level, Kaiser effect is evident when the pre-existing stress is smaller than the crack damage stress and ambiguous when pre-existing stress exceeds the crack damage stress. Upon reaching the crack damage stress, the cracks begin to propagate and coalesce in an unstable manner. Hence acoustic emission observations through Kaiser effect analysis can help to estimate the crack damage stresses reliably thereby improving the efficiency of design parameters.

• 한국신재생에너지학회:학술대회논문집
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• 2011.05a
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• pp.148.1-148.1
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• 2011

본 연구에서는 가스 하이드레이트의 미래 상업생산을 위한 연구활동으로 동해 울릉분지 현장시료를 채취하여 가스 하이드레이트 함유토의 열전도 현상에 관한 연구를 실시하였다. 두 종류의 현장시료를 이용하여 메탄 하이드레이트를 생성하여 공극비 및 포화도에 따라 조건을 달리하여 실험을 수행하였다. 열전도도 측정을 위하여 Transient Plane Source (TPS) 기법을 이용하였다. 현장시료의 사용에 앞서 예비실험으로써 F110표준사를 사용, 비교 분석 자료로써 활용하였다. 하이드레이트 생성 확률을 높이는 기법으로써 불포화시료를 동결, 해동 후 가스를 주입하였으며 동결된 불포화 시료의 열전달양상의 변화를 함께 고찰하였다. 실험결과, 하이드레이트의 포화도가 증가함에 따라 함유토의 열전도도의 증가함을 알 수 있어다. 거의 동일한 물과 GH의 열전도도에도 불구하고 하이드레이트 결정화 작용으로 동일한 포화도의 불포화 시료와 비교하여 약간의 상승을 보였다. 또한 공극비 및 흙을 구성하는 미네랄의 성분에 따라 열전도도의 발현 양상이 상이함을 관찰하였다. 이에 차후 하이드레이트 생산을 위한 현장 측정 및 전산 모사시 이에 관한 고려가 필요할 것으로 사료된다.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.28 no.7
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• pp.1021-1028
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• 2004

Kim et al. suggested an experimental method to determine the Q parameter in situ from the out-of-plane displacement and the in-plane strains on the surface of side necking near the crack tip. In this paper, the procedure to evaluate the stress triaxiality near a crack tip such as the Q parameter is to be polished in the details for simplicity and accuracy. That is, Q and hydrostatic stress are determined only from the out-of-plane displacement, but not using in-plane strain, which is hard to measure. And also, the plastic modulus is determined by an alternative way. Through three-dimensional finite element analyses for a standard CT specimen with 20% side-grooves, the validities of the new procedures are examined in comparison to the old ones. The effect of location where the displacements are measured to determine the stress triaxiality is explored.

• Proceedings of the Korean Society of Soil and Groundwater Environment Conference
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• 2002.04a
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• pp.30-33
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• 2002

In this study, feasibility of using hydrogen peroxide as a chemical oxidant for in-situ treatment by EK-Fenton technology were investigated. Kaolinite, kaolinite/sand mixture and illitic soil spiked by phenol and phenanathrene were used and variation of electrochemical characteristics were examined by EK-Fenton test. For kaolinite that having low buffer capacity, hydrogen peroxide was injected effectively from anode reservoir. However illitic soil that having relatively higher buffer capacity had low hydrogen peroxide introducing efficiency. The test results showed that Hydrogen ions generated by current increased during the treatment decreased under pH 3 in the most of kaolinite specimen. Therefore, stabilized hydrogen oxide was injected more effectively in the kaolinite specimen. This study suggests that efficiency of hydrogen peroxide injection by EK-Fenton thechnoloty is dependent of variation of pH in the soil

• Proceedings of the Korean Institute of Building Construction Conference
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• 2019.05a
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• pp.252-253
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• 2019

Corrosion of rebars in reinforced concrete structures is a major factor that shortens the life of the structure. As corrosion progresses, the adhesion between the concrete tissues and the rebar decreases and the cracks in the concrete due to the expansion of the oxide intensify. Although it is necessary to measure corrosion behavior of rebars inside the concrete to measure degradation of structures due to rebar corrosion, no studies have been conducted to measure corrosion of rebars in In-situ state. In this study, corrosion of rebars in reinforced concrete specimens was attempted to be quantified using micro-computer tomography. Since corrosion of concrete takes several months per 10mm of cover, accelerated corrosion techniques were applied. Accelerated corrosion on the specimen was conducted by applying a 10 V magnetic field to the buried rebar and external electrodes with the specimen submerged in a 10% calcium chloride solution. The experiment found that within two weeks, more than 40% of rebar reduction occurred, and the cracks in the radial cracks occurred through the concrete structure, leading to the transfer of the oxide produced through the cracks to the surface of the specimen.

• Steel and Composite Structures
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• v.9 no.3
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• pp.209-221
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• 2009

Heating correction, through heating and flattening a structure with a pressing machine, is the in-situ method used to repair buckled steel structures. The primary purpose of this investigation is to develop an FEM model which can predict the mechanical response of heat-corrected plates accurately. Our model clarifies several unsolved problems. In previous research, the location of the imperfection was limited to the center of the specimen although the mechanical behavior is strongly affected by the location of the imperfection. Our research clarifies the relationship between the location of the imperfection and the mechanical behavior. In addition, we propose further reinforcement methods and validate their effectiveness. Our research concludes that the strength of a buckled specimen can be recovered by heating correction and the use of an adequate stiffener.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 1999.11a
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• pp.233-239
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• 1999

The feasibility of an ultrasonic technique using a pulse-echo method of normal-incident compressional waves was evaluated for its sensitivity to the worn surface and near surface damage due to wear. Worn surfaces were generated at various oscillation frequency under a given load and amplitude and these surface were in situ monitored using a ultrasonic wave detection system. Analysis of the ultrasonic waves received from the worn surface revealed a close relationship between the surface and near-surface damage and the maximum echo-amplitude of the compressional waves. The ultrasonic technique was successful in assessing the level of severity of the worn surface in real time during the wear process. It is also shown that the wear depth can be easily measured by the calculation of change of the specimen thickness based on the wave speed measured for the specimen medium.

• Tribology and Lubricants
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• v.16 no.5
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• pp.351-356
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• 2000

The feasibility of an ultrasonic technique using a pulse-echo method of normal-incident compressional waves was evaluated for its sensitivity to the worn surface and near surface damage due to wear. Worn surfaces were generated at various oscillation frequency under a given load and amplitude and these surface were in situ monitored using a ultrasonic wave detection system. Analysis of the ultrasonic waves received from the worn surface revealed a close relationship between the surface and near-surface damage and the maximum echo-amplitude of the compressional waves. The ultrasonic technique was successful in assessing the level of severity of the worn surface in real time during the wear process. It is also shown that the wear depth can be easily measured by the calculation of change of the specimen thickness based on the wave speed measured for the specimen medium.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2004.10a
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• pp.1278-1281
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• 2004

Several workers reported the relationship between osteoporosis and age-related reductions in the BV/TV (bone volume fraction) of vertebral trabecular bones. However, there were few micro finite element (micro-FE) models to account for the treatments of the osteoporotic trabecular bone. In the present study, micro-FE models of osteoporotic and hormone-treated bone models were constructed to analyze the effect of specimen location and boundary condition on mechanical characteristics of hormone treatment model for osteoporotic trabecular bone. Top and bottom sections of specimens were also investigated individually to study the effect of specimen location. Hormone-treated models were allowed to have the same relative BV/TV (13.4％) as that used in models of previous researchers. The present study reported the elastic and plastic characteristics of the osteoporosis and hormone-treated bone models. In the present study, in-situ boundary condition was applied to the simulated compression tests for in-vivo condition of vertebral trabecular bone. The present study indicated that the hormone therapy was likely to improve the mechanical characteristics of osteoporotic bones and the mechanical characteristics of vertebral trabecular bone specimen were dependent on the captured location and boundary condition.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09a
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• pp.287-288
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• 2006

Two approaches for the fabrication of tailored powder composites with specially distributed pore-grain structure and chemical composition are investigated. Electrophoretic Deposition (EPD) followed by microwave sintering is employed to obtain functionally graded materials (FGM) by in-situ controlling the deposition bath suspension composition. $Al_2O_3/ZrO_2$ and zeolite FGM are successfully synthesized using this technique. In order to fabricate an aligned porous structure, unidirectional freezing followed by freeze drying and sintering is employed. By controlling the temperature gradient during freezing of powder slurry, a unidirectional ice-ceramic structure is obtained. The frozen specimen is then subjected to freeze drying to sublimate the ice. The obtained capillary-porous ceramic specimen is consolidated by sintering. The sintering of the graded structure is modeled by the continuum theory of sintering.