• 한국소음진동공학회논문집
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• 제18권11호
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• pp.1157-1169
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• 2008

This paper presents spectral element formulation which approximates Lamb wave propagation by PZT transducers bonded on a thin plate. A two layer beam model under 2-D plane strain condition is introduced to simulate high-frequency dynamic responses induced by a piezoelectric (PZT) layer rigidly bonded on a base plate. Mindlin-Herrmann and Timoshenko beam theories are employed to represent the first symmetric and anti-symmetric Lamb wave modes on a base plate, respectively. The Euler-Bernoulli beam theory and 1-D linear piezoelectricity are used to model the electro-mechanical behavior of a PZT layer. The equations of motions of a two layer beam model are derived through Hamilton's principle. The necessary boundary conditions associated with the electro-mechanical properties of a PZT layer are formulated in the context of dual functions of a PZT layer as an actuator and a sensor. General spectral shape functions of response field and the associated boundary conditions are obtained through equations of motions converted into frequency domain. Detailed spectrum element formulation for composing the dynamic stiffness matrix of a two layer beam model is presented as well. The validity of the proposed spectral element is demonstrated through numerical examples.

• 한국의류학회지
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• 제24권6호
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• pp.810-818
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• 2000

The purpose of this study was to analyze the effect of geometrical structure on the moisture transport properties of nonwoven batting materials. Two types of nonwovens were used such as single and double layered nonwovens. Steady and dynamic state water vapor transport properties were measured by absorption, evaporation and cobaltous chloride method respectively. The results of this study were as follows: 1) Geometrical structure affected water vapor evaporation, but there were no differences between single and double layered nonwovens in moisture absorption. Thickness and air permeability were influencing factor on water vapor transport rate. 2) Directionality of double layered nonwoven was observed both in steady and dynamic state moisture transport. There were differences between upper and lower layer of double layered nonwoven both in moisture absorption rate and color change by cobaltous chloride method. 3) In dynamic state of water vapor transport rate, single layered nonwoven reached more rapidly at the established relative humidity. It was confirmed that geometrical structure affected water vapor evaporation and hydrophilicity of fiber affected moisture absorption because there were much more water vapor transport rate by evaporation than absorption within the same period of time.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2006년도 춘계학술대회 논문집
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• pp.145-148
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• 2006

Cold gas dynamic spray is a relatively new coating process by which coatings can be produced without significant heating during the process. Cold gas dynamic spray is conducted by powder sprayed by supersonic gas jet, and generally called the kinetic spray or cold-spray. Cold-spray was developed in Russia in the early 1980s to overcome the defect of thermal spray method. Its low process temperature can minimize thermal stress and also reduce the deformation of the substrate. Most researches on cold-spray have focused on micro scale coating, but our research team tried to apply this method to macro scale deposition. The macro scale deposition causes deformation of a thin substrate which is usually convex to the deposited side. In this research, the main cause of the deformation was investigated using 6061-T6 aluminum alloy and properties of deposited aluminum layer such as coefficient of thermal expansion, Elastic modulus, hardness, electric conductivity were measured. From the result of the analysis, it was concluded that compressive residual stress was the main reason of substrate deformation while CTE had little effect.

• 한국재료학회지
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• 제26권5호
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• pp.271-280
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• 2016

When a single inorganic precursor is used for the synthesis of a sol-gel coating, there is a problem of cracking on the surface of coating layer. In order to solve this problem of surface cracking, we synthesized inorganic-organic coatings that have hybrid properties of inorganic and organic materials. Sols of various ratios (1:0.07, 0.2, 0.41, 0.82, 1.64, 3.26, 6.54, 13.2) of an inorganic precursor of Tetrabutylorthotitanate ($Ti(OBu)_4$, TBOT) and an organic precursor of ${\gamma}$-Methacryloxy propyltrimethoxysilane (MAPTS) were prepared and coated on stainless steels (SUS316L) by dip coating method. The binding structure and the physical properties of the synthesized coatings were analyzed by FT-IR, FE-SEM, FIB (Focused Ion Beam), and a nano-indenter. Dynamic polarization testing and EIS (electrical impedance spectroscopy) were carried out to evaluate the micro-defects and the corrosion properties of the coatings. The prepared coatings show hybrid properties of inorganic oxides and organic materials. Crack free coatings were prepared when the MAPTS ratio was above a critical value. As the MAPTS ratio increased, the thickness and the corrosion resistance increased, and the hardness decreased.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2008년도 춘계학술대회논문집
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• pp.189-195
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• 2008

The vibration isolator system(VIS) which has very low natural frequency could be designed by applying an axial compressive force to the beam-column flexure(BCF). In this paper a new shape of the BCF is suggested. It has stepwise axially varying properties by viscoelastic damping layer. So it has internal structural damping by damping layer during deformation. First the analytic solution is obtained for the BCF. And its critical load, buckling mode, stiffness and stress distributions are investigated. Also the dynamic properties of the VIS consist of the damping layered BCF are studied. Finally the optimal design procedure of damping layered BCF for the VIS is suggested. The improved performance of suggested VIS is verified by some experiments.

• 한국자기학회지
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• 제7권6호
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• pp.314-320
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• 1997

폴리에스터 film 위에 자성도료를 도포 후 자성체의 배향 거동을 살펴보았다. static orientation 처리하여 평가한 결과 자성도료가 도포된 film이 배향자석을 통과할 때 배향자석의 입구측과 출구측에서 배향성이 최대로 나타나나 출구측이 약간 낮게 나타났으며 배향자석의 출구를 지나면서 static energy의 감소와 entropy의 증가에 의하여 도막의 건조과정 중 배향성은 서서히 감소되다가 완전히 건조되면서 일정한 수준으로 유지되었다. 그리고 film의 중심부보다 양쪽의 edge 부위에서의 배향성은 떨어지는데 그 원인은 배향자석의 형태에 기인하는 것으로 생각된다. Dynamic orientation 처리하여 평가한 결과 자기 tape에서 자성도막의 배향성이 향상됨에 따라 전 대역에서의 출력 특성은 향상되었으며 건조 조건에 따라서도 tape의 배향성이 변하였다. 따라서 자기 tape의 출력특성을 향상시키기 위하여는 배향자석의 설계 및 자성도료의 건조 조건 등의 검토가 필요하다고 생각한다.

• 한국지반공학회논문집
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• 제31권11호
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• pp.41-48
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• 2015

대규모 지반침하 및 지반함몰로 인한 재산, 인명피해를 사전에 예방하기 위하여 지반의 공동 및 이완구간에 대한 조사는 필수적이다. 최근, 지하투과레이더를 이용한 지반침하 및 지반함몰 구간 예측과 관련된 연구가 활발히 진행되고 있으나, 기존의 지하투과레이더 탐사에서는 전기적 임피던스가 서로 다른 층간 경계면 심도만을 산정하므로 조밀한 지반과 느슨한 지반을 서로 반대로 예측하는 오류를 범할 수 있었다. 본 연구에서는, 지하투과레이더로부터 획득된 전자기파의 반사파 특성을 이용하여 이완구간 심도를 추정하고자 하였다. 이완구간에 따른 신호획득을 위하여 과거 침하이력이 있었던 현장을 대상으로 지하투과레이더 탐사가 수행되었으며, 결과의 상호비교 및 검증을 위하여 동적 콘 관입시험이 수행되었다. 전자기파의 반사특성 분석 결과, 지하투과레이더 안테나에서 처음 측정된 신호와 조밀한 지반에서 반사되어 측정된 전자기파는 동일한 위상을 보이며, 느슨한 지반에서 반사되는 경우 안테나에서 처음 측정된 신호와 반대 위상을 보이는 것으로 나타났다. 획득된 지하투과레이더 신호로부터 대상지반의 이완구간 심도 산정 및 동적 콘 관입지수와 상호비교 결과, 지하투과레이더 신호 분석으로부터 산정된 이완구간 또는 조밀한 구간의 심도는 높은 신뢰도로 산정되었다. 본 연구에서 수행된 지하투과레이더 신호획득 및 분석과정은 지반 불연속층의 심도산정뿐만 아니라 이완구간 산정에 활용될 수 있을 것으로 판단된다.

• 한국도로학회논문집
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• 제17권4호
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• pp.53-61
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• 2015

PURPOSES : The objective of this study is to evaluate the SDAR (solvent deasphaltene residue), which is obtained from the solvent deasphalting (SDA) process, as a pavement material. METHODS : The physical properties of the SDAR were evaluated based on its chemical composition, and asphalt mixtures with the SDAR were fabricated and used for the evaluation of mechanical properties. Firstly, the chemical composition of SARA (saturate, aromatic, resin and asphaltene) was analyzed using the TLC-FID (thin-layer chromatography-flame ionization detector). Moreover, the basic material properties of the asphalt binder with the SDAR were evaluated by the penetration test, softening point test, ductility test, and PG (performance grade) grade test. The rheological properties of the asphalt binder with the SDAR were evaluated by the dynamic shear modulus ($G^*$) obtained using the time-temperature superposition (TTS) principle. Secondly, the mechanical properties of the asphalt mixtures with the SDAR were evaluated. The compactibility was evaluated using the gyratory compacter. Moreover, the tensile strength ratio (TSR) was used for evaluating the moisture susceptibility of the asphalt mixtures (i.e., susceptibility to pothole damage). The dynamic modulus $E^*$, which is a fundamental property of the asphalt mixture, obtained at different temperatures and loading cycles, was used to evaluate the mechanical properties of the asphalt mixtures. RESULTS AND CONCLUSION : The SDAR shows stiffer and more brittle behavior than the conventional asphalt binder. As the application of the SDAR directly in the field may cause early failures, such as cracks on pavements, it should be applied with modifiers that can favorably modify the brittleness property of the SDAR. Therefore, if appropriate additives are applied on the SDAR, it can be used as a pavement material because of its low cost and strong resistance to rutting.

• 한국주조공학회지
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• 제27권5호
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• pp.203-208
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• 2007

The high temperature properties of vanadium and molybdenum added high silicon ductile iron, so called V-Mo-Si ductile iron, were investigated. The (V,Mo) complex carbides and Mo carbides precipitated at the cellular boundaries of the as-cast specimens. The microhardness of the (V,Mo) carbides were in the range of 553-619, while that of the Mo carbides in the range of 341-390. The thermo-mechanical tests were carried out with a Gleeble system at 700 and $800^{\circ}C$ under vacuum condition. The tensile strengths of the specimen tested at $700^{\circ}C$ with the dynamic deformation rate of 50 mm/sec and those with the static deformation rate of 0.15 mm/sec were 235.7 and 115.3 MPa, while the reduction in area were 23.7 and 22.4%, respectively. At the high dynamic deformation rates, the tensile strength was steeply increased due to promoting the brittle fracture of pearlite in the matrix of the specimens. But the changes of the reduction in area with the deformation rates on the same specimens were negligible. The weight gain of the V-Mo-Si specimens oxidized in the air atmosphere for 6 hours at 800 and $900^{\circ}C$ were 1.1 and 4.1.%, respectively. The cross-sectional microstructure of oxidized specimens consisted of the porous external scale layer grown outside from the original surface, the dense internal scale layer grown into the original surface, the decarburized ferrite layer between the internal scale and the matrix of base metal. The (V,Mo) carbides and Mo carbides formed in the matrix of as-cast specimen did not decompose during oxidation at 900 for 24 hours in air atmosphere.

• 공업화학
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• 제5권4호
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• pp.630-636
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• 1994

열화처리 후 고무와 황동이 피복된 강선코드의 접박계면 변화를 오제 광전자 분광기와 주사 전자현미경으로 조사하였다. 열열화 후에는 접착층의 부분 산화와 추가 성장이, 습윤열화 후에는 접착층과 황동의 부분 소실이, 동적열화 후에는 접착층의 파괴와 철심의 부식이 관찰되었다. 이러한 접착계면의 변화를 인장시험에서 측정된 접착 성질과 관련지어 고찰하였다.