• Proceedings of the Korean Society For Composite Materials Conference
• /
• 2000.04a
• /
• pp.59-62
• /
• 2000

In this study, the distribution of the effective modulus was investigated statistically Plain weave structures were modeled with random stacking phase shift angles and the effective modulus was calculated by the unit cell analysis. The analysis results indicated that the effect of random phase shift angles was significant on the modulus distribution. As the number of layers increased, the coefficient of variation decreased and higher degree of homogeneity was attained.

• Proceedings of the Korean Society For Composite Materials Conference
• /
• 2001.10a
• /
• pp.74-78
• /
• 2001

In this study, out-of-plane properties and CTEs were predicted for 8-harness satin weave textile composites. The properties were calculated by unit cell analysis for configurations with varied waviness ratio and phase shifts. Macro elements were employed to reduce the computer resource requirement. It was found that the out-of-plane properties and CTEs were varied as the phase shift changed. However the dependency was much weaker than the in-plane properties.

• Journal of the Korean Society for Nondestructive Testing
• /
• v.16 no.1
• /
• pp.19-28
• /
• 1996

This study has investigated the optimization of NDT method and the minimum detectable defect size for complex structures such as the solid propellant rocket motor using real time X-ray imaging system. Test specimens were made of steel plates with various defect size, and installed with proper thickness for which solid propellant, rubber, and case converted to the steel equivalent thickness according to the radiographic equivalent theory. As the results, this examination obtained optimum magnification and X-ray energy, dose rate according to steel equivalent thickness, also, obtained the relationship between minimum detectable defect size and the ratio(defect depot/object thickness). Thus, this simulated test is the preliminary procedure before performing NDT for real objects, and is possibly applied for NDT of other complex structures.

• Journal of the Computational Structural Engineering Institute of Korea
• /
• v.14 no.4
• /
• pp.455-467
• /
• 2001

In this study, the stacking phase shift effect on the effective property and stress distribution was investigated for 8-harness satin weave textile composites under uni-axial tension. Textile configurations with varied phase shifts were modeled by unit cells and repeating boundary conditions were applied at the outer periodic surfaces. The effective property and stress were calculated by the unit cell analysis using macro-element to reduce the computational resource. It was found that stresses were dependent on the variation of tow arrangement of adjacent layers. The in-phase and the shifted configurations showed large differences in the stress distribution pattern. The stress level was very high in the resin region and the distribution of the maximum stresses was widely scattered.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.31 no.9
• /
• pp.18-25
• /
• 2003

In this paper, thermal conductivities of carbon-phenolic 8-harness satin weave composite, ACP302, were measured and predicted. In the analysis, the satin weave unit cell was identified and modeled discretely by 3-dimensional finite elements, considering the interlaced fiber tow architecture microscopically. At the unit cell boundary, the corresponding periodic boundary conditions were applied. The results were analyzed to investigate the effect of microstructural parameters such as stacking phase shifts, waviness ratio, and fiber volume fraction. The conductivities were also obtained by experiments and compared with the numerical results.

• Journal of the Korean Chemical Society
• /
• v.40 no.5
• /
• pp.308-316
• /
• 1996

The electrochemical behavior of glassy carbon and PVDF synthesis graphite materials with compact surface have been characterized by impedance spectroscopy. The Faraday-impedance both carbon materials were depended highly on polarization and the difference of electrochemical behavior accord to structure of surface between glassy carbon and synthesis graphite was represented, in these evaluated equivalent circuits, PVDF synthesis graphite was indicated with form that is added resistance and capacitance by the hydrophobic binder to glassy carbon equivalent circuit.

• Electrical & Electronic Materials
• /
• v.3 no.4
• /
• pp.315-324
• /
• 1990

저저항(DuPont 1721, 100.OMEGA./sq.)과 고저항(1741, 10K.OMEGA./sq.)의 두 Ru계 후막저항체를 여러 조건에서 소결하여 소결막의 복소임피던스 특성과 임피던스의 주파수의존성을 1KHz-13MHz의 주파수 범위에서 조사하였다. 저저항 1721계의 경우 600.deg.C이상에서 소결한 모든 시편이 거의 저항성분(R)만으로 구성된 등가회로에 해당되는 복소임피던스 거동을 보였으며 임피던스에 미치는 주파수 의존성은 크게 나타나지 않았는데 5KHz까지는 주파수에 따라 변화가 없다가 그 이상의 주파수에서 주파수 증가에 따라 약간씩 증가하였다. 고저항 1741 후막저항체의 경우는 소결조건에 따라 복소임피던스 거동과 임피던스에 미치는 주파수 의존성이 달리 나타났다. 600.deg.C에서는 용량(C) 성분만으로 구성된 등가회로에 해당하는 복소임피던스 거동을 얻었고 주파수 증가에 따라 임피던스가 직선적으로 감소하였으며 700.deg.C이상 900.deg.C까지는 저항(R)과 용량(C)이 병렬로 연결되는 형태의 등가회로에 해당하는 복소임피던스 거동을 얻었고 이때의 임피던스의 주파수 의존성은 저주파수 영역에서는 임피던스가 주파수에 변함없이 일정하다가 5KHz이상의 주파수에서는 주파수 증가에 따라 임피던스가 직선적으로 감소하였다. 1000.deg.C반응에서의 복소임피던스 거동은 RCL성분이 병렬로 연결된 형태의 등가회로에 해당되는 결과를 얻었으며 임피던스도 작아지고 주차수 의존성도 현저하지 않았다.

• Fire Science and Engineering
• /
• v.31 no.6
• /
• pp.91-98
• /
• 2017

The present paper is a study on the tracking characteristics depending on accelerated degradation of PVC insulation material. In order to insulation degradation of PVC insulation material, the Arrhenius equation, a type of accelerated degradation test formula, was used to conduct accelerated degradation experiments with experiment samples prepared at the following age equivalents: 0, 10, 20, 30 and 40 years. Afterwards, a tracking experiment was conducted on the accelerated experiment samples as part of the KS C IEC 60112 criteria. When measuring the PVC tracking features according to the accelerated aging, the results showed that when 0.1% of ammonium chloride was added to the PVC insulating material, but no tracking occurred. However, depending on the age equivalent, The results of analyzing the current waveform and voltage waveform of the tracking propagation process showed the age equivalent from 0 years to 40 years displayed a break down in insulation resistance and even the BDB(before dielectric breakdown) sections did not maintain the same functionality of the original material. Based on a criterion of an age equivalent of 0 years, material with an age equivalent of 10 years posed a 1.4 times greater risk, material with an age equivalent of 20 years posed a 2 times greater risk, material with an age equivalent of 30 years posed a 4.6 times greater risk, and material with an age equivalent of 40 years posed a 7 times greater risk.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 1995.04a
• /
• pp.153-158
• /
• 1995

보 및 평판의 진동에 대해서 에너지의 손실은 재료감쇠를 이용한 표면감쇠처리나 지지부에서의 감쇠처리에 의하여 증가될 수 있다. 감쇠재료를 이용한 표면감쇠처리의 예로서 보/평판 표면에 접착되는 감쇠 테이프나 코팅등은 아주 효과적임이 입증되었다. 마찬가지로 지지부 감쇠처리는 점탄성재료의 삽입에 의해서 설명될수 있다[1]. 보/평판의 감쇠에 대한 최근의 많은 연구들은 진동하고 있는 보/평판의 표면에 적용하는 감쇠 테이프 혹은 적층형태의 감쇠 처리방법에 대해서 주로 수행되었다. 일반적으로 표면감쇠처리방법은 진동감소에 아주 효과적이지만 실제 적용상에서 항상 가능한 것은 아니며, 이와 같은 경웨는 지지부 감쇠 처리방법에 의존하게 된다[2]. 감쇠특성을 갖는 점탄성재료를 실제로 적용할 때 보/평판의 유한한 길이가 점탄성재료로 지지되며 점탄성재료의 물성치와 치수에 따라서 계의 모우드 매개변수(고유진동수, 계의 손실계수 그리고 모우드형상)가 크게 달라진다. 그리고 이와 같은 계에 대해서는 지지부의 거동보다는 전체 시스템의 고유진동수와 손실계수 그리고 보 영역에서의 모우드 형상에 더 관심이 있으므로 지지부 영역을 집중매개변수(lumped parameter)로 나타내어 계를 해석할 수 있다. 일반적으로 보와 평판의 경계에서는 병진 및 회전방향의 강성 뿐만 아니라 두 강성사이에 연성효과도 동시에 발생하게 되므로 이 항을 고려하여 계를 모델링해야 한다. 본 연구에서는 우선 점탄성 재료에 의한 지지부영역의 등가 강성계수들을 구하고 경계에 강성행렬을 갖는 보의 등가시스템을 얻는다. 그리고 등가시스템의 주파수방정식으로부터 모우드 매개변수에 대한 지지부의 영향을 살펴본다. 또한 시스템이 비교적 복잡한 사각 평판의 진동에 대해서도 동강성행렬법(dynamic stiffness matrix method)을 이용하여 해석하고자 한다. 수준임이 입증되었다. 본 연구의 결과를 토대로우리나라 젊고 건강한 남성에게 적합한 무게상수는 작업자군에 대하여 25.05kg, 학생군에 대하여 20.24kg 으로 나타나 이는 미국 NIOSH 안전기준과 대체로 일치함을 발견하였다.ive structures utilized in Client/server architecture for distribution and cooperative processing of application between server and client this study presents two different data management methods under the Client/server environment; one is "Remote Data Management Method" which uses file server or database server and. the other is "Distributed Data Management Method" using distributed database management system. The result of this study leads to the conclusion that in the client/server environment although distributed application is assumed, the data could become centralized (in the case of file server or database server) or decentralized (in the case of distributed database system) and the data management method through a distributed database system where complete responsi

• Journal of Korea Water Resources Association
• /
• v.42 no.8
• /
• pp.619-629
• /
• 2009

The objective of this study is to estimate bed-resistance in gravel-bed rivers using the equivalent roughness height($k_s$). We calculated the friction factor(f) with the measured data from 8 domestic gravel-bed rivers and investigated the size distributions of the bed materials. The averaged $k_s$ in each cross-section, which is determined under the hypothesis that the vertical velocity distribution follows the logarithmic law, is compared with the reach $k_s$ which is calculated with the cumulative grain diameter distribution curve of bed materials. Moreover, the applicability of existing formulae, such as Strickler type equations, is examined by comparing with Manning's n value converted from the $k_s$. According to the results, the reach $k_s$ proves to be a good indicator of representative characteristic of bed materials in a reach, and the Manning's n based on the reach $k_s$ is appropriate for practical estimation of the bed-resistance, for RMS errors between calculated and measured Manning's n is less than 0.003. The correlation between the $k_s$ and specified bed-material size($D_i$) is very low, so it is difficult to select a proper one among the existing empirical equations.