• 한국생산제조학회지
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• 제23권6호
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• pp.533-538
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• 2014

We fabricated grooved mushroom structures with anisotropic wettability on silicon substrates using basic MEMS processes. The geometry of these grooved mushroom structures could be changed by controlling the additional IPA solution during Si etching by TMAH solution. To understand anisotropic wettability, contact angles (CAs) of hexadecane droplets were measured in the orthogonal and parallel directions to grooved lines. The CA measurement results displayed anisotropic wetting on the grooved mushroom structures. However, specimens with $80{\mu}m$ distance between top layers displayed isotropic and superoleophobic wetting. This study demonstrates that the thickness of the top layer is more critical than the width or height of the ridge when determining the wettability of organic solvent. Despite the wide distance between top layers ($80{\mu}m$), the specimen with a thin top layer (100 nm) showed highly anisotropic wetting and low CA due to the pinning of droplets at the edge of the top layer.

• Composites Research
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• 제12권2호
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• pp.82-90
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• 1999

일반적 직교이방성 복합재료의 기계적 성질을 측정하기 위한 간단한 실험방법으로 편축시험편에 대한 인장시험 또는 굽힘시험이 흔히 사용된다. 이때 재료의 특성상 인장시험편에서는 전단변형이 발생될 수밖에 없으며, 굽힘시험편에서는 비틀림변형을 피할 수 없다. 그러나, 시험장치의 그림 또는 지지대에서의 구속은 커플링에 의한 변형을 수용할 수 없고, 따라서 이에 따른 응력집중을 유발한다. 결과적으로 불균일한 변형장과 응력장을 낳게되어 측정값의 정확도를 저하시키며, 조기 파손으로 인한 복합재료 강도의 과소평가를 가져오게 된다. 본 연구에서는 이를 완화하기 위한 방안으로 시험편 경계면 형상의 변화를 제안한다. 이를 위하여 경사좌표계에서의 적층이론을 유도하며, 각 시험조건에 대한 특성방정식을 구한다. 유한요소해석을 수행하여 특정방정식을 이용하여 수정된 시험편 형상의 유용성을 보인다.

• Steel and Composite Structures
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• 제33권5호
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• pp.629-640
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• 2019

This paper presents a theoretical and finite element (FE) study on the stress intensity factors of double-edged cracked steel beams strengthened with carbon fiber reinforced polymer (CFRP) plates. By simplifying the tension flange of the steel beam using a steel plate in tension, the solutions obtained for the stress intensity factors of the double-edged cracked steel plate strengthened with CFRP plates were used to evaluate those of the steel beam specimens. The correction factor α₁ was modified based on the transformed section method, and an additional correction factor φ was introduced into the expressions. Three-dimensional FE modeling was conducted to calculate the stress intensity factors. Numerous combinations of the specimen geometry, crack length, CFRP thickness and Young's modulus, adhesive thickness and shear modulus were analyzed. The numerical results were used to investigate the variations in the stress intensity factor and the additional correction factor φ. The proposed expressions are a function of applied stress, crack length, the ratio between the crack length and half the width of the tension flange, the stiffness ratio between the CFRP plate and tension flange, adhesive shear modulus and thickness. Finally, the proposed expressions were verified by comparing the theoretical and numerical results.

• 한국안전학회지
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• 제17권4호
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• pp.5-10
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• 2002

For fitness-for-service evaluation of high temperature plant components with defects, crack growth life must be assessed properly as indicated in the recent draft of API 579 code. Type 308 stainless steel has been widely used as a field weld material in the petrochemical industry. In this study, creep crack data of type 308 stainless steel are collected and re-analyzed using $C_t$ as a characterizing fracture parameter. A unique da/dt versus $C_t$ relationship was obtained despite of difference of creep deformation constant of the reviewed materials and specimen geometry of the tested specimens. The obtained results can be employed for crack growth life assessment and fitness-for-service evaluation for the cracks in high temperature components. It is also argued that since the effect of creep properties and other material variability on the creep crack growth behavior would be minor the obtained model may be applied for most of the 308 stainless steels.

• 한국실내디자인학회논문집
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• 제15권3호
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• pp.14-23
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• 2006

As a proto-modernist work the Amsterdam Exchange has been regarded as a specimen of Structural Rationalist's architecture. Because of its ma]or steel structure, use of geometry, and reminiscence of Gothic the designer of the building was labeled by Kenneth Frampton as one of the apostles of Viollet le Duc. The architect was Hendrick Petrus Berlage. Contrary to above Nicolaus Pevsner claimed that Berlage's architectural discourse was 'Anti-Rational' because of its anachronistic formal language, Expressionism. In terms of structure Berlage's idea is rational, whilst formally 'Anti-Rational'. These polarised view points were due to the legacies of Modern Architecture that was controled by hegemonic figures in terms not only of practical field but of historiography. The hegemonic figures wanted to see Berlage as what they wanted to see. With this idea, this paper is one of endeavours to collect fragmented history in the early modern architecture. The Amsterdam Exchange has a long term story until the opening. Without understanding the story we have to withhold an evaluation of Berlage's architecture.

• 한국해양공학회지
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• 제36권4호
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• pp.243-250
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• 2022

Subsea power cables are subjected to various external loads induced by environmental and mechanical factors during manufacturing, shipping, and installation. Therefore, the prediction of the structural strength is essential. In this study, experimental and theoretical analyses were performed to investigate the axial stiffness of subsea power cables. A uniaxial tensile test of a 6.5 m three-core AC inter-array subsea power cable was carried out using a 10 MN hydraulic actuator. In addition, the resultant force was measured as a function of displacement. The theoretical model proposed by Witz and Tan (1992) was used to numerically predict the axial stiffness of the specimen. The Newton-Raphson method was employed to solve the governing equation in the theoretical analysis. A comparison of the experimental and theoretical results for axial stiffness revealed satisfactory agreement. In addition, the predicted axial stiffness was linear notwithstanding the nonlinear geometry of the subsea power cable or the nonlinearity of the governing equation. The feasibility of both experimental and theoretical framework for predicting the axial stiffness of subsea power cables was validated. Nevertheless, the need for further numerical study using the finite element method to validate the framework is acknowledged.

• Steel and Composite Structures
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• 제51권3호
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• pp.325-335
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• 2024

Yielding dampers exhibit varying cyclic behavior based on their geometry. These dampers not only increase the energy dissipation of the structure but also increase the strength and stiffness of the structure. In this study, parametric investigations were carried out to explore the impact of angled U-shape damper (AUSD) dimensions on its cyclic behavior. Initially, the numerical model was calibrated using the experimental specimen. Subsequently, analytical equations were presented to calculate the yield strength and elastic stiffness, which agreed with the experimental results. The outcomes of the parametric studies encompassed ultimate strength, effective stiffness, energy dissipation, and equivalent viscous damper ratio (EVDR). These output parameters were compared with similar dampers. Also, the magnitude of the effect of damper dimensions on the results was investigated. The results of parametric studies showed that the yield strength is independent of the damper width. The length and thickness of the damper have the greatest effect on the elastic stiffness. Reducing length and width resulted in increased energy dissipation, effective stiffness, and ultimate strength. Damper width had a more significant effect on EVDR than its length. On average, every 5 mm increase in damper thickness resulted in a 3.6 times increase in energy dissipation, 3 times the effective stiffness, and 3 times the ultimate strength of the model. Every 15 mm reduction in damper width and length increased energy dissipation by 14% and 24%, respectively.

• 열처리공학회지
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• 제37권5호
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• pp.215-220
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• 2024

Slip lines and dislocation structures developed by deformation at 77 K, 292 K and 500 K have been investigated by an optical microscope and a high-voltage electron microscope. Slip patterns after the deformation by 4-5% at 77 K and 500 K are compared. From the slip line geometry, operation of both primary and secondary {111} slips have been confirmed. However, the primary slip lines formed at 77 K appear coarser and more pronounced than those at 500 K. This indicates that a larger number of dislocations have moved on the same plane at 77 K. Another characteristic difference noted here is that the slip lines are straight and pass through the specimen from one end to the other at 77 K. On the contrary, slip lines are rather faint at 500 K. The typical change found at 77 K is the increase in the [$0{\bar{1}}1$] dipole dislocations and generation of the [$10{\bar{1}}$] screw dipoles upon increase in the strain from 1.2% to 5.2%. This is the indication that the straight dipole dislocations were formed by a pinning effect due to jogs generated by mutual cutting between primary and secondary dislocations. Extremely fine slip has been noted after deformation at 500 K indicating that the usual Frank-Read source is not operative at high temperatures due to the strong KW locking.

• Composites Research
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• 제15권4호
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• pp.23-31
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• 2002

시편 게이지 면적($길이{\;}{\times}{\;}폭$)의 이차원 크기효과가 T300/924 $[45/-45/0/90]_3s$ 탄소섬유/에폭시 적층판의 압축거동에 대해 조사하였다. 개조된 압축시험치구(ICSTM)와 좌굴방지장치가 $30mm{\;}{\times}{\;}30mm,{\;}50mm{\;}{\times}{\;}50mm,{\;}70mm{\;}{\times}{\;}70mm,{\;}90mm{\;}{\times}{\;}90mm$의 게이지 길이와 폭을 가진 시편들의 압축시험에 사용하였다. 모든 경우의 파괴들은 시편 게이지 길이 내에서 주로 갑자기 발생하였다. 파괴 후 분석결과는 $0^{\circ}$층의 섬유의 미소좌굴에 의해 파괴를 시작하여 최종파괴를 일으키는 임계파괴기구일 것으로 생각되었다. 이것은 매트릭스 지배적인 파괴를 의미하며, 초기섬유굴곡에 따라 파괴가 지배적으로 시작된다는 것을 말한다 이것은 또한 제작공정과 품질이 압축강도를 결정하는 중요한 역할을 한다고 볼 수 있다. 좌굴방지장치를 장착하고 시험할 때 장치의 볼트 조임 토크에 따라 시편과의 접촉마찰 등에 의해 실제 압축강도 보다 크게 나타나는 결과를 보였다. 좌굴방지장치의 영향을 유한요소법을 이용하여 해석한 결과 실제 압축강도 보다 7% 정도 크게 나타남을 확인하였다. 부가적으로 홀을 갖는 시편들의 압축시험도 수행되었다. 홀에 의한 국부응력집중이 적층판 강도에 지배적 요인이었다. 파괴강도는 홀 크기와 시편 폭이 증가할수록 감소하였으나 탄성응력집중계수로 예측된 값보다는 일반적으로 크게 나타났다. 이것은 사용된 복합재가 이상적인 취성재질이 아니라는 것을 의미하며 홀 주위에서 다소간의 응력이완이 발생한다고 볼 수 있다. X선 검사 사진분석에서 섬유좌굴과 층간분리형태의 손상이 파괴하중의 약 80%에서 홀 가장자리로부터 시작되었고 임계파괴크랙길이인 2-3mm의 불안정한 상태에 도달하기 전까지는 하중 증가와 더불어 안정되게 파괴가 진전되었다(시편의 기하학적 크기에 의존함). 이 손상과 파괴는 선형 cohesive zone 모델로 해석되었다. 노치없는 시편의 압축강도와 평면 파괴인성의 측정된 적층판 변수들을 사용하여 홀의 크기와 시편 폭의 함수로서 홀을 갖는 적층판의 압축강도를 성공적으로 예측하였다.

• 한국지하수토양환경학회지:지하수토양환경
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• 제8권4호
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• pp.1-11
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• 2003

압축력의 변화에 따른 균열 간극변화 양상을 측정하고 간극변화와 수리전도도와의 관계를 파악하기 위해 이 연구에서는 다섯 단계의 수직 일축압축력을 균열면에 연속적으로 가하면서 고해상도의 공초점 레이저 스캔 현미경 (confocal laser scanning microscope; CLSM)을 이용하여 간극의 크기를 측정하고 디지털 이미지를 획득하였다. 기존의 연구들과는 달리 이 연구의 측정방법은 압력변화에 대한 동일시료 간극의 반응을 연속적으로 파악할 수 있는 점이 특징이다. 측정결과는 간극크기가 일정하지 않은 불평탄한 균열형태를 매우 잘 나타내었다. 균열 조도(roughness)로 인해 압력에 따른 간극 변화량은 일정하지 않고 부분마다 다름을 보였다. 각 압력단계에서 간극변화에 따른 투수성 변화양상을 파악하고자 실내투수시험을 병행하여 실시한 결과, 각 압력단계에서의 투수성 변화도 일정한 감소율을 나타내지 않고 간극 변화율이 크더라도 투수율은 오히려 작은 경우도 관찰되었다. 현미경을 통해 측정한 물리적 간극과 실제 유체유동 경로가 되는 수리간극의 크기 차이를 파악하기 위해 계산을 한 결과, 미미한 갈이지만 물리적 간극보다 작은 크기의 수리간극이 구해졌다. 또한, 실내투수시험 결과를 이용하여 구한 투수계수는 삼승법칙을 따르지 않는 것으로 드러났으며, 이러한 사실들은 균열 양쪽이 서로 평행하지 않고 불평탄한 양상을 가짐을 의미하는 것으로서, 현미경을 통해 직접 관찰한 간극양상과 잘 일치하는 것이다.