• Journal of the Korean Society for Nondestructive Testing
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• v.27 no.4
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• pp.321-327
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• 2007

In lock-in thermography, a phase difference between the defect area and the healthy area indicates the qualitative location and size of the defect. To accurately estimate these parameters, the shearing-phase technique has been employed which gives the shearing-phase distribution. The shearing-phase distribution has maximum, minimum, and zero points that help determine quantitatively the size and location of the subsurface defect. In experiment, the proposed technique is verified with artificial specimen and these related factors are analyzed.

• Polymer(Korea)
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• v.33 no.5
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• pp.446-451
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• 2009

Reliability evaluations of linear low density polyethylene (LLDPE) pipe with respect of thermal exposure time have been investigated in accordance with RS M 0042, which is a reliability standard for polymer pipe. As the thermal exposure time is prolonged, a progressive increase, until 250 days, in tensile strength and a slight increase in hardness are observed, while a proportional decrease in elongation at break is showed. These results can be explained by the increase of crystallinity, followed by the increase of crosslinking density, chain scission and the decrease in chain mobility, due to thermal oxidation as the exposure time increases. Long term hydrostatic pressure test result implies the existence of transition point from ductile to brittle fracture. Oxidation induction time (OIT) test is employed to monitor the thermo-oxidative degradation of LLDPE pipe. This result shows that after the exposure time is 250 days, the depletion of antioxidants added in LLDPE pipe occurs. An empirical equation as function of exposure time, under $100^{\circ}C$ thermal-degradation condition, is proposed to assess the remaining amount of antioxidants owing to thermo-oxidative degradation. Fourier transform infrared spectroscopy results show the increase of carbonyl (-C=O) and hydroxyl (O-H) function groups on the surface of thermally exposed LLDPE pipe. This result suggests that the hydrocarbon groups locally undergo the oxidation on the LLDPE surface due to thermal-degradation.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.28 no.3A
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• pp.341-347
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• 2008

Among coating systems used for steel bridge coatings on highway such as red lead-pigmented alkyd, chlorinated rubber, waterborne inorganic zinc, inorganic zinc/epoxy/urethane and inorganic zinc/epoxy/fluororesin, evaluation of deterioration degree and prediction of lifetime through regression analysis were carried out for coating systems widely used and grossly degraded. For evaluation of deterioration degree, 75 bridges on highway were selected, and evaluations were carried out according to point offering method regulated by Guideline of maintenance coating for steel bridges used in Korea Expressway Corporation. Lifetime prediction results showed 13.0~13.3 years for the whole nation, 11.8 years for urban and industrial region in the metropolitan area, 13.2 years for rural region except the metropolitan area, 13.5~13.7 years for chlorinated rubber coating systems, and 12.86 years for red lead-pigmented alkyd systems. For prediction of the rest life of coating, we tried to execute parallel translations of standard deterioration curve to current life and deterioration degree for both x and y axes, and it was thought that parallel translation for x axis corresponded to deterioration aspects in actual environment. Maximum and minimum equations were derived from standard deterioration equation by adding and subtracting error values deduced in regression analysis to/from each coefficient in order to establish maintenance coating criteria for overall steel bridges on highway. Whole domain was divided into 8 parts in order to predict the rest life of coating and optimum time of maintenance coating, and maintenance coating criteria for each 8 domains were presented.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.181-184
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• 2008

The concrete is relatively fireproof materials. However, long-term exposure to high temperatures in the concrete strength is a phenomenon that occurs in the rapid degradation. In such a case, even low-strength estimates concrete expression to the General Non-destructive inspection is not appropriate to use the estimate. To overcome this problem, various mix conditions of the concrete specimen under 23, 200, 400, 600, $800^{\circ}C$ to a temperature, the correlation relationship between the ultrasonic velocity and the strength of concrete specimen is investigated and analyzed. This analysis estimates the high-temperature strength of the damaged concrete expression Non-destructive inspection of the proposal.

• Journal of the Korea Institute of Military Science and Technology
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• v.4 no.1
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• pp.255-263
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• 2001

The main purpose of this paper is to investigate strength characteristics of Aluminum 2024-T3 in high temperature environment. Tensile test of Aluminum 2024-T3 has been carried out in high temperature environment. The stress-strain relations are investigated with temperature and Young's modulus, yield strength and ultimate strength are deduced from the test results. The modulus and strength of the test are compared with those of MIL HANDBOOK and tips on structural design in high temperature environment are suggested.

• Journal of Korean Society of Industrial and Systems Engineering
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• v.12 no.20
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• pp.25-32
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• 1989

열화수신포에 있어서 확률론적 신뢰도설계 및 단순스트레스와 강도의 고장모형은 렌덤 수치들로 구성된 각 분포의 간섭(Interference) 확률에 의해 이루어진다. 현재까지 이러한 분포모형들의 신경도는 분석적, 수치적 또는 모의실험방법론학에 의해서 단일추정치를 계산및 해석하여 왔으나 현실적으로는 스트레스 강도함수 분포의 간섭구간에 있어서 그 렌덤 변수들에 대한 완전한 실제의 분포들을 파악하기란 너무 복잡하고 때로는 불가능하다. 이를 위해서는 신뢰도의 상·하한 결정으로 신뢰도설계를 하는 방법이 고려된다. 본 연구에서는 스트레스와 강도의 렌덤 변수들에 대한 중복부분(Overlapping tails) 내에 있어서 각각의 주어진 구간확률을 제약조건으로 하여 최적신뢰도 한계를 결정 및 설계하는 새로운 기법을 제시한다. 설계신뢰도의 최적상한 및 하한 값은 제공하기 위하여 비선형모형인 Quadratic programming optimization 기법을 이용하여 신뢰도분석관점에 입각한 특수구조모형을 설정하고 이에 대한 수치예를 들어 예증하였다.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2012.07a
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• pp.330-332
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• 2012

H.264/AVC를 비롯한 대부분의 동영상 압축 표준에 의해 부호화 및 복호화된 영상은 블록화 현상(blocking artifacts)이 생긴다. 이러한 화질 열화 현상은 블록 기반의 정수형 이산코사인 변환(Integer DCT)을 수행한 후 계수를 양자화 하기 때문에 발생한다. 이러한 블록화 현상을 줄이기 위해 H.264/AVC에서는 디블록킹 필터를 이용한다. 본 논문에서는 H.264/AVC의 디블록킹 필터의 복잡도를 감소시키면서 화질을 유지하는 알고리듬을 제안하고 실험을 통한 평가를 제시한다. 복잡도를 줄이기 위해 제안하는 알고리듬에서는 블록 경계강도(Bs) 결정 과정에서 한 화소 줄의 경계강도를 이용하여 네 화소 줄 모두에 적용한다. 실험결과 경계강도 결정의 계산량을 줄이면서 주관적, 객관적 화질 또한 향상되는 결과를 보였다.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2011.04a
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• pp.166-169
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• 2011

현재 국내에서 사용하고 있는 교량구조물의 성능평가방법으로는 크게 공용하중에 대한 내하율을 구하기 위하여 허용응력개념이나 강도설계 개념을 적용한 내하력 평가 기법이 사용되고 있다. 그러나 위의 방법들은 일반적으로 공용연수의 경과에 따른 재료 및 구조적 성능의 손실과 여러 가지 하중 및 환경적 요인들의 불확실성으로 인하여 발생하는 손상 및 열화를 반영하기 어렵다. 그리고 제원 및 재료물성치의 불확실성에 대한 기존 설계 자료의 DB 부족으로 기존의 평가방법에서는 이러한 시간의 경과에 따른 성능저하를 정확히 산정할 수 없어 이론상의 값과 실제 구조물과의 차이로 인한 불확실성이 존재 한다. 이에 본 연구에서는 공용년수 경과에 따른 시설물의 재료 구조적인 성능 및 거동분석 수행, 신뢰성 해석 수행을 바탕으로 교량 안전성 평가의 합리성 및 현실성을 제고하며, 구조 신뢰성 해석을 수행함으로써 실제 구조물의 강도 한계상태에 대한 파괴확률을 산정하고 그에 대응하는 위험도를 평가함으로써 안전성 검토를 수행하였다.

• Korean Journal of Materials Research
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• v.7 no.11
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• pp.929-933
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• 1997

에폭시 수지 DGEBA/MDA/GN계의 트링 열화에 미치는 전압과 온도의 영향에 대한 고찰을 통하여 고분자 절연재료의 절연파괴 거동을 연구하였다. 전압 인가시간에 따라 트리의 성장속도은 역S자의 형태로 나타났다. 인가전압과 온도가 증가함에 따라 트리의 성장속도는 증가하였으며 트리형상의 복잡함, 즉 국부적인 트링열화의 정도는 인가전압이 감소하거나 온도가 증가한 경우에 높게 나타났다. 절연파괴 강도는 유리 전이온도 이상에서 급격히 감소하였다.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2002.05a
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• pp.705-710
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• 2002

Welding is used not only during the shipbuilding, but also during the repairing of ships. While repairing of ships, it is inevitable to weld new materials with degraded materials. In this case, it is predicted that the strength of both the sections is not identical each other. In this study, the respective welded joints in terms of mechanical properties such as microstructure, mechanical strength and fatigue crack propagation, with the component obtained from the barge used for a long-term period, were analyzed. It was found that the material degradation had a significant effect on the welded joints. The fatigue crack propagation in welded sections showed a big difference. The rate of fatigue crack growth of degraded material for both heat affected zone and parent metal was faster than that of new material. By contrast, The result within identical materials showed that the heat-affected zone was slower than that of parent metal