• 한국철도학회논문집
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• 제2권2호
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• pp.21-30
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• 1999

This study proposes the analysis and evaluation method of time series ultrasonic signal using the phase space-frequency domain. Features extracted from time series signal analyze quantitatively characteristics of weld defects. For this purpose, analysis objectives in this study are features of time domain and frequency domain. Trajectory changes in the attractor indicated a substantial difference in fractal characteristics resulting from distance shifts such as parts of head and flange even though the types of defects are identified. These differences in characteristics of weld defects enables the evaluation of unique characteristics of defects in the weld zone. In quantitative fractal feature extraction, feature values of 3.848 in the case of part of head(crack) and 4.102 in the case of part of web(side hole) and 3.711 in the case of part of flange(crack) were proposed on the basis of fractal dimension. Proposed phase space-frequency domain method in this study can integrity evaluation for defect signals of rail weld zone such as side hole and crack.

• 소성∙가공
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• 제15권8호
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• pp.550-555
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• 2006

In this study, effects of forming angle and friction coefficient on a initiation of the Mannesmann hole defect were analyzed by using a response surface method. The maximum effective plastic strain at center point of specimen is utilized for the prediction of the starting point of crack occurrence, which is suggested by the comparison of integrals of four different ductile fracture models between the histories of the effective plastic strain at center point. It was revealed that the principal stress at the center is the dominant element to the increase of the effective plastic strain. It was also verified by the simulation results from the comparison of experiment and simulation. It is provided that the forming angle of 25 degrees and the spreading angle of 1 degree can be a proper design condition without an occurrence of internal hole defect and an excessive slip.

• 소성∙가공
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• 제1권1호
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• pp.66-74
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• 1992

According to the variation of hydrostatic pressure on the central axis of deformable material, the V-shaped central bursting defect may be created in extrusion or drawing processes. The process factors which affect the generation of defects are semi-angle of die, reduction ratio of cross-sectional area, friction factor, material properties and so on. The combination of these factors can determine the possibility of defect creation and the shape of various round holes which have been created inside already. By the rigid plastic finite element method, this paper describes the observations of change in shape of round holes with process conditions such as semi-angle of die, reduction ratio of cross-sectional area and friction factor at the non-steady state of axisymmetrical extrusion process when the round hole is already existed inside the original billet. Also, the effects of process factors are investigated to prevent the possible defects.

• 대한안전경영과학회지
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• 제11권1호
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• pp.27-33
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• 2009

A study of fracture to material is getting interest in nuclear and aerospace industry as a viewpoint of safety. Acoustic emission (AE) is a non-destructive testing and new technology to evaluate safety on structures. In previous research continuously, all tensile tests on the pre-defected coupons were performed using the universal testing machine, which machine crosshead was move at a constant speed of 5mm/min. This study is to evaluate an AE source characterization of SM45C steel by using k-nearest neighbor classifier, k-NNC. For this, we used K-means clustering as an unsupervised learning method for obtained multi -variate AE main data sets, and we applied k-NNC as a supervised learning pattern recognition algorithm for obtained multi-variate AE working data sets. As a result, the criteria of Wilk's $\lambda$, D&B(Rij) & Tou are discussed.

• Journal of Welding and Joining
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• 제16권5호
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• pp.108-118
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• 1998

This study proposes th analysis and evaluation method of time series ultrasonic signal using the chaos feature extraction for ultrasonic pattern recognition. Features extracted from time series data using the chaos time series signal analyze quantitatively weld defects. For this purpose, analysis objective in this study is fractal dimension and Lyapunov exponent. Trajectory changes in the strange attractor indicated that even same type of defects carried substantial difference in chaosity resulting from distance shifts such as 0.5 and 1.0 skip distance. Such differences in chaosity enables the evaluation of unique features of defects in the weld zone. In quantitative chaos feature extraction, feature values of 4.511 and 0.091 in the case of side hole and 4.539 and 0.115 in the case of vertical hole were proposed on the basis of fractal dimension and Lyapunov exponent. Proposed chaos feature extraction in this study can enhances ultrasonic pattern recognition results from defect signals of weld zone such as side hole and vertical hole.

• 한국정밀공학회지
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• 제21권12호
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• pp.92-99
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• 2004

The formation degree of sustain (ITO pattern) decides quality of PDP (Plasma Display Panel). For this reason, it makes efforts in searching defects more than 30 un as 100%. Now, the existing inspection is dependent upon naked eye or microscope in off-line PDP manufacturing process. In this study developed prototype inspection system of PDP 170 glass is based on line-scan mechanism. Developed system creates information that detects and sorts kinds of defect automatically. Designed inspection technology adopts multi-vision method by slip-beam formation for the minimum of inspection time and detection algorithm is embodied in detection ability of developed system. Designed algorithm had to make good use of kernel matrix that draws up an approach to geometry. A characteristic of defects, as pin hole, substance, protrusion, are extracted from blob analysis method. Defects, as open, short, spots and et al, are distinguished by line type inspection algorithm. In experiment, we could have ensured ability of inspection that can be detected with reliability of up to 95% in about 60 seconds.

• 융합정보논문지
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• 제11권2호
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• pp.10-15
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• 2021

본 논문에서는 먼저 습식 코팅 방법으로 페로브스카이트 (CH3NH3PbI3) 박막을 글라스 상에 형성하고, 다양한 분석 기법을 이용하여 막의 두께, 표면거칠기, 결정성, 구성성분 및 가시광 영역에서의 이 물질의 반응에 대해 논한다. 완성된 반도체 물질은 막내부에 결함(defect)이 없고 균일하며, 표면거칠기는 매우 작으며, 가시광영역에서 높은 흡수율이 관찰되었다. 다음으로 이와 같이 형성된 유무기 층에 hole 형상을 구현하기 위하여, 구멍이 일정한 간격으로 있는 메탈마스크, 페로브스카이트 물질이 코팅되어 있는 유리, 자석 순서로 되어있는 구조의 샘플을 상압플라즈마 공법을 이용하여 시간에 따른 물질에 형성되는 hole 형태의 변화를 분석하였다. 시간이 길어짐에 따라 더 많이 식각되는 것을 알 수 있으며, 이 중에서 공정 시간을 가장 오래한 샘플에 대해서는 보다 자세하게 살펴보았고, 플라즈마의 위치에 따른 차이에 의해 7영역으로 분류할 수 있었다.

• Journal of the Korean Wood Science and Technology
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• 제44권1호
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• pp.1-8
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• 2016

목재 데크재에 인위적인 결함인 구멍을 부여하고 이들의 성능평가를 위해 초음파 비파괴 시험법을 적용하였다. 구멍의 크기와 개수를 달리하여 각각에 대한 초음파 전달속도를 측정하고 탄성계수를 산정하여 그 영향을 비교분석하였다. 시험결과 구멍의 크기가 커짐에 따라 초음파 전달속도와 탄성계수는 감소하였으며 이들 상호간에는 직선상관관계를 보였다. 구멍의 크기가 증가하면 초음파의 전달 길이는 증가하며 이에 따라 초음파속도는 감소하였지만 구멍의 크기가 15 mm 이하로 작은 경우에는 구멍이 없는 부재에 비해 그 차이가 작게 나타났다. 구멍의 개수가 많아짐에 따라 초음파 전달속도와 탄성계수는 감소하였으며 이들 상호간에는 높은 직선상관관계를 보였다. 구멍의 개수가 3개인 경우 초음파속도는 약 3.5% 정도 감소한데 비하여 탄성계수는 27% 정도로 현저히 감소하여 더 큰 감소경향을 나타내었다. 이들의 결과로부터 구멍의 크기와 개수는 초음파 전달속도와 탄성계수에 영향을 미치며 구멍의 크기가 크고 개수가 많아질수록 그 영향은 더욱 커질 것으로 여겨진다. 또한 작은 결함의 탐지를 위해서는 초음파 전달속도에만 의지할 것이 아니라 여러 초음파 변수를 고려하여 적용하는 방법을 고려하여야 할 것으로 생각된다.

• 한국융합학회논문지
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• 제5권1호
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• pp.23-27
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• 2014

본 연구에서는 소형 인장 시험편에 편심된 집중하중을 가하였을 때, 크랙 주변에서의 구멍의 존재유무, 개수 및 위치에 따른 전파 거동에 대하여 규명하였다. 시뮬레이션 해석을 통하여 시험편에서 발생하는 Strain energy와 변형량, 응력에 대해 알 수 있었다. 그리고 이들 Strain energy와 변형량을 바탕으로 응력확대계수를 구하였으며, 본 연구결과를 이용하면 구조물 내에 결함이나 구멍 등이 있을 때 그 파괴 가능성을 검증할 수 있다고 사료된다.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2005년도 추계학술대회 논문집 Vol.18
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• pp.252-253
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• 2005

The effects of As addition in amorphous selenium (a-Se) films on the carrier mobilities and the recombination lifetime have been studied using the moving photo-carrier grating (MPG) measurements. The electron and hole mobility, and recombination lifetime of a-Se films with arsenic (As) additions up to 1% have been obtained. We have found an increase in hole drift mobility and recombination lifetime, especially when 0.3% As is added into a-Se film, whereas electron mobility decreases with As addition due to the defect density from shallow traps.