• 에너지공학
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• 제14권2호
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• pp.153-158
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• 2005

본 연구에서는 폴리에틸렌 배관 전기융착부 단기성능 평가를 위한 비파괴검사를 실시할 경우 발견되는 결함에 대한 판정기준을 개발하였다. 인위적으로 $3.8mm\~25mm$ 내에서 6가지 크기의 결함을 삽입한 시험 편을 설계 및 제작하여 기계적 평가를 실시하고 또 이론적 해석을 하였다. 안전계수 2를 적용하여 유효 응력을 산정할 경우 최대 허용 가능한 결함 크기는 11 mm(열선 폭의 $30\%$)이며 안전 계수를 4를 적용할 경우에 최대 허용 가능한 결함 크기는 3.8mm(열선 폭의 $10\%$)이다.

• 비파괴검사학회지
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• 제29권1호
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• pp.27-35
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• 2009

본 논문에서는 개선된 특징추출을 이용한 원자력 발전소 증기발생기 세관의 결함 형태 분류에 대한 연구를 수행한다. 본 논문에서는 4가지 축대칭 결함, 즉 I-In 형태, I-Out 형태, V-In 형태, V-Out 형태 결함을 고려한다. 유한요소법에 기초한 수치해석 프로그램을 이용하여 결함의 폭과 깊이를 변화시켜가면서 400개의 와전류탐상시험(ECT) 신호를 생성하였다. 이와 같이 생성된 ECT 신호로부터 새로운 특징을 제안하였는데, 여기에는 최대 임피던스 값을 갖는 점과 최대 임피던스 값의 1/2의 값을 갖는 점 사이의 위상각과 최대임피던스 값을 갖는 점과 최대 임피던스 값의 10%, 20%, 30%, 40%를 갖는 점사이의 위상각들이 포함된다. 또한, 결함형태를 분류하기 위하여 은닉층이 하나인 다층퍼셉트론을 사용하였다. 컴퓨터 모의실험 연구를 통하여 제안된 방법이 최대오차와 평균제곱오차 측면에서 향상된 결함 분류 성능을 얻는다는 것을 보였다.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2002년도 하계학술대회 논문집
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• pp.310-313
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• 2002

Structures obtained with a direct boning of two FZ silicon wafers joined in such a way that a smooth surface of one wafer was attached to the grooved surface of the other were studied. A square net of grooves was made with a conventional photo lithography process. After high temperature annealing the appearance of voids and the rearrangement of structural defects were observed with X-ray diffraction topography techniques. It was shown that the formation of void free grooved boundaries was feasible. In the cases when particulate contamination was prevented, the voids appeared in the grooved structures could be eliminated with annealing. Since it was found that the flattening was accompanied with plastic deformation, this deformation was suggested to be intensively involved in the process of void removal. A model was proposed explaining the interaction between the structural defects resulted in "a dissolution" of cavities. The described processes may occur in grooved as well as in smooth structures, but there are the former that allow to manage air traps and undesirable excess of dislocation density. Grooves can be paths for air leave. According to the established mechanisms, if not outdone, the dislocations form local defect arrangements at the grooves permitting the substantial reduction in defect density over the remainder of the interfacial area.

• The Korean Journal of Ceramics
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• 제5권3호
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• pp.288-295
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• 1999

Partial conductivities contributed by electron holes, oxygen ions, and protons were caluclated in $SrZr_{0.95}Y_{0.05}O_{2.975}$, using the reported formulae derived from the defect chemistry of HTPCs. Required parameters were obtained from the graphical analysis of total conductivity variation against partial pressure of water vapor and oxygen. Predicted overall conductivities showed a reasonable agreement with experimental measurements. The conductivity of the material showed a linear increase with square root of the water vapor pressure. This increase was due to proton conduction in an almost pure ionic conductivity. The calculation of partial conductivities at $800^{\circ}C$ resulted in an almost pure ionic conductivity at $P_{02}=10^{-10}$ atm and a predominant hole conductivity at $P_{02}=10^{-10}$ atm. Pure proton conduction was not expected at this temperature, contrary to the earlier reports. Discussions were made in relation with reported thermodynamic data and defect structure of the material. It was shown that from the total conductivity dependence on water vapor pressure, the pure ionic conductivity at low oxygen partial pressures could be separated into protonic and oxygen ionic conductivity in $ZrO_2$-based HTPCs.

• Nuclear Engineering and Technology
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• 제52권11호
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• pp.2678-2685
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• 2020

The pipe bends and elbows in nuclear power plants (NPPs) are vulnerable to degradation mechanisms and can cause wall-thinning defects. As it is difficult to detect both the defects generated inside the wall-thinned pipes and the preliminary signs, the wall-thinning defects should be accurately estimated to maintain the integrity of NPPs. This paper proposes a deep fuzzy neural network (DFNN) method and estimates the collapse moment of wall-thinned pipe bends and elbows. The proposed model has a simplified structure in which the fuzzy neural network module is repeatedly connected, and it is optimized using the least squares method and genetic algorithm. Numerical data obtained through simulations on the pipe bends and elbows with extrados, intrados, and crown defects were applied to the DFNN model to estimate the collapse moment. The acquired databases were divided into training, optimization, and test datasets and used to train and verify the estimation model. Consequently, the relative root mean square (RMS) errors of the estimated collapse moment at all the defect locations were within 0.25% for the test data. Such a low RMS error indicates that the DFNN model is accurate in estimating the collapse moment for wall-thinned pipe bends and elbows.

• Journal of Magnetics
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• 제22권1호
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• pp.34-42
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• 2017

Material defects in the Steam Generator Tubes (SGT) of sodium cooled fast breeder reactor (PFBR) can lead to leakage of water into sodium. The water and sodium reaction will lead to major accidents. Therefore, the examination of steam generator tubes for the early detection of defects is an important requirement for safety and economic considerations. In this work, the Magnetic Flux Leakage (MFL) based Non Destructive Testing (NDT) technique is used to perform the defect detection process. The rectangular notch defects on the outer surface of steam generator tubes are modeled using COMSOL multiphysics 4.3a software. The obtained MFL images are de-noised to improve the integrity of flaw related information. Grey Level Co-occurrence Matrix (GLCM) features are extracted from MFL images and taken as input parameter to train the neural network. A comparative study on characterization have been carried out using feed-forward back propagation (FFBP) and cascade-forward back propagation (CFBP) algorithms. The results of both algorithms are evaluated with Mean Square Error (MSE) as a prediction performance measure. The average percentage error for length, depth and width are also computed. The result shows that the feed-forward back propagation network model performs better in characterizing the defects.

• Journal of Korean Neurosurgical Society
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• 제56권5호
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• pp.410-418
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• 2014

Objective : The epidural fluid collection (EFC) as a complication of cranioplasty is not well-described in the literature. This study aimed to identify the predictive factors for the development of EFC as a complication of cranioplasty, and its outcomes. Methods : From January 2004 to December 2012, 117 cranioplasty were performed in our institution. One-hundred-and-six of these patients were classified as either having EFC, or not having EFC. The two groups were compared to identify risk factors for EFC. Statistical significance was tested using the t-test and chi-square test, and a logistic regression analysis. Results : Of the 117 patients undergoing cranioplasty, 59 (50.4%) suffered complications, and EFC occurred in 48 of the patients (41.0%). In the t-test and chi-test, risk factors for EFC were size of the skull defect (p=0.003) and postoperative air bubbles in the epidural space (p<0.001). In a logistic regression, the only statistically significant factor associated with development of EFC was the presence of postoperative air bubbles. The EFC disappeared or regressed over time in 30 of the 48 patients (62.5%), as shown by follow-up brain computed tomographic scan, but 17 patients (35.4%) required reoperation. Conclusion : EFC after cranioplasty is predicted by postoperative air bubbles in the epidural space. Most EFC can be treated conservatively. However, reoperation is necessary to resolve about a third of the cases. During cranioplasty, special attention is required when the skull defect is large, since EFC is then more likely.

• Journal of Advanced Marine Engineering and Technology
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• 제33권5호
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• pp.672-678
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• 2009

Acoustic Emission (AE) technique is a non-destructive testing method and widely used for the early detection of faults in rotating machines in these days, because the sensitivity of AE transducers is higher than normal accelerometers. So it can detect low energy vibration signals. The faults in the rotating machines are generally occurred at bearings and gearboxes which are the principal parts of the machines. It was studied to detect the bearing faults by envelop analysis in several decade years. And the researches showed that AE had a possibility of the application in condition monitoring system(CMS) using the envelope analysis for the rolling bearing. And peak ratio (PR) was developed for expression of the bearing condition in condition monitoring system using AE. Noise level is needed to reduce to take exact PR value because the PR is calculated from total root mean square (RMS) and the harmonics peak levels of the defect frequencies of the bearing. Therefore, in this paper, the discrete wavelet transform (DWT) was added in the envelope analysis to reduce the noise level in the AE signals. And then, the PR was calculated and compared with general envelope analysis result and the result of envelope analysis added the DWT. In the experiment result about inner fault of bearing, defect frequency was difficult to find about only envelop analysis. But it's easy to find defect frequency after wavelet transform. Therefore, Envelop analysis added wavelet transform was useful method for early detection of default in signal process.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2008년도 하계학술대회 논문집 Vol.9
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• pp.81-81
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• 2008

Applications of CdS films in this study are to exhibit a high conductivity when they are exposed at light with visible wavelength and sequentially to show a low conductivity in dark state. For this purpose, CdS films should have a high photosensitivity, still maintaining a high conductivity at a visible light. In this study, CdS films were prepared at room temperature on glass substrates by rf magnetron sputtering. In order to increase the photo-conductivity in visible light, various defect levels should be located within the CdS band gap. In order to nucleate the defect sites within the CdS band gap, CdS films were deposited on glass substrates at room temperature using various $H_2$/(Ar+$H_2$) flow ratios by an rf magnetron sputtering. Through the investigation of the structural and photoconductive properties of CdS films by an addition of hydrogen, the relationship between photo- and dark-resistance in CdS films was investigated in detail. 200-nm-thick CdS films for photoconductive sensor applications were prepared at various $H_2$/(Ar+$H_2$) flow ratios on glass substrates at room temperature by rf magnetron sputtering. Sulfur concentration in CdS films crystallized at room temperature with (002) preferred orientation depends directly on the hydrogen atmosphere and the surface roughness of the films gradually increases with increasing hydrogen atmosphere. Films deposited at 8% of $H_2$/(Ar+$H_2$) exhibit an abrupt decrease of dark- and photo-resistance, showing a low photo-sensitivity ($R_{dark}/R_{photo}$). Onthe other hand, films deposited at a hydrogen atmosphere of 42% exhibit a photo-sensitivity of $5\times10^3$, maintaining a photo-resistance of an approximately $2\times10^4\Omega$/square. The dark- and photo-resistance values of CdS films were related with a composition, surface roughness, and defect sites within the band gap.

• Journal of the Korean Wood Science and Technology
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• 제44권5호
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• pp.726-735
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• 2016

본 연구는 두께 15 cm와 18 cm 크기 Douglas-fir, Hemlock, Radiata pine 정각재의 고온건조 특성을 평가하기 위해 수행되었다. 수종에 따른 최종함수율은 시험재의 두께에 관계없이 Radiata pine, Douglas-fir, Hemlock 순으로 Radiata pine에서 가장 낮았으며, 배할처리를 하였을 때 무처리재보다 낮은 함수율을 나타내었다. Radiata pine과 Hemlock의 경우 배할처리를 하였을 때 함수율과 뒤틀림 발생을 감소시키는 효과가 있는 것으로 나타났다. Douglas-fir는 수를 포함하지 않는 정목형태로 가공될 때 건조결함의 감소가 가능하였다.