• International Journal of Korean Welding Society
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• 제1권1호
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• pp.23-30
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• 2001

Among the various welding conditions, the welding current that is inversely proportional to the tip-to-work-piece distance is an essential parameter as to monitor the GMAW process and to implement the welding automation. Considering the weld pool surface geometry including weld defects, it should modify the signal processing method for automatic seam tracking in horizontal fillet welding. To meet the above necessities, a mathematical model related with the weld pool geometry was proposed as in a conjunction with the two-dimensional heat flow analysis of the horizontal fillet welding. The signal processing method based on the artificial neural network (Adaptive Resonance Theory) was proposed for discriminating the sound weld pool surface from that with the weld defects. The reliability of the numerical model and the signal processing method proposed were evaluated through the experiments of which showed that they are effective for predicting the weld bead shape with or without the weld defects in a horizontal fillet welding.

• 비파괴검사학회지
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• 제21권3호
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• pp.299-306
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• 2001

본 논문에서는 ESPI 시스템을 이용하여 복합재료 구조물의 인위, 자연 결함을 검출하였다. 복합재료 구조물에서의 ESPI의 적용성을 알아보기 위해 복합재료 적층판 시험편, 하니컴 구조물 시험편, 접착조인트 시험편을 사용하였다. 결함을 검출하기 위해 시편의 표변변형을 쉽게 발생시킬 수 있는 열하중법을 선택하였다. 실험결과는 ESPI를 이용하여 복합재료 구조물의 결함을 쉽게 검출말 수 있고, 다른 여러 복합재료 구조물의 결함의 걸출에도 적용할 수 있을 확인하였다.

• 한국지하수토양환경학회지:지하수토양환경
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• 제6권1호
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• pp.53-62
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• 2001

표면결함이 고밀도 폴리에틸렌 지오멤브레인의 열적 안정성과 응력균열저항성에 미치는 영향을 온도와 표면 결함 부여조건을 달리한 환경조건에서 역학적 특성, 화학저항성 및 피로시간을 측정하여, 조사하였다. 특별 고안된 장치를 사용하여 인위적으로 지오멤브레인 표면에 결함을 부여하였다. 표면결함은 표면결함 유도매체의 전단속도 100mm/min에서 표면결함 유도매체의 크기가 작을수록, 표면결함 부여횟수가 커질수록 증가하였다. 또한 이 조건에서 인장강도는 감소하였지만 인장신도는 증가하였다. 표면결함 부여조건이 같을 경우 고온으로 갈수록 그리고 침지시간이 길어질수록 인장강도는 감소되고 인장신도는 증가하여 표면결함이 부여된 지오멤브레인의 화학저항성은 저하되었다. 끝으로 응력균열저항성 시험 결과 온도가 높아질수록 표면결함이 부여된 지오멤브레인의 피로시간은 단시간 영역으로 이동되었다.

• 한국지반신소재학회논문집
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• 제2권3호
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• pp.19-24
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• 2003

폐기물 매립지 바닥층 및 사면에 적용되는 평편 형 및 텍스츄어드 형 고밀도 폴리에틸렌 지오멤브레인의 장기성능이 검토되었다. 특수 설계된 스크래치 장치를 이용하여 인위적으로 지오멤브레인 표면에 결함을 부여하였다. 결함 및 미결함 지오멤브레인의 역학적 및 마찰특성, 화학저항성 및 자외선 저항성 그리고 산화유도시간 등이 검토되었다. 텍스츄어드 형 지오멤브레인의 마찰특성이 평편 형 지오멤브레인 보다 우수함을 알 수 있었다. 끝으로 화학저항성, 자외선 저항성 그리고 산화유도시간 측정결과로부터 결함이 없는 지오멤브레인과 텍스츄어드 형 지오멤브레인의 장기성능이 결함이 있는 지오멤브레인보다 우수함을 알 수 있었다.

• 소성∙가공
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• 제23권7호
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• pp.425-430
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• 2014

The aim of the current study was to predict the plastic deformation behavior of a heated slab during hot rough rolling. FE-simulations were performed to investigate the metal flow and to locate the position of surface material from the slab through the rough rolling and onto the strip, using a material point tracking technique. In addition, experimental hot rolling trials were conducted where artificial defects were impressed onto a heated slab in order to validate the FE-simulation results. The simulated results show the same tendency of deformation behavior as the experimental measurements. The movement of slab defects from the side surface towards the strip center is directly linked to the extent of lateral spread during the rolling.

• 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.

• 한국생산제조학회지
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• 제22권5호
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• pp.795-799
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• 2013

This paper describes a novel hybrid surface polishing process combining non-traditional electrochemical polishing (ECP) with external artificial ultrasonic vibration. The purpose of this study is to develop an easier method for improving stainless steel surfaces. To this end, vibration electrochemical polishing (VECP), a novel ultrasonic manufacturing process, for enhancing electrochemical reaction and surface quality compared with that achieved using conventional ECP is suggested. In addition, for finding the optimized experimental conditions, the two methods are compared under various current densities. Localized roughness of the work material is measured with atomic force microscopy (AFM) and scanning electron microscopy (SEM) for obtaining detailed surface information.

• 한국전기전자재료학회논문지
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• 제18권10호
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• pp.902-908
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• 2005

Various stresses (such as electrical stress, mechanical stress, environmental and electrochemical stress, and defects of structure) result in insulation degradation of epoxy mold type insulators. Since the insulation degradation of BCT(Bushing Current Transformer) and bushing proceeds during fabrication process or operation time due to these causes, various methods to reduce the degradation in their insulation ability have been suggested. In this paper, we investigated surface temperature increment of these insulators due to PD(partial discharge). After the voltage applied into the insulator to generate the artificial PD, the surface temperature of the insulator was measured with non-contact thermometer using infrared rays. It was confirmed through the analysis based on PD experiments that the procession in the insulation degradation of the insulator could be estimated through the measurement of the surface temperature in the insulator.

• Corrosion Science and Technology
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• 제16권3호
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• pp.151-159
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• 2017

The MA8 alloy (formula Mg-Mn-Се) has been shown to have greater corrosion stability than the VMD10 magnesium alloy (formula Mg-Zn-Zr-Y) in chloride-containing solutions by Scanning Vibrating Electrode Technique (SVET) and by optical microscopy, gravimetry, and volumetry. It has been established that the crucial factor for the corrosion activity of these samples is the occurrence of microgalvanic coupling at the sample surface. The peculiarities of the kinetics and mechanism of the corrosion in the local heterogeneous regions of the magnesium alloy surface were investigated by localized electrochemical techniques. The stages of the corrosion process in artificial defects in the coating obtained by plasma electrolytic oxidation (PEO) at the surface of the MA8 magnesium alloy were also studied. The analysis of the experimental data enabled us to determine that the corrosion process in the defect zone develops predominantly at the magnesium/coating interface. Based on the measurements of the corrosion rate of the samples with PEO and composite polymer-containing coatings, the best anticorrosion properties were displayed by the composite polymer-containing coatings.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 2001년도 ICCAS
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• pp.109.4-109
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• 2001

We have developed a laser ultrasonic system for visualization of elastic waves propagating on a solid surface, in order to visualize ultrasonic waves propagating on opaque media. This system can produce a series of successive images as an animation of wave propagation, because of scanning an optical heterodyne probe to measure surface transient displacements. Using this visualization technique, we observed the scattering and diffraction of ultrasonic waves around various shapes of artificial defects, and examined its application to nondestructive inspection. This imaging system provides various kinds of visualization images such as propagation image, amplitude image, arrival time image and velocity image. We have been confident that this technique is available for nondestructive inspection and materials ...