• Journal of Ocean Engineering and Technology
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• v.13 no.4 s.35
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• pp.45-54
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• 1999

Non destructive test is applied to revise mechanical strength and assume material strength or defect of material, equipment and structure, instead of fracture test. Especially, ultrasonic test has the characteristics such as an excellent permeability high-sensitiveness to fine defect and an almost exact measurement for position, size and direction of inner defect which differ from other non destructive tests. In this study, the program is developed to evaluate optimal testing condition, to distinguish obstacle echo and defect position. This program on the basic of Ray-Tracing model shows generation and processing of ultrasonic pulse. The simulation is compared with testing in the 3 cases of an oblique angle transducer like $45^{\circ},\;60^{\circ}\;and\;70^{\circ}$. The test result for all conditions is well compared with simulation result when relative not is within $0.1{\sim}7.2%$. And the course of several echos is simply assumed through simulation.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.25 no.8
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• pp.1213-1219
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• 2001

In this paper, modeling of the multi-pass roll forming process with the finite element method and defect prediction in roll forming process are presented. In the roll forming process, there occurs the defect of scratch. It appears on tubes because of the friction between the strip and the roll, the unexpected sliding velocity and the contact pressure when fabricating the tubes. The surface of the product will be not uniform due to the defect. The scratch can be predicted with the simulation modeling of the finite element method, and can be avoided by modifying the design.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1998.11a
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• pp.17-20
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• 1998

Thermal behavior of Flow Pattern Defect (FPD) and Large Pit (LP) in Czochralski Silicon crystals was investigated by applying high temperature ($\geq$1100$^{\circ}C$) annealing and non-agitation Secco etching. For evaluation of the effect of LP upon device performance / yield, DRAM and ASIC devices were fabricated. The results indicate that high temperature annealing generates LPs whereas it decreases FPD density drastically, and LP does not have detrimental effects on the performance /

• Journal of Institute of Control, Robotics and Systems
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• v.21 no.10
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• pp.982-987
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• 2015

The inspection machine in SMT (Surface Mount Technology) line detects the assembly defects such as missing, misalignment, loosing, or tombstone. We propose a new method to classify the defect types of chip components by processing the image of PCB. Two original images are obtained from horizontal lighting and vertical lighting. The image of the component is divided into two soldering regions and one packaging region. The features are extracted by appling the PCA (Principle Component Analysis) to each region. The MLP (Multilayer Perceptron) and SVM (Support Vector Machine) are then used to classify the defect types by learning. The experimental results are presented to show the usefulness of the proposed method.

• Journal of the Korea Furniture Society
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• v.24 no.3
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• pp.302-308
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• 2013

To collection of field data for development of maintenance manual of Han-ok, we investigated defects which occurred in members of Han-ok by field investigation. The noticeable defects were wood cracks, gaps that developed between wood pillar and wall or wood window frame and tenon joints. The most common biological defect was blue stain which was created in log. The mold generation was observed on exterior wood and wall which get wet by precipitation. The gaps between members of Han-ok pointed out as defect that is urgently improved by residents of Han-ok. The reason is mainly due to poor of insulation in winter by bad confidentiality. The maintenance work of defect such as gap was conducted personally. As a result, the repair parts were ugly for unfamiliar repair work.

• Journal of the Korean Society for Heat Treatment
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• v.13 no.3
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• pp.158-162
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• 2000

The high temperature oxidation behavior and the surface defect in Fe-25Mn-1.5A1-0.5C steel was investigated by XRD (X-ray Diffractin) and electron microscopy. The intra- and inter-granular oxides were formed by the selective oxidation of manganese and aluminum, which were identified to MnAl2O4 phase. Aluminum nitride (AlN) was formed in front of these oxides. The ${\gamma}$-matrix was transformed to ${\alpha}$- and ${\varepsilon}$- phases by the selective oxidation of manganese. The surface defect, micro-scab was induced by the difference of the high temperature ductility between the matrix and the inter-granular oxide.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.11
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• pp.510-519
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• 2019

The aim of this study was to set a defect classification framework and evaluate the defect risks in apartment buildings For this, approximately 15,056 defect items for 133 apartment buildings were examined. As a result of the analysis, the major defect of the RC work was cracks, which were found mainly in public locations. Moreover, the RC work was found to exhibit a high defect risk of water problem and surface appearance, which are highly connected with cracks. Second, the finish work has a high defect risk because it is composed of various work types, and there are many kinds of materials and construction parts involved. Third, the major defects of the waterproof work were incorrect installation and missing tasks, which have high defect risks in the garage. This is because defects that require rework occur mainly in the underground garage. Based on these results, this study proposed countermeasures for defect risk management to be considered in the construction, handover, post-handover, and occupancy phases. These have been set in detail based on the three zones: low frequency high severity (LFHS), low frequency low severity (LFLS), and high frequency low severity (HFLS).

• Journal of Ocean Engineering and Technology
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• v.28 no.4
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• pp.268-273
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• 2014

To investigate the turbulence characteristics within the boundary layer over a flat plate, an experimental study was performed using a PIV technique in a circular water channel. For two water velocities, 0.92 and 1.99 m/s, the water velocity profiles were taken and analyzed to determine turbulent characteristics such as the Reynolds stress, Taylor micro-length scale, and Kolmogorov length scale within the defect law region of the boundary layer. These analysis methods may be applied to research on the friction drag reduction technology using micro-bubbles or an air sheet over the surface of a ship's hull, because the physical reason for the friction drag reduction could be found by understanding the variation of the turbulence characteristics and structures in the boundary layer.

• New & Renewable Energy
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• v.8 no.1
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• pp.24-34
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• 2012

The main issue of boron doped p-type czochralski-grown silicon solar cells is the degradation when they are exposed to light or minority carriers injection. This is due to the meta-stable defect such as boron-oxygen in the Cz-Si material. Although a clear explanation is still researching, recent investigations have revealed that the Cz-Si defect is related with the boron and the oxygen concentration. They also revealed how these defects act a recombination centers in solar cells using density function theory (DFT) calculation. This paper reviews the physical understanding and gives an overview of the degradation models. Therefore, various methods for avoiding the light-induced degradation in Cz-Si solar cells are compared in this paper.

• Proceedings of the KIEE Conference
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• 2002.07b
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• pp.770-772
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• 2002

In this paper, the eddy current sensor is develped for observing the ability of detecting defect with variation of frequency and velocity. The circuit designed for processing detected voltage and changing frequency is used for eddy current sensor to detect defect with variation of frequency. The ability of eddy current sensor to detect defects is studied with variation of velocity adjusted by rotating the circular plate. This study shows that the ability of eddy current sensor for detecting defect is increased and decreased by frequency. This fact means that the sensor has its best ability at a certain frequency. And the ability of eddy current sensor by velocity is decreased by increased velocity. Therefore, the eddy current sensor has to be developed with consideration of its operation velocity and frequency.