• 비파괴검사학회지
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• 제9권1호
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• pp.8-21
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• 1989

This paper presents the ultrasonic characteristics of weldment and detectability of defects of weldment in Austenitic Stainless Steel Type 304 that is composed of mostly coolant piping system in nuclear power plants. The results of this experient show as follows: 1. When the ultrasonic beam detects the defects on the side of base metal and on the opposite side of weldment, the indications which was detected on the screen show different amplitude and different metal path each. 2. The ultrasonically estimated notch depth is generally oversized than actual notch depth. 3. It is easy for the false indication to show up on the screen because of columnar structure of weldment in austenitic stainless steel. 4. The higher frequencies of transducer have more difficulties to detect the defects of the opposite side of weldment because of ultrasonic attenuation in weldment and the longitudinal transmitter-receiver transducer is the most effective in detecting the opposite side defects of weldment.

• 소성∙가공
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• 제14권4호
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• pp.360-367
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• 2005

The injection-molded plastic parts have many surface defects: warpage, weldline, flowmark, zetting, scratching, shading and so on. As weldline was one of the major surface defects in the case of desktop monitor, warpage and surface shrinkage are the bigger problems of LCD monitor in the pursuit of light weight and thinner thickness of parts. Some measures to improve these defects were introduced in this paper. Based on these, the laboratory work to find out the optimum processing conditions and to get the best parts was repeated injection moulding try-out after reflecting these improvements. The defects of warpage and surface shrinkage was significantly improved after the improvements in the case of the 20.1 inch even if in the 15 and 17inch case the warpage size was a lttle over the allowed specification because of not taking the measure for parts design within the allowable limits from the required specification in the cause of cost down.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2003년도 추계학술대회논문집
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• pp.201-206
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• 2003

Plastic injection mould have two kinds of trouble, one is in mould another in injection parts. Most of defects of the former take the cause in a design like in structure and working, the later weld line, transforming, sink mark, burning, flow mark, scratching, shading, black hole and so on. Most of problems of the later is difficult for making a clear definitely the reason of defects because of complexible. The purpose of this paper is to improve the quality of plastic injection mould and parts with inquiring the counter plan and rouble of the part of Flat TV Front Cover by flow control method and gas- assisted injection moulding. For minimizing defects from injection moulding parts, this paper was investigated with using computer aided injection mold filling simulations. Based on these numerical results, I established guidelines mould design and injection processing condition. As a results I got the improve of quality, minimizing surface defects moulded parts and troubles in mould.

• 한국정보디스플레이학회:학술대회논문집
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• 한국정보디스플레이학회 2004년도 Asia Display / IMID 04
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• pp.193-197
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• 2004

The effect of the temperature dependence of the smectic layer spacing in the smectic-A (SmA) phase on the formation of defects in the ferroelectric smectic-$C^{\ast}$ ($SmC^{\ast}$) phase is investigated with x-ray scattering technique. The study is based on thin parallel-aligned surface stabilized ferroelectric liquid crystal cells with two different alignment conditions, high pretilt $SiO_x$, alignment and low pretilt polyimide films. It is found that defects observed in the $SmC^{\ast}$ phase have much more profound dependence on the layer changes and chevron formation in the SmA phase than in the $SmC^{\ast}$ phase. We find that thermal layer expansion with decreasing temperature in the SmA phase suppresses the formation of defects observed in the SmC phase.

• 대한산업공학회지
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• 제21권3호
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• pp.371-385
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• 1995

The yield of semiconductor chips is dependent not only on the average defect density but also on the distribution of defects over a wafer. The distribution of defects leads to consider a cluster index. This paper briefly reviews the existing yield prediction models ad proposes a new cluster index, which utilizes the information about the defect location on a wafer in terms of the coefficient of variation. An extensive simulation is performed under a variety of defect distributions and a yield prediction model is derived through the regression analysis to relate the yield with the proposed cluster index and the average number of defects per chip. The performance of the proposed simulation-based yield prediction model is compared with that of the well-known negative binomial model.

• 한국전기전자재료학회논문지
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• 제20권9호
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• pp.780-786
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• 2007

This paper describes the influence on partial discharge characteristics of defects at the model XLPE/EPDM interfaces of power cable joints. The defects of void and copper which could inadvertently be present at the joint interface. We measured ${\Phi}-n,\;{\Phi}-q$ patterns by a computer-aided partial discharge measuring system. Several parameters i, e, maximum discharge $q_{max}$ [pC], average discharge q [pC/cycle], and average angle of discharge ${\Theta}g$ [deg] were found to depend upon the defect type varying applied voltage. As the result of time evaluation, partial discharges are small different at copper defects, but is decreasing obviously about 20 minutes at void defect. It considered that difference of magnitude of total positive discharge of Q+ [pC] and total negative discharge of Q- [pC] is SPMD(swarming pulsive micro discharges).

• 대한전기학회:학술대회논문집
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• 대한전기학회 2004년도 학술대회 논문집 정보 및 제어부문
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• pp.580-582
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• 2004

As the demand of large and high-resolution display panels is increased, the black light units (BLU) of the display devices play an important roles. In this study we'll deal with various defects of BLUs. Patterns of defects can be classified by the scratches, the non-uniform misprinting for the diffused reflection, the surface stains, spots and etc. Due to these distorted patterns the high-resolution and high-precision could be impeded. We'll propose the visual inspection system to detect various defects by pattern-matching.

• 비파괴검사학회지
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• 제13권1호
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• pp.40-45
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• 1993

The steam generator tubes of the nuclear power plant should be inspected using eddy current techniques. Recently the crack-like defects become a major concern for the integrity of the steam generator tubes. These defects could be detected by the MRPC(Motorized Rotating Pancake Coil) method, not by the conventional bobbin coil method. In this paper it has been attempted to estimate the length of the cracks at the tube expansion region using of MRPC technique. The lengths of both axial and circumferential cracks show a tendency of overestimation compared to the real lengths. As the depths of the defects decrease from 100% through 50% of the wall thickness, the error of the length estimation is increased.

• 한국해양공학회지
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• 제23권2호
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• pp.81-86
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• 2009

Infrared thermography was used to determine the location, size, and depth of defects under the surface of M.C nylon. Defects were created in a specimen by back-drilling circular holes. These defects were located at the maximum temperature difference that occurred. The sizes of the defects could be calculated by means of the full width at half of the maximum temperature difference. The depth of a defect could be calculated by the peak time and the maximum temperature difference. The maximum temperature difference between a defect and normal part was decreased with the depth of the defect. And the peak time also slowly appeared with the depth of the defect.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2005년도 춘계학술대회 논문집
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• pp.1083-1086
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• 2005

Light scattering measurement system that can evaluate light scattering characteristic from defects on silicon wafer surface has been developed. The system uses $Ar^+$ laser as an illumination source, and a highly sensitive photomultiplier tube (PMT) for detecting scattered light from defects. Unlike with conventional measurement system, our system has ability to measure scattered light pattern from wide range of scattering angles with changeable incidence condition. It is shown that our developed system is effective to discriminate the types and sizes of defects from basic experimental results using a microscatch and a PSL sphere.