• Composites Research
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• v.23 no.5
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• pp.30-38
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• 2010

Observing of GMT-Sheet in molding conditions, we have investigated unexpected phenomenons of moldings surface. In microscope investigation, we observe that there exist deficiencies on the surface of GMT-Sheet moldings, such as the spherulite, fiber projection, crack, fiber exposure, micro-weldline, pinhole and winding. They are caused to arise unevenness and phenomenons influence polish on surface. Especially, the major cause of the unevenness, effected to surface roughness, is a shrinking of matrix in the process of holding pressure and cooling temperature. The higher holding pressure load in a molding process and the lower demolding temperature in an annealing experiment, the better GMT-Sheet moldings improved its appearance.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.08a
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• pp.43-43
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• 2010

반도체 및 디스플레이의 진공부품은 알루미늄 모제에 전해연마법(electrolytic polishing), 양극산화피막법(anodizing), 플라즈마 용사법(plasma spray) 등을 사용하여 $Al_2O_3$ 피막을 성장시켜 사용되고 있다. 반도체 제조공정 중 30~40% 이상의 비중을 차지하는 식각(etching) 및 증착(deposition) 공정의 대부분 은 플라즈마에 의해 화학적, 물리적 침식이 발생하여 피막에 손상을 일으켜 피막이 깨지거나 박리되면서 다량의 particle을 생성함으로써 생산수율에도 문제를 야기 시킨다. 본 연구에서는 이러한 진공부품의 하나인 etcher용 상부전극을 양극산화피막법(Anodizing)으로 $Al_2O_3$ 피막을 성장시킨 샘플을 제작하여 플라즈마 처리에 따른 내전압, 식각율, 표면 미세구조의 변화를 관찰하였고 이를 종합적으로 고려하여 etcher용 상부전극의 Life Time 평가 방법을 연구하였다. 이러한 실험을 통해 플라즈마 처리 후 피막에 크랙이 발생되는 것을 확인할 수 있었고 피막의 손상으로 전기적 특성이 감소되는 것을 확인할 수 있었다. 또한 플라즈마 처리 중 ISPM 장비를 이용하여 플라즈마 공정에서 발생하는 오염입자를 실시간으로 측정할 수 있는 방법을 연구하였다. 이러한 결과를 이용하여 진공공정에서 사용되는 코팅부품이 플라즈마에 의한 손상정도를 정량화 하고 etcher용 상부전극의 Life Time 평가 방법을 개발하여 부품 양산업체의 진공장비용 코팅부품의 개발 신뢰성 향상이 가능할 것으로 기대된다.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.4
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• pp.443-446
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• 2013

An infrared thermography technique can be used to inspect a large area simultaneously and to detect defects such as cracks or delaminations in real time. Infrared thermography is a technique in which visual images are formed from the infrared range from subjects according to their thermal radiation. The molecules of all objects are disturbed by heat, and the molecular motion becomes more active when the temperature rises and less active when the temperature falls. In this study, the applicability and feasibility of ultrasound thermography for detecting defects in an engine block, which is a key component in the automobile industry, were verified. A nondestructive reliability test was conducted to study the defects, after which the results were analyzed.

• Journal of the Korean Society for Nondestructive Testing
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• v.24 no.2
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• pp.151-157
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• 2004

Ultrasonic testing is a kind of nondestructive test to detect a crack or discontinuity in materials or on material surfaces by sending ultrasound to it. This conventional ultrasonic technique has some limitations in reliably detecting crack or accurately assessing materials in the case of complex-shaped power plant components such as a turbine blade root. An alternative method for such a difficult inspection is highly needed. In this study, application of a phased array ultrasonic testing (UT) system to a turbine blade, one of the critical power plant components, has been considered, and the particular incident angle has been determined so that the greatest track detectability and the most accurate crack length evaluation nay be achieved. The response of ultrasonic phased array was also analyzed to establish a special method to determine the track )ength without moving the transducer. The result showed that the developed method for crack length assessment is a more accurate and effective method, compared with the conventional method.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.40 no.4
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• pp.51-57
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• 2003

The development of the communication network and the other network method can generate serious social problems. So, it is highly required to control security of network. These problems related security will be developed and keep up to confront with anti-security field such as hacking, cracking. The way to preserve security from hacker or cracker without developing new cryptographic algorithm is keeping the state of anti-cryptanalysis in a prescribed time by means of extending key-length. In this paper, we proposed M3 algorithm for the reduced processing time in the montgomery multiplication part. Proposed M3 algorithm using the matrix function M(.) and lookup table perform optionally montgomery multiplication with repeated operation. In this result, modified repeated operation part produce 30% processing rate than existed montgomery multiplicator. The proposed montgomery multiplication structured unit array method in carry generated part and variable length multiplication for eliminating bottle neck effect with the RSA cryptosystem. Therefore, this proposed montgomery multiplier enforce the real time processing and prevent outer cracking.

• Elastomers and Composites
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• v.44 no.4
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• pp.391-396
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• 2009

This paper presents the numerical analysis of thread rolling. Firstly, the analysis is focused on the effective analysis conditions that guarantee the reliability of the analysis results. The investigated parameters are the number of teeth and the number of elements. Using the analysis results, the number of elements and the number of teeth that guarantee the results are found. And then, the effects of the process parameters such as tool shape and temperature on the thread rolling are investigated. The analysis is carried out using DEFORM-3D. The results show that the flank angle and crest round have an effect on the thread rolling load. It is also shown that temperature have significant effects on the effective strain distribution, rolling load, and crack initiation. The crack initiation is predicted using the Cockcroft-Latham criterion.

• Journal of the Institute of Convergence Signal Processing
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• v.9 no.1
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• pp.10-17
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• 2008

The purpose of this thesis is to reduce of error for source location through acoustic emission(AE) signal, generated elastic wave from crack growth to leak for facility diagnosis. Especially, in order to overcome noise from original signal, this paper proposed enhancement of source location by using noise reduction based on wavelet transform. To evaluate actual performance in experiments, Pencil Lead Break is used crack signal source on the aluminum plate and drain valve of air compressor is used as substitute pressure vessel to generate leak signal. In signal processing, wavelet shrinkage and soft threshold are used to discriminate signal source and then source location techniques have been effectively used with group velocity using material property and time difference between sensor using cross correlation. Source location for crack and leak test have some difference, but the result show that improved 30% with a average length within 10.46mm in crack test and improved 2% compare with average filter in leak test when we applied wavelet transform.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.38 no.2
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• pp.205-210
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• 2014

Recently, pattern recognition methods have been widely used by researchers for fault diagnoses of mechanical systems. A pattern recognition method determines the soundness of a mechanical system by detecting variations in the system's vibration characteristics. Hidden Markov models (HMMs) and artificial neural networks (ANNs) have recently been used as pattern recognition methods in various fields. In this study, a HMM-ANN hybrid method for the fault diagnosis of a mechanical system is introduced, and a rotating wind turbine blade with a crack is selected for fault diagnosis. The existence, location, and depth of said crack are identified in this research. For improving the diagnostic accuracy of the method in spite of the presence of noise, a moment with a few specific frequencies is applied to the structure.

• Journal of the Korean Society for Nondestructive Testing
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• v.36 no.1
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• pp.45-52
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• 2016

Blast furnaces are crucial equipment for steel production. A typical furnace risks unexpected accidents caused by contraction and expansion of the walls under an environment of high temperature and pressure. In this study, an acoustic emission (AE) monitoring system was tested for evaluating the large-scale structural health of a blast furnace. Based on the growth of shell cracks with the emission of high energy levels, severe damage can be detected by monitoring increases in the AE energy parameter. Using this monitoring system, steel mill operators can establish a maintenance period, in which actual shell cracks can be verified by cross-checking the UT. From this study, we expect that AE systems permit early fault detection for structural health monitoring by establishing evaluation criteria based on the severity of shell cracking.

• Journal of the Korean Wood Science and Technology
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• v.32 no.1
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• pp.52-58
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• 2004

Oak is one of major species in this country as well as pine, but has been less utilized because of its refractory properties. The purpose of this study is to develope an effective method for drying the boards and disks of Quercus variabilis. Among four end-coaters used in this study thick coating with polyvinyl acetate chrolide glue (PVAc) was proved as the most effective. The average air-drying rate of boards was 1.2%MC/day, which did not exceed the safe drying rate recommended by United States Department of Agriculture (USDA). The kiln drying schedule used in this study gave a good result in drying the air-dried boards to 8%MC without any internal checks. An attempt to prevent oak disks from V-cracking during air-drying using special pallet-type stickers was not successful.