음향방출법에 의한 SM 490A 강의 복합용접성 평가(2)

이장규,우창기,김봉각,윤종희,인승현 한국공작기계학회 2003 한국공작기계학회 춘계학술대회논문집 Vol.2003 No.-

The object of this study is to investigate the effect of compounded welding by using an acoustic emission (AE) signals and doing a source location for weld heat affected zone (HAZ) through tensile testing. This study was carried out a SM 490A high tension steel for electronic shielded metal arc welding (SMAW), CO₂ gas arc welding and TIG welding. Data displays are based on the measured parameters of the AE signals, along with environmental variables such as time and load. These history plots are displays showing the chronological course of the test. Also, source location gives the X- and Y-coordinates of the AE source.

패혈증 백서 모델에서 비타민-C의 효과

이중의,신상도,표창해,서길준,정성은,윤여규 대한응급의학회 1999 대한응급의학회지 Vol.10 No.4

Background : Multi-organ failure from sepsis is very lethal disease entity, which is suspected to be caused by activated inflammatory cells. Inflammatory cells activated by endotoxins generate oxidants and cytokines such as TNF-α and IL-6, which in turn stimulate macrophages and neutrophils. Augmented inflammation makes an organ-injury deteriorate into an organ-failure, which may progress to multi-organ failure. This study is designed to evaluate the therapeutic effects of vitamin-C, a scavenger of oxidants, in sepsis. Methods : Male Sprague-Dawley rats were divided into 3 groups : a control group, a group injected intrapetoneally with LPS(lipopolysaccharide), and a group injected intraperitoneally with LPS and vitamin-C. Each eight rats were sacrified 24 hours and 48 hours after injection, and samples of the blood, the liver and the lung were obtained. Biochemical assays of TNF-α level in the blood and malondialdehyde(MDA)level, catalase activity and nitric oxide synthase(NOS)activity in the liver and the lung tissues were performed. Results : Serum TNF-α level, tissue lipid peroxidation and tissue i-NOS activity were dramatically increased, and tissue catalase activity was exhausted rapidly in sepsis. High dose vitamin-C administration decreased serum TNF-α level, tissue lipid peroxidation and tissue i-NOS induction, and protected against catalase exhaustion. Conclusion : high dose vitamin-C therapy was proved to have definite antioxidant effect in septic condition.

음향방출법에 의한 SM 490A 강의 복합용접성 평가 (3)

이장규,인승현,우창기,박성완,김봉각 한국공작기계학회 2003 한국공작기계학회 추계학술대회논문집 Vol.2003 No.-

The object of this study is to investigate the effect of compounded welding by using acoustic emission (AE) signals for weld heat affected zone (HAZ) in tensile testing. This study was carried out a SM 490A high tension steel for electronic shielded metal arc welding (SMAW), CO₂ gas arc welding and TIG welding. And correspondingly, the root openings are 3, 4 and 2.8㎜. Data displays are based on the measured parameters of the AE signals, along with environmental variables such as time and load. These history plots give us useful and powerful information to analyze the results of material evaluation testing.

인공신경회로망을 이용한 원공결함을 갖는 유한 폭 판재의 음향방출 음원특성과 파괴거동에 관한 연구

이장규,우창기 한국공작기계학회 2008 한국공작기계학회 추계학술대회논문집 Vol.2008 No.-

The objective of this study is to evaluate an acoustic emission (AE) source characterization and fracture behavior of the SM45C steel by using back-propagation neural network (BPN). In previous research Ref. [8] about k-nearest neighbor classifier (k-NNC) continuously, we used K-means clustering method as an unsupervised learning method for obtained multi-variate AE main data sets, such as AE counts, energy, amplitude, risetime, duration and counts to peak. Similarly, we applied k-NNC and BPN as a supervised learning method for obtained multi-variate AE working data sets. According to the error of convergence for determinant criterion Wilk's λ, heuristic criteria D&B(Rij) and Tou values are discussed. As the results show that BPN produced some empty classes before or at the same time k-NNC detect fracture signals. And confirmed that could save trouble to AE signal processing if suitable error of convergence or acceptable encoding error gives to BPN.

맞대기 용접 이음재 인장시험에서 발생한 음향방출 신호의 웨이블릿 변환과 응용

이장규,윤종희,우창기,박성완,김봉각,조대희 한국공작기계학회 2005 한국공작기계학회 춘계학술대회논문집 Vol.2005 No.-

This study was carried out fusion-welded butt joints in SWS 490A high strength steel subjected to tensile test that load-deflection curve. The windowed or short-time Fourier transform (WFT or SIFT) makes possible for the analysis of non-stationary or transient signals into a joint time-frequency domain and the wavelet transform (WT) is used to decompose the acoustic emission (AE) signal into various discrete series of sequences over different frequency bands. In this paper, for acoustic emission signal analysis to use a continuous wavelet transform, in which the Gabor wavelet base on a Gaussian window function is applied to the time-frequency domain. A wavelet transform is demonstrated and the plots are very powerful in the recognition of the acoustic emission features. As a result, the technique of acoustic emission is ideally suited to study variables which control time and stress dependent fracture or damage process in metallic materials.

음향방출을 이용한 일방향 탄소섬유강화 플라스틱의 손상평가에 관한 연구

이장규,박성완,김봉각,우창기 한국공작기계학회 2005 한국생산제조학회지 Vol.14 No.1

This study is to investigate a damage estimation of single edge notched tensile specimens as a function of acoustic emission(AE) according to the uni-directionally oriented carbon fiber/epoxy composites, CFRP. In fiber reinforced composite materials, AE signals due to several types of failure mechanisms are typically observed. These are due to fiber breakage, fiber pull-out, matrix cracking, delamination, and splitting or fiber bundle breaking. And these are usually discriminated on the basis of amplitude distribution, event counts, and energy related parameters. In this case, AE signals were analyzed and classified 3 regions by AE event counts, energy and amplitude for corresponding applied load. Bath-tub curve shows 3 distinct periods during the lifetime of a single-edge-notch(SEN) specimen. The characterization of AE generated from CFRP during SEN tensile test is becoming an useful tool for the prediction of damage failure or/and failure mode analysis.

음향방출 신호분류에 의한 SM45C 시효처리재의 인장변형 해석

이장규,우창기,김용배 한국공작기계학회 2009 한국공작기계학회 춘계학술대회논문집 Vol.2009 No.-

This study investigates tensile deformation of the stress aging heat-treated SM45C steel which are aging temperature at 250, 300℃, aging time at 1,3 hours, and applied load at 300, 400N conditions by using acoustic emission (AE). A signal processing technology used to evaluate an AE source characterization by 2 AE measurement systems, i.e., DiSP & PCI-2 AE hardware and AEwin™ software. In this study, most suitable aging condition appeared at 250℃, 3 hours and 300N. On the other hand, in case of 250℃, 3 hours, 400N and 300℃, 3 hours, 400N conditions, yield load decreased than other conditions according to the over-aging phenomena. Especially, In case of 300℃, 3 hours and 400N condition appeared AE energy in elastic limit fairly high than non-heat treatment specimen.

SWS 490A 강의 용접 열영향부 음향방출 특성에 대한 연구(1)

이장규,우창기,박성완,윤종희,조진호,김봉각,구영덕 한국공작기계학회 2004 한국생산제조학회지 Vol.13 No.4

The object of this study is to investigate the effect of compounded welding through the AE(Acoustic Emission) characteristics for weld HAZ(Heat Affected Zone) under the static tensile test. This study was carried out an SWS 490A, high tension steel for electric shield metal arc welding(SMAW), CO₂gas arc welding and TIG welding. Data displays are based on the measured parameters of the AE signals, along with environmental variables such as time and load. The accumulated AE event curve of HAZ definitely have the point of inflection subject to tensile test. The results of the tensile test of HAZ come out electric shield arc welding > CO₂ gas arc welding >TIG welding in case of single welding, but generally the tensile test of HAZ come out electric shield arc welding > TIG welding > CO₂ gas arc welding. These history plots give us useful and powerful information to analyze the results of material evaluation testing.

K-최근접 이웃 분류기를 이용한 원공결함을 갖는 유한 폭 판재의 음향방출 음원특성과 파괴거동에 관한 연구

이장규,우창기,오진수 한국공작기계학회 2008 한국공작기계학회 춘계학술대회논문집 Vol.2008 No.-

The objective of this study is to evaluate an acoustic emission (AE) source characterization and fracture behavior of the SM45C steel by using k-nearest neighbor (KNN) classifier. In previous research continuously, simple tension and AE tests were conducted against the 5 kind of circular hole defect coupons. Also, for this, we used K-means clustering as an unsupervised learning method for obtained multivariate AE main data sets, such as AE counts, energy, amplitude, risetime, duration and counts to peak. And we applied KNN classifier as a supervised learning pattern recognition algorithm for obtained multivariate AE working data sets. Through the classified results, i.e., determinant criterion (Wilk) and heuristic criteria (Rij & Tou), of the effectiveness of the proposed method is discussed.

Spot 가진을 이용한 평면결함의 음향방출 위치표정

이장규,박성완,우창기 한국공작기계학회 2004 한국생산제조학회지 Vol.13 No.5

From the results of AE(Acoustic Emission) source location occurred by the spot exciting as suggested in this research, it has been confirmed that AE technique is quite fruitful in figuring out the location of the occurrence, form, size and direction of the defects. As the results of examining the distribution of event for the angle of crack α to Xs and Ys, as the increases from 0˚~90˚, gradually changes its width from the axis Xs to the axis Ys. So event appears approximately similar in its size at the angle of crack α=45˚, yet opposite when a is lager. It is believed that this is a phenomenon where its crack length a, assumed as a planar defect, is to be projected toward the direction with a larger size. Thus, it is expected that the application of the experimental method suggested in this study would make it possible to identify the location of the defect in the material in the nondestructive way.