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맞대기 용접 이음재 인장시험에서 발생한 음향방출 신호의 웨이블릿 변환과 응용
이장규(Zhang-Kyu Rhee) 한국생산제조학회 2007 한국생산제조학회지 Vol.16 No.1
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 STFT) 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.
음향방출 신호분류에 의한 SM45C 고주파 열처리 강의 인장변형 해석
이장규(Zhang-Kyu Rhee),조규태(Kyu-Tae Cho),우창기(Chang-Ki Woo) 한국생산제조학회 2009 한국공작기계학회 추계학술대회논문집 Vol.2009 No.-
This study is deal with the high frequency induction hardening SM45C steel at 850℃, 120㎑ & 50㎾. And giving change to tempering temperature at 150℃, 300℃ & 450℃, tempering time at 0.5, 1.0 & 1.5 hours. The high frequency induction hardening specimen tempered at 150℃, did not appear any tempering effect of test pieces. A brittle fracture occurred at rounded area of tensile specimen, it showed that AE amplitude was relatively low at 45-60㏈. For the specimen which was tempered at 300 ℃, slip and fracture occurred at the hole area of tensile specimen. As it passes the yield point, the number of AE counts and energy value increased intermittently and amplitude was between 70~85㏈. In addition, after the maximum tensile load, it showed relatively high amplitude and energy distribution. Amplitude was between 45~70㏈. For the specimen which was tempered at 450℃, brittle fracture occurred as if it is torn in the direction of 45° on parallel area over the both sides of tensile specimen, which led to several peak value to be appeared in the number of AE counts. It was found that amplitude was relatively low and the energy value was high.
인공신경회로망을 이용한 원공결함을 갖는 유한 폭 판재의 음향방출 음원특성과 파괴거동에 관한 연구
이장규(Zhang-Kyu Rhee),우창기(Chang-Ki Woo) 한국생산제조학회 2009 한국생산제조학회지 Vol.18 No.2
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) continuity, we used K-means clustering method as an unsupervised learning method for obtaining 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 obtaining 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 a result, in k-NNC before fracture signal is detected or when fracture signal is detected, showed that produce some empty classes in BPN. And we confirmed that could save trouble in AE signal processing if suitable error of convergence or acceptable encoding error give to BPN.
SWS 490A 강의 용접 열영향부 음향방출 특성에 대한 연구(2)
이장규(Zhang-Kyu Rhee),우창기(Chang-Ki Woo) 한국생산제조학회 2006 한국생산제조학회지 Vol.15 No.5
The main objective of this study is to investigate the effect of compounded welding by using acoustic emission (AE) signals and doing a source location for weld heat affected zone (HAZ) through tensile testing. This study was carried out an SWS 490A high strength steel for electric shield metal arc welding, SMAW; CO₂ gas metal arc welding, GMAW(CO₂); and gas tungsten arc welding, GTAW/TIG. Data displays are based on the measured parameters of the AE signals, along with environmental variables such as time and load. For instance, Gutenberg-Richter magnitude-frequency relationship (G-R MFR) offers useful b-value in data analysis. Namely event identification, source location gives the X- and Y-coordinates of the AE source. And K-means clustering analysis by Euclidean distance confirmed that was powerful to source location. Generally, strength of welded metal zone was stronger than strength of base metal. As the result, confirmed certainly that fracture is produced in HAZ instead of welded metal zone from source location.
음향방출 신호를 이용한 SWS 490A 고장력강의 접합성 평가에 대한 실험적 연구
이장규(Zhang-Kyu Rhee),우창기(Chang-Ki Woo) 한국생산제조학회 2005 한국생산제조학회지 Vol.14 No.3
The object of this study is to investigate the effect of joinability by using acoustic emission(AE) signals and doing a pattern recognition for weld heat affected zone(HAZ) in tensile testing. This study was carried out an SWS 490A high tension steel for electric shielded metal arc welding(SMAW), CO₂ gas arc welding and TIG welding. And correspondingly, the root openings are 3, 4 and 2.8mm. The results of the tensile test of weld HAZ come out electric shield arc welding > CO₂ gas arc welding > TIG welding in case of single welding. It is believed that this is a phenomenon where difference of its root opening or base metal thickness. Also, the technique of AE is ideally suited to study variables which control time and stress dependent fracture or damage process in metallic materials.
오진수,우창기,이장규,Oh, Jin-Soo,Woo, Chang-Ki,Rhee, Zhang-Kyu 한국생산제조학회 2010 한국생산제조학회지 Vol.10 No.6
In this study, DAQ and TRA modules were applied to the CFRP single specimen testing method using AE. A method for crack identification in CFRP specimens based on k-mean clustering and wavelet transform analysis are presented. Mode I on DCB under vertical loading and mode II on 3-points ENF testing under share loading have been carried out, thereafter k-mean method for clustering AE data and wavelet transition method per amplitude have been applied to investigate characteristics of interfacial fracture in CFRP composite. It was found that the fracture mechanism of Carbon/Epoxy Composite to estimate of different type of fractures such as matrix(epoxy resin) cracking, delamination and fiber breakage same as AE amplitude distribution using a AE frequency analysis. In conclusion, the presented results provide a foundation for using wavelet analysis as efficient crack detection tool. The advantage of using wavelet analysis is that local features in a displacement response signal can be identified with a desired resolution, provided that the response signal to be analyzed picks up the perturbations caused by the presence of the crack.
조대희(Dae-Hee Jo),이장규(Zhang-Kyu Rhee),박성완(Sung-Oan Park),김봉각(Bong-Gag Kim),우창기(Chang-Ki Woo) 한국생산제조학회 2006 한국공작기계학회 춘계학술대회논문집 Vol.2006 No.-
This study is results of single-and two-spot resistance spot welding for spec steel. Test specimens were welded horizontally or vertically according to the rolling direction of base metal in two-spot welding. About whole occasions, measured acoustic emission(AE) signals are analyzed. As the results, in the case of two-spot welding, horizontal type increased elongation more than vertical type in tensile-shear test. Therefore, could know that it is profitable structurally that consider direction(or arrangement) of nugget of according to direction, if secondary process attains since resistance spot welding.
조대희(Dae-Hee Jo),이장규(Zhang-Kyu Rhee),박성완(Sung-Oan Park),조진호(Jin-Ho Cho),김봉각(Bong-Gag Kim),우창기(Chang-Ki Woo) 한국생산제조학회 2006 한국생산제조학회지 Vol.15 No.4
In this paper, for the purpose of investigation the acoustic emission(AE) behaviors during resistance spot welding process and tension test of SPCC steels. As the results present the resistance spot welding method that can get suitable welding qualities or structural integrity estimating method. The resistance spot welding process consists of several stages: set-down of the electrodes; squeeze; current flow; forging; hold time; and lift-off. Various types of AE signals are produced during each of these stages. For tensile-shear test and cross tensile test in resistance spot welded specimens, fracture patterns are produced: tear fracture; shear fracture; and plug fracture. Tensile-shear specimens strength appeared higher than cross tensile specimens one. In case of tensile-shear specimen happened tear fracture that crack happens in most lower plate. Also, in case of cross tensile specimens, upper plate and lower plate are detached perfect fracture was exposed increases a little as acting force is lower than ordinary welding condition. Therefore, the structure which is combined by resistance spot welding confirmed that welding design must attain so that shear stress may can interact mainly.
음향방출법에 의한 저항 점용접부의 파괴특성에 대한 연구
조대희(Dae-Hee Jo),이장규(Zhang-Kyu Rhee),박성완(Sung-Oan Park),김봉각(Bong-Gag Kim),우창기(Chang-Ki Woo) 한국생산제조학회 2007 한국생산제조학회지 Vol.16 No.2
In this paper, the acoustic emission(AE) behaviors were investigated with single- and 2-spot resistance spot welded SPCC specimens. Test specimens were welded horizontally and/or vertically according to the rolling direction of base metal in 2-spot welding. In the case of 2-spot welding, when tensile-shear test has below amplitudes: crack initiation 50~60㏈; tear fracture 40~50㏈. And when cross tensile test has below amplitudes: early stage 75~85㏈; yielding point 65~75㏈; post yielding 40~60㏈; plug fracture 70~80㏈ or 90~100㏈. Also, from the b-value that is slope of AE amplitude, we knew that there are lots of low amplitudes if b-value is big(i.e., tensile-shear specimen→tear fracture or shear fracture), and there are lots of high amplitudes if b-value is small(i.e., cross tensile specimen→plug fracture). As the results of fracture mechanism analyses through AE amplitude distributions, change of the b-value represented fracture patterns of materials. Correspondingly, low amplitude signals appeared in crack initiation, and high amplitude signals appeared in base metal fracture. We confirmed that these amplitude distributions represented the change or degradation of materials.