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김옥래(Ok Rae Kim),우창기(Chang Ki Woo) 한국생산제조학회 2011 한국생산제조학회지 Vol.20 No.4
In this paper, using by rapid heating and cooling systems for injection molding and temperatures to changes. In the process of molding temperature and pressure inside the mold was found. In addition, the tensile strength of test specimens were molded, mechanical properties of injection molded parts were identified on mold temperature. Copper could withstand more tensile force than NAK. Therefore, it can be concluded that materials with high heat conductivity must be used in thin walled products.
원공결함을 갖는 SM45C 인장시험편의 강도해석과 음향방출에 관한 사례연구
우창기(Chang-Ki Woo),이장규(Zhang-Kyu Rhee) 한국생산제조학회 2008 한국생산제조학회지 Vol.17 No.1
The SM45C metallic coupons have been tested under static tensile loading with acoustic emission (AE) as the load-deflection curve mainly. In this study, we used AE to detect the yielding of material and AE techniques was applied to rapidly estimate the mechanical characteristics of a material. First, coupons without an artificial defect were tested at different cross-head speed. For all cases in this analysis, yielding point of SM45C coupons did not appear definitely compared to mild steel, whereas coupons start to generate AE counts upon yielding. So all cases are normalized to know the possibility of accelerated life test of a material. And next, coupons with different from sizes of circular hole defects were tested at the same cross-head speed of 5 mm/min. Results were classified into 3 classes and analyzed by AE amplitude & signal strength as a function of time. Summarizing the specific conclusions, we need to additional research considering plate with width-ratio in order to estimate the fracture mechanism.
원공결함을 갖는 SM45C 인장시험편의 강도해석과 음향방출에 관한 사례연구
우창기(Chang-Ki Woo),이장규(Zhang-Kyu Rhee),조대희(Dae-Hee Jo) 한국생산제조학회 2007 한국공작기계학회 춘계학술대회논문집 Vol.2007 No.-
This study was analyzed about load-deflection curve of SM45C metallic coupons through AE (acoustic emission) techniques mainly. Coupons that artificial defect does not exist were tested according to the speed of crosshead. First, yielding point of SM45C steel did not appear definitely compares to mild steel. So normalized all above cases to know tendency, and confirmed possibility of accelerated life test of isotropic materials. And next, coupons with differs size of circular hole defect were tested in the equal cross head speed at 5 ㎜/min. Generally AE counts appeared continually before fracture over whole unlike example of mild steel. As a result, classified 3 classes by AE amplitude & signal strength as a function of time here for signal analysis with a circular hole defect 7.5 ㎜ and analyzed. Is judged that need addition research that consider subsequentness width-ratio for searching examination of correct fracture mechanisms for this part.
유효 K₁_d 산정을 위한 샬피 충격시험편의 노치형상에 관한 연구
우창기(Chang-Ki Woo),강동명(Dong-Myeong Kang),이하성(Ha-Sung Lee) 한국자동차공학회 1999 한국 자동차공학회논문집 Vol.7 No.6
This investigation evaluates effects of notch depth, fatigue precrack length and side groove in impact specimen for estimation of a valid K1d by instrumented Charpy impact test. Specimen material is 6005-T6. For notch depth 2.0mm and 2.5mm specimens or within about 2 mm fatigue precrack length with notch depth 2.0mm specimens, dynamic fracture toughness [K₁_d,(1)] obtained by crack initiation load (P_m) should be used. Dynamic fracture toughness of side grooved specimens are overestimated to that of standard impact specimen about 15%-20%. It is confirmed that the formula of dynamic fracture toughness obtained by impact absorbed energy is inappropriate for ductile materials.<br/>
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.
균열을 내재한 저압터빈 최종단 블레이드의 진동 특성 및 파괴 임계균열길이 해석
윤희철(Hee-Chul Youn),우창기(Chang-Ki Woo),이장규(Zhang-Kyu Rhee) 한국생산제조학회 2016 한국생산제조학회지 Vol.25 No.5
The sizes of last stage blades (LSB) in a low-pressure steam turbine have been getting larger for the development of high-capacity power plants. They are also larger than other blades in the same system. As a result, crack propagation in an LSB is caused by the large centrifugal force, low natural frequency, and repeated turbine startups. In this study, the critical crack length for a fracture and vibration characteristics, in accordance with crack propagation, were analyzed using a finite element method to calculate the stress intensity factor (SIF) and the natural frequency that was affected by the stress-stiffening effect. It was calculated that the frequency of the third and fifth modes passed the excited harmonic resonance (5X and 10X) and the observed calculated critical crack length matched that of the real fractured surface.
주파수 응답해석을 통한 제작공차를 가지는 저압터빈 케이싱의 고진동 원인 규명
윤희철(Hee-Chul Youn),우창기(Chang-Ki Woo),황재곤(Jai-Kon Hwang) 한국생산제조학회 2015 한국생산제조학회지 Vol.24 No.4
High vibration of a low pressure (LP) turbine casing caused safety problems and life at the facility it was housed in. The main focus of this study was the cause of the high vibration in a low pressure turbine casing with manufacturing defects by frequency response analysis, compared with the results of experiments. Therefore, excited accelerations were obtained from the LP casing fundamental, and frequency responses were analyzed. The measurement and the modal analysis showed that the natural frequency of the LP turbine casing was 61.26 Hz and the excited frequency of the turbine rotor was 60.25 Hz. The manufacturing defect caused a decrease in the casing natural frequency and resulted in the high vibration of the casing because it moved close to the resonant frequency.
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.