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피로균열 열림 및 닫힘에 따른 음향방출 신호 발생 특성 고찰
정중채(Jung-Chae Jeong),윤동진(Dong-Jin Yoon),박휘립(Philip Park),김기복(Ki-Bok Kim),이승석(Seung-Seok Lee) 대한기계학회 2002 대한기계학회 춘추학술대회 Vol.2002 No.3
The objective of this study was to investigate the effect of crack opening and closure in the AE activities during fatigue test. Laboratory experiment using various materials and test conditions were carried out to identify AE characteristics of fatigue crack propagation. Compact tension specimens of SWS 4908 and Al 7075-T6 aluminum alloy were prepared for fatigue test. AE activities were analyzed based on the phase of the loading cycle. Generally, most of AE were generated at the time of early stage of crack opening and closure, whereas a few in the peak loading of cycle. Also the time of high occurrence of AE event was different with each specimen. However, in the same material, the trend of AE activity was not affected by the change of cyclic frequency (0.1, 0.2, 1 ㎐). It was found that AE activities during crack opening and closure depend on material properties such as micro-structure, yield strength and elongation.
TiO$_2$/Mg 반응에 의한 흑색산화티타늄 제조시 반응 변수 연구
정중채,조정웅,이혁희,이종현,원창환,Jeong, Jung-Chae,Jo, Jeong-Ung,Lee, Hyeok-Hui,Lee, Jong-Hyeon,Won, Chang-Hwan 한국재료학회 2001 한국재료학회지 Vol.11 No.10
One of the important phase of black titanium oxide is $Ti_4O_7$</TEC> which has the excellent properties such as the greatest electrical conductivity among the titanium oxides, chemical resistance against acidic and alkalic conditions and electro-wave absorption etc., so it has been considered as a promising material to be used widely all over the parts of industries. In this study, $Ti_4O_7$</TEC> phase was successfully synthesized by the reaction of TiO$_2$/ Mg system. With the change of the mole of TiO$_2$to Mg, the most excellent blackness was appeared in the 3.5 mole which was the smaller amount than the stoichiometric 4.0 mole. In addition, we found that the blackness decreased as the mole ratio of reactent increased. With decreasing particle size of magnesium, blackness of titanium oxide increased. The reaction property was changed with the compaction pressure, and optimum pressure was found to be 10 MPa. At 55$0^{\circ}C$ of reduction temperature, the blackness increased as the reaction time increased. The blackness of synthesized black titanium oxide was 14 to 18, and the average particle size was 0.2 $\mu\textrm{m}$.
구조용 용접강 SWS 490B 의 피로균열 진전시 음향방출 거동
정중채(Jung-Chae Jeong),윤동진(Dong-Jin Yoon),박휘립(Philip Park),김기복(Ki-Bok Kim),이승석(Seung-Seok Lee) 대한기계학회 2002 대한기계학회 춘추학술대회 Vol.2002 No.5
The objective of this study was to investigate the effect of AE activities during fatigue test.<br/> Laboratory experiment was carried out to identify AE characteristics of fatigue cracks for compact<br/> tension specimen. Compact tension specimen of SWS 490B was prepared for fatigue test. The<br/> relationship between a stress intensity factor and AE signals activity as well as conventional AE<br/> parameter analysis was discussed. From the experimental results, the features of specific parameters<br/> such as the length of crack growth, the AE energy and the AE peak amplitude, showed the almost<br/> same trend in their increase as the stress intensity factor increased. The fracture surface of test<br/> specimens revealed both intergranular fracture and transgranular fracture. Size and density of slip<br/> band by fatigue crack propagation were varied as the stress intensity factor increased, AE activities<br/> were different according to the slip band shape.
FACS법에 의한 Fe-Al계 금속간화합물의 제조시 통전방식의 영향
윤기석,정중채,원창환,Yun, Gi-Seok,Jeong, Jung-Chae,Won, Chang-Hwan 한국재료학회 1999 한국재료학회지 Vol.9 No.7
Fe-Al계 금속간화합물이 FACS (Field-Activated Combustion Synthesis) 법에 의해 제조되었다. 이 계의 반응에 있어서 조성 (Fe:Al=3 : 1,2 : 1, 1 : 1.1 : 2, 1 : 3) , 성형압력 (150, 250, 350MPa), 저항 등이 조사되었는데. Al의 몰비, 성형압력, 전기장의 세가가 증가함에 따라서 연소온도와 연소속도는 증가하였다. 또한 이 계에 있어서 전류적용방식에 따른 반응에 대한 영향이 조사되었다. 전기장이 적용되지 않는 경우, 반응이 일어나기 위해서는 예열이 필요하였고, 예열을 하였을 경우라도 그 반응은 불안정연소파를 나타내어 완전한 반응이 이루어지지 않았다. 생성물은 X-ray, SEM, EDXS를 사용하여 그 구조와 조성을 관찰하였다 Fe-Al intermetallic compounds were manufactured by using the field-activated combustion synthesis process. Effects of chemical composition(Fe:Al= 3: 1,2:1, 1:1, 1:2, 1:3), Compaction pressure(150, 250, 350MPa) and electrical resistance on the reaction were investigated in this system. As the molar ratio of Al, compaction pressure and electric field increased, the combustion temperature and velocity were increased. The influences for reaction with current adjust way were investigated in this system. But in the absence of a electric field, the reaction could sustain a nonsteady combustion wave and was not completed. The reaction products were characterized with X-ray, SEM and EDXS to determine the structure and composition.
SHS법에 의한 $\textrm{Al}_2\textrm{O}_3$-SiC 복합분말 제조 및 소결특성
안창영,윤기석,정중채,원창완,An, Chang-Yeong,Yun, Gi-Seok,Jeong, Jung-Chae,Won, Chang-Wan 한국재료학회 1999 한국재료학회지 Vol.9 No.8
$Al_2$$O_3$-SiC 화합물 분말이 $SiO_2$, A1 그리고 C 분말들을 원료분말로 하여 SHS(self-propagating High-temperature Synthesis)법에 의해 제조되었다. 원료 분말에서의 몰비, 성형압력, 반응물의 초기온도의 영향이 생성물과 연소과정에 대해 연구되었다. $SiO_2$/A1/C계의 자전연소합성은 낮은 연소온도 때문에 $400^{\circ}C$ 이상으로 예열되어야 한다. 연소반응의 결과로서 최종생성물의 순도는 반응물의 순도보다 높았다. 이 계에서 $SiO_2$:Al:C의 적당한 몰비는 3.0:4.0:6.0이었고, free carbon은 30min 동안 $650^{\circ}C$에서 배소함으로써 제거되었다. 본 연구에서 상압소결은 $1700^{\circ}C$에서 powder bed를 사용한 표본의 분해를 제어하고 치밀한 소결체를 얻는데 매우 효과적이었다. hot-pressing으로 생성된 소결체는 이론비교밀도의 약 98%이었다. The $Al_2$$O_3$-SiC composite powder was prepared by Self-propagating High-Temperature Synthesis(SHS) process using $SiO_2$Al and C powders as raw material. The effects of the molar ratio in raw material, compaction pressure, initial temperature of reactants on the products and combustion process were studied. Self-propagating high temperature synthesis of $SiO_2$/Al/C system should be preheated above $400^{\circ}C$ owing to the low combustion temperature. As the result of the combustion reaction, the purity of final product became better than that of reactants. In this system, the optimum molar ratio of $SiO_2$:Al:C was 3.0:4.0:6.0. The free carbon was removed by roasting at $650^{\circ}C$ for 30min. In this study, pressureless sintering was very dffective both for controlling the disintegration of specimen with powder bed and for obtaining dense sintered-body at $1700^{\circ}C$. The sintered-body produced with hot-pressing was about 98% of the theoretical relative density.
윤동진(Dong-Jin Yoon),정중채(Jung-Chae Jeong),이영섭(Young-Sup Lee) 대한기계학회 2003 대한기계학회 춘추학술대회 Vol.2003 No.4
Water leak is one of topics with great concern in Korea and many other countries, because of<br/> decreasing water supplies and the deterioration of old pipeworks. Correlation techniques have been<br/> widely used in leak detection of water pipes, which allow to locate a leak point based on the<br/> correlation of leak noise at two sites along water pipes. In this study, both the cross-correlation<br/> method and the conventional arrival time difference method are applied in order to analyze and to<br/> locate a leak point of a water pipe. In experiment, a 150 m of whole length waterwork pipeline<br/> system was constructed in a ground, and several types of leak noise were installed on the pipeline in<br/> order to control leak condition. Both the cross-correlation technique and the arrival time difference<br/> method showed favorable results at leak detection with the experimental pipeline system.