암석폐재의 고화체 합성 기술의 개발과 고화기구의 평가에 관한 연구

나의균,유효선,정세희,Na, Ui-Gyun,Yu, Hyo-Seon,Jeong, Se-Hui 한국재료학회 1997 한국재료학회지 Vol.7 No.4

본 연구에서는 암석폐재를 대상으로 직경이 60mm인 고화체를 얻을 수 있는 수열 hot press 장치를 개발하였고, 고형화를 위한 최적조건을 찾아내는 내용을 다루었다. 이어 고화체의 기계적 성질을 평가하였고, 고화기구와 미시적 파괴거동을 규명하기위하여 SEM관찰 및 음향방출실험을 실시하였다. 고형화를 위한 최적조건은 NaOH용액이 10wt%, 수열온도가 30$0^{\circ}C$이고, 유지시간이 1시간이었다. 또한 수열반응동안에 다양한 제 2화합물들이 생성되었으며, 이들은 고화체의 기계적 성질에 큰 영향을 미쳤다. 아울러 원석의 경우에는 AE Counts가 초기화중에서부터 나타났으나, 고화체는 초기하중에서 전혀 AE Counts가 검출되지 않았다. 이와같은 사실로부터 수열 hot press법에 의해 얻어진 고화체는 원석과는 다르게 암석 입자간의 결합이 보다 치밀하게 이루어지고 있음을 유추할 수 있다.

수열 Hot press법에 의한 화강암폐재의 고화체형성과 AE특성 평가에 관한 연구

나의균,Na, Ui-Gyun,Toshiyuk, Hashida 한국재료학회 1996 한국재료학회지 Vol.6 No.3

본 연구는 화강암 폐재의 재활용을 목적으로 한 기초적인 연구로서, 분말형태의 화강암폐재를 Ca(OH2)와 혼합하여 수열 hot press 법에 의해 고화시켰다. 아울러 고화체의 기계적 성질을 평가하였으며, 미시적 조직구조의 변화 및 파괴거동을 파악하기 위해 음향방출실험을 실시하였다. 고화체의 기계적 성질은 수열온도의 의존성이 있었으며, 28$0^{\circ}C$에서 최대강도를 보였다. 또한 고화체의 파면은 수열온도에 따라 현저히 다른 양상을 보였으며, 수열실험동안 다양한 화합물이 생성되었다. 그 중에서 cyclowollastonite, tobermorite 및 rankinite 등은 강도를 향상시키는 주된 화합물이었고, crossite 및 xonotlite 등은 강도의 저하를 초래하였다. 한편, 기공이 많이 존재할수록 AE counts는 더많이 발생하였으며, 최대하중에서 AE counts는 최대치를 보였고, 강도가 증가함에 따라 AE신호는 보다 많이 방출되었다.

$CO_2$가스 배관용접부의 파괴인성평가에 관한 연구

나의균,유효선,오석형,Na, Ui-Gyun,Yu, Hyo-Seon,O, Seok-Hyeong 대한기계학회 2000 大韓機械學會論文集A Vol.24 No.7

The purpose of this study is to examine the fracture toughness of the welded pipe from the viewpoint of FATT for the S38 and S42 steels used widely as the pipe material. Post weld heat treatment(PW HT) was carried out like following conditions: temperature of 67$0^{\circ}C$, I hour of holding time and cooling in furnace. Fracture toughness was obtained by measuring the crack opening displacement(COD) of the notched specimens over the range of temperature from -14$0^{\circ}C$ to -$25^{\circ}C$. Hardness values at fusion line near around were the highest and the microstructures at welded zone were coarsened. Regardless of the pipe materials, COD and temperature curves of the as-welds were moved toward higher temperature compared with those of the parents. However, COD and temperature curves of the PWHT specimens were positioned at lower temperature compared with those of the as-welds. The more heat input causes to decrease the COD values at the constant temperature. It was verified through the recrystallization treatment that PWHT was attributed to move toward lower temperature region considerably due to the improved plastic deformation at the same applied COD value of 0.3mm and softening effect. In case of the weldment of S38 steel, cleavage fracture was observed at -105$^{\circ}C$ unlike the structural steels, in which brittle fracture mode was generally shown at - 196$^{\circ}C$.

암석폐재의 고화체 합성기술의 개발과 파괴인성평가에 관한 연구

나의균,유효선,김진용,이종기,정세희,Na, Eui-Gyun,Yu, Hyosun,Kim, Jin-Yong,Lee, Jeong-Gee,Chung, Se-Hi 대한기계학회 1997 大韓機械學會論文集A Vol.21 No.9

The hot press apparatus to obtain the solidified rocks with 60mm of diameter against rock waste was developed, and the optimum conditions for solidification were founded out, of which were 300.deg. C of temperature and 1hr of holding time. The solidified rocks reinforced with the fibers (carbon, steel) were made by means of a hydrothermal hot press method. Fracture toughness of those was obtained using the round compact tension(RCT) specimens. Load and displacement behaviours of the solidified rocks reinforced with the fibers were dependent upon the fiber volume fraction and kind of the fibers. Strength and fracture energy of the solidified rocks with steel were much larger than those of the solidified ones with carbon because of the Bridge's effect, multiple cracking and crack branching phenomena.

전기화학적 분극법에 의한 1.0Cr-0.5Mo강의 경년열화 평가에 관한 연구

나의균,김훈,이종기,Na, Eui-Gyun,Kim, Hoon,Lee, Jong-Gi 대한기계학회 1998 大韓機械學會論文集A Vol.22 No.1

The contents of this paper include a non-destructive technique for evaluating the degradation of the boiler superheater tube in a fossil power plant through an electrochemical polarization test. Correlation between Ip of polarization parameter and SP-DBTT for the superheater tubes in long-term use was obtained. 1.0Cr-0.5Mo steel was degraded by softening, and the degree of degradation was dependent upon carbides with Cr and Mo elements. Since brittle fracture at low temperature and ductile fracture mode at high temperature were shown, similarity between standard Charpy and small punch tests could be found. In addition, SP-DBTT showing the degree of degradation was higher, as the time-in use of the materials got longer. Electrolyte including picric acid of 1.3 g in distilled water of 100ml at 25.deg. C temperature and sodium tridecylbenzene sulfonate with 1g could be applied to evaluate the degradation of 1.0Cr-0.5Mo steel by means of the electrochemical polarization test. Ip and Ipa values measured through the electrochemical test are the appropriate parameters for representing the degradation of the superheater tube(1.0Cr-0.5Mo steel) for the fossil power plant. It is poassible to evaluate the degradation of materials with different time histories electrochemically, by Ip value only, at field test.

수열 Hot Press법에 의한 화강암 폐재의 고화체형성 및 평가기술의 개발에 관한 연구

나의균,정세희,Na, Eui-Gyun,Chung, Se-He,Takahashi, Hideaki 한국재료학회 1995 한국재료학회지 Vol.5 No.3

본 연구에서는 석재공장 주변의 오염원으로 되고 있는 화강암 폐재의 고화체의 형성과 평가 기술에 관한 내용을 다루었다. 이를 위해, 최근 고화체의 함성기술로서 높이 평가받고 있는 수열 Hot press법을 이용하여 분말형태의 화강암 폐기물을 고화시키는데 필요한 조건을 찾아내었다. 아울러 고화체의 기계적 성질과 파면의 양상 및 수열실험동안 발생된 생성물 사이의 상호 관계를 고찰하였다. 고화체의 기계적 성질은 수열실험조건에 의존성이 있었으며, 적절한 고화조건은 반응온도 30$0^{\circ}C$, 유지시간 1시간이었다. 또한 고화체의 파면은 반응온도 및 유지시간에 따라 현저히 다른 양상을 보였으며, 수열실험동안 다양한 화합물이 생성되었다. 그 중에서 Xonotlite와 Talc는 고화체의 강도를 저하시키는 주된 화합물이었다.

인가전위 하에서 HT-60강 용접부의 SCC특성 평가

나의균,Na, Ui-Gyun 대한기계학회 2002 大韓機械學會論文集A Vol.26 No.5

The susceptibility of SCC for the weldment and PWHT specimens of HT-60 steel was evaluated using a slow strain rate method under applied potential by means of the potentiostat in synthetic seawater. In case of the parent, anodic polarization voltage was inappropriate in elongating the time to failure(TTF). -0.8V corresponding to cathodic protection range is most effective in improving the SCC resistance against corrosive environment. In case of the weldment, the values of reduction of area(ROA) and TTF at -0.68V corresponding to cathodic polarization value were 45.2% and 715,809sec which were the largest and longest life among other applied potentials. Those were vise versa at -1.1V. In case of the PWHT specimens, TTF and ROA at -0.68V was longest and largest like the weldment. Besides, PWHT is effective in prolonging the time to failure of the welded off-shore structure due to softening of effect. Regardless of the weldment and PWHT specimen, as corrosion rate gets higher, TTF becomes shorter and deformation behaviour for the weldment and PWHT specimen at -1.1V was shown to be irregular. Finally, it was found that specimens showed brittle fracture at -1.1V, but more ductile fracture accompanying the micro-cracks at applied potential of -0.68V.

마이크로그리드 간 P2P 에너지 거래를 위한 거래 운영 알고리즘

나의균(Ui-Kyun Na),김준성(Jun-Sung Kim),정재성(Jae-Sung Jung) 대한전기학회 2021 전기학회논문지 Vol.70 No.9

Research on microgrids for efficient use of distributed resources and renewable energy is being actively conducted. In domestic, FIT(Feed-in-Traiff) was applied to increase the penetration rate of renewable energy and distributed resources, and research is being conducted to enable efficient operation through predict of power generation, demand forecast and anomaly detection algorithm by combining with AI to improve the stability of MG operation. A electric power transaction model between MGs, like P2P(peer to peer) trading, has been proposed, but it is still incomplete. In this paper, we propose electric power transaction model between MGs. A correlation and dependence between weather elements and loads is performed and a load prediction model is proposed. In addition, we propose a transaction calculation algorithm that determines the transaction unit price for P2P energy transactions between MGs and a power transaction model which is an optimal matching algorithm for transactions between MGs where both sellers and buyers generate profits.

자동차 차체 점 용접부 특성에 관한 연구

나의균(Euigyun Na),오석형(SeokhyungOsh),김장권(Jangkweon Kim),김연직(YoenjigKim) 한국자동차공학회 2012 한국자동차공학회 지부 학술대회 논문집 Vol.2012 No.5-2

The purpose of this study is to examine the characteristics of the spot weld region for the car body. Steel used was ss41 with cold work and 0.8mm of thickness. Spot weld was conducted in air. Finite element method(FEM) and experiment were conducted to investigate the characteristics of the spot weld region. Basic data against the steel were composed of the relations of the specific heat, conductivity, and temperature. Software used was SYS-weld. Node and mesh was made. Tension - shearing test was conducted against the spot weld specimens. Sputtering phenomena occurred at the initial spot weld stage which causes the inappropriate and poor weld for the car body. Residual stresses were produced around the spot weld region and maximum value was located 4mm away from the weld center. It was verified that maximum load around the spot weld region was dependent upon the weld current through the tension-shearing test.

비파괴법에 의한 압력용기 강 다층용접부의 균열선단에서 소성변형 역성장거동 평가에 관한 연구

나의균(Eui-Gyun Na),이상근(Sang-Guen Lee) 한국비파괴검사학회 2009 한국비파괴검사학회지 Vol.29 No.5

본 연구에서는 비파괴법을 이용하여 압력용기 강 다층용접부에서 채취한 표준 샤르피 시험편의 균열선단에서 형성되는 소성변형 거동을 평가하였다. 모재, 후열처리재 및 용접재를 대상으로 시험편에 기계적인 노치를 가공한 후 예균열(pre-crack)을 낸 다음 4점 굽힘실험과 음향방출(acoustic emission: AE)실험을 동시에 실시하였다. 균열선단은 용접재외 후열처리재의 경우 용융선 근처에 위치하도록 하였다. 하중이 가해짐에 따라 균열선단에서 형성되는 소성영역의 크기는 응력확대계수를 이용하여 구했으며, 각 시험편에 대한 소성역의 크기와 음향방출 특성과의 관계는 축적된 AE 에너지 관점에서 고찰하였다. 시험편에 관계없이 탄성역역에서는 거의 AE신호가 감지되지 않았으며, 대부분의 AE신호는 소성변형 과정에서 발생하였다. 또한, 용접재가 모재와 후열처리재에 비해 AE신호가 훨씬 많이 발생하였다. 모재와 후열처리재 및 용접재의 균열선단에서 소성영역 크기와 축적된 AE에너지와의 관계는 현저히 다르게 나타났으며, 용접재의 AE counts는 모재와 후열처리재에 비해 많이 발생하였다. The purpose of this study is to evaluate the behaviour of the plastic deformed zone at crack tip on the standard Charpy specimens which were taken from the multi-passed weld block of the pressure vessel steel. Notch was machined on the standard Charpy test specimens and pre-crack which was located around the fusion line was made under the repeat load. Four point bend and acoustic emission tests were carried out simultaneously. The size of plastic region at crack tip was calculated using stress intensity factor. Relationships between characteristics of acoustic emission and plastic zone size at crack tip were discussed through the cumulative AE energy. Regardless of the specimens, AE signals were absent within the elastic region almost and most of AE signals were produced at the plastic deformation region from yield point to the mid-point between yield and maximum load. More AE signals for the weldment were produced compared with the base-metal and PWHT specimen. Relations between plastic deformed zones at crack tip and cumulative AE energy for the weldment and PWHT specimen were different quietly from the base-metal. Besides, number of AE counts for the weldment was the larger than those of the base-metal and PWHT specimen.