Numerical Analysis on Crack Generation Behavior of Hypo Peritectic Steel in Continuous Casting Process

Jun‑hyun Jo,Min‑seok Park,Kyung‑woo Yi 대한금속·재료학회 2021 METALS AND MATERIALS International Vol.27 No.11

Hypo peritectic steels exhibit a high possibility of longitudinal crack during continuous casting. Therefore, many researchershave studied the mechanisms of crack generation in hypo peritectic steel. Stress in solidified shell, or volume contractionwith small liquid fractions were suggested as the mechanisms of crack generation. A new model was developed for predictingpossibility of crack generation by calculating strain rates in solid, volume contraction rate during solidification, and theprobability of liquid unfilling in continuous cooling processes. The results show that massive transformation from the δphase to the γ phase, and peritectic transformation during solidification can be the main crack generation mechanisms. Furthermore,a linear relationship exists between the amount of undercooling for peritectic transformation (dTp) and the carboncontent of the boundary for dividing the two crack generation mechanisms. Additionally, the longitudinal crack ratios ofthe field results are analyzed through strain rates in solid and liquid unfilling possibilities. Relative positions in the range ofhypo peritectic steel and effective carbon contents are suggested to analyze the crack ratio of steels with alloying elements. This analysis shows that the results obtained from the new models for crack generation possibility are usable, and dTpcangenerate the behavioral differences in crack generation according to the conditions.

Effect of Impact Velocity on Interface Characteristics of HT‑9 Steel Joints Fabricated by Magnetic Pulse Welding

Jun‑Woo Song,Jin‑Ju Park,Gyoung‑Ja Lee,Min‑Ku Lee,Kyu‑Hyun Park,Soon‑Jik Hong,Jung Gu Lee 대한금속·재료학회 2020 METALS AND MATERIALS International Vol.26 No.3

The weldability window in magnetic pulse welding (MPW) is proposed for the end-closure joining of HT-9 steel tubularworkpieces. Based on both theoretical and experimental investigations, the impact velocity of the flyer tube at the momentof collision had a dominant effect on the bonding characteristics of the resultant joints and the optimal impact velocity wasestimated to be in the range of 265–290 m/s in this alloy system. Under the optimal process conditions, no leak was detectedduring helium leak testing. Moreover, the integrity of the joint interface was preserved until the tube section ruptured duringinternal pressure burst testing. For HT-9 steel, the ductile δ-ferrite phase produced by the localized interfacial melting duringMPW acted as an effective obstacle to crack propagation, thereby enhancing the fracture resistance of the joint interface. Allof the results demonstrated the high integrity and durability of the HT-9 steel tube assembly fabricated by the MPW process.

Phase Transformation Modeling for Hypo Peritectic Steel in Continuous Cooling

Jun‑hyun Jo,Kyung‑woo Yi 대한금속·재료학회 2021 METALS AND MATERIALS International Vol.27 No.7

Phase change of steel during cooling affects the slab qualities in continuous casting. Especially, crack susceptibility of hypoperitectic steel is high because large volume shrinkage occurs by peritectic phase transformation during solidification andcooling. In continuous cooling, phase change is different from the behaviors under the equilibrium condition, such as undercoolingand extend of peritectic reaction, etc. Therefore, we develop a new phase change model considering thermodynamics,empirical equations, and carbon diffusion in each phase to predict phase change behavior during continuous cooling. Inthis model, phase change of hypo peritectic steel comprises 5 stages until all phases become the γ phase. The velocities ofthe δ/γ interface and phase fractions during cooling are calculated according to cooling rate, undercooling of the γ phase,and carbon contents. The results show that if solidification ends by the δ phase during dTp,the γ phase is formed by massivetransformation. On the contrary, if peritectic reaction starts with liquid, the γ phase is formed and grows by diffusionaltransformation. In latter case, massive transformation of remaining δ phase can occur with high undercooling or very fastcooling rates. This analysis shows that there are several different paths depending on carbon contents of hypo peritectic steels.

Dehydrocoupling of Bis(1-sila-3-butyl)benzene and 2-Phenyl-1,3-disilapropane to Polymers Using Zirconocene Combination Catalysts

Jun Lee, Jong-Hyun Kim, Soo-Yong Mo, Hee-Gweon Woo1, Do-Heyoung Kim, Jin Jun 조선대학교 기초과학연구원 2011 조선자연과학논문집 Vol.4 No.3

The catalytic dehydrocoupling of bis(1-sila-3-butyl)benzene 1 and 2-phenyl-1,3-disilapropane 2 by Cp2ZrCl2/Red-Al and Cp2ZrCl2/n-BuLi was reported to compare their catalytic efficiency. The dehydrocoupling of monomeric silanes 1 with the Cp2ZrC12/Red-Al and Cp2ZrCl2/n-BuLi combination catalysts produced two phases of polymers: one is a highly crosslinked insoluble solid, and the other is noncross-linked or slightly cross-linked soluble oil and could be a precursor for the solid polymer. The dehydrocoupling of 2 with the Cp2ZrCl2/n-BuLi combination catalyst similarly produced two phases of polymers. By contrast, the catalytic reaction of 2 with the Cp2ZrCl2/Red-Al combination catalyst produced a soluble polymer via redistribution/dehydrocoupling process.

Dehydrocoupling of Bis(1-sila-3-butyl)benzene and 2-Phenyl-1,3-disilapropane to Polymers Using Zirconocene Combination Catalysts

Jun Lee,Jong-Hyun Kim,Soo-Yong Mo,Hee-Gweon Woo1,Do-Heyoung Kim,Jin Jun 조선대학교 기초과학연구원 2011 조선자연과학논문집 Vol.4 No.3

Preparation of mechanically enhanced supramolecular carbon nanotube (CNT) film using a water‑soluble π–π bonding linker

Jun‑Woo Lee,Moonseong Yoo,Kun Won Kim,Hyein Jeong,Jae Woo Chung 한국탄소학회 2019 Carbon Letters Vol.29 No.5

Mechanically enhanced supramolecular carbon nanotube (CNT) films were prepared in water by employing the π-electronrich phenyl, naphthalenyl, and pyrenyl end-functionalized polyethylene oxides (PEOs) as supramolecular linkers, followed by vacuum filtration. Among them, the supramolecular CNT film produced by the pyrenyl end-functionalized PEO (PEOPy) exhibited the highest mechanical strength, which was ~ 1.5–2 times higher than that of the CNT films produced using the typical dispersant, Triton X-100, although the functionality of PEO-Py was lower than that prepared using other linkers, and the content of PEO-Py in the CNT films was lower than that obtained using Triton X-100. Fluorescence and UV–Vis spectroscopy demonstrated that the improved mechanical properties of the supramolecular CNT film result from the formation of π–π interactions between the CNT and the pyrene moieties of the PEO-Py linker. Finally, the supramolecular CNT film exhibited a 40–50 dB electromagnetic shielding efficiency through hybridization with silver nanowires.

순환식 운동프로그램이 대학 운동선수들의 전문체력 및 운동기능 향상에 미치는 영향

노동우(Noh, Dong?Woo),최현호(Choi, Hyun-Ho),이동준(Lee, Dong-Jun) 한국체육과학회 2019 한국체육과학회지 Vol.28 No.3

The purpose of this study was to investigate the effectiveness of elite volleyball players in improving their offense capabilities when combined with circuit training that improves their power and sense of balance that affects volleyball performance. In order to improve the power, agility and endurance of volleyball players, 10 volleyball players at M University were required to perform 13 moves twice a week in the six weeks after the league. As a results on the circuit exercise program, a significant improvement was shown in the extension-and-flexion muscular strength of the left, right pelvic limbs. Also, the back muscle strength and flexibility showed significant, sit-up to muscle endurance showed, side steps to agility were improved, standing height jumps, serve and spike speeds, which recognize the function of volleyball, showed a significant improvement after a circuit training program . These results suggest that the circuit exercise program will help improve the specific fitness and funcitional fitness of volleyball players.

탄소섬유 적층혼성부재의 계면수 변화에 따른 축 압궤 특성

서현경,박준우,양용준,황우채,양인영 朝鮮大學校 機械技術硏究所 2007 機械技術硏究 Vol.10 No.1

알루미늄과 CFRP는 대표적인 경량화 재료이다. 알루미늄 부재는 안정적인 소성 변형에 의해 에너지를 흡수하며, CFRP 부재는 비강성과 비강도가 우수하고 불안정한 취성파괴로 인해 에너지를 흡수한다. 이러한 각각 알루미늄과 CFRP 부재의 압궤 특성을 기초로 두 재 료의 결합에 의해 서로의 장점에 대한 시너지 효과를 얻기 위해 혼성구조부재를 제작하였다. 본 연구에서는 알루미늄 부재의 외측을 CFRP로 강화시킨 혼성구조부채를 제작하여 CFRP의 계면수 변화에 따른 축 방향 준정적 압궤실험을 행하여 사각 및 원형 단변 모형의 혼성구조부재의 압궤 특성을 조사하였다. 실험 결과 혼성구조부재는 내부의 알루미늄 부재의 연성 성질 때문에 CFRP 부재의 불안정한 취성 파괴를 보완하여 비교적 안정적인 압궤 모드를 보였다. 하지만 혼성구조부재는 계면수 변화에 대해 에너지 흡수성과 압궤 모드는 별다른 영향을 보이지 않았다. The aluminum or CFRP is representative of light-weight materials. The aluminum tubes absorb energy by stable plastic deformation and the CFRP tubes absorbs energy by unstable brittle failure with higher specific strength and stiffness. Based on the respective collapse characteristics of aluminum and CFRP tubes, the aluminum CFRP compound tubes were manufactured to get a synergy effect when the aluminum CFRP tubes were combined with the advantages of each tube. This paper is to investigate the collapse characteristics of square or circular shaped aluminum CFRP compound tubes subjected to quasi-static axial collapse tests which were conducted by changing the stacking conditions. Test results showed that the collapse of the aluminum CFRP compound tubes complemented unstable brittle failure of the CFRP tube due to the ductile characteristics of the inner aluminum tube. It turned out that interlaminar numbers of aluminum CFRP compound tubes have no influence on the energy absorption and collapse modes of the tubes.

가상공간의 가공 공정과 상태 구현에 관한 연구

이수훈,김봉석,홍민성,김종민,JUN NI,박상호,송준엽,이창우,하태호 한국공작기계학회 2005 한국공작기계학회 춘계학술대회논문집 Vol.2005 No.-

This paper presents virtual machining system in order to realize turning process in virtual space. A reliable virtual turning process simulation was developed based on the surface shaping system which is capable of considering geometric model, thermal error model, and vibration model. Accuracy of surface shape resulting from proposed machining simulator was verified experimentally. This paper also developed the watchdog agent that continuously assessed, diagnosed, and predicted performance of products and machines in machining. The Watchdog agent extracted feature signal using time-frequency analysis among various signals from multi-sensor and evaluated machining condition using performance confidence value.

S-344 : The Role of Skeletal Muscle Mass in Development of Metabolic Syndrome

( Byung Sam Park ),( Jun Sung Moon ),( Ji Sung Yoon ),( Kyu Chang Won ),( Hyoung Woo Lee ) 대한내과학회 2013 대한내과학회 추계학술대회 Vol.2013 No.1

Introduction: It has been well known that abdominal adiposity is related with insulin resistance and greater risk of metabolic disorder. Skeletal muscle plays central role in insulin mediated glucose disposal of whole body, but we only know a little about the association between skeletal muscle mass and MetS (MetS). The aim of this study is to clarify the clinical role of skeletal muscle mass in developing MetS through using skeletal muscle parameters by body impedance analysis (BIA). Methods: 1,042 healthy adults aged from 20 to 75 years who visited Yeungnam university health promotion center from Jun. 2008 to Jun. 2010 were enrolled. 204 subjects who had prior MetS or chronic disease that can affect to skeletal muscle mass were excluded. After 24 months from baseline, the metabolic parameters were assessed and the development of MetS was diagnosed using modified NCEP-ATP III criteria. From the BIA (Inbody 720), we obtained skeletal muscle mass (SMM, Kg), body fat mass (BFM, Kg), and visceral fat area (VFA, cm2). Then, we had defined as follows; percent of skeletal muscle mass (SMM%, %): SMM (kg)/weight (Kg), skeletal muscle index (SMI, Kg/m2): SMM (Kg)/height (m)2, skeletal muscle to body fat ratio (MFR): SMM (kg)/BFM (Kg) and skeletal muscle to visceral fat ratio (SVR, Kg/cm2): SMM (Kg)/VFA (cm2) Results: Mean follow up periods were 28.7±5.4 months. Among total 838 subjects (46.9±9.9 years, M:F=477:361), 88 (10.5%) were newly diagnosed MetS. 5th quintile of the SMM%, MFR and SVR was associated with decreased risk of development of MetS after adjusting for confounding factors. Conclusion: Decreased skeletal muscle mass may play critical role in development of the MetS and not absolute amount of skeletal muscle mass but relative ratio to body composition may be more important.