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냉간 정수압 성형시 금속분말과 맨드렐 사이의 마찰이 분말의 치밀화에 미치는 영향
이희태,김기태,Lee, Hui-Tae,Kim, Ki-Tae 대한기계학회 1997 大韓機械學會論文集A Vol.21 No.7
The effects of friction between powder and a mandrel on densification behavior of metal powder were investigated under cold isostatic pressing. The elastoplastic constitutive equations based on the yield function of Shima and Oyane were implemented into finite element program (ABAQUS) to simulate compaction responses of metal powders during cold isostatic pressing. The friction coefficients between powder and mandrels with different roughness were determined by comparing experimental data and finite element results. Density distributions in the powder compacts were also studied for different friction coefficients. Finite element results were compared with experimental data for pure iron powder under cold isostatic pressing.
이희태,김희연,박현진,조영은,유소영,이경진,정종선,고광표,Lee, Hee-Tae,Kim, Hee-Yeon,Park, Hyun-Jin,Cho, Young-Eun,Ryu, So-Young,Lee, Kyung-Jin,Jung, Jong-Sun,Ko, Gwang-Pyo 한국환경보건학회 2008 한국환경보건학회지 Vol.34 No.1
Lake Shiwha, an artificial lake located near metropolitan Seoul, offers a unique water environment and has been suspected to have high levels of chemical and microbiological contaminations. Lake Shiwha was originally connected to the sea but currently has four major surface water inputs from agricultural, municipal, industrial areas and in addition an occasional inflow from the sea. The objectives of this study are to investigate the relative contribution of microbial contaminants from each of the inflowing surface waters and to identify appropriate microbial indicator organisms in this unique water environment. We measured the levels of microbial contaminations in the four inflowing surface waters. A number of microbial indicator organisms including total coliform (TC), fecal coliform (FC), E. coli, Enterococci, somatic and male-specific coliphages were analyzed. Bacterial indicator microorganisms were detected and quantified by the $Colilert^{(R)},\;Enterolert^{(R)}$ kit. Surface water (50 l) was sampled by $ViroCap^{TM}\;5"$ cartridge filters and analyzed by the single agar layer method for detecting coliphages. The concentrations of TC, FC, E. coli, and Enterococci were 1543 CFU/100 ml${\sim}1.99{\times}10^6$ CFU/100 ml, 0 CFU/100 ml${\sim}202$ CFU/100ml, 0 CFU/100 ml${\sim}1.80{\sim}10^5$ CFU/100ml, 74 CFU/100 ml${\sim}3408$ CFU/100 ml, respectively. The male-specific and somatic coliphages were detected in three different inflowing surface waters. Isolated E. coli and Enterococci strains were further analyzed by 16s rDNA amplification and subsequent phylogenetic analysis from Jungwang-chun, Ansan-chun, Banwol-chun and penstock of inflowing surface water. Our results indicated that the concentrations of different fecal indicator microorganisms might not be highly correlated with each other. Multiple microbial indicator organisms should be used for monitoring microbial contamination and microbial source tracking methods.
멤브레인 LNG 운반선용 스카폴딩 시스템의 자동 설계 프로그램 개발
이희태,신상범,박윤기,Lee, Hee-Tae,Shin, Sang-Beom,Park, Yun-Ki 대한조선학회 2010 大韓造船學會 論文集 Vol.47 No.2
Scaffolding system in the membrane LNG carrier is a steel structure composed of various pipe-shaped members connected by specific coupling devices. In this study, the automatic design program for scaffolding system in membrane LNG carrier has been developed. It enables user to arrange members easily considering design constraints and input variables such as size of tank, position of legs, level height and so on. In addition to that, it creates finite element analysis model with loading and boundary conditions automatically and carries out structural analysis. With post processor based a state-of-the-art computer graphics, users can easily check the results of structural analysis and make a report for structural safety of scaffolding system.
상 변태를 고려한 HY-100강 용접부의 수축 및 잔류응력 예측에 관한 연구
이희태,신상범,Lee, Hee-Tae,Shin, Sang-Beom 대한용접접합학회 2007 대한용접·접합학회지 Vol.25 No.1
For high performance and structural stability, application of high strength steel has continuously increased. However, the change of the base metal gives rise to problems with the accuracy management of the welded structure. It is attributed to the martensite phase transformation of the high strength low alloy steel weldment. The purpose of this study is to establish the predictive equation of transverse shrinkage and residual stress for the HY-100 weldment. In order to do it, high speed quenching dilatometer tests were performed to define a coefficient of thermal expansion(CTE) at the heating and cooling stage of HY-100 with various cooling rates. Uncoupled thermal-mechanical finite element(FE) models with CTE were proposed to evaluate the effect of the martensite phase transformation on transverse shrinkage and residual stresses at the weldment. FEA results were verified by comparing with experimental results. Based on the results of extensive FEA and experiments, the predictive equation of transverse shrinkage and longitudinal shrinkage force at the HY-100 weldment were formulated as the function of welding heat input/in-plane rigidity and welding heat input respectively.
삼축응력 기반 파괴변형률 기준을 적용한 박스형 용접구조물의 파열압력 예측
이희태(Heetae Lee),석상민(Sangmin Seok),이재원(Jaewon Lee) 대한기계학회 2019 대한기계학회 춘추학술대회 Vol.2019 No.11
Despite design precautions to prevent internal arcing in oil-immersed transformers, there is always a residual risk of such an event, with the possibility of a subsequent tank rupture leading on to a fire or an explosion. This paper presents prediction of burst pressure for tanks, box-type welded structures, under internal arcing due to short-circuit failure of transformers. In this study, a stress-modified strain for SM490 steel was proposed as a function of stress triaxiality. To determine the stress-modified fracture strain, tension test of bars with four different notch radii, made of base metal, weldment, and HAZ, is performed. By using the fracture criterion and Finite Element Analysis(FEA), the burst pressure of the actual tank was proposed. Finally, the validity of predicted burst pressure of the tank was evaluated by comparing the result from hydraulic test of the tank.