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이종재료 마찰용접에 의한 초내열합금 대형 배기밸브 스핀들 개발
박희천,정호승,조종래,이낙규,오중석,한명섭,Park Hee-Cheon,Jeong Ho-Seung,Cho Jong-Rac,Lee Nak-Kyu,Oh Jung-Seok,Han Mvoung-Seoup 한국마린엔지니어링학회 2005 한국마린엔지니어링학회지 Vol.29 No.8
Inertia welding is a solid-state welding process in which butt welds in materials are made in bar and in ring form at the joint race, and energy required lot welding is obtained from a rotating flywheel. The stored energy is converted to frictional heat at the interface under axial load. The quality of the welded joint depends on many parameters, including axial force, initial revolution speed and energy amount of upset. working time, and residual stresses in the joint. Inertia welding was conducted to make the large exhaust valve spindle for low speed marine diesel engine. superalloy Nimonic 80A for valve head of 540mm and high alloy SNCrW for valve stem of 115mm. Due to different material characteristics such as, thermal conductivity and flow stress. on the two sides of the weld interface, modeling is crucial in determining the optimal weld geometry and Parameters. FE simulation was performed by the commercial code DEFORM-2D. A good agreement between the Predicted and actual welded shape is observed. It is expected that modeling will significantly reduce the number of experimental trials needed to determine the weld parameters. especially for welds for which are very expensive materials or large shaft. Many kinds of tests, including macro and microstructure observation, chemical composition tensile , hardness and fatigue test , are conducted to evaluate the qualify of welded joints. Based on the results of the tests it can be concluded that the inertia welding joints of the superalloy exhaust valve spindle are better properties than the material specification of SNCrW.
보리나무이종군의 날개에 대한 수량형태학적 분석 (동시목: 나무이과)
박희천,이창언,김훈수,Park, Hee-Cheon,Lee, Chang-Eon,Kim, Hoon-Soo The Korean Society of Systematic Zoology 1988 Korean Journal of Systematic Zoology Special Issue Vol.2 No.-
보리나무속식물의 유연종군에 서식하는 큰보리나무이종군의 날개형질을 다변량적 방법으로 분석한 결과는 다음과 같다. 1. 미기재종은 계절형과 성적인 변이형의 개체가 아닌 독립된 종으로 밝혀졌다. 2. 군분석에서 작은보리나무이는 종내 암.수의 형질 pattern이 높은 유사성을 나타내었다. 3. 4종의 군분석 결과는 작은보리나무이의 계절형이 다른 종에 결합하였으며, 큰보리나무이의 지리적변이가 개체군 사이에서 독립된 결합군으로 나타났다. 4. 명보리나무이와 큰보리나무이 및 미기재종의 암컷들은 세 종 모두 같은 그룹에 소속되었다. 5. 판별분석에서는 성별, 계절형 및 지리적 구분에 영향을 받지 않고 4종이 독립된 종군으로 동정되었다. The wing morphometric characters of P.elaeagni complex feeding on the genus Elaeagnus plants was analysed by the multivariate methods using clustering of generalized distance and discriminant analysis. On the clustering of the species, the effect of sexual differences, seasonal variation and geographic population sensitively appeared . However, four species of this group was precicely divided by the discriminant analysis.
이진희(Jin-Hee Lee),김효준(Hyo-Joon Kim),차재석(Jae-Seok Cha),박희천(Hee-Cheon Park) 한국조류학회II 2008 한국조류학회지 Vol.15 No.1
한국산 새매속(Genus Accipiter) 3종의 분자계통적 분석을 위해, 참매(Accpiter gentilis schvedovi), 조롱이(A. gularis), 새매(A. nisus)를 대상으로 mtDNA의 cyt b gene 염기서열을 분석하였다. 3개의 Accipiter clades로 분리되었으며, 제1그룹은 참매 분기군 A. gentilis gentilis, A. g. schvedowi and A. striatus 등이었으며, 제2그룹은 조롱이 분기군 A. gularis and A. nisus, 제3그룹은 대만새매 분기군 A. trivirgatus formosae으로 나뉘었으며, 그중 대만새매는 동북아시아 새매 그룹과는 확연히 구분되었다. The molecular phylogenetic study of three Korean species of the genus Accipiter infered from the mitochondrial cytochrome b gene, was conducted. The mtDNA cyt b gene Accipiter gentilis schvedowi, A. gularis, A. nisus were newly sequenced, and phylogenetic relationship of A. gentilis, A. striatus, and A. trivirgatus with Korean Accipiter species. Three Accipiter clades were appeared, the first group was A. gentilis gentilis, A. g. schvedowi and A. striatus, the second group was A. gularis and A. nisus, the third group was an isolated A. trivirgatus formosae, this Taiwan subspecies differed from other Northern species.
미세조직 변화를 고려한 대형 배기밸브 스핀들 제조공정 해석
정호승,조종래,박희천,Jeong Ho-Seung,Cho Jong-Rae,Park Hee-Cheon 한국마린엔지니어링학회 2005 한국마린엔지니어링학회지 Vol.29 No.8
The microstructure evolution in hot forging process is composed of dynamic recrystallization during deformation as well as grain growth during dwell time. Therefore, the control of forging parameters such as strain, strain rate. temperature and holding time is important because the microstructure change in hot working affects the mechanical properties. Modeling equations are developed to represent the flow curve. grain size. recrystallized volume fraction and grain growth phenomena by various tests. The developed modeling equations were combined with thermo-viscoplastic finite element modeling to predict the microstructure change evolution during hot forging process. The large exhaust valve spindle (head diameter of 512mm) was simulated by closed die forging with hydraulic press and cooled in air after forging. The preform was heated to each 1080 and 1150$^{\circ}C$. Numerical calculation was performed by DEFORM-2D. a commercial finite element code. Heat transfer can be coupled with the deformation analysis in a non-isothermal deformation analysis. In order to obtain the fine and homogeneous microstructure and good mechanical properties in forging. the FEM would become a useful tool in the simulation of the microstructure development. In forging, appropriate temperature, strain and strain rate and rapid cooling are required to obtain the fine grain microstructure The optimal forging temperature and effective strain range of Nimonic 80A for large exhaust valve spindle are about 1080$\∼$l120$^{\circ}C$ and 150$\∼$200$\%$.