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영상 처리 기술을 이용한 판재의 홀 확장성 평가 기술 개발
장승현(S. H. Jang),김영석(Y. S. Kim) 한국소성가공학회 2010 한국소성가공학회 학술대회 논문집 Vol.2010 No.10
Today, most interested area is production of vehicle which has collision safety and low emission requirement of CO2 gas in automobile industry. For this, high strength steel has developed like Dual Phase steel, Ferrite Bainite steel and etc. These are used various areas. These steels were formed by hole flanging which is one of sheet forming method to meet strength and goal of design. At this time, material was experimented by hole extension test for considering formability. But system which checks changing load can"t be applied for hole extension test unlike uniaxial tension test because of small difference of punch load before and after crack. This paper introduces judging system which finds crack using computer after attaining image from camera to complement problem that present method depend on human’s sense.
Ti-30Ta-(3~15)Nb 합금에 HA/Ti 복합 코팅한 표면의 교류임피던스 특성
정용훈(Y. H. Jeong),이호종(H. J. Lee),문영필(Y. P. Moon),박근형(G. H. Park),장승현(S. H. Jang),손미경(M. K. Son),최한철(H. C. Choe) 한국표면공학회 2008 한국표면공학회지 Vol.41 No.5
A.C. impedance properties of HA/Ti compound layer coated Ti-30Ta-(3~15)Nb alloys have been studied by electrochemical method. Ti-30Ta binary alloys contained 3, 7, 10 and 15 wt% Nb were manufactured by the vacuum furnace system. And then specimen was homogenized at 1000℃ for 24 hrs. The sample was cut and polished for corrosion test and coating. It was coated with HA/Ti compound layer by magnetron sputter. The non-coated and coated morphology of Ti alloy were analyzed by X-ray diffractometer (XRD), energy X-ray dispersive spectroscopy (EDX) and filed emission scanning electron microscope (FE-SEM). The corrosion behaviors were investigated using A.C. impedance test (PARSTAT 2273, USA) in 0.9% NaCl solution at 36.5±1℃. Ti-30Ta-(3~15 wt%)Nb alloys showed the α+β phase, and β phase peak was predominantly appeared in the case of increasingly Nb contents. The microstructures of Ti alloy were transformed from needle-like structure to equiaxed structure as Nb content increased. From the analysis of coating surface, HA/Ti composite surface uniformed coating layer with 750 ㎚ thickness. The growth directions of film were (211), (112), (300) and (202) for HA/Ti composite coating on the surface after heat treatment at 550oC, whereas, the growth direction of film was (110) for Ti coating. The polarization resistance (Rp) of HA/Ti composite coated Ti-alloys were higher than those of the Ti and HA coated samples in 0.9% NaCl solution at 36.5±1℃. Especially, corrosion resistance of Ti-Ta-Nb system increased as Nb content increased.
다양한 유사체액과 인공타액에서 치과용 임플란트의 전기화학적 특성
김태한(T. H. Kim),박근형(G. H. Park),손미경(M. K. Son),김원기(W. G. Kim),장승현(S. H. Jang),최한철(H. C. Choe) 한국표면공학회 2008 한국표면공학회지 Vol.41 No.5
Titanium and its alloy have been widely used in dental implant and orthopedic prostheses. Electrochemical characteristics of dental implant in the various simulated body fluids have been researched by using electrochemical methods. Ti-6Al-4V alloy implant was used for corrosion test in 0.9% NaCl, artificial saliva and simulated body fluids. The surface morphology was observed using scanning electron microscopy (SEM) and energy dispersive x-ray spectroscopy (EDX). The electrochemical stability was investigated using potentiosat (EG&G Co, 263A). The corrosion surface was observed using scanning electron microscopy (SEM). From the results of potentiodynamic test in various solution, the current density of implant tested in SBF and AS solution was lower than that of implant tested in 0.9% NaCl solution. From the results of passive film stability test, the variation of current density at constant 250 mV showed the consistent with time in the case of implant tested in SBF and AS solution, whereas, the current density at constant 250mV in the case of implant tested in 0.9% NaCl solution showed higher compared to SBF and AS solution as time increased. From the results of cyclic potentiodynamic test, the pitting potential and |Epit ? Ecorr| of implant tested in SBF and AS solution were higher than those of implant tested in 0.9% NaCl solution.
장재득,김철호,이희동,장승현,강병수,박봉혁,김태중,Jang, J.D.,Kim, C.H.,Lee, H.D.,Jang, S.H.,Kang, B.S.,Park, B.H.,Kim, T.J. 한국전자통신연구원 2016 전자통신동향분석 Vol.31 No.5
최근 이동통신 시장이 활성화되면서 모바일 스마트 기기가 하루가 다르게 발전하여 출시됨에 따라 사용자가 급속히 늘어나게 되어 현재의 무선 네트워크에서 소비되는 모바일 데이터 트래픽이 기하급수적으로 증가하고 있다. 이러한 모바일 사용자 트래픽 증가에 따른 수요를 충족하기 위해서는 기존의 무선 인프라를 넘어서는 새로운 무선기술이 개발되어야 한다. 이를 위하여 우리나라를 비롯하여 전 세계적으로 넓은 대역폭 확보가 가능한 밀리미터파 기반의 5세대 이동통신 RF 기술 개발이 활발히 진행되고 있다. 이와 같이 밀리미터파(mm-Wave) 무선 통신 기술은 30~300GHz의 초고주파를 이용하여 1GHz 이상의 대역폭을 사용하고 밀리미터(mm) 단위의 짧은 파장을 제어하여 대량의 멀티미디어 정보를 전송할 수 있는 5세대 이동통신 핵심 요소 기술로 연구개발 되고 있다. 본고에서는 서론에 이어 밀리미터파 대역 RF 기술 개요, 국내외 기술동향, 국내외 시장동향에 대하여 살펴보고자 한다.
박병철(B. C. Park),배경운(K. U. Bae),구선모(S. M. Gu),장승현(S. H. Jang),홍성훈(S. H. Hong),김영석(Y. S. Kim) 한국소성가공학회 2010 한국소성가공학회 학술대회 논문집 Vol.2010 No.5
The application of high strength steels(HSS) for automotive part is growing due to the expectation of considerable weight reduction. Chassis parts, for example control arms and trailing arms, have developed by applying various high strength steels for weight reduction design and increased fatigue durability. Besides, various high strength steels, i.e, dual phase steel(DP), ferrite bainite steel(FB), have been developed by the reduction for good durability as well as press formability. In flanging of high strength steels, edge cracking may occur. This article discussed the effects of edge quality and how it determines edge stretchability, as well as finite element simulation (FEM) for blanking and hole expanding processes. Special attentions are paid on the significance of sheared edge and burr orientation in the hole expansion ratio (HER) of high strength steels. From these studies we concluded that ferrite bainite steel shows better stretch-flangeability in comparison to dual phase steel due to the lower work hardening rate at the sheared edge.