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Feasibility studies of laser surface nitriding on Ti-6Al-4V alloy using a nitric acid solution
황태우,우영윤,Chester J. Van Tyne,문영훈 대한기계학회 2017 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.31 No.9
Feasibility studies for laser surface nitriding in a nitric acid solution were performed on a Ti-6Al-4V alloy. The susceptibility to surface cracking, hardness, bead shape, and the microstructure of the laser nitrided layers obtained at various concentrations of nitric acid were investigated over a wide range of processing variables. The results show that the hardness of the laser nitrided layer can be increased by increasing both the concentration of nitric acid and the energy density of the laser. The proposed process window shows that a high scanning speed, coupled with higher laser power, can result in crack-free nitriding, and also the hardness of the nitride layer can be finely controlled within this process window. Laser surface nitriding in nitric acid solution can increase the surface hardness without processinduced surface cracking. The proposed process is shown to be feasible and can be performed with a high degree of reliability.
질소가스를 이용한 Ti-6Al-4V의 레이저 표면 질화처리
황태우(T. W. Hwang),김재현(J. H. Kim),우영윤(Y. Y. Woo),길태동(T. D. Kil),문영훈(Y. H. Moon) 한국소성가공학회 2015 한국소성가공학회 학술대회 논문집 Vol.2015 No.5
Surface nitriding of Ti-6Al-4V can be achieved by laser melting in a flow of nitrogen gas, and high surface hardness values could be obtained. In this study, the effect of process parameters on surface nitriding of a Ti-6Al-4V alloy has been investigated to achieve higher surface hardness without process-induced cracks. The effects of process parameters were experimentally studied and process window is provided on the basis of microstructure, microhardness, and cracking of the nitride layers. It is shown that hardened layers having various depth and hardness can be obtained by controlling the processing parameters. High scanning speed coupled with lower nitrogen flow rate results in crack-free layer at the expense of both a lower hardness and a shallower melt depth.
질산을 이용한 Ti-6Al-4V의 레이저 표면 질화처리
황태우(T. W. Hwang),이성훈(S.H. Lee),문영훈(Y. H. Moon) 한국소성가공학회 2015 한국소성가공학회 학술대회 논문집 Vol.2015 No.10
Surface nitriding of Ti-6Al-4V to obtain high surface hardness can be achieved by performing the laser melting in a nitric acid. In this study, the effect of process parameters on the characteristics of surface nitriding has been investigated to achieve higher surface hardness without process-induced cracks. The effects of process parameters were experimentally studied and process window is provided on the basis of microstructure, microhardness, and cracking of the nitride layers. It is shown that hardened layers having various depth and hardness can be obtained by controlling the processing parameters. Low scanning speed coupled with higher nitric acid rate results in crack-free layer at the expense of both a higher hardness and a deeper melt depth.
기능적 생활중심 교육과정에 대한 정서장애학교 학부모의 요구 분석
백종남,황태우,박은송,김삼섭 한국특수교육학회 2008 특수교육학연구 Vol.43 No.2
The purpose of the study was to investigate the difference of functional skills between autism students and mental retardation students at school for students with emotional disorder in South Korea. The total number of 322 parents in special school for the emotional disturbance, 181 parents of autism students and 141 parents of mental retardation students, were participated in this survey. The findings of this study were as follows. First of all, overall difference of parents of autism and mental retardation students in special school for the emotional disturbance is this. The parents of mental retardation students focused on health and safety skills, while the parents of autism students focusing on personal physical care. Second, according to their grades, parents of mental retardation students in the elementary school focused on moving and traveling, while parents in middle and high school focusing on healthy and safety skills. Parents of autism students in the elementary and middle school focused on personal physical care, while parents in high school focusing on healthy and safety skills. Third, according to their gender, parents of mental retardation male students focused on healthy and safety, while parents of mental retardation female students focusing on personal physical care. Parents of male and female autism students focused on personal physical care. The result of the study is expected to help selecting and appling special education curriculum contents. 이 연구는 정서장애학교의 주요 대상인 자폐성 학생과 정신지체 학생 간에 학부모가 요구하는 기능적 기술의 우선순위가 어떻게 다른가를 알아보고자 하였다. 이를 위해 정서장애학교에 다니는 자폐성 장애 학생의 부모 181명과 정신지체 학생 부모 141명, 총 322명을 대상으로 기능적 기술의 우선순위를 조사하였다. 그 결과를 요약하면 다음과 같다: 첫째, 전반적인 우선순위를 알아본 결과, 정서장애학교에 다니는 정신지체 학생의 부모는 건강과 안전에 관한 기능적 기술을 가장 중요하게 생각하고 있고, 자폐성 학생의 부모는 신변처리 기술을 가장 중요하게 생각하였다; 둘째, 학교급별 우선순위를 알아본 결과, 정신지체학생 부모의 경우 초등부는 이동하기와 여행하기를, 중학부와 고등부는 건강과 안전 기술을 가장 중요하게 생각하고 있고, 자폐성 학생 부모의 경우 초등부와 중학부는 신변처리 기술을, 고등부는 건강과 안전 기술을 가장 중요하게 생각하고 있는 것으로 나타났다; 셋째, 성별 우선순위를 알아본 결과, 정신지체 학생 부모의 경우 남학생은 건강과 안전 기술을, 여학생은 신변처리 기술을 가장 중요하게 생각하고 있는 것으로 나타났으며, 자폐성 학생 부모는 남ㆍ여 모두 신변처리 기술을 가장 중요하게 생각하고 있는 것으로 나타났다. 이 연구의 결과는 정서장애학교에서 학교수준의 교육과정을 개발하는 데 기초자료로 활용할 수 있을 것으로 기대된다.
Feasibility studies on manufacturing tailored blanks by rolling partially stacked blanks
한상욱,황태우,오일영,문영훈 대한기계학회 2018 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.32 No.4
Tailored blanks with different blank thicknesses are semi-finished parts that can be used to produce lightweight vehicle parts. This study investigates a manufacturing process that can produce tailored blanks by rolling partially stacked blanks. The process was experimentally and numerically investigated using various processing conditions. To characterize the process, the deformation behaviors of upper and lower blanks were analyzed and quantified. The dimensional variations at the top end and the transition zones were analyzed based on the cross-sectional thickness profiles of formed blanks. The results show that the proposed process is feasible for the production of tailored rolled blanks that have both straight edges with a concave transition zone and convex edges with a straight transition zone.