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김민철(M. C. Kim),남찬희(C. H. Nam),남태현(T. H. Nam),강석순(S. S. Kang),전만수(M. S. Joun) 한국소성가공학회 2014 한국소성가공학회 학술대회 논문집 Vol.2014 No.5
In this paper, finite element analysis of die wear phenomenon in hot forging of a partially heated material for T-shape product is conducted using a rigid-thermoviscoplastic finite element method with an Archard wear model. The entire process including partial heating process and two hot forging stages is dealt with. The predictions are compared with experiments in terms of die wear in a qualitative manner. The comparison shows a good agreement between the predictions and experiments.
인장-전단 하중을 받는 SUS301L 다중접합 점용접 이음재의 파괴역학적 피로설계(Ⅱ)
남태현(T.H. Nam),정원석(W.S. Jung),배동호(D.H. Bae),손일선(I.S. Shon) 한국자동차공학회 2002 한국자동차공학회 춘 추계 학술대회 논문집 Vol.2002 No.5_2
Since stainless steel sheets have good mechanical properties, weldability, appearance and corrosion resistance, they are commonly used as one of the structural materials of the railroad cars or the commercial vehicles which are manufactured by the spot welding. Among the many kinds of spot welded lap joints, it can find that multi-lap joints are also employed in their body structures. But, fatigue strength of these joints are lower than that of base metal due to high stress concentration at the nugget edge of the spot weld and considerably influenced by welding conditions as well as the mechanical and geometrical factors. Thus, it is necessary to establish a reasonable and systematic fatigue design criterion for spot welded multi-lap joints. In this report, after numerically analyzing the stress distribution and deformation on spot welded multi-lap joints subjected to tensile shear load, first, fracture mechanically rearranged the ΔP-Nf curves in the ΔKⅡ-Nf relation with the stress intensity factor of Mode II. And next, evaluated the fatigue data on the ΔP-Nf curves with ΔKΦmax which is based on the maximum stress criterion on<br/> tangential direction. From the results obtained, both of them are applicable to fractural mechanical fatigue design of spot welded multi-lap joint.<br/> <br/>
그립의 기능을 강조한 롤단조 공정의 유한요소모델링 및 적용
진호태(H. T. Jin),남태현(T. H. Nam),강석순(S. S. Kang),전만수(M. S. Joun) 한국소성가공학회 2016 한국소성가공학회 학술대회 논문집 Vol.2016 No.4
In this paper, a finite element model of grip in roll forging is presented, which is believed to have a deep influence on both finite element predictions and real process. A fraction of roll separating force is exerted on the front end of the material to be pulled. The pulling force during forming is considered as surface traction at the end. Effect of the pulling force is examined, revealing that the predictions of final length and major deformed region have a distinct function of the fraction of the pulling force with respect to the roll separating force, which can be a characteristic property of the process. The approach is applied to aluminum roll forging of manufacturing an optimized perform for a stepped bar.
Ar가스 분위기에서 PLD방법으로 제작된 TiNi박막의 조성 및 결정성에 관한 연구
차정옥,신진호,여승준,안정선,남태현,Cha, J.O.,Shin, C.H.,Yeo, S.J.,Ahn, J.S.,Nam, T.H. 한국진공학회 2007 Applied Science and Convergence Technology Vol.16 No.2
Ti-50 at. % Ni 합금 타깃으로 PLD(pulsed laser deposition)방법을 사용하여 TiNi 형상기억합금 박막을 제작하였다. Ar분위기(200 mTorr)와 고진공분위기($5{\times}10^{-6}\;Torr$)에서 제작한 TiNi 박막의 조성 및 결정성의 변화를 조사했으며, 박막의 조성은 에너지 분산 엑스선 분광 분석(EDXS)을 이용하여 조사하였고, 박막의 결정성은 엑스선 회절장치(XRD)를 이용하여 조사하였다. 박막의 조성은 기판과 타깃의 거리에 의존되었지만, 기판의 온도와는 무관함을 알 수 있었으며, Ar 분위기에서 플룸 안쪽에 기판이 위치하였을 때 조성 제어가 용이함을 알 수 있었다. 또한, Ar 가스 분위기에서 증착 된 TiNi 박막은 고진공분위기에서 증착된 박막보다 더 낮은 온도(약 $400^{\circ}C$)에서 in situ로 결정화됨을 알 수 있었다. 이들 결과는, PLD방법으로 TiNi 형상기억합금 박막을 제작할 때 분위기 가스의 압력이 결정화 온도를 낮추어 주는 중요한 역할을 할 수 있음을 시사한다. TiNi shape memory alloy(SMA) was fabricated by PLD(plused laser deposition) using equiatomic TiNi target. Composition and crystallization of TiNi thin films which were fabricated in ambient Ar gas(200m Torr)and vacuum($5{\times}10^{-6}\;Torr$) were investigated. Composition of TiNi thin films was characterized by energy-dispersive X-ray spectrometry (EDXS) and crystallization was confirmed by X-ray diffraction (XRD). The composition of films depends on the distance between target and substrate but does not sensitively depend on the substrate temperature. It is found that the composition of films can be easily controlled when substrate is placed inside plume in ambient Ar gas. It is also found that the in situ crystallization temperature ($ca.\;400^{\circ}C$) in ambient Ar gas is lowered in comparison with that of TiNi film prepared under vacuum. The low crystallization temperature in ambient Ar gas makes it possible to prepare the crystalline TiNi thin film without contamination.
Ti-(45-X)Ni-5Cu-X(Mo,Cr,Al)(at.%) 합금의 B2-B19-B19` 변태거동 및 형상기억특성
李喜佑,崔美善,金載勳,南泰鉉 대한금속재료학회 2002 대한금속·재료학회지 Vol.40 No.6
Transformation behavior and shape memory characteristics in Ti-(45-X)Ni-5Cu-X(Mo, Cr, Al)(at.%) alloys were investigated by means of differential scanning calorimetry, X-ray diffraction and thermal cycling tests under a constant load. The substitution of Mo, Cr and Al for Ni in Ti-45Ni-5Cu alloy induced the B2→B19 martensitic transformation prior to the B2→B19' transformation, and consequently Ti-(45-X)Ni-5Cu-X(Mo, Cr, Al)(at.%) alloys transformed in two stages; the B2→B19→B19'. The B2→B19 and the B19→B19' transformations were completely separated in Ti-(45-X)Ni-5Cu-X(Mo, Cr) alloys, whereas they were not done in a Ti-44.3Ni-5Cu-0.7A1 alloy without applied stress. The substitution of Mo, Cr and Al in a Ti-45Ni-5Cu alloy decreased transformation hysteresis and the residual elongation. The maximum recoverable elongation of Ti-(45-X)Ni-5Cu-X(Mo, Cr, Al) alloys was about 5%.