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보이드 성장을 고려한 재료의 성형한계에 대한 비 국소 해석
김영석,원성연,Kim, Young-Suk,Won, Sung-Yeun 대한기계학회 2003 大韓機械學會論文集A Vol.27 No.6
In this paper, the strain localization of voided ductile material has been analyzed by nonlocal plasticity formulation in which the yield strength not only depends on an equivalent plastic strain measure (hardening parameter), but also on the Laplacian thereof. The gradient terms in yield criterion show an important role on modeling strain-softening phenomena of material. The influence of the mesh size on the elastic -plastic deformation behavior and the effect of the characteristic length parameter for localization prediction are also investigated. The proposed nonlocal plasticity shows that the load -strain curves converge to one curve. Results using nonlocal plasticity also exhibit the dependence of mesh size is much less sensitivity than that for a corresponding local plasticity formulation.
MEMS 부품 제조를 위한 나노 리소그래피 공정의 3차원 분자동력학 해석
김영석,이승섭,나경환,손현성,김진,Kim, Young-Suk,Lee, Seung-Sub,Na, Kyoung-Hoan,Son, Hyun-Sung,Kim, Jin 대한기계학회 2003 大韓機械學會論文集A Vol.27 No.10
The atomic force microscopy (AFM) based lithographic technique has been used directly to machine material surface and fabricate nano components in MEMS (micro electro mechanical system). In this paper, three-dimensional molecular dynamics (MD) simulations have been conducted to evaluate the characteristic of deformation process at atomistic scale for nano-lithography process. Effects of specific combinations of crystal orientations and cutting directions on the nature of atomistic deformation were investigated. The interatomic force between diamond tool and workpiece of copper material was assumed to be derived from the Morse potential function. The variation of tool geometry and cutting depth was also evaluated and the effect on machinability was investigated. The result of the simulation shows that crystal plane and cutting direction significantly influenced the variation of the cutting forces and the nature of deformation ahead of the tool as well as the surface deformation of the machined surface.
다구치 직교배열을 이용한 평면변형률 장출실험용 금형의 최적설계
김영석,Kim, Yeong-Seok 대한기계학회 1997 大韓機械學會論文集A Vol.21 No.12
Recently, the plane strain puch stretching test(called PSST) has been developed and used successfully in the evaluation of the press formability of automotive steel sheets. In this paper, the optimum punch geometry of the original PSST tool was investigated by the FEM analysis. The puch length, crown and corner radius are chosen to be optimized according to the Taguchi's experiment technique with the $L_4$ orthogonal array.