• Bulletin of the Korean Chemical Society
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• 제34권3호
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• pp.725-730
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• 2013

An investigation of the coordination behavior of sulfur-containing mixed-donor tribenzo-macrocycles $L^1-L^3$ ($L^1$: 20-membered $O_3S_2$, $L^2$: 20-membered $O_2S_3$, and $L^3$: 23-membered $O_4S_2$) with $d^{10}$-metal ($Ag^+$, $Hg^{2+}$, and $Pb^{2+}$) salts is reported. The X-ray structures of five complexes (1-5) with different structural types and stoichiometries, including mono- to dinuclear species have been determined. Reactions of $L^2$ and $L^3$ with the silver(I) salts ($PF_6{^-}$ and $SCN^-$) afforded two dinuclear 2:2 (metal-to-ligand) complexes with different arrangements: a sandwich-type cyclic dinuclear complex $[Ag_2(L^2)_2](PF_6)_2{\cdot}3CH_2Cl_2$ (1) and a linear dinuclear complex $[Ag_2(L^3)_2(SCN)_2]$ (2), in which two monosilver(I) complex units are linked by an Ag-Ag contact. Reactions of $L^1$ and $L^2$ with mercury(II) salts ($SCN^-$ and $Cl^-$) gave a mononuclear 1:1 complexes $[Hg(L^1)(SCN)_2]$ (3) and $[Hg(L^2)Cl_2]$ (4) with anion coordination in both cases. $L^2$ reacts with lead(II) perchlorate to yield a mononuclear sandwich-type complex $[Pb(L^2)_2(ClO_4)_2]$ (5), giving an overall metal coordination geometry of eight with a square antiprism arrangement. From these results, the effects of the donor variation and the anioncoordination ability on the resulting topologies of the soft metal complexes are discussed.

• 대한기계학회논문집A
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• 제20권1호
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• pp.88-99
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• 1996

The explicit scheme for finite element analysis of sheet metal forming problems has been widely used for providing practical solutions since it improves the convergency problem, memory size and computational time especially for the case of complicated geometry and large element number. The explicit schemes in general use are based on the elastic-plastic modeling of material requiring large computataion time. In the present work, a basic formulation for rigid-plastic explicit finite element analysis of plain strain sheet metal forming problems has been proposed. The effect of some basic parameters involved in the dynamic analysis has been studied in detail. Thus, the effective ranges of parameters have been proposed for numerical simultion by the rigid-plastic explicit finite element method. A direct trial-and-error method is introduced to treat contact and friction. In computation, sheet material is assumed to possess normal anisotropy and rigid-plastic workhardening characteristics. In order to show the validity and effectiveness of the proposed explicit scheme, computations are carried out for cylindrical punch stretching and the computational results are compared with those by the implicit scheme as well as with a commercial code. The proposed rigid-plastic exlicit finite element method can be used as a robust and efficient computational method for analysis of sheet metal forming.

• 한국해양공학회지
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• 제12권1호
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• pp.10-22
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• 1998

In the present work the elastic-plastic FE formulations using dynamic explicit time integration schemes are used for numerical analysis of a large auto-body panel stamping processes. For analyses of more complex cases with larger and more refined meshes, the explicit method is more time effective than implicit method, and has no convergency problem and has the robust nature of contact and friction algorithms while implicit method is widely used because of excellent accuracy and reliability. The elastic-plastic scheme is more reliable and rigorous while the rigid-plastic scheme require small computation time. In finite element simulation of auto-body panel stamping processes, the roobustness and stability of computation are important requirements since the computation time and convergency become major points of consideration besides the solution accuracy due to the complexity of geometry conditions. The performnce of the dynamic explicit algorithms are investigated by comparing the simulation results of formaing of complicate shaped autobody parts, such as a fuel tank and a rear hinge, with the experimental results. It has been shown that the proposed dynamic explicit elastic-plastic finite element method enables an effective computation for complicated auto-body panel stamping processes.

• 대한기계학회논문집A
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• 제22권1호
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• pp.1-15
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• 1998

In this paper, thermo-viscoplastic finite element analysis of the effect of tool edge radius on cutting process are performed. The thermo-viscoplastic cutting model is capable of dealing with free chip geometry and chip-tool contact length. The coupling with thermal effects is also considered. Orthogonal cutting experiments are performed for 0.2% carbon steel with tools having 3 different edge radii and the tool forces are measured. The experimental results are discussed in comparison with the results of the FEM analysis. From the study, we confirm that this cutting model can well be applied to the cutting process considered the tool edge radius and that a major causes of the "size effect" is the tool edge radius. With numerical analysis, the effects of the tool edge radius on the stress distributions in workpiece, the temperature distributions in workpiece and tool, and the chip shape are investigated.estigated.

• 센서학회지
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• 제9권3호
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• pp.224-232
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• 2000

표면 미세가공 공정에서 Al 공정을 이용하면 Al 전극의 제작에 의해 접촉 저항이나 선 저항 등을 줄여 전기적인 신호 손실을 줄일 수 있고, 산화막을 희생층으로 사용하는 간단한 공정에 의해 Al 구조물 제작이 가능한 장점을 지닌다. 그러나 실제 공정에서는 Al 전극이나 Al 구조물이 희생층 제거 시에 사용되는 HF 용액에 의해서 부식되는 문제점이 있다. 이러한 문제점을 해결하기 위해 사용되는 희생층 식각액인 BHF/glycerine 혼합 용액에 대한 PSG와 Al의 기본적인 식각 특성은 표면 미세가공에서 발생하는 구조적인 제한 조건에 따라 상당히 달라진다. 본 논문에서는 이러한 희생층의 구조적 특성과 Al 박막의 증착 표면 거칠기의 변화로 인한 식각 특성의 변화를 고려하여 실제로 표면 미세가공에 적용 가능한 혼합 용액의 조건을 조사하였다. 희생층 식각 조건변화에 따른 BHF/glycerine 혼합용액의 최적 혼합비는 $NH_4F$:HF:glycerine=2:1:2에서 가장 좋은 식각 선택비를 보이는 것으로 나타났으며 이 실험 결과를 실제 Al 전극 제작에 적용한 결과 Al 패턴이 희생층 식각액에 대해서 우수한 내식성을 보였다. 또한 Al의 식각액에 대한 내식성을 향상시키기 위하여 CMP 공정을 도입하여 증착 표면을 개선시켰으며 이를 Al 구조물의 제작에 적용하여 식각 특성을 분석하였다. 이러한 분석을 통해 본 논문에서 제시한 식각 조건을 이용하면 Al 전극과 Al 구조물을 표준적인 표면 미세가공 공정을 통하여 간단하게 제작할 수 있다.