• 대한기계학회:학술대회논문집
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• 대한기계학회 2007년도 춘계학술대회A
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• pp.268-273
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• 2007

As the industrial society develops rapidly, the weight reduction and high strength are gradually demanded. In case of the welded joint for the rolling stock which receives the repeated load, the fracture can be easily occurred. However, the durability and fatigue characteristics can be improved if the shot peening technique is applied. The optimal peening process should be applied to the metal surface because the over peening can lower the durability of parts. Thus, the fatigue characteristics and Fractography of welded A6061-T6 alloy for a rolling stock were studied in the paper. The optimal peening condition and Fractography were examined. The experimental result show that over peening can lower fatigue life caused by micro crack, fold and incrustation. The fatigue life of welded A6061-T6 was tremendously improved.

• 소성∙가공
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• 제16권5호통권95호
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• pp.375-380
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• 2007

The bimetals of home appliances are mainly manufactured by cladding process and these are almost consisted with Cu alloy and Ni alloy. But it is very difficult to clad these alloys, because the brittle $Cu_3O_4$ oxide film formed easily on Cu alloy surface during cladding process. Clad rolling and heat treatment processes were applied for the development of bimetals by using the Ni alloy and the 3 types of Cu alloys. Optical microstructure, micro-hardness, specific resistance, and deflection and line profile of newly processed bimetals specimens were observed and measured in this paper. Inter-diffusion was observed between Cu and Ni element in the interface of heat treated Cu alloy and Ni alloy clad material. The C1220 and Invar36 clad material showed the best property of deflection among the 3 kind of clad materials.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1996년도 추계학술대회 논문집
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• pp.933-937
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• 1996

In this paper, the behavior of plastic zone in the notch tip was studied under Loye's Micro Vickers Hardness Measurement Method. The direction forming maximum plastic zone was estimated by finite element analysis. In the experiments, cold rolling sheet SGCD3, SK5 and hot rolling sheet SS41, S4SC was used to study the influence of carbon contents on plastic zone. The standard hardness test specimen and the notch hardness test specimen was made and loaded cyclically. The specimen was aged to stabilize the hardness. After aging treatment, the notch specimen was made and simple tension load of 50% yield strength was applied. The hardness test at the notch tip until the hardness data of standard hardness specimen was checked was performed.

• 한국표면공학회:학술대회논문집
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• 한국표면공학회 2015년도 춘계학술대회 논문집
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• pp.123-123
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• 2015

0.087 wt.% Gd-lean duplex stainless steels were inert arc-melted and cast in a mold. The micro-hardnesses of the rolling, transverse, short transverse directions were 258.5, 292.3, 314.7 HV, respectively. The 33% cold rolled specimen had the crystallographic texture that mainly (100) pole was concentrated to normal direction and (110) pole was concentrated in the center of normal and rolling directions. The corrosion potential and corrosion rate in artificial sea water were in the range of $105.6-221.6mV_{SHE}$, $0.59-1.06mA/cm^2$, respectively. The friction coefficient and wear loss of the 0.087 wt.% Gd-lean duplex stainless steels in artificial sea water were about 67% and 65% lower than in air, whereas, the wear efficiency was 22% higher. The corrosion and wear behaviors of the 0.087 wt.% Gd-lean duplex stainless steels significantly depended on the gadolinium phases.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2002년도 Proceedings of the International Welding/Joining Conference-Korea
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• pp.720-725
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• 2002

In recent years, techniques for micro-assembly with high repeatability under a scanning electron microscope (SEM) are required to construct highly functional micro-devices. Adhesion phenomenon is more significant for smaller objects, becanse adhesional force is proportional to size of the objects while gravitational force is proportional to the third power of it. It is also known that adhesional force between micro-objects exposed to Electron Beam irradiation of SEM increases with the elapsed time. Therefore, mechanical manipulation techniques using a needle-shaped tool by adhesional force are often adopted in basic researches where micro-objects are studied. These techniques, however, have not yet achieved the desired repeatability because many of these could not have been supported theoretically. Some techniques even need the process of trial-and-error. Thus, in this paper, mechanical and adhesional micro-manipulation are analyzed theoretically by introducing new physical factors, such as adhesional force and rolling-resistance, into the kinematic system consisting of a sphere, a needle-shaped tool, and a substrate. Through this analysis, they are revealed that how the micro-sphere behavior depends on the given conditions, and that it is possible to cause the fracture of the desired contact interfaces selectively by controlling the force direction in which the tool-tip loads to the sphere. Based on the acquired knowledge, a mode diagram, which indicates the micro-sphere behavior for the given conditions, is designed. By refening to this mode diagram, the practical technique of the pick and place manipulation of a micro-sphere under an SEM by the selective interface fracture is proposed.

• 한국공작기계학회:학술대회논문집
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• 한국공작기계학회 2002년도 춘계학술대회 논문집
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• pp.422-428
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• 2002

In this study, actuator, sensor, guide, power transmission element and control method are considered for ultra-precision positioning apparatus. Through previous process, single plane X-Y stage with ultra-precision positioning is manufactured. Global stage for the purpose of materialization with robust system, is combined by using AC servo motor and ball screw and rolling guide. And ultra-precision positioning system is developed by micro stage with elastic hinge type and piezo element. global servo and micro servo for the purpose of materialization positioning accuracy with nm(nanometer) are controlled simultaneously by using incremental encoder and laser interferometer as displacement measurement sensor. Through previous process, ultra-precision positioning system (100mm stroke and ${\pm}$ 10nm positioning accuracy) with single plane X-Y stage are materialized.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2001년도 춘계학술대회 논문집
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• pp.245-249
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• 2001

This paper is concerned with numerical analyses for bulk forming of a single crystal milli-product, whose typical size ranges from a few hundreds ${\mu}m$ to a few mm. The numerical formulation invoked in this paper combines the crystal plasticity theory considering texture development and the ductile damage mechanics for growth of micro voids, since orientation development and growth of micro voids become the primary factors for bulk forming of milli-size products. As applications, milli-extrusion of a single crystal round bar and milli-rolling of a single crystal plate are simulated and the results are discussed in detail.

• 한국공작기계학회논문집
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• 제11권5호
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• pp.65-72
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• 2002

In this study, actuator, sensor, guide, power transmission element and control method are considered for ultra-precision positioning apparatus. Through previous process, single plane X-Y stage with ultra-precision positioning is manufactured. Global stage for the purpose of materialization with robust system, is combined by using AC servo motor and ball screw and rolling guide. And ultra-precision positioning system is developed by micro stage with elastic hinge type and piezo element. global servo and micro servo for the purpose of materialization positioning accuracy with nm(nanometer) are controlled simultaneously by using incremental encoder and laser interferometer as displacement measurement sensor. Through previous process, ultra-precision positioning system(100mm stroke and $\pm$ l0nm positioning accuracy) with single plane X-Y stage are materialized.

• Journal of Mechanical Science and Technology
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• 제20권5호
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• pp.621-633
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• 2006

To reflect the size effect of material $(1\sim15{\mu}m)$ during plastic deformation of polycrystalline copper, a constitutive equation which includes the strain gradient plasticity theory and intrinsic material length model is coupled with the finite element analysis and applied to plane strain deformation problem. The method of least square has been used to calculate the strain gradient at each element during deformation and the effect of distributed force on the strain gradient is investigated as well. It shows when material size is less than the intrinsic material length $(1.54{\mu}m)$, its deformation behavior is quite different compared with that computed from the conventional plasticity. The generation of strain gradient is greatly suppressed, but it appears again as the material size increases. Results also reveal that the strain gradient leads to deformation hardening. The distributed force plays a role to amplify the strain gradient distribution.

• 대한기계학회논문집A
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• 제38권9호
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• pp.1043-1048
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• 2014

체결부품의 사이즈가 작아질수록 실제 접합부의 면적이 줄어들기 때문에 체결력은 감소한다. 이러한 체결부품의 체결력을 결정하는 요소는 소재(Material), 구조(Geometry), 마찰(Friction)이 있다. 본 연구에서는 체결부품의 사이즈가 줄어들면서 체결력을 향상시킬 수 있는 방법 중의 하나인 소재 변경에 대하여 연구하였다. SWCH18A 와 SUS XM7 을 적용하여 초소형 나사를 제작하였으며, 3 차원 치수 측정을 통하여 피치정밀도와 두께정밀도를 측정하였다. 비커스 경도 측정을 통하여 나사가 외부의 힘에 의해 변형에 대한 저항력을 분석하였다. 또한 파단토크 시험과 SEM 을 이용한 파단면 분석을 통해 파단특성을 분석한다.