• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2000년도 춘계학술대회 논문집
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• pp.820-823
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• 2000

The characteristics of wire deflection, surface roughness and roundness were observed on changing discharge time for electrical discharge machining(EDM) of tungsten carbide in various conditions of thickness. The wire deflection was decreased as increasing discharge time and wire tension, the gap of deflection was decreased after thickness 60mm and discharge time of 6$\mu\textrm{s}$ due to the changing from fundamental mode to vibration mode. The deflection is the smallest at the water specific resistivity of 7.5 kΩ ㆍcm. The deflection is found to be decreased as increasing dwell time, and the result is due to the vibration of the pressure and the amount of the dielectric. The component of copper(Cu) and zinc(Zn), which is the main material of wire electrode, was observed for rough wire-cutting EDM of STD-11. This phenomena is found to be decreased as the number of EDM is increased. But it will be improved by changing the material and the shape of wire. The roundness of middle is found to be worse than that of upper and it is increased as the thickness of material is increased.

• 한국정밀공학회지
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• 제23권4호
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• pp.116-123
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• 2006

During the last two decades, many researchers investigated influences of stress triaxiality on ductile fracture for various specimens and structures. With respect to a transferability issue, the local approach reflecting micro-mechanical specifics is one of effective methods to predict constraint effects. In this paper, the applicability of the local approach was examined through a series of finite element analyses incorporating modified GTN (Gurson-Tvergaard-Needleman) and Rousselier models as well as fracture toughness tests. To achieve this goal, fracture resistance (J-R) curves of several types of compact tension (CT) specimens with various crack length, with various thickness and with/without 20% side- grooves were estimated. Then. the constraint effects were examined by comparing the numerically estimated J-R curves with experimentally determined ones. The assessment results showed that the damage models might be used as useful tool for fracture toughness estimation and both the crack length and thickness effects should be considered for realistic structural integrity evaluation.

• 한국정밀공학회지
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• 제18권3호
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• pp.99-106
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• 2001

Model trains should have very similar motion characteristics to real trains in order to provide realistic feeling to their operators. Main purpose of dynamic analysis of model trains is to predict velocities in straight and circular tracks and estimate stopping distance after power shut off. Equations of motion for a model train are derived that relates velocity, traction, rolling resistance, and pulling force. Also, energy equations for calculating stopping distance after power shut off are derived. Experiments with model trains are preformed to measure velocity, rolling resistance, slip, and stopping distance. The results are compared with the prediction based on the equations of motion, and they showed good agreement. It can be concluded that the prediction is more accurate when the slip between wheel and rail is accounted for. The analysis procedures can be applied to determining various design factors in model trains.

• 한국정밀공학회지
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• 제27권10호
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• pp.84-92
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• 2010

In this study a numerical analysis has been conducted for the flow characteristics and pumping performance of a piezoelectric-based micropump with electromagnetic resistance exerted on electrically conducting fluid. Here, electromagnetic resistance is alternately applied at the inlet and outlet with alternately applied magnetic fields in association with the reciprocal membrane motion of the piezoelectric-based micropump. A model of Prescribed Deformation is used for the description of the membrane motion. The internal flow characteristics and pumping performance are investigated with the variation of magnetic flux density, tube size, displacement of membrane and the frequency of the membrane. It turns out that the current micropump has a wide range of pumping flow rate compared with diffuser-nozzle based micropumps.

• 한국정밀공학회지
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• 제27권10호
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• pp.23-28
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• 2010

Resistance trimming and cutting processes of printed circuit board by making use of high power UV laser with nano-second pulse width have been proposed and investigated experimentally. Also laser-based application system with high flexibility and complex has been designed and adopted power controller, auto beam size control, auto-focusing and control program developed for ourselves. The function of each module shows that they can be reliable for industrial equipments. Resistance trimming method used a plunge and double cut process with $20{\mu}m$ spot size beam. Results show that double cut process is more effective to control resistance trimming in precision than plunge cut process.

• 한국정밀공학회지
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• 제19권9호
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• pp.98-105
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• 2002

Some materials exhibit a rising K-R curve, while the K-R curve for other materials is flat. The shape of the K-R curve depends on material behavior and, to a lesser extent, on the configuration of the cracked structure. The K-R curve for an ideally brittle material is flat because the surface energy is an invariant material property. However, the K-R curve can take on a variety of shapes when nonlinear material behavior accompanies fracture. Five different hot-rolled thin plates are tested to investigate K-R curve behavior. A special experimental apparatus is used to prevent specimens from buckling.

• 한국정밀공학회지
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• 제22권2호
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• pp.180-187
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• 2005

This paper is focused on the development of the flexible electrode for disc-type polymer actuators using Segmented Polyurethane(SPU). This paper consists of two parts. The one is about the mechanical property such as elastic modulus. these parameters mainly affect behaviors of polymer actuators and the other is about the electro-chemical property such as the surface resistance of the composite electrode affects the strength of electrostatic force, results in the deformation of polymer actuators. The Young's modulus was measured by UTM. As result, by increasing the modulus of a body of polymer actuators, the maximum displacement of polymer actuators are decreased. The surface resistance of the electrode was measured by 4 point probe system. Compared with the conductive silver grease, the displacement of polymer actuators using carbon black(CB) composite electrodes is comparably small but CB composite electrode should be the practical approach for the improvement of the performance of all-solid actuators, compared with another types of electrode materials.

• 한국정밀공학회지
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• 제20권12호
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• pp.126-134
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• 2003

In order to investigate the effect of surface treatment in Aluminium alloy and Titanium alloy which are used to armor material during ballistic impact, a ballistic testing was conducted. Anodizing was used to achieve higher surface hardness of Aluminium alloy and Iron plating in PVD(Physical Vapor Deposition) method was used to achieve higher surface hardness of Titanium alloy. Surface hardness test were conducted using a Micro victor's hardness tester. Ballistic resistance of these materials was measured by protection ballistic limit(V-50), a statical velocity with 50% probability penetration. Fracture behaviors and ballistic tolerance, described by penetration modes, are respectfully observed from the results of V-50 test and Projectile Through Plates (PTP) test at velocities greater than V-50. PTP tests were conducted with 0$^{\circ}$obliquity at room temperature using 5.56mm ball projectile. V-50 tests were conducted with 0$^{\circ}$obliquity at room temperature with projectiles that were able to achieve near or complete penetration during PTP tests. Surface hardness, resistance to penetration. and penetration modes of surface treated alloy laminates are compared to those of surface non-treated alloy laminates. A high speed photography was used to analyze the dynamic perforation phenomena of the test materials.

• 한국정밀공학회지
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• 제16권4호통권97호
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• pp.13-18
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• 1999

섬유강화금속적층재(Fiber Reinforced Metal Laminates. FRMLs)는 고강도금속과 섬유강화복합재료(Fiber Reinforced Composite Materials)를 적층한 새로운 종류의 하이브리드 재료이다. 국산 아라미드 섬유인 헤라크론(Heracron, 코오롱)과 국내 복합재료 제작기술(한국화이바)을 사용하여 섬유강화금속적층재를 제작하고, 이를 HERALL(Heracron Reinforced Aluminum Laminate)이라 명명하였다. HERALL(Heracron Reinforced Aluminum Laminate)의 피로균열성장특성 및 피로균열진전 방해기구를 ARALL(Aramid-fiber Reinforced Aluminum alloy Laminates) 및 Al 2024-T3과 비교해석하였다. HERALL과 ARALL은 균열진전을 저지하는 아라미드 섬유로 인해 뛰어난 피로균열성장특성 및 피로저항성을 보여주었다. 아라미드 섬유의 균열브리드징으로 인한 $K_{max}$의 감소량과 Al 2024-T3의 균열닫힘으로 인한 $K_{max}$의 증가량을 구할 수 있는 응력-COD법을 사용하여 실제로 균열성장에 영향을 준 유효응력확대계수범위를 측정하였다. 균열선단으로부터 균열을 가공하면서 COD 변화량을 측정하여 균열브리징 영역을 구하였다.

• 한국정밀공학회지
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• 제31권6호
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• pp.505-511
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• 2014

In this paper, silver pastes were printed on polyethylene terephthalate (PET) film using screen printing and evaluated the drying characteristics by using dry oven and NIR drying system. The printed Ag films were dried at $140^{\circ}C$ and the drying time was changed from 10 to 90 seconds. To evaluate the electrical properties of printed Ag film, sheet resistance was compared. The sheet resistance of the dried thin silver film by using NIR drying system more rapidly decreased. To clarify this phenomena, the morphology and component of the dried surfaces were measured by using the scanning electron microscope (SEM) and the energy dispersive X-ray Spectroscopy (EDX), respectively. In the EDX measurement results, the oxidation of the surface was observed in the dried thin film by using the dry oven. The NIR drying system is more applicable than conventional hot air drying to apply continuous printing system.