• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.06a
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• pp.181-181
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• 2008

DLC (Diamond-like Carbon) 박막은 높은 내마모성과 낮은 마찰 계수, 화학적 안정성 및 적외선 영역에서의 높은 투과율과 낮은 광 반사도, 높은 전기저항과 낮은 유전율, 전계방출특성 등 여러 가지 장점을 가진 물질이다[1]. 최근에는 DLC 박막의 여러 장점들과 산과 염기 유기용매에 대한 화학적 안정성으로 인하여 인조관절에서 인공심장의 판막에 이르기까지 의공학 관련 부품소재로 응용되고 있으며 내구성과 안정성에 있어서 탁월한 성능을 보여주고 있다. 또한 DLC 박막의 높은 경도와 낮은 마찰 계수, 부드러운 박막 표면 (수nm의 RMS 거칠기)의 장점을 살려 마그네틱 미디어와 하드디스크의 슬라이딩 표면에 사용되어지고, MEMS (Micro-Electro Mechanical System) 소자와 MMAs (Moving Mechanical Assemblies)의 고체윤활코팅으로 활용하여 미세기계의 내구성과 성능 향상을 도모할 수 있다. 이와 같이 DLC 박막은 다양한 분야에 응용되고 있으며, 박막이 지닌 여러 가지 장점들로 인하여 더 많은 분야에 응용될 가능성을 지닌 물질이다. 그러나 수 ${\mu}m$이상의 두께에서 박막이 높은 잔류응력 (residual stress)을 가지고, 열에 취약하여 이의 개선에 관한 연구들이 진행되어 지고 있다 [2]. 따라서 사용되는 목적에 따라 용도에 맞는 양질의 DLC 박막을 합성하기 위해선 합성 장치의 개발과 다양한 실험을 통한 최적의 합성조건 도출 등의 노력이 요구된다. 또한 DLC 박막 합성시의 여러 가지 증착 방법에 따른 박막 물성에 대한 재현성 확보 및 박막 증착에 관한 명확한 메커니즘 규명이 아직까지는 불분명하여 이에 관한 연구가 시급하다. 따라서 본 연구에서는 MEMS 소자와 MMAs의 고체윤활코팅으로 사용가능한 DLC 박막을 RF PECVD (Plasma Enhanced Vapor Deposition) 방식으로 합성하고 후열처리 온도에 따른 DLC 박막의 마찰계수 변화를 박막에 훼손을 주지 않는 FFM (Friction Force Microscopy) 방식을 사용하여 분석하였다.

• Structural Engineering and Mechanics
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• v.88 no.1
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• pp.1-12
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• 2023

In this study, forced vibration behavior of a piezo magneto electric sandwich Timoshenko beam is investigated. It is assumed a sandwich beam with porous core and graphene platelet reinforced composite (GPLRC) in facesheets subjected to magneto-electro-elastic and temperature-dependent material properties. The magneto electro platelets are under linear function along with the thickness that includes a cosine function and magnetic and electric constant potentials. The governing equations of motion are derived using modified strain gradient theory for microstructures. The effects of material length scale parameters, temperature change, different distributions of porous, various patterns of graphene platelets, and the core to face sheets thickness ratio on the natural frequency and excited frequency of a sandwich Timoshenko beam are scrutinized. Various size-dependent methods effects such as MSGT, MCST, and CT on the natural frequency is considered. Moreover, the final results affirm that the increase in porosity coefficient and volume fractions lead to an increase in the amount of natural frequency; while vice versa for the increment in the aspect ratio. From forced vibration analysis, it is understood that by increasing the values of volume fraction and the length thickness of GPL, the maximum deflection of a sandwich beam decreases. Also, it is concluded that increasing the temperature, the thickness of GPL, and the initial force leads to a decrease in the maximum deflection of GPL. It is also shown that resonance phenomenon occurs when the natural and excitation frequencies become equal to each other. Outcomes also reveal that the third natural frequency owns the minimum value of both deflection and frequency ratio and the first natural frequency has the maximum.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.15 no.10
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• pp.5974-5979
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• 2014

Lightweight parts with very uniform precision are manufactured by an indent method and the press technique has been improved. Upon assembly with an indent method, a deformation force due to the compressive force occurs between the pin and hole and the contact surface is affected by damage. Therefore, a 3 dimensional model was made using the CATIA program and the damage on the surface contacted with indent was estimated through the ANSYS program in this study. In the analysis result, the maximum load applied at the PCB plate was 21.3 N when the pin goes through the PCB plate. When PCB plate came out of the pin, the maximum load was 19.24 N. As the structural analysis result, the maximum equivalent stress of Pin 1 was 192.96MPa because the maximum stress occurs at Pin 1 among all parts of this study model. By examining the damage property of the contacted indent and applying this study result to the design of real indentation, the damage can be prevented and the durability can be estimated.

• International Journal of Automotive Technology
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• v.7 no.3
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• pp.329-336
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• 2006

The resistance spot-welded region in most current finite element crash models is characterized as a rigid beam at the location of the welded spot. The region is modeled to fail with a failure criterion which is a function of the axial and shear load at the rigid beam. The calculation of the load acting on the rigid beam is important to evaluate the failure of the spot-weld. In this paper, numerical simulation is carried out to evaluate the calculation of the load at the rigid beam. At first, the load on the spot-welded region is calculated with the precise finite element model considering the residual stress due to the thermal history during the spot welding procedure. And then, the load is compared with the one obtained from the model used in the crash analysis with respect to the element size, the element shape and the number of imposed constraints. Analysis results demonstrate that the load acting on the spot-welded element is correctly calculated by the change of the element shape around the welded region and the location of welded constrains. The results provide a guideline for an accurate finite element modeling of the spot-welded region in the crash analysis of vehicles.

• Journal of Aerospace System Engineering
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• v.15 no.6
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• pp.42-49
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• 2021

To develop a high-resolution electro-optical/infrared (EO/IR) payload to be mounted on a high-speed and performance fighter aircraft in an external POD for acquiring daytime and nighttime image information on tactical targets, simulations, including flight environments and maneuvers, should be performed. Such simulations are pertinent to predicting the performance of several variables, such as aerodynamic force and inertia load acting on the payload. This paper describes the development of a flight data acquisition and analysis system based on flight simulation software (SW) for mission simulation of super-maneuverability fighter equipped with EO/IR payload. The effectiveness of the system is verified through comparison with actual flight data. The proposed flight data acquisition and analysis system based on FlightGear can be used as an M&S tool for system performance analysis in the development of the EO/IR payload.

• Transactions of The Korea Fluid Power Systems Society
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• v.8 no.4
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• pp.1-8
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• 2011

Injection molding machine is the assembly of many kinds of mechanical and fluid power part and electro-electronic control system. From in these, fluid power is a part where becomes the first core of this machine. Fluid power systems of injection molding machine are modelled and analyzed using a commercial program AMESim. The analysis model which is detailed about the parts applied a publishing catalog data. Sub system models which is divided according to functional operation are made and its analysis results shows how design parameters work on operational characteristics like displacement, pressure, flow rates at each node and so on. Total fluid power circuit model is also made and analyzed. The results made by analysis will be used design of fluid power circuit of injection molding machine.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.64 no.9
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• pp.1269-1275
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• 2015

Turbine-generator torsional response is caused by interaction between electrical transient air-gap torque and mechanical characteristics of turbine-generator shafts. There are various factors that affects torsional interaction such as fault, circuit breaker switching and generator mal-synchronizing, etc. Fortunately, we can easily simulate above torsional interaction phenomena by using ElectroMagnetic Transient Program (EMTP). However, conventional EMTP shows the incomplete response of super- synchronous torsional mode since it does not consider turbine blade section. Therefore, in this paper, we introduced mechanical-electrical analogy for detailed modeling of turbine-generator shaft system including low pressure turbine blade section. In addition, we derived the natural frequencies of modeled turbine-generator shaft system including turbine blade section and analyzed the characteristics of mechanical torque response at shaft coupling and turbine blade root area according to power system balanced/unbalanced faults.

• Smart Structures and Systems
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• v.18 no.4
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• pp.787-800
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• 2016

The aim of the paper is to analyze nonlinear transverse vibration of an embedded piezoelectric plate reinforced with single walled carbon nanotubes (SWCNTs). The system in rested in a Pasternak foundation. The micro-electro-mechanical model is employed to calculate mechanical and electrical properties of nanocomposite. Using nonlinear strain-displacement relations and considering charge equation for coupling between electrical and mechanical fields, the motion equations are derived based on energy method and Hamilton's principle. These equations can't be solved analytically due to their nonlinear terms. Hence, differential quadrature method (DQM) is employed to solve the governing differential equations for the case when all four ends are clamped supported and free electrical boundary condition. The influences of the elastic medium, volume fraction and orientation angle of the SWCNTs reinforcement and aspect ratio are shown on frequency of structure. The results indicate that with increasing volume fraction of SWCNTs, the frequency increases. This study might be useful for the design and smart control of nano/micro devices such as MEMS and NEMS.

• Journal of Sensor Science and Technology
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• v.21 no.2
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• pp.114-120
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• 2012

This paper describes the design, fabrication and testing of a micromachined resonant accelerometer consisting of a symmetrical pair of proof masses and double-ended tuning fork(DETF) oscillators. Under the external acceleration along the input axis, the proof mass applies forces to the oscillators, which causes a change in their resonant frequency. This frequency change is measured to indicate the applied acceleration. Pivot anchor and leverage mechanisms are adopted in the accelerometer to generate larger force from a proof mass under certain acceleration, which enables increasing its scale factor. Finite element method analyses have been conducted to design the accelerometer and a silicon on insulator(SOI) wafer with a substrate glass wafer was used for fabricating it. The fabricated accelerometer has a scale factor of 188 Hz/g, which is shown to be in agreement with analysis results.

• Journal of the Microelectronics and Packaging Society
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• v.11 no.1
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• pp.43-47
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• 2004

We have been using Moisture Barrier Bags for dry packing of semiconductor packages to prevent moisture from absorbing during shipping. Moisture barrier bag material is required to be waterproof, vapor proof and offer superior ESD (Electro-static discharge) and EMI shielding. Also, the bag should be formed easily to the shape of products for vacuum packing while providing excellent puncture resistance and offer very low gas ＆ moisture permeation. There are some problems like pinholes and punctured bags after sealing and before the surface mount process. This failure may easily result in package pop corn crack during board mounting. The bags should be developed to meet the requirements of excellent electrical and physical properties by means of optimization of their raw material composition and their thickness. This study investigates the performance of moisture barrier bags by characterization of their mechanical endurance, tensile strength and through thermal analysis. By this study, we arrived at a robust material composition (polyester/Aluminate) for better packing.