• Transactions of the Korean Society of Mechanical Engineers A
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• v.26 no.7
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• pp.1340-1347
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• 2002

Finite element simulations are being widely used to increase the efficiency and effectiveness of design of bulk metal forming processes. In such simulations, proper consideration of friction condition is crucial in obtaining reliable results. For this purpose, tip test based on backward extrusion was proposed recently. In this lest, a cylindrical billet is positioned in a shallow groove of a counter punch for centering purpose and formation of a radial tip is induced on the extruded end of the workpiece. In this study, the effect of centering groove on tip test was investigated. The quantitative ratio of the shear friction factors between the punch and die was numerically determined depending on the shape of centering groove. Also, surface expansion and pressure distribution along the punch and die were considered in order to better understand the reason that friction condition at the punch compared to the one of die was more severe.

• Journal of the Korean Society of Industry Convergence
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• v.6 no.1
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• pp.43-48
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• 2003

점용접은 자동차를 제작하는데 사용하는 가장 유용한 용접법이다. 그러나 산업현장에서 직면하고 있는 가장 큰 문제점 중의 하나는 점용접의 용접성에 관한 문제이다. 본 연구에서는 강판의 두께가 1.6mm인 경우와 1.2mm인 경우에 대해 2점 점용접을 실시하여 인장강도를 증가시키고 용접의 흔적을 남기지 않게 하기 위한 조건을 찾는 것을 목적으로 하였다. 용접성에 영향을 미치는 많은 요소들이 있다. 그중에서 용접전극의 형상이 인장강도를 증가시키는 요소로 집중을 하면서 연구를 수행하여 다음과 같은 결과를 얻었다. 인장강도는 용접전극의 형상 및 팁직경 거리와 전류가 클수록 증가하였다. 시행 착오법을 통해 최적용접조건을 찾았고 그에 따른 최적전류인 9,000A와 전극의 형상 RF형을 찾았다. 경도시험결과는 인장력이 시험편에 작용할 때 열 영향부인 HAZ부에서 왜 파괴가 일어나는지를 설명해 주었다.

• Journal of the Korean Society for Nondestructive Testing
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• v.30 no.5
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• pp.471-478
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• 2010

Thin films play an important role in many technological applications including microelectronic devices, magnetic storage media, MEMS and surface coatings. It is well known that a thin film's material properties can be very different from the corresponding bulk properties and thus there has been a strong need for the development of a reliable test method to measure the mechanical properties of a thin film. We have developed an alternative and convenient test method to overcome the limitations of previous membrane deflection experiment and uniaxial tensile test by adopting a white light interferometer having sub-nanometer out-of-plane displacement resolution. The freestanding aluminium specimens are tested to verity the effectiveness of the test method developed and get the tensile properties. The specimens are 0.5 rum wide, $1{\mu}m$ thick and fabricated through MEMS processes including sputtering. 1 to 5 specimens are fabricated on Si dies. The membrane deflection experiments are carried out by using a homemade tester consisted of a motor-driven loading tip, a load cell, and 6 DOF alignment stages. The test system is compact enough to set it up beneath a commercial white light interferometric microscope. The white light fringes are utilized to align a specimen with the tester. The Young's modulus and yield point stress of the aluminium film are 62 GPa and 247 MPa, respectively.

• Journal of Conservation Science
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• v.25 no.4
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• pp.431-438
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• 2009

We have investigated the suitable measuring method and condition on the hardness testing for the earthenwares excavated from Poongnap mud castle in Hanseong Baekje period. The earthenwares which used on hardness testing have been classified according to Mohs hardness and external form and color. The Ultrasonic and Equotip testing method have used to the hardness testing on the surface of the earthenwares and the Rockwell and Micro-vickers testing methods have used to the hardness testing on the cross section of the earthenwares. As the results, the two methods applied to the surface of the earthenwares were very hard on the precise measurement and the measuring values were incompatible with the tendency classified according to Mohs hardness and external form and color. On the testing for the cross section of earthenware, the Rockwell-superficial hardness testing method was more suitable for the soft texture earthenware and highest reproducibility of the measuring value obtained at the test load and indentor are 15kgf and 1/16 “iron ball, respectively. The Micro-Vickers hardness testing method was suitable for the hard texture earthenware and highest reproducibility and accuracy of the measuring value obtained at the test load is 100gf. This results show strong possibility of progress on the classifying and comparing study for hardness of the earthenware and therefore active studies are expected on the field.

• Proceedings of the Korea Institute of Fire Science and Engineering Conference
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• 2010.04a
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• pp.75-78
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• 2010

고발포 소화약제의 발포력은 화재시 포소화약제의 성능을 검증하는데에 중요한 요소이다. 이러한 발포력 검증은 한국소방산업기술원의 "포소화약제의 형식승인 및 검정기술기준(KOFEIS 0103)"에서 제시하고 있는 표준발포기를 이용한 측정법을 통해 검증한다. 본 연구에서는 기존 방법의 제작 비용 및 측정의 번거로움을 보완하기 위한 약제 개발단계에서의 포소화약제 발포력 검증을 위한 실험실적인 측정법을 고안하여 적용성을 분석한다. 측정은 1000ml 시험관내에 3%의 수용액 $100m{\ell}$를 첨가하여 수용액 내부에 정량펌프를 통해 일정한 기포량 및 기포크기로 분사하여 발포시켰으며, 기포의 노즐은 거품의 정확도를 향상시키기 위해 마이크로 피펫팁 $0.2m{\ell}$ 용량을 사용하여 적용성을 분석하였다.

• Korean Journal of Crystallography
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• v.12 no.2
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• pp.102-112
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• 2001

The mechanical properties of silicon crystals are important from the viewpoint of wafer and device fabrication processes. It is now widely recognized that silicon undergoes a series of phase transformations when subjected to high pressures, using conventional high pressure devices, such as diamond anvils or indenters. Diamond tip scratching on a silicon surface in the various conditions introduces various kinds of mechanical damage and stressed states. Micro Raman spectroscopy was used to observe the phase transition of single crystal silicon. As results, different morphologies were observed as functions of scratching speed and loading condition and various phases were observed as functions of scratching speed and loading condition.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.38 no.10
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• pp.955-965
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• 2010

The MH-75 propeller for the MAV propulsion is designed using a free vortex design method which considers design parameters such as the hub-tip ratio, the twist angle distribution, the maximum camber location and the chord length of the propeller blade. Aerodynamic characteristics of the MH-75 propeller are predicted by changing the flight speed using the frequency domain panel method. And, the thrust characteristics of the MH-75 propeller are measured using the balance system of the subsonic wind tunnel for the validation of numerical results. The performance characteristics of the MH-75 propeller satisfied with design requirements. Numerical results of the MH-75, which are predicted by the frequency domain panel method, are more agree with experimental results compare with XFOIL.

• Polymer(Korea)
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• v.37 no.4
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• pp.455-461
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• 2013

Mar behavior and visibility were investigated by applying a constant load to various gloss-coated urethane-acrylate surfaces. Using a area-contact scratch tip which can apply a relatively low stress level to the coated surfaces, the mar damages were generated on the surfaces. When evaluating the mar-induced damage by means of delta-gloss (${\Delta}G$) and delta-luminance (${\Delta}L$) with existing test methodologies, an increase in constant load on the same gloss-coated surface leads to an increase in ${\Delta}G$ and ${\Delta}L$. However, these are not suitable for evaluating and comparing the surface damages of different gloss-coated samples because of a disagreement between the measured values and the mar visibility. It is shown that new mar test assessment proposed in this work not only can be used to quantitatively evaluate the mar damage, but also accounts for the correlation that the increases of the normalized gloss and luminance on coated surfaces correspond with an increase in the mar visibility.

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.7
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• pp.1373-1380
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• 1992

The local cyclic strain distribution near the crack tip has been investigated by the fine Dot Grid Strain Measurement Method, which had been suggested strain measurement method to resolve experimental difficulties by authors. It has been found that the magnitude of the local cyclic strain distribution(.DELTA..epsilon.$_{eq}$ )near a crack tip has been varied by the applied cyclic load level and material, but the shape of the local cyclic strain distribution near the crack tip has been experimentally scrarcely altered : that is .DELTA..epsilon.$_{eq}$ = .DELTA.A.f(.theta.). $r^{-1}$ . Consequently, the local cyclic strain field near the crack tip could be favorably characterized by a single parameter fatigue strain intensity factor .DELTA.A. In addition, with the viewpoint that .DELTA.A depends on material and load level, .DELTA.A has been applied to evaluate the fatigue crack propagation rate and usefulness of the result has been considered. As a result, it has been ascertained that .DELTA.A has been a useful parameter to evaluate the fatigue crack propagation rate.

• Journal of Dental Rehabilitation and Applied Science
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• v.34 no.4
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• pp.270-279
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• 2018

Purpose: The aim of this study was to assess the patients' perception, acceptance, and preference of the difference between a conventional impression and digital impression through questionnaire survey. Materials and Methods: Thirteen (6 male, 7 female) subjects who experienced both digital and conventional impression at the same day were enrolled in this study. Conventional impression were taken with polyvinylsiloxane and digital impression were performed using a newly developed intra-oral scanner. Immediately after the two impressions were made, a survey was conducted with the standardized questionnaires consisting of the following three categories; 1) general dental treatment 2) satisfaction of conventional impression 3) satisfaction of digital impression. The perceived source of satisfaction was evaluated using Likert scale. The distribution of the answers was assessed by percentages and statistical analyses were performed with the paired t-test, and P < 0.05 was considered significant. Results: There were significant differences of the overall satisfaction between two impression methods (P < 0.05). Digital impression showed high satisfaction in less shortness of breath and odor to participants compared to conventional impression. The use of an oral scanner resulted in a discomfort of TMJ due to prolonged mouth opening and in lower score of the scanner tip size. Conclusion: It was confirmed that the preference for the digital impression using intraoral scanner is higher than the conventional impression. Most survey participants said they would recommend the digital impression to others and said they preferred it for future prosthetic treatment.