• 대한기계학회논문집B
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• 제28권6호
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• pp.659-664
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• 2004

It is important to measure precisely the size and velocity of micro-bubbles used in various field. The synchrotron X-ray micro-imaging technique was employed to measure the size and velocity of micro-bubbles moving in an opaque tube simultaneously. Phase contrast images were obtained at interfaces of micro-bubbles between water and air due to their different refractive indices. The X-ray micro-imaging technique was found to measure an optical fiber with an accuracy of 0.2%. Micro-bubbles of 20∼60$\mu\textrm{m}$ diameter moving upward in an opaque tube (${\Phi}$＝2.7mm) were tested to measure bubble size and up-rising velocity. For DI water, the measured velocity of micro-bubbles is nearly proportional to the square of bubble size, agreed well with the theoretical result. In addition, the synchrotron X-ray micro-imaging technique can measure accurately the size and velocity of several overlapped micro-bubbles.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 춘계학술대회
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• pp.1744-1748
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• 2004

It is important to measure precisely the size and velocity of micro-bubbles used in various field. The synchrotron X-ray micro-imaging technique was employed to measure the size and velocity of micro-bubbles moving in an opaque tube simultaneously. Phase contrast images were obtained at interfaces of micro-bubbles between water and air due to their different refractive indices. The X-ray micro-imaging technique was found to measure an optical fiber with an accuracy of 0.2%. Micro-bubbles of $10{\sim}60{\mu}m$ diameter moving upward in an opaque tube (${\phi}=2.7mm$) were tested to measure bubble size and up-rising velocity. For DI water, the measured velocity of micro-bubbles is nearly proportional to the square of bubble size, agreed well with the theoretical result. In addition, the synchrotron X-ray micro-imaging technique can measure accurately the size and velocity of several overlapped micro-bubbles.

• 대한기계학회논문집
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• 제12권2호
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• pp.278-285
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• 1988

본 연구에서는 SM15C재와 SM35C재에 퍼얼라이트, 페라이트 조직의 영향을 배재한 비교적 균질한 조직인 구상화시멘타이트조직과 SM35C재에 실용조직 이면서 비교적 균질한 조직인 마르텐사이트 조직을 만들고, 가공하였다.

• Advances in materials Research
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• 제8권3호
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• pp.219-235
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• 2019

This research is devoted to analyzing mechanical-thermal post-buckling behavior of a micro-size beam reinforced with graphene platelets (GPLs) based on geometric imperfection effects. Graphene platelets have three types of dispersion within the structure including uniform-type, linear-type and nonlinear-type. The micro-size beam is considered to be perfect (ideal) or imperfect. Buckling mode shape of the micro-size beam has been assumed as geometric imperfection. Modified couple stress theory has been used for describing scale-dependent character of the beam having micro dimension. Via an analytical procedure, post-buckling path of the micro-size beam has been derived. It will be demonstrated that nonlinear buckling characteristics of the micro-size beam are dependent on geometric imperfection amplitude, thermal loading, graphene distribution and couple stress effects.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2000년도 하계학술대회 논문집 C
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• pp.2263-2265
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• 2000

본 연구에서는 광 픽업의 소형, 경량 제작을 위해 MEMS 기술을 이용하여 planar micro optics 방법으로 광 픽업을 구성하는 micro lens, actuator, beamsplitter 등을 설계, 제작하고 집적화한 픽업헤드를 구성하여 그 특성을 분석하였다. 특성분석 결과 disk에 focusing 되는 beam의 형상은 circle type의 비교적 양호한 결과를 얻을 수 있었고 beam spot size는 약 22$\mu m$로 실제 system에서 요구되는 0.9$\mu m$이내의 beam spot size에 비해 약 25배 가량 큰 beam spot size를 얻을 수 있었다.

• 한국가시화정보학회:학술대회논문집
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• 한국가시화정보학회 2003년도 추계학술대회 논문집
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• pp.45-46
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• 2003

The x-ray micro-imaging technique was employed to measure the size and velocity of micro-bubbles moving in an opaque tube simultaneously. Phase contrast images were obtained at interfaces of micro-bubbles between water and air due to different refractive index. Micro-bubbles of $20\~120{\mu}m$ diameter moving upward in an opaque tube $(\phi=2.7mm)$ were tested. For two different working fluids of tap water and DI water, the measured velocity of micro-bubbles is roughly proportional to the square of bubble size.

• 한국정밀공학회지
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• 제15권10호
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• pp.128-139
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• 1998

In this paper, a finite element method for predicting the temperature and stress distributions in micro-machining is presented. The work material is oxygen-free-high-conductivity copper(OFHC copper) and its flow stress is taken as a function of strain, strain rate and temperature in order to reflect realistic behavior in machining process. From the simulation, a lot of information on the micro-machining process can be obtained; cutting force, cutting temperature, chip shape, distributions of temperature and stress, etc. The calculated cutting force was found to agree with the experiment result with the consideration of friction characteristics on chip-tool contact region. Because of considering the tool edge radius, this cutting model using the finite element method can analyze the micro-machining with the very small depth of cut, almost the same size of tool edge radius, and can observe the 'size effect' characteristic. Also the effects of temperature and friction on micro-machining were investigated.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2004년도 추계학술대회 논문집
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• pp.217-222
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• 2004

The aim of this paper is to investigate the effect of micro-dimple size on reduction friction and to understand the potential of friction reduction through micro-scale dimple to fabricate by photolithography on pin-on-disk test using flat-on-flat contact geometry. It was verify that the friction property with respect to the same pitch has been influence on the size of dimple under lubricated sliding contact. Also, we can recognize from Stribeck curve that the friction property has a connection with the size of dimple. It can explain a relationship between the friction coefficient and a dimensionless parameter for lubrication condition. The friction property has been an effect on the size of surface texture on reduction friction, not only because the density of dimple, but also because the ratio of diameter/pitch. This ratio of approximately 0.5 is recommend under the tested friction condition. It suggested that the ratio of d/p is an important parameter for surface texture design.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2005년도 제25회 추계학술대회논문집
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• pp.278-281
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• 2005

본 논문은 적층된 전극 구조의 노즐을 이용한 정전기 마이크로 추진 장치의 새로운 메커니즘을 제시한 구조에 대해 크기에 따른 영향을 연구하였다. 구조의 크기에 따른 실험결과를 비교해 볼 때 500volt 이하의 요구 전압이 가능함을 보여주고 있다.

• 한국해양공학회지
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• 제1권2호
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• pp.74-82
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• 1987

This study has been made to investigate into the behavior of fatigue limit, of fatigue crack initiation, and of fatigue crack propagation under the condition of rotating bending stress; specifically on the independency of stress field as well as the crack behavior of surface micro hole defect, which is made artificially through the specimen. The results obtained can be summarized as followa; 1) For the single micro hole defect, initiation of fatigue crack is occurred at both tips of microhole defect simultaneosly along the slip which are produced in the range of maximum principal stress arround micro hole defect independent of the size of micro hole defect. 2) For the neighbored deuble micro hole defects with equal size, in the range ($\frac{L}{r}$)ratio $\gtrsim$ 3 defined as the size of micro hole defect(2r) to the distance between the centers of micro hole defects (2L), the crack behavior of the micro hole defects is same as single one. However, for the range of $\frac{L}{r}$<3, the interference effect becomes significant as the ratio approaches to 1.