• 한국구조물진단유지관리공학회 논문집
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• 제20권1호
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• pp.18-24
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• 2016

본 논문은 강섬유의 일부를 철근집합체로 대체하여 초고강도 섬유보강 철근 콘크리트 I 형보의 연성거동을 유도하는 것을 목적으로 한다. 강섬유와 철근집합체의 조합을 가진 초고강도 콘크리트 I 형보 대한 휨거동 실험을 수행하였다. 강섬유의 혼입률은 0%, 0.7%, 1%, 1.5%, 2%이다. 철근집합체와 PS강연선 집합체가 압축구역에서 콘크리트를 구속하기 위해 사용되었다. 철근집합체와 강연선 집합체의 길이도 실험요소 중 하나이다. 이러한 실험요소를 조합하여 9개의 초고강도 철근 콘크리트 I 형보를 제작하였다. 강섬유 뿐만 아니라 종방향의 철근 집합체도 초고강도 철근 콘크리트 I형 보의 연성거동을 유도하는데 효과를 가지고 있다. 강섬유 혼입률 0.7% 또는 1%와 철근집합체를 사용한 조합이 I형 보의 효과적인 연성 거동을 보여주고 있다. 하중과 처짐관계 및 균열양상 등이 좁은 간격을 가진 작은 직경의 종방향 철근 집합체의 유용성을 나타내고 있다.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2003년도 가을 학술발표회 논문집
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• pp.136-139
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• 2003

The re-bar work in the construction of nuclear power plants is difficult, due to the large diameter and the congestion of reinforcements. The mechanical anchorage offers a potential solution for this problem. However, the requirements or the standards for the shape of anchor plate of mechanical anchor has not been clearly established up to now. In this paper, the required performance of the mechanical anchorage for large diameter reinforcements in nuclear power plants are proposed, and the anchor plates are designed through nonlinear finite element analysis. The diameters of anchor plate are determined to be $\sqrt{5}$ times of reinforcement diameter for longitudinal reinforcements and $\sqrt{10}$ for shear reinforcements. The thickness of anchor plates is optimized as 0.3-0.35 times of reinforcement diameter for longitudinal reinforcements and 0.5~0.56 times for shear reinforcements.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2003년도 하계학술대회 논문집 Vol.4 No.2
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• pp.728-731
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• 2003

This paper deals with a flat type ultrasonic motor, which uses a longitudinal-bending multi mode vibrator of rectangular form. A linear ultrasonic motor was designed by combination of the first longitudinal and eighth bending mode, and the motor consisted of a straight aluminum alloy bar bonded with piezoelectric ceramic elements as a driving element. The geometrical dimensions of the rectangular aluminum vibrator were determined by Euler-Bernoulli theory ANSYS was used to analyze the resonance frequency and the displacement of the stator vibrator. The resonance frequency of the motor provides the elliptical motion. and ANSYS was used to analyze elliptical motion and elliptical trajectory of stator vibrator when thickness of piezoelectric ceramics was varied respectively 0.763, 1.526, 2.289[mm] and width of stator vibrator was varied respectively 16, 12, 8, 4[mm]. When thickness of piezoelectric ceramics was decreased, the displacement of the stator vibrator was increased. And when width of stator vibrator was decreased, the displacement of the stator vibrator was increased.

• 항공우주시스템공학회지
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• 제14권2호
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• pp.28-35
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• 2020

In this paper, we present a design for a retraction-type actuator (ReACT) that has the characteristics of both thermomechanical metamaterials and displacement amplification mechanisms. The ReACT consists of an actuating bar, a diamond-shaped displacement amplification (DA) structure, and a slot for loading thin-film heaters formed through the actuating bar. When power is supplied to the thin film heater, the actuating bars contacting the heater thermally expand, and the diamond-shaped DA structures retract in the longitudinal direction. The performance characteristics of the ReACT, such as temperature distribution and retracting displacement, were calculated with thermomechanical analysis methods using the finite element method (FEM). Subsequently, the ReACTs were fabricated using a polymer-based 3D printer that can easily execute complex structures, and the performance of the ReACT was evaluated through repeated tests under various temperature conditions. The results of the performance evaluation were compared with the results of the FEM analysis.

• 한국주조공학회지
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• 제16권2호
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• pp.116-123
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• 1996

The equipment for the horizontal continuous casting was built to produce hyper-eutectic Al-Si bars with a small cross-section of 25mm in diameter. The manufacturing processes including withdrawal cycle and secondary cooling methods were modified to refine the primary and the eutectic Si. The longitudinal casting speeds varied over the ranges of 670-1100mm/min for pure Al, and 200-350mm/min for Al-17wt%Si alloy. Due to the difference of cooling rate in the mould, microstructural asymmetry between the lower and the upper part of bar was observed. Thus, manufacturing processes such as cooling and withdrawal method were optimally combinated to get the homogeneous cast structure. With the increase of casting speed, the primary Si size was refined down to $30{\mu}m$ near the surface, and $80{\mu}m$ in the center of the bar.

• Advanced Composite Materials
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• 제16권2호
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• pp.167-180
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• 2007

The tensile strength of unidirectional carbon fiber reinforced plastics under a high strain rate was experimentally investigated. A high-strain-rate test was performed using the tension-type split Hopkinson bar technique. In order to obtain the tensile stress-strain relations, a special fixture was used for the impact tensile specimen. The experimental results demonstrated that the tensile modulus and strength in the longitudinal direction are independent of the strain rate. In contrast, the tensile properties in the transverse direction and the shear properties increase with the strain rate. Moreover, it was observed that the strain-rate dependence of the shear strength is much stronger than that of the transverse strength. The tensile strength of off-axis specimens was measured using an oblique tab, and the experimental results were compared with the tensile strength predicted based on the Tsai-Hill failure criterion. It was concluded that the tensile strength can be characterized quite well using the above failure criterion under dynamic loading conditions.

• 한국지진공학회논문집
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• 제7권5호
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• pp.25-35
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• 2003

소성힌지영역에 50%의 주철근 겹침이음을 갖는 교각의 거동특성을 파악하기 위하여 축소교각모형실험을 수행하였다. 모델의 단면형상은 사각단면으로 중공 및 중실단면으로 각각 1기씩 제작하였다. 주철근은 연속철근과 주철근지름(d$_{b}$)의 39배의 겹침이음을 갖는 철근을 교대로 배치하였다. 겹침이음에 의한 거동특성을 파악하기 위하여 횡철근에 의한 구속효과와 축력에 의한 영향은 배제하였다. 두 시험체 모두 전형적인 휨파괴 형태를 보였으며 비교적 연성적인 거동을 나타내었다. 이로부터 50%의 주철근 겹침이음이 성능기초 내진설계를 위한 주철근상세의 하나의 대안으로서 유효성이 있음을 확인하였다.

• 대한기계학회논문집A
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• 제39권8호
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• pp.793-799
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• 2015

막대형 금속 구조물을 통하여 전파되는 종파와 횡파의 전달 현상을 전산구조해석 모델을 이용하여 시뮬레이션 하였으며 실험 결과와 비교 분석하였다. 실험 및 해석은 막대 구조물 전체가 알루미늄인 경우 및 파동 전파 경로인 알루미늄 막대 중간 부분에 액체층을 포함한 경우 등 두 가지 조건에 대해 수행되었다. 연구 결과 해석 및 실험을 통해 구한 종파 및 횡파 전파 특성과 전파 속도가 이론치와 잘 일치하는 것을 확인하였으며, 본 연구에서 이루어진 고체-유체 경계면을 가지는 구조물을 통과하는 파동 전파 해석을 위한 전산해석 모델링 기법은 고체-유체 상호작용을 고려해야 하는 보다 복잡한 시스템에 대해서도 확장 가능하다.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2003년도 추계학술대회 논문집 Vol.16
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• pp.356-359
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• 2003

This paper deals with a flat type ultrasonic motor, which uses a longitudinal-bending multi mode vibrator of rectangular form. This ultrasonic motor was designed by combination of the first longitudinal and eighth bending mode, and the motor consisted of a straight aluminum alloy bar bonded with piezoelectric ceramic elements as a driving element. The geometrical dimensions of the rectangular aluminum vibrator were determined by Euler-Bernoulli theory In the experimental device, piezoelectric ceramics ( a piece of ceramic for the L-mode, $24\;{\times}\;8\;{\times}\;1[mm]$, and four pieces for the B-mode, $12.5\;{\times}\;8\;{\times}\;1[mm]$) were attached to one side of a aluminum plate($100\;{\times}\;8\;{\times}\;1[mm]$), and the stator was supported with a plastic case. As results, no-load rpm was 50[rev./m] when applied voltage was 150[Vrms] at the resonance frequency, and as the voltage was increased, the rpm was increased.

• 센서학회지
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• 제18권2호
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• pp.139-146
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• 2009

A Multilayered microelectrode design is presented for large area travelling wave dielectrophoresis (TwDEP) separators. Most of typical TwDEP chip has been arrayed with 1000 electrodes in $20{\times}20\;mm^2$. However, there is a limitation of the device area that is critical in throughput, because when the area of TwDEP becomes larger, the resistance of microelectrodes for bus bar is also increased. In this paper, we successfully developed a novel TwDEP chip with extremely large area ($31{\times}25\;mm^2$) by a unique multilayered bus bar design. According to the resistance simulation of our microelectrodes, it is possible to realize a TwDEP chip with an infinite longitudinal length. We demonstrated the feasibility of our suggestion with latex microbeads and showed the potential of extremely high throughput separation with TwDEP technique.