• Structural Engineering and Mechanics
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• 제69권2호
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• pp.121-129
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• 2019

The present study investigates the propagation of shear waves in a composite structure comprised of imperfectly bonded piezoelectric layer with a micropolar half space. Piezoelectric layer is considered to be initially stressed. Micropolar theory of elasticity has been employed which is most suitable to explain the size effects on small length scale. The general dispersion equations for the existence of waves in the coupled structure are obtained analytically in the closed form. Some particular cases have been discussed and in one particular case the dispersion relation is in well agreement to the classical-Love wave equation. The effects of various parameters viz. initial stress, interfacial imperfection and micropolarity on the phase velocity are obtained for electrically open and mechanically free system. Numerical computations are carried out and results are depicted graphically to illustrate the utility of the problem. The phase velocity of the shear waves is found to be influenced by initial stress, interface imperfection and the presence of micropolarity in the elastic half space. The theoretical results obtained are useful for the design of high performance surface acoustic devices.

• International Journal of Control, Automation, and Systems
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• 제1권4호
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• pp.511-514
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• 2003

The Infrared Camera usually detects only Infrared waves emitted from the light in order to illustrate the temperature distribution. An Infrared diagnosis system can be applied to various fields. But the defect discrimination can be automatic or mechanized in the special shoes total inspection system. This study introduces a method for special shoes nondestructive total inspection. Performance of the proposed method is shown through thermo-Image.

• 대한전기학회논문지:전력기술부문A
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• 제50권10호
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• pp.489-492
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• 2001

The connection method of CCPU has been changed from connection between sheath and grounding to connection between sheaths without grounding since 1997. In domestic, there is so many cases that cables circuits were installed before 1997, added in same route after that, operated as multi-connecting systems of CCPU in same route. This paper examine the problem of multi-connecting system by EMTP simulation, and presents methods to improve the system characteristics.

• 접착 및 계면
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• 제4권2호
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• pp.1-9
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• 2003

Epoxy-amine liquid prepolymers are extensively applied onto metallic substrates and cured to obtain painted materials or bonded joint structures. Overall performances of such systems depend on the created interphase between the organic layer and the substrate. When epoxy-amine liquid mixtures are applied onto more or less hydrated metallic oxide layer, concomitant amine chemical sorption and hydroxide dissolution appear lending to the chelate formation. As soon as the chelate concentration is higher than the solubility product, these species crystallize as sharp needles. Moreover, intrinsic and thermal residual stresses are developed within painted or bonded systems. When residual stresses are higher than the organic layer/substrate adhesion, buckling, blistering, debonding may occur leading to a catastrophic drop of system performances. Practical adhesion can be evaluated with either ultimate parameters (Fmax or Dmax) or the critical strain energy release rate, using the three point flexure test (ISO 14679-1997). We observe that, for the same system, the ultimate load decreases while residual stresses increase when the liquid/solid time increases. Ultimate loads and residual stresses depend on the metallic surface treatment. For these systems, the critical strain energy release rate which takes into account the residual stress profile and the Young's modulus gradient remains quite constant whatever the metallic surface treatment was. These variations will be discussed and correlate to the formation mechanisms of the interphase.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2002년도 Proceedings of the International Welding/Joining Conference-Korea
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• pp.402-407
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• 2002

Laminate tooling process is a fast and simple method to make metal tools directly for various molding processes such as injection molding in rapid prototyping field. Metal sheets are usually cut, stacked, aligned and joined with brazing or soldering. Through the joining process, all of the metal sheet layers should be rigidly joined. When joining process parameters are not appropriate, there would be defects in the layers. Among various types of defects, non-bonded gaps of the tool surface are of great importance, because they directly affect the surface quality and dimensional accuracy of the final products. If a laminate tool with defects has to be abandoned, it could lead to great loss of time and cost. Therefore a repair method for non-bonded gaps of the surface is essential and has important meaning for rapid prototyping. In this study, a rapid laminate tooling system composed of a CO2 laser, a furnace, and a milling machine was developed. Metal sheets were joined by furnace brazing, dip soldering and adhesive bonding. Joined laminate tools were machined by a high-speed milling machine to improve surface quality. Also, repair brazing and soldering methods of the laminates using the $CO_2$ laser system have been investigated. ill laser repair process, the beam duration, beam power and beam profile were of great importance, and their effects were simulated by [mite element methods. The simulation results were compared with the experimental ones, and optimal parameters for laser repair process were investigated.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2008년도 춘계 학술발표회 제20권1호
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• pp.121-124
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• 2008

교량 하부의 급속시공 기술은 교량 설계의 새로운 경향이다. 부착 강봉으로 프리스트레스를 도입하는 프리캐스트 교각 시스템을 제안한다. 이 논문에서는 부착 강봉으로 프리스트레스가 도입된 프리캐스트 원형 교각의 준정적 실험을 통해 내진 성능 평가를 하였다. 기둥의 세그먼트 연결부의 전단강도 보강을 위해 모르터로 충전된 원형강관을 사용하였다. 프리캐스트 교각의 변위연성도와 에너지 소산능력을 평가하였다. 제안된 프리캐스트 교각 시스템은 요구연성도보다 더 좋은 내진성능을 보였다. 실험적 연구를 바탕으로 경전철 교량의 하부구조를 설계하고, 설계 고려사항에 대해 검토하였다.

• 콘크리트학회논문집
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• 제20권6호
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• pp.765-772
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• 2008

철근콘크리트 구조물은 일반적으로 재료적 특성에 따른 크리프 및 건조수축으로 인하여 장기변형이 발생하며, 이러한 변형으로 인한 구조물의 처짐을 허용 한계 이하로 유지시키는 것이 사용성 확보 측면에서 중요하다 할 수 있다. 노후된 RC보의 성능 개선을 위하여 다양항 보수 보강 방법이 사용되고 있으며 이중 대표적인 방법으로 FRP 외부부착 공법이 있다. 재료적인 성질이 우수한 FRP는 RC구조물의 보강 재료로써 현재 널리 사용되고 있으며, 일시적인 하중 뿐만 아니라 지속 하중 하에서도 향상된 보강 성능을 제공해야 한다. 따라서 FRP가 외부 부착된 RC 부재에 지속 하중이 작용할 때 콘크리트의 크리프 및 건조수축의 영향으로 인한 시간 의존적 장기 거동을 정확히 예측하는 방법이 필요하다. 본 논문에서는 FRP가 외부 부착된 RC보의 장기 처짐 예측을 위해서, CFRP와 GFRP로 보강된 실험체를 제작하고, 25 kN의 지속하중을 470일간 가하여 시간 변화에 따른 처짐을 측정하였다. 또한, 이러한 처짐의 예측을 위하여 ACI-209 code 및 CEB-FIP code에 근거하여 크리프계수와 건조수축변형률을 산정하였으며, EMM과 AEMM을 사용한 ACI-318기준, Branson's method 그리고, Mayer's method를 사용하여 FRP가 외부 부착된 RC보의 장기 처짐을 예측하였다. 실험 결과, CFRP보 보강된 실험체가 가장 높은 장기 사용성을 보였으며, Mayer's method가 장기처짐에 대한 실험값을 가장 근사하게 예측한다는 것을 확인할 수 있었다.

• Restorative Dentistry and Endodontics
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• 제38권1호
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• pp.43-47
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• 2013

Objectives: The aim of this study was to determine an appropriate application duration of sodium ascorbate (SA) antioxidant gel in reducing microleakage of bonded composite restoration in intracoronally-bleached teeth. Materials and Methods: Eighty endodontically-treated human incisors were randomly divided into eight groups: control, no bleaching; IB and DB, immediate and delayed bonding after bleaching, respectively; S10m, S60m, S24h, S3d and S7d, bleaching + SA gel for 10 min, 60 min, 24 hr, 3 day and 7 day, respectively. For bleaching, a mixture of 30% hydrogen peroxide and sodium perborate was applied for 7 day. All access cavities were restored using One-Step adhesive (Bisco Inc.) and then Aelite LS Packable composite (Bisco Inc.). The bonded specimens were subjected to 500 thermal cycles, immersed in 1% methylene blue for 8 hr, and longitudinally sectioned. Microleakage was assessed with a 0 - 4 scoring system and analyzed using nonparametric statistical methods (${\alpha}$ = 0.05). Results: Group IB showed a significantly higher microleakage than the control group (p = 0.006) and group DB a statistically similar score to the control group (p > 0.999). Although groups S10m, S60m, and S24h exhibited significantly higher scores than group DB (p < 0.05), the microleakage in groups S3d and S7d was statistically similar to that in group DB (p = 0.771, p > 0.999). Conclusions: Application of SA gel for 3 day after nonvital bleaching was effective in reducing microleakage of composite restoration in intracoronally-bleached teeth.

• 대한치과교정학회지
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• 제43권5호
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• pp.242-247
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• 2013

Objective: To test the null hypothesis that no difference exists between the effects of at-home bleaching and in-office bleaching on shear bond strength (SBS) with bracket bonding at 4 different time intervals after dental bleaching. Methods: Ninety extracted human premolars were randomly divided into 9 groups (n = 10) according to the bleaching methods used (at-home bleaching and in-office bleaching) and the storage time in artificial saliva (30 min, 1 day, 2 weeks, and 3 weeks before bonding). The control group was stored in artificial saliva for 7 days. Brackets were bonded with the Transbond XT adhesive system, and SBS testing was performed. The adhesive remnant index (ARI) was used to assess the amount of resin remaining on the enamel surfaces after debonding. The SBS data were analyzed by analysis of variance (ANOVA) and the Tukey test. For the ARI, the Kruskal-Wallis test was performed. Significance for all statistical tests was predetermined to be p < 0.05. Results: The SBS of the unbleached group was significantly higher (p < 0.05) than that of the bleached groups (except for the group bonded 30 min after at-home bleaching). Conclusions: The null hypothesis was not totally rejected. All bleaching groups tested had decreased SBS of the brackets to the enamel, except for the group bonded 30 min after at-home bleaching. The SBS returned to values close to those of the unbleached enamel within 3 weeks following bleaching.

• 비파괴검사학회지
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• 제32권1호
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• pp.34-40
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• 2012

본 연구에서는 FRP 보강판 부착 콘크리트에서의 유도초음파 기본 모드의 전파 특성에 부착제인 epoxy의 두께와 물성이 미치는 영향을 알아보고자 하였으며, 이를 위해 FRP-epoxy-concrete로 구성된 다층 유도초음파 시스템을 모델링하고 모드 해석을 수행하였다. Epoxy 층의 두께와 탄성계수를 변수로 하여 해석을 수행한 결과, A0 모드에 비해 S0 모드가 epoxy 층의 두께와 탄성계수 변화에 큰 영향을 받으며, 이로부터 경계층인 Epoxy 층의 상태 평가에는 A0 모드에 비해 S0 모드가 유효하리라는 결론을 얻었다.