• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.34 no.9
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• pp.45-52
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• 2006

In this study, a nonlinear control by feedback linearization method, one of nonlinear control schemes based on the nonlinear model, is proposed to suppress the flutter of a supersonic composite panel using piezoelectric materials. Most of the previous panel flutter controllers are the LQR(Linear Quadratic Regulator) which is based on the linear model. A nonlinear feedback linearizing controller proposed in this study considers the nonlinear characteristics of the system model. We use the actuator implemented by piezoceramic PZT. Using the principle of virtual displacements and a finite element discretization with the conforming four-node rectangular element, we first derive the discretized dynamic equations of motion, which are transformed into a nonlinear coupled-modal equations of motion of state space form. The effectiveness of the proposed method is also compared with the LQR based on the linear model through numerical simulations in the time domain using the Newmark method.

• Composites Research
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• v.28 no.4
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• pp.148-154
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• 2015

In order to detect damage in early stages and properly maintaining structures, the structural health monitoring technology is employed. In most cases, active-sensing SHM needs many piezoelectric (PZT) sensors and actuators. Thus, if there is a defect on PZT used for active-sensing SHM, the structural status could be misclassified. This study, for reliable SHM performance, investigated to detect defects of sensors by using the admittance-based sensor diagnostics. This study also introduced an algorithm that can diagnose sensor defects based only on data measured from the sensors in case that information about the changes in adhesive and environmental investigation, this study confirms that the proposed algorithm could be efficiently applied to real-world structures in which a significant temperature variation could take place.

• Journal of Adhesion and Interface
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• v.9 no.3
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• pp.20-26
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• 2008

It is well know that the structure of shape memory alloy (SMA) can change from martensite austenite by either temperature or stress. Due to their inherent shape recovery properties, SMA fiber can be used such as for stress or cure-monitoring sensor or actuator, during applied stress or temperature. Incomplete superelasticity was observed as the stress hysteresis at stress-strain curve under cyclic loading test and temperature change. Superelasticity behavior was observed for the single-SMA fiber/epoxy composites under cyclic mechanical loading at stress-strain curve. SMA fiber or epoxy embedded SMA fiber composite exhibited the decreased interfacial properties due to the cyclic loading and thus reduced shape memory performance. Rigid epoxy and the changed interfacial adhesion between SMA fiber and epoxy by the surface treatment on SMA fiber exhibited similar incomplete superelastic trend. Epoxy embedded single SMA fiber exhibited the incomplete recovery during cure process by remaining residual heat and thus occurring residual stress in single SMA fiber/epoxy composite.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.10
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• pp.424-429
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• 2018

In this study, an expansion joint that is susceptible to waterhammer was tested for its vibration durability. The operation data for the hydraulic actuator was the expansion length of the expansion joint when the waterhammer occurred. In the case of the vibration durability test, the internal temperature status of the expansion joint was assumed to be a stress factor and a lifespan prediction model was assumed to follow the Arrhenius model. A test was carried out by increasing the internal temperature status at $30^{\circ}C$, $50^{\circ}C$, and $65^{\circ}C$. By a linear transformation of the lifespan data for each temperature, a constant value and activation energy coefficient was induced for the Arrhenius equation and verified by comparing the value of a lifetime prediction model with the experimental value at $85^{\circ}C$. The failure modes of the ongoing or finished test were leakage, bellows separation, and internal deformation. In the future, a composite lifespan prediction model, including two more stress factors, will be developed.

• Journal of the Korean Applied Science and Technology
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• v.36 no.4
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• pp.1253-1258
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• 2019

The solid-state electrolyte based on polymer is applicable to various electrochemical devices including supercapacitor, battery, sensor, actuator and has great attention to develop its ionic conductivity from conventional polymer electrolyte by uisng wide range of ionic liquids. The research about ion gel as a solid state electrolyte with the ionic liquid has focused on the wearable and flexible electronic device to use as the high electrical and electrochemical performances, mechanical strength of polymer. In this work, we have investigated and developed solid-state electrolyte based on the ionic liquid and polymer with enhanced ionic conductivity and stability.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.11a
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• pp.346-346
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• 2007

압전세라믹 재료는 현재 압전 변압기, actuator, transducer, sensor, speaker 등에 광범위하게 이용이 되고 있다. 이 중에서 압전세라믹 소결체를 이용한 스피커의 제조는 가공이 까다롭고, 대형의 크기로 제작 시 소자가 깨지는 등의 많은 제약을 받고 있으며, 저음 특성이 떨어져 응용 범위가 한정되어 있다. 따라서 최근에는 이러한 단점을 극복하기 위하여 세라믹/고분자 복합체를 이용한 필름 스피커를 제작하고자 시도하고 있다. 이러한 세라믹/고분자 0-3형 압전 복합체를 이용할 경우, 제품의 경량화를 실현할 수 있고, 크기나 환경의 영향을 거의 받지 않으므로, 고기능성 스피커로의 응용에 적합할 것으로 보인다. 따라서 본 연구에서는 PZT계의 세라믹와 PVDF, PVDF-TrFE, Polyester, acrylic resin 등의 여러 고분자 물질과의 복합체를 제조하여 압전특성을 평가하였다. 본 실험은 먼저 $(Pb_{1-a-b}Ba_aCd_b)(Zr_xTi_{1-x})_{1-c-d}(Ni_{1/3}Nb_{2/3})_c(Zn_{1/3}Nb_{2/3})_dO_3$ (이하 PZT라 표기)의 최적화 조성을 선택하여, $1050^{\circ}C$에서 소결된 분말을 48시간 ball milling방법 로 약 $1{\mu}m$ 크기로 분쇄하였다. 고분자 물질들은 알맞은 용제들을 선택하여 녹였다. 그 다음 소결된 PZT분말과 고분자를 50:50, 60:40, 65:35, 70:30등의 무게 분율로 혼합하고, 분산제, 소포제 등을 첨가하여 3단 roll mill을 이용하여 충분히 분산시켜 페이스트 (Paste)를 제조하였다. 제조된 페이스트를 ITO가 코팅된 PET필름 위에 스크린 프린팅 법을 사용하여 인쇄하여 $120^{\circ}C$에서 5분간 건조하였다. 코팅된 복합체의 두께는 약 $80{\mu}m$ 정도로 측정되었다. Ag 페이스트를 이용한 상부 전극 형성에도 스크린 프린팅 법을 적용하였다. 이를 $120^{\circ}C$에서 4 kV/mm의 DC 전계로 분극 공정을 수행한 후 전기적 특성을 평가하였다. 유전특성을 조사하기 위해서 LCR meter (EDC-1620)를 사용하였고, 시편의 결정구조는 XRD (Rigaku; D/MAX-2500H)을 통해 분석하였으며, 전자현미경(SEM)을 이용하여 미세구조를 분석하였다. 압전 전하상수$(d_{33})$ 값은 APC 8000 모델을 이용하여 측정하였다. PZT의 혼합비가 증가할수록 비유전율 및 압전 전하 상수 등의 전기적 특성이 증가되었다. 또 여러 고분자 물질 중에서 PVDF-TrFE 수지가 가장 우수한 특성을 보였다. 이는 PVDF-TrFE 수지가 압전성을 나타내기 때문인 것으로 판단되었다.