• Steel and Composite Structures
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• 제33권6호
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• pp.891-906
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• 2019

This study considers the instability behavior of sandwich plates considering magnetorheological (MR) fluid core and piezoelectric reinforced facesheets. As facesheets at the top and bottom of structure have piezoelectric properties they are subjected to 3D electric field therefore they can be used as actuator and sensor, respectively and in order to control the vibration responses and loss factor of the structure a proportional-derivative (PD) controller is applied. Furthermore, Halpin-Tsai model is used to determine the material properties of facesheets which are reinforced by graphene platelets (GPLs). Moreover, because the core has magnetic property, it is exposed to magnetic field. In addition, Kelvin-Voigt theory is applied to calculate the structural damping of the piezoelectric layers. In order to consider environmental forces applied to structure, the visco-Pasternak model is assumed. In order to consider the mechanical behavior of structure, sinusoidal shear deformation theory (SSDT) is assumed and Hamilton's principle according to piezoelasticity theory is employed to calculate motion equations and these equations are solved based on differential cubature method (DCM) to obtain the vibration and modal loss factor of the structure subsequently. The effect of different factors such as GPLs distribution, dimensions of structure, electro-magnetic field, damping of structure, viscoelastic environment and boundary conditions of the structure on the vibration and loss factor of the system are considered. In order to indicate the accuracy of the obtained results, the results are validated with other published work. It is concluded from results that exposing magnetic field to the MR fluid core has positive effect on the behavior of the system.

• Composites Research
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• 제28권4호
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• pp.148-154
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• 2015

구조건전성 모니터링은 구조물에 발생된 손상을 조기에 감지 및 적절한 유지보수를 통해 재정적 혹은 인명 피해를 방지하기 위해 실시된다. 대부분의 능동센싱 기반 구조건전성 모니터링에서는 많은 수의 압전체(piezoelectric transducer) 센서와 구동기(actuator)를 필요로 한다. 구조건전성 모니터링 시 사용된 압전센서에 결합이 존재하는 경우, 구조물의 상태진단에 문제가 발생할 수 있다. 본 연구에서는 신뢰성 있는 구조건전성 모니터링 결과를 위해 임피던스 기반 센서 자가 진단법을 사용하여 다수 센서의 결함을 탐지하였다. 또한 사용된 접착제와 센서의 정보가 충분치 못한 경우, 사용된 센서로부터 측정된 데이터만을 토대로 센서결함 진단을 위한 알고리즘을 소개하였다. 알고리즘이 적용 가능한 온도 범위를 실험적으로 분석함으로써 개발된 기법이 실제 환경에서 응용이 가능함을 확인하였다.

• Composites Research
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• 제35권3호
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• pp.134-138
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• 2022

본 연구에서는 기존 폴리머 콘크리트의 진동 감쇠 효과를 향상시키기 위해 압전 재료 중 하나인 PZT 파우더를 첨가하여 티타늄 파우더/폴리머 콘크리트 복합재료를 제작하였다. 티타늄 파우더는 압전 효과를 이용한 진동특성 변화를 극대화하기 위해 일정한 비율로 유지하였고, PZT 파우더를 첨가하지 않은 시편, PZT 파우더를 2.5 wt%, 5 wt% 첨가한 세 가지 종류의 복합재료 시편을 제작하였으며, 모든 시편에 대해 진동 특성 및 압축 물성 분석을 진행하였다. 그 결과, PZT 파우더 첨가 비율이 높아질수록 티타늄 파우더/폴리머 콘크리트에서 발생한 진동이 전달될 때 압전 효과로 인해 공진주파수에서 전달 함수 Inertance 값이 작아지는 것을 확인하였고, 특히 PZT 파우더 5 wt% 첨가 시편의 경우, 공진주파수에서 Inertance 값은 PZT가 첨가되지 않은 시편에 비해 약 19.3% 감소하는 것으로 나타났다. 시간에 따른 가속도 변화 폭 역시 PZT 파우더가 첨가됨에 따라 크게 감소하는 것으로 나타나 PZT 첨가에 따른 효과를 확인할 수 있었다. 또한, 압축강도 시험을 통해 5 wt%까지의 PZT 첨가에 의한 압축 물성 저하 정도는 미미한 것으로 나타났고, 시편 단면 분석을 통해 파우더가 고르게 분산된 것을 확인하였다.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2005년도 춘계학술발표대회 논문집
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• pp.1-4
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• 2005

A higher order zig-zag shell theory is developed to refine accurately predict deformation and stress of smart shell structures under the mechanical, thermal, and electric loading. The displacement fields through the thickness are constructed by superimposing linear zig-zag field to the smooth globally cubic varying field. Smooth parabolic distribution through the thickness is assumed in the transverse deflection in order to consider transverse normal deformation. The mechanical, thermal, and electric loading is applied in the sinusoidal distribution function in the in-surface direction. Thermal and electric loading is given in the linear variation through the thickness. Especially, in electric loading case, voltage is only applied in piezo-layer. The layer-dependent degrees of freedom of displacement fields are expressed in terms of reference primary degrees of freedom by applying interface continuity conditions as well as bounding surface conditions of transverse shear stresses. In order to obtain accurate transverse shear and normal stresses, integration of equilibrium equation approach is used. The numerical examples of present theory demonstrate the accuracy and efficiency of the proposed theory. The present theory is suitable for the predictions of behaviors of thick smart composite shell under mechanical, thermal, and electric loadings combined.

• Composites Research
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• 제15권3호
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• pp.18-29
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• 2002

본 논문에서는 얇은 벽보로 모델링 한 위성체 구조물에 입사되는 열 하중에 의해 발생하는 굽힘 진동과 열적 플러터에 대하여 연구하였다. 복합재료 얇은 벽보는 회전관성과 1차, 2차 와핑, 전단변형의 비고전적 요소를 포함한다. CUS구조물로 모델링한 복합재료 얇은 벽보의 열 진동 특성은 적층 순서와 섬유강화복합재료의 방향특성인자로부터 기인된 종방향 굽힘과 횡방향 굽힘의 언성과 관련하여 연구되었다. 수치 해석적인 방법으로 열적 플러터의 안정성 영역의경계값을 구하였으며, 태양 열 플럭스의 입사각, 감쇠계수, 섬유각의 변화에 의한 보의 변위를 구하였다. 주 구조물에 압전소자를 부착하여, 감지기와 작동기로 사용하여 제어해석을 수행하였다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2005년도 창립60주년 기념 추계 학술대회
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• pp.126.1-126.1
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• 2005

• 한국세라믹학회지
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• 제45권6호
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• pp.309-319
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• 2008

This study evaluates a range of materials that may be used to design prostheses for bone. It is found that nanocrystalline ceramic-polymer composite could be the best material for prosthetic bone with respect to biocompatibility, morphology, chemistry, and compatibility with the piezoelectric and mechanical behavior of long human bones, such as the femur.

• Journal of Mechanical Science and Technology
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• 제17권3호
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• pp.380-390
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• 2003

This paper addresses the problem of the modeling and vibration control of tapered rotating blade modeled as thin-walled beams and incorporating damping capabilities. The blade model incorporates non-classical features such as anisotropy, transverse shear, secondary warping and includes the centrifugal and Coriolis force fields. For the rotating blade system, a thorough validation and assessment. of a number of non-classical features including the taper characteristics is accomplished. The damping capabilities are provided by a system of piezoactuators bonded or embedded into the structure and spread over the entire span of the beam. Based on the converse piezoelectric effect, the piezoactuators produce a localized strain field in response to a voltage and consequently, a change of the dynamic response characteristics is induced. A velocity feedback control law relating the piezoelectrically induced transversal bending moment at the beam tip with the appropriately selected kinematical response quantity is used and thebeneficial effects upon the closed-loop dynamic characteristics of the blade are highlighted.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2001년도 춘계학술발표대회 논문집
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• pp.9-12
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• 2001

An active control of the vibration transmitted by longitudinal load in flight control system is investigated numerically. The flight control system is modeled as a finite, thin shell cylinder with constant thickness. A vibration source is generated by exterior monopole source. Distributed piezoelectric actuator is used to control of the vibration. Thin shell theory is used to formulate the numerical models. The amplitude of vibration at discrete location and power transmission are minimized by analytical optimization method. Genetic algorithm is used as numerical optimization method to search optimal actuator position and size which amplitude of vibration is minimized.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1989년도 하계종합학술대회 논문집
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• pp.341-344
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• 1989

A Modified equivalent circuit by combining a series and parallel of polymer matrix for estimating the dielectric constant ${\bar{K}}_{33}$ values changing the volume percent of $PbTiO_3$, the dependences of frequency for the 713 and dissipation factor for 0 - 3 composites was derived. The difference of the dielectric constant and dissipation factor between the calculated and measured values became smaller at higher volume percent of $PbTiO_3$. There was, good agreement between the calculated and observed results for 70 volume percent of $PbTiO_3$ and 30 volume percent of Eccogel composite at 1(KHz), 25($^{\circ}C$). The optimized variable x was 0.94 in $PbTiO_3$ ceramics. $PbTiO_3$ powder and Eccogel polymer were used as piezoelectric fillers and matrix, respectively.