• Smart Structures and Systems
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• 제13권4호
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• pp.501-515
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• 2014

This paper presents a linear computational homogenization framework to evaluate the effective (or generalized) electromechanical coupling coefficient (EMCC) of adaptive structures with piezoelectric structural fiber (PSF) composite elements. The PSF consists of a silicon carbide (SiC) or carbon core fiber as reinforcement to a fragile piezo-ceramic shell. For the micro-scale analysis, a micromechanics model based on the variational asymptotic method for unit cell homogenization (VAMUCH) is used to evaluate the overall electromechanical properties of the PSF composites. At the macro-scale, a finite element (FE) analysis with the commercial FE code ABAQUS is performed to evaluate the effective EMCC for structures with the PSF composite patches. The EMCC is postprocessed from free-vibrations analysis under short-circuit (SC) and open-circuit (OC) electrodes of the patches. This linear two-scale computational framework may be useful for the optimal design of active structure multi-functional composites which can be used for multi-functional applications such as structural health monitoring, power harvest, vibration sensing and control, damping, and shape control through anisotropic actuation.

• E2M - 전기 전자와 첨단 소재
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• 제7권3호
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• pp.187-199
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• 1994

In order to find an effect of structural changes due to variation of addition ratio of anhydride hardener and postcuring herat-treatments upon electrical properties of epoxy composites, the dielectric properties over a frequency range from 30[Hz] to l[MHz] were investigated in the temperature range of 20-180[.deg. C]. From the dielectric properties, the a peaks related with glass-transition phenomena of epoxy network appeared near 130[.deg. C], the conduction loss in high temperature region above 150[.deg. C] due to thermal dissociation of hardener started off with the low frequency side and the .betha. peak concerned with contribution of movable unreacted terminal epoxy groups and curing agents in the glass states concurred with the high-frequency side below 20[.deg. C]. And an effect of an hydride hardener upon structural changes and of postcuring heat treatments upon structural stability in epoxy composites would be explained through the estimation of the distribution of relaxation times and the activation energy for a .alpha. peak according to the WLF equations.

• Composites Research
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• 제32권2호
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• pp.108-112
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• 2019

최근 복합재를 적용한 경량화에 관한 연구가 지속적으로 수행됨에 따라 탄소섬유 복합재료를 사용하여 강성대비 경량화를 목표로 하는 부품 연구가 증가하고 있다. 복합재료는 등방성 재료와는 달리 적층판의 방향과 적층 순서에 따라 물리적 특성이 변화한다. 그러므로 복합재료 사다리의 경우 계획한 설계를 검증하기 위해서 구조 해석을 수행하는 것이 필수적이다. 본 연구에서는 패브릭 소재를 적용하여 사다리를 설계하였다. 또한 유한요소해석을 통하여 하중 위치가 사다리에 미치는 영향을 분석하고 가장 문제가 되는 위치를 선정하여 구조적 성능을 분석하였다. 다양한 적층 순서를 적용하여 구조해석을 실시하고 각 층에서의 파손 값을 측정함으로써 적층 순서가 사다리의 구조 강도에 미치는 영향을 분석하였다.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2005년도 춘계학술발표대회 논문집
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• pp.55-58
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• 2005

The present study aims to design electrically and structurally effective antenna structures in order that the structural surface itself could become the antenna. The basic design concept is composite sandwich structure in which microstrip antenna is embedded and this is termed composite smart structure (CSS). The most important outstanding problem is that composite materials of structural function cannot be used without reducing antenna efficiency. Unfortunately, such materials have high electrical loss. This is a significant design problem that needs to be solved in practical applications. Therefore, the effects of composites facesheet on antenna performances are investigated in the first stage and changes in the gain of microstrip antenna due to composites facesheet have been determined. ‘Open condition’ is defined when gain is maximized and is a significant new concept for the design of high-gain antennas considering bandwidth in practical application. The open condition can be made with the outer facesheet by controlling its position. In the design of CSS, glass/epoxy composites and Nomex honeycomb were used with exploiting open condition. Experiments, confirm that the gain is improved and the bandwidth is also as wide as specified in our requirements. With the open condition, wideband antenna can be integrated with mechanical structures without reducing any electrical performances, as confirmed experimentally here.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2005년도 춘계학술대회논문집
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• pp.346-349
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• 2005

The present study aims to design electrically and structurally effective antenna structures in order that the structural surface itself could become the antenna. The basic design concept is composite sandwich structure in which microstrip antenna is embedded and this is termed composite smart structure (CSS). The most important outstanding problem is that composite materials of structural function cannot be used without reducing antenna efficiency. Unfortunately, such materials have high electrical loss. This is a significant design problem that needs to be solved in practical applications. Therefore, the effect of composites facesheet on antenna performances is studied in the first stage. Changes in the gain of microstrip antenna due to composites facesheet have been determined. 'Open condition' is defined when gain is maximized and is a significant new concept in the design of high-gain antennas considering bandwidth in practical application. The open condition can be made with any thickness of outer facesheet by controlling its position. In the design of CSS, glass/epoxy composites and Nomex honeycomb were used with exploiting open condition. Experiments, confirm that the gain is improved (over 11 dBi) and the bandwidth is also as wide as specified in our requirements (over 10% at 12.2 GHz). With the open condition, wideband antenna can be integrated with mechanical structures without reducing any electrical performances, as confirmed experimentally here.

• Structural Engineering and Mechanics
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• 제61권3호
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• pp.325-334
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• 2017

In the present study, a numerical model for probability analysis of optimal design of fatigue non-uniform crack growth behaviour of a cracked aluminium 2024 T3 plate repaired with a bonded composite patch is investigated. The proposed 3D numerical model has advanced in literatures, which gathers in a unique study: problems of reliability, optimization, fatigue, cracks and repair of plates subjected to tensile loadings. To achieve this aim, a finite element modelling is carried out to determine the evolution of the stress intensity factor at the crack tip Paris law is used to predict the fatigue life for a give n crack. To have an optimal volume of our patch satisfied the practical fatigue life, a procedure of optimization is proposed. Finally, the probabilistic analysis is performed in order to a show that optimized patch design is influenced by uncertainties related to mechanical and geometrical properties during the manufacturing process.

• 한국전산구조공학회논문집
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• 제21권4호
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• pp.383-390
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• 2008

이 논문에서는 단일방향 및 크로스-플라이 섬유강화 복합재에서의 동적 균열 전파를 모사하기 위해 특별히 고안된 스펙트랄 방법의 정식화와 수치적 구현 방법에 대해 제시한다. 이 방법은 균열면에서 작용하는 힘과 변위 사이의 스펙트랄 관계식에 기초하고 있고, 재료는 횡등방성 고체로 가정된다. 본 논문에서 제안된 방법에 의해 섬유보강 복합재에서 전파하는 균열문제가 대해 검토 해석되며, 실험 및 문헌에 나와 있는 결과와 비교된다. 이 방법은 FRP 보강 철근 콘크리트 구조물에서의 균열해석문제에 직접 적용이 가능하다.

• Structural Engineering and Mechanics
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• 제70권2호
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• pp.233-243
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• 2019

This paper depicts the development and characterizations of laminated composites made with cellulosic giant cane (Arundinaria gigantea) fiber mats and epoxy resin. Zirconia-toughened mullite (ZTM) is used as a filler material in the laminated composite which was prepared from sillimanite through plasma processing technique. The mechanical characterizations of this composite have been carried out as per ASTM standards to evaluate its usability as a structural material. The effects of varying weight percentages of the filler and two different fiber orientations namely, angle-ply [$+45^{\circ}/-45^{\circ}/+45^{\circ}$] and balanced cross-ply [$0^{\circ}/90^{\circ}/0^{\circ}$] on the physical and mechanical properties such as density, microhardness, impact strength, tensile strength and interlaminar shear strength of the layered composite specimens have been investigated. The study indicates that the inclusion of zirconia-toughened mullite in the composite laminate as filler improves its mechanical properties. Moreover, the use of giant cane fiber mat in the laminate is more eco-friendly than the synthetic fibers. This research also helps in generating additional data to enrich the repository of natural fiber reinforced laminated composites.

• 한국세라믹학회지
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• 제45권11호
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• pp.667-674
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• 2008

In this study, we prepared Fe-activated carbon fiber(ACF)/$TiO_2$ composites with titanium (VI) n-butoxide (TNB) as the titanium source for ACF pre-treated with iron compounds through the impregnation method. In terms of textural surface properties, the composites demonstrate a slight decrease in the BET surface area of the samples and an increase in the amount of iron compounds treated. The surface morphology of the Fe-ACF/$TiO_2$ composites was characterized by means of SEM. The composites have a porous texture with homogenous compositions of Fe and titanium dioxide distributed on the sample surfaces. The phase formation and structural transition of the iron compounds and titanium dioxide were observed in X-ray diffraction patterns of the Fe-ACF/$TiO_2$ composites. The chemical composition of the Fe-ACF/$TiO_2$ composites, which was investigated with EDX shows strong peaks for the C, O, Fe and Ti elements. The photo degradation results confirm that the Fe-ACF/$TiO_2$ composites show excellent removal activity for the COD in piggery waste due to photocatalysis of the supported $TiO_2$, radical reaction by Fe species, and the adsorptivity and absorptivity of ACF.

• Bulletin of the Korean Chemical Society
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• 제34권1호
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• pp.99-106
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• 2013

Polyaniline-yttrium trioxide (PAni-$Y_2O_3$) composites were synthesized by the in-situ polymerization of aniline in the presence of $Y_2O_3$ The composite formation and structural changes in these composites were investigated by X-ray diffraction (XRD), Fourier transform infra red spectroscopy (FTIR), scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HRTEM). The direct current (DC) electrical conductivity of the order of $0.51{\times}10^{-2}\;S\;cm^{-1}-0.283\;S\;cm^{-1}$ in the temperature range 300 K-473 K indicates semiconducting behavior of the composites. Room temperature AC conductivity and dielectric response of the composites were studied in the frequency range of 10 Hz to 1 MHz. The variation of AC conductivity with frequency obeyed the power law, which decreased with increasing weight percentage (wt %) of $Y_2O_3$. Studies on dielectric properties shows the relaxation contribution coupled by electrode polarization effect. The dielectric constant and dielectric loss in these composites depend on the content of $Y_2O_3$ with a percolation threshold at 20 wt % of $Y_2O_3$ in PAni. Electromagnetic interference shielding effectiveness (EMI SE) of the composites in the frequency range 100 Hz to 2 GHz was in the practically useful range of -12.2 dB to -17.2 dB. The observed electrical and shielding properties were attributed to the interaction of $Y_2O_3$ particles with the PAni molecular chains.