• Advances in nano research
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• 제7권5호
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• pp.311-324
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• 2019

The present study aims to evaluate the nonlinear and post-buckling behaviors of orthotropic graphene sheets exposed to end-shortening strain by implementing a semi-Galerkin technique, as a new approach. The nano-sheets are regarded to be on elastic foundations and different out-of-plane boundary conditions are considered for graphene sheets. In addition, nonlocal elasticity theory is employed to achieve the post-buckling behavior related to the nano-sheets. In the present study, first, out-of-plane deflection function is considered as the only displacement field in the proposed technique, which is hypothesized by an appropriate deflected form. Then, the exact nonlocal stress function is calculated through a complete solution of the von-Karman compatibility equation. In the next step, Galerkin's method is used to solve the unknown parameters considered in the proposed technique. In addition, three different scenarios, which are significantly different with respect to concept, are used to satisfy the natural in-plane boundary conditions and completely attain the stress function. Finally, the post-buckling behavior of thin graphene sheets are evaluated for all three different scenarios, and the impacts of boundary conditions, polymer substrate, and nonlocal parameter are examined in each scenario.

• 한국전기전자재료학회논문지
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• 제26권1호
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• pp.33-37
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• 2013

The properties of LTCC green sheets formed by the MLS-22 powder of NEG Inc. were investigated for acrylic binders with different PVB and Tg in the variation of temperature. The elongation of the green sheets showed large variation depending on the temperature, and was rapidly decreased near the Tg of the sheets. With the increase of the ratio of plasticizer/binder (P/B), large elongation of the sheets was observed due to the decrease of the Tg. In the stacking process of the multilayer ceramic, the optimal control of the temperature is highly required depending on the Tg of the binder and the ratio of P/Buniform coating.

• Korean Chemical Engineering Research
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• 제60권3호
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• pp.446-451
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• 2022

본 연구에서는 용량 및 장기 안정성을 개선하기 위하여 나노 실리콘 시트와 CNT를 정전기적 결합을 통해 피치가 코팅된 나노 실리콘 시트/CNT 복합체를 합성하였다. NaCl의 결정면에 스토버 법을 통해 제조된 나노 실리카 시트를 마그네슘 열 환원법을 사용하여 나노 실리콘 시트로 환원하였다. 산 처리를 통해 음으로 도전된 CNT와 APTES 표면처리를 통한 양으로 도전된 나노 실리콘 시트를 결합하여 나노 실리콘 시트/CNT 복합소재를 합성하였으며, 석유계 피치를 코팅하기 위하여 THF를 용매로 사용하였다. 제조된 음극복합소재의 물리적 특성은 FE-SEM, XRD, EDS를 통하여 분석하였고, LiPF₆ (EC:DMC:EMC = 1:1:1 vol%)를 전해액으로 사용하여 전지를 제조하였으며, 전기화학적 특성을 충·방전 사이클, 율속, differential capacity, EIS 테스트를 통해 조사하였다. 높은 조성의 실리콘과 전도성이 좋은 CNT를 사용할 경우 고용량 및 안정성이 우수한 음극소재를 제조할 수 있음을 알 수 있었다. 피치가 코팅된 나노 실리콘 시트/CNT 음극복합소재는 초기 방전 용량이 2344.9 mAh/g을 보였으며, 50 사이클 이후 용량 유지율이 81%로 피치가 코팅되지 않은 복합소재에 비해 개선된 전기화학적 성능을 확인할 수 있었다.

• Structural Engineering and Mechanics
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• 제69권4호
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• pp.439-455
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• 2019

This research deals with thermo-electro-mechanical buckling analysis of the sandwich nano-beams with face-sheets made of functionally graded carbon nano-tubes reinforcement composite (FG-CNTRC) based on the nonlocal strain gradient elasticity theory (NSGET) considering various higher-order shear deformation beam theories (HSDBT). The sandwich nano-beam with FG-CNTRC face-sheets is subjected to thermal and electrical loads while is resting on Pasternak's foundation. It is assumed that the material properties of the face-sheets change continuously along the thickness direction according to different patterns for CNTs distribution. In order to include coupling of strain and electrical field in equation of motion, the nonlocal non-classical nano-beam model contains piezoelectric effect. The governing equations of motion are derived using Hamilton principle based on HSDBTs and NSGET. The differential quadrature method (DQM) is used to calculate the mechanical buckling loads of sandwich nano-beam as well as critical voltage and temperature rising. After verification with validated reference, comprehensive numerical results are presented to investigate the influence of important parameters such as various HSDBTs, length scale parameter (strain gradient parameter), the nonlocal parameter, the CNTs volume fraction, Pasternak's foundation coefficients, various boundary conditions, the CNTs efficiency parameter and geometric dimensions on the buckling behaviors of FG sandwich nano-beam. The numerical results indicate that, the amounts of the mechanical critical load calculated by PSDBT and TSDBT approximately have same values as well as ESDBT and ASDBT. Also, it is worthy noted that buckling load calculated by aforementioned theories is nearly smaller than buckling load estimated by FSDBT. Also, similar aforementioned structure is used to building the nano/micro oscillators.

• 한국자기학회:학술대회 개요집
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• 한국자기학회 2008년도 Asian Magnetics Conference
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• pp.144.1-144.1
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• 2008

• Smart Structures and Systems
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• 제26권2호
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• pp.185-193
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• 2020

Nonlinear vibration of sandwich plate with functionally graded material (FGM) core and carbon nano tubes reinforced (CNTs) nano-composite layers by considering temperature-dependent material properties are studied in this paper. Base on Classical plate theory (CPT), the governing partial differential equations of motion for sandwich plate are derived using Hamilton principle. The Galerkin procedure and multiple scales perturbation method are used to find relation between nonlinear frequency and amplitude of vibration response. The dynamic responses of the sandwich plate are also investigated in both time and frequency domains. Then, the effects of nonlinearity, excitation, power law index of FG core, volume fraction of carbon nanotube, the function of material variations of FG core, temperature changes, scale transformation parameter and damping factor on the frequency responses are investigated.

• Smart Structures and Systems
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• 제20권3호
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• pp.329-342
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• 2017

In this paper, the dispersion characteristics of elastic waves propagation in sandwich nano-beams with functionally graded (FG) face-sheets reinforced with carbon nanotubes (CNTs) is investigated based on various high order shear deformation beam theories (HOSDBTs) as well as nonlocal strain gradient theory (NSGT). In order to align CNTs as symmetric and asymmetric in top and bottom face-sheets with respect to neutral geometric axis of the sandwich nano-beam, various patterns are employed in this analysis. The sandwich nano-beam resting on Pasternak foundation is subjected to thermal, magnetic and electrical fields. In order to involve small scale parameter in governing equations, the NSGT is employed for this analysis. The governing equations of motion are derived using Hamilton's principle based on various HSDBTs. Then the governing equations are solved using analytical method. A detailed parametric study is conducted to study the effects of length scale parameter, different HSDBTs, the nonlocal parameter, various aligning of CNTs in thickness direction of face-sheets, different volume fraction of CNTs, foundation stiffness, applied voltage, magnetic intensity field and temperature change on the wave propagation characteristics of sandwich nano-beam. Also cut-off frequency and phase velocity are investigated in detail. According to results obtained, UU and VA patterns have the same cut-off frequency value but AV pattern has the lower value with respect to them.

• 한국분말재료학회지
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• 제14권4호
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• pp.265-271
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• 2007

Electromagnetic wave absorbing materials have been developed to reduce electromagnetic interference (EMI) for electronic devices in recent years. In this study, Fe-Si-B-Nb-Cu base amorphous strip was pulverized using a jet mill and an attritor and heat-treated to get flake-shaped nanocrystalline powders, and then the powders were mixed, cast and dried with dielectric $Al_{2}O_{3}$ powders and binders. As a result, the addition of $Al_{2}O_{3}$ powders improved the absorbing properties of the sheets noticeably compared with those of the sheets without dielectric materials. The sheet mixed with 2 wt% $Al_{2}O_{3}$ powder showed the best electromagnetic wave absorption, which was caused by the increase of the permittivity and the electric resistance due to the dielectric materials finely dispersed on the Fe-based powder.

• 마이크로전자및패키징학회지
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• 제25권4호
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• pp.95-99
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• 2018

최근 고집적 고출력 전자 패키지의 효율적인 열전달을 위한 기판 및 방열소재로서 절연성 고열전도 필름의 수요가 커지고 있어, 알루미나, 질화알루미늄, 질화보론, 탄소나노튜브 및 그래핀 등의 고열전도 필러소재를 사용한 고방열 복합소재에 대한 많은 연구가 이루어지고 있다. 그 중에서도 육방정 질화보론(h-BN) 나노시트가 절연성 고열전도 필러 소재로서 유력한 후보 물질로 선택되고 있다. 본 연구는 이 h-BN 나노시트와 PVA로 된 세라믹/폴리머 복합체 필름의 방열특성 향상에 관한 것이다. h-BN 나노시트는 h-BN 플레이크 원료 분말을 유기용매를 사용한 볼밀링과 초음파 처리에 의한 물리적 박리공정으로 만들었으며, 이를 사용한 h-BN/PVA 복합 필름을 제조한 결과 성형된 복합필름의 면방향과 두께방향 열전도도는 50 vol%의 필러함량에서 각각 $2.8W/m{\cdot}K$ 및 $10W/m{\cdot}K$의 높은 열전도도가 나타났다. 이 복합필름을 PVA의 유리전이온도 이상에서 일축 가압하여 h-BN 판상분말의 얼라인먼트를 향상시킴으로써 면방향 열전도도를 최대 $13.5W/m{\cdot}K$까지 증가시킬 수 있었다.

• 한국분말재료학회지
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• 제15권1호
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• pp.53-57
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• 2008

The amorphous $Fe_{73}Si_{16}B_7Nb_3Cu_1$(at%) alloy strip was pulverized using a jet mill and an attrition mill to get flake-shaped powder. The flake powder was mixed with dielectric $BaTiO_3$ powder and its dispersant to increase the permittivity. The powders covered with dielectric powders and its dispersant were mixed with a binder and a solvent and then tape-cast to form sheets. The absorbing properties of the sheets were measured to investigate the roles of the dielectric powder and its dispersant. The results showed that the addition of $BaTiO_3$ powders and its dispersant improved the absorbing properties of the sheets noticeably. The powder sheet mixed with 5 wt% of $BaTiO_3$ powder and 1 wt% of dispersant showed the best electromagnetic wave absorption rate because of the increase of the permittivity and the electrical resistance.