• Wind and Structures
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• v.32 no.1
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• pp.31-46
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• 2021

The current research deals with, stability/instability and cylindrical composite nano-scaled shell's resonance frequency filled by graphene nanoplatelets (GPLs) under various thermal conditions (linear and nonlinear thermal loadings). The piece-wise GPL-reinforced composites' material properties change through the orientation of cylindrical nano-sized shell's thickness as the temperature changes. Moreover, in order to model all layers' efficient material properties, nanomechanical model of Halpin-Tsai has been applied. A functionally modified couple stress model (FMCS) has been employed to simulate GPLRC nano-sized shell's size dependency. It is firstly investigated that reaching the relative frequency's percentage to 30% would lead to thermal buckling. The current study's originality is in considering the multifarious influences of GPLRC and thermal loading along with FMCS on GPLRC nano-scaled shell's resonance frequencies, relative frequency, dynamic deflection, and thermal buckling. Furthermore, Hamilton's principle is applied to achieve boundary conditions (BCs) and governing motion equations, while the mentioned equations are solved using an analytical approach. The outcomes reveal that a range of distributions in temperature and other mechanical and configurational characteristics have an essential contribution in GPLRC cylindrical nano-scaled shell's relative frequency change, resonance frequency, stability/instability, and dynamic deflection. The current study's outcomes are practical assumptions for materials science designing, nano-mechanical, and micromechanical systems such as micro-sized sensors and actuators.

• Composites Research
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• v.32 no.3
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• pp.134-140
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• 2019

Graphene nanoplatelets (GNP), one of the graphene derivatives is famous as the most proper candidate for industrial applications. However, current performance of GNPs as reinforcing filler in composites is limited by their agglomeration and physicochemical heterogeneity. Herein, an approach to produce non-covalently functionalized GNPs (F-GNPs) is reported which possesses potential to be extended as the industrial level of mass production. The one-step functionalization process uses melamine, a low-cost chemical, to prevent agglomeration and dispersion in polar solvents. Furthermore, a purification strategy called salting-out process based on differences in the dispersibility of the individual F-GNP flakes is reported to separate F-GNPs. The functionalization and separation process developed in this paper provides a strategy to use GNPs at the industrial level in composite applications.

• Korean Journal of Materials Research
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• v.25 no.10
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• pp.531-536
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• 2015

GNPs have several excellent mechanical properties including high strength, a good young's modulus, thermal conductivity, corrosion resistance, electronic shielding, etc. In this study, CF/GNP/Epoxy composites were manufactured using GNP weight ratios of 0.15 wt%, 0.3 wt%, 0.5 wt%, 0.7 wt% and 1 wt%. The composites were manufactured with a mechanical method (3-roll-mill). Tensile, impact and wear tests were performed according to ASTM standards D3039, D256 and D3181, respectively. The results show that the CF/GNP0.3wt%/Epoxy composites have good mechanical properties, e.g., tensile strength and impact and wear resistance. In this study, both carbon fabric and GNPs were used as reinforcements in the composites. The mechanical properties increased and weight loss decreased as the GNP content in the resin films was increased.

• Advances in nano research
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• v.13 no.3
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• pp.233-245
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• 2022

Resently, the use of smart structures has been heightened up rapidly. For this issue, vibration analysis related to a graphene nanoplatelet composite (GPLRC) nanodisk which is attached to a piezoelectric layer and is subjected to thermal loads is explored in the current paper. The formulation of this study is obtained through the energy method and nonlocal strain gradient theory, and then it is solved employing generalized differential quadrature method (GDQM). Halpin-Tsai model in addition to the mixture's rule are utilized to capture the material properties related to the reinforced composite layer. The compatibility conditions are presented for exhibiting the perfect bounding between two layers. The results of this study are validated by employing the other published articles. The impact of such parameters as external voltage, the radius ratio, temperature difference, and nonlocality on the vibrational frequency of the system is investigated in detail.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.187.2-187.2
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• 2014

최근 다양한 카본 나노소재들이 열 전도성 필러로써 고분자 복합체의 열전도도 향상을 위해 연구되고 있다. 그러나 구조적 이방성을 갖는 탄소나노튜브(CNT) 혹은 그래핀나노플레이트(Graphene Nanoplatelet)를 복합체에 적용할 경우, 복합체의 수직 방향과 수평 방향에서의 열전도도가 3배 이상 차이가 나는 문제가 있다. 따라서 본 연구에서는 2차원의 GNP 표면 위에 1차원의 CNT를 직접 성장시킨 하이브리드 탄소소재를 이용하여 이러한 열전도도 이방성을 개선하고자 하였다. 하이브리드 탄소소재는 무전해 도금법과 열기상법으로 제조하였다. 합성된 하이브리드 탄소소재 및 CNT를 단독 혹은 혼합하여 필러를 만들고 이를 에폭시 기지 내에 분산시켜 복합체를 제작하였다. 필러 함량별, 필러 비율별로 제작된 복합체의 열전도도를 레이저 플래시 법으로 측정 비교하였다. 결과적으로 기존의 단일 필러들보다 열전도도 이방성이 1.5배 이상 개선된 방열용 에폭시 복합체를 제작할 수 있었다. 한편 하이브리드 탄소와 2% 이하의 CNT 배합에서 단독 필러 투입에 비해 45% 이상의 열전도율 향상을 확인하였다. 이는 미세구조 분석 및 성분 분석 결과, 필러 분산 정도가 열전도도 향상의 주요 인자로 작용하는 것을 확인하였고 기지 내 CNT가 열전도도 경로로 작용하기보다는 하이브리드 탄소소재의 균일한 분산에 영향을 준 것으로 사료된다.

• Composites Research
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• v.28 no.3
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• pp.124-129
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• 2015

CNT and GNP have several excellent mechanical properties including, high strength, Young's modulus, thermal conductivity, corrosion resistance, electronic shielding and so on. In this study, CF/CNT, GNP/epoxy composites were manufactured by varying the CNT weight ratio at 2wt% and 3wt%, GNP weight ratio at 0.5wt% and 1 wt%. The composites were manufactured by mechanical method (3-roll-mill). Tensile, impact and wear tests were performed according to ASTM standards D638, D256 and D3181 respectively. The results showed that, CF/GNP0.5 wt%/epoxy composites gave good mechanical property in all composites, e.g., tensile strength, impact and were resistance.

• Steel and Composite Structures
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• v.43 no.5
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• pp.581-601
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• 2022

The main objective of this research work is to investigate the free vibration behavior of annular sandwich plates resting on the Kerr foundation at thermal conditions. This sandwich configuration is composed of two FGM face sheets as coating layer and a porous GPLRC (GPL reinforced composite) core. It is supposed that the GPL nanofillers and the porosity coefficient vary continuously along the core thickness direction. To model closed-cell FG porous material reinforced with GPLs, Halpin-Tsai micromechanical modeling in conjunction with Gaussian-Random field scheme is used, while the Poisson's ratio and density are computed by the rule of mixtures. Besides, the material properties of two FGM face sheets change continuously through the thickness according to the power-law distribution. To capture fundamental frequencies of the annular sandwich plate resting on the Kerr foundation in a thermal environment, the analysis procedure is with the aid of Reddy's shear-deformation plate theory based high-order shear deformation plate theory (HSDT) to derive and solve the equations of motion and boundary conditions. The governing equations together with related boundary conditions are discretized using the generalized differential quadrature (GDQ) method in the spatial domain. Numerical results are compared with those published in the literature to examine the accuracy and validity of the present approach. A parametric solution for temperature variation across the thickness of the sandwich plate is employed taking into account the thermal conductivity, the inhomogeneity parameter, and the sandwich schemes. The numerical results indicate the influence of volume fraction index, GPLs volume fraction, porosity coefficient, three independent coefficients of Kerr elastic foundation, and temperature difference on the free vibration behavior of annular sandwich plate. This study provides essential information to engineers seeking innovative ways to promote composite structures in a practical way.

• Carbon letters
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• v.11 no.4
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• pp.279-284
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• 2010

Graphene is one of the most promising materials for many applications. It can be used in a variety of applications not only as a reinforcement material for polymer to obtain a combination of desirable mechanical, electrical, thermal, and barrier properties in the resulting nanocomposite but also as a component in energy storage, fuel cells, solar cells, sensors, and batteries. Recent research at Michigan State University has shown that it is possible to exfoliate natural graphite into graphite nanoplatelets composed entirely of stacks of graphene. The size of the platelets can be controlled from less than 10 nm in thickness and diameters of any size from sub-micron to 15 microns or greater. In this study we have investigated the influence of melt compounding processing on the physical properties of a polyamide 6 (PA6) nanocomposite reinforced with exfoliated graphite nanoplatelets (xGnP). The morphology, electrical conductivity, and mechanical properties of xGnP-PA6 nanocomposite were characterized with electrical microscopy, X-ray diffraction, AC impedance, and mechanical properties. It was found that counter rotation (CNR) twins crew processed xGnP/PA6 nanocomposite had similar mechanical properties with co-rotation (CoR) twin screw processed or with CoR conducted with a screw design modified for nanoparticles (MCoR). Microscopy showed that the CNR processed nanocomposite had better xGnP dispersion than the (CoR) twin screw processed and modified screw (MCoR) processed ones. It was also found that the CNR processed nanocomposite at a given xGnP content showed the lowest graphite X-ray diffraction peak at $26.5^{\circ}$ indicating better xGnP dispersion in the nanocomposite. In addition, it was also found that the electrical conductivity of the CNR processed 12 wt.% xGnP-PA6 nanocomposite is more than ten times higher than the CoR and MCoR processed ones. These results indicate that better dispersion of an xGnP-PA6 nanocomposite is attainable in CNR twins crew processing than conventional CoR processing.