• Steel and Composite Structures
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• v.48 no.6
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• pp.709-725
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• 2023

This paper uses a new type of deformation theory to establish the free vibration and static buckling equations of nanoplates resting on two-parameter elastic foundations, in which the flexoelectric effect is taken into account. The proposed approach used in this work is not only simpler than other higher-order shear deformation theories but also does not need any shear correction coefficients to describe exactly the mechanical responses of structures. The reliability of the theory is verified by comparing the numerical results of this work with those of analytical solutions. The results show that the flexoelectric effect significantly changes the natural frequency and the critical buckling load of the nanoplate compared with the case of neglecting this effect, especially when the plate thickness changes and with some different boundary conditions. These are new results that have not been mentioned in any publications but are meaningful in engineering practice.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2017.11a
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• pp.153-154
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• 2017

Graphene is a nanomaterial and is known to have very high mechanical strength, thermal and electrical properties. However, graphene is known to be difficult to disperse among carbon-based materials due to van der Waals force. In this study, to solve the dispersion problem of graphene nanoplatelet, oxidized graphene nanoplatelet was prepared by oxidizing GNP in nitric acid. The prepared GO was dispersed in ethanol and distilled water before incorporation into the epoxy paint to confirm dispersibility. In addition, GNP/Epoxy and GO/Epoxy tensile specimens were prepared by mixing GNP and GO at 0.1, 0.3, 0.5 and 1.0 wt.% In epoxy coatings and tensile stress-strain characteristics were investigated.

• Proceedings of the Korean Vacuum Society Conference
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• 2015.08a
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• pp.252.1-252.1
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• 2015

최근 화석연료 고갈 문제를 해결하기 위해 대체에너지 개발과 다양한 형태의 에너지 개발에 관한 연구가 활발히 이루어지고 있다. 특히, supercapacitor는 high energy density, high power density, longer life-time과 같은 특성으로 인해 에너지 저장 소자로 각광 받고 있다. Supercapacitor는 석유를 대체할 수 있으며 이산화탄소 배출이 없는 친환경 에너지인 태양광, 풍력, 수소연료전지 등의 신재생에너지 저장장치로써 큰 비중을 차지한다. Supercapacitor의 종류인 electrical double layer capacitors (EDLCs) 는 전극과 전해질 사이에 발생하는 전기 이중층에 축적되는 전하를 이용하여 에너지를 저장하는 반응 메커니즘을 가지며 전극 재료로는 탄소 소재를 사용한다. 탄소 소재는 환경 오염이 적고 가격이 저렴하며 넓은 표면적이라는 장점이 있다. 하지만 기존 탄소 소재는 이러한 장점을 가지지만 supercapacitor로써의 효율이 좋지 않게 나온다. 이런 문제를 개선하기 위하여 그래핀 나노플레이트(Graphene nanoplate, GNP) 위에 직접 탄소나노튜브(Carbon nanotube, CNT)를 성장 시킴으로써 GNP-CNT 하이브리드 탄소 소재를 제조하여 전극으로 사용하였다. 이 GNP-CNT 하이브리드 탄소 소재는 다차원 구조를 가짐으로써 기존 탄소 소재들보다 분산이 잘되고 전해질과의 작용하는 비표면적이 넓다. 전극을 제작하여 Cyclic voltammetry(CV)와 galvano를 측정한 결과는 기존 탄소나노튜브보다 5배 정도의 정전용량(Capacitance)를 가졌다. 이 전극의 구조적 특성을 관찰하기 위해 SEM, TEM 등을 측정하였다.

• Steel and Composite Structures
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• v.29 no.1
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• pp.53-66
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• 2018

A high-order nonlocal strain gradient model is developed for wave propagation analysis of porous FG nanoplates resting on a gradient hybrid foundation in thermal environment, for the first time. Material properties are assumed to be temperature-dependent and graded in the nanoplate thickness direction. To consider the thermal effects, uniform, linear, nonlinear, exponential, and sinusoidal temperature distributions are considered for temperature-dependent FG material properties. On the basis of the refined-higher order shear deformation plate theory (R-HSDT) in conjunction with the bi-Helmholtz nonlocal strain gradient theory (B-H NSGT), Hamilton's principle is used to derive the equations of wave motion. Then the dispersion relation between frequency and wave number is solved analytically. The influences of various parameters (such as temperature rise, volume fraction index, porosity volume fraction, lower and higher order nonlocal parameters, material characteristic parameter, foundations components, and wave number) on the wave propagation behaviors of porous FG nanoplates are investigated in detail.

• Structural Engineering and Mechanics
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• v.74 no.6
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• pp.809-819
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• 2020

For the first time, the influence of in-plane magnetic field on wave propagation of Graphene Nano-Platelets (GNPs) polymer composite nanoplates is investigated here. The impact of three- parameter Kerr foundation is also considered. There are two different reinforcement distribution patterns (i.e. uniformly and non-uniformly) while the material properties of the nanoplate are estimated through the Halpin-Tsai model and a rule of mixture. To consider the size-dependent behavior of the structure, Eringen Nonlocal Differential Model (ENDM) is utilized. The equations of wave motion derived based on a higher-order shear deformation refined theory through Hamilton's principle and an analytical technique depending on Taylor series utilized to find the wave frequency as well as phase velocity of the GNPs reinforced nanoplates. A parametric investigation is performed to determine the influence of essential phenomena, such as the nonlocality, GNPs conditions, Kerr foundation parameters, and wave number on the both longitudinal and flexural wave characteristics of GNPs reinforced nanoplates.

• Smart Structures and Systems
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• v.19 no.6
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• pp.601-614
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• 2017

In this work, free vibration analysis of size-dependent functionally graded (FG) nanoplates resting on two-parameter elastic foundation is investigated based on a novel nonlocal refined trigonometric shear deformation theory for the first time. This theory includes undetermined integral variables and contains only four unknowns, with is even less than the conventional first shear deformation theory (FSDT). Mori-Tanaka model is employed to describe gradually distribution of material properties along the plate thickness. Size-dependency of nanosize FG plate is captured via the nonlocal elasticity theory of Eringen. By implementing Hamilton's principle the equations of motion are obtained for a refined four-variable shear deformation plate theory and then solved analytically. To show the accuracy of the present theory, our research results in specific cases are compared with available results in the literature and a good agreement will be demonstrated. Finally, the influence of various parameters such as nonlocal parameter, power law indexes, elastic foundation parameters, aspect ratio, and the thickness ratio on the non-dimensional frequency of rectangular FG nanoscale plates are presented and discussed in detail.

• Structural Engineering and Mechanics
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• v.68 no.1
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• pp.103-119
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• 2018

In the present research, an attempt is made to obtain a semi analytical solution for both nonlinear natural frequency and forced vibration of embedded functionally graded double layered nanoplates with all edges simply supported based on nonlocal strain gradient elasticity theory. The interaction of van der Waals forces between adjacent layers is included. For modeling surrounding elastic medium, the nonlinear Winkler-Pasternak foundation model is employed. The governing partial differential equations have been derived based on the Mindlin plate theory utilizing the von Karman strain-displacement relations. Subsequently, using the Galerkin method, the governing equations sets are reduced to nonlinear ordinary differential equations. The semi analytical solution of the nonlinear natural frequencies using the homotopy analysis method and the exact solution of the nonlinear forced vibration through the Harmonic Balance method are then established. The results show that the length scale parameters give nonlinearity of the hardening type in frequency response curve and the increase in material length scale parameter causes to increase in maximum response amplitude, whereas the increase in nonlocal parameter causes to decrease in maximum response amplitude. Increasing the material length scale parameter increases the width of unstable region in the frequency response curve.

• Korean Journal of Materials Research
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• v.27 no.11
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• pp.609-616
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• 2017

We investigated a Leidenfrost effect in the growth of ZnO nanostructures on silicon substrates by ultrasonic-assisted spray pyrolysis deposition(SPD). Structural and optical properties of the ZnO nanostructures grown by varying the growth parameters, such as substrate temperature, source concentration, and suction rate of the mist in the chambers, were investigated using field-emission scanning electron microscopy, X-ray diffraction, and photoluminescence spectrum analysis. Structural investigations of the ZnO nanostructures showed abnormal evolution of the morphologies with variation of the substrate temperatures. The shape of the ZnO nanostructures transformed from nanoplate, nanorod, nanopencil, and nanoprism shapes with increasing of the substrate temperature from 250 to $450^{\circ}C$; these shapes were significantly different from those seen for the conventional growth mechanisms in SPD. The observed growth behavior showed that a Leidenfrost effect dominantly affected the growth mechanism of the ZnO nanostructures.

• Advances in nano research
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• v.9 no.4
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• pp.237-250
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• 2020

An accurate plate theory for assessing sandwich structures is of interest in order to provide precise results. Hence, this paper develops Layer-Wise (LW) theory for reaching precise results in terms of buckling and vibration behavior of Functionally Graded Carbon Nanotube-Reinforced Composite (FG-CNTRC) annular nanoplates. Furthermore, for simulating the structure much more realistic, its edges are elastically restrained against in-plane and transverse displacement. The nano structure is integrated with piezoelectric layers. Four distributions of Single-Walled Carbon Nanotubes (SWCNTs) along the thickness direction of the core layer are investigated. The Differential Quadrature Method (DQM) is utilized to solve the motion equations of nano structure subjected to the electric field. The influence of various parameters is depicted on both critical buckling load and frequency of the structure. The accuracy of solution procedure is demonstrated by comparing results with classical edge conditions. The results ascertain that the effects of different distributions of CNTs and their volume fraction are significant on the behavior of the system. Furthermore, the amount of in-plane and transverse spring coefficients plays an important role in the buckling and vibration behavior of the nano-structure and optimization of nano-structure design.

• Structural Engineering and Mechanics
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• v.76 no.4
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• pp.551-559
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• 2020

On the basis of nonlocal strain gradient theory, considering the material properties of porous FGM changing with thickness and the influence of moment of inertia, the wave equation of FG nano circular plate is derived by using the first-order shear deformation plate theory, by introducing dimensionless parameters, we transform the equations into dimensionless wave equations, and the dispersion relations of bending wave, shear wave and longitudinal wave are obtained by Laplace and Hankel integral transformation method. The influence of nonlocal parameter, porosity volume fraction, strain gradient parameters and power law index on the propagation characteristics of bending wave, shear wave and longitudinal wave in FG nano circular plate.