• Composites Research
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• 제22권5호
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• pp.8-14
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• 2009

유리섬유 강화 CNT-에폭시 나노복합재료의 계면특성은 미세역학적 시험법과 젖음성 측정을 통하여 평가하였다. CNT-에폭시 나노복합재료의 접촉저항은 전기적 접촉부가 일정하게 점차적으로 증가하는 경사형 (gradient) 시편으로 측정되었다. CNT-에폭시나노복합재료의 접촉저항은 2-점법 대신에 4-점법을 사용하여 평가하였다. 불균일한 표면에 존재하는 소수성 영역 때문에 CNT-에폭시 나노복합재료의 어떤 부분은 초소수성보다는 다소 낮은 접촉각인 120도를 가졌다. 표면처리된 유리섬유는 에칭된 섬유 표면의 흠이 있지만 인장 강성도는 약간의 변화가 나타나는 반면에, 인장강도는 현저하게 감소하였다. 에칭된 유리섬유와 CNT-에폭시 나노복합재료는 표면 에너지와 거친 정도가 증가함으로써, 계면전단강도가 증가되었다 열역학적 에너지 일인 $W_a$가 증가함에 따라, 기계적 계면전단강도와 겉보기 강성도 모두 상호일치하게 증가를 보여주었다.

• Structural Engineering and Mechanics
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• 제76권1호
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• pp.27-56
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• 2020

In this paper, the deflection and buckling analyses of porous nano-composite piezoelectric plate reinforced by carbon nanotube (CNT) are studied. The equations of equilibrium using energy method are derived from principle of minimum total potential energy. In the research, the non-local strain gradient theory is employed to consider size dependent effect for porous nanocomposite piezoelectric plate. The effects of material length scale parameter, Eringen's nonlocal parameter, porosity coefficient and aspect ratio on the deflection and critical buckling load are investigated. The results indicate that the effect of porosity coefficient on the increase of the deflection and critical buckling load is greatly higher than the other parameters effect, and size effect including nonlocal parameter and the material length scale parameter have a lower effect on the deflection increase with respect to the porosity coefficient, respectively and vice versa for critical buckling load. Porous nanocomposites are used in various engineering fields such as aerospace, medical industries and water refinery.

• Advances in nano research
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• 제12권3호
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• pp.231-251
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• 2022

Dynamic behavior of temperature-dependent Reddy functionally graded (RFG) nanobeam subjected to thermomagnetic effects under the action of moving point load is carried out in the present work. Both symmetric and sigmoid functionally graded material distributions throughout the beam thickness are considered. To consider the significance of strain-stress gradient field, a material length scale parameter (LSP) is introduced while the significance of nonlocal elastic stress field is considered by introducing a nonlocal parameter (NP). In the framework of the nonlocal strain gradient theory (NSGT), the dynamic equations of motion are derived through Hamilton's principle. Navier approach is employed to solve the resulting equations of motion of the functionally graded (FG) nanoscale beam. The developed model is verified and compared with the available previous results and good agreement is observed. Effects of through-thickness variation of FG material distribution, beam aspect ratio, temperature variation, and magnetic field as well as the size-dependent parameters on the dynamic behavior are investigated. Introduction of the magnetic effect creates a hardening effect; therefore, higher values of natural frequencies are obtained while smaller values of the transverse deflections are produced. The obtained results can be useful as reference solutions for future dynamic and control analysis of FG nanobeams reinforced nanocomposites under thermomagnetic effects.

• Steel and Composite Structures
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• 제37권1호
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• pp.27-35
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• 2020

This study examines the wave propagation of the functionally graded polymer composite (FG-PC) nanoplates reinforced with graphene nanoplatelets (GNPs) resting on elastic foundations in the framework of the nonlocal strain gradient theory incorporating both stiffness hardening and softening mechanisms of nanostructures. To this end, the material properties are based on the Halpin-Tsai model, and the expressions for the classical and higher-order stresses and strains are consistently derived employing the second-order shear deformation theory. The equations of motion are then consistently derived using Hamilton's principle of variation. These governing equations are solved with the help of Trial function method. Extensive numerical discussions are conducted for wave propagation of the nanoplates and the influences of different parameters, such as the nonlocal parameter, strain gradient parameter, weight fraction of GNPs, uniform and non-uniform distributions of GNPs, elastic foundation parameters as well as wave number.

• Advances in nano research
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• 제17권1호
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• pp.9-18
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• 2024

This paper presents the development of an educational management model for analyzing the dynamic instability of nanocomposite sandwich beams. The model aims to provide a comprehensive framework for understanding the behavior of sandwich micro beams with foam cores, featuring top and bottom layers made of smart and porous functionally graded materials (FGM) nanocomposites. The bottom layer is influenced by an external electric field, and the entire beam is supported by a visco-Pasternak foundation, accounting for spring, shear, and damping constants. Using the Kelvin-Voigt theory to model structural damping and incorporating size effects based on strain gradient theory, the model employs the parabolic shear deformation beam theory (PSDBT) to derive motion equations through Hamilton's principle. The differential quadrature method (DQM) is applied to solve these equations, accurately identifying the improvement in student understanding (ISU) of the beams. The impact of various parameters, including FGM properties, external voltage, geometric constants, and structural damping, on the DIR is thoroughly examined. The educational model is validated by comparing its outcomes with existing studies, highlighting the increase in ISU with the application of negative external voltage to the smart layer. This model serves as a valuable educational tool for engineering students and researchers studying the dynamic stability of advanced nanocomposite structures.

• Transactions on Electrical and Electronic Materials
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• 제11권6호
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• pp.261-265
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• 2010

In this paper, we attempt to improve the electrical characteristics of epoxy resin at high temperature (above $80^{\circ}C$) by adding magnesium oxide (MgO), which has high thermal conductivity. Scanning electron microscopy (SEM) of the dispersion of specimens with added MgO reveals that they are evenly dispersed without concentration. The dielectric breakdown characteristics of $SiO_2$ and MgO nanocomposites are tested by measurements at different temperatures to investigate the filler's effect on the dielectric breakdown characteristics. The dielectric breakdown strength of specimens with added $SiO_2$ decreases slowly below $80^{\circ}C$ (low temperature) but decreases rapidly above $80^{\circ}C$ (high temperature). However, the gradient of the dielectric breakdown strength of specimens with added MgO is slow at both low and high temperatures. The dielectric breakdown strength of specimens with 0.4 wt% $SiO_2$ is the best among the specimens with added $SiO_2$, and that of specimens with 3.0 wt% and 5.0 wt% MgO is the best among those with added MgO. Moreover, the dielectric strength of specimens with 3.0 wt% MgO at high temperatures is approximately 53.3% higher than that of specimens with added $SiO_2$ at $100^{\circ}C$, and that of specimens with 5.0 wt% of MgO is approximately 59.34% higher under the same conditions. The dielectric strength of MgO is believed to be superior to that of $SiO_2$ owing to enhanced thermal radiation because the thermal conductivity rate of MgO (approximately 42 $W/m{\cdot}K$) is approximately 32 times higher than that of $SiO_2$ (approximately 1.3 $W/m{\cdot}K$). We also confirmed that the allowable breakdown strength of specimens with added MgO at $100^{\circ}C$ is within the error range when the breakdown probability of all specimens is 40%. A breakdown probability of up to 40% represents a stable dielectric strength in machinery and apparatus design.

• Composites Research
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• 제23권2호
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• pp.24-30
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• 2010

니켈-나노분말/에폭시 복합재료의 계면 특성과 소수성을 자체-감지능과 작동기 측정을 위해 평가하였다. 경사형 시편을 사용하여 접촉 저항 및 저항도를 측정하였다. 자기장에서 복합재료의 작동성을 세가지 파형들, 즉, 싸인, 삼각, 그리고 사각파를 사용하여 평가하였다. 균일하지 않은 표면에 존재하는 소수성 영역 때문에 Ni-에폭시 나노복합재료의 어떤 부분은 초소수성보다는 다소 낮은 접촉각인 110도를 가졌다. 동적 접촉각은 정적 접촉각과 경향이 상호 일치함을 보였다. 니켈-나노분말의 고유의 금속성질 때문에 자체 감지를 확인하였으며, 또한 전자기장에 작동 반응을 잘 하였다. 니켈-나노분말/에폭시 복합재료의 최대 및 최적의 성능을 얻기 위해서, 레이져 변위 센서를 사용하여, 파형, 주파수, 그리고 전압의 함수로 작동기의 변위를 평가하였다. 니켈-나노분말/에폭시 복합재료의 작동은 적용된 주파수와 전압의 함수로써 증가하였다. 작동된 복합재료들의 연신율은 전압의 증가에 따라 삼각 혹은 사각파보다 싸인파에서 더욱 빨리 증가하였다.