• Proceedings of the Korean Society Of Semiconductor Equipment Technology
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• 2005.09a
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• pp.27-30
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• 2005

A nanoelectromechanical (NEM) switching device based on carbon nanotube (CNT) was investigated using atomistic simulations. The model schematics for a CNT based three-terminal NEM switching device fabrication were presented. for the CNT-based three-terminal NEM switch, the interactions between the CNT-lever and the drain electrode or the substrate were very important. When the electrostatic force applied to the CNT-lever was the critical point, the CNT-lever was rapidly bent because of the attractive foroe between the CNT-lever and the drain. The energy curves for the pull-in and the pull-out processes showed the hysteresis loop that was induced by the adhesion of the CNT on the copper, which was the interatomic interaction between the CNT and the copper.

• Bulletin of the Korean Chemical Society
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• v.33 no.3
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• pp.901-905
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• 2012

In this study, we investigated the pure geometrical effect of porous materials in gas adsorption using the grand canonical Monte Carlo simulations of primitive gas-pore models with various pore geometries such as planar, cylindrical, and random pore geometries. Although the model does not possess atomistic level details of porous materials, our simulation results provided many insightful information in the effect of pore geometry on the adsorption behavior of gas molecules. First, the surface curvature of porous materials plays a significant role in the amount of adsorbed gas molecules: the concave surface such as in cylindrical pores induces more attraction between gas molecules and pore, which results in the enhanced gas adsorption. On the contrary, the convex surface of random pores gives the opposite effect. Second, this geometrical effect shows a nonmonotonic dependence on the gas-pore interaction strength and length. Third, as the external gas pressure is increased, the change in the gas adsorption due to pore geometry is reduced. Finally, the pore geometry also affects the collision dynamics of gas molecules. Since our model is based on primitive description of fluid molecules, our conclusion can be applied to any fluidic systems including reactant-electrode systems.

• Composites Research
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• v.33 no.4
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• pp.198-204
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• 2020

In this study, we employ the full atomistic molecular dynamics simulation and finite element homogenization method to predict the thermo-mechanical properties of nanocomposites including carbon nanotube bundle. As the number of carbon nanotubes within the single bundle increases, the effective in-plane Young's modulus and in-plane shear modulus decrease, and in-plane thermal expansion coefficient increases, despite the same volume fraction of carbon nanotubes. To investigate the thickness of interphase zone, we employ the radial density distribution. It is investigated that the interphase thickness is almost independent on the number of carbon nanotubes within the single bundle. It is assumed that the matrix and interphase are isotropic materials. According to the predicted thermo-mechanical properties of interphase zone, the Young's modulus and shear modulus of interphase zone clearly decrease, and the thermal expansion coefficient increases. Based on the thermo-mechanical interphase behavior, we developed the multiscale homogenization model to predict the thermo-mechanical properties of PLA nanocomposites that include the carbon nanotube bundle.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.38 no.2
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• pp.121-127
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• 2014

An atomistic-based finite bond element model for predicting the tearing mode (mode III) fracture of a single-layer graphene sheet (SLGS) is developed. The model uses the modified Morse potential for predicting the maximum strain relationship of graphene sheets. The mode III fracture of graphene under out-of-plane shear loading is investigated with extensive molecular mechanics simulations. Molecular mechanics is used for describing the displacements of atoms in the area near a crack tip, and linear elastic fracture mechanics is used outside this area. This work shows that the molecular mechanics method can provide a reliable and yet simple method for determining not only the shear properties of SLGS but also its mode III fracture toughness in the armchair and the zigzag directions; the determined mode III fracture toughness values of SLGS are $0.86MPa{\sqrt{m}}$ and $0.93MPa{\sqrt{m}}$, respectively.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.32 no.7
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• pp.60-68
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• 2004

High velocity impacts are accompanied with large deformations, which generate a large amount of heat due to plastic works, resulting in a significant temperature rise of the material. Because the elevated temperature affects the dynamic properties of materials, it is important to predict the temperature rise during high-stram-rate deformations. Both existing vacancies and excess vacancies are credited to the stored energy, yet it is difficult to distinguish one from another in contribution to the stored energy using macroscopic level materials models. In this study, an atomistic material model for fee materials such as copper is set up to calculate the stored energy using molecular dynamics (MD) simulations. It is concluded that excess vacancies play an important role for the stored energy during a high-strain-rate deformation.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.38 no.2
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• pp.105-113
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• 2014

The mode II fracture behavior of a single-layer graphene sheet (SLGS) containing a center crack was characterized with the results of an atomistic simulation and an analytical model. The fracture of zigzag graphene models was analyzed with molecular dynamics and the mode II fracture toughness was found to be $2.04MPa{\sqrt{m}}$. The in-plane shear fracture of a cellular material was analyzed theoretically for deriving the $K_{IIc}$ of SLGS, and FEM results were obtained. Mixed-mode fracture of SLGS was studied for various mode I and mode II ratios. The mixed-mode fracture criterion was determined, and the obtained fracture envelope was in good agreement with that of another study.

• Nuclear Engineering and Technology
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• v.54 no.10
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• pp.3855-3863
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• 2022

An evaluation of the radiation shielding performance of high-Z-particle-loaded polylactic acid (PLA) composite materials was pursued. Specimens were produced via fused deposition modeling (FDM) using copper-PLA, steel-PLA, and BaSO₄-PLA composite filaments containing 82.7, 75.2, and 44.6 wt% particulate phase contents, respectively, and were tested under broad-band flash x-ray conditions at the Sandia National Laboratories HERMES III facility. The experimental results for the mass attenuation coefficients of the composites were found to be in good agreement with GEANT4 simulations carried out using the same exposure conditions and an atomistic mixture as a model for the composite materials. Further simulation studies, focusing on the Cu-PLA composite system, were used to explore a shield design parameter space (in this case, defined by Cu-particle loading and shield areal density) to assess performance under both high-energy photon and electron fluxes over an incident energy range of 0.5-15 MeV. Based on these results, a method is proposed that can assist in the visualization and isolation of shield parameter coordinate sets that optimize performance under targeted radiation characteristics (type, energy). For electron flux shielding, an empirical relationship was found between areal density (AD), electron energy (E), composition and performance. In cases where ${\frac{E}{AD}}{\geq}2MeV{\bullet}cm{\bullet}g^{-1}$, a shield composed of >85 wt% Cu results in optimal performance. In contrast, a shield composed of <10 wt% Cu is anticipated to perform best against electron irradiation when ${\frac{E}{AD}}<2MeV{\bullet}cm{\bullet}g^{-1}$.