Browsing by Author "Mesquita, E"

Now showing 1 - 4 of 4

Open Access
Atomic-scale finite element modelling of mechanical behaviour of graphene nanoribbons
(Springer Netherlands, 2019-03) Damasceno, D. A; Mesquita, E; Rajapakse, R. K. N. D; Pavanello, R
Experimental characterization of Graphene NanoRibbons (GNRs) is still an expensive task and computational simulations are therefore seen as a practical option to study the properties and mechanical response of GNRs. Design of GNR elements in various nanotechnology devices can be approached through molecular dynamics simulations. This study demonstrates that the atomic-scale finite element method (AFEM) based on the second generation REBO potential is an efficient and accurate alternative to the molecular dynamics simulation of GNRs. Special atomic finite elements are proposed to model graphene edges. Extensive comparisons are presented with MD solutions to establish the accuracy of AFEM. It is also shown that the Tersoff potential is not accurate for GNR modeling. The study demonstrates the influence of chirality and size on design parameters such as tensile strength and stiffness. Graphene is stronger and stiffer in the zigzag direction compared to the armchair direction. Armchair GNRs shows a minor dependence of tensile strength and elastic modulus on size whereas in the case of zigzag GNRs both modulus and strength show a significant size dependency. The size-dependency trend noted in the present study is different from the previously reported MD solutions for GNRs but qualitatively agrees with experimental results. Based on the present study, AFEM can be considered a highly efficient computational tool for analysis and design of GNRs.
Open Access
Atomistic modelling of size-dependent mechanical properties and fracture of pristine and defective cove-edged graphene nanoribbons
(Multidisciplinary Digital Publishing Institute, 2020-07) Damasceno, D. A; Rajapakse, R. K. N. D; Mesquita, E
Cove-edged graphene nanoribbons (CGNR) are a class of nanoribbons with asymmetric edges composed of alternating hexagons and have remarkable electronic properties. Although CGNRs have attractive size-dependent electronic properties their mechanical properties have not been well understood. In practical applications, the mechanical properties such as tensile strength, ductility and fracture toughness play an important role, especially during device fabrication and operation. This work aims to fill a gap in the understanding of the mechanical behaviour of CGNRs by studying the edge and size effects on the mechanical response by using molecular dynamic simulations. Pristine graphene structures are rarely found in applications. Therefore, this study also examines the effects of topological defects on the mechanical behaviour of CGNR. Ductility and fracture patterns of CGNR with divacancy and topological defects are studied. The results reveal that the CGNR become stronger and slightly more ductile as the width increases in contrast to normal zigzag GNR. Furthermore, the mechanical response of defective CGNRs show complex dependency on the defect configuration and distribution, while the direction of the fracture propagation has a complex dependency on the defect configuration and position. The results also confirm the possibility of topological design of graphene to tailor properties through the manipulation of defect types, orientation, and density and defect networks.
Open Access
Atomistic simulation of tensile strength properties of graphene with complex vacancy and topological defects
(Springer Vienna, 2020-08) Damasceno, D. A; Rajapakse, R. K. N. D; Mesquita, E; Pavanello, R
Defects including topological and vacancy defects have been observed in graphene during fabrication. Defects are also introduced to break the lattice symmetry of graphene and thereby obtain enhanced optoelectronic and other properties. It is important that gains in certain properties due to the presence defects are not at the expense of mechanical strength which is important in handling graphene and device fabrication. This paper presents a comprehensive study of the tensile strength and fracture strain of monolayer graphene with commonly observed topological defects and nanopores. Both molecular dynamics and the atomic-scale finite element method (AFEM) are used in this study, and the accuracy of AFEM in simulating complex topological and vacancy defects including line defects is established. It is found that the tensile strength properties have a complex dependency on the defect shape, size, and chirality. Certain defect geometries are found to be mechanically superior to other defect geometries thereby supporting the concept of topological design of graphene to optimize properties. The study also establishes AFEM as an efficient and potential tool for topological optimization of the mechanical behaviour of graphene.
Embargo
Vertical vibrations of an elastic foundation with arbitrary embedment within a transversely isotropic, layered soil
(Elsevier, 2014) Labaki, J; Mesquita, E; Rajapakse, R. K. N. D
Analytical methods based on linear elasticity have been used to model the dynamic response of foundations. These solutions commonly assume that soils are isotropic and elastic. Incorporation of anisotropy and the twophased nature of soils (solid skeleton with pores filled with water) is important in the study of dynamic response of foundations. This paper presents the explicit analytical solutions for a transversely isotropic poroelastic soil half-space under a buried time-harmonic vertical load and a time-harmonic pore pressure discontinuity. These versatile fundamental solutions are derived by using Hankel integral transforms. They can be used to analyze a variety of dynamic problems in geomechanics. The fundamental solutions are then applied to solve the timeharmonic vertical vibration of a flexible circular foundation by using variational methods. Selected numerical results are presented to demonstrate the influence of soil anisotropy, poroelasticity, foundation flexibility, depth of embedment and frequency of excitation on the vertical dynamic response of foundation and the force transmitted to soil.