Multiscale modeling of the properties of two-dimensional materials
1 online resource (170 pages) : PDF
University of North Carolina at Charlotte
The main objective of this dissertation is to study the thermal and mechanicalproperties of two dimensional materials. For this purpose, we use and combine atomiclevel simulations with continuum level simulations. In this dissertation, moleculardynamics method is used to study the fracture properties of monolayer molybdenumdisulfide (MoS2) and hexagonal boron nitride (h-BN). Our results predict that thecritical stress intensity factor of single layer MoS2 and BN are 1.2~1.8 and 4.5~7 respectively. Moreover, our results predict that the chirality of the crack edges, the tip configuration and loading phase angle can significantly impactthe critical stress intensity factor and the propagation path of the cracks.Also, molecular dynamics simulations are used to study the thermal conductivityof single layer MoS2. The results show that by increasing the nanoribbon's length, thethermal conductivity of nanoribbons increases. For monolayer MoS2, zigzag nanoribbonshave higher thermal conductivity than armchair nanoribbons. Our results showthat defect such as vacancies significantly impact the thermal conductivity of nanoribbons.By increasing the atomic vacancy density, the thermal conductivity of MoS2nanoribbon is reduced. We have studied the impact of uniaxial stretching on thethermal conductivity of MoS2 nanoribbons. The MD simulations predict that, thethermal conductivity of MoS2 is independent of the axial strain.The high computation cost of MD simulations imposes severe constrains on the size of modeling domain. To overcome this limitation, the molecular dynamics can beused only on the part of the domain which needs a high accuracy, while nite elementscan be used in the rest of domain. Such coupling can reduce the computation costbut the artifacts associated with the presence of an interface between MD and FEzone should be removed. In this dissertation, a coupling technique is presented toalleviate the atomic-continuum interface effect. The proposed method is based onthe bridging domain method (BDM). Using numerical examples, we show that theproposed method significantly improves the performance of bridging domain method.This is specially significant when discontinuities such as cracks are present in thedomain or when the integration time step is small.Since the nite element method is a mesh-based method, special techniques arerequired to simulate the fracture phenomenon. For example, a common way is tosplit a cracked element into two new elements. However, this method requires there-meshing, which is not only time consuming, but also reduces the accuracy. Peridynamicsis a more recently developed technique, which can resolve the issues associatedwith modeling cracks using FEM. In a peridynamics formulation, the domain is discretizedby node only. Thus, without the re-meshing, the peridynamics can simulatethe fracture phenomenon. In this dissertation, the peridynamics method is used tosimulate the fracture behavior of the single layer MoS2 and h-BN, at a continuumlevel.Since peridynamics is a nonlocal method, computationally, it is more expensivethan FEM. To reduce the computational cost, we propose to couple PD with FEM.In this coupling technique, the peridynamics method is used to simulate the part which (may) contains cracks, while the nite element method is used for the restdomains. Two dimensional and three dimensional examples are used to verify theperformance of the proposed method.
BRIDGING DOMAIN METHODH-BNMOLECULAR DYNAMICSMOS2MULTISCALE ANALYSISPERIDYNAMICS
Wei, QiumingPoler, JordanWeggel, David
Thesis (Ph.D.)--University of North Carolina at Charlotte, 2017.
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