Mechanical and fracture characterization of polymer CNT nanocomposites using atomistic simulations
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Date
2025-03-10
Authors
Δελασούδας, Ιάκωβος
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Abstract
Computational physics is regarded as a crucial domain in scientific research worldwide, as it bridges the gap between experimental and theoretical studies. It provides a powerful framework for addressing complex problems from perspectives and under conditions that are often inaccessible through experimental methods due to physical or financial constraints. This is particularly evident in materials science, where atomistic and molecular-level insights are essential. Computational methods are employed, not only to complement and guide experimental efforts but also to drive the development of more accurate macroscopic models.
The importance of computational modeling in understanding complex systems, such as polymers and nanocomposites, is highlighted by the growing demand for advanced industrial materials with tailored properties for everyday applications. These models elucidate the relationships between structure, properties, processing, and performance. As a result, materials that are more cost-effective, environmentally sustainable, and energy-efficient can be developed.
Fracture, is identified as a critical phenomenon that must be explicitly studied to enable the proper design of new materials and structures. A material’s resistance to crack propagation is influenced by processes occurring across multiple length scales. In this dissertation, fracture behavior in carbon-based nanocomposite polymers is examined using atomistic simulations in three different levels.
At the first level, interfacial failure between the filler and the matrix is studied in terms of the interfacial shear strength (IFSS). IFSS is commonly determined in molecular dynamics studies through mechanical pull-out experiments by measuring the drop point in stress-strain curves. However, non-periodic boundaries are often employed along the pull-out direction, rendering these approaches susceptible to size-related effects. In this work, an established method based on the kinetics of local failure mechanisms is extended to study the interface between single-wall carbon nanotubes (SWCNTs) and epoxy under fully periodic boundary conditions. Shear deformation simulations are conducted across a wide range of temperatures and shear stresses using molecular dynamics (MD). Failure times are recorded and analyzed within the framework of the extended Boltzmann-Arrhenius-Zhurkov kinetic equation, enabling the determination of various parameters, including IFSS.
At the second level, predictions of fracture properties for bulk systems are undertaken. A scale-bridging method is proposed to forecast the fracture behavior of highly cross-linked epoxy networks. Classical force fields are combined with the REACTER protocol in the LAMMPS package, utilizing a parameter for bond breaking based on an experimentally derived distance criterion. Macroscopic fracture energy of the epoxy network is anticipated using a continuum fracture mechanics model developed for fibrils. Additionally, the stress intensity factor is extracted from the analysis.
At the third and final level, the methodology developed for bulk systems is extended to predict the fracture properties of carbon-based nanocomposites. This contributes to the overarching goal of the dissertation, which is to accurately predict the fracture properties of polymer nanocomposites using atomistic simulations. The methodology, which combines empirical force fields with experimental data, enhances the computational efficiency of the calculations while ensuring consistency with experimental results.
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Keywords
Fracture mechanics, Atomistic simulations, Epoxy networks, Nanocomposite materials, Carbon nanotubes, Molecular dynamics