Influence Of Random Defects On The Mechanical Behavior Of Carbon Nanotubes Through Atomistic Simulation

Carbon nanotubes (CNTs) have drawn great interest and shown great promise in recent years in the areas of composite materials, sensors, and small electronic devices owing in a large part to their extraordinary mechanical properties. Yet an enormous scatter is observed in available laboratory results on the stiffness and strength of CNTs. Surface defects including vacancies, pentagon and heptagons have been commonly observed in CNT samples, and are found to have significant influence on the mechanics of CNTs. However, any link between the randomness in CNTs mechanical properties and CNT defects has not been investigated systematically before. Moreover, the fracture of CNTs due to mechanical loading is an important issue likely to affect the durability and reliability of CNT-based materials and devices; yet, based on the author's knowledge, the fracture resistance of CNTs has not been quantified before. This dissertation, trying to build up these missing links, studies the effects of randomly distributed vacancies and Stone-Wales (SW or 5-7-7-5) defects on the mechanical properties of single-walled nanotubes (SWNTs) using the technique of atomistic simulation (AS), and quantifies the fracture resistance of zigzag SWNTs with fracture mechanics concepts. Basic principles and key issues of atomistic simulation and multiscale modeling are reviewed. A series of displacement controlled tensile tests of CNTs are modeled with atomistic simulation. Armchair and zigzag SWNTs, with and without defects are studied. A modified Morse potential is adopted to model the interatomic forces. Time histories of energies, displacements and forces are generated from the simulations, and three mechanical properties & mdash;stiffness, ultimate strength and ultimate strain & mdash;are further calculated. Effects of loading speed and geometry are discussed. Further details of CNT structure changes, especially the evolution of defects during the loading process are monitored. In studying the fracture resistance of CNTs, the strain energy release rate, G, is computed through a series of simulated mechanical loading of zigzag SWNTs with preexisting cracks of various lengths. A significant dependence of the critical strain energy release rate, Gc, on crack length, a, is observed: Gc increases with a initially, and tends to reach a constant value as a becomes large. The temperature dependence of Gc is also investigated up to 500K: Gc drops substantially as temperature increases for all tube diameters.

This volume presents the characterization methods involved with carbon nanotubes and carbon nanotube-based composites, with a more detailed look at computational mechanics approaches, namely the finite element method. Special emphasis is placed on studies that consider the extent to which imperfections in the structure of the nanomaterials affect their mechanical properties. These defects may include random distribution of fibers in the composite structure, as well as atom vacancies, perturbation and doping in the structure of individual carbon nanotubes.

Carbon nanotubes are one of the newest materials to be discovered, being barely 20 years old. They are also the most promising one, with one particular sample of multi-walled nanotube attaining a tensile strength of 63GPa, and with carbon nanotubes in general having a specific strength of up to 48000kNm/kg: effectively a direct exploitation of the covalent sp2 bonding between carbon atoms. Plastic deformation begins at about 5% strain. The nanotubes can be produced in lengths of up to 550mm, and thicknesses as small as 4.3Å; making them perfect reinforcement fibres for composites. They also have many other properties which may be useful in electronics, gas storage , etc. The present compilation focuses on the various characteristic types of defect which are found in carbon nanotubes, plus the relatively limited number of diffusion studies which have been performed. The 418 entries cover the period from 1994 to 2014.

Defects in Advanced Electronic Materials and Novel Low Dimensional Structures provides a comprehensive review on the recent progress in solving defect issues and deliberate defect engineering in novel material systems. It begins with an overview of point defects in ZnO and group-III nitrides, including irradiation-induced defects, and then look at defects in one and two-dimensional materials, including carbon nanotubes and graphene. Next, it examines the ways that defects can expand the potential applications of semiconductors, such as energy upconversion and quantum processing. The book concludes with a look at the latest advances in theory. While defect physics is extensively reviewed for conventional bulk semiconductors, the same is far from being true for novel material systems, such as low-dimensional 1D and 0D nanostructures and 2D monolayers. This book fills that necessary gap. Presents an in-depth overview of both conventional bulk semiconductors and low-dimensional, novel material systems, such as 1D structures and 2D monolayers Addresses a range of defects in a variety of systems, providing a comparative approach Includes sections on advances in theory that provide insights on where this body of research might lead

Carbon nanotubes offer huge potential in so many fields due in part to their significant mechanical properties, including extraordinary rigidity, resilience, toughness, and flexibility. Mechanical deformation of carbon nanotubes is known to cause considerable changes in their physical and chemical properties through the nontrivial structure-propert

This book contains a collection of the state-of-the-art reviews written by the leading researchers in the areas of nanoscale mechanics, molecular dynamics, nanoscale modeling of nanocomposites and mechanics of carbon nanotubes. No other book provides reviews of recent discoveries such as a nanoscale analog of the Pauli’s principle, i.e., effect of the spatial exclusion of electrons or the SEE effect, a new Registry Matrix Analysis for the nanoscale interfacial sliding and new data on the effective viscosity of interfacial electrons in nanoscale stiction at the interfaces. This volume is also an exceptional resource on the well tested nanoscale modeling of carbon nanotubes and nanocomposites, new nanoscale effects, unique evaluations of the effective thickness of carbon nanotubes under different loads, new data on which size of carbon nanotubes is safer and many other topics. Extensive bibliography concerning all these topics is included along with the lucid short reviews. Numerous illustrations are provided for molecular dynamic simulations, fascinating nanoscale phenomena and remarkable new effects. It is of interest to a wide range of researchers and students.

Mechanical Behaviors of Carbon Nanotubes: Theoretical and Numerical Approaches presents various theoretical and numerical studies on mechanical behaviors of carbon nanotubes. The main theoretical aspects included in the book contain classical molecular dynamics simulation, atomistic-continuum theory, atomic finite element method, continuum plate, nonlocal continuum plate, and shell models. Detailed coverage is also given to structural and elastic properties, trace of large deformation, buckling and post-buckling behaviors, fracture, vibration characteristics, wave propagation, and the most promising engineering applications. This book not only illustrates the theoretical and numerical methods for analyzing the mechanical behavior of carbon nanotubes, but also contains computational results from experiments that have already taken place. Covers various theoretical and numerical studies, giving readers a greater understanding of the mechanical behavior of carbon nanotubes Includes multiscale methods that provide the advantages of atomistic and continuum approaches, helping readers solve complex, large-system engineering problems Allows engineers to create more efficient carbon nanotube structures and devices