Effect of ending surface on energy and Young's modulus of an armchair single-walled carbon nanotubes

The energy and Young's modulus as a function of tube length for (10, 10) armchair single-walled carbon nanotubes (SWCNTs) are investigated by using a linear scaling self-consistent-charge density functional tight binding (SCC-DFTB) method. It is found that the formula derived from total energy for a zigzag SWCNT [Physica B404, 3930 (2009)] can be also used to explain these calculated length-dependent properties. Moreover, a transition occurs from fast change of length-dependent properties of the SWCNT to their slow change. This transition corresponds to the SWCNT's length of about 5 nm. The length for the armchair SWCNT is about one half of that of the corresponding Zigzag SWCNTs. In addition, a definition of volume for a short SWCNT is discussed.     

Simulation of the elastic response and the buckling modes of single-walled carbon nanotubes

The mechanical behavior of carbon nanotube (CNT) is one of the basic problems on the nanotube composite and nano machinery. Molecular dynamics is an effective way of investigating the behavior of nano structures. The compression deformation of single-walled carbon nanotubes (SWCNTs) is simulated, using the Tersoff–Brenner potential to describe the interactions of atoms in CNT. From the MD simulation for some SWCNTs whose diameters range from 0.5 nm to 1.7 nm and length ranges from 7 nm to 19 nm, respectively, we get the Young’s modulus from 1.25 TPa to 1.48 TPa. The Young’s modulus of CNT decreases as the radius of CNT increases. The Young’s modulus of zigzag CNT is higher than that of armchair CNT. The results also show that there are two different buckling modes for SWCNTs. The difference between the buckling behavior in macroscopic scale and that in nano scale is studied.     

Molecular dynamic simulations on tensile mechanical properties of single-walled carbon nanotubes with and without hydrogen storage

Using a bond order potential, molecular dynamics (MD) simulations have been performed to study the mechanical properties of single-walled carbon nanotubes (SWNTs) under tensile loading with and without hydrogen storage. (10,10) armchair and (17,0) zigzag carbon nanotubes have been studied. Up to the necking point of the armchair carbon nanotube, two deformation stages were identified. In the first stage, the elongation of the nanotube was primarily due to the altering of angles between two neighbor carbon bonds. Young's Modulus observed in this stage was comparable with experiments. In the second stage, the lengths of carbon bonds are extended up to the point of fracture. The tensile strength in this stage was higher than that observed in the first stage. Similar results were also found for the zigzag carbon nanotube with a lower tensile strength. Hydrogen molecules stored in the nanotubes reduced the maximum tensile strength of the carbon nanotubes, especially for the armchair type. The effect may be attributed to the competitive formation between the hydrogen–carbon and the carbon–carbon bonds.     

Effect of matrix glass transition on reinforcement efficiency of epoxy-matrix composites with single walled carbon nanotubes,multi-walled carbon nanotubes,carbon nanofibers and graphite

This study compares the mechanical and thermal properties of glassy and rubbery epoxy–matrix composites reinforced with 1 and 4 wt.% single-walled carbon nanotubes (SWCNTs), multi-walled carbon nanotubes (MWCNTs), graphite, and carbon nanofibers (CNFs). The tensile modulus of most glassy composites was higher than that of the epoxy and increased with higher filler concentration and 4% graphite/epoxy and 4% SWCNT/epoxy exhibited approximately the same highest tensile modulus. The elongation of glassy composites was significantly lower than that of the epoxy and decreased with increasing filler loading. Most rubbery composites showed a higher tensile modulus and elongation than the epoxy and the modulus increased with rising filler content and 4% SWCNT/epoxy showed the highest tensile modulus and tensile strength. In the rubbery regime, glassy and rubbery composites displayed a higher storage modulus than the corresponding epoxy and 4 wt.% SWCNT/epoxy composites showed a 300% improvement in storage modulus compared to the epoxy.     

Poly(phenylene sulphide) and poly(ether ether ketone) composites reinforced with single-walled carbon nanotube buckypaper: II – Mechanical properties,electrical and thermal conductivity

The mechanical properties, electrical and thermal conductivity of single-walled carbon nanotube (SWCNT) buckypaper (BP) embedded in poly(ether ether ketone) (PEEK) or poly(phenylene sulphide) (PPS) matrices were investigated. Dynamic mechanical analysis demonstrated a significant increase in the storage modulus and glass transition temperature of the polymers, indicating strong SWCNT–matrix interfacial adhesion. The composites showed improved stiffness and strength, as revealed by tensile and flexural tests, while their ductility and toughness moderately decreased. Exceptional enhancements in the electrical and thermal conductivity of PPS and PEEK were found. Their Young’s moduli and thermal conductivities were compared with the predictions of theoretical models. This investigation indicates that SWCNT-BPs possess great potential to improve the performance of thermoplastics and satisfy a wide variety of demands in multi-disciplinary technological applications.     

Molecular dynamics study of the influence of functionalization on the elastic properties of single and multiwall carbon nanotubes

The effect of carboxylation on axial Young’s modulus of carbon nanotubes is investigated using a molecular dynamics (MD) approach. COMPASS force field is used to model the interatomic interactions in single wall (SWCNT) and multiwall carbon (MWCNT) with different amounts of –COOH groups attached to their surfaces. The results of the MD simulations show how an increase of the number of carboxylic groups on the CNT surface leads to a decrease on the Young moduli of the CNTs. The decrease of MWCNT Young’s modulus is found to be lower than in the case of SWCNT.     

An Investigation into the Mechanical Behavior of Single-Walled Carbon Nanotubes under Uniaxial Tension Using Molecular Statics and Molecular Dynamics Simulations

This study performs a series of Molecular Dynamics (MD) and Molecular Statics (MS) simulations to investigate the mechanical properties of single-walled carbon nanotubes (SWCNTs) under a uniaxial tensile strain. The simulations focus specifically on the effects of the nanotube helicity, the nanotube diameter and the percentage of vacancy defects on the bond length, bond angle and tensile strength of zigzag and armchair SWCNTs. In this study, a good agreement is observed between the MD and MS simulation results for the stress-strain response of the SWCNTs in both the elastic and the plastic deformation regimes. The MS simulations reveal that in the plastic deformation regime, the tensile strength of the armchair and zigzag SWCNTs increases with an increasing wrapping angle. In addition, it is shown that the tensile strength reduces significantly at larger values of the nanotube diameter. Moreover, it is observed that the tensile strength of both SWCNTs reduces as the percentage of defects within the nanotube structure increases. Finally, it is found that the results obtained from the molecular statics method are relatively insensitive to instabilities in the atomic structure, particularly in the absence of thermal fluctuations, and are in good agreement with the predictions obtained from the molecular dynamics method.     

A comparison of the effect of hot stretching on microstructures and properties of polyacrylonitrile and rayon-based carbon fibers

The effect of a different stretching stress at different heat treatment temperatures (HTT) on the structure and the mechanical properties of polyacrylonitrile (PAN)- and rayon-based carbon fibers was studied. The tensile strength increases first and then decreases with increasing stretching stress, whereas the Young’s modulus of the fibers continuously increases. The behavior of PAN- and rayon-based carbon fibers is similar with increasing stretching stress, but the tensile strength of PAN fiber decreased while that of rayon fiber increased with increasing HTT, what is more, the latter have a considerable lower tensile strength and modulus for equivalent processing conditions. The structure of the fibers was investigated with X-ray diffraction. A continuous change toward a nanostructure with a higher order was observed, which explains the increase in the Young’s modulus. For more complex dependence of the tensile strength on the processing conditions, a quantitative model to describe the effect of stretching stress at different HTT on preferred orientation degree and shear modulus is proposed. From the critical stress fracture of carbon fiber analysis, we can understand the different changes of tensile strength of both type fibers with stretching stress at different HTT.     

Modeling and mechanical performance of carbon nanotube/epoxy resin composites

The effect of multi-walled carbon nanotube (MWCNT) addition on mechanical properties of epoxy resin was investigated to obtain the tensile strength, compressive strength and Young’s modulus from load versus displacement graphs. The result shows that the tensile strength, compressive strength and Young’s modulus of epoxy resin were increased with the addition of MWCNT fillers. The significant improvements in tensile strength, compressive strength and Young’s modulus were obtained due to the excellent dispersion of MWCNT fillers in the epoxy resin. The dispersion of MWCNT fillers in epoxy resin was observed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analysis.Also, Halpin–Tsai model was modified by considering the average diameter of internal/external of multi-walled nanotube and orientation factor (α) to calculate the Young’s modulus of multi-walled carbon nanotubes (MWCNTs)/epoxy resin composite. There was a good correlation between the experimentally obtained Young’s modulus and modified Halpin–Tsai model.     

The effect of carbon nanotube orientation and content on the mechanical properties of polypropylene based composites

Finite element method (FEM) is used to predict the tensile and compressive stress–strain curves of single wall carbon nanotube (SWCNT) reinforced polypropylene (PP) composites. The numerical simulations, using shell and tetrahedron elements, are first carried out to investigate the effect of SWCNT orientation on the mechanical properties of the nano-composites. Second, the Grunfest–Young constitutive equation is selected to determine the effect of strain rate and solve the finite element program to analyze the mechanical behavior of the nano-composites. Third, the effect of SWCNT volume fraction is studied. In all cases, the shear and normal stresses distribution along the nanotube axis are investigated and compared with the macroscopic tensile or compressive stresses on the composites. At the same time, the stresses of the interface between SWCNT and the matrix along the loading direction are analyzed. Finally, the effects of SWCNT orientation, content and strain rate on the strength of the nano-composites are studied. From the results obtained, it was shown that strain rate can substantially affect the tensile and shear stresses of the composites, but do not significantly influence the initial tensile or compressive elastic moduli. This is especially the case for SWCNT orientation angles less than 30° and volume fractions higher than 0.74%.