Mechanical Behavior Of Carbon Nanotubes Research Articles

Mechanical behavior of carbon nanotubes reinforced polymer

Abstract Carbon nanotubes (CNTs) have garnered significant attention due to their extraordinary mechanical and other physical characteristics. This study demonstrates that incorporating a small number of carbon nanotubes, ranging from 0.1 to 0.9 wt.%, into a polymer, can effectively enhance its mechanical properties. In comparison to the pure polymer, the addition of −0.3 % carbon nanotubes resulted in a notable 24.1 % increase in tensile strength, a 4.4 % increase in compressive strength, a significant 319.5 % increase in the fatigue life cycle at 0.1 % carbon nanotubes, and a remarkable 43.0 % increase in fracture toughness at 0.3 wt.% carbon nanotubes.

A single carbon nanotube-entangled high-performance buckypaper with tunable fracture mode.

It is well known that the traditional buckypaper (BP) is composed of a certain number of short carbon nanotubes (CNTs) intertwined with each other and sliding always happens when the BP is under tensile and impact loading, which results in inferior mechanical properties compared to single CNTs. In this work, a highly-entangled single-wire BP (SWBP) structure is constructed by a modified self-avoiding random walk approach. The in-plane mechanical properties and impacting behaviors of the SWBPs with different entanglement degrees and interface frictions are systematically investigated via newly developed coarse-grained molecular dynamics (CGMD) simulation. A coarse-grained method can effectively reflect the inter-tube van der Waals (vdW) interactions and the mechanical behaviors of CNTs, including tension, bending and adhesion. In this work, from the tensile simulations of the SWBP, the results showed that the self-locking mechanism between entangled CNTs could significantly enhance the tensile resistance of the film. Besides, the mechanical properties of the SWBP are highly dependent on the entanglement degree and the interface friction between CNTs. Furthermore, two distinct fracture modes, ductile fracture and brittle fracture, are revealed, which can be efficiently controlled by changing the related friction between CNTs. From the impacting simulations, it is found that the impacting performance can be effectively tuned by adjusting the entanglement degree of the film. In addition, the kinetic energy of the projectile could be rapidly dissipated through the stretching and bending of CNTs in the SWBP. This work provides an in-depth understanding of the effect of interface friction and entanglement degree on the mechanical properties of the buckypaper and provides a reference for the preparation of strong CNT-based micromaterials.

A coarse‐grained molecular dynamics study on the mechanical behavior of carbon nanotubes reinforced vulcanized natural rubber composites

AbstractIn the present study, coarse‐grained (CG) molecular models of carbon nanotubes (CNTs) strengthened vulcanized natural rubber (VNR) composites are constructed to systematically investigate the effects of length, inter‐tube cross‐linking, and polymer‐grafting of CNTs on the stress–strain behavior of VNR composites under uniaxial tension. The interfacial CG force field between CNTs and VNR is derived via the energy matching approach. The results demonstrate that increasing the length of CNTs is able to effectively enhance the mechanical performance of VNR composites, and the reinforcing efficiency increases gradually and tends to stabilize with increasing CNT length. Moreover, the cross‐linking and polymer‐grafting of CNTs are also effective approaches to significantly enhance the mechanical performance of VNR composites. The enhancement mechanism of CNTs is interpreted from the perspective of CNT networks, VNR networks, CNT‐VNR interface networks, and the interfacial load‐transfer behavior. Specifically, the dispersion of CNTs, the orientation of CNTs and VNR molecular chains, and the wrapping and interlocking behaviors between CNTs and the VNR matrix reveal a detailed structure‐mechanics relationship of CNTs‐reinforced VNR composites at the molecular level. These findings present theoretical instruction for the structural design of high‐performance rubber composites.Highlights A coarse‐grained model of carbon nanotube‐natural rubber composites is built. The composite network structures are quantitatively characterized. The length, cross‐linking, and grafting effects of carbon nanotubes are studied. The reinforcement mechanisms of carbon nanotubes are revealed.

Evaluation of shear modulus and buckling loads of SWCNT's using numerical and analytical techniques

With the introduction of carbon nanotubes, their fascinating features, including outstanding strength, exceptional stiffness, low density, and structural integrity at the nanoscale, became evident. These qualities generated excitement for a variety of technological applications. Over the last ten years, an evolving understanding of carbon nanotube mechanics has been shaped by a combination of experimental validation, the refutation of theoretical predictions, and the application of various computer simulation techniques. The objective of this research was to explore theoretical predictions concerning the visualization and manipulation of minute structures. The central focus is on examining mechanical characteristics, including Young's modulus, Poisson's ratio, shear modulus, and buckling criteria in diverse configurations of single-walled carbon nanotubes. Beam elements are utilized in this study to model the covalent bonds between Carbon-Carbon (C-C) atoms in Carbon Nanotubes (CNTs). Using a continuum mechanics framework, the paper aims to predict the characteristics of these beam elements. Baseline values for the properties of C-C bonds are established through numerical analysis to conduct simulations. The paper employs a finite element methodology to scrutinize the mechanical behavior of carbon nanotubes and carries out a parametric investigation to evaluate the influence of single-walled carbon nanotube diameter on shear modulus and buckling loads.

Effect of pulse laser treatment at different process variables on mechanical behavior of carbon nanotubes electrophoretically deposited on titanium alloy

Purpose Titanium and its alloys are widely used as biomaterials for long-term implants, but they are usually surface-modified due to their weak bioactivity and wear resistance. Laser processing was used to modify the surface layer, and elemental carbon was a component of the deposited coatings. This research aims to use a combination of both methods based on preliminary electrophoretic deposition of multi-wall carbon nanotubes (MWNCTs) followed by pulse laser treatment. Carbon nanotubes were chosen due to their mechanical and chemical stability as well as their tubular shape, resulting in enhanced mechanical properties of laser-modified layers. Methods The pulse laser power and laser scanning speed were defined as variable process parameters. The microstructure, roughness Ra, nanohardness H, Young`s modulus E, and indent depth values were measured, and the H/E, H3/E2, and relative changes of all these values in comparison to MWCNTs-coated and non-coated surfaces, were calculated. Results The obtained results show that the best mechanical properties of MWCNTs-coated and laser-treated specimens are obtained at a laser power of 900 W and laser feed of 6 mm/s. The observed relations can be explained considering processes occurring on the surface such as deposition of carbon nanotubes, melting and re-crystallization of the surface layer, formation and possible partial decomposition of titanium carbides, and associated changes in local chemical composition, phase composition, and a level of residual stresses beneath the surface. Conclusions The developed process can substitute the time and money-consuming carbonization of titanium and its alloys.

The Effect of Thermal Cycling on the Tensile and Shear Behaviors of the Carbon Nanotube-Reinforced Epoxy

The aim of this research is to study the tensile and shear properties and mechanical behavior of carbon nanotube- (CNT-) reinforced epoxy after the resulting composites have been exposed to different thermal cycling environments. Single-walled carbon nanotubes (SWCNTs) are cylindrical molecules that consist of rolled-up sheet of single-layer carbon atoms (graphene) with a diameter of less than 1 nanometer (nm). Thermal cycling environments can exist in many conditions, such as in-earth orbit for satellites which rotate around the earth and pass through the sun illumination and earth’s shadow, and for airplanes which fly in different altitudes with different temperatures. Carbon nanotube-reinforced epoxy is one of the nanocomposite materials which have been broadly used in many applications such as aerospace, automotive, electronics, and other industries. The goal of this study is to fabricate this nanocomposite with different multiwall and single-wall CNT concentrations and expose it to different thermal cycle numbers and determine the changes in tensile and shear properties and failure characteristics. For this purpose, tension and short-beam tests have been used in this research. The addition of multiwall CNT produces better mechanical properties compared to the use of SWCNT reinforcement. However, unreinforced epoxy showed the highest mechanical properties.

Computational analysis of the mechanical behavior of carbon nanotubes in a rail-wheel system

Currently, railway systems have presented many problems associated with friction and wear due to movement between the interface of the wheel-rail system, a situation that has been demanding large investments and railway costs in transport companies due to the frequent change of pieces of the system. As a possible solution, the addition of carbon nanotubes (CNTs) has been underway in some modified lubricants to increase the antifriction properties. In this investigation, computational simulations were developed to analyze the behavior of the CNTs as a reducing component of the friction of the material. A constitutive model was considered by Hooke’s law for the wheel-rail system and the CNTs. Numerical lattices were designed to develop the computational simulations. The constitutive equations were solved by the Finite Differences Method (F.D.M.). The computational models were subjected to transverse loads emulating the movement of the system. Simulations were performed for one wheel-rail model with insert of 0.01 percent of CNTs. The results identified in the report of the insertions of the CNTs in the wheel-rail system show a dissipative-absorbent behavior of the deformation energy is detected, combined with rotation effects of the CNTs, a condition that may allow a reduction in friction and wear CNTs can contribute to improve the tribological properties of lubricants in affected railway systems and a longer service life of mechanical elements. The computational developments carried out in this research can facilitate the analysis of behaviors of nanostructured materials under conditions of extreme functionality where the experimental processes are complex.

Mechanical behavior of carbon nanotube reinforced polymethylmethacrylate foam: A multi-scale finite element method approach

In the present study, considering the random distribution of carbon nanotubes in polymethylmethacrylate (PMMA) polymer, a multi-scale finite element method has been developed to investigate the mechanical behavior of these materials. In order to make realistic assumptions, the interface zone between the nanotubes and the matrix is simulated using the interfacial zone model (IZM), with its parameters obtained by calibrating the finite element model results with the results of experimental tests. Tensile tests and scanning electron microscopy (SEM) were used to study the mechanical properties and morphology of the PMMA foam samples reinforced with 0 wt%, 1 wt% and 2 wt% carbon nanotubes. Experimental results show that by adding 1 wt% and 2 wt% carbon nanotubes to PMMA foam, the tensile strength of the foam increases by 8% and 22%, respectively, compared to pure foam. Based on the results of the finite element models, the optimum percentage of the carbon nanotubes is 3.3 wt%, which gives the optimum modulus and tensile strength of 87 MPa and 4.02 GPa, respectively. The finite element model developed in the present study shows good agreement with the experimental results. Therefore, the impact of effective parameters on the mechanical properties of the foam can be easily studied based on the finite element method (FEM) results.

RETRACTED: Multiscale MDFEM for modeling mechanical behavior of carbon nanotubes

This article has been retracted: please see Elsevier Policy on Article Withdrawal ( https://www.elsevier.com/about/our-business/policies/article-withdrawal ). This article has been retracted at the request of the authors: the authors did not cite their colleagues’ previous publications and did not include them as co-authors of this paper. The authors apologize for their mistake and for any inconvenience this may have caused to readers and researchers citing this paper.

Twist induced plasticity and failure mechanism of helical carbon nanotube fibers under different strain rates

Twist has been well identified as an effective parameter to tune the mechanical behavior of carbon nanotube (CNT) fibers, e.g., tensile strength, strain, modulus and elastic-plastic behaviors. In this contribution, we uncover the twist-induced plastic deformation and failure behaviors of CNT fibers shrunk by ethanol (E-CNT fiber) and polyvinyl alcohol (P-CNT) solutions under low strain rate of 0.001 s−1 and high strain rate of 1300 s−1, which are essentially important for designing high-performance composites with respect to long term stability and short-term collision, respectively. It is found that the strain-induced microstructural evolution processes of CNT fibers depends on twist angle as a result of the strengthening effect of inter-CNT friction and the weakening effect of CNT obliquity. The tensile strength, failure strain and modulus of CNT fibers are more sensitive to strain rate as the twist angle increases. The optimum twist angle provides not only the higher tensile strength, but also the better data repeatability. The numerical results reveal that the brittle/ductile properties of filaments and their interfacial interaction will contribute to the plastic behaviors of a twist fiber. The empirical constitutive equations were built to describe the stress-strain curves of CNT fibers by taking the strain, helical geometry, twist-induced damage and strain rate into consideration.

Mechanical behavior of carbon nanotubes reinforced AA 4032 bimodal alloys

The bimodal structured composites of aluminum – carbon nanotubes prepared using powder metallurgy technique with coarse grained AA 4032 powders and nanocrystalline structured AA 4032 powders. Microstructural observations by optical microscope and transmission microscope ensure the complete densification and uniform distribution of carbon nanotubes. These bimodal composites exhibited high compressive yield strength with good ductility. The result shows improved mechanical properties of composites than alloy.

Unraveling the influence of grain boundaries on the mechanical properties of polycrystalline carbon nanotubes

The ability to produce homogeneous defect-free carbon nanotubes (CNTs) represents a major challenge in terms of utility and cost. Specifically, the existence of grain boundaries (GBs) are ubiquitous in large diameter CNTs obtained by various large-scale growth methods and their effects on the mechanical properties of CNTs are not fully explored. Understanding the influence of the grain size and the GB orientation upon the mechanical behavior of CNTs is crucial for their functional and structural applications. The significance and novelty of the current work lies in its ability to establish the mechanical properties and the fracture behavior of CNTs containing grain boundaries of varied size, orientation and structure to an applied uniaxial load using comprehensive molecular dynamics simulations. A specially developed program, using Voronoi tessellation method and Delaunay triangulation, was implemented to generate the atomistic descriptions of the considered polycrystalline CNTs with a variety of GB morphology. Our results reveal that the mechanical performance of CNTs is significantly affected by the orientations of the GBs, diameter and temperature. In terms of the fracture strength, the resulting failure patterns indicate that the polycrystalline CNTs fail in a brittle fashion and that pentagon-heptagon defects along the GBs serve as crack nucleation sites.

Parametric study on Topology of carbon Nanotubes Effects on Mechanical properties

From last two decades usage of composite materials in Aerospace structural applications have widely aroused many researchers to study the mechanical behaviors of Carbon Nanotubes (CNTs) reinforced Nanocomposites. Many studies have been reported superior properties of CNTs by means of various experiments, Quantum calculations and Atomic simulations. Since because all studies had conducted at Nanoscale, we could able see the wide scatter in the results. Conducting the experiments on Nanocomposites at Nanoscale is very inconceivable to predict the mechanical properties. Molecular Dynamics was vastly used by many researchers to analyze properties of CNTs in atomistic scale with various interaction potentials (Force fields). The Carbon nanotubes were assumed to be rolled from hexagonal carbon network of Sp2 carbon atoms. The topology of carbon nanotube was derived from major parameters like Chiral indices and Chiral Vector. So many researchers has carried out wide study on the Zigzag and Armchair nanotubes. From the literature we could able see the variation between experiment and theoretical results. As of main topology parameters concerns, there is the possibility of variety of CNTs topology at one diameter like Zigzag, Armchair and Chiral. This paper mainly deals about effect of topology parameters of carbon nanotubes used in Molecular Dynamics study for analyzing the mechanical properties of CNTs based on AIREBO potential.

Stability analysis of an embedded single-walled carbon nanotube with small initial curvature based on nonlocal theory

ABSTRACTMany experimental observations have shown that most nanostructures, such as carbon nanotubes, are often characterized by a certain degree of waviness along their axial direction. This geometrical imperfection has profound effects on the mechanical behavior of carbon nanotubes. In the present work, stability of a slightly curved carbon nanotube under lateral loading is investigated based on Eringen's nonlocal elasticity theory. Euler Bernoulli and Timoshenko beam theories are employed to obtain equilibrium equations. Winkler-Pasternak elastic foundation is used to approximate the effect of matrix. Effects of initial curvature, nonlocal parameter, beam length, and elastic foundation parameters on initiation of critical conditions are investigated.

A multiscale modeling of CNT-reinforced cement composites

A multiscale approach for computational modeling of the mechanical behavior of carbon nanotube (CNT) reinforced cement composites is presented. In a macroscopic scale treatment, reinforcement is assumed to be embedded in the overall domain in the corresponding volume fraction. Accounting for the volume fraction, orientation and arrangement of the reinforcing components, CNTs and a matrix are simulated by different nonlinear constitutive models to represent the composites, CNTs are considered as one-dimensional and distributed in a uniform orientation. A mesoscopic scale description is considered in order to depict the mesostructured morphology of the reinforced composites and the bond–slip of its mutual interaction. Two length-scale systems of equations are coupled together using a staggered technique, and the Newton–Raphson method is adopted to solve the nonlinear system equations in order to track the full load–displacement path of the composites. A number of available experimental tests are reproduced by which to illustrate the feasibility of the proposed model, which proves to be effective in the nonlinear framework. Meanwhile, computational accuracy and efficiency are also demonstrated through the solving of several benchmark problems.

Mechanical behaviour of carbon nanotubes under combined twisting–bending

The main objective of this paper is to investigate the mechanical behaviour (strength and stiffness) of carbon nanotubes (CNTs) under combinations of bending and twisting. In order to achieve this goal, molecular dynamics (MD) simulations of bended and twisted CNTs are performed. The LAMMPS code is used, the AIREBO potential is considered for CC bonds, the temperature is kept at 300K and incremental bending and twisting rotations are imposed to the CNT. Two types of CNTs are analyzed, including zig-zag (8,0) and armchair (5,5) CNTs with similar radius and length. The CNTs are also analyzed for pure bending and pure twisting. The main results are shown in the form of diagrams of energy and moment against imposed rotations. Some relevant conclusions are drawn concerning the influence of loading (bending and twisting) on the stiffness, strength and failure of CNTs: namely, it is concluded that armchair CNTs possess higher strength and fracture toughness under twisting–bending loading than zigzag CNTs; additionally, it is found that both CNTs (armchair and zigzag) still support moderate-to-high bending levels without failure after being extremely twisted and torsionally buckled, even for twisting angles four times those corresponding to torsional buckling; finally, the results prove that CNTs, mostly armchair ones, exhibit very high twisting–bending stiffness and strength and can be used with confidence as torsional spring elements in nanoelectromechanical systems (NEMS).

Molecular dynamics studies of CNT-reinforced aluminum composites under uniaxial tensile loading

Abstract This paper investigates the mechanical behavior of carbon nanotube (CNT)-reinforced aluminum composites (CNT–Al composites) under a tensile loading condition using molecular dynamics (MD) simulations. A review of current computational and experimental studies highlights the benefits of CNT–Al composites from a structural point of view. However, quantitative and qualitative investigations on the improvements due to the inclusion of CNTs are still rare. This study shows that, compared to pure aluminum, the Young's moduli are improved by 31% for (4,4)CNT–Al, 33% for (6,6)CNT–Al, and 39% for (8,8)CNT–Al. Moreover, the corresponding toughness values are significantly enhanced by 37%, 72%, and 100%. Furthermore, the MD simulations provide insights into various fracture behaviors at the atomic scale, including lattice disordering, local changes in lattice structures due to stacking faults, and void nucleation/growth. The component analysis shows that the mechanical properties of CNT–Al composites improve significantly, even with a small amount of CNT, due to the considerable load-bearing capacity of CNT.

Mechanical behavior of carbon nanotube and graphene junction as a building block for 3D carbon nanostructures

The incorporation of defects in junction area of 1D and 2D carbon nanostructures has a major impact on properties of their 3D structures. In the present study, molecular dynamics simulation is utilized to examine the mechanical behavior of graphene sheet (GS) in carbon nanotube (CNT)-GS junctions. The tensile load was applied along the GS in connection with CNTs of different chiralities. The adaptive intermolecular reactive empirical bond order potential was chosen to model C-C interactions. It provided a reliable model for CNT, GS and their junctions. The results revealed that the connection of CNT to the GS with a hole could improve the mechanical properties of defective GS, which appeared to be independent of CNT type. It was found that the high strength C-C bonds postpone the crack propagation and motivates new crack nucleation. When a hole or CNT placed on the GS, it caused stress concentration, exactly along a line on its side. The lower mechanical properties were consequently associated with crack nucleation and propagation on both sides in a way that cracks encountered each other during the failure; while, the cracks in pristine GS propagate parallel to each other and could not encounter each other.

A quantitative understanding on the mechanical behaviors of carbon nanotube reinforced nano/ultrafine-grained composites

The mechanical responses of carbon nanotube (CNT) reinforced nano/ultrafine-grained metal matrix composites (MMCs) with the reinforcement located at grain boundaries and atomically disordered regions near the reinforcement have not been discussed yet. Here a theoretical model based on dislocation-controlling constitutive relations of metal matrix and strain gradient effect is adopted to quantitatively understand the contributions of strengthening mechanisms to the mechanical response of these composites. CNT-reinforced nano/ultrafine-grained MMCs will be treated as a two-phase composite with CNT-free regions surrounded by CNT-containing domains, whose mechanical behaviors are different from that of the matrix-only regions. The predictions of this model are in excellent agreement with available experimental results. During the process of deformation, geometrically necessary dislocations induced by strain gradient and thermal mismatch are limited within CNT-containing domains, and the thicknesses of these regions are obtained to be linearly proportional to matrix grain size by fitting with the experimental results. When the size of the reinforcement is large, the effect of thermal mismatch strengthening mechanism on the strength of MMCs is slight and can be ignored compared with the roles of Hall–Petch strengthening or load transfer effect.

Effects of nanobuds and heat welded nanobuds chains on mechanical behavior of carbon nanotubes

This study reports an investigation on the effects of nanobuds and heat welded nanobuds chains (C60 chains attached or embedded on the surface of a SWCNT) on the mechanical properties of carbon nanotubes by molecular dynamics (MD) simulations. The bond order change and the stress concentration in the distorted connection area of nanobuds when C60 attaches to the surface of the SWCNT are first studied. Then the effect of multiple randomly scattered and attached C60 fullerenes on the ultimate tensile strength of SWCNT is discussed. It is found that both nanobuds and heat welded nanobuds chains lower the ultimate tensile strength of individual defect-free SWCNT. However, the mean post-peak strength of the CNT (after necking) is significantly enhanced by heat welded nanobuds chains. Moreover, the ultimate tensile strength of the SWCNT with vacancy defects does not decrease by heat welded nanobuds chains; interestingly, the maximum tensile strength of the SWCNTs bundles with intertube bridging and vacancy defects even can be enhanced by more than 20% by heat welded nanobuds chains.