Mechanical Properties Of Carbon Nanotubes Research Articles

Carbon nanotubes and their composites


 
 
 Carbon nanotubes have been the focus of considerable research since their observation from 1991 onwards. The extensive basic studies performed by physicists and chemists in the processing of carbon nanotubes during the past decade have established a sound foundation for exploring their technological application. The exceptional mechanical properties of carbon nanotubes can be exploited in the development of nanotube-based composite materials that may far exceed the properties of existing fiber-reinforced composites. Nanocomposites of carbon tubes that have extraordinary specific stiffness and specific strength represent a tremendous opportunity for application in the 21st century. This paper provides a concise review of the recent advancement in carbon nanotubes and their composites. We examine the research work reported in the literature on the structure and processing of carbon nanotubes, as well as the characterization and modeling of the properties of carbon nanotubes and their composites.
 
 

A new approach for the reinforcement of SS 304L via arc welding: Using nanostructured flux cored electrode

Carbon nanotubes (CNT) are revolutionary materials and, since its discovery, the scientific community seeks ways to use the unique electrical and mechanical properties of CNT as in nanocomposites, incorporated in metal matrices via processes such as welding and thermal spraying. Despite an increasing number of researches involving the success in incorporating CNTs in metals, such as copper and aluminum, the knowledge concerning the use of stainless steel (SS) as metal matrix is yet underdeveloped. This paper uses the Mechanical Alloying (MA) process to incorporate Multi Walled Carbon Nanotubes in a Stainless Steel (SS) 304L powder. The mixture of SS 304L and 5 wt% MWCNTs was placed in a planetary ball mill along with a ball-to-powder ratio of 30:1, and rotated at 200 rpm. Samples with 0 min, 30 min, 60 min and 90 min of MA process were collected to be characterized using X-ray Diffraction (XRD), Raman spectroscopy and Scanning Electron Microscope (SEM). The results indicated that the 60 min sample achieved homogeneous dispersion and aggregation in the metal matrix, which qualifies such parameters as more suitable to produce the nanostructured powder of 304LSS-CNT. Thus, for the nanostructured cored flux electrode conception, a tubular electrode was filled with 304LSS-CNT powder from 0 min and 60 min of MA for welding via Pulsed Gas Tungsten Arc Welding (P-GTAW). Vickers hardness tests analyzed the mechanical properties, with 25% and 30% improvement of lateral hardness for the 60 min of MA, if compared to 0 min and SS powder only, respectively.

Agglomeration effects of carbon nanotube on residual stresses in polymer nano composite using experimental and analytical method

Since, mechanical properties of carbon nanotubes (CNTs) reinforced polymers and their composites are affected by poor dispersion of CNTs, the present study has been done to investigate the effect of CNT agglomerates on the residual stresses in a fiber reinforced Nano composite using experimental measurements and analytical method. CNTs are incorporated into an epoxy matrix with two weight fractions of 0.1% and 0.5% and are reinforced by unidirectional carbon fibers (CFs) to fabricate laminated composites with [02/902]s layup. The hole-drilling method is employed to measure the residual stresses in cross-ply CNT/CF/epoxy composite laminates. The CNT/epoxy sample is produced where the degree of agglomeration is changed from perfectly dispersed state up to fully agglomerated one. Based on the classical laminate theory, analytical solution is used to calculate the residual stress caused by thermal treatment. The residual stresses measured by incremental hole-drilling method are in good agreement with the theoretical residual stresses calculated by each layer of the laminates. The results show that dispersed samples perfectly are produced lower residual stresses compared to poor dispersed samples and this phenomenon is more significant in case of Nano composite with higher weight fractions of CNTs.

Effect of CNTs dispersion on electrical, mechanical and strain sensing properties of CNT/epoxy nanocomposites

Abstract The remarkable electrical and mechanical properties of carbon nanotubes (CNTs) render CNT-reinforced nanocomposites as potentially attractive materials for strain-sensing and monitoring purposes. The dispersion state of CNTs in polymeric matrix has a significant role on the physical and the mechanical properties of the resulting CNT reinforced nanocomposites. In this study, a series of experiments were designed to investigate the effect of dispersion process parameters and CNT concentration, as well as their interactions on electrical, mechanical and strain sensing properties of CNT/epoxy nanocomposites. Composite samples were produced under different CNT/resin dispersion conditions based on a design of experiments approach, and were characterized using tensile testing, conductivity measurements and micrography. Based on the results, two regression models were established to predict the electric conductivity and the tensile strength of the CNT/epoxy nanocomposites. The robustness and accuracy of the models were verified by implementing verification tests. It was found that the nanocomposites fabricated by dispersing of lower amount of CNT with high mixing speeds and long mixing times had improved sensory properties and were more suitable for strain sensing applications. The effect of post dispersion state on electrical conductivity was also investigated by curing nanocomposites into a magnetic field. A straight forward 2D percolation-based model was used to predict the electrical conductivity and piezoresistivity of the magnetized nanocomposites. Both Experimental and numerical results showed that the electric conductivity could be increased significantly with post dispersing of CNTs using magnetization.

Elastic behaviour of hybrid cross-linked epoxy-based nanocomposite reinforced with GNP and CNT: experimental and multiscale modelling

Experimental method and multiscale modelling based on molecular dynamics simulation have been used to determine mechanical properties of carbon nanotube and graphene nanoplatelet hybrid nanocomposites. Samples containing two different mix ratios of hybrid nanofillers were subjected to tensile loading. Also, micrographs were obtained from samples fracture surfaces using field emission scanning electron microscope and SEM. These images showed that nanofillers were well dispersed in the matrix. In multiscale modelling, a new method has been developed to estimate the Young’s moduli of hybrid nanocomposite samples. To this end, atomistic modelling has been employed to investigate the mechanical properties of molecular samples at nanoscale level. In this step, epoxy cross-linked atomic models have been constructed utilizing molecular dynamics. Next, micromechanical modelling was used to bridge elastic constants of molecular samples from nanoscale to microscale. Also, the calculated Young’s moduli of the hybrid nanocomposite samples obtained from multiscale modelling were compared with experimental measurements and differences less than 7% were observed. Finally, the effects of effective fibre aspect ratio on elastic modulus of hybrid nanocomposite were investigated using the multiscale method. The results indicated an increase in hybrid nanocomposite Young’s modulus with effective fibre aspect ratio. In summary, this paper presents a new method for calculating the hybrid polymer-based nanocomposite properties using a multiscale method.

Storage of Mechanical Energy Based on Carbon Nanotubes with High Energy Density and Power Density.

Energy storage in a proper form is an important way to meet the fast increase in the demand for energy. Among the strategies for storing energy, storage of mechanical energy via suitable media is widely utilized by human beings. With a tensile strength over 100 GPa, and a Young's modulus over 1 TPa, carbon nanotubes (CNTs) are considered as one of the strongest materials ever found and exhibit overwhelming advantages for storing mechanical energy. For example, the tensile-strain energy density of CNTs is as high as 1125 Wh kg-1 . In addition, CNTs also exhibit great potential for fabricating flywheels to store kinetic energy with both high energy density (8571 Wh kg-1 ) and high power density (2 MW kg-1 to 2 GW kg-1 ). Here, an overview of some typical mechanical-energy-storage systems and materials is given. Then, theoretical and experimental studies on the mechanical properties of CNTs and CNT assemblies are introduced. Afterward, the strategies for utilizing CNTs to store mechanical energy are discussed. In addition, macroscale production of CNTs is summarized. Finally, future trends and prospects in the development of CNTs used as mechanical-energy-storage materials are presented.

On thermo-mechanical vibration analysis of multi-scale hybrid composite beams

This article is primarily organized to analyze the thermo-elastic vibrational characteristics of multi-scale hybrid composite beams according to a refined beam model. In this novel type of composites, multi-scale reinforcing elements, carbon fiber (CF) and carbon nanotube (CNT) in particular, are presumed to be dispersed in an initial resin. The homogenization process is carried out employing a mixture of the Halpin–Tsai model and the rule of mixture. The effect of temperature and its gradient on the mechanical properties of CNTs and epoxy resin is rendered to present a more reliable thermal analysis. On the other hand, a refined trigonometric shear deformable beam theory is extended to derive the kinematic relations of the beam needless of any external shear correction coefficient. On the basis of Hamilton's principle, the partial differential equations of motion are developed. Thereafter, the natural frequencies are achieved by the means of Galerkin's method for both simply supported and fully clamped edge conditions. Then, the validity of the presented model is shown by comparing these results with those of previously published researches. Finally, effects of different parameters on the natural frequency of composite beams are rendered in the framework of some numerical case studies. It can be found that multi-scale hybrid composite beams can satisfy higher frequencies once compared with each of the CF- or CNT-reinforced composite beams.

Effect of thermal cycling on the mechanical properties of carbon nanotubes reinforced copper matrix nanolaminated composites

The effect of thermal cycling on the mechanical properties of metal matrix composites (MMCs) reinforced with micro-fillers have been studied for a long time, but that for nano-size-reinforcements remains largely unexplored, such as carbon nanotubes (CNTs). We have fabricated CNTs/Cu laminated MMCs with well-balanced tensile strength and elongation via flake powder metallurgy. In this work, the effect of thermal cycling on their mechanical properties are investigated in a temperature range of –196/+ 200 °C. The thermal cycling results in reductions in strength and elongation and modulus, but the strengthening role of CNTs remains in some extents as compared to the pure Cu counterpart. Tensile tests at room temperature show that high strain hardening ability can be regained even after a sharp stress drop in the thermally cycled composites. The observations on transmission electron microscope (TEM) and scanning electron microscope (SEM) show that the amount of crack increases gradually in the composites upon thermal cycling. Nevertheless, CNT bridges are often found bestriding the cracks and impeding their propagating. The TEM results indicate high density of dislocation in the Cu matrix after thermal cycling, but it decreases after enough thermal cycles, which might be attributed to the stress releasing caused by crack propagation. The failure mode is dominated by the inter-carbon-layer fracture of the multi-walled CNTs in the composites subjected to thermal cycling and tensile loading.

Effect of temperature on vibrations and buckling behavior of carbon nanotube-based mass sensors using a new temperature-dependent structural model

In last decade, structural mechanics (SM) approach has been one of the most known and effective tools for the determination of the mechanical properties of carbon nanotubes (CNTs) such as elastic modulus, shear modulus, natural frequency, and critical axial buckling strain. Considering increasing applications of CNTs as resonators at low and high temperatures, a new temperature-dependent structural mechanics model is presented here. The proposed model can be utilized to predict the effect of temperature on the mechanical response of CNTs as functional resonators. Mechanical and geometrical properties of equivalent beam element are correlated to the CNT's coefficient of thermal expansion (CTE). Owing to elaborate series of finite element simulations, the frequency shift of a CNTs-based mass sensor with different attached mass and aspect ratio in temperature range of 0–1600 K is calculated. Afterwards, the critical buckling temperature of CNTs-based mass sensor due to increasing the axial force by changing ambient temperature is obtained. Results show that decreasing the first natural frequency is clearly appeared by attaching a mass more than about 1 zg on the CNTs structure. In other words, CNTs can be used to detect particles with mass above 1 zg. Moreover, it is shown that the variation of CTE versus temperature is a critical parameter that influences the vibration and buckling behavior of CNTs-based mass sensors. Increasing temperature leads to decreasing natural frequency due to rising axial forces along the CNTs axis. As a result, the natural frequency approaches to zero when the temperature rises up to the critical buckling temperature. In addition, increase in temperature over the critical buckling temperature changes the mode shape of CNT vibration to the next mode shape.

Multi-Scale Study of Tensile Mechanical Properties of Carbon Nanotube Film under Lateral Loading

In this paper, tensile mechanical properties of carbon nanotube (CNT) film under lateral loading are measured. Comparing with works before, it is found that elastic modulus of CNT film under lateral stretch is higher than that under longitudinal stretch, which is an interesting experimental result. With multi-scale experimental methods including SEM and micro-Raman spectroscopy, the change of CNT bundle network of the film under lateral stretch and axial elongation of CNTs in the loading direction are measured. Based on the experimental results, the control mechanism on difference of lateral and longitudinal mechanical properties of CNT film is analyzed.

Preparation and mechanical properties of CNTs-AlSi10Mg composite fabricated via selective laser melting

Selective laser melting（SLM）exhibits unique advantages in the fabrication of micro- and nano-particle reinforced metal matrix composites. Here, we studied the effect of scan speed on the microstructures and mechanical properties of carbon nanotubes (CNTs) reinforced AlSi10Mg composites printed by SLM. To investigate the effects of CNTs on SLM parts, single track scans, single layer scans and test parts of 1 wt%CNTs/AlSi10Mg were created via SLM. The results indicated that as the scan speed increased, the width of the scan line generally decreased and the height of the scan line generally increased. The mechanical properties of the test parts increased at first but then decreased with increasing scan speed. A laser scan speed of 1300 mm/s produced test parts with the highest mechanical properties: the relative density, hardness and tensile strength were 98.53%, 143.33 HV and 499 MPa, respectively. The hardness increased by approximately 10%, and the tensile strength increased by approximately 20% compared to those values exhibited by the unreinforced AlSi10Mg. The CNTs were detected in the fabricated parts. It was found that the CNTs were distributed along the boundaries of the cells of AlSi10Mg. Some of the CNTs reacted to Al4C3 during the SLM process. The combination of CNTs and Al4C3 created a pining effect, while the CNTs still maintained their tubular structure and played a role in loading; this improved the hardness and strength of the matrix material.

Strengthening carbon nanotube fibers with semi-crystallized polyvinyl alcohol and hot-stretching

The tensile mechanical properties of carbon nanotube (CNT) fiber, which is a one-dimensional assembly of ultra-strong CNTs, are still far short of our expectations. This is mainly due to their high porosity and relatively weak intertube load transfer efficiency. Previous studies have demonstrated that the fiber strength can be enhanced by the infiltration of polymer chains into the fiber. In this work, polyvinyl alcohol (PVA) was pre-infiltrated into loosely packed CNT ribbons, and the composite ribbons were then densified into the fiber form. This enabled a homogeneous dispersion of polymer chains within the CNT fibers. To enhance the mechanical properties of the CNT/PVA composite fibers, isothermal crystallization and ultrasonic treatments were implemented to increase the crystallization of PVA in the ribbon, and the composite fibers were hot-stretched to improve the alignment of both CNTs and PVA chains within the fibers. It was found that the tensile strength and modulus of the final composite fiber were 210% and 193.6% higher than those of the pristine CNT fiber. The structural evolution during these treatments and the mechanism of fiber strengthening were systematically investigated.

Imperfections in carbon nanotubes structure and their impact on the basic mechanical properties

Theoretical and experimental research of nanocomposite materials have shown that usage of carbon nanotubes as a reinforcement, significantly improves the mechanical properties of aforementioned composites. Carbon nanotubes rarely appear in ideal form. Different defects within nanotube structure such as vacancy defects, or waved shape of the nanotube, can greatly influence the mechanical properties of carbon nanotube and thus, decrease the final mechanical properties of carbon nanotube reinforced composites. The paper at hand investigates degradation of basic mechanical properties of single and double walled carbon nanotubes, straight and waved, with different vacancy and topological defects. Also, various nanotube patterns are considered.

Carbon nanotube reinforced titanium composites: An experimental and molecular dynamics study

In this study, the mechanical properties of carbon nanotube reinforced titanium (CNT–Ti) composites have been predicted using molecular dynamics approach. An experimental study was also conducted in which spark plasma sintering was used for preparing the composites. The effect of variation in carbon nanotube volume fraction ( V f), temperature, and strain on the elastic moduli ( E11, E22, and E33) and the shear modulus ( G Reuss) of CNT–Ti composites was studied. The elastic and shear moduli were all found to increase significantly because of the increasing carbon nanotube V f. Even at temperatures approaching 1 K, the CNT–Ti composites show high values of elastic and shear moduli. The elastic moduli tend to attain a constant value at high levels of strain. The results obtained from experiments corroborated the molecular dynamics results.

A hierarchical nano to macro multiscale analysis of monotonic behavior of concrete columns made of CNT-reinforced cement composite

There is an increasing demand for the use of high performance concrete in buildings to reduce significant damage due to extreme loadings. Carbon nanotubes (CNT) with their superior properties are among new materials, which can be used in concrete members. A hierarchical multiscale approach is adopted in this research to obtain the monotonic behavior of CNT-reinforced concrete, noting that, to the best knowledge of the authors, no experimental results are available for its monotonic behavior. At the nano scale, the mechanical properties of carbon nanotubes (CNT) is derived by the molecular dynamics approach. Afterwards, a micromechanical finite element method is adopted at the micro scale to determine the stress-strain curve of CNT-reinforced cement. The whole structure of a concrete sample, including all its major phases, is simulated at the meso scale by the finite element method. Finally, at the macro scale, the monotonic behavior of a concrete column made of CNT-reinforced cement is studied. The results of simulations indicate that by increasing the volume fractions of CNTs, the energy absorption capacity, the curvature ductility and the ultimate moment capacity of the CNT-reinforced concrete columns increase significantly.

Multi-scale Modeling Approach to Predict the Nonlinear Behavior of CNT-reinforced Concrete Columns Subjected to Service Loading

Due to the susceptibility of concrete structures to severe damage under earthquake loading, an increasing demand on high-strength and high performance concrete materials has been arising recently. Among several new materials, carbon nanotubes (CNTs) with their superior mechanical properties are being widely used in construction industry. In this study, a multi-scale method is proposed to identify the mechanical properties of CNT-reinforced concrete columns under monotonic loading. At the nano-scale, the mechanical properties of CNTs are obtained using a molecular dynamics approach. These properties are fed into a larger scale framework to estimate the ultimate tensile and compressive strengths of CNT-reinforced cement paste based on the finite element simulation. Furthermore, the mechanical properties of a concrete sample, including three major phases, cement, aggregate and interfacial transition zone is derived at the meso-scale using finite element simulations. Ultimately, the monotonic behavior of two concrete columns containing ordinary concrete and CNT-reinforced concrete is investigated by OpenSees software. A comparision between the responses of the two columns indicates that, adding CNTs to the concrete columns can increase the key mechanical properties of concrete such as ultimate moment capacity, energy absorption capacity and curvature ductility.

Compacting CNT sponge to achieve larger electromagnetic interference shielding performance

The present study reports a simple route for the synthesis of 3D carbon nanotube (CNT) sponges by vacuum assisted filtration of CNT bundles of variable compaction ratios and its epoxy (EP) composites with superior electromagnetic interference (EMI) shielding performance. The electrical and mechanical properties of CNT sponge/EP composites were investigated and findings enabled identification of a sponge compaction ratio of 70% as optimum for the improvement of the electrical conductivity and EMI shielding effectiveness of the material, by 138 and 41%, respectively, compared to uncompacted samples. Mechanical properties of the composites were also enhanced with the yield strength and elastic modulus of the composite of a compaction ratio of 70% improved by 17 and 25%, respectively compared to pure epoxy. These results indicate that CNT sponge with a higher compaction ratio is a potential filler for mechanically strong and high-performance EMI shielding nanocomposites.

Influence of imperfections on double walled carbon nanotube mechanical properties

The mechanical properties of nanocomposite materials are notably improved with the usage of carbon nanotubes as a reinforcement, according to many theoretical and experimental researches. Since carbon nanotubes rarely appear in ideal form, it is interesting to explore the influence of different defects within nanotube structure, such as vacancies, waved shape, etc., on mechanical properties of carbon nanotube, mainly because it ultimately leads to decline of nanocomposites mechanical properties. The given paper investigates the degradation of the basic mechanical properties of double walled carbon nanotubes. Different double walled carbon nanotubes patterns are considered, with different waviness ratio and vacancy defects.

Investigation of mechanical properties of carbon nanotubes reinforced aluminium composite by metal injection molding

The work presents the metal injection molding (MIM) of carbon nanotubes reinforced aluminium matrix nanocomposite. The paraffin wax (PW), high density polyethylene (HDPE), stearic acid (SA) is used as a binder. Sintering of aluminium is a critical issue in injection molding. The new blind mold cavity sintering method is adopted to impart the strength in the MMC. The surface morphology is observed by the SEM. It is seen that aluminium particles uniformly welded and wide pores are visible in the MMC- Al product. Further the low temperature blind mold sintering helps to retain CNTs in the MMC-Al matrix. This imparts the higher hardness which is comparable with the aluminium alloy. The hardness tests carried out on sintered samples shows the results ranging from 42 to 73 BHN. The pores in these samples tested are in the ranges from 0.25µm to 1.0µm.

Studying The Influence of Various Geometrical Parameters of Single-Walled Carbon Nano-Tubes of ‎Armchair Chirality Type on Its Mechanical Behavior

In the present work, the profound information on the mechanical properties of carbon nano-tubes (CNTs) were presented as an application of nano-technology in nano-materials are being most powerful in the current world. This would focuses/emphasis for designing and optimizing the CNTs based materials. Computational modeling technique was applied and developed to examine the mechanical characteristics for single-walled carbon nano-tube (SWCNT) of armchair chirality type. The atomistic based finite element method (FEM) was used to investigate the influence of various geometrical properties (diameter, wall thickness, and height-to-diameter ratio) of SWCNT armchair of chirality type on Poisson’s ratio and Young’s modulus values. Atomistic based finite element modeling was successfully developed and explored the mechanical behaviour of SWCNT exactly. The results were shown that the investigated geometrical parameters had much influenced on the mechanical properties of SWCNTs.