Distribution Of Carbon Nanotubes Research Articles

Bending Behavior of Sandwich Plates with Aggregated CNT-Reinforced Face Sheets

The main aim of this paper is to investigate bending behavior in sandwich plates with functionally graded carbon nanotube reinforced composite (FG-CNTRC) face sheets with considering the effects of carbon nanotube (CNT) aggregation. The sandwich plates are assumed resting on Winkler-Pasternak elastic foundation and a mesh-free method based on first order shear deformation theory (FSDT) is developed to analyze the deflection of sandwich plates. In the face sheets, volume fraction of CNTs and their clusters are considered to be changed along the thickness. To estimate the material properties of the nanocomposite, Eshelby-Mori-Tanaka approach is applied. In the mesh-free analysis, moving least squares (MLS) shape functions are employed to approximate the displacement field and transformation method is used for imposition of essential boundary conditions. The effects of CNT volume fraction, distribution and degree of aggregation, and also boundary conditions and geometric dimensions are investigated on the bending behavior of the sandwich plates. It is observed that in the same value of cluster volume, FG distribution of clusters leads to less deflection in these structures.

Buckling and postbuckling of axially-loaded CNT-reinforced composite cylindrical shell surrounded by an elastic medium in thermal environment

Buckling and postbuckling behaviors of nanocomposite cylindrical shells reinforced by single walled carbon nanotubes (SWCNTs), surrounded by an elastic medium, exposed to a thermal environment and subjected to uniform axial compression are investigated in this paper. Material properties of carbon nanotubes (CNTs) and isotropic matrix are assumed to be temperature dependent, and effective properties of nanocomposite are estimated by extended rule of mixture. The CNTs are embedded into matrix via uniform distribution (UD) or functionally graded (FG) distribution along the thickness direction. Governing equations are based on Donnell’s classical shell theory taking into account von Karman-Donnell nonlinear terms and interaction between the shell and surrounding elastic medium. Three-term form of deflection and stress function are assumed to satisfy simply supported boundary conditions and Galerkin method is applied to obtain load-deflection relation from which buckling and postbuckling behaviors are analyzed. Numerical examples are carried out to analyze the effects of CNT volume fraction and distribution types, geometrical ratios, environment temperature and surrounding elastic foundation on the buckling loads and postbuckling strength of CNTRC cylindrical shells.

Agglomeration effects on the vibrations of CNTs/fiber/polymer/metal hybrid laminates cylindrical shell

This work studies the agglomeration effect of continuously graded single-walled carbon nanotubes (SWCNTs) on the vibration of SWCNTs/fiber/polymer/metal laminates cylindrical shell. The strain-displacement relations are applied according to the Kirchhoff Love's first approximation shell theory, whereas the dimensionless frequencies of the structure are obtained by means of the beam modal function model. Fiber, carbon nanotubes (CNTs), polymer matrix and metal are four phases constituting the agglomerated CNTs/fiber/polymer/metal laminate (CNTFPML) cylindrical shell. In the first step, we introduce the CNTs randomly within the matrix, such that the volume fraction can be assumed to be continuously graded in the thickness direction. We determine the effect of the CNTs agglomeration on the elastic properties of CNT-reinforced composites, by means of the Eshelby-Mori-Tanaka approach here applied on an equivalent fiber. In the second step, the fiber is introduced as reinforcement phase in the CNT-reinforced composite. Finally, the adhesive fiber prepreg is combined with the thin metal layers. Thus, we study the sensitivity of the vibration behavior of the cylindrical shell to the following input parameters, namely: the CNTs agglomeration and distribution, the mass and volume fractions of the fiber, the boundary condition and lay-ups.

Nonlinear primary and super-harmonic resonances of functionally graded carbon nanotube reinforced composite beams

The nonlinear primary and super-harmonic resonances of functionally graded carbon nanotube reinforced composite (FG-CNTRC) beams under transverse harmonic excitation are studied. Taking into account four different distribution patterns of carbon nanotubes (CNTs), the material properties of FG-CNTRC beams are predicted through the extended rule of mixture. The equations of motion for the transverse, longitudinal and rotational motions are derived from Timoshenko beam theory and von Kármán type of geometric nonlinearity. These nonlinear partial differential equations are reduced into nonlinear ordinary differential equations by the Galerkin method. The discretized equations of motion are solved by using the incremental harmonic balance (IHB) method, resulting in the vibration responses of the nonlinear system. For all the three coupled motions, the frequency response curves of primary, 2 super-harmonic and 3 super-harmonic resonances are constructed. Comparison studies on the dimensionless natural frequencies, nonlinear to linear frequency ratios and numerical simulation of the frequency response are conducted to verify the correctness and accuracy of this study. The numerical results illustrate the influences of CNT distributions, CNT volume fraction, slenderness ratio, dimensionless transverse excitation and damping coefficient on the primary and super-harmonic resonant responses.

Conductive Cellulose based Foam Formed 3D Shapes—From Innovation to Designed Prototype

In this article, we introduce for the first time, a method to manufacture cellulose based electrically conductive non-woven three-dimensional (3D) structures using the foam forming technology. The manufacturing is carried out using a minimum amount of processing steps, materials, and hazardous chemicals. The optimized solution applies a single surfactant type and a single predefined portion for the two main processing steps: (1) the dispersing of nanocellulose (NC) and carbon nanotubes (CNT) and (2) the foam forming process. The final material system has a concentration of the used surfactant that is not only sufficient to form a stable and homogeneous nanoparticle dispersion, but it also results in stable foam in foam forming. In this way, the advantages of the foam forming process can be maximized for this application. The cellulose based composite material has a highly even distribution of CNTs over the NC network, resulting a conductivity level of 7.7 S/m, which increased to the value 8.0 S/m after surfactant removal by acetone washing. Also, the applicability and a design product case ‘Salmiakki’ were studied where the advantages of the material system were validated for a heating element application.

Thermomechanical nonlinear stability of pressure-loaded CNT-reinforced composite doubly curved panels resting on elastic foundations

AbstractNonlinear stability of nanocomposite spherical and cylindrical panels reinforced by carbon nanotubes (CNTs), resting on elastic foundations and subjected to uniform external pressure in thermal environments is investigated in this paper. CNTs are embedded into matrix phase through uniform distribution (UD) or functionally graded (FG) distribution, and effective properties of CNT-reinforced composite are estimated through an extended rule of mixture. Governing equations are based on classical shell theory taking geometrical nonlinearity, initial geometrical imperfection and panel-foundation interaction into consideration. Approximate solutions of deflection and stress functions are assumed to satisfy simply supported boundary conditions and Galerkin method is applied to obtain nonlinear load-deflection relation. Numerical examples show the effects of volume fraction and distribution type of CNTs, in-plane condition of edges, curvature of panel, thermal environments, elastic foundations and imperfection size on the nonlinear response and snap-through instability of the curved panels. The present study reveals that efficiency of CNT distribution type depends on curvature of panel and in-plane behavior of boundary edges, and bifurcation type buckling response of pressure-loaded panels may occur at elevated temperature.

A comprehensive micromechanical analysis of the thermoelastic properties of polymer nanocomposites containing carbon nanotubes with fully random microstructures

A new mixed micromechanics method for a comprehensive analysis of the coefficient of thermal expansion (CTE) of carbon nanotube (CNT)/polymer nanocomposites with fully random microstructures is established. Comparisons between the model results and experiment clearly prove that for a more realistic prediction, considering random orientation and random distribution of CNTs, interphase region created due to the non-bonded van der Waals interactions between the CNT and polymer, non-straight shape and transversely isotropic behavior of CNT is essential in the modeling. The effects of interphase characteristics, geometrical properties and type of random distribution of CNTs on the nanocomposite CTEs are examined.

Stress distributions in nanocomposite sandwich cylinders reinforced by aggregated carbon nanotube

In order to improve the static response of thick hollow cylinders, a sandwich cylinder with two carbon nanotube (CNT)‐reinforced nanocomposite face sheets are proposed in this article. Moreover, due to the use of optimum amount of high cost CNTs, the CNT distribution is suggested to be functionally graded (FG) along the thickness of cylinder. The stress and deflection profiles of the proposed sandwich cylinders subjected to internal and external pressures have been investigated using a finite element method (FEM) based on an axisymmetric model. The significant effect of formation of CNT agglomerations in the surrounded matrix is considered and the material properties of the resulted nanocomposite are estimated by Eshelby‐Mori‐Tanaka approach. Using the developed axisymmetric FEM model, the effects of CNT aggregation state, volume fraction, and distribution as well as geometrical dimension and loading condition on the stress and deflection distributions of the nanocomposite sandwich cylinders have been characterized. The extensive simulations have revealed that instead of adding higher volume fraction of CNT, the selection of suitable distribution for CNTs can lead to a nanocomposite sandwich cylinder with less deflection. POLYM. COMPOS., 40:E1918–E1927, 2019. © 2019 Society of Plastics Engineers

Dynamic instability region analysis of sandwich piezoelectric nano-beam with FG-CNTRCs face-sheets based on various high-order shear deformation and nonlocal strain gradient theory

In this research, the dynamic instability region (DIR) of the sandwich nano-beams are investigated based on nonlocal strain gradient elasticity theory (NSGET) and various higher order shear deformation beam theories (HSDBTs). The sandwich piezoelectric nano-beam is including a homogenous core and face-sheets reinforced with functionally graded (FG) carbon nanotubes (CNTs). In present study, three patterns of CNTs are employed in order to reinforce the top and bottom face-sheets of the beam. In addition, different higher-order shear deformation beam theories such as trigonometric shear deformation beam theory (TSDBT), exponential shear deformation beam theory (ESDBT), hyperbolic shear deformation beam theory (HSDBT), and Aydogdu shear deformation beam theory (ASDBT) are considered to extract the governing equations for different boundary conditions. The beam is subjected to thermal and electrical loads while is resting on Visco-Pasternak foundation. Hamilton principle is used to derive the governing equations of motion based on various shear deformation theories. In order to analysis of the dynamic instability behaviors, the linear governing equations of motion are solved using differential quadrature method (DQM). After verification with validated reference, comprehensive numerical results are presented to investigate the influence of important parameters such as various shear deformation theories, nonlocal parameter, strain gradient parameter, the volume fraction of the CNTs, various distributions of the CNTs, different boundary conditions, dimensionless geometric parameters, Visco-Pasternak foundation parameters, applied voltage and temperature change on the dynamic instability characteristics of sandwich piezoelectric nano-beam.

The Characteristics of LiFePO4/Copper Nanoparticles/Carbon Nanotubes Composites Used as Lithium Ion Battery Cathode

Copper nanoparticles and carbon nanotubes (CNTs) have been used to form a LiFePO4/Cu nanoparticle/CNT (LFP/Cu/CNT) composites and applied as an active material in lithium ion battery cathode. The composites were prepared by mixing commercial LFP powders with a variation of copper nanoparticles and or CNT compositions in a vacuum mixer. The mixture was then applied onto an aluminium foil as a cathode current collector. For the characterization, X-ray diffraction (XRD) was used to confirm the phase, grain size and the presence of the impurities, whereas the morphology of the surface was characterized by using field emission scanning electron microscope equipped with energy dispersive X-ray spectroscopy (FESEM/EDX). The electrical conductivity of this cathode material was tested by using electrochemical impedance spectroscopy (EIS). XRD results showed that the composite has single phase LFP form and that the presence of copper nanoparticles and CNT were not detected in the crystal structure. Morphology and distribution of CNT and copper nanoparticle analysed using FE-SEM/EDX showed mixed materials in the variation of copper nanoparticles and CNTs with homogenous and even distribution of particle size in the range 100-300 nm. The electrical conductivity of LFP increased with the addition of copper nanoparticles at a certain level with 1-order of magnitude, whereas almost 3-order of magnitude with the addition of both copper nanoparticles and CNTs. The addition of CNTs alone, however, is more effective in increasing the conductivity as compared to the addition of copper nanoparticles due to the inevitable formation of secondary phase revealed by the EIS diagrams.

Chiral-selective etching effects on carbon nanotube growth at edge carbon atoms.

Chemical vapor deposition (CVD) utilizing metal cluster nanoparticle catalysts is commonly used to synthesize carbon nanotubes (CNT), with oxygen-containing species such as water or alcohol included in the feedstock for enhanced yield. However, the etching effect of these additives on the growth mechanism has rarely been investigated, despite evidence suggesting that etching potentially affects the chirality distribution of product CNTs. We used quantum chemical methods to study how water-based etchant radicals (OH and H) may enhance the chiral selectivity during CVD growth using CNT cap models. Chemical reactivities of the caps with the etchant radicals were evaluated using density functional theory (DFT). It was found that the reactivities on the cap edges correlate with the chirality of the caps. These results suggest that proper selection of etchant species can provide opportunities for selective chirality control of the product CNTs. © 2018 Wiley Periodicals, Inc.

Enhanced carbon nanotubes dispersion in epoxy matrices using a CNT tailored block copolymer

Carbon nanotubes (CNT) have been extensively studied, and special attention has been given to their introduction in epoxy matrices, for further reinforcement of carbon fibre reinforced composites. However, the obtained improvements are highly dependent on the level of CNT dispersion and distribution. In this work, we report the use of block copolymers (BCPs) as a solution to provide enhanced compatibility of the CNT in an epoxy-based matrix and as means to provide them further nanostructuration. Studied BCPs were especially formulated for epoxy matrices, being one of them customised to also have strong compatibility for CNT. BCPs were added to CNT without introduction of additional solvents. Different formulations were studied and the CNT dispersion, distribution and interaction with matrix were evaluated by rheology, electron microscopy and dynamic mechanical analysis. The results suggest that the customised BCP can have a significant improvement in the dispersion of the CNT, on the adhesion between the polymeric matrix and the CNT and can provide a mean for nanostructuration.

Effect of carbon nanotubes reinforcement on the mechanical properties of alumina and ZTA composites for ballistic application

Abstract Toughened and hardened alumina/carbon nanotubes and zirconia-toughened alumina (ZTA)/carbon nanotubes nanocomposites were developed by conventional ceramics route using pressureless sintering for the ballistic application. The multiwall carbon nanotubes (CNT) were functionalized with nitric acid oxidation reaction. Moreover, the surfactants sodium dodecyl sulphate and gum arabic were used to promote a homogeneous distribution of CNT in the ceramic matrix. Ceramic powders were prepared with pure alumina, alumina with the addition of 20 wt% of tetragonal zirconia/yttria, alumina/CNT and ZTA/CNT with the addition of 0.1 and 0.5 wt% of CNT. The morphology of nanocomposites was characterized by SEM-FEG. The mechanical properties of sintered samples were evaluated by flexural bending, Vickers microhardness and fracture toughness by SEVNB method. The addition of CNT in the ceramic and composite caused a general increase in densification, hardness, flexural strength and fracture toughness. ZTA composite with the addition of 0.1 wt% of CNT yielded the best results.

Flexural and Free Vibration Analysis of CNT-Reinforced Functionally Graded Plate.

This paper examines the effect of uniaxially aligned carbon nanotube (CNT) on flexural and free vibration analysis of CNT-reinforced functionally graded plate. The mathematical model includes expansion of Taylor’s series up to the third degree in the thickness co-ordinate. Since there is a parabolic variation in transverse shear strain deformation across the thickness co-ordinate, the shear correction factor is not necessary. A nine-node two-dimensional (2D) C0 isoparametric element containing seven nodal unknowns per node was developed in the finite element code. The final material properties of CNT-reinforced functionally graded plate are estimated using the extended rule of mixture. The effect of CNT distribution, boundary condition, volume fraction and loading pattern are studied by developing a finite element code. An additional finite element code was developed for the study of the influence of concentrated mass on free vibration analysis of CNT-reinforced functionally graded plate.

Processing and Properties of CNTs/ADC12 Nanocomposite

Carbon nanotubes (CNTs)-reinforced ADC12 nanocomposite was successfully fabricated via casting. The CNTs-Al master alloy was prepared by hot extrusion, and the CNTs were dispersed into the matrix by a high-intensity ultrasonic treatment during the casting process to yield 0.5, 1.0, 1.5 wt.% of the CNTs/ADC12 composite. The key step in arriving at homogeneous distribution of CNTs was preparation of the CNTs-Al master alloy and the introduction of a high-intensity ultrasonic treatment method. The cavitation bubbles that adhered to the aggregated CNTs closed rapidly and released large amounts of energy, which had an impact via the cavitation effect, which made the aggregated CNTs dissociate and disperse homogeneously into the melt. Under the conditions of ultrasonic power of 2.1 kW and ultrasonic time of 10 min, the mean diameter of α-Al was 53.2 μm, which was 58.9% lower than that of the matrix. The microhardness and the ultimate tensile strength (UTS) of nanocomposite with 1.0 wt.% CNTs addition increased by 29.3 and 27%, respectively, as compared with the matrix. CNTs can be dispersed in the matrix homogeneously. It was observed by scanning electron microscope (SEM) that CNTs as a load-bearing element were embedded in the matrix independently, enhancing the mechanical properties. This suggested that the improvement of mechanical properties could be attributed to the size and degree of CNTs clustering, the load transfer from the matrix to the CNTs and the grain refinement of the nanocomposite.

Bending analysis of functionally graded CNT reinforced doubly curved singly ruled truncated rhombic cone

The bending analysis of functionally graded carbon nanotube (CNT) reinforced doubly curved singly ruled truncated rhombic cone is investigated. In this study, a simple C0 isoparametric finite element formulation based on third order shear deformation theory is presented. To characterize the membrane-flexure behavior observed in a CNT reinforced truncated rhombic cone, a displacement field involving higher-order terms in in-plane fields is considered. The proposed kinematics field incorporates for transverse shear deformation and nonlinear variation of the in-plane displacement field through the thickness to predict the overall response of the CNT reinforced truncated rhombic cone in an accurate sense. The material properties of the CNT reinforced truncated rhombic cone are estimated according to the rule of mixture. The present model eliminates the need of shear correction factor and imposed zero-transverse shear strain at upper and lower surface of the truncated rhombic cone. The new feature in present model is simultaneous inclusion of twist curvature in strain field as well as curvature in displacement field that makes it suitable for moderately thick and deep truncated rhombic cone. The proposed new mathematical model is implemented in finite element code written in FORTRAN. The proposed model has been validated with analytical, experimental, and finite element results from the literature. This is first attempt to study bending response of CNT reinforced doubly curved singly ruled truncated rhombic cone. The effect of CNT distribution, boundary condition, loading pattern, and other geometric parameters are also examined.

Ultralight Cellulose Porous Composites with Manipulated Porous Structure and Carbon Nanotube Distribution for Promising Electromagnetic Interference Shielding.

Lightweight conductive polymer composites based on biomass could be a promising candidate for electromagnetic interference (EMI) shielding application. Herein, tailoring porous microstructure and regulating the distribution of carbon nanotubes (CNTs) in cellulose composites are attempts to achieve highly efficient EMI shielding properties accompanying desired mechanical property and low density. Specifically, aligned porous structure is fabricated by ice-template freeze-drying method; meanwhile, CNT is regulated to decorate inside the cellulose matrix (CNT-matrix/cellulose porous composites) or to directly bind over the cellulose cell walls (CNT-interface/cellulose porous composites). It is found that, owing to the preferential distribution of CNT on the cell walls, the CNT-interface/cellulose porous composites possess a very high electrical conductivity of 38.9 S m-1 with an extremely low percolation threshold of 0.0083 vol % with regard to CNT-matrix/cellulose porous composites. Therefore, a shielding effectiveness of 40 dB with merely 0.51 vol % CNT under a thickness of 2.5 mm is achieved in CNT-interface/cellulose porous composites, which is attributed to efficient multiple reflections and the accompanying absorption with promoted conductivity and better-defined porous structure. More laudably, the CNT-interface/cellulose porous composites reveal a superior mechanical property with a specific modulus of 279 MPa g-1 cm3. The value behind the current work is to pave an effective way to fabricate environmentally benign, high-performance EMI shielding materials to practically boost numerous advanced applications of cellulose.

A higher-order free vibration analysis of carbon nanotube-reinforced magneto-electro-elastic plates using finite element methods

This article deals with the free vibration analysis of Carbon Nanotube-reinforced magneto-electro-elastic (CNTMEE) rectangular and skew plates using finite element (FE) methods. The plate kinematics is assumed to follow a higher-order shear deformation (HSDT) theory. The coupled equations of motion are derived with the aid of Hamilton's principle. The material properties of CNTMEE material are estimated using the rule of mixture. The various carbon nanotube (CNT) distribution fashions such as UD, FG-X, FG-O, and FG-V are employed in the present analysis. Further, the FE formulation is extended for skew CNTMEE plates to assess the effect of geometrical skewness on the natural frequencies of the plate. A special emphasize is provided on analyzing the influence of various multi-physical fields such as magnetic, electric and elastic fields on the coupling characteristics of CNTMEE plates. In this article, a detailed parametric study on the effect of boundary conditions, CNT distributions and volume fraction, aspect ratio, length-to-width ratio are considered. The research outcome of this article suggests that these parameters have a significant influence on the coupled free vibration characteristics of CNTMEE plate. It is believed that the results presented in this article may serve as a benchmark in the design and analysis of smart CNTMEE structures for sensors and actuators, energy harvesting application.

Nonlinear buckling of CNT-reinforced composite toroidal shell segment surrounded by an elastic medium and subjected to uniform external pressure

Buckling and postbuckling behaviors of Toroidal Shell Segment (TSS) reinforced by single-walled carbon nanotubes (SWCNT), surrounded by an elastic medium and subjected to uniform external pressure are investigated in this paper. Carbon nanotubes (CNTs) are reinforced into matrix phase by uniform distribution (UD) or functionally graded (FG) distribution along the thickness direction. Effective properties of carbon nanotube reinforced composite (CNTRC) are estimated by an extended rule of mixture through a micromechanical model. Governing equations for TSSs are based on the classical thin shell theory taking into account geometrical nonlinearity and surrounding elastic medium. Three-term solution of deflection and stress function are assumed to satisfy simply supported boundary condition, and Galerkin method is applied to obtain nonlinear load-deflection relation from which buckling loads and postbuckling equilibrium paths are determined. The effects of CNT volume fraction, distribution types, geometrical ratios and elastic foundation on the buckling and postbuckling behaviors of CNTRC TSSs are analyzed and discussed.

A new approach to reinforce the fiber of nanocomposite reinforced by CNTs to analyze free vibration of hybrid laminated cylindrical shell using beam modal function method

This research deals with a study of the free vibration of fiber metal laminate thin circular cylindrical shell reinforced by single walled carbon nanotubes with different boundary conditions. The representative volume element is consisting of four phases: fiber, carbon nanotubes (CNTs), polymer matrix and metal. Initially, the CNTs have been added to the matrix and then the fiber phase has been reinforced by them. Finally, the adhesive fiber prepreg has been combined with the thin metal layers. The generated cylindrical shell can be named CNT/fiber/polymer/metal laminate (CNTFPML) cylindrical shell. In this study, Love's first approximation shell theory has been used to obtain the strain-displacement relations and also, beam modal function model has been utilized to satisfy the governing equations of motion. The effects of mass fraction of CNTs, volume fraction of fiber and metal, axial and circumferential modal numbers, and different distributions of CNTs subjected to different boundary conditions on the vibration of the shell have been considered. In addition, the influences of different lay-ups and different material properties of fiber have been investigated.