Distribution Of Carbon Nanotubes Research Articles

Thermomechanical nonlinear analysis of axially compressed carbon nanotube-reinforced composite cylindrical panels resting on elastic foundations with tangentially restrained edges

ABSTRACTBuckling, postbuckling, and nonlinear responses of composite cylindrical panels reinforced by single-walled carbon nanotubes (CNTs), supported by an elastic foundation, exposed to elevated temperature and axially compressed by uniform load are investigated in this article. Distribution of CNTs is uniform or graded in the thickness direction and the effective properties of CNT-reinforced composite are assumed to be temperature dependent, and are estimated by extended rule of mixture through a micromechanical model. Governing equations are established based on thin shell theory taking von Kármán–Donnell nonlinearity, initial geometrical imperfection, Pasternak-type elastic foundation and tangential elastic constraints of boundary edges into consideration. Approximate solutions of deflection and stress functions are assumed to satisfy simply supported boundary conditions, and Galerkin method is applied to derive explicit expressions of load–deflection relation from which critical buckling loads can be obtained. Unlike works in the literature, the present study accounts for elasticity of tangential restraint of two unloaded straight edges in model of cylindrical panel. The study also gives conditions for which bifurcation type buckling response can occur and novel findings in numerical examples.

Effect of physical and geometrical parameters on low-velocity impact response of sandwich beams with carbon nanotube reinforced face sheets

The response of sandwich beam with carbon nanotube (CNT) reinforced composite face sheets and soft core when subjected to the action of an impacting mass is analysed theoretically. Contact force between the impactor and the beam is obtained using the conventional Hertz law. The field equations are derived via the Ritz based applied to the total energy of the system. The solution is obtained in the time domain by implementing the well-known Runge–Kutta method. After examining the validity of the present solution, the effects of distribution of CNTs, nanotube volume fraction, core-to-face sheet thickness ratio, initial velocity of the impactor and the impactor mass are studied in detail. Finally, it is concluded that, the highest peak contact force and the lowest indentation of the top face sheet belong to the sandwich beam with V-distribution figure of face sheet, followed by the uniformly distributed and Λ-ones, respectively. Keywords: Carbon nanotube fibers, sandwich beam, soft core.

Effect of functionalized process and CNTs aggregation on fracture mechanism and mechanical properties of polymer nanocomposite

There is no doubt about the importance of the mechanical properties of polymer nanocomposite reinforced by carbon nanotubes (CNTs) in terms of the exclusive characteristics of both polymer and CNTs. The mechanical performance of carbon nanotubes/polymer nanocomposite (CPNC) depends on several uncertainties such as CNTs’ structural defects and covalent bonds created during functionalized process, CNTs’ distribution, curvature, waviness, aggregation, and polymer net properties. To cover all of the mentioned effective parameters, a multiscale method is defined in which CNTs’ structure and interfacial phase are studied in a nanoscale model and CNTs’ distribution, curvature, and aggregation are studied in a microscale model. According to the neat polymer's properties, both increase and decrease in CNTPN's strength are possible by variations in CNTs curvature, waviness, distribution, and aggregation. Moreover, in CNTs’ functionalization process, CNTPN's ultimate strength and material brittleness are increased and decreased, respectively. But, Young's modulus of nanocomposite is decreased according to the presence of CNT's structural defects created during the functionalization process. Additionally, the improving effect of functionalization process is significantly decreased by increasing the curvature of CNTs, and the functionalized CNTs polymer nanocomposite's (FCPNC) ultimate strength is close to the intact CNTs polymer nanocomposite's (ICPNC's) strength properties. CNTs’ aggregation has also an adverse effect on Young's modulus and changes the fracture mechanism.

Free vibration analysis of carbon nanotube reinforced composite Timoshenko beam

The paper deals with the free vibration analysis of nano-composite beams. The nano-composite beams are a combination of single walled carbon nano-tubes (SWCNT) as reinforcement fibre and are dispersed in the epoxy matrix. Material properties of the resulting nano-composite material are extracted using the Timoshenko beam theory. Finite element method (FEM) is employed to solve the governing equations of motion. The effect of various parameters such as boundary conditions, carbon nanotube (CNT) volume fraction, slenderness ratio and the distribution of nano-material on the natural frequency of the composite structure are studied and presented. The obtained results reveal that CNT volume fraction and distribution have substantial effect on the properties of the nano-composite beam.

Free vibration analysis of carbon nanotube reinforced composite Timoshenko beam

The paper deals with the free vibration analysis of nano-composite beams. The nano-composite beams are a combination of single walled carbon nano-tubes (SWCNT) as reinforcement fibre and are dispersed in the epoxy matrix. Material properties of the resulting nano-composite material are extracted using the Timoshenko beam theory. Finite element method (FEM) is employed to solve the governing equations of motion. The effect of various parameters such as boundary conditions, carbon nanotube (CNT) volume fraction, slenderness ratio and the distribution of nano-material on the natural frequency of the composite structure are studied and presented. The obtained results reveal that CNT volume fraction and distribution have substantial effect on the properties of the nano-composite beam.

A new quasi-3D higher shear deformation theory for vibration of functionally graded carbon nanotube-reinforced composite beams resting on elastic foundation

This study deals with free vibrations analysis with stretching effect of nanocomposite beams reinforced by single-walled carbon nanotubes (SWCNTs) resting on an elastic foundation. Four different carbon nanotubes (CNTs) distributions including uniform and three types of functionally graded distributions of CNTs through the thickness are considered. The rule of mixture is used to describe the effective material properties of the nanocomposite beams. The significant feature of this model is that, in addition to including the shear deformation effect and stretching effect it deals with only 4 unknowns without including a shear correction factor. The governing equations are derived through using Hamilton\'s principle. Natural frequencies are obtained for nanocomposite beams. The mathematical models provided in this paper are numerically validated by comparison with some available results. New results of free vibration analyses of CNTRC beams based on the present theory with stretching effect is presented and discussed in details. The effects of different parameters of the beam on the vibration responses of CNTRC beam are discussed.

Nonlinear Forced Vibration Analysis of FG-CNTRC Cylindrical Shells Under Thermal Loading Using a Numerical Strategy

Employing an efficient numerical strategy, the nonlinear forced vibration analysis of composite cylindrical shells reinforced with single-walled carbon nanotubes (CNTs) is carried out. It is assumed that the distribution of CNTs along the thickness direction of the shell is uniform or functionally graded and the temperature dependency of the material properties is accounted. The governing equations are presented based on the first-order shear deformation theory along with von-Karman nonlinear strain-displacement relations. The vectorized form of energy functional is derived and directly discretized using numerical differential and integral operators. By the use of variational differential quadrature (VDQ) method, discretized nonlinear governing equations are obtained. Then, the time periodic differential operators are applied to perform the discretization procedure in time domain. Finally, the pseudo-arc length continuation method is employed to solve the nonlinear governing equations and trace the frequency response curve of the nanocomposite cylindrical shell. A comparison study is first presented to verify the efficiency and validity of the proposed numerical method. Comprehensive numerical results are then given to investigate the effects of the involved factors on the nonlinear forced vibration characteristics of the structure. The results show that the changes of fundamental vibrational mode shape have considerable effects on the frequency response curves of composite cylindrical shells reinforced with CNTs.

Thermal Buckling of Nanocomposite Stiffened Cylindrical Shells Reinforced by Functionally Graded Wavy Carbon Nanotubes with Temperature-Dependent Properties

We study the thermal buckling behavior of cylindrical shells reinforced with Functionally Graded (FG) wavy Carbon NanoTubes (CNTs), stiffened by stringers and rings, and subjected to a thermal loading. The equilibrium equations of the problem are built according to the Third-order Shear Deformation Theory (TSDT), whereas the stiffeners are modeled as Euler Bernoulli beams. Different types of FG distributions of wavy CNTs along the radial direction of the cylinder are herein considered, and temperature-dependent material properties are estimated via a micromechanical model, under the assumption of uniform distribution within the shell and through the thickness. A parametric investigation based on the Generalized Differential Quadrature (GDQ) method aims at investigating the effects of the aspect ratio and waviness index of CNTs on the thermal buckling of FG nanocomposite stiffened cylinders, reinforced with wavy single-walled CNTs. Some numerical examples are here provided in order to verify the accuracy of the proposed formulation and to investigate the effects of several parameters—including the volume fraction, the distribution pattern of wavy CNTs, and the cylinder thickness—on the thermal buckling behavior of the stiffened cylinders made of CNT-reinforced composite (CNTRC) material.

Carbon nanotube immobilized membrane with controlled nanotube incorporation via phase inversion polymerization for membrane distillation based desalination

Abstract In this paper, we present an optimized method for carbon nanotube immobilization on membrane surface for seawater desalination via direct contact membrane distillation (DCMD). Carbon nanotube immobilized membranes (CNIM) are fabricated via phase inversion technique using a controlled approach for carbon nanotube (CNT) incorporation which provides additional pathways for water vapor diffusion. Surface morphology differed for membranes fabricated with varying PVDF concentrations which altered the CNT distribution and its interaction with water vapor. The water vapor flux by CNIM membrane was as high as 51.4 L/m2 hr, which was 76% higher than the unmodified support membrane at 60 °C. No significant salt leakage was observed with modified membrane. The overall mass-transfer coefficient for phase inversion membrane was nearly 1.8 times higher than unmodified membrane.

Probabilistic mechanical properties and reliability of carbon nanotubes

Carbon nanotubes (CNTs) and their products such as polymer nanocomposite (PNC) are an undeniable part of future materials. To use such future materials, it is necessary to have an accurate evaluation of their properties. Several uncertainties such as structural defects and their distributions cause change in the properties of CNTs that could be considered probabilistic variables. A novel procedure is presented for evaluating CNTs’ probabilistic fracture properties and structural reliability using stochastic finite element methods. By employing two dimensionless parameters, both types of Stone–Wales 5-7-7-5 defects are randomly applied to CNTs. Section defect density and critical section defect density are defined and used to manage the distribution and geometrical configuration of CNTs’ structural defects. A probabilistic method is used to evaluate the effect of defects’ distribution on Young's modulus, ultimate strain, and ultimate stress. It has been observed that normal and Weibull distribution functions are suitable for describing Young's modulus distribution and ultimate stress distribution, respectively. Defect density ratio is defined and, using this parameter, the effect of aggregated defects on mechanical properties is evaluated. It is demonstrated that the defects out of critical section have an unavoidable effect on Young's modulus and ultimate strain; but they have an insignificant effect on ultimate stress. A reliability analysis is performed on armchair (15,15) CNTs and it is investigated that the reliability of CNTs depends on critical defect density significantly. In addition, the reliability is equal to one for the stress of less than 50GPa and this value is equal to zero for the stress of higher than 100GPa, independent from the changes of critical defect density. Eventually, a procedure is described to estimate the reliability of armchair CNTs using critical defect density and the results’ accuracy is discussed and evaluated.

An exact solution for the free-vibration analysis of functionally graded carbon-nanotube-reinforced composite beams with arbitrary boundary conditions

We present an exact method to model the free vibration of functionally graded carbon-nanotube-reinforced composite (FG-CNTRC) beams with arbitrary boundary conditions based on first-order shear deformation elasticity theory. Five types of carbon nanotube (CNT) distributions are considered. The distributions are either uniform or functionally graded and are assumed to be continuous through the thickness of the beams. The displacements and rotational components of the beams are expressed as a linear combination of the standard Fourier series and several supplementary functions. The formulation is derived using the modified Fourier series and solved using the strong-form solution and the weak-form solution (i.e., the Rayleigh–Ritz method). Both solutions are applicable to various combinations of boundary constraints, including classical boundary conditions and elastic-supported boundary conditions. The accuracy, efficiency and validity of the two solutions presented are demonstrated via comparison with published results. A parametric study is conducted on the influence of several key parameters, namely, the L/h ratio, CNT volume fraction, CNT distribution, boundary spring stiffness and shear correction factor, on the free vibration of FG-CNTRC beams.

Carbon nanotubes reinforced copper composite with uniform CNT distribution and high yield of fabrication

Dispersion of carbon nanotubes (CNTs) in metal matrix composites has been an unsolved issue since the discovery of CNTs. This paper presents a newly developed fabrication process of bulk Cu/CNT composite with uniformly distributed CNTs. That is, copper encapsulated CNTs powders were firstly fabricated by an electrochemical deposition where CNTs can be completely dispersed in the copper electrolyte assisted by sonication, and then the fabricated composite powders were used to make bulk Cu/CNT composite by a powder metallurgy process. The increment in microhardness of Cu/CNT composite after compaction and sintering was observed to be ~47.6% per 1% CNTs. The developed fabrication process of Cu/CNT composite powders by electrochemical co-deposition can be scaled up to meet specific application needs, and a similar process is expected to be applicable for other metals.

Large amplitude vibration of FG-CNT reinforced composite annular plates with integrated piezoelectric layers on elastic foundation

The aim of the present study is to investigate the applications of piezoelectric layers and carbon nanotubes (CNTs) in enhancing nonlinear vibration behaviors of functionally graded carbon nanotube reinforced composite (FG-CNTRC) annular plates. A nonlinear formulation is developed with regard to the first-order shear deformation theory, von Karman geometrical nonlinearity in conjunction with the Hamilton principle. A Pasternak elastic foundation is assumed to be in contact with the annular plate during deformation. The distribution of electric potential across the thickness of piezoelectric layers is simulated via a combination of sinusoidal and linear functions. Both closed and open circuit electrical boundary conditions are taken into account for the bottom and top surfaces of piezoelectric layers. Generalized differential quadrature method is utilized to discretize the nonlinear equations of motion, Maxwell equation and boundary conditions, and then direct iterative method is used to solve the nonlinear system of equations. An extensive parametric study is directed to provide an insight into effects of the thickness of piezoelectric layers, piezoelectric materials, volume fraction and distribution of CNTs, geometrical parameters, elastic foundation coefficient, and mechanical/electrical boundary conditions on the nonlinear dynamic responses of the annular plate. It is found that both distribution and volume fraction of CNTs have a remarkable effect on nonlinear natural frequencies of FG-CNTRC annular plates. It is also revealed that the type of piezoelectric materials, thickness of piezoelectric layers and electrical boundary condition play a pivotal role in improving dynamic responses of FG-CNTRC annular plates. It is also found that presence of elastic foundation increases hardening responses of FG-CNTRC annular plates.

Co-production of hydrogen and carbon nanotubes from the decomposition/reforming of biomass-derived organics over Ni/α-Al2O3 catalyst: Performance of different compounds

Four types of biomass-derived organics (toluene/1-methylnaphthalene/phenol/ethanol) were catalytically decomposed and steam reformed over Ni/α-Al2O3 for co-production of hydrogen and carbon nanotubes (CNTs). In the decomposition reaction, the oxygen functional group in phenol and ethanol promoted the co-production of hydrogen and CNTs, while a small amount of toluene and 1-methylnaphthalene were cracked to hydrogen and amorphous carbon. In the reforming reaction, the yields of hydrogen and CNTs sharply increased. More than 2000mmol/(g-cata∗h) of H2 and 260mg/(g-cata∗h) of CNTs were produced after the reforming of toluene and ethanol. However, 1-methylnaphthalene was difficult to be reformed and small amount of CNTs were formed. The organics with low molecular weight and low degree of unsaturation conduced to the formation of hydrogen and CNTs. The growth of CNTs on Ni/α-Al2O3 mainly follows the tip-growth mechanism. The diameter distribution of CNTs is not only influenced by Ni particle size, but also related to the different organics and steam addition.

Multi-functionality of carbon nanotubes reinforced 3 mol% yttria stabilized zirconia structural biocomposites

The effect of the addition of carbon nanotubes (CNT) on the densification, microstructural, mechanical, wear performance and biocompatibility of 3mol% yttria stabilized zirconia (3YSZ) have been investigated in the present study. The retention of high temperature phases (tetragonal and cubic) was found to increase with CNT addition in 3YSZ. Enhancement in the mechanical properties (hardness and elastic modulus) with CNT reinforcement is attributed to the refinement of grain size, enhanced densification and homogeneous distribution of CNT (up to 6vol%). Correspondingly, fracture toughness increased from 5MPam1/2 (in 3YSZ) to 10.1MPam1/2 with CNT reinforcement (for 12vol%) through energy dissipating mechanisms such as crack branching, CNT bridging, and crack-deflection, evidenced by the fractographs of 3YSZ-CNT composites. The toughening contribution with CNT reinforcement is observed to dominate over that of t→m transformation up to 38 times, evaluated using a modified fractal model. However, this effectiveness decreased with CNT agglomeration. The physical damage in the bacterial cell is observed to increase with CNT addition. The present findings promote 3YSZ-CNT as an optimal structural and antibacterial multifunctional biomaterial.

Postbuckling analysis of smart FG-CNTRC annular sector plates with surface-bonded piezoelectric layers using generalized differential quadrature method

The purpose of the present study is to introduce the application of carbon nanotubes (CNTs) and piezoelectric layers in suppressing the postbuckling deflection of functionally graded carbon nanotube reinforced composite (FG-CNTRC) annular sector plates. To achieve this objective, a structural model is developed based on the first-order shear deformation theory (FSDT) along with the von Karman geometrical nonlinearity. The distribution of electric potential across the thickness of piezoelectric layers is modeled by a combination of linear and sinusoidal functions and the closed circuit electrical boundary condition is taken into account for the top and bottom surfaces of the piezoelectric layers. Generalized differential quadrature method (GDQM) is implemented to discretize the nonlinear stability equations, boundary conditions and Maxwell equation. The nonlinear system of equations is solved via a direct iterative method. A detailed parametric study is conducted to explore effects of geometrical parameters, boundary conditions, piezoelectric materials, thickness of the piezoelectric layers, external electric voltage, CNT distribution, and volume fraction on the postbuckling responses of FG-CNTRC annular sector plates with surface-bonded piezoelectric layers. Results indicate that both volume fraction and distribution of CNTs play a key role in enhancing the postbuckling strength of CNTRC annular sector plates. It is found that the type of piezoelectric materials, thickness of piezoelectric layers and the external electric voltage have a significant effect on suppressing the postbuckling deflection of FG-CNTRC annular sector plates. It is also found that the distribution of CNTs plays a pivotal role in changing buckling mode shapes of CNTRC annular sector plates. Besides, the proposed solution procedure has shown clear advantages over existing methods and demonstrated itself as a general, stable and accurate numerical method in solving strongly coupled nonlinear partial differential equations.

Effect of carbon nanotube concentration on cooling behaviors of oil-based nanofluids during the immersion quenching

Oil-based nanofluids including 0.75%—1.75% (mass fraction) carbon nanotubes (CNTs) without any surfactants have been synthesized by a two-step process. The probes machined from 45# steel with 22mm diameter and 50mm length are quenched in the as-synthesized CNT nanofluids for testing the cooling behaviors of the nanofluids. The laser diffraction particle size analyzer, scanning electronic microscope (SEM), X-ray diffractometer and transmission electron microscope (TEM) are used to characterize the quality and distribution of CNTs in the nanofluids. The wettability and viscosity of 30# oil and oil-based CNT nanofluids are measured by a goniometer at 15 ◦C and a rotational type viscometer at 40 ◦C, respectively. The results show that the cooling efficiency of the oil-based CNT nanofluids is better than that of 30# oil. Moreover, the cooling rate of the naonofluids increases with the further increase of the CNT concentration. When the mass fraction of CNTs increases to 1.75%, the cooling rate of the naonofluids reaches a maximum at 760 ◦C and it is increased by 77.8% as compared to that of base oil. The improved cooling rate of oil by CNTs is mainly due to the uniform distribution and excellent thermal conductivity of CNTs.

Experimental Study and Numerical Modelling of Low Velocity Impact on Laminated Composite Reinforced with Thin Film Made of Carbon Nanotubes

In this work, polymer laminated composites based on Epon 862 Epoxy resin, T300 6 k carbon fibers and carbon nanotubes (CNTs) were tested with the aim to elucidate the effect of CNTs on impact properties including impact force and capacity to absorb impact energy. The polymer matrix was reinforced by a random distribution of CNTs with fraction ranging from 0.5 to 4.wt%. Composite panels were manufactured by using the infusion process. Taylor impact test was used to obtain the impact response of specimens. Projectile manufactured from a high strength and hardened steel with a diameter of 20 mm and 1.5 kg of mass was launched by a compressed gas gun within the velocity of 3 m/s. Impact force histories and absorbed energy of specimens were recorded. A numerical model was employed to simulate the impact performance. This model has been accomplished by forming a user established subroutine (VUMAT) and executing it in ABAQUS software. Finally, the effect of CNTs amount on dynamic properties of laminated composites was discussed.

Carbon nanotube based polyvinylalcohol-polyvinylpyrolidone nanocomposite hydrogels for controlled drug delivery applications

Controlled drug release systems present a significant alternative to the conventional drug dosages providing drug release for prolonged time periods. Nanocomposite hydrogels offer an important potential for drug release with enhanced physicochemical properties. In this study, the preparation of carbon nanotube (CNT)-based Polyvinylalcohol-Polyvinylpyrolidone (PVA/PVP) nanocomposite hydrogels namely, CNT-25, CNT-50 and CNT-100 were succedded via the freeze/thawing method with the addition of different amounts of CNT. The nanocomposite hydrogels were characterized by swelling tests, FT-IR, DSC, SEM and BET measurements. It was determined that CNT-50 was the most suitable hydrogel for drug release studies having better morhological properties with homogenous distribution of CNT throughout the polymeric nanocomposite matrix. The release of 5-fluororacil (5-FU) as a model drug was investigated in-vitro. The release of 5-FU from CNT-based PVA/PVP nanocomposite hydrogels was exhibited controlled release for one week at pH 7.4. The amount of released of 5-FU was effectively increased with the addition of CNT into the hydrogel matrix. Korsmeyer-Peppas model was well fitted for determining the release mechanism of 5-FU from CNT-based PVA/PVP nanocomposite hydrogels corresponding the combination of diffusion of the drug and the dissolution of polymer chains.

Static and free vibration analysis of functionally graded conical shells reinforced by carbon nanotubes

This study investigates the static and free vibration behavior of rotating functionally graded (FG) truncated conical shells reinforced by carbon nanotubes (CNTs) with a gradual distribution of the volume fraction through the thickness. CNTs are here selected as reinforcement, because of their noteworthy physical and chemical properties, together with their ability to enhance the mechanical properties of the whole composite structure. A two-parameter agglomeration model is considered to describe the micromechanics of such particles, which tend to agglomerate into spherical regions when scattered in a polymer matrix. From the macro-mechanical point of view, the conical structures are characterized by a gradual variation of their mechanical properties along the thickness direction, since different distributions are explored to describe the volume fraction of the reinforcing phase. The governing equations of motion for the rotating truncated composite conical shells are derived and solved numerically by means of the Generalized Differential Quadrature (GDQ) method combined with the third-order shear deformation theory (TSDT) in small deformations. The GDQ approach has recently emerged as a very promising numerical tool to solve complex problems without passing through any variational formulation, but solving directly the equations of motion in a strong form. In this paper, a parametric study based on the GDQ is systematically performed to exploit the effect of some geometry parameters, i.e. the length, the radius, the thickness and the semi-vertex angle of the cone, as well as the different distribution of CNTs along the thickness, on the frequency at different circumferential wave numbers and rotating speeds. A convergence study of the numerical results is also made in terms of deflection and stress distributions of the structure, which proves the efficiency of the GDQ approach, also for coarse mesh discretizations in the meridional direction.