Random Distribution Of Carbon Nanotubes Research Articles

A two-dimensional finite element model for Cu-CNT composite: The impact of interface resistances on electrical and thermal transports

Copper (Cu)-carbon nanotube (CNT) composites are considered as potential alternatives for pure Cu based on the theoretical predictions of their superior electrical, thermal, and mechanical properties. However, the conductivities of experimentally synthesized Cu-CNT composites rarely exceed those of Cu primarily due to the large inherent interface resistances. Here, this article presents a two-dimensional (2D) finite element model (FEM) which accounts for the interface resistances both at CNT-CNT and Cu-CNT contacts, random distribution of CNTs, and CNT fractions up to 80%. The model predicts that the high concentration of single-walled CNTs in Cu matrix may enhance the composite electrical and thermal conductivity by up-to ∼5 times at 27℃ only when interface resistances are highly regulated below 1 kΩ and 10−7 m2K/W. The streamlines of electrical current and heat flow reveal that the CNTs serve as an effective conduction medium only with the low levels of interface resistance. This work elucidates the importance of interface resistances for the electrical and thermal transport in Cu-CNT composites.

A multi-scale finite element approach to mechanical performance of polyurethane/CNT nanocomposite foam

Manufacturing and testing of polymer nanocomposites reinforced with nanoparticles is not cost effective due to high costs of nanomaterials and nanoparticles dispersion problems, and is very time consuming. Therefore, predicting the mechanical properties of these materials using finite element methods is a suitable solution. Accordingly, in the present study, multi-scale finite element method considering the random distribution of carbon nanotubes (CNT) in polyurethane foam is developed to investigate the mechanical behavior of these foams. Experimentally examinations under uniaxial compressive load and SEM tests are performed on samples of polyurethane foam reinforced with 2 wt% and 4 wt% carbon nanotubes. In order to consider the realistic assumptions, the interface between the nanotubes with the matrix is simulated using the cohesive zone model, whose parameters are obtained by calibrating the finite element model results with the experimental results of the polyurethane/CNT nanocomposite foam. The results show that the multi-scale finite element model developed in this study shows the good agreement with experimental results. Moreover, with this method simulation of the mechanical behavior of polyurethane foam reinforced with carbon nanotubes with real conditions becomes possible. Hence, it is easy to determine the impact of effective parameters on mechanical properties of these materials. Experimental results show that in comparison with pure foam, by adding 2 wt% and 4 wt% carbon nanotubes to polyurethane foam, the compressive strength of foam is enhanced by 49 % and 82 %, respectively.

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.

A new numerical approach for low velocity impact response of multiscale-reinforced nanocomposite plates

In this paper, the low velocity impact analysis of carbon nanotube (CNT)/carbon fiber (CF)-reinforced hybrid nanocomposite plates is presented using variational differential quadrature (VDQ) method due to its numerical essence and the framework of implementation. The hybrid nanocomposite plate deformation is formulated based on classical plate theory and the contact force between the plate and projectile is estimated using Hertzian contact law. Also, a new micromechanics approach is presented to calculate the effective mechanical properties of the CNT/CF polymer hybrid nanocomposites. Five important factors including, random orientation and random distribution of CNTs, CNT/polymer interphase region, waviness and transversely isotropic behavior of CNT are incorporated in the micromechanical analysis. The accuracy of the present approach is verified with the available open literature results showing a clear agreement. The effects of various factors such as volume fraction and non-straight shape of CNT, CNT/polymer interphase region, CF volume fraction, random and regular arrangement of CFs, plate geometrical parameters and impactor velocity on the low velocity impact behavior of the CNT/CF-reinforced hybrid nanocomposite plates are studied.

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.

Mechanical behavior of carbon nanotubes-based polymer composites under impact tests

This study was focused on the effect of carbon nanotubes on the impact resistance and damage evolution in laminate carbon nanotubes/epoxy composites under an impact loading. The composite panels were made from carbon fibers and carbon nanotubes randomly distributed into epoxy resin. The amount of carbon nanotubes dispersion was varied up to 4% by weight. Taylor impact tests were carried out to obtain the impact response of specimens with dimensions of 70×70×4 mm3. A 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, 7 m/s and 12 m/s. For the experimental test, three velocity levels were used: 3 m/s for the elastic deformation, 7 m/s for the penetration of the impactor and 12 m/s for the perforation of panels. Deformation histories and damage modes in specimens were recorded during the impact test using a high-speed camera. Processing of carbon nanotubes dispersed in laminates, testing, damage, and key findings is reported. It is observed that the impact resistance of laminates reinforced with a random distribution of carbon nanotubes increases up to 15.6% at high-strain rate compared with that of 0% of carbon nanotubes. It is also observed that the resistance to damage initiation and evolution increases with the addition of carbon nanotubes concentration.

Low velocity impact analysis of beams made of short carbon fiber/carbon nanotube-polymer composite: A hierarchical finite element approach

ABSTRACTThe low velocity impact response of beams made of carbon nanotube (CNT)/short carbon fiber (SCF)-reinforced polymer is investigated based on a hierarchical finite element approach. First, the random distribution of CNTs into the polymer matrix is modeled using a three-phase representative volume element (RVE); and the elastic modulus and density of CNT-reinforced polymer are predicted. In the RVE, the interphase region formed due to the interaction between CNTs and the matrix is considered. Then, reinforcement with SCFs is considered, and the elastic properties of SCF-CNT-polymer hybrid composite are obtained. Finally, the low velocity impact response of composite beams is analyzed.

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.

A new micromechanics approach for predicting the elastic response of polymer nanocomposites reinforced with randomly oriented and distributed wavy carbon nanotubes

A comprehensive investigation is carried out into the elastic behavior of carbon nanotube-reinforced polymer nanocomposites using two combined analytical micromechanical methods. A unit cell-based micromechanical method is developed to model the random distribution of carbon nanotubes within the polymer matrix. Also, the Eshelby method is used for modeling the random orientation state of carbon nanotubes within the matrix. Two fundamental aspects affecting the mechanical behavior of carbon nanotube/polymer nanocomposites, including the carbon nanotube waviness and the interphase formed due to the non-boned interaction between the carbon nanotube and the surrounding polymer, are considered in the unit cell method. Comparisons between the results of present method and experimental data reveal that for more realistic predictions, five important factors including, random orientation and random distribution of carbon nanotubes, interphase, waviness and transversely isotropic behavior of carbon nanotube should be considered in the modeling of carbon nanotube-reinforced polymer nanocomposites. The effects of volume fraction, number of waves and waviness factor of carbon nanotube as well as the type of random distribution of CNTs within the matrix on the elastic modulus of the polymer nanocomposites are studied.

Dynamic properties of carbon nanotubes reinforced carbon fibers/epoxy textile composites under low velocity impact

Abstract In this study, the impact response of polymer composites containing a random distribution of carbon nanotubes (CNTs) has been investigated by considering energy profile diagrams and associated force-time curves. The composite consists of CNTs initially filled Epon 862 Epoxy resin and implanted between plies of T300 6k Carbon fiber with 5HS (satin) weave. Different mass fractions of CNTs were used: 0% as reference, 0.5%, 1%, 2% and 4%. 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 7 m/s. Deformation histories and damage modes of specimens were recorded during impact using high-speed camera. The effect of CNTs amount on dynamic properties and damage process was discussed.

Performance analysis for randomly distributed mixed carbon nanotube bundle interconnects

During the recent past, carbon nanotubes (CNTs) have rapidly gained importance in an intensely growing researched area of interconnects. For various reasons, bundled CNTs are often preferred over single-walled CNTs (SWCNTs) or multi-walled CNTs (MWCNTs). However, during fabrication, it is difficult to control the growth of a densely packed bundle having SWCNTs with uniform diameters or MWCNTs with an identical number of shells. Therefore, a realistic CNT bundle is in fact a mixed CNT bundle (MCB) that consists of SWCNTs and MWCNTs. In light of these facts, an analytical model of a MCB that follows the random distribution of CNTs in a bundle is introduced. Depending on the probability of distribution of CNTs having different diameters, a compact multi-conductor transmission line (MTL) and a simplified equivalent single conductor (ESC) model are presented. Encouragingly, the simplified ESC model exhibits an average error of only 2.44% at different interconnect lengths compared with the delay obtained through the MTL approach. Mean diameter and tube density of the MCB are mapped to the ESC model to analyse the propagation delay, power dissipation and crosstalk. Irrespective of interconnect lengths, it is observed that the performances are significantly improved for higher tube density in a MCB.

Studies of nanocomposites of carbon nanotubes and a negative dielectric anisotropy liquid crystal

It has been widely recognized that the combination of carbon nanotube (CNT) and liquid crystals (LCs) not only provides a useful way to align CNTs, but also dramatically enhances the order in the LC phases, which is especially useful in liquid crystal display (LCD) technology. As the measure of this phase behavior, the complex specific heat is presented over a wide temperature range for a negative dielectric anisotropy alkoxyphenylbenzoate liquid crystal (9OO4) and CNT composites as a function of CNT concentration. The calorimetric scans were performed under near-equilibrium conditions between 25 and 95 °C, first cooling and then followed by heating for CNT weight percent ranging from ϕ(w) = 0 to 0.2. All 9OO4/CNT mesophases have transition temperatures ~1 K higher and a crystallization temperature 4 K higher than that of the pure 9OO4. The crystal phase superheats until a strongly first-order specific heat feature is observed, 0.5 K higher than in the pure 9OO4. The transition enthalpy for the nanocomposite mesophases is 10% lower than that observed in the pure 9OO4. The strongly first-order crystallization and melting transition enthalpies are essentially constant over this range of ϕ(w). Complementary electroclinic measurement on a 0.05 wt. % sample, cooling towards the smectic-C phase from the smectic-A, indicates that the SmA-SmC transition remains mean-field-like in the presence of the CNTs. Given the homogeneous and random distribution of CNTs in these nanocomposites, we interpret these results as arising from the LC-CNT surface interaction pinning the orientational order uniformly along the CNT, without pinning the position of the 9OO4 molecule, leading to a net ordering effect for all phases. These effects of incorporating CNTs into LCs are likely due to "anisotropic orientational" coupling between CNT and LC, the change in the elastic properties of composites and thermal anisotropic properties of the CNTs.

Parameters influencing the stiffness of composites reinforced by carbon nanotubes – A numerical–analytical approach

Due to their high stiffness and strength, as well as their electrical conductivity, carbon nanotubes are under intense investigation as fillers in polymer matrix composites. The nature of the carbon nanotube/polymer bonding and the curvature of the carbon nanotubes may strongly reduce the reinforcing effect of the carbon nanotubes when added to a matrix to create composites. Here the effects of carbon nanotube waviness and the interaction with the matrix on the stiffness of the composite are investigated. Using a mixed numerical–analytical model, a parametric study of the waviness and volume fraction influence of CNTs on the elastic behavior of the nanocomposite is presented. The model used allows to predict the elastic properties of carbon nanotube (CNT)/polymer composites containing a random distribution of CNTs. This hybrid approach is a significant advance over micromechanical modeling and can be applied to all nanostructured composites.

A numerical-analytical model for the characterization of composites reinforced by carbon nanotubes

A mixed model, numerical-analytical, is presented that allows one to predict the elastic properties of carbon nanotube (CNT)/polymer composites containing a random distribution of CNTs, while taking account of the curvature that they show when immersed in the polymer. This hybrid approach is a significant advance over micromechanical modeling and can be applied to all nanostructured composites.