جستجوی مقالات مرتبط با کلیدواژه "نانولوله ی کربنی" در نشریات گروه "مکانیک"

The use of empirical and semi-empirical models to model the properties of nano composites to predict mechanical properties and failure leads to cost and time reduction and optimal design. In this study, discontinuous (short) fiber models were used to model the mechanical properties and fracture behavior of carbon nanotube reinforced polymer nanocomposites with volume fractions of 0.5%, 0.75%, and 1%. In previous studies, the discontinuous fiber model was used to determine the macro scale properties of composites reinforced with discontinuous fibers. In this study, a model that considers the geometric similarity between short fibers and nanotubes was used. Using this model and the model of random distribution of nanotubes in the epoxy matrix, simulations were performed using the Python programming language and the mechanical properties and fracture behavior were investigated at the Nano and mesoscales.

This paper discusses the nonlinear dynamic behavior of nanocomposite microplates reinforced with carbon nanotubes in contact with static fluids. Equations of motion are derived using the first-order shear deformation theory of plates and considering the size effects and large deformations. Effective mechanical properties are determined by applying the law of mixtures. By use of the Galerkin method, the nonlinear equations governing motion are discretized and the numerical solution is obtained. The results have been verified and the effect of micro-plate geometrical characteristics, small size parameter, fluid height and weight fraction of the carbon nanotubes studied on natural linear and nonlinear frequencies and the dynamic response has been evaluated. The results indicate that the natural frequency of the system decreases with increasing fluid height. The reinforcement of microplates by carbon nanotubes also results in a softening of the stiffening behavior of the spring and a substantial bending of the response curve. Depending on the excitation frequency, this bending may result in jump instability. By examining the time response, phase, and Poincaré map of the system, periodic, quasi-periodic, and chaotic vibration behavior can be observed.

In the recent years, superhydrophobic coatings have attracted considerable research atention due to their excellent properties and wide practical applications. In the present study, the surface of nickel-carbon nanotube composite coating was modified by two methods A) Increasing the roughness, and B) Modification with low-surface-energy material(Stearic Acid = SA). The morphology, wetting angle and corrosion resistance of the prepared coatings were examined by field emission scanning electron microscop (FESEM), contact angle measuring instrument and potentiostat, respectively. The results showed that the contact angle of the 4 microliter water drop on the composite coating modified with SA reached 157 degrees, which indicates the superhydrophobicity of the coating. The current density and corrosion rate of the SA modified coating showed a reduction of more than 97% compared to the highly roughness coating. It was concluded that, the presence of the SA in super hydrophobic coating can act as a barrier against the penetration of corrosive ions through the coating and consequently can reduce the corrosion rate.

In this article, the Mori-Tanaka micromechanical approach is used to obtain the elastic and piezoelectric properties of a hybrid composite with a polyamide matrix and reinforced with piezoelectric particles of lead zirconate titanate and carbon nanotubes. Modeling consists of two steps, first, the effect of carbon nanotube distribution in the polyamide matrix is calculated, In the next step, the obtained results were used to calculate the addition of piezoelectric particles. The model has been validated with experimental results and previous studies. the increase in the volume fraction of piezoelectric particles causes an increase in the elastic and shear moduli and piezoelectric constants. Modeling for uniform and non-uniform distribution of carbon nanotubes has been done. The results show that by adding carbon nanotubes, the elastic moduli and piezoelectric constants increase. Also, the agglomeration of carbon nanotubes reduces these modules.

In the present study, the effect of adding carbon nanotubes on the tensile and flexural behavior of basalt fiber reinforced epoxy composites was investigated. In the first step, in order to better interact the nanotubes with the epoxy surface, their surface modification was performed. Surface-modified carbon nanotubes were applied at different weight percentages relative to the matrix (0.1%, 0.3%, and 0.5%) and then the resulting mixtures were used as a matrix in the fabrication of basalt fiber-reinforced composites. In order to investigate the effect of adding carbon nanotubes on the mechanical behavior of composites, three-point tensile and flexural tests were performed on them. The results show that, firstly, the highest effectiveness of surface-modified carbon nanotubes on tensile and flexural strength is obtained in composites containing 0.3% by weight. Secondly, the positive effect of carbon nanotubes in a certain amount on flexural strength is greater than the effect of the same amount on the improvement of tensile strength. Energy was obtained in a sample containing 0.3% by weight.

In this research, buckling of polymer matrix composite plates containing unidirectional glass fibers under in-plane pressure load is investigated. Moreover, the effect of adding carbon nanotubes as reinforcement into the matrix material on the critical buckling load of composite plates is studied. Using hand lay-up method, rectangular glass/epoxy composite plates with and without carbon nanotubes were fabricated. 0.25, 0.5 and 1.0 weight percent of carbon nanotubes were added to the epoxy resin and composite plates were subjected to the longitudinal in-plane pressure load. The plates were tested under fix ended boundary conditions utilizing Instron hydraulic universal testing machine. Based on the results, adding 0.5 weight percent of carbon nanotubes has the most influence on the critical buckling load of the plates. Results show that adding 0.5 weight percent of carbon nanotubes into the matrix material increases the critical buckling load of the carbon nanotubes /glass/epoxy plate more than two times with respect to that of glass/epoxy composite plate. Furthermore, when the carbon nanotubes weight percent reaches 1 %, because of carbon nanotubes agglomeration, carbon nanotubes are not dispersed well into the epoxy resin and the critical buckling load of the composite plate decreases. To validate the results, buckling analysis of glass/epoxy composite plate was done in Abaqus finite element software. Finite element models confirm the experimental results obtained.

In this research, an approach based on the isogeometric method is developed to study the free vibration behavior of functionally graded carbon nanotubes reinforced composite skew folded plates. In this method, non-uniform rational B-splines basis functions are used for approximation of the geometry as well as the displacement field. The plates are reinforced by single-walled carbon nanotubes which are assumed to be graded through the thickness direction with different distribution patterns. The effective mechanical properties of composite skew folded plates are captured by the modified rule of mixtures approach. Modeling of the skew folded plate is accomplished by two non-uniform rational B-splines patches which is one of the strengths of the research. The equations of motion of each patch are derived based on classical plate theory and then are discretized using non-uniform rational B-splines basis functions. The final form of the discretized equations is generated after the transformation of the element matrices of each patch and then applying the continuity conditions along the boundary of the patches with the aid of the bending strip method. Afterward, several numerical examples are provided to prove the accuracy and reliability of the proposed formulation. The results exhibit that the present approach can precisely predict the natural frequencies of skew folded plates with a low computational cost. Eventually, a set of new results are presented for different geometrical and material parameters of the skew folded plate.

In this paper, the free vibrations of a composite cylindrical grid shell reinforced with carbon nanotubes are investigated. Equilibrium equations are derived based on first-order shear deformation theory. The orientation of carbon nanotubes is assumed to be uniaxial in the direction of the assumed thickness and the elastic modulus of the polymer composite reinforced with carbon nanotubes is calculated using the Rule of mixture. In order to achieve the stiffness parameter equivalent to the shell of grid cylinders, Smeared method has been used to suppress the effect of ribs. Abaqus software and valid references have been used to validate the obtained results. According to the results, the presence of peripheral ribs in the structure increases the frequency and reduces the radial displacement. Also, the thickness and angles of the ribs are important in improving the frequency and the presence of carbon nanotubes plays an important role in strengthening the structure and Increases the frequency and decreases the radial displacement due to the applied load.

In this study, a theoretical model based on the modified nonlocal Euler-Bernoulli is presented for the detection of biologically adsorbed particles on doubly clamped carbon nanotubes as resonant nano-bio-sensors. The basis of the work of these resonant nano-bio-sensors is the accurate calculation of the change in the resonant frequency because of the change in the mass due to the surface adsorption of the viruses. In most studies, simply supported ends have been used for simplicity of calculations, while it is almost impossible to build such supports at nano-scale. For this purpose, a doubly clamped ends was used to analyze this problem and for the first time, the closed-form vibration frequency response of a doubly clamped nano-sensor was presented according to the geometric and mechanical characteristics of the nanotubes along with nonlocal, surface and rotary inertia effects. Although many researchers have ignored the effects of surface stress and rotary inertia on the vibration analysis of nano-sensors, this study found that these effects at nano-scale played a major role in changing the frequency and accuracy of resonant nano-bio-sensors. Also, based on the obtained results, six different types of viruses were examined. Based on the sensitivity analysis, the designed nano-bio-sensor was able to separate the frequency change and identify them, consequently.

In the present study, multilayer nanocomposites fabricated by accumulative roll bonding (ARB) process. Aluminum sheets, copper sheets (with 0.1 and 0.3mm thickness) and multiwall carbon nanotubes (MWCNTs) were used as experimental materials. The rolling process continued to five cycles. Then, microstructure, hardness, tensile strength and electrical conductivity of nanocomposites were investigated. Necking and fracturing recognized as mechanisms of copper layers distribution in the aluminum matrix. The bonding strength between layers increased with the number of cycles due to the improvement of MWCNTs distribution. The results show that the hardness of aluminum increased with increasing copper layer thickness and these increases were about 30 and 32% for composites without nano reinforcements and nanocomposites contain MWCNTs, respectively. The highest hardness (147HV), is related to the sample containing carbon nanotubes and 0.3mm copper sheet, after five rolling cycles (446% increase compared to aluminum sheets). The results confirm the positive effect of copper and the MWCNTs on the improvement of strength. The highest strength and elongation is observed in the aluminum-copper-MWCNTs nanocomposite after four cycles. The results also indicated that the addition of copper and MWCNTs can simultaneously increase the strength and electrical conductivity of the resulted composites.

This study explores the free vibration analysis of a functionally-graded rectangular plate which has been reinforced by carbon nanotubes (CNT) using the novel theory of trigonometric higher-order shear deformation. Carbon nano-tubes have been distributed through the thickness direction in a linear, symmetric and non-symmetric fashion. The foundation pertaining to Pasternak , or rather duo-parameter, has been utilized in the modeling; moreover, the new mixtures rule has been used for estimating the plate properties. The governing equations have been derived using the Hamilton’s principle, and the Navier’s solution has been used for dealing with a rectangular plate boundary conditions. Lastly, the effects of diverse parameters have been examined upon the vibrational behavior of the plate, such as the different distributions of CNT and the geometric properties of the plate. The results show that the amount of natural frequencies rise in proportion with an increase in the ratio of thickness to the width of the plate (h/b); a decrease in the ratio of length to the width of the plate (a/b); as well as an increase in the coefficients of the elastic foundation, such that the changes in the amounts of natural frequencies will be tremendously decreased in proportion with K> 10000 and K> 1000, and such changes will not be tangible.Furthermore, the highest amounts of frequencies will be pertinent to the X distribution, and the lowest amounts of frequencies will be pertinent to the O distribution

Due to the different application of the beam-attached mass structures, and also increment of the importance of nanocomposite materials, in this paper, the study on nonlinear vibrations of composite cantilever beam with tip mass under the harmonic excitation is presented. The equations of motion are derived using a geometrically exact formulation based on the Cosserat theory for rods. The Muri-Tanaka model is implemented to formulate the mechanical properties of carbon nanotube reinforced beam. The Galerkin approach is implemented to derive the linear natural frequencies and corresponding mode shapes of the mentioned beam with tip mass. The extracted mode shapes are employed to discretize the equation of motion. The discretized equations of motion, which includes geometrical and inertial non-linearitites, are solved using the method of multiple scales and the frequency response is extracted. The effect of attached mass, carbon nanotube volume fraction and the excitation force amplitude on the frequency response of the system is investigated.

In this research, free vibration analysis of functionally graded carbon nanotube reinforced composite (FG-CNTRC) conical shells subjected to high temperature environment is investigated. The material properties of FG-CNTRC are assumed to be graded through the thickness direction. Two kinds of carbon nanotube reinforced composites including uniformly distributed (UD), CNTs are distributed uniformly through the shell thickness, and functionally graded (FG), CNTs are graded with three different distribution, are considered. The effect of thermal loading is considered as an initial stress. Applying the Hamilton’s principle based on classic theory and considering Von Karman strain-displacement relation, the governing equations are obtained. The analytical Galerkin method together with beam mode shapes as weighting functions is employed to solve the equations of motion. The results are compared with those presented in literature. In addition, the effect of various parameters such as thermal loading, boundary conditions, and different geometrical conditions are studied. It is shown that the initial thermal stresses have significant effects on the natural frequencies and cannot be neglected. Moreover, the critical buckling temperature rise of the shells can be extracted from the presented diagrams of the fundamental frequency parameters verses the temperature rise.

Carbon nanotubes are obtained from rolling a graphene sheet of a given size and at a specific direction. Due to the strong carbon-carbon covalent bonds, nanotubes have unique mechanical and electrical properties. In this paper, using finite element and molecular mechanics methods, the covalent bonds between the carbon atoms in the nanotube have been modeled using linear beam element. Carbon nanotubes with different diameter and length ranges have been analyzed. The effects of nanotube length, diameter and chirality on nanotubes Young's and shear Modului have been investigated, independently. Also, the decrease in nanotube modulus due to the number and position of vacancy defects has been determined. The results show that, nanotube diameter has a larger effect, compared to nanotube length, on elastic properties, especially Young's modulus. Comparing the results obtained for armchair, zigzag, and chiral nanotubes, vacancy defect had the most effect on chiral nanotube Young's modulus, with a chiral angle of 49.15 degrees.

In this paper, free vibration of functionally graded carbon nanotube annular sector plates is studied. Distribution of carbon nanotubes is continuous and meaningful and gradual changes of materials in the direction of thickness are in the form of volume fraction. Annular sector plate is placed on the Winkler-Pasternak two parameters elastic foundation. The motion equations of plate are derived using the Hamilton principle and the refined plate theory. These coupled differential equations are transformed to ordinary equations using the trigonometric series expansion of space variation functions and then are solved with the help of differential quadrature method. The obtained results are compared with the other researcher’s results and an excellent agreement can be observed between them. Finally, the effects of different geometric parameters, different distributions of carbon nanotubes in the thickness direction, elastic foundation, and also different boundary conditions on the natural frequencies are investigated.

Multi-wall carbon nanotubes (MWCNTs) which are mixed in polymer materials could be used as a piezoresistive strain sensor for the purpose of structural health monitoring in engineering structures. In this paper, stain sensing sensitivity of CNT-epoxy nanocomposite is presented with changes in electrical resistance. Nanocomposite sensor is sticked on the aluminum cantilever beam to apply strain on it. Initially, MWCNTs with varying content from 0.01 wt% to 1.5 wt% were uniformly dispersed in the epoxy matrix. Dispersion process was conducted with shear mixing device. Therefore, a smart material was created, which was suitable for strain sensing. The microstructure of the sensor was evaluated using scanning electron microscopy to characterize typical distribution of the MWCNTs inside the epoxy matrix and form conductive networks. The effect of the preparation method (type of initial mixing, curing temperature and MWCNTs weight percent) studied on the strain and electrical changes during mechanical loading. The results showed that, initial mixing of epoxy and hardener resulted in higher sensitivity of electrical changes. Also, nanocomposite was more sensitive to strains in cantilever beam when filler content of nanocomposite was closed to the percolation threshold. In addition, sample preparation at various temperatures of 80 and 100 oc showed that the samples in lower curing temperature were more sensitive to the applied strain.

In this study, Nonlinear low-velocity impact response of carbon fiber reinforced polymer(CFRP) composite plates enhanced with carbon nanotubes resting on elastic foundations in thermal environments is investigated. The effective material properties of the multi phase nanocomposite are calculated using Halpin–Tsai equations and fiber micromechanics in hierarchy. The carbon nanotubes are assumed to be uniformly distributed and randomly oriented through the epoxy resin matrix. Contact force between the impactor and the plate is obtained with the aid of the modified nonlinear Hertzian contact law models. The governing equations are derived based on principle of virtual work and solved by the finite element method with Newmark’s numerical integration method. Numerical results reveal that a small amount of CNT (1–2 percent) can increases the peak contact and decreases the peak indentation. Also the contact time duration and central deflection have decreased with increasing the CNT percentage.

In recent years, many attentions have been paid to decrease of the weight of components in automotive, transport and aeronautical industries, in respect of reduction of energy consumption and environmental pollution. Therefore, low-density aluminum alloys reinforced with nanoparticles especially CNT and Al2O3 have been broadly considered for application in such industries due to high strength/weight ratio. In current work, Al-CNT-Al2O3 nanocomposite was produced by accumulative roll bonding (ARB) after 6 passes. CNT-Al2O3 composite with 1wt% multi-wall carbon nanotube (MWCNT) and 2wt% nano-alumina was prepared by ball milling process. The effect of the ARB cycles on the microstructure and mechanical properties of nanocomposite were studied by field emission scanning electron microscopy images (FESEM), X-ray diffraction data, tensile and micro hardness results. FESEM images showed the uniform distribution and high quality bonding of carbon nanotubes in the matrix. X-ray diffraction analysis indicated the composite nanostructure formation with the crystal size of 53.3 nm after 6 cycles of ARB compared to 77 nm of Al after pass 11. The results obtained by the tensile and hardness tests showed that at the end of ARB process, ultimate strength was 5.9 times, and hardness was 3 times more than those of the annealed aluminum.

In this study, free vibrations and resonances analysis of a nanocomposite beam with internal damping is investigated. For this purpose the various distributions of carbon nanotubes with arbitrary average volume fractions are considered. System includes the geometry and inertia nonlinearities. With the aid of Hamilton principle the equations of motion are derived and using the Galerkin method are reduced to ordinary ones. To analyze the system the multiple scales method is utilized. In free analysis the analytical expressions for amplitude, phase and nonlinear natural frequency are obtained. Also, the effect of system parameters such as damping coefficients, kind of the carbon nanotube distribution, average volume fraction of nanotubes in them are probed. In free analysis, it is observed that by increasing the external damping the amplitude is decreased. Also, by increasing the average volume fraction, the nonlinear natural frequency is increased. In resonance analysis, by depicting the frequency response curves, it is observed that by increasing internal damping coefficient the amplitude is decreased and the loci of the bifurcations is changed. Also carbon nanotube distribution and average volume fractions of them on the solution and bifurcations have an important effect. Also, it is seen that by decreasing the external force, the amplitude of the system is decreased and bifurcations occur in higher internal damping coefficients. An isotropic beam in the highest and a nano-composite beam in the lowest values of internal damping coefficients become completely stable.

The purpose of this paper is to deal with fracture behavior of carbon nanotubes with presenting a revised structural molecular mechanics model in the finite element method. Structural molecular mechanics modified model, uses a three-dimensional beam element with general section to make nanotube structural model in which bending stiffness and inversion are defined independently. In analysis which are done, a bridged carbon nanotube with constant strain rate is examined under tensile stress until the failure of nanotube. Carbon-carbon bonds behavior has been assumed nonlinearly and will be ruptured when the strain reaches 19%. It is predicted that fracture behavior in carbon nanotubes depends on the environment temperature due to mechanical behavior of carbon nanotube's bonds. Based on the present research, we found that by increasing the temperature, Poisson's ratio increases and Young's modulus decreases. Further, it can be said while the temperature increases, both the fracture ultimate strain and stress decrease. Finally, a nonlinear relationship is presented in which the constants depend on chirality of the carbon nanotubes.