جستجوی مقالات مرتبط با کلیدواژه « carbon nano tube » در نشریات گروه « فنی و مهندسی »

In this paper, the piezo-resistivity effect is utilized to experimentally investigate self-diagnostic behavior of composite laminates in determining delamination. In order to do so, composite laminated beams with unidirectional carbon fibers and epoxy resin containing CNT are produced while Teflon tape is placed between layers of some samples to artificially insert delamination. Three-point bending tests are conducted and stress-strain curves and electrical resistance of the samples are measured for not-damaged and damaged beams. The stress-strain curves are applied to interpret and determine damage mechanisms and to extract time data for the evolution of each damage mechanism. This time data is then used to determine the self-diagnostic behavior based on the variation of electrical resistance of the samples. The results show that in general, the electrical resistance of the not-damaged samples is higher than the damaged ones. This fact shows that piezo-resistivity effect can determine the existence of the delamination in the samples. Moreover, the propagation of delamination leads to electrical resistance increase when the delamination is placed far from the neutral axis of the beam. In addition, decreasing the dimension of the delamination reduces the sensitivity of the self-diagnosing behavior, which means that the variation of electrical resistance cannot determine the evolution of small sized delamination. On the other hand, the longitudinal location of delamination does not have a sensible effect on the behavior.

In this research, semi-solid powder processing was used to fabricate Al7075-CNT nanocomposite. The effect of process variables including compression time, semi-solid temperature and the CNT percent on the sample’s hardness and microstructure was investigated. The 1%-CNT nanocomposite is observed to be superior in hardness compared to the base alloy, but the 2%-CNT sample’s hardness was between the base alloy and 1%-CNT sample. It was observed that the compression time and semi-solid temperature do not have a significant effect on the sample’s hardness. Compression for 10 minutes and forming temperature of 620 °C were selected as the suitable variables. Microstructural examination showed that in 1%-CNT alloy, the reinforcing phase is completely penetrated in the aluminum matrix and there is no CNT accumulation on the sample’s surface unlike the 2%-CNT sample. Quantitative analysis showed that a proper percentage of CNT had the greatest effect on the hardness. Increasing the temperature from 600 to 620 °C by 10% and increasing the compression time from 5 to 15 minutes by 2% increased the hardness of 1%-CNT samples compared to the base alloy.

Electrical discharge machining is a non-traditional machining process, which is widely used for machining high-strength metals and alloys with low machinability. Due to the thermoelectric nature of this process, the poor surface integrity of the parts produced by this method is one of its weaknesses. In this research, the electric discharge machining method has been used for the machining of Ti-6Al-4V alloy using carbon nanotubes added to the dielectric. In this study, input variables include discharge current intensity, pulse duration, and dielectric; the effect of their changes on the shape of the output pulses, material removal rate, tool wear ratio, surface rouhness and heat affected layer has been investigated. The results show that the addition of carbon nanotubes to the dielectric reduces the harmful pulses and increases the effective pulses in machining, reduces the matrial removal rate and decrease the tool wear rate. The presence of carbon nano tubes significantly improves the surface quality and reduces the heat-affected layer.

In recent years Epoxy/fiberglass composite due to its good properties and low cost of has attracted much attention. Relatively low flexural and interlaminar shear strength are the two most important weaknesses of this composite, which limit its uses. One way for improving these properties is by increasing particles to the matrix, in other words, producing hybrid composites. Carbon nanotube and nanoparticles of clay, based on their good function in the epoxy matrix as reinforcements have attracted much attention for such purpose. Although, adding these kinds of particles will improve the properties of epoxy/fiberglass composite, but generally will increase its production cost, which is why these researches have had no practical uses for the industry yet. In this study, nanoparticles of clay and carbon nanotube were added to the epoxy matrix by a regular mechanical mixer with a speed of 300-400 rpm, and the flexural strength and the interlaminar shear strength were investigated and compared with the epoxy/fiberglass composite. The results show that increasing the nono clay particles to the matrix increase the flexural strength of the composite. The sample with 0.5 wt. % of nono clay shows the greatest increase in flexural strength, which is about 25 % more than the sample without nanoparticles. The interlaminar shear strength is also increased by about 5%, by adding 2 wt.% of nanoparticles of clay. The addition of carbon nanotubes in this method has a bad effect on properties.

In this study, aluminum sheets reinforced by carbon nanotubes were fabricated using the Accumulative Roll Bonding (ARB) method. The ARB process was chosen among the severe plastic deformation methods to strengthen metal sheets using carbon nanotubes owing to the enhanced microstructure and mechanical properties of final products. In order to evaluate the mechanical properties of the specimens, tensile tests were carried out and the strength of sheets made by ARB method was compared to single-layer pure aluminum and reinforced composite sheets. Microstructural changes of composite sheets were studied by optical microscopy after each cycle of rolling process. The results showed that spreading of (0. 5 to 1.5) wt% of CNTs increased the ultimate strength of the composite sheets while by aggregating the CNTs more than 1.5 wt% a decreasing trend of the ultimate strength was observed. Furthermore, the composites fabricated from 7 cycle of rolling process had a homogeneous distribution of particles and strong bonding between particles and matrix without having any porosity. Also it was found that the tensile strength of composite sheets also increased as the number of cycles increased.

In this paper, the thermal analysis of a solar wall equipped to nano phase change material is carried out, numerically. The governing equation of transient heat conduction is solved by a finite difference technique based on enthalpy method. The validation of numerical results of present study is carried out with the experimental data. There is a fair agreement between numerical results and experimental data. In parametric studies the volume fraction effect of carbon nano tubes and alumina nano particles and the thickness of phase change material is investigated. Present study results showed that suitable improvement in solar wall thermal performance is obtained due to the addition of carbon nano tubes and alumina nano particles to base phase change material. However, carbon nano tubes yield better performance. Performance improvement reasons include the increase of heat transfer speed due to the increase of thermal conductivity and the completion of melting and solidification process. Occurrences resultant leads to a 9% increase in the thermal efficiency of solar wall for 3% volume fraction of carbon nano tubes. Generally, the results of present study give the possibility of the design of a solar wall equipped to phase change material with about 40% of thermal efficiency.

Nanofluids as new groups of the heat transfer environments with unique and special properties have attracted particular attention in recent decades. Knowing the characteristics of the nanofluid is the first step in the nanofluid study, which is very important in describing its behavior. Although many attempts have been made to modeling the thermodynamic properties of nanofluids, a comprehensive model for predicting these properties has not yet been provided. In this work has been studied the dynamic viscosity of water-single wall carbon nanotube nanofluid and the effect of volume fraction and size of nanoparticles and nanofluid temperature on it in ranging from 〖25〗^°C to 〖65〗^°C with an interval of 10 °C and 0.125% to 0.734% (0.125%, 0.25%, 0.5%, 0.734%) respectively. After the full explanation of the interaction between base fluid and nanoparticle atoms and analyzing the shear stress autocorrelation function, the results show that the presence of nanoparticles in the base fluid and the addition of its, reducing the temperature, as well as reducing the size and diameter of the carbon nanotubes, increase the dynamic viscosity of nanofluids. Finally, the interpretation and conclusion of the results is discussed.

In this research, nano composites of epoxy /carbon nanotube reinforced by one layer of Finemet amorphous alloy with chemical composition of  which was fabricated by planner flow melt spinning was used to investigate the electromagnetic interference shielding. X-ray diffraction test was done to characterize the Finemet amorphous alloy. Besides, vibrating sample magnetometer test was selected to measure the amount of magnetization of nanocomposites. Shielding effectiveness of composites over the X-band (8 to 10 GHz) was carried out by rectangular waveguide based on the WR90 standard. The results showed that the shielding effectiveness at X-ray band reaches 15 and 20 dB, respectively, in samples of nanocomposite of epoxy containing 0.1 and 0.5 wt.% carbon nanotube which was reinforced by one layer of Finemet amorphous alloy.

The present research work was aimed at developing conductive polymer-based composites in order to have a higher conductivity than the standard level of the Energy Institute of America. In this case, the composites can be applied to make electrodes. For this purpose, carbon clack particles, carbon nanotube and expanded graphite with different weight percentages (5%, 10%, 15%, 25%, and 35%) were added to the epoxy resin and the electrical conductivity of the samples was measured according to the four-point standard method. The average electrical conductivity threshold for carbon clack particles, carbon nanotube and expanded graphite was determined at 25, 10, and 15, respectively. Furthermore, the effect of different construction parameters such as the use of vacuum pumps and heating on the electrical conductivity of the composite samples was also investigated. The experiments revealed that the use of the vacuum pump increased the electrical conductivity by 10.8%, 11.4% and 9.6% in carbon black, carbon nanotube, and expanded graphite samples, respectively. In order to increase the mechanical strength of the conductive polymer samples, ten layers of unidirectional carbon fabric were used. The results obtained showed that the use of carbon fibers enhanced the electrical conductivity by 23.2%, 27.3%, and 24.7% for carbon black, expanded graphite, and carbon nanotube samples, respectively. Ultimately, using the scanned electron microscopy images, the quality of the nanoparticle distribution in the samples was investigated.

In this research, the performance, efficiency, and properties of anti-fouling and flux of poly vinylidene fluoride (PVDF) nano-composite membranes with concentration of 15wt.% and 18 wt.%, mixed with different functional  carbon nanotubes (-OH, -COOH, -NH2), were made and studied using phase inversion and normal methylpyrrolidone (NMP) solvent; moreover, the  nano-composite membranes tested for flux, fouling, contact angle, porosity and  protein rejection rate. Also, by using empirical test results, (1) flux and (2) fouling parameters were modeled based on the input variables including nanoparticle percentage, polymer percentage, porosity, contact angle and protein rejection rate. In this model, four intelligent systems including multiple layer percepton, radial basis function, least squares support vector machine and adaptive neuro-fuzzy inference system and  three optimization algorithms including generic algorithm, simulated annealing and particle swarm optimization have been used. The results showed that for both flux and fouling parameters, the best models are GA-RBF and Conjugate-ANFIS with high correlation coefficient. In the next section, modeling was used to obtain optimal values of the best models made for both outputs (minimum fouling and maximum flux) and then the combined algorithm of the genetic algorithm and particle swarm optimization values were obtained. Afterward, by using optimization results for each type of polymer (15wt% and 18wt%), the membranes were made in the laboratory, and then flux, fouling, contact angle and porosity tests were performed, and the results were compared with the results of  the model. Finally, the results showed that 0.07 wt.% single-walled carbon nanotube-PVDF nanocomposite membrane functionalized with hydroxyl group and 0.17 wt.% single-walled carbon nanotube-PVDF nanocomposite membrane functionalized with  hydroxyl group had  the best performance with the polymers of 15 wt.% and 18 wt.% of PVDF respectively.

The available analytical and finite element methods set the values of elastic modulus of nanocomposites more than the values obtained from the test. In this thesis, a new linear and continuous analysis method is used to determine the best and most similar value of elastic modulus for polymer nanocomposites to laboratory value is provided. For this purpose, the governing elasticity equations in polar coordinates have been solved for nanocomposite representative volume element (RVE) with shear-lag model by assuming perfect bond condition between CNT and matrix. Then, using the finite element modeling with Ansys software, elastic modulus of connectivity states of almost complete and half break between the two phases are calculated and finally the proposed new model that is modeling with spring in the states of almost complete connectivity and half break between the two phases are provided and elastic modulus is calculated. In this method, shear stress is also offering a new relationship between CNT and matrix areas that have been. To ensure the validity of the results of presented model to determine the elastic modulus, the obtained results are compared with laboratory method results of other researchers that in all cases the proposed elastic modulus is much closer to laboratory sample and finite element models and good agreement

In the present research the effect of adding multi wall Carbon nano tubes (with 10-15 nano meter diameter) on the heat transfer coefficient of a heat exchanger is investigated. This work is performed by a co current flexible double pipe heat exchanger made of PVDF. To this end, the viscosity and thermal conductivity of nano fluids is measured experimentally for various temperatures and concentrations. The nano fluid temperature is set at 35°C, 40°C, 45°C and 50°C. The flow rate of nano fluid inside the inner tube was adjusted at 100 , 200 , 300 while, the cold water flow rate of the outer tube is 100 The results shows that heat transfer coefficient of the heat exchanger improves with increasing the fluid temperature, concentration and flow rate. The most effective factor on the heat transfer coefficient is flowrate. Obtained results indicate that using this nano fluid enhances heat transfer coefficient 75%.

In the present research, silicon carbide synthesis via magnesiothermal method was investigated using MCM-48 as a silica source and different types of Carbon including CNT and MCM-48/CNTF nano composites through in-situ preparation. The experiments were accomplished with different molar ratios of MCM-48, carbon and magnesium at 650-700˚C in argon atmosphere. Properties of MCM-48, carbon nanotubes and synthesized samples were clarified using BET, XRD, FTIR, FESEM, EDX and TEM techniques. After preparation and characterization of MCM-48 and carbon nano tubes, the effect of amounts and types of carbon on reaction progress were also investigated for silicon carbide synthesis. Comparison of XRD phase analysis for samples consisting of different carbon sources showed that types and morphologies of carbon and also localization mode of reactors are important factors of silicon carbide synthesis. According to obtained results it was clear that micro structure of synthesized silicon carbide was fibrous and was dependent to CNT precursor pattern. Also functionalized carbon nano tube caused better contact between MCM-48 and CNT in magnesia thermal process, therefor efficiency of magnesia thermal reaction was improved.

The full adder circuit is one of the most significant and prominent fundamental parts in digital processors and integrated circuits since it can be used for implementing all four basic computational functions including: addition، subtraction، multiplication، and division. so، in this paper a new low power and high performance full adder cell has been proposed with the benefit of using carbon nano tube field effect transistors. The proposed design contains 12 CNTFET transistors which are connected in pass transistor logic style to make the desired functionality. Carbon Nano Tube Field Effect Transistor (CNTFET) has modified electrical characteristics such as low power consumption and high speed in comparison with MOSFET transistor; The proposed design is simulated using Hspice software based on CNTFET model and 0. 65V supply voltage. the simulations are done considering three different frequencies، and three different load capacitors. The simulation results، which demonstrated in tables and diagrams، proved the superiority of proposed design in terms of power consumption and performance (PDP) compared to the existing counterparts.

Since the nanoscinence is an interdisciplinary field of science¡ various industries and sciences have been influenced. The use of nanotechnology in the manufacture of new materials is increasing day by day. Due to significant influence of these additives on important the quality and properties of materials caused a significant increase in researches of this field. The main role of pavement is to persist again the detriment effects of traffic loading and climate conditions. This goal can be better achieved¡ by applying the nanotechnology in pavement engineering. This paper investigates the results of various researches about effects of three groups of nano materials consist of Sio2¡ Tio2 and Carbon nano tube on the engineering properties of cement concrete mixes that have been designed to use in pavement application. Based on obtained results. The results show that the optimum contents of nano-particles improved the mechanical properties of concrete mix such as tensile strength¡ flexural and compressive strength. Subsequently¡ the strength properties of concrete reduced with increasing the nano-particles quantity more than the optimum content.

The removal of benzene and toluene from aqueous solutions by single and multi walled carbon nano tubes (SWCNT and MWCNT) and hybrid carbon nano tube (HCNT) were evaluated. In this study nanomaterials in a dose of 1 g/l and contact time 10 min with benzene and toluene concentrations of 10 mg/l and pH 7 were chosen. Synthetic samples were analyzed by GC/MS. In order to analysis data Design of Experiment (DOE) softwere was used. The equilibrium amount (qe) (mg/g) for SWCNT (B: 9. 98 mg/g، T: 9. 96 mg/g) was found higher than MWCNT and HCNT. The amount of uptake for SWCNT was T > B، that was due to increasing of water solubility and decreasing of its molecular weight. It could be concluded that recycling by heating at 105±2ºC provide better adsorption performance for recycled CNTs than their initial state. So that benzene and toluene removal efficiency improved to 99. 8 percent. This study showed the SWCNTs are efficient as benzene and toluene adsorbents in environmental pollution control technology.