Abstract: Carbon nanotubes (CNTs) have been used in making composites because CNTs have high strength, large aspect-ratio and excellent thermal and electrical conductivity. However, to realize the wide applications of CNT composites, further R&D must be carried out. This review will discuss some fabrication, characterisation and application issues of CNT polymer composites. Aspects to outline are purification, dispersion, alignment, stress transfer, interface bonding, wear and friction and rheological properties. Some research challenges will be briefly highlighted as well, including the mass production of long and aligned CNTs at low cost, and the optimization of the microstructures, properties and functioning features of CNT composites.
Abstract: The effects of matrix stiffness and the content of multi-walled carbon nanotubes on the mechanical properties of the nanocomposites have been examined in this investigation. The matrix stiffness was controlled by changing the mixture ratio between the epoxy and hardener. Two different contents (1 wt.%. and 2 wt.%) of the multi-walled carbon nanotubes (MWCNT) were added to the epoxy matrix. Three-Point-Bending and Shore’s hardness tests were conducted to determine the Young’s modulus and hardness of the nanocomposites, respectively. Experimental results showed that the Young’s modulus of the nanocomposites was significantly increased with the increase of the addition of MWCNTs. However, the improvement of the hardness of the epoxy was insignificant with the addition of the MWCNTs. The reinforcement role of the multi-walled carbon nanotubes decreased while increasing the stiffness matrix.
Abstract: In this paper, a kind of piezoelectric ceramics model based on hysteretic nonlinear theory has been developed. Van de Pol nonlinear difference item was introduced to interpret the hysteresis phenomenon of the voltage-strain curve of piezoelectric ceramics. The coupling relationship between voltage and stress was obtained in partial least-square regression method to describe the driftage phenomenon of the voltage-strain curve in different stress. Based on above, the final relationship among strain, stress and voltage was set up. The results of significance test showed that the new model could describe the hysteresis characteristics of piezoelectric ceramics in different stress well. The new piezoelectric ceramics model considers the effect of stress, and is easy to be analyzed in theory, which is helpful to vibration control.
Abstract: This paper presents a mesh-free numerical modeling approach for carbon nanotubes (CNTs) subjected to bending loads. The higher-order Cauchy-Born rule was employed to construct the higher-order continuum constitutive model. An initial equilibrium single-walled CNT (SWCNT) was viewed as been formed by rolling up a graphite sheet into a cylindrical shape. The deformation from an original SWCNT to the current configuration was approximated with the moving least-square (MLS) approximation, and the mesh-free computational framework was established in the theoretical scheme of higher-order gradient continuum. Mesh-free numerical simulations were carried out for SWCNTs, and the accuracy and convergence were discussed in comparison with the results of atomistic simulation. The buckling behavior was studied for various types of SWCNTs upon bending, and the buckling mechanism was investigated in virtue of the continuum variables, which showed that the maximum axial compressive strain played a vital role in the development of kinking.
Abstract: The structural and elastic properties of HfN and Hf-Si-N have been studied, using first principles calculations based on the density functional theory. These calculations provide the lattice parameter, cohesive energy and elastic constants of fcc (NaCl)-HfN, the N-deficient Hf-Si-N and the Hf-deficient Hf-Si-N solution phase. In order to study the relative stability, binding energy of all configurations has been calculated. The results showed that it was difficult to add a Si atom into the center of the HfN cell because the cohesive energy decreased. However, if an Hf atom or an N atom was missing in the HfN, a silicon atom was possible to occupy the vacant site and form the Hf-Si-N substitutional solid solution. Moreover, the bulk modulus, shear modulus and elastic modulus increased accordingly, the mechanical properties were improved.
Abstract: Nanocomposite tool materials are developing very fast in engineering field for their highlighted advantage in mechanical properties and stability under high temperature. However, there are lots of puzzles to be discussed in the materials design theory and the fabrication processing due to the difference between the traditional materials and the nanocomposite. Therefore, in this paper, a new nanocomposite tool materials design method has been proposed based on the interface strengthening theory. The sintering temperature and the soaking time could be optimized based on the interface strengthening theory and the relative density of the tool materials. Meanwhile, a series of experiments were carried out to fabricate the nanocomposite tool materials under the guider of the interface strengthening theory. Results showed that experimental data agreed well with the calculation and the model was proved to be correct.
Abstract: Nanometer calcium carbonate (nano-CaCO3) is an inorganic material that does not have the rheological properties of a magneto-rheological fluid (MRF) but has some effects on the sedimentary stability and rheological properties of MRF. The MRF was prepared by adding nano-CaCO3 to improve its comprehensive and practical properties. The results showed that, with an increase in the amount of nano-CaCO3, the sedimentary stability of MRF would be improved. The off-state viscosity of MRFs increased with an increasing amount of nano-CaCO3. The shear stress of MRF was decreased slightly by adding nano-CaCO3. To some extent, the comprehensive and practical properties can be improved by adding a certain amount of nano-CaCO3. However, there is also certain localization that properties of MRF are improved by adding Nano-Inorganic Materials in the high temperature environment.
Abstract: Water-based Fe3O4 nano-magnetic fluid for seal was prepared by coprecipitation. In order to obtain nano-magnetic fluid preparation technology which can produce industrially, the choice of second coating surfactant has been studied. Factors affecting nano-particle size and particle saturation magnetization were investigated using five factors and three level orthogonal experimental design. The size of nano-particles and particle saturation magnetization were characterized by transmission electron microscopy (TEM) and WSM vibration magnetometer. The results showed that the adding speed of NaOH solution and heat-maintaining time after adding, adding speed and reaction temperature of sodium oleate solution, as well as the heating temperature of sodium oleate solution influence the properties of nano-magnetic particles more. With the optimum process parameters, Fe3O4 nano-magnetic fluid which is below 15nm and can meet the nano-magnetic fluid sealing technology requirements has been prepared.
Abstract: The temperature distribution in nanoscale cylindrical representative volume element (RVE) with centered carbon nanofiber (CNF) was modeled by the developed hybrid finite element approach, which used the axisymmetric Green’s function to approximate the interior field within the element, while the independent element boundary field with conventional shape functions was assumed to keep the continuity of field variables between adjacent elements. As a result, coupling with the constructed hybrid functional to link the independent interior and boundary fields, the solving linear system of equations with boundary integrals only were obtained. Numerical examples were given to show the accuracy of the proposed approach, and results were found in good agreement with those of ABAQUS. Also, it was obvious that the surface temperature of nanofiller almost kept constant during heat transfer, due to the large difference of thermal properties between nanofiller and matrix.