Although carbon nanotubes (CNT) have been employed as reinforcements in nanocomposites, presence of nano scale defects such as Stone-Wales and vacancy defects in carbon nanotubes (CNT) weakens the mechanical properties of these materials. In this paper the effects of defects in CNTs on nanocomposite elastic behavior are investigated using molecular dynamics. Stiffness matrices of CNT and nanocomposite indicated the transversely isotropic behaviour of nanocomposite molecular model. Longitudinal and transverse Young's moduli for both perfect and defected CNT/epoxy nanocomposites are determined. A comparison between the results illustrates that the number and type of CNT defects have significant effects on mechanical behaviour of nanocomposite. Based on molecular dynamics results, CNT defects significantly affect the Young's modulus particularly in the transverse direction. Comparison between molecular simulation predictions and rule of mixtures results indicates that some correlation factors must be incorporated when using the micromechanical theories at nano scales. پرونده مقاله

Equal channel angular extrusion (ECAE) is one of the most powerful processes for manufacturing microstructure and nanostructure ‎materials. This process is a kind of severe plastic deformation technique, which requires large extrusion force. In this study, the numerical and experimental investigation of extrusion ‎force in ultrasonic assisted equal channel angular extrusion process (UAECAE) is carried out. ABAQUS Software is used for 2D ‎finite element analysis of the process considering superimposed ultrasonic vibrations to the round billet work material. Experimentally, the conventional and ultrasonic assisted ECAE are performed with copper material to validate simulation results. The reduction in extrusion force is observed due to ultrasonic vibrations. In order to achieve more ‎average force reduction, it is recommended that the ‎extrusion speed decreases and (or) vibrations amplitude ‎increases. Stress and strain distributions are numerically investigated in various vibrational conditions and die angles. The best die angle to obtain optimum force ‎reduction is 120º. In other die angles, vibrations ‎amplitudes of 15‎ μm‎ and higher ‎is necessary. Ultrasonic vibrations lead to oscillatory stresses with reduced ‎average value, but do not influence the amount of plastic strain ‎distribution. Achieving the beneficial products in ‎ECAE requires heavy special equipment, whereas using UAECAE will lead to more accessible equipment. ‎Finally, some optimal process parameters such as die angle, vibrations amplitude, for the proper application of these vibrations are ‎proposed. پرونده مقاله

The effects of flexoelectricity on thermo-electro-mechanical behavior of a functionally graded electro-piezo-flexoelectric nano-plate are investigated in this paper using flexoelectric modified and the Kirchhoff classic theories. Moreover, using the variation method and the principle of minimum potential energy for the first time, the coupled governing nonlinear differential equations of the nano-plate and their associated boundary conditions are obtained. The functionally graded nano-plate is modeled using a power law equation along the plate thickness direction. The nano-plate behavior is analyzed under mechanical, electrical, and thermal loadings with different boundary conditions. It should be noted that the direct and reverse flexoelectric effects under different loading conditions were investigated. Finally, the important quantities such as: the nano-plate deflection, the induced electrical voltage for different values of the length parameter, the power index related to the functionally graded behavior model and the geometric ratio parameter are determined. The results indicate that in the presence of flexoelectricity, the rigidity of the nano-plate increases. Also, the deflection and the generated electric potential along nano-plate thickness decreases. Finally, induced polarization decreases as a linear temperature variation is applied on the nano-plate. پرونده مقاله

In this paper, vibration of the protein microtubule, one of the most important intracellular elements serving as one of the common components among nanotechnology, biotechnology and mechanics, is investigated using stress and strain gradient elasticity theory and orthotropic elastic shells model. Microtubules in the cell are influenced by internal and external stimulation and play a part in conveying protein substances and taking medications to the intended targets. Therefore, in order to control the biological cell functions, it is important to know the vibrational behavior of microtubules. For this purpose, using the cylindrical shell model which fully corresponds to microtubule geometry, and by considering it as orthotropic which is closer to reality, based on gradient elasticity theory, frequency analysis of the protein microtubule is carried out by considering Love’s thin shell theory and Navier solution. Also, the effect of size parameter and other variables on the results are investigated. پرونده مقاله