In this paper, considering a more realistic model for the carbon nanotube (CNT) conveying viscous fluid which is embedded in a visco-elastic medium, the effect of viscosity of the medium surrounding the CNT has been investigated. By taking into account the influence of the fluid viscosity and using the Navier-Stokes equations, the governing equation of motion has been derived and a new analytical technique based on the power series is presented for its vibration analysis. The frequency equation of the system is obtained by applying the boundary conditions. The influence of the medium parameters and the fluid viscosity on the natural frequencies of the CNT has been studied. The results show that the medium damping has a marked effect on the natural frequencies and the critical fluid velocity. Furthermore, by increasing the fluid viscosity, the natural frequencies and the critical fluid velocity increase. There is a good agreement between the results obtained through the proposed method and the data reported in the literature. The two main advantages of the proposed method are the applicability of the method to all kinds of the boundary conditions and its rapid convergence.
In the current study, stability analysis of cracked functionally graded material (FGM) columns under the effect of piezoelectric patches is analytically investigated. Configuration of the patches is somehow chosen to create axial load in the column. The crack is modeled by a rotational massless spring which connects the two intact parts of the column at the crack location. After applying the boundary and compatibility conditions at the crack location and the ends of the piezoelectric patches, the governing equation of buckling behavior of the cracked FGM column is derived. The effect of important parameters on the first and second buckling load of the column such as crack parameters (location and depth), location and length of the patches and also applied voltage is studied and discussed. Results show that a crack significantly reduces the column load capacity which is dependent on location and depth of the crack. By applying static load to the column, piezoelectric patches produce local torque, and controlling this torque leads to reduced crack effects on the column. Using piezoelectric patches with proper location and length compensates the effect of the crack. Despite the first buckling load, positive voltage increases the second buckling load of the column.
In this paper, a new approach for evaluating the cryogenic machining process of the carbon nanotube reinforced aluminum matrix composites is developed based on finite element method. Finite element modeling in commercial code ABAQUS/Explicit was used to simulate high-speed machining of carbon nanotube reinforced composites under dry and cryogenic conditions, where different parameters (carbon nanotubes loading and the cutting speed) were investigated. The matrix phases are given a Johnson–Cook failure criterion. For considering more realistic assumptions, mechanical and thermal properties of the materials are assumed as a function of temperature. Results shown that at the cutting velocity of 60 m/s, cryogenic cooling has caused decrease of workpiece plastic strain by 12% in comparison with the dry cooling. The model can be used to study the effect of weight fraction, orientation, and length of the carbon nanotubes on the manufacturing of the nanocomposites.
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