In this research, vibration analysis of a viscoelastic sandwich plate rested on a visco-Pasternak foundation is investigated. Sandwich plate consists of a magnetorheological (MR) fluid core and viscoelastic nanocomposite face sheets which include piezoelectric matrix and functionally graded carbon nanotubes (FG-CNTs) fiber. Core and face sheets are affected by applying magnetic and electric fields, respectively. The elastic medium is simulated by a visco-Pasternak model which is considered in terms of the effects of springiness, shear and damping of foundation. At first, the constitutive equations of sandwich plate are expressed by employing the geometric continuity conditions. Then, the equations of motion are derived by applying the energy method and Hamilton’s principle and an appropriate analytical approach is proposed to solve them. This approach can be considered as the different boundary conditions. Finally, the influences of various parameters such as the type of MR material, core to face sheets thickness ratio, volume fractions and symmetric distributions of CNTs in face sheets, magnetic and electric fields, viscoelastic constant of face sheets and elastic medium on the dimensionless natural frequencies of sandwich plate are studied. The results show that increasing core-to-face sheet thickness ratio leads to a decrease in the natural frequencies because the MR fluid core is softer than nanocomposite face sheets. Thus, the MR fluid core acts like a damper. Also, the loss factor of the MR fluid core decreases with increasing magnetic field intensity, and consequently, the natural frequency grows. In addition, increasing the volume fraction of CNTs causes the stiffness of the structure to increase. The results of this research can be utilized to realize applicable semi-active devices with controllable stiffness.

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In the present research, vibration and instability of visco‐elastically coupled carbon nanotube reinforced composite (CNTRC) microtubes conveying fluid is investigated. Single‐walled carbon nanotubes are arranged in a longitudinal direction inside poly methyl methacrylate matrix. The longitudinal magnetic field is applied on coupled system. The surrounding medium is simulated by visco‐Pasternak model due to considerable damping and shearing effects. Based on Mori–Tanaka theory, the properties of composite microtubes are obtained. In order to achieve more accurate results, strain gradient theory is developed in Timoshenko beam model. The motion equations are derived utilizing Hamilton's principle and solved by means of differential quadrature method. Considering slip flow regime, the influences of various parameters such as magnetic intensity, elastic medium, Knudsen number, and volume fraction of CNTs on the vibration characteristics of coupled system are studied in details. Results demonstrated that the stability of coupled system can be significantly improved by applying magnetic field. The result of this study can be useful to control and improve the performance of micro‐mechanical systems conveying fluid. POLYM. COMPOS., 37:1375–1383, 2016. © 2014 Society of Plastics Engineers

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