Nonlinear vibration of embedded smart composite microtube conveying fluid based on modified couple stress theory

Electro-thermo-mechanical nonlinear vibration and instability of a fluid conveying smart composite microtube made of polyvinylidene fluoride (PVDF) are investigated in this article based on the modified couple stress theory and Timoshenko beam model. The composite matrix is reinforced by double-walled boron nitride nanotubes (BNNTs). Mechanical, electrical, and thermal characteristics of equivalent composite are determined based on micromechanical model. The surrounded elastic medium is taken into account using Winkler and Pasternak models. Considering the small-size effects and slip boundary conditions of microflow through Knudsen number and applying Hamilton's principle, the coupled differential equations, containing displacement and electric potential terms, are obtained. The differential quadrature method is applied to discretize the coupled governing equations and boundary conditions, which are then solved to obtain the nonlinear frequency and critical fluid velocity of the fluid-conveying microtube. The detailed parametric study is conducted, focusing on the combined effects of the Knudsen number, nonlocal parameter, BNNT volume percent, temperature change, elastic medium, and aspect ratio on the nonlinear frequency and critical fluid velocity. Results indicate that the natural frequency and the critical fluid velocity of the smart composite microtube increase with increasing the small-scale parameter. POLYM. COMPOS., 36:1314-1324, 2015. (c) 2014 Society of Plastics Engineers