Electro-thermo-mechanical torsional buckling of a piezoelectric polymeric cylindrical shell reinforced by DWBNNTs with an elastic core

The effect of partially filled poly ethylene (PE) foam core on the behavior of torsional buckling of an isotropic, simply supported piezoelectric polymeric cylindrical shell made from polyvinylidene fluoride (PVDF), and subjected to combined electro-thermo-mechanical loads has been analyzed using energy method. The shell is reinforced by armchair double walled boron nitride nanotubes (DWBNNTs). The core is modeled as an elastic environment containing Winkler and Pasternak modules. Using representative volume element (RVE) based on micromechanical modeling, mechanical, electrical and thermal characteristics of the equivalent composite were determined. Critical buckling load is calculated using strains based on Donnell theory, the coupled electro-thermo-mechanical governing equations and principle of minimum potential energy. The results indicate that buckling strength increases substantially as harder foam cores are employed i.e. as E_c/E_s is increased. The most economic in-fill foam core is at η = 0.6, as cost increases without much significant improvement in torsional buckling at higher η’s.     

Nonlocal wave propagation in an embedded DWBNNT conveying fluid via strain gradient theory

Based on the strain gradient and Eringen’s piezoelasticity theories, wave propagation of an embedded double-walled boron nitride nanotube (DWBNNT) conveying fluid is investigated using Euler–Bernoulli beam model. The elastic medium is simulated by the Pasternak foundation. The van der Waals (vdW) forces between the inner and outer nanotubes are taken into account. Since, considering electro-mechanical coupling made the nonlinear motion equations, a numerical procedure is proposed to evaluate the upstream and downstream phase velocities. The results indicate that the effect of nonlinear terms in motion equations on the phase velocity cannot be neglected at lower wave numbers. Furthermore, the effect of fluid-conveying on wave propagation of the DWBNNT is significant at lower wave numbers.