Wave propagation in functionally graded piezoelectric sandwich nanoplates based on nonlocal strain gradient theory incorporating surface effects

In this study, wave propagation characteristics in functionally graded (FG) piezoelectric sandwich nanoplates under electro-thermal loading are investigated. The sandwich nanoplates comprise piezoelectric layers, with a FG layer in the middle. The nanoplates are deposited on a viscoelastic foundation, and the effective material parameters of the FG interlayers are determined using the Mori-Tanaka homogenization model. To specifically examine the influence of surface effect (SE) and scale effect, governing equations are derived from the unified shear deformation theory and Hamilton’s principle, incorporating the theoretical frameworks of surface piezoelectricity theory and nonlocal strain gradient theory. Thereafter, the characteristic equations are analytically solved to obtain numerical effects of wave dispersion relations. The effects of various parameters, such as surface parameters, scale parameters, viscoelastic parameters, and external loads on the wave propagation characteristics are investigated in detail. The piezoelectric SE is related to the scale parameters. Surface density decreased the frequency, and the degree of influence of both surface piezoelectric parameters and residual stress on the frequency decreased rapidly with the increase in the thickness of the piezoelectric layer.