In the review of the vibration study of FG structures, Qian and
Ching [2] analyzed the static deformation, free and forced vibration
of a two-dimensional FG cantilever beam by using meshless
local Petrov-Galerkin (MLPG) method. Aydogdu and Taskin [3]
obtained the analytical results of free vibration of simply supported
FG beams by using Hamilton's principle. Alshorbagy et al.
[4] presented the free dynamic characteristics of a FG beam with a
material graduation in axial or transversal (thickness) directions
with power law function by finite element method. Ferreira et al.
[5] employed the global collocation method, the first and the
third-order shear deformation plate theories to analyze the free
vibration of functionally graded plates. Zhao et al. [6] used the
element-free kp-Ritz method and the first order shear deformation
plate theory to analyze the free vibration of FG plates. Liu et al.
[7] investigated the free vibration of FGM plates with an in-plane
material inhomogeneity based on the classical plate theory. The
free vibration of the two-dimensional FG beams and FG sandwich
beams were also conducted by Yang et al. [8,9] by a meshfree
boundary-domain integral equation method.